The reliability of functional and systemic markers of muscle damage in response to a flywheel squat protocol.

Purpose: To characterize the magnitude, timescale, and reliability of changes in functional and systemic outcome markers following moderate (MIR) and high (HIR) isoinertial resistance flywheel squat protocols (FSP).

Methods: Twenty-four resistance-trained males completed two exercise trials (ET1 & ET2) separated by 32 days. Functional and systemic markers were assessed at pre-exercise (PRE), immediately post-exercise (IP), and 24 (24H), 48 (48H), and 72 (72H) hours post-exercise. Three-way group x trial x time repeated measures ANOVAs were conducted to compare all dependent variables between groups (MIR & HIR) and experimental trials across time. Test-retest reliability between trials was assessed using intraclass correlation coefficients (ICC).

Results: At IP, both groups exhibited significantly decreased active range of motion, perceived recovery status, squat maximal voluntary isometric contraction force, and vertical jump performance, along with significantly increased muscle thickness and echo intensity (ultrasound), muscle soreness, and creatine kinase when compared to PRE. Most outcomes remained perturbed at 24H and 48H, especially in the HIR group. By 72H, only a subset of variables remained significantly changed from PRE. No significant attenuation of outcomes between trials were observed and test-retest reliability between trials was excellent for the FSP and moderate to excellent for most outcomes in both groups.

Conclusion: Our findings indicate that the FSP is a robust and repeatable exercise stimulus capable of eliciting significant exercise-induced muscle damage and reliable subsequent perturbations to functional and systemic markers of muscle damage. Our findings also support the use of crossover designs in future EIMD research designs with resistance-trained men.