Motor Variability as a Predictor of Strength Adaptation: The Role of Complexity in Resistance Training

ABSTRACT: López-Fernández, M, García-Aguilar, F, Caballero, C, Moreno, FJ, and Sabido, R. Motor variability as a predictor of strength adaptation: the role of complexity in resistance training. J Strength Cond Res XX(X): 000-000, 2026-This study investigated the relationship between initial motor variability, measured using Fuzzy Entropy (FuzzyEn), and adaptability to resistance training, hypothesizing that individuals with greater initial variability would exhibit superior strength adaptations. Fifty-eight subjects (36 men, 22 women) completed a 9-week resistance training protocol focused on lower-body exercises. Subjects were stratified into stronger (SG) and weaker (WG) groups based on their squat 1RM/body mass ratio. They were further divided into high variability (HV) and low variability (LV) subgroups based on baseline FuzzyEn values derived from acceleration signals during squat repetitions. Strength gains and the relationship between initial variability and adaptability were analyzed using mixed ANOVA and correlation tests. Both SG and WG showed significant strength gains postintervention (p < 0.001). In SG, HV subjects achieved greater strength gains (25.18 ± 12.98 kg; 19.93 ± 11.55%) than LV subjects (15.77 ± 9.03 kg; 14.47 ± 9.35%, p = 0.029), with a significant positive correlation between FuzzyEn and strength gains (r = 0.550, p < 0.01). Conversely, no significant differences in strength gains were observed between HV and LV subgroups within WG. The results suggest that HV in SG indicates greater neuromuscular adaptability, whereas in WG, variability may represent noise that does not promote adaptability. Initial motor variability could be a valuable tool for predicting resistance training adaptability in stronger individuals, with HV being associated with greater relative strength gains. Motor variability should be considered when designing individualized training programs, because higher initial variability may indicate greater adaptative potential in advanced athletes, allowing for more targeted loading and periodization decisions.