Sex-specific reliability and multidimensional stability of responses to tests assessing neuromuscular function.

The objective of this study was to estimate sex-specific effects in the test-retest cross-reliability of peripheral and central changes in nonlinear and linear measures of a surface electromyography signal during a brief (5 second) and sustained (2minute) isometric maximal voluntary contraction, combined with superimposed electrical stimulation involving the ankle plantar flexors over five identical trials. In this study, we repeated the testing protocol used in our previous study of 10 women (age 20.9, SD=0.3 years) (Bernecke et al., 2015) in a group of 10 men (age 21.2, SD=0.4 years). Despite the central (sex effect; p<0.05, ηp2>0.71, SP>70%) and peripheral fatigability (sex effect; p<0.01, ηp2>0.8, SP>90%) during sustained isometric maximal voluntary contraction, and lower reliability for central activation ratio during brief (intraclass correlation coefficient [ICC]=0.95 for men and ICC=0.82 for women) and sustained maximal voluntary contraction (ICC>0.82 for men and ICC>0.66 for women) over ankle plantar flexors expressed in women more than in men, all the ICCs of all indices measured by tests assessing neuromuscular function across the five identical test-retest trials were found as meaningful (correlation significance of p<0.05 was reached) and no significant differences were found between trials for any of the measured variables. In conclusion, the present study demonstrated greater central and peripheral fatigue for female participants following sustained (2minute) isometric maximal voluntary contraction of the plantar flexor muscles for all repeated trials and indicated an acceptable agreement between measurements of the characteristic variables made using the three different devices (dynamometry, electrical stimulation, and surface electromyography) over time for both sexes.