Relationship between sprint performance of front crawl swimming and muscle fascicle length in young swimmers.

The purpose of this study was to investigate the relationship between 25-m sprint front crawl swimming performance and muscle fascicle length in young male swimmers. 23 swimmers were selected and divided into two groups according to their best records of 25-m sprint performance: 14.6-15.7 sec (S1, n = 11) and 15.8-17 sec (S2, n = 12). Muscle thickness and pennation angle of Biceps Brachii (BB; only muscle thickness), Triceps Brachii (TB), Vastus Lateralis (VL), Gastrocnemius Medialis (GM) and Lateralis (GL) muscles were measured by B-mode ultrasonography, and fascicle length was estimated. Although, there was no significant differences between groups in anthropometrical parameter as standing height, body mass, arm length, thigh length and leg length (p < 0.001), however, S1 significantly had a greater muscle thickness in VL, GL, and TB muscles (p < 0.05). Pennation angle only in TB was significantly smaller in S1 (p < 0.05). S1 in VL, GL, and TB muscles significantly had greater absolute fascicle length and in VL and TB muscles had relatively (relative to limb length) greater fascicle length (p < 0.05). Moreover, there was a significant relationship between sprint swimming time and absolute and relative fascicle length in VL (absolute: r = -0.49 and relative: r = -0.43, both p < 0.05) and GL (absolute: r = -0.47 and relative: r = -0.42, both p < 0.05). Potentially, it seems that fascicle geometry developed in muscles of faster young swimmers to help them to perform their high speed movement. Key PointsThis study investigated the relationship between muscle fascicle length and sprint front crawl performance in young male swimmers.It seems that young swimmers with faster front crawl sprint swimming performance trend to have smaller pennation angle and greater absolute and relative fascicle length (relative to limb length) in their locomotor muscles.Potentially, fascicle geometry developed in faster swimmers to help them to perform higher speed movement via higher output power, however, the adaptive response of fiber length follownig training is not well underestood.