Peak ground reaction forces during step aerobics, walking and jogging

Step aerobics has emerged as a popular form of exercise being offered in a number of health and fib'less centers throughout the world. The step workout involves stepping up and down off a 0.15 to 0.30 meter high box to music. The stepping can include a wide variation of leg and arm movements. Since the introduction of the step workout some participants and instructors have expressed concern about the impacts involved in stepping and the possibility of injury. The peak vertical ground reaction force (GRF) during foot landing has been noted by Nigg, Denoth and Neukomm (1981) as a possible cause of soft tissue and bone injury. Scott and Winter (1990) have determined that peak loads at chronic running in jury sites are related to the combination of GRF and the active muscle forces. During running the peak vertical GRF has been measured by Frederick and Hagy (1986) to be 2.86 times body weight (BW) for subjects running at 16 kilometers per hour (kph) and Mero, Komi, Rusko and Hirvonen (1987) found peak vertical GRF of 3.7 BW to 4.8 BW at maximum running speeds. Francis, Francis, Miller & Hurst (1990) present data on the GRF in the vertical direction during stepping on and off a 0.25 meter platform at a cadence of 120 steps per minute (spm). These forces were compared with running across the forceplate at 11.2 kph and walking at 4.8 kph. hese forces were compared with running across the forceplate at 11.2 kph and walking at 4.8 kph. The study reported peak vertical forces of approximately 1.75 BW for stepping, 1.25 BW for walking and 3.0 BW for running. It was concluded that the vertical GRF during stepping was only slightly higher than that of walking and both activities were considerably less stressful than running. A thorough evaluation of impact forces during landing has been published by Dufek and Bates (1990) which emphasizes the importance of a toe-heel foot plant and increased knee flexion as movement techniques to decrease impact forces. The objective of this study was to compare the peak ground reaction forces during walking, running and step aerobics using bench heights of 0.20, 0.25 and 0.30 meters. The effect of increasing bench height on impact force was also assessed.