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. Moreover, training status and exercise type/modality could influence the magnitude of MVC(loss24-48h).