Probing muscle recovery following downhill running using precise mapping of MRI T₂ relaxation times

Purpose: Postexercise recovery rate is a vital component of designing personalized training protocols and rehabilitation plans. Tracking exercise-induced muscle damage and recovery requires sensitive tools that can probe the muscles' state and composition noninvasively. Methods: Twenty-four physically active males completed a running protocol consisting of a 60-min downhill run on a treadmill at −10% incline and 65% of maximal heart rate. Quantitative mapping of MRI T₂ was performed using the echo-modulation-curve algorithm before exercise, and at two time points: 1 h and 48 h after exercise. Results: T₂ values increased by 2%–4% following exercise in the primary mover muscles and exhibited further elevation of 1% after 48 h. For the antagonist muscles, T₂ values increased only at the 48-h time point (2%–3%). Statistically significant decrease in the SD of T₂ values was found following exercise for all tested muscles after 1 h (16%–21%), indicating a short-term decrease in the heterogeneity of the muscle tissue. Conclusion: MRI T₂ relaxation time constitutes a useful quantitative marker for microstructural muscle damage, enabling region-specific identification for short-term and long-term systemic processes, and sensitive assessment of muscle recovery following exercise-induced muscle damage. The variability in T₂ changes across different muscle groups can be attributed to their different role during downhill running, with immediate T₂ elevation occurring in primary movers, followed by delayed elevation in both primary and antagonist muscle groups, presumably due to secondary damage caused by systemic processes.