Toyoyuki Honjo

Ischemic preconditioning accelerates muscle deoxygenation dynamics and enhances exercise endurance during the work-to-work test

Ischemic preconditioning (IPC) improves maximal exercise performance. However, the potential mechanism(s) underlying the beneficial effects of IPC remain unknown. The dynamics of pulmonary oxygen uptake (VO2) and muscle deoxygenation during exercise is frequently used for assessing O2 supply and extraction. Thus, this study examined the effects of IPC on systemic and local O2 dynamics during the incremental step transitions from low‐ to moderate‐ and from moderate‐ to severe‐intensity exercise. Fifteen healthy, male subjects were instructed to perform the work‐to‐work cycling exercise test, which was preceded by the control (no occlusion) or IPC (3 × 5 min, bilateral leg occlusion at >300 mmHg) treatments. The work‐to‐work test was performed by gradually increasing the exercise intensity as follows: low intensity at 30 W for 3 min, moderate intensity at 90% of the gas exchange threshold (GET) for 4 min, and severe intensity at 70% of the difference between the GET and VO2 peak until exhaustion. During the exercise test, the breath‐by‐breath pulmonary VO2 and near‐infrared spectroscopy‐derived muscle deoxygenation were continuously recorded. Exercise endurance during severe‐intensity exercise was significantly enhanced by IPC. There were no significant differences in pulmonary VO2 dynamics between treatments. In contrast, muscle deoxygenation dynamics in the step transition from low‐ to moderate‐intensity was significantly faster in IPC than in CON (27.2 ± 2.9 vs. 19.8 ± 0.9 sec, P < 0.05). The present findings showed that IPC accelerated muscle deoxygenation dynamics in moderate‐intensity exercise and enhanced severe‐intensity exercise endurance during work‐to‐work test. The IPC‐induced effects may result from mitochondrial activation in skeletal muscle, as indicated by the accelerated O2 extraction.

Ischemic Preconditioning Enhances Muscle Endurance during Sustained Isometric Exercise

Ischemic preconditioning (IPC) enhances whole-body exercise endurance. However, it is poorly understood whether the beneficial effects originate from systemic (e. g., cardiovascular system) or peripheral (e. g., skeletal muscle) adaptations. The present study examined the effects of IPC on local muscle endurance during fatiguing isometric exercise. 12 male subjects performed sustained isometric unilateral knee-extension exercise at 20% of maximal voluntary contraction until failure. Prior to the exercise, subjects completed IPC or control (CON) treatments. During exercise trial, electromyography activity and near-infrared spectroscopy-derived deoxygenation in skeletal muscle were continuously recorded. Endurance time to task failure was significantly longer in IPC than in CON (mean±SE; 233±9 vs. 198±9 s, P<0.001). Quadriceps electromyography activity was not significantly different between IPC and CON. In contrast, deoxygenation dynamics in the quadriceps vastus lateralis muscle was significantly faster in IPC than in CON (27.1±3.4 vs. 35.0±3.6 s, P<0.01). The present study found that IPC can enhance muscular endurance during fatiguing isometric exercise. Moreover, IPC accelerated muscle deoxygenation dynamics during the exercise. Therefore, we suggest that the origin of beneficial effects of IPC on exercise performance may be the enhanced mitochondrial metabolism in skeletal muscle.

Scapula behavior associates with fast sprinting in first accelerated running

The arm-swing motion is important for coordinated lower limb movement during a fast sprint and is composed of three-dimensional scapulothoracic and glenohumeral joint motion. Here, we aimed to clarify the role of the scapula during the initiation of a sprint running when sprinter run with high horizontal acceleration. Ten sports-active students participated in four 5-m dashes, with scapular constraint using non-elastic therapy tape (constraint condition) and without scapular constraint (free condition). The sprinting kinematics was assessed by a 16-camera motion capture system. In the constraint condition, the 2-m sprint time was significantly longer than that in the free condition. At the instants of foot-contact and take-off during the first step, no significant difference in the humerothoracic flexion angle was seen between these two conditions. In contrast, at the instants of foot-contact and take-off during the first step, the humerothoracic extension angle in the constraint condition was significantly smaller than that in the free condition. The forward leaning vector angle of center of mass during the first step was significantly greater than that in the constraint condition. Although no significant difference in hip extension and foot forward leaning angles was seen at the instant of foot contact during the first step between the two conditions, at the instant of take-off, the hip extension and foot forward leaning angles in the constraint condition were significantly smaller than those in the free condition. Therefore, scapular behavior in first accelerated running contributes to larger upper- and lower-limb motions and facilitates coordinating whole-body balance for a fast sprint.

Remote ischemic preconditioning accelerates systemic O2 dynamics and enhances endurance during work-to-work cycling exercise

The effect of remote ischemic preconditioning (RIPC) on whole‐body exercise performance and its potential mechanism remains poorly understood. In this study, we examined whether RIPC can accelerate systemic and local O2 dynamics and can enhance endurance during the work‐to‐work cycling exercise. Thirteen healthy men were instructed to perform the work‐to‐work test, which was preceded by the RIPC (bilateral arm occlusion, 3 × 5 minutes) or control (CON; no occlusion) condition. This test involved gradually increasing the exercise intensity as follows: low intensity at 30 W for 3 minutes, moderate intensity at 90% of the gas exchange threshold (GET) for 4 minutes, and severe intensity at 70% of the difference between the GET and VO2 peak until exhaustion. During the test, breath‐by‐breath pulmonary VO2 and near‐infrared spectroscopy‐derived vastus lateralis muscle deoxygenation were recorded continuously. Pulmonary VO2 dynamics during moderate‐intensity exercise was significantly faster in RIPC than in CON. In contrast, no such difference in muscle deoxygenation kinetics was observed between the two conditions. Time until exhaustion during severe‐intensity exercise was significantly longer in RIPC than in CON. These findings suggest that RIPC may be a beneficial strategy for enhancing whole‐body exercise performance, which may partially result from accelerated systemic O2 dynamics during exercise.

Development of Concentric-only Exercise Machine with Estimation of Whole Body Dynamics

Recently, the effects of concentric and eccentric training have been evaluated to determine how to make exercise more effective. Some researchers have reported that concentric exercise increases the concentric strength. In this case, concentric exercise may enhance the concentric force performance with or without lower muscle damage and pain. Therefore, we developed a concentric training machine for lower extremities that we call iSAAC. This machine has an electromagnetic brake to generate a safe resistance load for exercise. The magnitude of the resistance power is less than or equal to the human-applied power. We calculated whole body dynamics such as the joint torque and work of the lower extremities based on the inverse dynamics of the whole body without constraints. We verified the effectiveness of the system through squat-like knee extension exercise and inverse dynamics analysis. The proposed machine provided safe training for concentric knee extension and information on the whole body dynamics during exercise.