Lower-limb electromyographic responses across four recumbent cycling configurations in healthy young men

Recumbent cycling provides an adjustable configuration in which backrest angle and crank-axis height can alter lower-limb loading. Backrest angle changes the orientation of the active musculature relative to gravity, whereas crank-axis height modifies the foot-pedal interface and the ankle lever arm. Whether such positioning is associated with differences in lower-limb electromyographic (EMG) activation across both factors together has not been examined. Using a randomized crossover design, fifty-nine healthy young men cycled at 100 W and 50 rpm under four conditions combining two backrest angles (30°, 75°) and two crank-axis heights (Rh, high, 77 cm; Rl, low, 45 cm). Surface EMG from the rectus femoris (RF), biceps femoris (BF), and gastrocnemius medialis (GAS) was analyzed for root mean square (RMS) amplitude, absolute onset sequence, and relative recruitment timing (%Sequence, derived using Telescan software and referenced to RF). RMS amplitude did not differ across conditions for any muscle (all p ≥ 0.356), and absolute onset sequence showed no condition effect (all p ≥ 0.197). For GAS %Sequence, the Greenhouse-Geisser-corrected omnibus test was significant (F(1.32, 76.56) = 28.45, p < 0.001), driven by a within-30° contrast in which %Sequence was lower under Rl than Rh (paired t(58) = 10.39, Holm-adjusted p < 0.0001; mean difference 22.0 percentage points, 95 % CI [17.8, 26.3]; dz = 1.35). Because %Sequence is referenced to RF, this exploratory shift should be interpreted cautiously. Lower-limb activation may be constrained by the closed-chain nature of pedaling, whereas distal recruitment timing may be sensitive to crank-axis height and the foot-pedal interface.