Author(s): KAKEHATA, G., ÖRS, T., SAHROM, S., LIM, J., WYLDE, M., ISO, S., LOW, C.Y., Institution: WASEDA UNIVERSITY, Country: JAPAN, Abstract-ID: 1472

INTRODUCTION:
The adolescent period represents are phase of development in not only structure (e.g., muscle size, body height) but also neural factors (e.g., muscle activation). It is known that during sprinting the thigh muscle plays an important role in the swing phase, rapidly moving the leg forwards and backwards. Previous research has reported that step frequency is associated with earlier timing of rectus femoris (RF) muscle activation among high-level adult sprinters. However, such neuromuscular characteristics of the lower limbs during sprinting in youth athletes is an area that has been under researched. Therefore, the purpose of this study is to investigate the difference in strategy in the neuromuscular activation patterns of the lower limb muscles among youth athletes during maximal sprinting.
METHODS:
Eighteen youth male athletes were divided into two groups based on age; 17-19 years (U19: N=8) and 13-16 years (U16: N=10). Subjects ran 50 m with maximal effort. The spatiotemporal variables (e.g., running speed, step frequency, and step length) were measured over a distance from 30 m to 50 m using a high-speed camera (240 Hz) and timing gate systems. Electromyography (EMG) signals were obtained using wireless EMG sensors (2000 Hz) from ten lower limb muscles (RF, biceps femoris: BF, semitendinosus: ST, gluteus maximus: Gmax, gluteus medius: Gmed, vastus lateralis: VL, vastus medialis: VM, tibial anterior: TA, gastrocnemius: GAS, and soleus: SOL). The running cycle was divided into four phases from foot-strike and foot-off timings from both feet that consisted of contact, early-swing, mid-swing, and late-swing phases. Root mean squares (RMSs) were calculated every four phases. The RMSs were normalized maximal voluntary contraction value (% MVC)
RESULTS:
The U19 group showed significantly greater spatiotemporal variables than the U16 group. Muscle activation patterns during one gait cycle were similar, but there was a significant interaction of RMS of hip flexor (RF) (P = 0.003, F = 5.257). Post-hoc tests showed that the U19 group produced greater activation of RF during early-swing phases than the U16 group (P = 0.033). However, RMS of other muscles was found to be similar between both groups of athletes.
CONCLUSION:
The main finding in this study was that the U19 group showed greater hip flexor (RF) activation (RMS) than the U16 group. Rectus femoris muscle is a biarticular muscle and the major role of RF during sprinting is hip flexion rather than knee extension. Thus, greater performance in the U19 group may be explained by strong RF activation during the early swing phase. This recruitment of more RF would allow the youth athlete to swing the leg forward more rapidly and produce greater maximum velocity. Our results suggest that not only muscle growth, but also neuromuscular adaptations would be acquired during sprint-specific training among youth athletes and that the recruitment of RF is greater in older youth athletes.