Simulation to clarify the effect of paddling motion on the hull behavior of a single kayak in a sprint race

The cause and effect relationship between the paddling motion and the hull behavior of a kayak in a sprint race has not been sufficiently investigated. The objective of this study was to investigate the effect of the paddling motion on the hull behavior by numerical simulation. A dynamic simulation model of a paddler, paddle and hull in a single kayak, which was previously developed, was used for the simulation. One standard paddling motion and three modified motions were prepared for the simulation. Three modified motions were created based on suggestions by coaches of the Japan Olympic team. These motions were thought to be often seen in paddlers of lower skill level and, therefore, empirically considered to be typically bad motions. From the simulation results, the following findings were obtained: in the simulation of the standard paddling motion, the averaged hull velocity was 5.4 m/s. This was consistent with the actual hull velocity of 5.5 m/s. Typically bad motions which induced undesirable hull fluctuations reduced the propulsive efficiency.     

Functional differences in the activity of the hamstring muscles with increasing running speed

Abstract

In this study, we examined hamstring muscle activation at different running speeds to help better understand the functional characteristics of each hamstring muscle. Eight healthy male track and field athletes (20.1 ± 1.1 years) performed treadmill running at 50%, 75%, 85%, and 95% of their maximum velocity. Lower extremity kinematics of the hip and knee joint were calculated. The surface electromyographic activities of the biceps femoris and semitendinosus muscles were also recorded. Increasing the running speed from 85% to 95% significantly increased the activation of the hamstring muscles during the late swing phase, while lower extremity kinematics did not change significantly. During the middle swing phase, the activity of the semitendinosus muscle was significantly greater than that of the biceps femoris muscle at 75%, 85%, and 95% of running speed. Statistically significant differences in peak activation time were observed between the biceps femoris and semitendinosus during 95%max running (P < 0.05 for stance phase, P < 0.01 for late swing phase). Significant differences in the activation patterns between the biceps femoris and semitendinosus muscles were observed as running speed was increased, indicating that complex neuromuscular coordination patterns occurred during the running cycle at near maximum sprinting speeds.