The Effect Of Hip Position/Configuration On EMG Patterns In Cycling

Abstract

From the results of previous investigations examining the effect of changes in hip angles on cycling performance, it had been concluded that there is an optimal hip position/configuration which maximizes aerobic and anaerobic work. But why and how this hip position/configuration affects cycling perfonnance is unknown. Therefore, it was the purpose of this investigation to determine whether differences in cycling performance with changes in hip position/configurations are reflected and can be explaincd by changes in EMG patterns. Five male recreational cyclists were tested in 5 different hip position/configuration (0,25,50,75, and 100 degrees), as defined by the angie formed between the bicycle seat tube and a vertical line (perpendicular to the ground) passing through the pedal axis. By rotating the seat to maintain a backrest perpendicular to the ground, a systematic decrease in hip angle from the 0 to 100 degree position was induced. For each condition, the seat to pedal distance was adjusted to remain 100% (to within 3/4 inch or 1.905 cm) of the total leg length, as measured from the greater trochanter of the femur of the right leg to the ground. In each position, the minimum and maximum hip, knee, and ankle angles were obtained for one complete pedal revolution. A cycle ergometer was used with a resistance of 65 gm/kg of the subject'S body mass (3.82 joules/pedal rev/kg BM) at a pedaling frequency of 60 rpm. Each subject was strapped to the seat-backrest at the waist and hips, and pedal toeclips were worn. For each test condition, EMG activity of 6 muscle groups of the right limb were each collected at a rate of 2000 Hz with surface electrodes. A recorder and a micro-switch interfaced to a microcomputer was used to record EMG activity and pedal position. For a complete pedal cycle in each hip position, a waveform data analysis program was used to determine: (l) the sequence of activity by the different muscle groups; (2) the duration of activity; and (3) the pedal position each muscle group was active and inactive. ReANOVA's and post-hoc tests revealed significant differences in the pedal position location that the rectus femoris, gluteus maximus, vastus medialis and biceps femoris were active and inactive during a pedal cycle with changes in hip position/configuration. With a systematic change in hip position from 0 to 100 degrees, there is a backward shift in pedal position loca tion that the muscles were active and inactive. It was concluded that differences in cycling performance with changes in hip position/configuration are reflected and can be explained by differences in EMG patterns. Supported by a grant-in-aid of research from Sigma XI, The Scientific Research Society.