Gotta Go Fast: Intended Concentric Effort Produces Divergent Myoelectric Spectral Profiles During Fatiguing, Load-Equated Resistance Exercise

ABSTRACT: Benitez, B, Kwak, M, Succi, PJ, Mitchinson, CJ, Snell, ER, and Bergstrom, HC. Gotta go fast: Intended concentric effort produces divergent myoelectric spectral profiles during fatiguing, load-equated resistance exercise. J Strength Cond Res XX(X): 000-000, 2026-The aim of this study was to examine how intended concentric velocity, that is, the volitional effort applied to accelerate a load, influences the spectral characteristics of the surface electromyographic (sEMG) signal during fatiguing, load-equated resistance exercise. Twenty recreationally active adults (10 men and 10 women) performed unilateral leg extensions to task failure at 70% 1 repetition maximum under 2 within-participant conditions as follows: maximal intended concentric velocity (Vmax) and 50% of individualized Vmax (50%Vmax). Bipolar sEMG from the vastus lateralis was decomposed into 10 frequency bands using wavelet-based time-frequency analysis. Band-specific spectral intensities were modeled with a lognormal generalized linear mixed-effects model, and Lin's concordance correlation coefficient (ρc) was computed between condition-specific spectral profiles across pairwise time points. The mean propulsive concentric velocity and total repetitions to task failure were secondary outcomes. Significance was set at p ≤ 0.05. The 3-way interaction of condition × frequency × repetition was significant (χ2(3) = 23.98, p < 0.001). Across the set, Vmax redistributed spectral power bidirectionally, increasing the low bands while suppressing the high bands, whereas 50%Vmax increased across the entire spectrum without high-frequency suppression. Despite these divergent profiles, the conditions converged at task failure (ρc = 0.98), and the convergence was asymmetric. The fatigued 50%Vmax profile approximated the fresh Vmax profile (ρc = 0.97) rather than the reverse (ρc = 0.74), indicating that submaximal effort approached the maximal-effort state as fatigue accumulated. The mean propulsive concentric velocity also declined 3.6 times more steeply under Vmax despite similar repetitions. Intended concentric velocity appears to shape the spectral profile of muscle excitation under fixed loading.