Peak Ground and Joint Forces in Step-Exercise Depending on Step-Pattern and Stepping-Rate

Abstract

The assessment of biomechanical loading is quite important for exercise prescription and injury prevention in the scope of Exercise Biomechanics. The study of ground reaction forces, joint forces and joint moments of force at ankle, knee and hip, allows the understanding of the magnitude of external and internal loading experienced by the lower extremity joints and the pattern of force-absorbing adjustments while performing a dynamic activity. The main purposes of this study were to compare the peak values of those forces, during the ascending and the descending phases of four Step-Exercise patterns (basic-step, knee-lift, run-step and knee-hop), performed at varying stepping-rate conditions (125, 130, 135 and 140 beats per minute), in a group of 18 skilled females. The results showed that vertical ground reaction forces and joint forces at ankle varied from: 1.6-1.7 BW (body weight) in basic-step, 1.3-1.6 BW in knee-lift, 1.7-2.1 BW in runstep and, 1.0-1.8 BW in knee-hop; vertical joint forces at knee and hip varied from: 1.5-1.7 BW in basic-step, 1.2-1.5 BW in knee-lift, 1.5-2.0 BW in run-step and, 0.8-1.8 BW in knee-hop. Significant greater values were found in run-step for all parameters. No significant differences were found among conditions of stepping-rate. The anterior-posterior forces varied from 0.2-0.6 BW considering the four movements. Significant greater values were found in the two propulsive movements. Also, these forces increased with faster stepping-rates. The joint moments of force varied from 0.1-1.0 Nm/BW considering the four movements. Significant greater values were found: at ankle, in basic-step and run-step; at knee, in run-step and knee-hop (ascending-phase); and at hip, in run-step. No significant differences were found among conditions of stepping-rate, at ankle and at knee (decending-phase). Joint moments increased with faster stepping-rates at knee (ascending-phase) and at hip. The results suggest that experienced steppers are capable of stepping at different cadences, with generally similar patterns of kinematics and kinetics. We concluded that lower extremity internal loading can be effectively controlled by varying stepping-rate during Step classes.