Ramp Position Influences Lower Extremity Biomechanics while Exercising on the Elliptical Trainer

Abstract

The elliptical trainer, developed to simulate running while minimizing joint loads, elicits a unique lower extremity biomechanical response. PURPOSE: To examine the angular kinematics, peak net joint moments, and peak joint powers at the hip, knee and ankle joints while exercising at three different ramp settings on the elliptical trainer exercise machine (Precor EFX). METHODS: Twenty-six healthy individuals with no history of lower extremity injury and with previous experience exercising on an elliptical trainer volunteered for this study (age: 22.19 ± .85 y, 169.9 ± 9.8 cm, 74.0 ± 19.3kg). Motion was captured with two cameras as subjects performed exercise (120 steps/min) at three ramp conditions (13, 25, and 40 degree incline). The pedal resistance was kept constant at the lowest setting. The pedals of the elliptical were fitted with three orthogonal load cells. Video (60Hz) and force data (600Hz) were synchronized and used to perform a 2D inverse dynamics analysis. RESULTS: As the ramp inclination increased, subjects demonstrated greater amounts of ankle dorsiflexion, knee flexion, hip flexion and lesser degrees of plantar flexion and hip extension (p<.000). Mean peak moments at the ankle joint were not significantly different across the three ramp settings. Peak knee extensor and hip flexor moments increased (knee=.05 to .28 Nm/kg; hip=.20 to .56 Nm/kg) and flexor moments at the knee and extensor moments at the hip decreased (knee:2.27 to .49 Nm/kg; hip:2.08 to .27 Nm/kg) as the ramp settings increased (p<.000). While both peak positive and negative ankle joint powers reached statistical significance across the three ramp settings, the effect size of the ramp on power generation was small. As the ramp increased, peak positive power at both the knee and hip significantly decreased (knee:2.86 to .41 watts/kg; hip:4.25 to 0.98 watts/kg) and negative power decreased at the knee joint (1.13. to 0.44 watts/kg) (p<.000). CONCLUSIONS: Distinct from running, where the ankle joint contributes significantly to the overall power for forward propulsion, the hip and knee joints were observed as the primary sources of power during exercise on the elliptical trainer. This report on mechanics of the elliptical stride makes a valuable contribution to the fitness and rehabilitative arenas. Pedal load cells provided by Precor, Inc.