In this study, we investigated the differences in performance and kinematics between overground and treadmill running using the same amount of subjective effort. Fourteen female participants performed a 50-m sprint, running at maximum effort (100% subjective effort) as the maximal task on the ground. Subsequently, based on 100% subjective effort, they performed the grading task on the ground and on the treadmill at 30, 50, and 70% subjective effort. The running motion was recorded using a high-speed camera. We observed a significant difference in running velocity between the overground and treadmill conditions because treadmill running was recognized as having a greater load than overground running. The running velocity could be adjusted according to the subjective effort required for both overground and treadmill running. On the treadmill, running velocity was adjusted by maintaining flight time with increased subjective effort. Additionally, running velocity was adjusted by both step frequency and step length on the treadmill, whereas overground running velocity was adjusted by step frequency rather than step length. We also observed that overground, the knee angle was more flexible with an increase in subjective effort through one gait cycle, and the ankle joint was fixed at a high subjective effort. On the treadmill, the knee angle was adjusted only during the swing phase, and greater dorsiflexion was observed at high subjective effort.
This study aimed to investigate motor control characteristics of the upper limbs through bilateral simultaneous grading tasks. The participants included 18 healthy right-handed women. They were instructed to perform isometric elbow flexion tasks under unilateral and bilateral conditions. The grading tasks were aimed at increasing the maximum voluntary force (MVF) from 10% to 30% or 50%. In the unilateral condition, participants performed tasks with the right or left upper limb. In the bilateral condition, participants increased their force level to 30% MVF with the right limb and then to 50% MVF with the left limb, or they increased their force level to 50% MVF with the right limb and then to 30% MVF with the left limb. Participants were asked to perform tasks as rapidly and accurately as possible. We evaluated the rapidity, accuracy, and reproducibility. Regarding the rapidity, the reaction time at 30% MVF was longer than that at 50% MVF, while the adjustment time at 50% MVF was longer than that at 30% MVF. Regarding the total adjustment time, there was no difference between both limbs in both bilateral conditions. Accuracy and reproducibility were higher when the task was performed at 30% MVF. These results suggest that when different levels of force are exerted by both upper limbs, the movement time is drawn to the side that exerts larger force, and the accuracy of force exertion increases on the limb that exerts less force.
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