Characterising lower limb muscle activity and test-retest repeatability of EMG measures in healthy adults during upright pedalling

Abstract

Background: Upright pedalling (UP) has similarities to walking in terms of both muscle activation and biomechanical activity. Therefore, UP is a potential rehabilitation therapy for enhancing walking recovery. The development of UP as a rehabilitation intervention requires understanding of muscle activity patterns elicited during pedalling in a range of participants, including young healthy adults. The aims of this study were: to characterise muscle activation patterns during UP in young healthy adults, and to investigate the test-retest repeatability of EMG-derived measures used to characterise activity patterns. Methods: Participants (total n=8, females: n=7) performed two UP sessions, separated by a 1-hour rest period. During UP, muscle activity of rectus femoris (RF) and biceps femoris (BF) was recorded using surface EMG. Lower limb muscle activity was characterised by average, integrated activity (iEMG) for each muscle group according to four 90° phases of the 360° wheel turn. This procedure provided a measure of muscle activity throughout the pedalling cycle. Testretest repeatability of mean iEMG values for each pedal revolution was calculated using an intraclass correlation coefficient (ICC) with 95% confidence intervals (CI). Results: Characterisation of activity: muscle activity for all participants during UP demonstrated reciprocal muscle activation of BF and RF. More specifically, RF exhibited double bursts of activity at 0–135° and 270–360°, whereas BF demonstrated a single burst at 135–270°. Test-retest repeatability: appeared high for RF when considering the point estimate (ICC=0.837), but the associated wide CIs (-0.224–1.39) mean that this finding is imprecise. A lack of repeatability observed for BF (ICC=0.02) was also inconclusive due to wide CI's (-0.258–0.737). Conclusions: UP elicited a reciprocal muscle activation pattern in RF and BF in a small sample of young healthy volunteers. Definitive test-retest repeatability of recorded measures was not established. Implications: This study has contributed normative data on muscle activation patterns during walking-like activity, and data to inform sample size for definitively testing intra-participant variance.