EFFECT OF PEDAL REVOLUTIONS ON ENERGY EXPENDITURE DURING STATIONARY CYCLING.
by
Marla A. Thomas and J. L. Mayhew
Human Performance Laboratory, Northeast Missouri State University, Kirksville, MO

Original Publication Information:
IAHPERD Journal Volume 29. No.2 Spring, 1996.
INTRODUCTION
Cycling has become one of the most widely used forms of exercise training and rehabilitation. Because of this popularity, the question arises as to be best procedure for maximizing energy expenditure. Can an individual burn as many calories riding with less resistance at higher revolutions per minute (rpm) as he/she can at lower rpms against heavier resistance? If an equivalent amount of energy could be expended at higher rpms, less stress might be placed on the knee joints, a primary concern in an older population or in individuals undergoing rehabilitation. In addition to the metabolic demands, the effect of various pedal frequencies on cardiac stress might be an additional consideration. Therefore, the purpose of this study was to determine the effect of increasing pedal rpms on oxygen consumption (VO2) and cardiac stress during cycling at a constant work output.

METHODS
Ten moderately trained men (age = 27.0 ± 7.9 y; VO2max = 48.9 ± 4.6 ml/kg/min) volunteered to participate after being informed of the risks and benefits. Each subject performed a constant-load, successively increasing pedal rpm workbout on a bicycle ergometer (Monark, Model 814). The pedal rpms were 50, 60, 76, and 87 with correspondingly appropriate resistances to produce a constant work output of 150 W. Each pedal rpm level was maintained for four minutes with no pause between levels. VO2 was monitored throughout the test using a metabolic cart (SensorMedic, model 2900). Heart rates (HR) were taken by auscultation during the last 20 seconds of each minute. The 3rd and 4th minute values were averaged to represent the metabolic demand of a given pedal rpm.

The peak VO2 was determined at the conclusion of the submaximal workbouts. The pedal cadence was set at 60 rpm, and the resistance adjusted to a level appropriate for the subject's exercise background. The resistance was increased by 50 W every two minutes until voluntary fatigue or until the subject could not maintain the rpm within four counts of the required pace.

RESULTS
Repeated measures ANOVA indicated that pulmonary ventilation (VE)(F = 4.27) and HR (F = 10.82) increased significantly across the four rpm levels. A Duncan's multiple range post hoc analysis found that the 50 and 60 rpm levels had significantly lower VE and HR values than the 74 and 87 rpm levels. The 76 and 87 rpm levels did not differ significantly. VO2 (F = 0.49), caloric expenditure (F = 0.46), and respiratory exchange ratio (F = 0.27) did not change significantly with increasing rpms. The values for these parameters remained within a range of 1.0% to 2.4% of each other across all four work levels.

DISCUSSION
The results of this study indicated that although the ventilatory and cardiac stresses increased significantly at the higher rpm levels, the metabolic demand remained relatively constant. The caloric expenditure remained within 0.4 Kcal/min across all four rpm levels. Since the work output was constant, the unaltered work input indicated that the mechanical efficiency was approximately the same for the different rpm levels (18.6%).

Previous research has indicated that there is an upward drift in VO2 during a constant-load cycle ergometer work task (Hagberg, Mullin, & Nagle, 1978). The present study noted no such upward shift in VO2 but did reveal an upward "cardiac drift" in HR. The increase in HR at a constant VO2 might indicate a decrease in stroke volume during the 16 minutes of exercise. Since the exercise time and stress (59.5% VO2max) would indicate there was not a large loss of fluid from the blood, a hemoconcentration could not be the cause for the cardiac drift.

Hagberg et al. (1978) indicated that the increase in VO2 during 20 minutes of stationary cycling was probably caused by the increased energy cost of pulmonary ventilation and rise in body temperature. They reported an 11.4 l/min increase in VE while exercising at 65 %VO2max. That is comparable to the 8.3 l/min increase in our subjects exercising at 59.5% VO2max. Furthermore, Hagberg et al. (1978) indicated that the elevation in body temperature might be tied to the rise in ventilation. However, contrary to their findings, we did not note an increase in VO2 during the workbout despite a 15.1% increase in VE.

This study supports the concept of equal caloric expenditure for equal work output regardless of the manner in which that work output is achieved. Individuals interested in utilizing exercise as a weight control medium can benefit equally well from cycling at a faster cadence against a lighter resistance as from cycling at a slower cadence against a heavier load. However, the current study also agreed with reports of higher HR at faster rpms (Michielli & Stricevic, 1977), a consideration with older adults, less fit individuals, or those involved in a cardiac rehabilitation setting. While it might be less demanding on joints to pedal at a higher cadence, it produces a greater cardiac stress.

Hagberg, Mullin, Giese & Spitznagel (1981) have noted that the most efficient pedaling frequency was 91 rpm in a group of trained road cyclists. Extensive training had ingrained this as the preferred pedal frequency. In the current study there was very little difference in pedaling efficiency across the four rpm values, with a range of only 18.3% to 18.9%. This was in contrast to the findings of Gaesser and Brooks (1975) who noted a decline in efficiency with increases in pedal frequency in "well-conditioned" men. Peak efficiency in the current study was noted at the 76-rpm level. Although well-conditioned, none of the subjects had trained for road racing and thus may more accurately represented the average fitness enthusiast.

From the current results, it appears that maximum efficiency during cycling prior to increasing cardiac stress may be realized between 70 and 80 rpm. Given the option, most exercisers subjectively chose a pedal rate of about 70 rpm as most comfortable. This may be because of maximum efficiency at this level or because this is the point perceived as most comfortable prior to an increase in cardiac stress. Further investigations using a perceived exertion scale might lend support to this speculation.

aWork output constant at 150 W.
bF = 4.20 significant at p<0.01.
TABLE 1. Metabolic Responses at Different Pedal Revolutions at a Constant Work Output (n = 10).
Pedal Revolutionsa
Varable 50 60 76 87 Fb
VE (L/min) 54.8 58.6 59.4 63.1 4.27
VO2 (L/min) 2.33 2.25 2.23 2.31 0.74
R 0.95 0.96 0.95 .095 0.27
Kcal/min 11.4 11.2 11.1 11.5 0.46
HR (bpm) 137 142 146 151 10.82

REFERENCES