Version May 2024
INTRODUCTION — Physical inactivity is a major health problem worldwide, and it predisposes to a wide variety of chronic degenerative diseases, including cardio-cerebrovascular disease, metabolic disease, musculoskeletal disorders, and frailty. Physical exercise has well-documented, beneficial effects on numerous health outcomes, including cardiovascular disease and all-cause mortality [1]. Strength training has attracted increasing attention in the biomedical literature as a powerful and beneficial form of exercise [2-4].
To properly prescribe and monitor strength training for their patients, clinicians need to understand the different forms of strength training, basic concepts of strength training programs, benefits and risks, contraindications, and necessary modifications for special populations.
This topic will discuss the different forms of strength training, key principles and some specific guidelines for implementing basic strength training programs, and common misconceptions about strength training. The benefits of strength training for a myriad of medical conditions, potential risks from strength training, and strength training in the pediatric population are reviewed separately. (See "Strength training for health in adults: Terminology, principles, benefits, and risks" and "Physical activity and strength training in children and adolescents: An overview".)
BASIC PHYSIOLOGY OF STRENGTH TRAINING: HOW WE GET STRONGER — The development of muscular strength depends on a combination of structural changes in the musculoskeletal system as well as neural adaptations in response to the physiologic stress provided by sequential bouts of resistance training. These structural changes include increases in muscle cross-sectional area, alterations in muscle architecture that are thought to enhance actin-myosin cross-bridging and improve force transmission, and increases in musculotendinous stiffness [5,6].
Muscle cross-sectional area and force production capacity are strongly correlated, suggesting that muscular hypertrophy is one of the primary drivers of strength development [5]. Muscle protein accretion (and thus net hypertrophy) results when the rate of myofibrillar muscle protein synthesis (MPS) exceeds the rate of muscle protein breakdown (MPB). In general, MPS is governed by the mammalian target of rapamycin (mTOR) system [7,8]. Mechanical tension, such as that generated during resistance training, is transduced into a chemical signaling cascade that ultimately activates mTOR complex 1 (mTORC1) and its downstream effects on MPS. In the context of exercise, other metabolic factors such as intramyocellular calcium flux, adenosine triphosphate (ATP) turnover, hypoxia, and redox balance are also thought to influence mTOR activation. In addition, nutritional factors play important roles in the activity of mTOR and subsequent muscular hypertrophy [9-11]. (See 'Nutrition for adult trainees' below.)
Neurologic adaptations to strength training include increases in motor unit recruitment, firing frequency, and synchronization that result in more efficient use of existing muscle mass. Motor units are recruited in sequence, from smallest to largest, based on the total force production and rate of force production required by a given task. The threshold for motor unit recruitment is lowered as fatigue increases, such that full muscular recruitment can be achieved as fatigue accumulates while lifting submaximal loads. Low-force activities such as jogging depend primarily on low-threshold motor units containing fatigue-resistant type I ("slow-twitch") muscle fibers, although type II ("fast twitch") motor units may transiently be recruited under conditions of significant fatigue.
By contrast, maximal force production in the context of general strength training, as well as maximal rates of force production in the context of ballistic weightlifting, recruit not only low-threshold motor units but also high-threshold units containing type II muscle fibers and thus preferentially promote the neural adaptations favoring the ability to produce high force. The available evidence suggests that the majority of the age-related decline in skeletal muscle mass is attributable to a preferential denervation (and subsequent loss) of type II muscle fibers. This partially explains the concomitant decrease in muscular force and power production with aging known as dynapenia [12]. Fortunately, long-term progressive resistance training in older adults has been shown to stimulate muscular hypertrophy and type II muscle fiber growth, thereby preventing or limiting dynapenia [13]. Low-force activity does not have this effect. The extensive benefits of strength training are discussed in greater detail separately. (See "Strength training for health in adults: Terminology, principles, benefits, and risks", section on 'What are the benefits of strength training?'.)
FORMS OF STRENGTH TRAINING — Strength training is often referred to in medical and exercise physiology literature as resistance training. Any form of exercise that challenges the muscles' ability to produce force can serve as a form of strength training, although some approaches are more productive than others.
Bodyweight training — Bodyweight exercises use the subject's own weight as the source of resistance. This form of resistance training includes familiar exercises such as push-ups (picture 1), pull-ups (picture 2), crunches, and unloaded squats ("air squats") (picture 3 and picture 4). It also includes less familiar exercises such as lunges (movie 1), dips (picture 5), and back extensions. Other examples of bodyweight exercises can be found in the United States' National Institutes of Aging's Go4Life program: Upper body strength exercises and Lower body strength exercises.
This form of strength training can be valuable, especially in untrained individuals, provided that exercises are selected carefully and performed properly [14]. Bodyweight exercises can be particularly useful as introductory exercises in general and resistance training in particular. However, the force that can be produced for any exercise in this mode of training is limited by the trainee's bodyweight, and beyond this point, progressive overload can only be practically imposed by modulating sets, repetitions, and frequency. We have found that adjuncts such as weight belts, vests, and benches have limited capacity to improve upon the inherent limitations of bodyweight exercises to impose progressive overload and promote continued long-term adaptation and performance improvement.
Performing sets of greater and greater repetitions (eg, increasing from a set of 20 bodyweight squats to a set of 30, 40, or 50) gradually induces a greater endurance-conditioning stimulus and less of a strength-hypertrophy stimulus. Therefore, barring patient refusal to participate in any other form of resistance training, the authors have found that while it may serve a useful introductory purpose in specific circumstances, the exclusive use of bodyweight exercise provides an inferior long-term resistance training solution compared with the other modalities presented herein.
Resistance bands — Resistance bands offer a slightly greater range of resistances compared with bodyweight exercises. Bands are generally fabricated from elastic materials of varying thickness (thus varying the resistance) and can be used to load a wide range of body movements, as seen in the following examples (picture 6 and picture 7).
Resistance bands offer many of the benefits of strength training for beginning trainees and are more portable and convenient than machines or free weights. They may be less intimidating to older clients (and their clinicians). However, the gradation in resistance offered by these products is limited, and we have not found them to be effective tools for the progressive, long-term development of strength and muscle mass.
A 2015 meta-analysis of seven randomized trials studying the effect of resistance band training in adults with type 2 diabetes found that lower extremity strength improved among trainees, but no statistically significant improvements were found in upper extremity strength or decreases in hemoglobin A1c [15]. A trial of 117 older adults found that those assigned to six months of resistance band exercise displayed significant improvements in physical function compared with those assigned to cognitive training [16].
Weight training machines — Machines designed for resistance training come in a wide variety and offer a broader selection of training loads than bodyweight or resistance band training, although they are typically not as finely calibrated as free weights (eg, barbells). Many machines use plates that come in 5- or 10-pound increments or 2.5- or 5-kg increments. This limits the precision of dosing (ie, the amount of weight used for an exercise) and calibrating progressive overload (ie, the amount of any allowable increase in weight as the trainee gains strength).
Another important consideration is that most machine-based exercises are performed while seated or lying down. This may be preferable to standing exercises for certain patients (eg, those with impaired balance, vision, or vestibular function; severe neuropathy; orthostasis; or amputations). However, due to the lack of axial loading, we would not expect machines to promote increased bone mineral density in the axial skeleton and hips to the same degree as free weights, although there are no dispositive data on this point. For similar reasons, machine-based exercises generally offer little in the way of balance training, which is an important benefit of free-weight training with standing exercises.
Advantages of machine-based training include that it may be less intimidating to novice trainees and that the movement patterns, being constrained by the design of the machine, are easier to master. They require less expert supervision and may be better suited for some frail or disabled trainees. When machines are used, the authors favor those that train large, multijoint movement patterns, such as the leg press (picture 8 and picture 9), chest press, shoulder press (picture 10), seated row (picture 11), or lat (short for latissimus) pulldown (picture 12) over those that train single-joint movement patterns, such as the biceps curl and triceps extension. This strategy offers a more potent systemic stimulus per exercise, thus reducing the time required for full-body training and potentially improving adherence. We find no compelling data demonstrating the clear superiority of any particular type of machine (Bowflex, Nautilus, variable resistance, etc) over another for any clinically relevant outcome.
Machines offer fewer opportunities for dropped weights or bars, and this is a reasonable safety consideration. However, the available data do not support the common claim that machines are safer than free-weight training, nor have we found this to be the case in our practice. Resistance training for strength is remarkably safe across modalities [17,18]. The safety of strength training is reviewed in detail separately. (See "Strength training for health in adults: Terminology, principles, benefits, and risks", section on 'What are the risks of strength training?'.)
Because machines allow rapid switching between exercises, they are favored for circuit training, in which one resistance exercise is followed rapidly by another to promote simultaneous development of strength and endurance. In light of the well-documented interference when strength and endurance training are performed simultaneously [19-23], the effectiveness of a circuit training approach for achieving optimal strength gains remains contentious.
Dumbbells and kettlebells — Dumbbells and kettlebells are versatile implements and can be useful in strength training programs. Dumbbells are hand-held weights (picture 13) available in varying resistances (picture 14). We find them useful primarily for introductory, accessory, or rehabilitative exercises. As examples, dumbbells are frequently used to strengthen the rotator cuff after injury (picture 15) or to train pressing movements (picture 16 and picture 17) in patients with shoulder mobility limitations that preclude bench pressing or overhead pressing with barbells. Dumbbells can also be used as very low-weight resistance for trainees being introduced to the squat (picture 18) or deadlift.
Kettlebells are spherical or polygonal weights incorporating a semicircular handle at one end (picture 19). They can be used similarly to dumbbells for some applications (as for goblet squats (movie 2) or kettlebell deadlifts (picture 20)) and also for conditioning work, in which they are repeatedly swung overhead or to shoulder-level from below the waist (movie 3). Like dumbbells and bands, their limited range and gradation of available resistances place constraints on the magnitude and precision of progressive loading that can be imposed for driving long-term strength increases.
Barbell training — Strength training with barbells (picture 21) has been used for many decades to develop the highest levels of strength and athletic performance safely and effectively and has advantages over other forms of resistance training. Barbell training provides for the ergonomic loading of natural human movement patterns through a complete range of motion, allowing for the imposition of training stresses to a large volume of musculoskeletal tissue using just a few exercises [24-26].
Fundamental barbell exercises include the squat, deadlift, and press. For individuals with movement limitations due to prior injury or advanced age, these basic exercises can be modified. Examples of the standard exercises and some common modifications are shown in the following photographs:
●Squat – Standard low-bar back squat (picture 22 and movie 4); high-bar, low-bar, and front squat (picture 23 and picture 24); leg press (picture 8)
●Deadlift – Standard barbell deadlift (picture 25), kettlebell deadlift (picture 20 and picture 26), rack pull deadlift (picture 27)
●Press – Overhead press (picture 28), T-bar press (picture 29), seated dumbbell press (picture 16)
●Bench press – Bench press (picture 30), incline bench press (picture 31)
●Curl – Barbell curl (picture 32)
Barbell training offers the widest range of loading intensities that may be imposed with great precision and thus the ability to simultaneously load multijoint movement patterns and large volumes of muscle. Because the movement patterns loaded by barbells are unconstrained (as they are by any machine), they allow for a more natural expression of the user's anthropometry (ie, the body can move freely within the bounds of its anatomic relationships and proper exercise technique).
Barbell-based exercise likely imposes a more potent training stress than machines. As an example, an electromyographic (EMG) study compared muscle activity in the barbell squat and squats performed in the Smith machine. EMG activity in the barbell squat was significantly higher in the gastrocnemius, biceps femoris, and vastus medialis, and no muscle displayed superior activation in the Smith machine variant [27]. Another EMG study reported greater muscle activation with the free-weight bench press compared with the machine bench press [28].
Free-weight training may invoke a greater hormonal response than machine training or other forms of resistance exercise. In an observational study of 10 young males with resistance training experience, elevations in the serum concentrations of testosterone, growth hormone, and cortisol were found to be higher immediately after workouts using free-weight squats than the machine leg press [29].
Proper barbell programs for general strength acquisition rely heavily on standing exercises. Standing exercises impose an axial load, thereby promoting increased bone mineral density in the axial skeleton and hips. In addition, standing exercises require the lifter to maintain stability as the combined center of mass of the barbell-lifter system changes during the exercise movement [30-33]. Thus, standing exercises develop balance.
Barbells allow for precise loading and progression of loads and thus represent an exquisitely titratable form of exercise medicine. As little as half a pound (0.25 kg) can be added at a time. In summary, properly programmed barbell training is a simple, safe, and comprehensive form of exercise with a wide therapeutic window [24]. This form of training is a rational option in selected patients, including frail and older adult patients, who require strength training.
IMPLEMENTING A STRENGTH TRAINING PROGRAM
General approach — The strength training recommendations of various health and fitness organizations differ considerably. However, most forms of resistance training advocated by these organizations can produce significant improvements in strength and muscle mass, and the associated health benefits, when properly implemented. Commonly recommended approaches for beginners involve training with machines in the 8- to 12-repetition range at varying percentages of the trainee's one-repetition maximum (1RM; the heaviest weight a person can lift a single time when performing a particular exercise). Although not the preferred approach of the authors, recommendations published by the American College of Sports Medicine are one example (table 1) [34,35].
Whenever possible, our preference is for training with free weights (eg, barbells) rather than machines for reasons described above. However, the initial assessment of a new trainee may reveal indications for the use of alternative methods during the initial period of training, with a goal of progressing towards compound, multijoint movements over time. Any individual who can ambulate independently and is otherwise considered medically safe to exercise may begin a strength training program, likely using some form of free-weight-based exercise scaled to their strength and skill level. Conversely, individuals who cannot ambulate independently or who have functionally limiting medical conditions (eg, visual deficits, extremity amputations) but are otherwise safe to exercise may require a more conservative initial approach (for example, using machine-based exercise). (See 'Forms of strength training' above and "Strength training for health in adults: Terminology, principles, benefits, and risks".)
When implementing a progressive resistance training program, primary considerations include:
●Effectiveness for achieving desired outcomes (eg, increased strength, improved mobility)
●Efficiency (which facilitates compliance)
Importance of progressive overload — Progressive overload is the fundamental principle for implementing any form of resistance training. This principle dictates that the physical stress delivered via the volume and intensity of exercise must increase over time in order to continue stimulating adaptation. Conversely, any exercise modality or training prescription (including those designed for "maintenance" purposes) that lacks specific methods for incorporating progressive overload will not only fail to induce long-term adaptation but likely result in regression as the changes of aging or comorbid disease proceed. (See "Strength training for health in adults: Terminology, principles, benefits, and risks", section on 'Strength training: Definition and key principles'.)
This phenomenon is commonly observed in clinical practice, where patients fail to meet current exercise standards despite reporting that they are "active" and regularly engage in activities of daily living, walking short distances around their neighborhoods, gardening, and the like. As they age, these adults commonly develop frailty, sarcopenia, and other comorbidities that are preventable with higher-intensity, progressively overloaded exercise. As an example, according to a review of data taken from health surveys sponsored by the US Centers for Disease Control and Prevention (CDC), adults self-reported 324.5±18.6 minutes per week of moderate physical activity and 73.6±3.9 minutes per week of vigorous physical activity, which would put them well above the 2008 Physical Activity Guidelines for Americans [36]. However, when tracked with accelerometers, these adults actually performed just 45.1±4.6 minutes per week of moderate physical activity and 18.6±6.6 minutes per week of vigorous physical activity. These results suggest that less than 10 percent of adults meet physical activity recommendations. We therefore encourage progressive overload to ensure that adequate exercise intensity is maintained over the long-term for the maximum health benefit.
It is acknowledged that continuous, lifelong increases in resistance training loads are not feasible and that, after a certain level of adaptation has been attained, individuals may prefer a maintenance-type approach. This is an option to consider and discuss on a case-by-case basis with patients who have been actively engaged in resistance training and made substantial progress. Any program designed to maintain strength must ensure that sufficient exercise intensity, volume, and frequency continue to be applied to prevent regression. The specific dose of training stress necessary for strength maintenance varies widely; for example, more anabolically resistant individuals (eg, due to genetic factors, older age, or comorbid disease) detrain more rapidly than others and may require greater training stimulus to maintain strength. However, in the initial phase of training, all individuals can respond to, and should therefore be subjected to, a program using progressive increases in resistance (ie, progressive overload), even if this is done using very small increments in weight [37].
Authors' program for beginners — Using barbell-based, free-weight exercises allows for the delivery of a potent whole-body training stimulus using only a few multijoint exercises and relatively low repetition ranges. By incorporating the major movement patterns, these multijoint exercises enable functional training of all the major muscle groups. This approach is effective, efficient, and safe when properly programmed and coached. By contrast, a program using machine-based or other single-joint or otherwise limited movements typically requires many exercises and high repetition ranges in order to provide a comparable whole-body stimulus sufficient to maximize strength adaptations and consequent health benefits.
Training schedule — In our clinical and coaching practices, we typically begin strength training on two to three nonconsecutive days per week using a basic barbell-based program. A sample barbell-based program appropriate for novice trainees is provided in the following table (table 2). For this program, workouts A and B alternate. When using a three-day program, a typical pattern would be Monday: A, Wednesday: B, Friday: A, Monday: B, Wednesday: A, etc. For a two-day program, the pattern might be Monday: A, Thursday: B, Monday: A, etc. The selection of a two-day versus a three-day program depends on patient attributes and preferences and is an issue for shared decision-making among the patient, clinician, and any fitness professional supervising the training.
Exercise selection and programs — The authors' basic barbell program (table 2) includes the following exercises:
●Squat (movie 4 and picture 22)
Trainees unable to perform the low-bar back squat initially due to weakness or mobility limitations may perform alternative versions of the squat or the leg press (picture 3 and picture 18 and picture 24 and picture 8).
●Deadlift (movie 5 and picture 25)
Weak, novice trainees may need to begin the deadlift using lighter kettlebells or dumbbells (picture 26). Trainees with mobility limitations or poor back position control may perform the rack-pull deadlift (picture 27).
●Bench press (picture 30)
Trainees unable to perform the standard barbell bench press due to weakness, mobility limitations, or anthropometry may use the incline bench press (picture 31) or a number of other variants, including dumbbell presses.
●Overhead barbell press (movie 6 and picture 28)
Trainees unable to perform the overhead barbell press initially due to weakness, balance, or mobility limitations may perform alternative exercises such as the seated dumbbell press (picture 16) or T-bar press (picture 29). For trainees unable to perform any type of standing press, the barbell curl may be a suitable replacement exercise (picture 32).
An alternative, machine-based sample program is provided in the following table (table 3). The machine-based program may be useful for patients reluctant to use barbells or those with medical comorbidities that present challenges for free-weight training (eg, impaired balance or vision, vestibular problems, severe neuropathy, orthostasis, amputations).
The alternative, machine-based program includes the following exercises:
●Leg press (picture 8 and picture 9)
●Chest press (picture 33)
●Lat pulldown (picture 12)
●Overhead press (picture 10)
●Seated row (picture 11)
Both the free-weight and machine-based programs exploit the principle of progressive overload by maintaining constant exercise selection and volume (ie, sets and repetitions) while increasing intensity from one workout to the next.
The approaches presented in the text and tables above can be used by a broad range of individuals. We have used them successfully even in very frail patients in the eighth or ninth decade of life. Specific exercise selection and starting loads require careful evaluation and individualization with increasing age and debility. Our general approach is to determine which movement patterns (free weight, machine, or combination) the patient can perform at very low weight and increase these weights gradually within the specified set-repetition ranges. (See 'Important considerations for strength training in older adult patients' below.)
Determining how much weight to use — Notwithstanding the frequent use in exercise literature of a predetermined 1RM to guide weight selection, we recommend against testing 1RM efforts in practice. Instead, the first session with a new trainee begins with very light weight that the patient can perform easily for five repetitions. Weight is added in small increments during this first session for subsequent sets of five until the exercise begins to become difficult and the movement pattern slows by 50 to 70 percent. This weight constitutes the initial work set weight and is performed for two additional sets to constitute the first workout for that exercise. This approach minimizes the form breakdown and risk of injury that obtain when single-repetition maximal loading is attempted in untrained individuals.
As the trainee progresses, weight is added to target work sets in judicious increments, typically 1 to 2.25 kg (2.5 to 5 lbs) per session, but as little as 0.25 kg (approximately 0.5 lbs) may be used, establishing the progressive overload necessary to generate continued strength adaptations. This incremental approach often can be continued for several months before further adjustments to the training program are required. Such intermediate and advanced programs, as well as approaches to exercise selection, modification, and substitution, are beyond the scope of this topic but are discussed at length elsewhere [24,38-40].
We recommend against performing exercises until muscular failure. Both 1RM testing and training to muscular failure routinely cause significant breakdown in technique, which confers no benefit and compromises safety, irrespective of the modality of strength training (eg, barbells, machines, bodyweight).
In our practice, rest periods between work sets begin at three to five minutes to optimize recovery and maintain performance from set to set as well as to aid hypertrophy and strength adaptation. As individuals gain strength and heavier loads are used, rest intervals will increase.
Determining appropriate strength goals — Little direct evidence is available to help determine what levels of strength are needed to reap maximal health benefits. Moreover, achievable strength gains will vary depending on a range of factors, including age, sex, comorbidities, injury history, training capacity, anabolic resistance, and psychological factors (eg, motivation), among others. With these important limitations in mind, maximal health benefits may be achievable by reaching the following strength thresholds:
For males:
●Lower body strength: Leg press 1.9-times bodyweight
●Upper body strength: Bench press 1.1-times bodyweight
For females:
●Lower body strength: Leg press 1.14-times bodyweight
●Upper body strength: Bench press 0.55-times bodyweight
Few studies have looked directly at how much strength must be gained to reap reported health benefits. Two systematic reviews found a dose-response relationship between strength gain and improvements in resting blood pressure and hemoglobin A1C (HbA1C) [41,42]. In both studies, subjects that gained the most strength experienced the greatest benefit (ie, reduced their blood pressure or HbA1C by the greatest amount).
To quantify the relationship between levels of absolute or relative strength and health trajectory, researchers followed 8762 men aged 20 to 82 for an average of 18.9 years [43]. They found that the upper tertile (ie, one-third) of strength performance was associated with the lowest risk for all-cause, cardiovascular-related, and cancer-related mortality. Thresholds for the upper tertile were the following:
●Lower body strength: Leg press 1.9-times bodyweight
●Upper body strength: Bench press 1.1-times bodyweight
Strength gains among men in the middle tertile remained associated with a reduced risk of all-cause, cardiovascular-related, and cancer-related mortality compared with those in the lowest tertile. Thresholds for the middle tertile were the following:
●Lower body strength: Leg press 1.7-times bodyweight
●Upper body strength: Bench press 0.9-times bodyweight
After controlling for potential confounders, including cardiorespiratory fitness, the significant and inverse association between muscular strength and all-cause mortality and cancer-related mortality persisted across ages and body mass indices, but the association between muscular strength and cardiovascular-specific mortality did not remain statistically significant.
No prospective studies of strength performance thresholds for adult females have been published. Available data indicate that males and females demonstrate similar relative strength improvements in response to exercise [44,45]. On average, females seem to be approximately 50 and 60 percent as strong as men in upper and lower body exercises, respectively [46]. When corrected for overall lean body mass, there are no significant differences between men and women's lower body strength, whereas upper body strength appears to be greater in men [47]. This may be due to training histories and muscle mass distribution [48].
Using these findings and extrapolating from the upper tertiles of strength in males reported in the study above, the following approximate "upper tertile" strength thresholds for adult females appear reasonable:
●Lower body strength: Leg press 1.14-times bodyweight
●Upper body strength: Bench press 0.55-times bodyweight
Again, little evidence is available to extrapolate strength performance from other exercises, such as machine-based resistance, dumbbells, or other resistance implements. This limits our ability to provide objective strength thresholds for all exercises. Regardless of the tools used, we recommend that clinicians encourage their patients to participate in a resistance exercise program that produces demonstrable increases in strength (eg, perform a given number of repetitions with greater load, or perform more repetitions with a given load) while meeting or exceeding the resistance training component of the current United States Physical Activity Guidelines.
Incorporating cardiovascular exercise — In patients with metabolic disturbances (eg, obesity, diabetes, metabolic syndrome, and comparable conditions), we recommend adding cardiovascular training involving high-intensity interval training (HIIT) or low-intensity steady state (LISS) training depending on the patient's needs, limitations, and resources:
●For non-older adults who are obese, diabetic, or otherwise metabolically compromised, we recommend a combination of HIIT and LISS training, each performed once per week, ideally on separate days from strength training. When cardiovascular and strength training are performed simultaneously, the former interferes with strength development [19-23]. If strength and conditioning training days must be combined for practical or scheduling reasons, we recommend performing conditioning after the completion of resistance training. For HIIT, we routinely use 20 to 30 seconds of vigorous effort alternating with 90 seconds of rest. HIIT can be implemented using a weight sled, stationary bicycle, or rowing machine. It is reasonable to start with four to seven rounds of interval training (8 to 14 minutes total) and increase training volume as tolerated.
●For previously sedentary adults who are older or deconditioned, we usually recommend 20 to 30 minutes of LISS conditioning performed one to two times per week in addition to strength training. This can be performed on a rowing machine, recumbent or air bicycle, elliptical machine, or similar commercial equipment.
IMPORTANT CONSIDERATIONS FOR STRENGTH TRAINING IN OLDER ADULT PATIENTS — Older adults can gain substantial strength by following a proper strength training program and may derive the greatest health benefits from such training [49,50]. This population is prone to sarcopenia, osteopenia, frailty, and insulin resistance. The loss of muscle in older adults appears to be disproportionately due to the atrophy or loss of type II high-power (fast-twitch) muscle fibers. However, the available data indicate that many if not most of these fibers remain, even in the eighth decade and beyond. With an appropriate strength training program, such as that described below, these fibers can be rescued and developed [13,51,52]. (See "Normal aging" and "Frailty".)
Older subjects represent a far more heterogenous training population than younger adults, and thus, a high degree of individualization is necessary when selecting exercises and designing a strength program. Nevertheless, the same general principles of strength training apply across all populations. (See "Strength training for health in adults: Terminology, principles, benefits, and risks", section on 'Strength training: Definition and key principles'.)
Exercise selection — Training is most productive, safe, and well tolerated when the program focuses on what the patient can do, rather than what they cannot do. This means loading the largest multijoint movement patterns the patient can perform and progressing from there. Thus, some older patients will be unable to perform squats or overhead presses through a full range of motion but will be able to perform leg presses and standing barbell curls. Almost all patients who are able to stand can perform the deadlift or a deadlift variant with light bars and light weight plates, and it is unusual to encounter subjects even of very advanced age who cannot perform some version of the bench press. As an example, an older adult whose relative immobility prevents them from squatting or pressing can still make remarkable progress with progressive overload using primarily the deadlift and bench press [24], accumulating impressive levels of strength and improving power, muscle mass, bone density, and insulin sensitivity.
Programming — The same programming principles apply across training populations. Application of a training stress, allowance for proper recovery, and display of a performance increase remain the cornerstones of training in older subjects, including those of advanced age. However, older trainees will generally make slower progress, require smaller increases in loading, and require more assiduous attention to recovery variables like sleep, nutrition, and active rest [24,38].
Most adults in their sixth or seventh decade can begin training with the careful application of the same training programs used in younger subjects but will tend to require more and earlier modification of training variables on an individualized basis [24]. Older trainees are often able to make and maintain progress with reduced frequency of training, but the authors' experience with this population indicates that they require relatively more frequent exposure to heavy loading to maintain strength gains than younger subjects.
The overall training frequency required for progress and the frequency of exposure to high-intensity loading is highly individual and depends on many factors, including age, sex, attention to recovery variables, genetic factors, comorbidities, medications, level of training, and others. As training progresses, individual factors become more important, and post-novice programming becomes increasingly individualized. Referral to a strength and conditioning professional experienced in the design and conduct of strength training programs for older adults is highly recommended.
The program goals for all older adults are similar to those for younger trainees: optimization of strength and function within the constraints of safety, time availability, recovery parameters, and physical potential. An untrained 80- or 90-year-old gains strength with training just like a younger trainee, although improvements in performance plateau sooner. In later stages of training, older clients may require highly individualized programs just to maintain strength or to minimize declines in force production.
Some researchers and health organizations advocate exercise programs for older adults that include strength training exercises using only light or moderate resistance combined with separate exercises to improve balance and gait. Based on their experience training many older adults, the authors would argue strongly that a well-designed and properly implemented strength training program that emphasizes multijoint exercises using barbells is more than sufficient to address problems with balance and gait in the large majority of individuals. As older adults gain strength, function improves.
NUTRITION FOR ADULT TRAINEES — While a complete discussion of sports nutrition is outside the scope of this article, there are several clinically relevant nutrition considerations for adults engaging in strength training regarding dietary protein, energy intake, and supplements that should be mentioned.
Protein requirements — An accumulating body of data suggests that standard nutritional recommendations are inadequate for adults engaged in physical training programs [53,54]. This is particularly true of protein, a critical macronutrient for all strength trainees and even more so for older adults who exhibit a decreased sensitivity to both dietary protein and resistance training in general [55-57]. Anabolic resistance is the term used to describe diminished muscle protein synthesis (MPS) in response to either ingestion of dietary protein or sessions of resistance training. Anabolic resistance is caused by numerous age-related vascular, hormonal, and metabolic changes.
With respect to dietary protein, decreased blood flow to the splanchnic and muscle tissues combined with age-related decreases in serum testosterone, various growth hormones, and other trophic factors compromise the potential anabolic effects of postprandial increases in serum concentrations of amino acids. However, this diminished response can be mitigated with increased dietary protein [58-60]. As an example, in a retrospective analysis, there was no difference in MPS in healthy younger and older men once a threshold of high-quality dietary protein ingestion was achieved [61]. These thresholds were 0.24 and 0.40 g per kg of bodyweight in younger and older participants, respectively.
Based on the sum of available evidence, we recommend the consumption of between 1.6 and 2.2 grams per kg of bodyweight per day of dietary protein (maximum suggested dose 250 grams) for those participating in strength training programs [62]. It is reasonable to use total bodyweight to estimate protein requirements.
Contrary to widely held assumptions, this level of protein intake does not harm the healthy kidney and is necessary to optimize muscle protein accretion in response to training [63,64]. Protein derived from a variety of plant sources, fish, and other unprocessed animal sources does not appear to increase health risks [65].
It is important to counsel patients that most of their dietary protein should be of high quality, which refers to bioavailability and concentrations of both essential amino acids (EAAs) and branched-chain amino acids (BCAAs). BCAAs (ie, leucine, valine, and isoleucine) appear to be indispensable, as they are key to the activation of mammalian target of rapamycin (mTOR), a central modulator of protein synthesis [53,54,66]. Nearly all animal-derived proteins (eg, chicken, beef, fish, eggs, dairy, whey) possess sufficient levels of bioavailable EAAs to meet dietary protein needs.
A growing body of evidence suggests that equivalent outcomes may be achieved with plant-based sources of protein, if these are consumed in sufficient quantities (greater than 1.6 g/kg bodyweight per day), although the majority of these studies involved younger subjects [67-70]. When consuming plant protein sources with a lower content or bioavailability of EAAs and BCAAs, larger amounts may be required to achieve equivalent effects to animal-based protein sources.
Our recommendations for protein consumption and strength training intensity are supported by the findings of a study in which 208 healthy adults over 65 years were randomly assigned to one of three nutritional strategies (carbohydrate supplementation, collagen protein supplementation, or whey protein supplementation) combined with either low- or high-intensity strength training [71]. The study was completed by 184 subjects. At one year, only the group taking whey protein supplementation and following a high-intensity strength training program increased both their quadriceps cross-sectional area and lower extremity strength.
Energy requirements — With respect to overall energy requirements in those participating in strength training, the clinician must consider the needs of the individual to make appropriate recommendations. As an example, a patient with frank metabolic disturbance (eg, type 2 diabetes) or obesity would be best managed by prescribing a calorie-restricted diet, whereas a patient who desires to increase lean body mass should be prescribed a caloric surplus. In practice, we recommend manipulation of carbohydrate or dietary fat consumption while maintaining protein intake to achieve the correct energy balance.
While it is true that strength training relies almost entirely on adenosine triphosphate (ATP), phosphocreatine, and glycolytic energy systems, available evidence does not support a benefit of higher carbohydrate intake relative to dietary fat or vice versa. Rather, the more important dietary inputs for body fat loss, increased strength, and increased muscle mass appear to be dietary protein intake and dietary compliance.
COMMON MEDICAL MISCONCEPTIONS ABOUT STRENGTH TRAINING — Clinicians, allied health care professionals, patients, and even some fitness professionals may have been exposed to misconceptions about the risks, benefits, and implementation of strength training. In this section, we survey some of the most common myths about this form of exercise.
The Valsalva maneuver — Medical and fitness professionals routinely advise against use of the Valsalva maneuver when training for strength, although evidence supporting this proscription is entirely lacking. The Valsalva maneuver, in which the breath is held against a closed glottis, increases pressure within the thoracoabdominal cavity, which is commonly presumed to help support the spine [72,73], although definitive data on this point are lacking.
Holding the breath is a completely natural and unavoidable response to lifting a heavy load [72,74]. Nevertheless, the Valsalva maneuver is routinely discouraged on the basis that it will increase intracranial and intra-arterial pressures and precipitate intracranial hemorrhage or other vascular catastrophes. However, there are no empirical data causally linking the Valsalva maneuver to stroke or myocardial infarction. Indeed, data in the neurosurgical literature indicate that the practice is protective against aneurysmal rupture by moderating the transmural pressure on an occult intracranial aneurysm during loading [72,75-78].
Field experience is even more compelling; millions of people perform billions of heavy repetitions under Valsalva every day. Yet, intracranial hemorrhage during strength training is an extremely rare event and does not appear to occur with any greater frequency or temporal association than hemorrhage during sneezing, sex, defecation, or conversation [79-81]. Our evaluation of the available evidence and our combined experience as coaches indicate that this ubiquitous practice is safe in patients without thoracic, abdominal, ocular, or intracranial vascular abnormalities.
Strength training during pregnancy — Resistance training is not contraindicated by uncomplicated pregnancy. Our experience with this population, along with limited published evidence [82], suggests that heavy resistance training is tolerated well into the third trimester. However, while there are virtually no dispositive data on this subject, most guidelines from national and international organizations recommend a much more conservative approach to resistance training during pregnancy. These guidelines and further information about exercise during pregnancy are reviewed separately. (See "Exercise during pregnancy and the postpartum period".)
Pediatric populations — Properly prescribed and supervised strength training is beneficial and safe for children and adolescents. Frequently voiced concerns that such training damages growth plates and "stunts growth" lack empirical substantiation. The use of strength training in this population is discussed separately. (See "Physical activity and strength training in children and adolescents: An overview".)
Osteoarthritis — A common concern among some clinicians and patients is that the loading used in progressive resistance exercise increases skeletal "wear and tear," thereby inducing joint damage and osteoarthritis (OA). However, the available evidence shows that progressive resistance training induces clinically significant improvements in muscle strength, functional ability, and pain scores even in patients with advanced OA. Moreover, chronic inactivity and obesity in patients with OA are both significant risk factors for further cartilage loss and progressive functional disability that are modifiable with resistance training [83]. Earlier intervention to attenuate the progressive loss of muscle strength associated with OA may retard progression of this disease. (See "Strength training for health in adults: Terminology, principles, benefits, and risks", section on 'Musculoskeletal'.)
Concerns over the feasibility of high-intensity resistance training in patients with symptomatic OA have been challenged by studies showing the safety of intensities above 80 percent one-repetition maximum (1RM) without exacerbation of pain symptoms. Higher-intensity training programs tend to show greater effect sizes for improvements in strength, functional status, and decreases in pain [84-88].
Hypertension — A widespread and persistent misconception has held that strength training precipitates or worsens high blood pressure, and this myth has been given new impetus on the basis of some findings that arterial compliance is slightly decreased by training. However, the clinical impact of this "arterial stiffening" effect is unclear at best, especially in light of data that strength training does not worsen and actually improves hypertension. Patients with controlled hypertension should be encouraged to participate in strength training. (See "Strength training for health in adults: Terminology, principles, benefits, and risks", section on 'Hypertension' and "Exercise in the treatment and prevention of hypertension", section on 'Type of exercise'.)
Mobility — Mobility is a trainable attribute, and strength training with proper exercise selection and technique can improve mobility. Indeed, it is a common coaching experience that strength training using full range of motion, multijoint movement patterns loaded with barbells or other resistance improves mobility and function among trainees.
In a systematic review and meta-analysis of 55 studies involving 2756 primarily young adult participants (mean age 23.9 ± 6.3 years), resistance training with external loads (ie, not bodyweight exercise) was found to produce significant improvements in range of motion [89]. No statistical difference was noted between the mobility effects of such resistance exercise and stretch training, either alone or in combination with strength training.
"Bulking up" in females — Much of the general public and some clinicians confuse strength training with bodybuilding. Bodybuilding is not focused on the optimization of strength, power, and mobility, but rather on promoting profound muscle hypertrophy and the realization of an "idealized" physique. Females and their clinicians who do not grasp the important distinction between strength training and bodybuilding may be concerned that females who engage in resistance training will be at risk for developing the unwanted appearance of a hypertrophic, masculine-appearing, "bulky" phenotype. In general, female patients who follow a strength training program for general fitness and health do not tend to develop such an appearance, and this concern should not prevent females from engaging in a properly prescribed resistance training program.
Benefits of low weight performed for high repetitions — Available evidence suggests that training with heavier loads (>60 percent of 1RM weight) tends to provide superior outcomes in strength compared with training with lighter loads (<60 percent 1RM) [90,91]. This is likely due to the greater neuromuscular adaptation stimulated in response to higher intensities [92]. A 1RM is the heaviest weight a person can lift a single time when performing a particular exercise.
By contrast, equivalent outcomes in terms of muscle hypertrophy can be achieved across a variety of loading ranges when sets are performed close to volitional failure. Therefore, to the extent that strength is the stated goal of a training program, exposure to heavier loads is recommended, assuming that this is accomplished using carefully planned progressive overloads over time. (See 'Implementing a strength training program' above.)
Low-intensity programs have not been demonstrated to be safer or more effective for strength outcomes than programs using higher intensity. However, for the reluctant patient, initiating strength training with lower intensities (ie, lighter loads) may be a reasonable starting point, with the understanding that long-term progressive overload will be required to achieve continued gains in strength.
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Exercise in adults".)
SUMMARY AND RECOMMENDATIONS
●Physiology – The development of muscular strength depends on structural changes to the nervous and musculoskeletal systems in response to the physiologic stress provided by sequential bouts of resistance training. (See 'Basic physiology of strength training: How we get stronger' above.)
●Forms of training – Strength or resistance training can be performed using bodyweight exercises, resistance bands, weight training machines, dumbbells, kettlebells, and barbells. Strength training with barbells (picture 21) provides for the ergonomic loading of natural human movement patterns through a complete range of motion, allowing for the imposition of training stresses to a large volume of musculoskeletal tissue using just a few exercises. (See 'Forms of strength training' above.)
●Implementation – Most forms of resistance training advocated by major fitness organizations can produce significant improvements in strength. Whenever possible, the authors' preference is for training with barbells. (See 'Barbell training' above.)
Any individual who can ambulate independently and is medically safe to exercise may begin a strength training program using some form of free-weight-based exercise; individuals who cannot ambulate independently or who have functionally limiting medical conditions but are otherwise safe to exercise may require a more conservative initial approach (eg, machine-based training). (See 'Implementing a strength training program' above.)
●Importance of progressive overload – Progressive overload is the fundamental principle for resistance training. This principle dictates that the physical stress delivered via the volume and intensity of exercise must increase over time in order to continue stimulating adaptation. Any strength training prescription (including those designed for "maintenance" purposes) that lacks specific methods for incorporating progressive overload will not only fail to induce long-term adaptation but likely result in regression as the changes of aging or comorbid disease proceed. (See 'Importance of progressive overload' above.)
●Sample programs – A sample barbell-based program appropriate for novice trainees is provided (table 2), as is an alternative, machine-based sample program (table 3). Details pertaining to the implementation of these programs are provided in the text. (See 'Authors' program for beginners' above.)
●Training for older adults – Older adults may derive the greatest health benefits from strength training, as this population is prone to sarcopenia, osteopenia, frailty, and insulin resistance. Guidelines for implementing a strength program for older adults are described in the text. Key points include focusing on exercises the older trainee can perform, making accommodations as necessary for movement restrictions and slower progress, and paying assiduous attention to recovery variables like sleep, nutrition (particularly ensuring adequate dietary protein), and active rest. Older adults require relatively more frequent exposure to heavy loading to maintain strength gains than younger subjects. (See 'Important considerations for strength training in older adult patients' above and "Strength training for health in adults: Terminology, principles, benefits, and risks".)
●Common misconceptions – Misconceptions about strength training abound. The following statements are true:
•Holding the breath (Valsalva maneuver) is a natural and unavoidable response to lifting a heavy load. It is safe in trainees without vascular abnormalities. (See 'The Valsalva maneuver' above.)
•Resistance training is not contraindicated by uncomplicated pregnancy. (See "Exercise during pregnancy and the postpartum period".)
•Properly prescribed and supervised strength training is beneficial and safe for children and adolescents, and it does not impair growth. (See "Physical activity and strength training in children and adolescents: An overview".)
•Properly performed strength training is beneficial to patients with osteoarthritis (OA). (See "Strength training for health in adults: Terminology, principles, benefits, and risks", section on 'Musculoskeletal'.)
•Properly performed strength training improves hypertension. (See "Strength training for health in adults: Terminology, principles, benefits, and risks", section on 'Hypertension' and "Exercise in the treatment and prevention of hypertension", section on 'Type of exercise'.)
•Properly performed strength training improves mobility. (See 'Mobility' above.)
•Properly performed strength training (as opposed to bodybuilding) typically does not cause females to develop a bulky, excessively muscular appearance. (See '"Bulking up" in females' above.)
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