Feasibility of vertical force–velocity profiles to monitor changes in muscle function following different fatigue protocols

Purpose: This study aimed to explore the feasibility of vertical force–velocity (F–V) profiles to monitor changes in muscle function following different fatigue protocols. The between-day reliability of vertical F–V profiles and the acute effects of two fatigue protocols on the changes of lower limb muscle function were examined. 

Methods: Twelve resistance trained males completed a preliminary session to determine their back squat one-repetition maximum (1RM). Afterwards, they randomly performed two experimental sessions that only differed in the fatigue protocol applied: heavy-load traditional (HLT; five repetitions at 80% 1RM) and light-load ballistic (LLB; five repetitions at 30% 1RM) squat protocols. Participants’ vertical F–V profiles (maximum theoretical force [F 0], maximum theoretical velocity [v 0], and maximum power output [P max]) were calculated before and immediately after each fatigue protocol. 

Results: F 0, v 0, and P max showed acceptable to good between-day reliability (coefficient of variation ≤ 4.4%; intraclass correlation coefficient ≥ 0.84). Both fatigue protocols promoted a comparable reduction in P max (−10.1% for HLT and −12.2% for LLB). However, the LLB squat protocol reduced more v 0 (−9.7%) than F 0 (−0.4%), while the HLT squat protocol reduced F 0 (−8.4%) more than v 0 (−4.1%). 

Conclusions: The vertical F–V profile can be used to monitor changes in muscle function given its acceptable between-day reliability and its high sensitivity to detect the acute effect of force-oriented and velocity-oriented fatigue protocols on specific maximal neuromuscular capacities.