18 METABOLIC DEMANDS FOR SWIMMING

18 METABOLIC DEMANDS FOR SWIMMING S.W. TRAPPE Human Performance Laboratory, Ball State University, Muncie, IN USA Abstract The majority of swimming ...
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METABOLIC DEMANDS FOR SWIMMING S.W. TRAPPE Human Performance Laboratory, Ball State University, Muncie, IN USA

Abstract The majority of swimming events are less than 2 minutes in duration. During exercise bouts of this brief duration, anaerobic ATP production is the primary energy source for the active skeletal muscles. More importantly, the rate at which ATP is delivered also influences muscle contraction and in turn, swimming speed. Thus, it would appear that a large capacity for anaerobic energy production is beneficial for fast swimming. Information describing the anaerobic capacity reveals distinct differences between sprint and endurance trained athletes for both the capacity and the rate at which fuel is supplied to the contracting muscles during high-intensity exercise. This high glycolytic demand corresponds well with glycogen breakdown and glycolytic enzyme activities of the muscles when exercising at supramaximal intensities (>100% V(hmax). However, lactate alone appears to be a poor indicator of total anaerobic energy yield during high-intensity exercise. These data emphasize the importance of ananerobic energy release during swimming competition. Currently, the swimming community advocates volume overload training to produce optimal performances. Due to the high degree of muscle plasticity and physiological adaptability, coaches and athletes should be aware of the specific adaptations during this type of swimming training. Practical methods on the pool deck (a stopwatch) and proper nutritional guidelines can serve to gauge the effectiveness of their training plan on swimming speed. Keywords: Anaerobic Capacity, Glycogen, Lactate, Metabolism.

1.

Introduction

By most opinions, swimming is considered an endurance and power sport. This has made designing a swimming training program that will elicit the ideal metabolic adaptations for optimal swimming performance a challenging task. The intensity and volume of training generally employed during swimming practice stresses both the aerobic and anaerobic energy systems; however, anaerobic energy production is the major contributor during competition. This is further emphasized by the fact that more than 80% of competitive swimming events are less than 2 minutes in duration. Tnus, a large anaerobic capacity may be a prerequisite for fast swimming. This presentation will begin with a brief overview on

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muscular adaptations from swim training, followed by the importance ~f ru:aerobic ener~y contribution during high-intensity exercise. In closing, practical apphcatwns along with unsolved issues will be presented. 2.

Muscular Adaptations

Endurance training induces major alterations in skeletal muscle and has been examined quite extensively [cf. 2, 3]. Experience has shown that the endurance capacit;Y o~ an athle~e is usually attained within the first 6-8 weeks of training and further gams m aerobic endurance are minimal. The high volume nature of swimming training also lends itself to numerous endurance attributes in the skeletal muscle. Most notably, there is a significant increase in the size and density of mitochondria, the aerobic powerhouse of the muscle cell [4]. Oxidative enzymes, such as citrate synthase have also been shown to increase during the course of a swim season [5]. However, the degree to which glycolytic enzyme concentrations are altered with swimming training is debatable. This is related to the relatively high capacity of the glycolytic system in less-trained individuals, and may actually be compromised with mild endurance activity. The capillary vasculature within the muscle bed also increases dramatically following periods of high volume, high intensity training. This plays a paramount role in oxygen delivery to the tissues as well as the removal of carbon dioxide and the efflux of various metabolites from the muscle. In addition, blood volume increases with training [6], and when coupled with the increased capillary network, may allow for greater perfusion of the skeletal muscle during "all-out" swimming. Swimming training also induces muscle hypertrophy which is mediated through structural adaptations in the muscle fibers. However, the degree of muscle hypertrophy greatly depends upon the type of training stimulus provided to the muscle fibers. The increase in muscle fiber size has been shown to be more pronounced in the type II muscle fibers with exercise training [7, 8]. Furthermore, these alterations have been suggested to be primarily related to increases in actin and myosin filaments, resulting in a greater number and size of myofibrils [9]. The contractile and mechanical properties of skeletal muscle have been shown to change with swimming training. This was examined using single muscle fibers from the human deltoid muscle during periods of heavy swim training [10]. There was no change in the force-velocity relationship or peak tension (P0 ) in the different fiber types. However, a subsequent decrease in maximal shortening velocity (Vmax) of type II fibers was observed. These alterations may have a direct impact upon the ability of skeletal muscle to generate tension. More importantly, if the contractile network is compromised with endurance training, it may be responsible for subpar swimming performances. More research is needed in this area to determine how the contractile machinery responds to different training modalities.

3. Anaerobic Energy Yield From the previous discussion, it is apparent that swim training significantly enhances the endurance potential of the muscle. However, the competition needs of swimming require the muscle to perform at the highest sustainable work rate for the duration of the event. In doing this, the glycolytic component of the muscle cells are placed under severe stress to

Metabolic demands for swimming

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