Training to failure vs not-to-failure with progressive volume reduction: neuromuscular and metabolic responses in untrained individuals

Resistance training to failure (RT _F ) acutely increases neuromuscular and metabolic demands but also induces fatigue that may compromise subsequent training stimuli. Small reductions in volume at the same intensity, while avoiding failure, may attenuate fatigue while preserving training stimuli. Therefore, this study compared the acute effects of RT _F and non-failure resistance training (RT _NF ) during knee extension exercise. Eleven untrained men completed five RT _NF conditions, each involving an individualized reduction ranging from 10–50% relative to number of repetitions performed during RT _F . Outcomes included maximum voluntary isometric contraction (MVIC), electromyography (EMG), muscle swelling of the rectus femoris (RF) and vastus lateralis (VL), blood lactate concentration, and perceived exertion (RPE). RT _F elicited greater increases in muscle cross-sectional area of both RF and VL (p < 0.01) compared with all RT _NF conditions. EMG amplitude was higher in RT _F than in the 30–50% reduction conditions (p = 0.01 for VL and RF), while MVIC (p = 0.02) and EMG frequency differed across protocols (p = 0.02 for RF; p = 0.03 for VL). Additionally, lactate and RPE (p < 0.01) responses were highest following RT _F . In summary, RT _F maximizes muscle swelling and metabolic stress, whereas performing repetitions up to 20% short of failure provides a comparable neuromuscular stimulus, while minimizing metabolic stress.