BlOMECHANICAL CHANGES DURING THE 200 M BUTTERFLY EVENT: A COMPARISON BETWEEN ADULT AND INFANT SWIMMERS

Abstract

INTRODUCTION-Due to environmental specificity, swimming technique and biomechanics plays a determinant role in swimming performance. Once fatigue seem to be able to change technique (Weiss et al, 1988), a rigorous evaluation of this effects must be of outstanding importance for practice. Nevertheless, only a few papers were published concerning changes, during a swimming event, on biomechanical parameters. The purpose of this study was to characterise and compare biomechanical changes of butterfly technique during a 200 m event among adult and infant swimmers. METHODS-Ten well trained male swimmers (5 adults and 5 infants) were studied (21.2±3.5 and 12,O±0 years of age: 179A±5,7 and 159A±5.3 cm height; 76.6±10A and 45,8±3.8 kg of weight, respectively for adults and infants) Each swimmer performed a maximal 200 m butterfly test, videotaped in the sagital plane, both underwater (30 cm bellow surface) and overwater (30 cm overwater) with SVHS cameras. 80th images were mixed using a Panasonic WJMX50 mixing table in order to obtain a dual-media final image. The cameras were placed at a 5 m distance, with the optical axis perp ndicular to the swimmers plane of displacement!. In each 200m performance, the 2nd, 4th, 6th and 8th 25 m laps were evaluated using the Peak Performance 20 system using a sampling frequency of 50 Hz and 10 digitised anatomical land marks, One last point was digitised in order to define the water surface, The parameters studied were (i) swimming velocity (V); (ii) stroke length (SL); (iii) stroke rate (SR); (iv) maximum depth of the hand (HO); (v) total antero-posterior horizontal displacement of the hand (HA-PHO): (vi) index of horizontality of the hand path (IH = HAPHO*HO-t); (vii) maximal vertical amplitude of the hip displacement during one stroke cycle (HiTOSP); (viii) CM maximal velocity, associated to the final of the upsweep (Vmax); (ix) CM velocity during the entry of the hands (Vent); (x) CM 'velocity velocity during the exit of the hands (Vex); (xii) CM acceleration during the recovery of the arms (AR); (xiii) CM acceleration during the upsweep (AU): (xiv) "dropped elbow index" (OE) calculated through the verticai distance between the finger tip of the middle finger and the elbow. RESU TS-The results of this study where significant differences were found are presented in Table 1. CONCLUSIONS-The results of this study pointed out that: (i) a number of biomechanical parameters of swimming technique are changed along the 200m butterfly event, both for adult and infant swimmers, probably related to fatigue; (ii) some of the significant differences were observed earlier for infant than for adult swimmers; (iii) differences in swimming velocity among infant and adults were probably a combined effect of multiple factors. REFERENCES Weiss et al. (1988). In: B. E. Ungereehts, K. Wilke and K. Reisehle (eds.), Swimming Seienee V, pp 295-304. HKP, Champaign, IIlinois.