Identifying a Muscle Activation-Matched Eccentric Intensity and Characterizing Vastus Lateralis Spectral Fatigue Using Surface Electromyography During Incremental Eccentric and Concentric Cycling: A Pilot Study

Eccentric cycling generates greater mechanical output with lower muscle activation and metabolic demand than concentric cycling. However, eccentric cycling intensity is commonly prescribed based on concentric cycling workloads, which may not provide comparable neuromuscular loading between cycling modes. The eccentric intensity required to match muscle activation during a clinically relevant concentric workload and its frequency-domain surface electromyographic (sEMG) characteristics remain unclear. This pilot study aimed to identify an eccentric cycling workload eliciting vastus lateralis (VL) muscle activation comparable to a submaximal concentric workload and to compare frequency-domain sEMG characteristics between cycling modes. Twenty-one healthy females completed concentric and eccentric incremental cycling exercise tests (CICET and EICET). VL sEMG was recorded throughout both tests. The workload closest to 70% of concentric peak power output (PPO) served as the reference, and the eccentric workload producing the closest normalized root mean square (RMS) amplitude was identified as the muscle activation-matched workload. RMS, median frequency (MDF), and normalized MDF slope (NMDF slope) were analyzed. A muscle activation-matched eccentric workload was successfully identified. This workload was significantly higher than the concentric reference workload (p < 0.001), while normalized mean RMS was comparable between conditions. EICET showed significantly higher MDF at the initial and final stages and a significantly less negative NMDF slope than CICET. Preliminary evidence suggests that muscle activation-matched eccentric cycling requires 1.69 times the power output of concentric cycling, based on the ratio of group means, while inducing less neuromuscular fatigue. Larger studies are needed to confirm these findings.