Strength-Endurance: Interaction Between Force-Velocity Condition and Power Output.

Context: Strength-endurance mainly depends on the power output, which is often expressed relative to the individual's maximal power capability ( ). However, an individual can develop the same power, but in different combinations of force and velocity (force-velocity condition). Also, at matched power output, changing the force-velocity condition results in a change of the velocity-specific relative power ( ), associated with a change in the power reserve. So far, the effect of these changing conditions on strength-endurance remains unclear.

Purpose: We aimed to test the effects of force-velocity condition and power output on strength-endurance.

Methods: Fourteen sportsmen performed (i) force- and power-velocity relationships evaluation in squat jumps and (ii) strength-endurance evaluations during repeated squat jump tests in 10 different force-velocity-power conditions, individualized based on the force- and power-velocity relationships. Each condition was characterized by different (i) relative power (% ), (ii) velocity-specific relative power (% ), and (iii) ratio between force and velocity ( ). Strength-endurance was assessed by the maximum repetitions ( ), and the cumulated mechanical work ( ) performed until exhaustion during repeated squat jump tests. Intra and inter-day reliability of were tested in one of the 10 conditions. The effects of % , % , and on and were tested via stepwise multiple linear regressions and two-way ANOVAs.

Results: exhibited almost perfect intra- and inter-day reliability (ICC=0.94 and 0.92, respectively). and were influenced by % and ( = 0.975 and 0.971; RSME=0.243 and 0.234, respectively; both < 0.001), with the effect of increasing with decreasing % (interaction effect, = 0.03). % was not considered as a significant predictor of strength-endurance by the multiple regressions analysis. and were higher at lower % and in low force-high velocity conditions (i.e., lower ).

Conclusion: Strength-endurance was almost fully dependent on the position of the exercise conditions relative to the individual force-velocity and power-velocity relationships (characterized by % and ). Thus, the standardization of the force-velocity condition and the velocity-specific relative power should not be overlooked for strength-endurance testing and training, but also when setting fatiguing protocols.