The Joint Powers during the Standing Long Jump and Maximum Isokinetic Strength of the Lower Limb Joints .
The jumping motion is a basic movement of the human body and plays a fundamental role in sports and physical performance. Jumping from a standing start with maximum effort exerted at once (the vertical jump) requires maximum power output by the lower limb muscles. However, in jumping motions that involve complex technical aspects associated with the control of the jump direction, as with the standing long jump ,short- term isokinetic training of the lower limb muscles does not directly lead to improved performance, as using the full potential of the muscles is difficult.
Determining the factors limiting performance in jumping exercises (the jump distance in the case of the standing long jump) and their relationships with muscular strength will be useful in evaluating the performance of various types of exercise for which power output is important.
In recent years, numerous studies have evaluated the relationship between the vertical jump height and maximum strength. In various studies that assessed static single-joint strength, the correlation between the isometric strength of the three joints in the lower limbs and the vertical jump height was shown to depend on the presence of counter- movement and whether the subjects were athletes. Convicting reports have either shown that the ground reaction force during the mid-thigh isometric clean pull is correlated with the vertical jump height, or that no such correlation exists. Additionally, a correlation has been reported to exist between the isometric leg-press strength and the jump height. Furthermore, it has been reported that the vertical jump height is correlated with the knee joint isokinetic strength and the 1 repetition maximum in the squat or power clean. However, muscular activity and lower limb kinetics during the jumping motion were not investigated in these previous studies.
Therefore, an assessment of the cause of the observed relationship between maximum strength and jump performance is difficult; the roles of the lower limb muscles in jump performance cannot be sufficiently explained based solely upon the observation of a correlation between maximum strength and jumping ability. A biomechanical analysis of the jumping motion is important in the assessment of the roles of the lower limb muscles in the jumping motion.
Research on the relationship between the maximum strength and performance in the standing long jump is scarce compared to that for the vertical jump. Other studies have biomechanically analyzed the take-off motion in the standing long jump, with comparison between the presence/absence of an arm swing , starting postures, or standing long/vertical jumps . In addition, the optimal take-off angle has been evaluated biomechanically. Although the motion characteristics for highly experienced athletes and the changes in biomechanics due to technical training have been investigated, few studies have investigated the limiting factors for the jump distance.
A clarification of the relationship between the take-off motion in the standing long jump and isokinetic strength may aid in the elucidation of the limiting factors for exercises in which power output is important. Therefore, the purpose of this study was to analyze the take-off technique in the standing long jump biomechanically, and identify the limiting factors for the jump distance and take-off technique. To this end, we evaluated the relationships between joint power during the propulsion phase of the standing long jump and the maximum isokinetic strength of the lower limb joints.
Therefore, although the jump distance depended on lower limb joint power during the propulsion phase, power was not directly modulated by isokinetic strength. This phenomenon might be derived from the use of strategies that enhance lower limb power, which include a counter-movement and the coupling of an arm swing to the lower limb motion.
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