Short-term arm immobilization reduces maximal force and alters fatigue responses to a relative-intensity task in team-sport athletes: a randomized controlled trial

Background Short-term limb immobilization induces rapid losses in muscle size and strength, but its effects on performance fatigability and the underlying central and peripheral neuromuscular mechanisms remain unclear. This study examined the effects of three weeks of non-dominant arm immobilization on neuromuscular function and exercise-induced fatigability in team-sport athletes. Methods In a parallel-group randomized controlled trial, 24 team-sport athletes were randomly allocated to an immobilization group or a control group. Twelve team-sport athletes underwent three weeks of non-dominant arm immobilization (IMMO), while twelve served as controls (CG). Before and after the intervention, participants performed a sustained isometric contraction at 50% of maximal voluntary contraction (MVC) of the elbow flexors until task failure. Because the target force was recalculated as 50% of the MVC measured at each visit, the absolute target force was lower after immobilization in the IMMO group. Biceps brachii activation was assessed by electromyography (EMG), while central and peripheral components were quantified using voluntary activation (VA), potentiated twitch force (Q tw,pot ), and M-wave responses. Upper-arm muscle-and-bone area (MBA) was estimated anthropometrically. Results In the IMMO group, immobilization reduced anthropometrically estimated MBA (−7.3%) and pre-exercise MVC (−22.9%), whereas neither changed in the control group. Consequently, the absolute target force of the fatiguing task was lower after immobilization in the IMMO group (89.9 ± 17.5 N before vs 69.3 ± 11.9 N after). Under this lower absolute demand, endurance time increased (220.88 ± 102.7 vs 281.65 ± 99.65 s, p < 0.001) and the exercise-induced decline in MVC was smaller (−31.5 ± 10.2% before vs −14.4 ± 7.8% after immobilization; group × condition × exercise interaction, F(1,22) = 15.74, p < 0.001, η p ² = 0.42, 95% CI 0.10–0.62). The exercise-induced decline in Q tw,pot was also smaller after immobilization in the IMMO group (−38.9% before vs −15.2% after; interaction F(1,22) = 4.58, p = 0.044, η p ² = 0.17, 95% CI 0.00–0.42), whereas it remained large in the control group. Voluntary activation (VA) and RMS/M max decreased after exercise, but no group × condition × exercise interaction was detected for VA (p = 0.130) or RMS/M max (p = 0.391). Given the sample size, these non-significant interactions indicate that a differential central or sarcolemmal response was not detected, not that it was absent. Conclusions In conclusion, short-term immobilization impaired maximal force-generating capacity while increasing endurance time during a sustained submaximal task performed at the same relative, but a lower absolute, intensity. The exercise-induced declines in both maximal force and potentiated twitch force were attenuated after immobilization, whereas no differential change in voluntary activation or M-wave responses was detected. Because this peripheral signature occurred under a lower absolute load, it most plausibly reflects a smaller peripheral fatigue response to a reduced absolute demand rather than an intrinsic enhancement of contractile fatigue resistance. These findings describe altered fatigability during a relative-intensity task and should not be interpreted as improved intrinsic fatigue resistance. Clinical trial registration https://pactr.samrc.ac.za/ , identifier PACTR202607531230552.