Intermuscular and intramuscular distributions of sprint-induced thigh muscle activation in male sprinters: a T2-weighted MRI study

Superior sprint performance is associated with greater activation of the lower-limb muscles, particularly the thigh muscles, during sprinting. T2-weighted magnetic resonance imaging (MRI) is an ideal method for assessing spatial patterns of thigh muscle activation in response to dynamic whole-body movements. In this T2-weighted MRI study, we examined the intermuscular and intramuscular distributions of sprint-induced activation across 13 thigh muscles in male sprinters using a low-volume sprint protocol designed to preserve maximal performance while minimizing fatigue. Specifically, we evaluated intermuscular activation patterns and intramuscular regional differences in thigh muscle activation. Thirty-two well-trained male collegiate sprinters (100-m seasonal best time: 11.02 ± 0.28 s) completed the low-volume sprint protocol consisting of three maximal 60-m sprints with 2-min recovery intervals on an indoor track. T2-weighted MRI scans were acquired before and after the sprint protocol. Intermuscular activation patterns were assessed by comparing the percentage change in T2 across 13 thigh muscles. Intramuscular regional differences were assessed by comparing T2 changes among regions within each muscle. During the low-volume sprint protocol, 60-m sprint times did not differ significantly among the three maximal sprints ( P = 0.349). Despite this minimized approach, significant T2 increase were observed across 12 of the 13 thigh muscles (3.1–19.1%, all P < 0.05), with the greatest increase in the semitendinosus. In particular, T2 changes in the hamstrings and adductors were markedly greater than those in the quadriceps femoris. Furthermore, significant regional differences in T2 changes were identified in six of the 11 muscles analyzed (all P < 0.05). Notably, the T2 change in the proximal region of the biceps femoris long head was significantly greater than those in the middle and distal regions (both P < 0.05), which may be relevant to the regional susceptibility to hamstring strain injury. These findings suggest that maximal sprint performance in male sprinters involves complex muscle recruitment mechanisms characterized by intermuscular and intramuscular distributions of thigh muscle activation. A better understanding of these features may contribute to the development of novel sprint strategies to enhance sprint performance and prevent sprint-related sports injuries in sprinters.