Biomechanical Comparison of Two Lower Extremity Exercise Machines Used for Knee Injury Rehabilitation

Abstract

2004 The goals of rehabilitation after an ACL reconstruction include improving cardiovascular and muscular fitness. Although stationary bicycles are commonly used to accomplish this task, recumbent stepping ergometers have been shown to achieve the same goals. Few data exist regarding the use of recumbent steppers by individuals who have ACL surgery. PURPOSE: To evaluate the knee joint reaction forces and lower extremity muscle activity during stepping and cycling. METHODS: Fourteen healthy individuals with no history of lower extremity injury (age: 22.9 ± 1.9 y, 173.6 ± 11.3 cm, 76.7 ± 13.2kg) and 10 individuals who had undergone ACL reconstruction in their right knees (age: 22.2 ± 4.1 y, 175.3 ± 7.6 cm, 73.0 ± 12.9 kg, 43 ± 32 months post-op) participated. Subjects were videotaped with two cameras as they performed moderate (RPE = 3) exercise on a stepper and a cycle. Four seat positions were utilized resulting in minimum knee flexion angles of 0° (full extension), 15°, 30°, and 45°. The right pedals of the stepper and bike were fitted with a load cell. Video (60Hz) and force data (900Hz) were synchronized and used to perform an inverse dynamics analysis. To assess the myoelectric activity of selected lower extremity muscles, six pairs of surface electrodes were attached to the right side of the body over the following muscles: vastus lateralis (VL), vastus medialis (VM), rectus femoris, biceps femoris, medial gastrocnemius, and soleus. RESULTS: Statistical analyses (ANOVA) revealed that proximal/distal forces were significantly decreased for the stepper compared to the cycle (p = .029) while medial/lateral forces increased (p<.001). When compared to the cycle, significantly reduced muscle activity was detected for the VL (p = .005) and VM (p = .001) for the stepper. Significant main effects (increased muscle activity with increasing knee angle) were found in the VM (p = .012) and VL (p = .058). CONCLUSION: Our results indicate that lower extremity biomechanics on the two machines tested are not affected by knee surgery status. The reduced compressive knee force, equal anterior shear force, and the similar muscle activity for 4 of the 6 lower extremity muscles tested, indicate that a recumbent stepper is a viable rehabilitation modality after ACL surgery. Supported by NuStep, Inc. (UPN#01061905)