Masters Theses

Date of Award

12-1981

Degree Type

Thesis

Degree Name

Master of Science

Major Professor

Edward T. Howley

Committee Members

Craig Wrisberg, Robert W. Leyen

Abstract

At the beginning and end of exercise the heart makes rapid changes in contraction rate coincident with the sudden changes in activity level. Several factors that influence the speed at which the HR returns to its pre-exercise value have been identified; how-ever, the influence of these factors on the sudden heart-rate deceleration that occurs during the first 30-seconds post-exercise is not known. The purpose of this study was to determine if the magnitude of the heart-rate during exercise and/or the habitual activity level of the subject influence the speed of heart-rate deceleration immediately post-exercise.

Eighteen healthy young male nonsmokers volunteered for this investigation. One-half of the subjects were trained cyclists. They rode an average of six times per week, 12 to 24 mph, and 3 to 55 miles per ride. The other half were untrained. Each had ridden less than twice monthly during the last three months.

Each subject rode a cycle ergometer four minutes, four times, at a constant pedal frequency (60 rpm--untrained, 80 rpm--trained). Work load was arbitrarily set so that a heart rate of 135 bpm or 170 bpm was reached during the fourth minute of exercise. Two rides were performed at each exercise heart-rate level. Six to 15 minutes of rest were allowed between rides. During the first five minutes of recovery, the subject sat silently and nearly motionless on the cycle ergometer. All subjects were familiar with the investigator, the equipment, and the procedures. Room temperature (19-23°C) and humidity (39-50 percent) were fairly constant. Heart rate was monitored with an oscilloscope and recorded with hardline electrocardiography during exercise and the first five minutes of recovery. Heart rate was measured and calculated at five second intervals beginning 2 seconds before the end of exercise and ending at 62 seconds of recovery.

ANOVA and linear regression analysis were used to test the effects of training and exercise heart-rate on the 30-second recovery heart-rate slope. The trained cyclists had a 30-second recovery heart-rate slope that was significantly faster than the untrained subjects' slope at the 135-bpm exercise heart-rate level. This training effect was not significant at the 170 bpm exercise heart-rate level. The effect of exercise heart-rate on the 30-second recovery heart-rate slope was significant but only for the trained subjects. They recovered faster from the slower exercise heart-rate. A large inter-subject variance may have precluded this effect from being realized in the untrained subject population.

The speed of heart-rate deceleration ranged from .93 ± .08 bpm/second to 1.32 ± .07 bpm/second during the first 30-seconds of recovery from submaximal exercise. The difference in the 30-second recovery rates in trained cyclists due to exercise heart-rate level (3.9 ± 1.2 bpm/10 seconds.) is measurable from a practical standpoint. When all subjects were grouped irrespective of training or fitness, the difference due to exercise heart-rate level (1.7 ± .9 bpm/10 seconds) is not practically measurable unless electrocardiography is used. The difference in the 30-second recovery rates due to training frequency at the 135-bpm exercise heart-rate level (3.9 ± 1.3 bpm/10 seconds) is measurable. The determination of measurable differences presented here is based upon a 10-second heart-rate count taken at 30-seconds immediately post-exercise.

When using the post-exercise heart rate to estimate the heart rate during exercise, a correction factor of 1 bpm should be added to a 10-second count that is started within one second following moderate to strenuous exercise. This correction factor should be halved when using the same procedure following maximal exercise. By counting the heart rate before 15 seconds of recovery have elapsed, the effects of training, fitness, and work intensity (exercise heart rate) on the speed of heart-rate decline can be ignored.

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