Expiratory flow-volume curve showing a "knee" pattern, which is considered to be a normal variant most commonly seen in young adults.
TLC: total lung capacity; RV: residual volume.
Modified from:
Shin HH, Sears MR, Hancox RJ. Prevalence and correlates of a 'knee' pattern on the maximal expiratory flow-volume loop in young adults. Respirology 2014; 19:1052.