AN INVESTIGATION OF ADDING A STEP-UP APPROACH
TO A SWIMMING RELAY START

S.P. McLean (1), K.D. Beckett (2), P.F. Vint (3), and E. Kendrick (1)

(1) Department of Health and Human Performance, Iowa State University, Ames, IA 50011
(2) Department of Physical Education and Athletics, The College of Wooster, Wooster, OH 44691
(3) Department of Exercise Science and Physical Education, Arizona State University, Tempe, AZ 85287

Presented at the 20th Annual Meeting of the American Society of Biomechanics
Atlanta, Georgia. October 17-19, 1996

INTRODUCTION

The addition of an approach to a vertical jump has been shown to increase the height of the jump. Because of this, a trend in competitive swimming has developed in which a single or double-step approach is added to the traditional relay start. This is thought to increase the swimmer's forward velocity prior to beginning the traditional starting movement using only an arm swing. Thus total momentum will increase such that the swimmer will achieve a higher forward takeoff velocity. The effectiveness of this technique remains in question as evidenced by the continued use of the traditional relay start in national and international competition. This may be in part due to the lack of systematic, scientific study of this technique. This study was undertaken with the intent of comparing the ability of the traditional relay start and the new step-up approach to achieve forward takeoff velocity.

REVIEW AND THEORY

The movements performed in a swimming start are closely related to those of a vertical jump with the difference being the direction of motion. A flat start in swimming may be likened to a squat jump since the swimmer moves only forward during the start. A relay start more closely resembles a counter-movement jump. In addition a relay start provides a swimmer with an advantage because forward movement of the body begins prior to the finish of the incoming swimmer. Maglischo (1993) suggests that this may provide the swimmer with an advantage of 0.6 to 1.0 s over a flat start.

It is reasonable to assume that the performance of the start can be enhanced using the principles applicable to vertical jumping given the similarities between these activities. Kayambashi (1977) and Enoka (1971) found that the inclusion of an approach to a vertical jump improved performance. Therefore, the addition of a step-up approach to a swimming start should enable the swimmer to increase forward takeoff velocity.

The purpose of this study was to compare the performance of a traditional arm swing (AS) relay start to that of a relay start incorporating a single-step (SS) and double-step (DS) approach. The hypotheses proposed for this study were: 1) horizontal takeoff velocity will be highest for the DS start, 2nd highest for the SS start, and lowest for the AS start, and 2) the arms will contribute a greater proportion of forward lift to the AS start than either step-up start.

METHODS

Ten collegiate swimmers (five males, five females) provided informed consent to participate in this study. All subjects had received prior instruction and practice in the performance of the three relay starting techniques. Each subject completed two maximal effort relay starts using each technique. A flat start condition was included as a baseline.

Two-dimensional video data were collected at 60 Hz in the sagittal plane. One trial from each condition was chosen for analysis. Twenty-one points were used to define a 14 segment model of the body. Whole body CM location during the trial was computed using segmental masses and center of mass locations obtained from the mean data of De Leva (in press). Data were smoothed using a quintic spline algorithm.

The CM velocity at takeoff was computed using a finite difference differentiation of the smoothed position data. Forward lift was defined as the change in horizontal relative momentum between the initiation of forward movement and the instant of takeoff from the starting block. Forward lift was computed using the method of Ae and Shibukawa (1980). The contributions of the head and trunk, arms, and legs to forward lift were defined as the proportion of whole body relative momentum during the propulsion phase. Net forward lift was defined as the difference in relative momentum at the instant of takeoff and the start of the propulsive phase. Peak forward lift was defined as the maximum difference in relative momentum between the instant of takeoff and the instant of peak forward velocity. Statistical comparisons were made using matched-pairs t-tests. To control type II errors the alpha level was adjusted using the Bonferroni procedure to 0.004.

RESULTS

The mean horizontal velocity of the center of mass at takeoff for the AS start was 0.3 m/s slower than both the SS and DS starts (see Table 1). These differences were not statistically different but were characterized by moderate effect sizes (ES=0.53 and 0.54, respectively for SS and DS).

The net forward lift values for the legs, were greater than 100% at the instant of takeoff for each starting condition (see Table 1). No significant differences between conditions were found. With the exception of the SS start the head and trunk, and arms had negative contributions to net forward lift. This difference was characterized by moderate effect sizes (0.4-0.6).

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Start Vx Ptrunk Parms Plegs (m/s) (%) (%) (%)
flat 3.5 -2.3 -0.2 102.7 (0.6) (6.8) (1.1) (7.0)
arm swing 3.4- 2.2 -1.0 103.4 (0.4) (6.0) (1.7) (7.1)
single step 3.7 0.5 -0.7 100.4 (0.5) (5.4) (1.8) (4.8)
double step 3.7 -1.2 -1.5 102.8 (0.5) (4.1) (1.2) (3.7)
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Table 1 - Comparison of mean horizontal CM velocity and percent of forward lift. (SD)

Investigation of the change in forward lift of the arms throughout the propulsive phase of the start indicated that the peak forward lift was reduced only for the arms in flat starts (see Table 2 and Figure 1).

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Start Arms Time of Peak (N s) (%)
flat 13.6 63.3 (2.8) (16.9)
arm swing 18.9 69.1 (4.8) (5.7)
single step 19.0 71.3 (5.3) (8.0)
double step 19.1 72.6 (4.8) (5.9)
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Table 2 - Peak forward lift of the arm and time of peak during the propulsive phase. (SD)

Figure 1 - Representative graph of forward lift throughout the propulsive phase of a start.

DISCUSSION

The data supported hypothesis #1. The horizontal velocity of takeoff was increased in the starts which incorporated the use of a step-up approach. However, the overwhelming contribution to net forward lift from the legs did not support hypothesis #2. All starts received similar contributions to net forward lift from the arms. It was believed that the inclusion of a step-up approach would increase the contribution to net forward lift from the trunk and head to compensate for an inability to fully use the arm swing as in the traditional relay start. The lack of difference in the percent of net forward lift from each segment did not support this (see Table 1). However, a limitation of the relative momentum approach is that it represents a finite difference in momentum values. It does not provide an assessment of the changes in momentum throughout the movement.

An alternative to using net forward lift was considered. This technique examined the momentum relative to the initial point as it changed throughout the propulsive phase. These data for the arms indicated that they generated a higher peak forward lift contribution in the relay starts than in the flat start.

The lack of an arm swing in the flat start was responsible for its inability to match the relay starts in peak forward lift contribution. However, assuming that the arm swing was not compromised during the step-up approach, the peak forward lift contribution should have been greater for the arms because the body was moving forward during either step-up approach. This forward velocity of the body should have added to the forward velocity of the arm center of mass caused by its radial motion. This would have increased the resultant velocity of the arm and thus increased its forward lift contribution. The similar peak values for the arm forward lift (see Table 2) in each relay start suggested that the arm swing was compromised when using a step-up approach.

The incorporation of a step-up approach in a swimming relay start resulted in a greater forward takeoff velocity. This suggested that it had advantages over the traditional arm swing relay start. The lack of increase in the contribution to forward lift from the arms when using a step-up approach suggested that future development of this technique should focus on an enhanced arm swing.

REFERENCES

Ae, M., & Shibukawa, K. (1980). Japanese J. Phys. Ed.

De Leva, P. (in press). J. Biomechanics

Enoka, R.M. (1971). New Zealand J. Health, Phys. Ed.and Rec.

Kayambashi, K. (1977). Unpublished Masters Thesis, Western Illinois University.

Maglischo, E.W. (1993). Swimming Faster.