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

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. 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. 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. 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.