Timing Matters: Assessing Fatigue During and After Resistance Training

Background: Monitoring neuromuscular fatigue during resistance training informs load prescription and recovery management. Two common approaches, namely within-training assessment (immediately after each set) and post-training assessment (after session completion), differ in their methodological demands, yet their acute responses and within-session reliability remain insufficiently characterized. Hypothesis: Fatigue levels would be influenced by training protocol, value type (maximum vs average), and set number or timepoint, with corresponding differences in within-session reliability. Study Design: Randomized, counterbalanced crossover study. Level of Evidence: Level 2. Methods: A total of 13 well-trained male athletes completed 3 protocols in randomized order: 5 sets of fixed-repetition squats (Fixed), 5 sets of velocity-loss-threshold-controlled squats (VLT), and a control condition. Countermovement jump (CMJ) height was assessed at baseline, after each set, and at 8 post-training timepoints (5-60 minutes). Fatigue was quantified as the percentage of CMJ height relative to baseline, using both maximum and average values of 2 trials. Within-session reliability was evaluated via coefficient of variation (CV) and intraclass correlation coefficient (ICC). Results: For within-training assessment, significant main effects emerged for protocol ( P = 0.006), value type ( P = 0.031), and set number ( P < 0.001), with lower values (greater fatigue) observed when using average values and in the final 2 sets. All protocols demonstrated acceptable within-session reliability (CV ≤ 5.29%, ICC ≥ 0.745). For post-training assessment, time point significantly affected fatigue ( P < 0.001), with the lowest values at 30 to 40 minutes. ICC was low during 0 to 15 minutes post-training; acceptable reliability was achieved only with maximum values from 10 minutes onward (CV ≤ 7.29%, ICC ≥ 0.750). Conclusion: Both within-training and post-training fatigue assessments are feasible for monitoring resistance training fatigue, but methodological choices substantially influence measured values and reliability. Clinical Relevance: For within-training fatigue monitoring, average values provide greater sensitivity in detecting fatigue; for post-training assessment, maximum values should be used after ≥10 minutes of rest to ensure acceptable reliability.