The acute effects and reproducibility of resistance training fatigue on load-velocity relationship variables

Since the load-velocity relationship was validated as a useful tool for assessing fatigue, its reliability and reproducibility have yet to be established, which are crucial for programming training plans and monitoring athletes’ physiological status. Therefore, this study aimed to explore the acute effects of resistance training fatigue on load-velocity (L-V) relationship variables (maximal theoretical force capacity [ L 0 ], maximal theoretical velocity capacity [ v 0 ], and maximal theoretical power capacity [A line ]) under different set configurations and whether the fatigue was reproducible. Fourteen male athletes performed back squats at 80% of their one repetition maximum under 20% velocity loss across three sets configurations (6, 4, and 3 sets), with each configuration performed twice. L-V relationship variables were established in pre-fatigue and 15 min post-fatigue for all sessions. Fatigue resulted in significant decline in v 0 （F = 27.084, p < 0.001）and A line （F = 72.552, p < 0.001）, but not in L 0 (F = 0.466, p = 0.508). The three set configurations produced similar fatigue levels for all L-V relationship variables. The effects of fatigue on L-V relationship variables were reproducible in all set configurations for all variables (ICC ≥ 0.759, CV ≤ 9.3%). The findings suggest that, under a fixed 20% VL, the acute effects of L-V relationship variables were reproducible from resistance training fatigue, no matter how many training sets were applied. Hence, the L-V relationship variables are a reliable tool to measure acute resistance training fatigue.