Author(s): SEKI, K., KYRÖLÄINEN, H., Institution: NIHON UNIVERSITY, Country: JAPAN, Abstract-ID: 1442

INTRODUCTION:
Biomechanical factors affecting mechanical efficiency (ME) are among the topics that have received sustained attention. ME may be related to endurance exercise performance. Although sledge jumping has been used to evaluate ME in stretch–shortening cycle actions (e.g., Kyröläinen and Komi, 1995), the relationship between ME and joint work has also been examined using a sledge jump. A previous study (Seki and Kyröläinen, 2024) compared ME and joint kinetics between different load conditions using three sledge inclinations, and they suggested that the hip and knee joint work might be associated with ME. However, their results might be affected by different loads. Therefore, the present study aimed to examine the relationship between ME and joint kinetics during a sledge jump with the same load at different inclinations.
METHODS:
Twenty Japanese long-distance runners participated in this study. They performed three bouts of sledge jumping, each lasting 4 min. Each bout was conducted at a different sledge inclination (18.5°, 23.0°, and 27.5°) with the same load, which was determined as 50% of the maximal jump height at 23.0°. Lower-limb kinematics, ground reaction forces, and expired gases were measured using a motion capture system (Vicon), a force platform (Kistler), and a gas analyzer (Minato), respectively. ME was calculated as the ratio of the external work to energy expenditure. Ankle, knee, and hip joint work were calculated by integrating the joint power, defined as the inner product of joint torque and joint angular velocity. Differences between inclinations were tested using a repeated-measures analysis of variance. The relationship between ME and joint kinetics was tested using Pearson’s correlation coefficient.
RESULTS:
ME, knee joint work, and external work were significantly lower at an inclination of 27.5° than at 18.5° and 23.0° (p ≤ 0.002). Energy expenditure did not differ across inclinations. ME was correlated positively with knee joint work (r = 0.494, p < 0.001) and hip joint work (r = 0.556, p < 0.001), but not with ankle joint work (r = −0.153, p = 0.242).
CONCLUSION:
Previously, relative contribution of lower limb joint work has been shown to associate with ME (Farris and Sawicki, 2018). In particular, greater ankle joint work has been considered to improve ME. In the present study, however, ME was positively correlated with hip and knee joint work, but not with ankle joint work. This is well in line with our previous study (Seki and Kyröläinen, 2024) although that study compared conditions with different load. The present study further revealed that hip and knee joint work may improve ME even under the same load condition. This may be attributed to coordination between these two joints.