Reproducible voluntary muscle performance during constant work rate dynamic leg exercise

Area of Science:

• Exercise Physiology
• Muscle Physiology
• Sports Science

Background:

• Assessing progressive muscle fatigue during exercise is challenging.
• Endurance time is often difficult to reproduce consistently.
• Dynamic knee extension (DKE) offers a potential solution for tracking fatigue.

Purpose of the Study:

• To evaluate the reproducibility of performance indices during dynamic knee extension (DKE) exercise.
• To assess the reliability of maximal voluntary contraction (MVC) force measurements for tracking leg fatigue.
• To determine the utility of DKE for evaluating experimental interventions, such as altitude exposure.

Main Methods:

• Eleven healthy women performed identical constant work rate 1-leg DKE (1 Hz) on two separate days.
• Measured performance indices included MVC force, rate of MVC force fall, time to exhaustion, and %MVC at exhaustion.
• Nine participants were re-tested at 4,300 m altitude within 24 hours.

Main Results:

• High reproducibility was found for all measured indices: MVC(rest) (CV% 4.9%), MVC force fall (CV% 26.5%), time to exhaustion (CV% 7.5%), and %MVC(rest) at exhaustion (CV% 5.6%).
• No statistically significant mean differences were observed between the two test days.
• Low variability in performance indices facilitated the description of acute altitude exposure effects on muscle function.

Conclusions:

• Dynamic knee extension exercise combined with serial MVC measurements provides a reproducible method for quantifying leg muscle fatigue.
• This approach enhances the ability to detect subtle changes in muscle function due to interventions like altitude.
• The DKE protocol is valuable for research investigating exercise performance and fatigue under various physiological conditions.