Appropriateness of indirect markers of muscle damage following lower limbs eccentric-biased exercises: A systematic review with meta-analysis

Purpose The aim of this review was to (1) characterize the time-course of markers of exercise-induced muscle damage (EIMD) based on the level of maximal voluntary contraction torque loss at 24-48h post-exercise (MVC_loss24-48h), (2) identify factors (e.g., exercise and population characteristics) affecting the level of MVC_loss24-48h, and (3) evaluate the appropriateness of EIMD markers as indicators of MVC_loss24-48h. Methods Magnitude of change of each EIMD markers was normalized using the standardized mean differences method to compare the results from different studies. Time-course of EIMD markers were characterized according to three levels of MVC_loss24-48h based on a clustering analysis of the 141 studies included. Association between MVC_loss24-48h levels and participant´s characteristics or exercise type/modalities were assessed. Meta-regressions were performed to investigate the associations between MVC_loss24-48h and EIMD markers changes at <6h, 24h, 48h, 72h and >96h after exercise. Results Time-course of EIMD markers recovery differs between levels of MVC_loss24-48h. Training status and exercise type/modality were associated with MVC_loss24-48h level (p<0.05). MVC_loss24-48h was correlated to changes in myoglobin concentration (<6h), jump height (24h) and range of motion (48h) (p<0.001). Conclusion As the exercise could differently affect markers as function of the EIMD severity (i.e., MVC_loss24-48h levels), different markers should be used as function of the timing of measurement. Mb concentration should be used during the first hours after the exercise (<6h), whereas jump height (24h) and range of motion (48h) could be used as surrogate for maximal voluntary contraction later.