How to Maintain Maximal Straight Path Running Speed on a Curved Path in Sprint Events.

This study aims to clarify the ideal technique for running on a curved path during sprinting events. Participants were twelve male track and field athletes including long jumpers and sprinters. The participants performed a 60-m sprint with maximal effort on straight and curved paths. Participants were divided into "good curve runners" and "poor curve runners" according to the curved path running speed relative to that of the straight path. Kinematic variables and ground reaction forces (GRFs) were registered and compared between the groups and paths. The running speed, step length, and flight distance of the outside leg on the curved path were lower than on the straight path only in poor curve runners. The medial-lateral GRF and impulse showed an increase during curved path running for both groups. However, the maximum posterior GRF and impulse decreased only in poor curve runners. The ideal technique for running on a curved path is to maintain the same kinematics and kinetics in the sagittal plane as on a straight path.

Oxygenation in the motor cortex during exhaustive pinching exercise.

The purpose of this study was to examine the effect of fatigue resulting from exhaustive pinching exercise on frontal and motor cortex activity. Eight healthy subjects (four male and four female) participated in the present study. All subjects performed at 70% of maximal voluntary contraction (MVC) pinching exercise until reaching a state of volitional fatigue. Frontal cortex and motor cortex oxygenation was measured by near-infrared spectroscopy throughout the exhaustive exercise. Frontal cortex and motor cortex oxygenation increased significantly at the 90 and 120 s after the start of exercise compared with the pre-exercise values and these decreased with the time passage. Frontal cortex oxygenation at exhaustion was significantly lower than the 90 and 120 s after the start of exercise, while motor oxygenation at exhaustion was the same value with the pre-exercise value. These findings suggest that the exhaustive exercise induces the decrease of cerebral function and that the fatigue resulting from dynamic exercise decreases the motor cortex activity.

Mechanical power during maximal treadmill walking and running in young and elderly men.

This study determined mechanical power during movements specific to maximal walking and running using a non-motorized treadmill in 38 elderly [69.4 (5.0) years] and 50 young [24.3 (3.4) years] men. The mean mechanical power over a period of time covering six steps, during which the belt velocity peaked and then kept almost plateau, was determined as a performance score in each of maximal walking (WP) and running (RP). In terms of the value relative to body mass, the relative difference between the two age groups was greater for RP (61.7%) than for WP (21.4%) or isometric knee extension (34.1%) and flexion torque (43.8%). In the two groups, WP was significantly ( P<0.05) correlated to knee extension (r=0.582 for the elderly and r=0.392 for the young) and flexion torque (r=0.524 for the elderly and r=0.574 for the young). Similarly, RP was also significantly (P<0.05) correlated to knee extension (r=0.627 for the elderly and r=0.478 for the young) and flexion torque (r=0.500 for the elderly and r=0.281 for the young). In these relationships, the WP adjusted statistically by thigh muscle torque was similar in the two age groups. However, the corresponding value for RP was significantly higher in the young than in the elderly. The findings here indicate that: (1) the difference between the young and elderly men in mechanical power is greater during maximal running than maximal walking, and (2) although the thigh muscle torque contributes to the power production during the two maximal exercise modes in the two age groups, the RP is greater in the young than in the elderly regardless of the difference in the thigh muscle torque.

The influence of circulatory difference on muscle oxygenation and fatigue during intermittent static dorsiflexion.

This study aimed to examine the influences of circulatory difference on the utilization of O(2) and the progression of fatigue in the tibialis anterior (TA) muscle during dorsiflexion exercise, with reference to different body postures. The subjects performed intermittent static dorsiflexion at 50% of maximal voluntary contraction (MVC) up to exhaustion with the right leg either up or down relative to the heart. These exercises were performed with and without occluding muscle blood flow. Simultaneously with the surface electromyogram (EMG) measurement, total hemoglobin volume change and tissue oxygenation ( S(t)O(2)) of TA were measured using near-infrared spectroscopy (NIRS). When the subjects performed an exhaustive intermittent dorsiflexion exercise at 50% MVC, the endurance time decreased in the leg up position. Also, the progression of fatigue in TA detected using EMG signals (i.e. integrated EMG and mean power frequency of EMG) was faster with the leg elevated. The NIRS data indicated a lower blood volume and S(t)O(2) with the leg up than with the leg down during the exercise, which suggests that the deficit in the O(2) supply to exercising muscle's demand was more apparent in the leg up position. However, these differences in EMG and NIRS data disappeared when the blood flow was restricted in both positions. From these results it is concluded that the difference in exercising muscle oxygenation between two different body postures influenced the progression of muscle fatigue and caused the difference in endurance performance.

Local blood circulation among knee extensor synergists in relation to alternate muscle activity during low-level sustained contraction.

The relation between local circulation and alternate muscle activity among knee extensor synergists was determined during low-level sustained knee extension at 2.5% of maximal voluntary contraction for 60 min in seven subjects. Blood volume of rectus femoris (RF) and vastus lateralis (VL) was assessed by using near-infrared spectroscopy. Surface electromyogram (EMG) was recorded from RF, VL, and vastus medialis (VM). Alternate muscle activity was observed between RF and either VL or VM. Cross-correlation analysis was used to investigate the relation between blood volume and integrated EMG (iEMG) sequences throughout the task. One negative peak in the cross-correlation function was seen between the iEMG and blood volume with time lag of 30-60 s, indicating that muscle activity increases (or decreases) with the decrease (or increase) in local circulation with the corresponding time lag. Two cases in the emergence of alternate muscle activities, i.e., an increase in the EMG of RF accompanied by a decline of EMG in VL (case I) and vice versa (case II) were further analyzed. The time lag between iEMG and blood volume was longer in case I than that in case II. These results were statistically significant in the RF but not in the VL. It is concluded that even during low-level sustained contraction, local circulation is modulated by the alternate muscle activity of knee extensor synergists, and a negative correlation between the muscle activity and blood volume sequences was found in only RF but not in VL.