Michael J. Buys and Dr. Allen Parcel, Physical Education

Introduction

An important part of maximizing performance in competitive swimming is a progressive reduction of training before championship competitions called “tapering” (Johns et al. 1992). Because the high volume and intensity of training used during in-season swim workouts may adversely affect muscle strength and performance (Hakkinen et al. 1989; Stone et al. 1984), a short-term reduction in training is used to enhance performance. Tapering involves a significant reduction of duration, intensity and frequency of training over a period of 1-4 weeks. Experimental evidence supports the effects of taper on physiological improvements such as swim power (Costill et al. 1985; Johns et al. 1992; Hooper et al. 1998), performance (Houmard et al. 1994; Shepley et al. 1992), and distance per stroke (Johns et al. 1992). Such benefits have been attributed to changes in psychometric factors such as mood states, stress, and rating of perceived exertion (Hooper et al. 1998; Pyke et al. 1988), rest from over training (Banister et al. 1998), and changes in musculature such as hypertrophy of muscle fibers and increase in contractile velocity (Trappe et al. 2000). Muscle strength increases during training due to a number of factors. Hypertrophy of the muscle fibers, increased motor unit recruitment and decreased contractile inhibition all contribute to increased muscle strength.

By using Electromyography (EMG) measurements during a muscle contraction, it is possible to determine a change in size and number of motor units being recruited by the size of the EMG signal. It is also possible to determine the predominant muscle type being recruited by using median frequency data from the EMG reading. When this EMG data is compared with muscle force measurements, correlations can be made between changes in neuromuscular characteristics and muscle force.

The hypothesis of this study is that, after a 28-day taper, the subjects will experience an improvement in performance times, an increase in muscle force, an increase in motor unit recruitment (larger EMG signal), and a shift towards type IIa muscle fiber recruitment (increase in median frequency (MF) value). The purpose of this study is to look at the possibility of increased muscle strength due to neural adaptations during taper.

Methods

Highly trained collegiate male swimmers from Brigham Young University and six nonswimmers were recruited to participate in this investigation. Thirteen days before the start of the taper, and two days after the championship meet (a total of 36 days between measurements), all subjects completed a swim performance measurement and an isometric strength measurement performed on an isometric Dynamometer (Biodex). During all strength measurements, neural activity of the right posterior deltoid and right latissimus dorsi muscles was monitored by surface electrode EMG. The EMG was measured using bipolar, disc surface electrodes on the muscle bellies of the posterior deltoid and the pectoralis major muscles.

Results

On average, swimming times improved by 4.4 ± 2.6% (P<0.05) at the championship meets versus the pre taper meets. Regardless of their events, all swimmers improved their times (P<0.05). Individual improvements ranged from 2.8-12.9%.

In the isometric force test, there was no significant change of maximal force production or rate of force development in either the swim or control groups (P>0.05).

Maximum EMG and median frequency readings for the ramp and ballistic test also showed no significant difference in either group of subjects.

Discussion

In conclusion, the results from this study indicate that after a 21-day taper, swimming performance improved, but no change was detected during an isometric contraction in maximal muscle force, rate of force development, maximal EMG or median frequency for the selected muscles and arm position. In order to more effectively use isometric contractions to measure changes in force and EMG readings in tapered swimmers, future studies may want to choose major muscle movers used during pull-through and test each muscle according to its movement specificity.

References

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