The Load-velocity Relationship: Neuromuscular Adaptations to Resistance Training

The primary aim of this project is to compare the effect of VBT with that of PBT on muscular hypertrophy and neuromuscular RT adaptations during an intervention of similar volume lasting 10 weeks. As a secondary purpose, the investigators also intend to examine the relationship between these adaptations with post-training gains in different forms of muscle strength (slow and fast-speed strength, as well as endurance muscle strength). As a tertiary purpose, the investigators aim at determining how neuromuscular fatigue, training stress and muscular damage evolve in response to VBT and PBT during the 10-week intervention. As a quaternary purpose, the investigators intend to assess if the results are consistent for both upper-body and lower-body RT exercises.

The investigators hypothesize that, after 10 weeks of RT, (i) despite showing larger increases in strength, power and muscular activation [increases in motor unit firing rate and recruitment due to high speed contractions ] , due to a lower level of mechanical tension during training , participants assigned to VBT will display less muscular hypertrophy; (ii) participants assigned to VBT will present larger increases in slow- and fast-speed strength and athletes assigned to PBT will present larger increases in endurance strength ; (iii) participants assigned to VBT will present less neuromuscular fatigue, training stress and muscular damage; (iv) the aforementioned hypothesized outcomes will be consistent for both upper- and lower-body RT exercises.

Research Plan and Methods Participants Recruitment Healthy male participants aged 18-30 years without neurologic conditions, lower and upper limb disabilities, or any known disease will be recruited. All participants must be familiar with RT (≥ 3 times per week, for at least 3 years of practice). Additional exclusion criteria will be known metabolic, cardiovascular, respiratory disorders or other orthopedic conditions that limit exercise. The participants will need to sign an informed consent before participation, already approved by the institutional review board (CEFMH Nº 28/2023).

Study Design Participants will be randomly allocated to one of three groups: PBT, VBT or VBT performed as fast as possible (VBT-F). All groups will entail a RT intervention and all groups will be assessed at baseline, 4 weeks, and 10 weeks (T0, T4, and T10, respectively).

Sample Size Justification Based on the effect size of the differences in the back-squat one-repetition maximum (1RM) after 6 weeks of PBT and VBT (and accounting for a 25% attrition rate due to the study's longitudinal nature) a total of 30 participants (10 per group) will be recruited to provide 95% statistical power .