BIOMECHANICS OF SWIMMING ANALYSED BY THREE-DIMENSIONAL TECHNIQUES

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1 BIOMECHANICS OF SWIMMING ANALYSED BY THREE-DIMENSIONAL TECHNIQUES JANE M. CAPPAERT U.S. Swimming, International Center for Aquatic Research, Colorado Springs, Colorado, USA ABSTRACT The following paper summarises analyses of the swimming strokes using video methods. The analyses were made during Olympic and World Championship competitions as well as noncompetitive situations. The whole body technique of elite swimmers was quantified using three-dimensional analyses for each of the four strokes. Additionally, differences between 1 OOm and 200m swimmers in each stroke were analysed. Keywords: three-dimensional stroke analysis, active drag, propulsion INTRODUCTION Mid-pool swimming velocity during competition has been studied by many (Arellano et al., 1994; Kennedy, Brown, Chengalur, and Nelson, 1990; Craig and Pendergast, 1979; Craig, Skehan, Pawelczyk, and Boomer, 1985). Of the velocity components, stroke rate (SR) and stroke length (SL), it has been concluded that SL is the most critical factor in achieving success in swimming races (Arellano et al., 1994; Kennedy et al., 1990; Craig and Pendergast, 1974). Although there is general agreement that performance differences between swimmers are more related to SL than SR, specific factors contributing to long SL are less well known. To increase maximal swimming speed and SL, swimmers must: 1) maximise propulsion and propelling efficiency, and 2) reduce active drag from the water. The specific technique aspects of the four strokes that produce high level performance are not well defined. The purpose of this paper is to investigate both propulsion and propelling efficiency as well as active drag and their effects on maximising performance and SL using the methods of video analysis to understand the three-dimensional movements of swimming. THREE-DIMENSIONAL ANALYSIS STUDIES The swimmers for these studies were competitors of the 1992 and 1996 Olympics and the 1991 World Championships. Swimmers were filmed during the competition using a four camera system and subsequent three-dimensional analyses (DLT method; Abel-Aziz and Karara, 1971) of the swimmers was undertaken (for method details, see Cappaert, Pease, and Troup, 1995). Swimmer highlights from each stroke are presented below. Freestvle: The elbow angle had the highest impact on the stroke. A straighter arm was associated with a longer pull pattern and slower stroke cycle rate. During the insweep phase. the elbow angle played an important role in the production of force for the whole stroke and particularly the fmish phase of the stroke. Larger elbow angles during the insweep were associated with smaller resultant and effective forces during this phase. This may imply that a straight back pulling motion is not as effective as a sculling motion on the insweep. However, the average insweep elbow angle was degrees. So while the sculling motion is important, the elbow did not bend to 90 degrees. 141

2 Higher forces during the finish phase were also associated with a more bent elbow in the insweep phase. This bent elbow position could effect the finish phase by: l) setting the hand in proper position or 2) placing the arm in a position to get more muscle activity from the internal rotators - specifically latissimus dorsi. Also more body roll was associated with higher forces during the finish phase. In comparing sprint (200m and below, n=5) and distance freestylers (above 200m, n=4), the only significant difference (p<0.05) was that the sprint group had a deeper pulling pattern. However, definite trends (p<o.lo) existed between groups. Sprinters were characterised by more knee bend during the kick. Increasing the knee bend increases the range of motion of the foot through the water, which may give more propulsion. The higher trunk angle of the sprinters may have been created by extra propulsion from the kick. Less body roll during the catch phase of the stroke was also seen in the sprint group. Due to the rapid nature of sprinting events, these swimmers may not spend as much time lengthening their stroke during the catch phase to emphasise body roll. Table I: Differences Between Sprint and Distance Freestylers Variables Sprint Distance Stroke Depth (m) Knee Ang min (deg) Trunk Ang (deg) Shoulder roll Catch Phase (deg) p=0.03l p=0.086 p=0.091 p=0.082 Butterfly: Swimmers who stayed lower in the water were able to extend their elbows to a straighter position during the finish phase of the pulling pattern. The maximum elbow angle was positively correlated with the efficiency of the stroke. Staying lower in the water may be an advantage in swimming butterfly. In order to stay lower in the water (lower trunk angle), the vertical undulation must be minimised to a certain extent. The loom butterfliers (n=5) were higher in the water (hip height), but had a lower maximum trunk angle than the 200m butterfliers (n=7). These sprinters seemed to have less undulation overall as evidenced by lower trunk angle during the finish and recovery of the stroke. The 1 OOm butterfliers produced more resultant (38.6N vs. 29.4N) but were similar in propulsive forces (21.6N vs. 21.3N). The finish elbow angle was straighter for the loom butterfliers. Straighter elbows were associated with propelling efficiency and the straighter elbows gave the loom butterfliers higher finish phase raiio between propulsive forces and resultant forces. Table 2: Differences Between Sprint and Distance Buttert1iers Variables Sprint Distance Hip Heighr (m) Max Trunk Ang (deg) Finish Phase Elbow Ang (deg) Finish Phase Trunk Ang (deg) Recovery Trunk Ang (deg) Prop force! Result force -finish phase (o/c) p=0.040 p=0.04l p=0.007 p=o.ol8 p==0.044 p==0.020 Breaststroke: The correlation with shoulder depth and insweep propelling efficiency show that higher propelling efficiencies were found with the swimmers having the shallowest shoulder depth. This implies better stroking efficiencies for swimmers that were higher in the water during that insweep. This does not necessarily mean a higher trunk angle in the water. Previous analysis suggests that breaststrokers are able to stay higher in the water and still have trunk angles under 40 degrees by using a pull pattern that creates a forward lunging action with the trunk while 142

3 breathing. Although there was no significant correlations with the trunk angle, the group average trunk angle was 39.8 degrees. During the outsweep phase, the maximum elbow angle was degrees. Smaller outsweep elbow angles were correlated with higher outsweep effective forces. Also, smaller elbow angles (153.8 deg) during the outsweep was associated with higher outsweep efficiency (1.5%). These data suggest that the swimmers who receive propulsive forces on the outsweep do not straighten their elbows. Rather they use slightly bent elbows of approximately 160 degrees. They also seem to keep their elbows more bent during the entire outsweep. This bent elbow position may be allowing these swimmers to flex their wrists more on the outsweep and increase the efficiency of this phase. Group differences show that the shoulder and hips of loom breaststrokers (n=5) are significantly higher in the water than the 200m breaststrokers (n=6). Other trends in the group data show that the minimum elbow angle, occurring at the beginning of the recovery, for the loom breaststrokers was lower. This may indicate that the 100-m group achieved a more streamlined position on the recovery by concentrating on tucking the hands and forearms in toward the body and then recovering forward along a straighter line. The angle of the knee during leg recovery was higher for the 1 OOm group. They did not flex the knee to as great a degree as the distance group. This could have served to quicken the time of the leg recovery for the kick and increase stroke rate. Stroke rate was slightly faster for the loom group ( 1.2 sec/stroke vs. 1.4 sec/stroke) although this was not significantly different between the groups. Table 3: Differences Between Sprint and Distance Breaststroke Variables Sprint Distance Shoulder Depth (m) p=0.030 Hip Depth (m) p=0.020 Min Elbow Ang (deg) p=0.067 Min Knee Ang (deg) p=0.077 Backstroke: The maximum elbow angle during the upsweep (172.5 deg) had a negatively correlated with the propulsive force and the propelling efficiency of the stroke. A slightly bent elbow, less than 170 degrees was more efficient and produced more propulsive force. Body roll during the catch phase of the stroke was even more significant in backstroke than freestyle. The average body roll was 44.9 deg. The increased body roll may have allowed backstrokers to get a deeper catch in the water. The knee angle ranged from almost straight ( deg) to deg. This indicates that backstrokers, like sprint freestylers, take full advantage of increasing the kicking range of motion. I OOm backstrokers produced higher resultant and effective forces during the catch phase of the stroke by possibly grabbing water immediately with a different hand orientation. The angle of pitch during the catch phase was higher for the sprinters than the 200m backstrokers (48.8 vs deg) although this was not statistically significantly different. Table 4: Differences Between Sprint and Distance Backstroke Variable Sprint Distance Downsweep Elbow Ang (deg) Hand Velocity (m/s) Stroke Rate (sedstroke) Finish Phase Body Roll (deg) l p=0.025 p=0.057 p=0.083 p=

4 The shoulders were slightly higher out of the water for the sprint group although this did not mean more body roll with the 100-m group during the catch phases of the stroke. The stroke rate of the 100 meters was faster and possibly body roll had to be minimised in order to obtain the faster turnover rate. ACTIVE DRAG AND TECHNIQUE STUDIES Active drag and technique studies were performed on 24 male and 24 female member of the U.S. National and Junior National team as well as 1996 U.S. Olympic Trials Qualifiers. The active drag and the hydrodynamic coefficient of the swimmers while swimming at maximal velocity were determined by the velocity perturbation method (for method details, see Kolmogorov & Duplisheva, 1992). This method required subjects to perform two 30 meter trials at maximal effort. Active drag and the hydrodynamic coefficient (Co) were subsequently calculated. For technique analysis, swimmers were video taped by two 60 Hz cameras during the active drag test. One camera was placed in an underwater housing to record a front view of the swimmer. The second camera was positioned above water to record a side view of the swimmer. Both cameras taped the swimmer as he/she passed through the calibrated m of the pool (for method details, see Cappaert and Gordon, 1998a). This series of studies investigated areas of active drag based on the fluid drag force equation: F 0 = 1/2 p A Co v 2 (1) Studies relating active drag with velocity and its components, SL and SR revealed that active drag and velocity as well as active drag and SL are significantly related. However, when the active drag values were normalised for maximum swimming velocity (using the hydrodynamic coefficient, C 0 ) the relationship was not significant (Cappaert and Gordon, 1998b ). The results with C 0 and maximal swimming velocity and SL are consistent with the results of Hollander et al.( 1988). Measured frontal surface area A, seems to be influenced by the vertical displacement between the mid-shoulders and the mid-hips. The C 0 is more influenced by excessive arm and leg motions throughout the stroke (Cappaert and Gordon, l998c). REFERENCES I. Abdel-Aziz, Y. I. and Karara, H. M. (1971) Direct linear transformation: From comparator coordinates into object coordinates in close-range photogrammetry (ASP Symposium on Close-Range Photogrammetry). Falls Church, V A: American Society of Photogrammetry. 2. Arellano, R., Brown, P., Cappaert, J. and Nelson, R. C. (1994) Analysis of 50-, loo-, and 200-m freestyle swimmers at the 1992 Olympic Games. Journal of Applied Biomechanics, 10,! Cappaert, J. M., Pease, D. L., Troup, J. P (1995) Three-dimensional analysis of the men's loo meters freestyle during the 1992 Olympic Games. Journal of Applied Biomechanics, 11: Cappaert, J. M., Gordon, B. J. (l998a) Frontal surface area measurements in elite freestyle swimmers. Spans Engineering, in press. 5. Cappaert, J. M., Gordon, B. J. (l998b) The relationship between active drag and stroke length in freestyle swimming. Journal of Sports Sciences, in review. 6. Cappaert, J. M., Gordon, B. J. (1998c) Technique factors affecting the hydrodynamic coefficiem and frontal surface area in freestyle swimming. Journal of Biomechanics, in review. 7. Clarys, J. P. (1979) Human morphology and hydrodynamics. In Swimming Ill: Proceed- 144

5 ings of the Third International Symposium of Biomechanics in Swimming, (edited by J. Terauds and W. Bedingfield), pp Baltimore: University Park Press. 8. Clarys, J. P., Jiskoot, J., Rijken, H., and Brouwer, P. J. (1974) Total resistance in water and its relationship to body form. In Biomechanics IV (edited by R.C. Nelson and C.A. Morehouse), pp Baltimore: University Park Press. 9. Craig, A. B., and Pendergast, D. R. (1979) Relationships of stroke rate, distance per stroke and velocity in competitive swimming. Medicine and Science in Sport, 11, Craig, A. B., Skehan, P. L., Pawelczyk, J. A., and Boomer, W. L. (1985) Velocity, stroke rate, and distance per stroke during elite swimming competition. Medicine and Science in Sports and Exercise, 17, Hollander, A. P., Toussaint, H. M., De Groot, G., and Van Ingen Schenau, G. J. (1985) Active drag and swimming performance. New Zealand Journal of Sports Medicine, 13, Kennedy, P. K., Brown, P. L., Chengalur, S. N., and Nelson, R. C. (1990) Analysis of male and female Olympic Swimmers in the loo-meter events. International Journal of Sport Biomechanics, 6, Kolmogorov, S. V., Rumyantseva, 0. A., Gordon, B. 1., and Cappaert, J. M. (1997) Hydrodynamic characteristics of competitive swimmers of different genders and performance levels. Journal of Applied Biomechanics, 13,