Single-session measures of quadriceps neuromuscular function are reliable in healthy females and unaffected by age

Abstract

ObjectiveThe inter-session reliability of a wide range of measures used to characterize the aging neuromuscular system is unknown, particularly in females. The aim of this study was to determine the inter-session reliability of quadriceps neuromuscular function assessed via maximal voluntary and evoked force and electromyography responses in healthy young and older females. MethodsTwenty-six females aged 19 - 74 years completed two identical testing sessions 9 {+/-} 7 days apart. Quadriceps neuromuscular function measurements included isometric maximal voluntary force (MVC), high and low frequency twitch force, voluntary and evoked electromyography (EMG) in superficial quadriceps (RMS, M-wave and H-reflex), and maximal torque (T0), velocity (V0) and power (PMAX) derived from torque-velocity and power-velocity relationships. Intra-class correlation coefficients (ICC), coefficients of variation (CoV) and Bland-Altman plots were used to assess inter-session reliability. The effect of participant age on inter-session reliability was assessed by linear regression. ResultsExcellent reliability (ICC > 0.8) was shown for all voluntary and evoked mechanical outcomes and systematic bias was essentially absent. Similarly, all vastus lateralis EMG outcomes showed excellent reliability (ICC > 0.8) with CoVs < 12%, which were better than vastus medialis and rectus femoris outcomes. Participant age was not associated with inter-session reliability (P > 0.05). ConclusionExcellent reliability of voluntary and evoked force and vastus lateralis EMG outcomes measured in healthy females can be attained in one testing session, irrespective of age, increasing feasibility for future research. The random error should however be considered when quantifying age-related differences and/or adaptation to exercise in female neuromuscular function. New and NoteworthyThe test-retest reliability of a diverse range of measures used to quantify neuromuscular function were assessed in younger and older females for the first time. We show that reliable measures of maximal voluntary and evoked quadriceps force and electromyography outcomes can be obtained in one testing session, irrespective of participant age. Thus, neuromuscular function can be accurately assessed across the female lifespan with minimal inconvenience imposed on participants, increasing feasibility for future research.