Temporal changes in pectoralis major mechanical properties during and following velocity-based resistance training: a repeated-measures myotonometric study

Abstract Background Resistance training induces fatigue-related responses that may reduce force-generating capacity through metabolic and neuromuscular mechanisms. Muscle mechanical properties, including stiffness, elasticity, and resting tone, assessed via myotonometry, provide information about the passive mechanical state and functional status of skeletal muscle. However, limited evidence exists regarding how these properties change during and immediately following velocity-based resistance training sessions, and whether their temporal behavior corresponds with performance, metabolic, and perceptual responses. Methods Twenty resistance-trained men (25.8 ± 4.6 years) completed a repeated-measures experimental protocol consisting of four sets of Smith machine bench press performed at 70% of estimated one-repetition maximum, with 3 min of rest between sets. Sets were terminated upon reaching a 30% loss in mean propulsive velocity (MPV). Muscle mechanical properties and blood lactate concentration were assessed at rest, following each set, and at 5 and 10 min post-session. Performance variables were recorded throughout the protocol. Results Stiffness and resting tone remained stable across sets. At 10 min post-session, stiffness was lower than baseline and the post-set values, whereas resting tone was lower than the post-set values but did not differ significantly from baseline. Elasticity showed no significant pairwise differences over time. Blood lactate progressively increased throughout the protocol. Performance declined across sets, evidenced by reductions in the number of repetitions and movement velocity, accompanied by increased perceived exertion. Conclusions Velocity-based resistance training induced fatigue-related responses, as reflected by decreased mechanical performance and increased metabolic and perceptual markers. However, muscle mechanical properties assessed via myotonometry were primarily altered during the post-exercise recovery phase. Within the constraints of this single-session and protocol-specific design, myotonometric changes were detected mainly during the early post-exercise recovery period rather than following each set. Myotonometry may therefore provide complementary information on short-term post-exercise muscle responses; however, these findings do not establish its suitability for real-time fatigue monitoring across different exercises, loading schemes, or repeated training sessions.