COMPARISON OF TWO ELLIPTICAL MOTION RUNNING MACHINES AND TREADMILL RUNNING

Abstract

INTRODUCTION: One of the major problems associated with rehabilitation from impact- associated running injuries is maintaining cardiovascular fitness. Recently, elliptical motion exercise machines have been developed in an attempt to simulate running while minimizing impact forces. These machines have been shown to maintain cardiovascular fitness. However, they have not yet been shown to truly simulate the running motion. The purpose of this study was to provide a quantitative comparison of two elliptical motion exercise machines (C1 and C2) and treadmill running (C3). METHODS: Both of the elliptical motion machines fixed stride length, although one allowed a greater stride length (C1). Eight subjects were tested in each of three submaximal exercise conditions during a 15 minute bout. Subjects performed at a stride frequency that resulted in a heart rate of 65% of their age-predicted maximum heart rate. Five 60 Hz digital cameras were used to collect lower extremity kinematic data. Pre-amplified surface electrodes measured the muscle activity of seven lower extremity muscles. Impact forces were assessed using a 1.7g PCB accelerometer placed on the distal medial aspect of the tibia. Both the accelerometer and EMG data were collected concurrently on a microcomputer sampling at 600 Hz. Lower extremity joint and segment parameters, onset and offset of muscles during stride, peak impact force and time to peak impact force were calculated. An analysis of variance was used to compare the measured parameters between each machine condition and to identify whether the duration of the exercise bout had an effect. RESULTS: There were no significant differences in stride duration with controlled stride frequency. The results of the analysis of the kinematic data showed that the majority of the differences between the machines and treadmill running occurred at the ankle and knee joints. At the ankle and knee joints, the touchdown angle was greater for the two machines (C1 and C2) than for treadmill running (ankle: 11.97 o and 22.14 o versus 2.23o; knee: 34.94 o and 33.89 o versus 12.05 o). At the ankle joint, the maximum plantar flexion angle was greatest in treadmill running, while there were no significant differences in any knee angles subsequent to touchdown. There were no differences in any of the hip angles at any time in the stride. Impact values on the two machines were 30% of those measured during treadmill running, and the time of occurrence of the impact was substantially longer into the stride. The results of the EMG data showed that the duration of muscle activity throughout the stride was different in the triceps surae, rectus femoris and vastus lateralis. In each case, the duration of the stride in which these muscles were active was least in treadmill running. CONCLUSIONS: In conclusion, while there are a few differences between the elliptical machines and running, it appears that the machines could be considered representative of running with distinctly less impact. Thus, these machines could be used as rehabilitation tools for runners recovering from impact-related injuries.