Neuromuscular adaptations to caffeine supplementation in low-load resistance training with blood flow restriction.

Background: Although blood flow restriction (BFR) resistance training effectively enhances muscle strength, it increases fatigue susceptibility due to hypoxic stress. This study investigated whether combining caffeine - a common ergogenic aid - with BFR could provide additional training benefits.

Methods: Twenty-eight young adults completed a 4-week low-load resistance training program for wrist extensors, divided into two groups: BFR (n = 14) and BFR with caffeine (BFRC, n = 14). Both groups performed the same occluded training at 20% of maximal voluntary contraction (MVC), with the BFRC group consuming 6 mg·kg^{- 1} caffeine one hour prior. Pre- and posttests assessed MVC and force control during a task involving gradual force increase and release.

Results: The results demonstrated comparable training-related increases in MVC and precision of control of force in both groups (p > .05). However, only the BFRC group exhibited a significant training-related decline in the size of force fluctuations (p = .002) with enhanced complexity during force release (p = .036). Consistent with the characteristic changes in force fluctuations, the BFRC group exhibited smaller variability (p = .002) and a higher mean frequency (p = .023) of pooled motor unit discharges during force release.

Conclusions: While caffeine does not significantly enhance strength gains after four weeks of isometric BFR training in untrained individuals, it improves force release precision by globally reducing motor unit discharge variability.