Quantitative MRI evaluation of the effects of rest and different intensities of running on the recovery of thigh muscle microdamage after a half marathon.

OBJECTIVE: To explore the application value of quantitative magnetic resonance multi-parameter imaging technology, Diffusion Tensor Imaging (DTI) combined with T2 mapping, in evaluating the effects of rest and different intensities of running on the recovery of thigh muscle microdamage after a Half Marathon (HM). METHODS: Twenty-four amateur marathon runners were enrolled and randomly divided into three groups to compare different post-marathon recovery strategies: the High-Intensity Running (HIR) group, the Moderate-Intensity Running (MIR) group, and the Rest (REST) group. MR scans were performed on the participants before the race (pre-run) and at 3 h (post-3 h), 24 h (post-24 h), 48 h (post-48 h), and 72 h (post-72 h) after the race. The Fractional Anisotropy (FA), Apparent Diffusion Coefficient (ADC), and T2 relaxation time (T2 value) of the thigh muscle groups were measured. RESULTS: Compared with pre-run, all groups showed significantly decreased FA (p < 0.001) and increased T2 (p < 0.001) at post-3 h, indicating HM-induced microdamage (characterized by myofiber disruption and interstitial edema). REST group FA recovered to baseline at post-72 h, while MIR group recovered partially and HIR group showed no recovery. T2 trends aligned with FA. No significant ADC differences were observed. CONCLUSION: Our findings suggest that quantitative MR multi-parameter imaging can sensitively detect muscle microdamage and the recovery process after HM. The REST group shows the fastest recovery, while moderate- and high-intensity running delay recovery. Therefore, it is not recommended to use moderate- or high-intensity running as an intervention within 3 days after the race.