Effect of pedal rate on cardiorespiratory responses during continuous exercise

Area of Science:

• Exercise Physiology
• Sports Science
• Human Physiology

Background:

• The influence of pedal rate on physiological responses during continuous submaximal exercise remains unclear.
• Understanding these effects is crucial for optimizing exercise protocols and interpreting physiological data.

Purpose of the Study:

• To investigate the effect of different pedal rates (60 rpm vs. 90 rpm) on ventilation (VE), heart rate (HR), and oxygen uptake (VO2) during moderate and high-moderate intensity cycle ergometry.
• To determine the contributing factors to the gradual increase in VO2 during prolonged exercise at varying pedal rates.

Main Methods:

• Five trained males performed 45-minute cycling sessions at moderate (127 W) and high-moderate (166 W) intensities.
• Each intensity was tested at two pedal rates: 60 revolutions per minute (rpm) and 90 rpm.
• Measurements included VE, HR, VO2, rectal temperature (Tr), and blood lactate levels.

Main Results:

• Both power output and pedal rate additively increased mean VE, HR, and VO2.
• HR increased by approximately 10.8% across all conditions, independent of power output and pedal rate.
• VE increased by 7.4% (moderate intensity) and 10% (high-moderate intensity), independent of pedal rate.
• Oxygen uptake (VO2) showed a greater increase at 90 rpm (8.2%) compared to 60 rpm (4.4%) for the same power outputs.
• Factors like increased rectal temperature and oxygen cost of ventilation accounted for only 31-36% of the VO2 increase, suggesting muscle use contributed 64-69%.

Conclusions:

• Pedal rate significantly influences the rate of increase in oxygen uptake during continuous submaximal exercise.
• While HR and VE responses are largely independent of pedal rate, VO2 is sensitive to it.
• The majority of the gradual increase in VO2 during exercise is attributed to factors related to muscle utilization.