Presented at NACOB 98:
North American Congress on Biomechanics
Canadian Society for Biomechanics - American Society of Biomechanics

University of Waterloo
Waterloo, Ontario, Canada
August 14-18, 1998

EFFECT OF PEDAL CRANKARM LENGTH
ON CYCLING DURATION IN A RECUMBENT POSITION

D. Too 1 , G.E. Landwer 2
1 Department of PE and Sport, State University New York at Brockport, NY 14420
2 Department of Health and Physical Education, University of Nevada, Las Vegas, NV 89154

INTRODUCTION

In cycling, adjustments in seat-to-pedal distance, seat tube angle, and trunk angle with respect to the ground, result in changes in hip, knee, and ankle angles, affecting performance (Too, 1990). Changes in joint angles can alter muscle length, moment arm length, angle of pull, joint range of motion, and/or the force/torque/power generated by different muscle groups. Manipulation of pedal crankarm length (CL) will alter joint angles and can affect cycling performance. How performance is affected by changes in CL will provide information in the development of faster and more effective human powered vehicles.

REVIEW AND THEORY

It is well documented that recumbent human powered vehicles are more effective aerodynamically than the standard cycling position (Kyle, 1982). It also appears that greater power can be produced in a recumbent position and is attributed to differences in joint angles during the pedal cycle (Too, 1996b). To determine the recumbent position and joint angles that would maximize cycling performance, investigations have included systematic manipulation of (a) seat-tube angles (Too, 1991); (b) body orientation (Too, 1994); and (c) seat-to-pedal distance (Too, 1993). To continue along this line of inquiry, it is the purpose of this investigation to determine the effect of changes in CL on cycling duration in a recumbent position, and to report the hip, knee and ankle angles.

PROCEDURES

Twenty-two volunteer male subjects (26.4 ± 4.5 yr.) were each tested in 5 CL (110, 145, 180, 230, 265 mm) using an adjustable pedal shaft mechanism. The recumbent position used, was defined by a 75° angle formed between the bicycle seat tube and a vertical line passing through the crank spindle (Too, 1991). To obtain this seating position, a variable seating apparatus, allowing for manipulations in seat tube angle, backrest angle, and seat to pedal distance, was used and interfaced to a Monark cycle ergometer (Model 814E). The seat- backrest was kept perpendicular to the ground and the seat-to-pedal distance adjusted to 100% (to within 1.9 cm) of the total leg length of each subject, as measured from the greater trochanter of the right femur to the ground (Too, 1991).

In each CL condition, pedal toe-clips were worn, and the minimum and maximum hip, knee, and ankle angles were measured statically with a hand held goniometer for one complete pedal revolution. Each subject was tested in all 5 CL conditions according to a randomly determined sequence, with a minimum of 24 hours rest between sessions. The test protocol consisted of pedaling to a metronome at 60 rpm with an initial load of 0.5 kg resistance. The ergometer resistance was incremented 0.5 kg every minute until test termination by the subject, or until the subject could no longer maintain the required pedaling rate. Pedal cadence and time of test termination was monitored and recorded with a microcomputer in conjunction with an optical sensor, reflective markers, and a SMI (Sports Medicine Industry) software program. Repeated measures ANOVA and post-hoc tests were used to determine if there were significant differences in cycling duration with changes in CL and where these differences occurred.

RESULTS

With changes in CL, the mean values for the following variables are presented in Table 1: time of cycling duration; hip, knee, and ankle angles (minimum, maximum, and range of motion). The range of motion (ROM) was determined as the difference between the maximum and minimum angle measured. From Table 1 it can be observed that with changes in CL from 110-265 mm, cycling duration is best described by an inverted U-curve; whereas there appears to be a decrease in minimum joint angles, an increase in the joint ROM, and no obvious trend in maximum joint angles. Repeated measures ANOVA revealed significant differences (p < .01) in cycling duration with changes in CL, with F(4,82) = 7.89. Post-hoc comparisons (Scheffe) revealed cycling duration to be significantly greater (p < .05) in the 145 and 180 mm CL when compared to the 110 and 265 mm CL. No significant differences in cycling duration were found between the 145, 180, and 230 mm CL.

Crankarm Length (mm)
110145180230265
Time (sec)604737715694 592
Hip (deg)
min756962 56 50
max101102101104105
rom26333948 55
Knee (deg)
min9685736049
max142142138138138
rom4657657988
Ankle (deg)
min92898682 78
max10410010096 94
ave989593 8986
rom1211141417

Table 1: Cycling Duration and Joint Angles with Changes in Crankarm Length

DISCUSSION

No literature can be found examining the effect of changes in CL on cycling duration in a recumbent position.. The literature available on CL, generally involves upright cycling positions, where power production (Inbar et al, 1983), and constant average power (Hull et al., 1988) are examined. The trend in peak power (inverted U- curve) found by Inbar et al. (1983) with 5 CL (ranging from 125-225 mm) was similar to the trend found in the current investigation, except the 166 mm CL was reported to maximize power production. Only one investigation was found involving CLs and a recumbent position, but power production was examined instead of cycling duration (Too, 1996a). With an increment in CL (110-265 mm), Too (1996a) reported a decreasing trend in peak power, and an inverted U-curve to describe mean power. The differences in trend for these investigations, may be attributed to a variety of factors such as differences in joint angles (from manipulations in positions and CL), variables examined, and the interaction between CL, pedal rate, and load for a given power output (Hull et al., 1988).

The trend in cycling performance with changes in CL, found in this investigation, may not necessarily be appropriately compared with those in the literature. But the comparisons do provide information in the direction where research is needed to improve cycling performance. In conclusion, more investigations are required before the mechanisms and interactions involved in cycling performance are fully understood, and the limits of human powered vehicles reached.

REFERENCES

Hull M.L. et al., J. Biomech., 21, 839-849, 1988.

Inbar O. et al., Ergon., 26, 1139-1146, 1983.

Kyle C.R. Bicycling, 23, 59-66, 1982.

Too D. Int. J. Spt. Biom., 7, 359-370, 1991.

Too D. Med. Sci. Spt. Exer., 25, S68, 1993.

a Too D. Proc. ISBS-1995, 350-353, Lakehead University, 1996.

b Too D. Proc. Can. Soc. Biom., 184-185, Simon Fraser University, 1996

Too D. Res. Quart. Exer. Spt., 65, 308-315, 1994.

Too D. Spts. Med., 10, 286-302, 1990.