The behaviour of T2* and T2 relaxation time in extrinsic foot muscles under continuous exercise: A prospective analysis during extended running

Abstract

Objectives: Previous studies on T2* and T2 relaxation time of the muscles have shown that exercise leads to an initial increase, presumably representing different intramuscular physiological processes such as increase in intracellular volume or blood oxygenation level dependent effects with a subsequent decrease after cessation of exercise. Their behaviour during prolonged exercise is still unknown but could provide important information for example about the pathophysiology of overuse injuries. The aim of this study was to evaluate the temporal course of T2* and T2 relaxation time in extrinsic foot muscles during prolonged exercise and determine the optimal mapping technique.

Methods: Ten participants had to run a total of 75 minutes at their individual highest possible running speed, with interleaved MR scans at baseline and after 2.5, 5, 10, 15, 45 and 75 minutes. The examined extrinsic foot muscles were manually segmented, and relaxation time were analysed regarding its respective time course.

Results: T2* and T2 relaxation time showed an initial increase, followed by a plateau phase between 2.5 and 15 minutes and a subsequent decrease. For the T2* relaxation time, this pattern was also apparent, but less pronounced, with more muscles not reaching significance (p<0.05) when comparing different time points.

Conclusions: T2* and T2 relaxation time showed a similar course with an initial rapid increase, a plateau phase and a subsequent decrease under prolonged exercise. Moderate but long-term muscular activity appears to have a weaker effect on T2* relaxation time than on T2 relaxation time.

Fig 1. Schematic diagram of the scanning and running procedure.

Vertical black broken lines indicate (from left to right) the start of the protocol, the onset of running and the end of running. Vertical grey broken lines indicate the interleaved MRI-Scans.

Fig 2. Mean T2* and T2 relaxation time of the 10 participants.

Abbreviations: MG = medial gastrocnemius muscle, LG = lateral gastrocnemius muscle, SOL = soleus muscle. Note: the time intervals between the time points indicated in the x-axis are variable.

Fig 3. Mean T2* and T2 relaxation time of the 10 participants.

Abbreviations: TP = tibialis posterior muscle, PER = peroneus longus muscle, EDL = extensor digitorum longus muscle, TA = tibialis anterior muscle. Note: the time intervals between the time points indicated in the x-axis are variable.