Supplemental Information 1: Raw data
The current study tested the hypothesis that voluntary activation during maximal voluntary contraction (MVC) conditionally depends on sex and joint action. Twentyeight healthy adults (14 of each sex) performed knee extensor MVC and plantar flexor MVC at extended and flexed knee positions. Voluntary activation during MVC was assessed using a twitch interpolation technique. The voluntary activation during plantar flexor MVC at the extended knee position was significantly lower (P = 0.020, 95%
... (P = 0.020, 95% confidence interval 1.4 to 14.6, Cohen's d for between-subject design = 0.94) in women (88.3% ± 10.0%) than in men (96.2% ± 6.6%). In contrast, no significant sex differences were shown in the voluntary activation during knee extensor MVC (93.7% ± 5.9% (women) vs. 95.0% ± 3.9% (men)) and during plantar flexor MVC at the flexed knee position (90.4% ± 12.2% (women) vs. 96.8% ± 5.6% (men)). The voluntary activation during knee extensor MVC was significantly higher (P = 0.001, 95% confidence interval 2.1 to 8.8, Cohen's d for within-subject design = 0.69) than that during plantar flexor MVC at the extended knee position in women, whereas the corresponding difference was not observed in men. The results revealed that the existence of sex difference in the voluntary activation during MVC depends on joint action and joint angle. Subjects Anatomy and Physiology, Kinesiology . 2017. Effect of knee alignment on the quadriceps femoris muscularity: cross-sectional comparison of trained versus untrained individuals in both sexes. PLOS ONE 12:e0183148 DOI 10.1371/journal.pone.0183148. Fukunaga T, Roy RR, Shellock FG, Hodgson JA, Day MK, Lee PL, Kwong-Fu H, Edgerton VR. 1992. Physiological cross-sectional area of human leg muscles based on magnetic resonance imaging. Journal of Orthopaedic Research 10:928-934. Gondin J, Guette M, Ballay Y, Martin A. 2005. Electromyostimulation training effects on neural drive and muscle architecture. Medicine and Science in Sports and Exercise Saltin B. 1996. Whole-muscle and single-fibre contractile properties and myosin heavy chain isoforms in humans. Pflügers Archiv-European Journal of Physiology 432:913-920 DOI 10.1007/s004240050215. Hopkins WG, Marshall SW, Batterham AM, Hanin J. 2009. Progressive statistics for studies in sports medicine and exercise science. Medicine and Science in Sports and Exercise 41:3-13. Hunter SK. 2014. Sex differences in human fatigability: mechanisms and insight to physiological responses. Acta Physiologica 210:768-789 DOI 10.1111/apha.12234. Hunter SK, Pereira HM, Keenan KG. 2016. The aging neuromuscular system and motor performance. Journal of Applied Physiology 121:982-995 (73)90023-3. Kennedy PM, Cresswell AG. 2001. The effect of muscle length on motor-unit recruitment during isometric plantar flexion in humans. Experimental Brain Research . 2009. Effects of strength training and detraining on regional muscle in young and older men and women.