Ryouta Matsuura

Effects of resistive load on performance and surface EMG activity during repeated cycling sprints on a non-isokinetic cycle ergometer

Objectives To determine the effects of resistive load on performance and surface electromyogram (SEMG) activity during repeated cycling sprints (RCS) on a non-isokinetic cycle ergometer. Methods Participants performed two RCS tests (ten 10-second cycling sprints) interspersed with both 30- and 360-second recovery periods under light (RCSL) and heavy load conditions (RCSH) in a random counterbalanced order. Recovery periods of 360 seconds were set before the fifth and ninth sprints. Results In the 9th and 10th sprints, the values of peak power output divided by body mass were significantly higher in RCSH than in RCSL. Changes in blood lactate concentration were not different between the two conditions. In RCSL, the root mean square calculated from the SEMG was significantly lower in the ninth sprint than in the first sprint, but there were no differences between the root mean square in the first sprint and that in the ninth sprint in RCSH. Conclusions During RCS on a non-isokinetic cycle ergometer, performance and SEMG activity are influenced by resistive load. It is thought that regulation of skeletal muscle recruitment by the central nervous system is associated with fatigue during RCS with a light resistive load.

Effects of awareness of change in load on ventilatory response during moderate exercise

This study was designed to determine whether awareness of change in load alters ventilatory response during moderate exercise. Subjects performed two incremental exercise protocols on a cycle ergometer. The load was increased from 1.0 to 1.5kp in steps of 0.1kp every 3min. Subjects were provided true information about the load in the control protocol and untrue information that the load would remain constant in the deception protocol. Slope of ventilation against CO2 output was significantly lower in the deception protocol than control protocol. Integrated EMG (iEMG) and ratings of perceived exertion (RPE) were similar between the two protocols, but awareness of change in load was significantly attenuated by the deception protocol. However, there was no temporal coincidence between awareness and actual change in load. These results suggest that ventilatory response during moderate exercise depends not so much on RPE but mainly on awareness or attention that is closely connected to information detection.

Effects of heat exposure in the absence of hyperthermia on power output during repeated cycling sprints

The aim of this study was to investigate the effects of heat exposure in the absence of hyperthermia on power output during repeated cycling sprints. Seven males performed four 10-s cycling sprints interspersed by 30 s of active recovery on a cycle ergometer in hot-dry and thermoneutral environments. Changes in rectal temperature were similar under the two ambient conditions. The mean 2-s power output over the 1st–4th sprints was significantly lower under the hot-dry condition than under the thermoneutral condition. The amplitude of the electromyogram was lower under the hot-dry condition than under the thermoneutral condition during the early phase (0–3 s) of each cycling sprint. No significant difference was observed for blood lactate concentration between the two ambient conditions. Power output at the onset of a cycling sprint during repeated cycling sprints is decreased due to heat exposure in the absence of hyperthermia.

EFFECTS OF BLOOD LACTATE ON OXYGEN UPTAKE KINETICS DURING RECOVERY AFTER SPRINT IN HUMANS

The purpose of this study was to examine the effects of blood lactate level (La) on oxygen uptake ( · VO2) kinetics during recovery after short-term exercise with maximal effort (sprint). Three sprints were performed on a cycle ergometer with a load of 8% of body weight at maximal rotation rate. · VO2 kinetics and oxygen debt were determined after three sprint tests: one 10-s cycling sprint, five repeated 10-s cycling sprints with 6-min intervals and one 30-s cycling sprint. There was no significant difference between peak power outputs in the 10-s sprint and five sprints. There was no difference in · VO2 kinetics during recovery from one sprint and during recovery after five sprints. La peaked at 5 min. The peak value of La was significantly lower in one sprint (4.41 ± 0.9 mM) than in five sprints (7.01 ± 2.2 mM). Thus, despite a difference in La, there was no difference between · VO2 kinetics during recovery after one sprint and after five sprints. There was a significant difference in · VO2 between the five sprints and 30-s sprint from 70 s to 320 s during recovery, but there were no significant differences in La after 5 min of recovery. There were two phases in · VO2. They consisted of fast oxygen debt and slow oxygen debt. There were also no differences in slow and fast oxygen debts between the two 10-s sprints despite significant differences in blood lactate during recovery. Peak La in the five sprints was not significantly different from that in the 30-s sprint (8.68 ± 1.2 mM). However, slow oxygen debt was significantly greater in the 30-s sprint than in the five sprints. It is concluded that · VO2 kinetics during recovery are not affected by an increase in blood lactate.