Isometric fatigue induced by different levels of rhythmic exercise

Abstract

Three subjects were trained in leg extensor isometric contractions and in cycling. They then cycled for three consecutive bouts, each of 2.75 min at a constant level of VO2, from 20 to 80% VO2 max. Fifteen seconds after each bout of cycling the subjects exerted an isometric contraction of the right leg at 40% of the maximum voluntary contraction. In each experiment, the duration of the three successive isometric contractions decreased as in hand-grip contractions. There was also a linear reduction in isometric endurance as the severity of the preceding rhythmic exercise increased. In other experiments, after three bouts of rhythmic exercise at 20% VO2 max (each followed by a fatiguing contraction at 40% MVC), further bouts of cycling at increasing levels of severity up to 60% VO2 max resulted in a linear fall in isometric endurance which could be reversed by interposing a lighter level of cycling. The heart rates during these experiments showed a steady increase during the isometric exercise, to about 150 beats X min-1, as the bouts of preceding rhythmic exercise became progressively more severe. The isometric contractions had little influence on the heart rate during cycling. But the rhythmic cycling exercise markedly increased the heart rate achieved at the end of the isometric contractions while decreasing the increment in heart rate during the contraction.

Experiments on Factors That Influence Muscular Function in Man.

“…Muscle temperature was dependent on both the duration and severity of the rhythmic exercise, with a * 2-3 0 C difference between cycling at 20% and 802 V0 2 max for the same duration. This change corresponds exactly to the increments postulated in our .7 * a, -65previous study (Lind et al 1982), but the reduction in endurance was much greater than predicted based solely on this increment of temperature. Muscle temperature was not the sole determinant of isometric endurance since similar temperatures, produced by cycling at different intensities and durations or by passive manipulation, did not result in the same endurance.…”

The effect of previous weight training and concurrent weight training on endurance for functional electrical stimulation cycle ergometry

“…Typical nonparalyzed subjects can sustain 4-6 kPa of load at the onset of bicycle studies (Lind et al 1982). Further, even after the greatest degree of training as seen here, these subjects still had less than 30% of the average strength reported for these muscle groups by ourselves in nondisabled subjects (Lind et al 1982). Therefore, continuous strength training, while perhaps unnecessary for the able-bodied population, was critical in increasing cycle endurance here.…”

“…If the subjects were able-bodied athletes, the effect of strength on endurance training would probably be much less pronounced than here, where muscle strength did not even allow 1 min of cycle ergometry against only 0.1 kPa of load. Typical nonparalyzed subjects can sustain 4-6 kPa of load at the onset of bicycle studies (Lind et al 1982). Further, even after the greatest degree of training as seen here, these subjects still had less than 30% of the average strength reported for these muscle groups by ourselves in nondisabled subjects (Lind et al 1982).…”