The mechanical characteristics of single-leg squat exercise with emphasis on pelvic elevation / 体力科学

Movement control and muscle function for pelvic movement in the frontal plane (pelvic elevation) are important for various single-leg sports activities. We aimed to clarify mechanical characteristics of pelvic squat (P-Sq: single-leg squat exercise with emphasis on pelvic elevation, developed by our research group) compared with the double-leg squat (D-Sq) and single-leg squat (S-Sq). Twelve male track and field athletes performed D-Sq, S-Sq, and P-Sq exercises at various loads (90%, 75%, and 60% of 1-repetition maximum [1RM]), using maximum effort. Kinematic and kinetic data were calculated using data recorded with a motion capture system and force platforms. We observed the highest values with P-Sq, followed by S-Sq and D-Sq under all load conditions as follows: peak vertical ground reaction force and rate of force development (RFD), range of pelvic elevation, peak pelvic elevation velocity, peak powers associated with hip abduction torque and trunk lateral flexion torque. In P-Sq, RFD at 90% 1RM was smaller than under the other load conditions, whereas peak vertical ground reaction force at 90% 1RM was larger than under the other load conditions. There were no differences among load conditions with regard to hip abduction and trunk lateral flexion torques and powers. Therefore, characteristics of P-Sq compared to those of D-Sq and S-Sq are 1) larger and faster pelvic elevation, using related muscles (hip abductors and trunk lateral flexors) under all load conditions, 2) larger peak ground reaction force with pelvic elevation under large load conditions, and larger RFD in pelvic elevation under low load conditions.

Evaluation of specific strength and power at the lower extremity of jumpers using the rebound jump test / 体力科学

<p>We aimed to investigate the characteristics of lower-limb strength and power used for lower-limb mechanical variables in rebound jump (RJ) test by using a new system (Quick Motion Analysis System), which calculates mechanical variables in real time. Thirty-three male jumpers performed the RJ test. The performance (RJ index, contact time, and jump height) and joint kinetics (joint work and joint contribution) in RJ were calculated. IAAF Scoring Tables of Athletics were used to calculate jump event performance (IAAF score). IAAF score was positive correlated with RJ index, jump height, and joint work at the ankle and hip joints. Elite jumpers achieved higher RJ performance by larger ankle and hip joint work. As performance variables, jumping height and contact time were converted to T scores, and evaluation method was proposed to use the relative merits of these values to classify athletes into four types. The IAAF score showed no differences among the four types. These results indicate that there is no relation among jump events performance and characteristics of the four types. Moreover, focusing on stiffness, based on the contact time and jump height, jumpers with a longer contact time and higher jump height type showed lower stiffness (compliant spring characteristics), whereas those with the opposite features showed higher stiffness (stiffer spring characteristics). Therefore, for evaluating lower-limb strength and power characteristics, the use of performance and joint kinetics are effective, in addition to focusing on type characteristics based on the contact time and jump height in RJ.</p>

Time-series relationship to achieve performance on rebound drop jump / 体力科学

<p>The aim of this study was to demonstrate a time-series relationship in drop jump (DJ) from a pre-set state with improved performance. Twelve male college athletes performed a DJ from a height of 0.60 m. DJ performance was assessed with a DJ-index (jump height/contact time). Short-interval intracortical inhibition (SICI) was assessed as intracortical inhibitory circuit excitability in a pre-set state, calculated by using paired-pulse transcranial magnetic stimulation for the medial gastrocnemius muscle (MG). The H-reflex of the left MG and the ankle joint torque were calculated in the early phase of take-off. A significant correlation was shown between ⊿SICI during the pre-set state and the DJ index. Thus, we examined the relationships between phases, focusing on time-series relationships throughout the jump period. The results showed a significant correlation between ⊿SICI during the pre-set state and %H-reflex during the early phase of take-off, and peak ankle joint torque during take-off was also significantly correlated with %H-reflex during the early phase of take-off. A significant correlation was also demonstrated between ankle joint torque during take-off and the DJ-index. In conclusion, we observed a time-series relationship between DJ from a pre-set state and improved performance. A decrease of intracortical inhibitory circuit excitability in the pre-set state affects stretch-reflex facilitation during the early phase of take-off; stretch-reflex facilitation results in the development of a large force in the ankle joint during take-off, and this force develops ankle joint torque. These findings may be used to improve jump performance.</p>