Step Aerobics: A Kinematic And Kinetic Analysis

Abstract

Step aerobics has become a popular form of aerobic exercise. Information regarding the mechanical stresses on the lower extremity during step aerobics may guide in determining the factors contributing to the risk of injury during progressions within this activity. Therefore, the purpose of this study was to investigate selected kinematic and kinetic variables during step aerobics at three heights and two cadences. Nine female subjects, mean age of 25.22 ± 4.3 yrs and mean height of 164 . 81 ±4.5 cm, performed conventional step aerobics. A conventional step was defined as right foot up, left foot up, right foot down, and left foot down. Three step heights of 4,6, and 8 in. and two cadences of 100 and 120 steps/minute (SPM) were performed by each subject in random order. These conditions were similar to those used in a typical step aerobics class. High speed cinematographic data collected at 90 frames/second were used to determine 2-D coordinates of the right leg in the sagittal plane. A Kistler force platform was used to measure ground reaction forces (GRF) of the right foot during step down. Identical mean vertical peak GRF were observed for both cadences. These forces were 1. 60, 1 .66, and 1 .76 percent body weight, at 4,6, and 8 in. respectively. Thus, increasing cadence from 100 to 120 SPM did not increase the risk of experiencing higher GRF in the lower extremity. Significant differences were found only between compressive joint forces and step heights at the ankle, knee, and hip. The magnitude of these joint forces were similar, indicating that there was no dissipation of forces throughout the lower extremity, unlike what has been observed during walking and running. Examination of the knee and hip moments revealed oscillating patterns that varied at different heights and cadences. This may indicate that these joints were used uniquely by individuals in stabilization of the body during the step down phase. With the possible exception of injury due to the lack of force dissipation, these findings suggest that progression of height and/or cadence may not be risk factors contributing to injury.