BASIC STEP VS. POWER STEP. PEAK VALUES OF VERTICAL GRF ANALYSIS

INTRODUCTION: Step training aerobics has replaced or been combined with traditional aerobics in many fitness programs. Participants follow a routine which involves stepping up and down on steps of varying heights, at varying cadences, in order to achieve an aerobic workout. Originally introduced as a low impact activity, step classes now include propulsive movements that have changed the nature of the activity impact. Regular exposure to moderately high levels of force is desirable because mechanical stress will produce structural changes that toughen important anatomical structures contributing inclusively to the increase of the bone density (Kotani et al., 1970; Huddleston et al., 1980; Panush, 1994) and capacity of resistance of tendons and ligaments tension (Woo, 1982). However these same forces can produce undesirable effects. If they are too high, the discomfort is increased and a potencial risk of injury arises. This situation is more visible when the forces are too repetitive in a period of time (Nigg et al., 1981) and during a step class there can be 6000 feet impacts. The purpose of this study was to compare the peak vertical ground reaction forces (GRF) of the basic step with the power variations: leap, hop and jump. METHODS: Sixteen skilled females performed 20 trials of each movement at a 0.15 m Kistler force plate height using a 120 bpm tempo. In addition, the parameters time of each trial (D tt), total time contact (D tc), total time between peaks (D tP), were analysed. RESULTS: The paired T-tests using the mean of each subject’s 20 trials showed significant differences between variations for GRF and D tP. Vertical GRF were 1.05 BW (basic), 1.68 BW (leap), 1.88 BW (hop) and 2.30 BW (jump). CONCLUSION: The study supports the present advice that replacing nonpropulsive steps (basic) with propulsive steps (power) represents an increase in the impact of the activity. The results suggest the need of a broader investigation in this domain. In effect, variables like platform height and music tempo tend to increase the peak values of GRF (Newton & Humphries, 1991; Farrington & Dyson, 1975; Bezner et al., 1996; Maybury et al., 1997; Terriet, 1997) and should be equated when prescribing step as an exercise program intended to promote health. REFERENCES: Bezner, S. A., Chinworth, S. A., Drewlinger, D. M., Kern, J. C., Rast, P. D. Robinson, R. D., Wilkerson. (1996). Step Aerobics: a Kinematic and Kinetic Analysis. Denton: Texas Women’s University, 252 - 254. Farrington, T., Dyson, R. J. (1995). Ground Reaction Forces During Step Aerobics. Journal of Human Movement Studies 29, 89 - 98. Huddleston, A., Rocckwell, D., Harrison, R. (1980). Bone Mass in Lifetime Tennis Athletes. Journal of the American Medical Assotiation 244, 1107- 1109. Kotani, P., Ichikawa, N., Wakabayashi, W., Yoshii, T., Koshimune, M. (1970). Studies of Spondylosis Found Among Weight-Lifters. British Journal of Sports Medicine 6, 4 -8. Maybury, M. C., Waterfield, J. (1997). An Investigation into the Relation Between Step Height and Ground Reaction Forces in Step Exercise: a Pilot Study. Journal Sports Medicine 31, 109-113. Newton, R., Humphries, B. (1991). Peak Ground Reaction Forces During Step Aerobics, Walking and Jogging. In C. Tant, P. Patterson, S. York (Eds.), Biomechanics in Sports IX. Ames, Iowa: State University, 67 - 71. Nigg, B., Denoth, J., Neukomm, P. (1981). Quantifying the Load on the Human Body: Problems and Some Possible Solutions. In A. Moreki, K. Fidelus, K. Kedzior, S. Wit, S. (Eds.), Biomechanics VII-B. Champaign, Ill.: Human Kinetics, 89 -99. Panush, R. S.. (1994). Physical Activity, Fitness and Osteoarthritis. In C. Bouchard, R. Shephard, T. Stephens (Eds.), Physical Activity, Fitness and Health - International Proceedings and Consensus Statement. Champaign, Ill.: Human Kinetics Publishers, 712 - 723. Teriet, C. R., Finch A. (1997). Effects of Varied Music Tempo and Volumes on Vertical Impact Forces Produced in Step Aerobics. In J. D. Wilkerson, W. J. Zimmermann, K. Ludwig (Eds.), Biomechanics in Sports - Proceedings, XV ISBS in Sports, 148. Woo, S., Gomez, M., Woo, Y., Akeson, W. (1982). Mechanical Properties of Tendons and Ligments. Biorheology 19, 397