Acute Effects of Interset Proprioceptive Neuromuscular Facilitation Stretching on Repetition Performance and Blood Lactate Responses in Resistance-Trained Young Men

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Abstract
Purpose : This study aimed to investigate the acute effects of different interset proprioceptive neuromuscular facilitation (PNF) stretching protocols on repetition performance, total load, blood lactate concentration, and rating of perceived exertion during a resistance training session. Methods : Twelve resistance-trained men (age: 20.83 [1.03] y; height: 1.79 [0.04] m; body mass: 73.50 [5.60] kg; body mass index: 22.99 [1.67] kg/m 2 ) participated in a randomized crossover design. Participants completed 4 interset rest protocols: Combined PNF (COM), Hold–Relax (HR), Contract–Relax (CR), and Passive Rest (PASREST). Butterfly and lat pulldown exercises were performed, with all sets completed to muscular failure. Repetition performance, total load, blood lactate concentration, and rating of perceived exertion were assessed for each protocol. Results : The CR protocol resulted in higher repetition performance and total load compared with PASREST and HR across both exercises ( P < .05), while COM produced superior repetition performance and total load compared with PASREST in the butterfly exercise ( P < .05). Blood lactate concentration was lower in COM compared with PASREST and HR at selected time points ( P < .05), with both COM and CR demonstrating relatively lower lactate concentrations than PASREST at the postexercise time point (T3). Rating of perceived exertion values were higher in COM and HR, whereas CR demonstrated lower perceived exertion alongside maintained performance. Conclusions : Among the interset PNF stretching protocols, the CR method provides the most balanced performance–fatigue profile, combining high repetition performance with lower perceived exertion. In contrast, the COM may offer a metabolically favorable response, as indicated by lower lactate concentrations at selected time points, although this is accompanied by higher perceptual load. These findings should be considered exploratory and hypothesis-generating, given the small sample size and the absence of prospective registration. Practical Applications : Interset PNF strategies may be used to optimize performance and metabolic responses in resistance-trained individuals, particularly in multiset, upper-body resistance training performed to muscular failure. Coaches may select specific protocols based on training goals, using CR to sustain performance with lower perceptual strain, or COM when targeting metabolic responses despite higher perceptual load.

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