The influence of muscle morphology and strength characteristics on sprint running performance, especially at elite level, is unclear. Purpose: This study aimed to investigate the differences in muscle volumes and strength between male elite sprinters, sub-elite sprinters, and untrained controls; and assess the relationships of muscle volumes and strength with sprint performance. Methods: Five elite sprinters (100 m seasons best [SBE100]: 10.10 ± 0.07 s), 26 sub-elite sprinters (SBE100: 10.80 ± 0.30s) and 11 untrained control participants underwent: 3T magnetic resonance imaging scans to determine the volume of 23 individual lower limb muscles/compartments and 5 functional muscle groups; and isometric strength assessment of lower body muscle groups. Results: Total lower body muscularity was distinct between the groups (controls < sub-elite +20% < elite +48%). The hip extensors exhibited the largest muscle group differences/relationships (elite, +32% absolute and +15% relative [per kg] volume vs sub-elite; explaining 31-48% of the variability in SBE100), whereas the plantarflexors showed no differences between sprint groups. Individual muscle differences showed pronounced anatomical specificity (elite vs sub-elite, absolute volume range +57% to -9%). Three hip muscles were consistently larger in elite vs. sub-elite (TFL, sartorius, gluteus maximus; absolute +45-57% and relative volume +25-37%), and gluteus maximus volume alone explained 34-44% of the variance in SBE100. Isometric strength of several muscle groups was greater in both sprint groups than controls, but similar for the sprint groups and not related to SBE100. Conclusions: These findings demonstrate the pronounced inhomogeneity and anatomically specific muscularity required for fast sprinting, and provides novel, robust evidence that greater hip extensor and gluteus maximus volumes discriminate between elite and sub-elite sprinters and are strongly associated with sprinting performance.

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We tested a hypothesis that low-load squat training with slow movement and tonic force generation (LST) would increase muscle size and strength but not necessarily power. Healthy young men were assigned to LST [50% one-repetition maximum (1-RM) load, 3 s for lowering/lifting without pause: n=9] or low-load normal speed (LN: 50% 1-RM load, 1 s for lowering/lifting with 1-s pause; n=7) groups. Both groups underwent an 8-week squat training program (10 repetitions/set, 3 sets/day, and 3 days/week) using the assigned methods. Before and after the intervention, quadriceps femoris muscle thickness, maximal torque during isometric hip extension and knee extension, 1-RM squat, lifting power from squatting position and rate of electromyography rise (RER) in knee extensors during the task, leg extension power and vertical jump height were measured. After the intervention, the LN group showed no changes in all the variables. The LST group significantly (P<0.05) increased muscle thickness (6-10%), isometric hip extension torque (18%) and 1-RM squat (10%), but not isometric knee extension torque, lifting power and RER, leg extension power and vertical jump height. These results suggest that LST can increase muscle size and task-related strength, but has little effect on power production during dynamic explosive movements.

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