Swim City

Back to Basics: Improving Swimming Fitness – by David Pyne

INTRODUCTION

The way to achieve success in swimming is obviously to swim faster over a given distance. The various swimming strokes (freestyle, butterfly, backstroke, breaststroke) are quite different in terms of the patterns of muscle recruitment, the force and power produced, and the energy required for a given swimming speed.

However, success in all of the different swimming events depends on the ability to develop power and reduce the resistance or drag. This article examines some of the major factors that contribute to a swimmer’s ability to produce power and speed.

BASIC DEFINITIONS

Swimming speed is determined by how effectively the swimmer can generate and sustain power and overcome resistance and drag.

Power depends on the rate of energy expenditure that can be sustained throughout a swim and the efficiency with which that energy is converted into mechanical power. The intensity and distance of a swim will determine the relative contributions of anaerobic and aerobic energy sources.

Aerobic power, anaerobic threshold and anaerobic power relate to the underlying physiological power and capacities of the energy systems responsible for muscular contraction.

Mechanical and metabolic efficiency is dependent on the efficiency with which muscles convert the energy stored in carbohydrate and fat into useful mechanical work.

Neuromuscular skill required to swim the different strokes is optimised when swimmer has learned to recruit only those motor units required to produce maximal power output.

Drag in swimming is derived from three main sources: form drag, wave drag and surface drag.

ENERGY SUPPLY FOR COMPETITIVE SWIMMING EVENTS

The ability to swim a fast 50 or 100m depends on:

the ability to sustain energy production by the muscles, and
the ability to apply that muscular energy efficiently to overcome resistance or drag.
Power is the ability to apply force over a given distance (or time) quickly and can be considered as the product of strength and speed. Unfortunately, absolute maximal muscular power can be sustained for only a fraction of a second.

When energy requirements are extremely high as in the 50 and 100m swimming events most of the muscular energy is supplied by two fuels, phosphocreatine (PCr) and glycogen, stored in small amounts within the muscles.

Because these two fuels can be broken down for energy without the use of oxygen, this process is known as anaerobic (without air) energy production. In contrast, aerobic energy production occurs at a much slower rate as fats and carbohydrates are broken down (metabolised) with the aid of oxygen to sustain muscle contraction.

Explosive training drills like dive starts, turns 5m in – 5m out, and 20m maximal efforts activities rely largely on the anaerobic breakdown of PCr and muscle glycogen for energy. Both PCr degradation and anaerobic glycolysis are activated instantaneously at the onset of high-intensity exercise.

Measurements of PCr and lactate in muscle biopsies taken after sprint efforts confirm the rapid breakdown of PCr and accumulation of lactate. At the onset of less intense exercise, PCr degradation and anaerobic glycolysis occurs at a slower rate because the mismatch between energy demand and aerobic supply is reduced during moderate intensity training.

The rate of anaerobic energy provision is critical to the sprint events. Elite strength and power athletes (e.g. weightlifters and powerlifters) produce power outputs that are 10-20 times greater than that required to elicit the maximal rate of aerobic energy supply (VO2max).

However, power outputs at these levels can be maintained for only a fraction of a second. 100m track sprinters can achieve power outputs that are 3-5 times VO2max, but obviously they can only sustain this level for a few seconds. Power output over 30 seconds (i.e. 50m events in each of the four swimming strokes) can be sustained at almost twice the power output at VO2max. Estimates of the rates of anaerobic provision of energy are calculated in two different ways.

Firstly, changes in the concentration of high energy compounds in muscles following sprint exercise (primarily cycling studies) clearly indicate the extent of anaerobic energy production.

Secondly, measuring the so-called MAOD (maximal accumulated oxygen deficit) is a popular and non-invasive method. Oxygen uptake is measured in the same manner as used for the determination of the maximal oxygen uptake (VO2max). In swimming, this practice is restricted to the flume (swimming treadmill), and at present there are no suitable facilities available in Australia.

The rate of anaerobic energy provision decreases as the distance swum increases. To determine the changes in energy supply with high intensity exercise, we must look to some basic studies conducted in the laboratory using cycle ergometry. In maximal effort exercise of about 60 seconds duration (equivalent to a maximal 100 m swim), the average rate that from anaerobic sources is provided is about the same as that from maximal aerobic metabolism.

In other words, the energy supply to these types of events (400m running, 1000m cycling, 100m swimming) is approximately 50% aerobic and 50% anaerobic. In the last few years, some sports scientists have revised upwards the aerobic contribution to these types of high intensity events.

Older textbooks usually state the aerobic contribution to the 100m swimming event to be in the order of 20-30%. While anaerobic contribution is substantial for the 100m it is clear that energy derived from PCr sources becomes depleted between 10 and 30 seconds of maximal exercise. Beyond this distance, it appears that only glycolysis can provide for further anaerobic energy production.

Most swimming coaches employ various combinations of interval training when preparing swimmers for competition. As discussed earlier, most of the energy for single bouts of short duration high-intensity exercise is derived from anaerobic sources.

However, the ability to recover during rest periods, a function of aerobic fitness, is essential for success in this type of activity. While a number of studies have examined the energy requirements of single bouts of exercise, few have examined the requirements of multiple bouts of exercise during standard interval training sessions. With repeated sprinting, energy production from anaerobic glycolysis is progressively more difficult to achieve.

Presumably, the accumulation of lactic acid in the active muscles plays a major role in the inability to continue producing energy by anaerobic glycolysis. Therefore, after repeated high intensity intervals, PCr is the only potential anaerobic energy source that can be relied upon. It is essential that adequate recovery be provided between repeat efforts to allow PCr stores to be adequately replenished in the muscles.

The maximal rate of aerobic energy production (VO2max) can only be sustained for a few minutes or about the duration of the 400m event. In the 800 and 1500 m, the better swimmer is likely to have a higher speed at VO2max and/or who can sustain aerobic energy production at a higher proportion of its maximal rate (the so-called anaerobic threshold).

Another way of saying this is that the swimmer who can produce energy aerobically at a high rate without accumulating a large amount of lactic acid in the blood is likely to be better off. The swimmer who produces a large amount of lactic acid at a given speed may not be able to continue to perform at that pace for as long as the swimmer who does not accumulate as much lactic acid. A swimmer who has the ability to exercise at a high intensity before blood lactic acid begins to accumulate is said to have a high lactate or anaerobic threshold.

The other factor to consider is the degree of muscle buffering capacity. The body has developed a number of buffering systems (e.g. the bicarbonate buffering system) to counter the build-up of lactate in the muscle and bloodstream. The capacity of these systems is improved by a combination of aerobic and anaerobic training.

Carbohydrate and water are critical for sustaining endurance performance. Muscles obviously cannot produce energy without fuels derived from nutrients obtained in the diet. It is well established that dietary carbohydrate consumption before, during, and after exercise can make an important contribution to training and competition performance.

Carbohydrate consumption acts primarily by increasing the body’s stores of glycogen in muscles and in the liver before exercise and by increasing the availability of glucose for use by the muscles during exercise. Fluid intake during prolonged training sessions limits the negative effects of dehydration on performance. When dehydration reduces blood volume, oxygen delivery to the muscles by the blood can be compromised, and this reduces the ability of the muscles to produce energy aerobically.

Dehydration involving as little as a 2-3% decrease in body weight (1.5 to 2.0kg for an average 65kg swimmer) also compromises the ability of the body to regulate its temperature. This situation may adversely affect the swimmer’s ability to sustain a high rate of energy production. Sports drinks containing carbohydrate-electrolyte are suggested as the most effective way to supply both carbohydrate and fluid.

In summary, the energy required for explosive starts and 25m efforts is largely derived from PCr sources; for the 100m events, energy supply is derived evenly from anaerobic and aerobic sources (with PCr sources declining and anaerobic glycolysis increasing); while for middle-distance and distance events there is increasing reliance on aerobic energy sources.

SEQUENCING TRAINING : AEROBIC TO ANAEROBIC

One of the goals of training is to improve the swimmer’s ability to sustain high rates of energy production. At the onset of a training season, it is generally accepted that a swimmer should establish a solid aerobic training foundation by training primarily at relatively low to moderate intensities.

Aerobic work will help develop a greater blood volume, an improved ability of the heart to pump blood, and better capillarisation in muscles. These cardiovascular adaptations facilitate improved delivery of oxygen to the muscles and an enhanced ability of the muscles to sustain high rates of aerobic energy production.

Metabolic adaptations with aerobic training are likely to enhance the ability of the muscles to utilise fat for energy and to spare muscle glycogen, resulting in less accumulation of lactic acid in the blood at a given pace or intensity. This means that the swimmer’s lactate threshold will be increased and aerobic energy production can be sustained at a greater rate than was possible before training.

Despite the emphasis on aerobic training, some short speed work should be included to maintain anaerobic capacities and neuromuscular adaptations (muscle memory) right through the season.

For the bulk of the swimmer’s speed or anaerobic training, the specific muscle groups involved in the competitive event should be overloaded, and the swimmer should train at a pace or intensity similar to that used in competition (the so-called race pace training).

This type of training can lead to improved stores of glycogen and PCr in muscle so that greater energy reserves will be present before competition begins. During high intensity, anaerobic interval training, the duration of recovery intervals should be long enough to allow the muscles to replenish most of the PCr depleted in the previous effort.

With maximal effort dive start repeats over 50 to 100m the rest or cycle time should be at least three minutes. If these recovery intervals are too brief, the supply of PCr in the exercising muscles will be inadequate. The swimmer will be forced to exercise at a lower intensity (slower pace) and inappropriate muscle groups may be recruited to finish off demanding training sets.

If this occurs, the swimmer will be learning incorrect movement patterns during training that may adversely affect competitive performance.

REDUCING DRAG

Drag is a special form of resistance in which the friction of water around a swimmer retards forward motion. Swimmers move at relatively lower velocities than runners because they encounter large drag forces from the water as well as from the turbulence at the surface of the water.

There are three major sources of active drag: form drag, wave drag and surface drag. The magnitude of drag encountered by a swimmer is a function of body mass and the shape of the body (frontal surface area). Swimming speed is a function of power production relative to the drag encountered at competitive speeds.

Surface drag can be reduced by shaving down, wearing a swim cap and wearing body tight swim wear. In simple terms, swimming speed can be increased either by improving power output, reducing drag or a combination of the two.

The ability to teach and refine the skills and techniques required for swimming is fundamental for successful coaching. Through experience most coaches (and eventually swimmers) learn intuitively the importance of good technique.

In swimming, effective techniques and body positions have been adopted in order to reduce resistance and drag in water. The body position in each of the four swimming strokes must be maintained in a streamlined position: horizontal with minimal disruption to the flow of water around the body. A streamlined dive start entry and a streamlined position coming off the walls during each of the turns is critical.

Competitive analysis undertaken by the Australian Institute of Sport (and other groups) has shown that start and turn times are just as important as ?free swimming? times. In the May-June 1997 edition of Australian Swim Coach, Dr Bruce Mason reported results from the 1996 Atlanta Olympic Games which showed that several Australian swimmers were the fastest swimmers between the turns, but lost time in the turns or at the start or finish.

Clearly, skills and techniques are critical for optimal performance.

Another way to reduce resistance and drag is to reduce body mass (weight). While this is obviously a big factor in sports such as distance running, the circumstances are different for swimmers. Weight reduction is not as important in swimming because the body mass is subject to buoyancy by being immersed in water.

Differences in swimmers’ individual body builds could play a significant role in determining whether or not weight loss improves swim performance. The physiological effects of reducing body mass also need to be considered.

Some swimmers feel weaker and more prone to fatigue, illness and injury when their body weight falls below a critical threshold. Measurement of body fat and weight in parallel is necessary to distinguish between lean body mass and fat mass.

MECHANICAL EFFICIENCY

Mechanical efficiency is defined as the ratio of the mechanical power output to the total energy expended to produce that power.

Two of the principal factors that determine the mechanical efficiency of an swimmer in a sport event are: i) the efficiency with which the active muscles convert the chemical energy stored in carbohydrate and fat to the mechanical energy required to shorten the contractile elements in the muscles, and ii) the neuromuscular skill with which the swimmer performs the event.

Muscle efficiency has two components. The first component is the efficiency that chemical energy from carbohydrate and fat is converted to adenosine triphosphate (ATP), the only form of chemical energy that can power muscle contraction. The process of ATP synthesis is about 40% efficient, i.e., 40% of the metabolic energy in carbohydrate and fat is transferred into ATP synthesis, whereas 60% of the energy is lost as heat.

The second component, the efficiency with which the energy released during ATP hydrolysis is converted to muscle fibre shortening, is more variable than that converting stored fuels to ATP.

There is little that the coach and swimmer can do to improve muscle efficiency because the chemical efficiency of converting fuels to ATP and the proportion of slow-twitch fibres involved in various movements are largely determined by heredity.

However, it is possible that months or years of training may enhance recruitment of the more efficient slow-twitch muscle fibres and fewer of the less efficient fast-twitch fibres

IMPROVING SWIMMING EFFICIENCY

No matter how efficiently a swimmer transforms chemical energy into mechanical energy, the overall mechanical efficiency will be lower if the swimmer has poor technique. Contrast the relative efficiency of novice and elite swimmers.

The novice may produce a great deal of power, but because they are relatively unskilful, the power output is misdirected with lots of thrashing about but slow forward velocity.

The elite swimmer, on the other hand, has learned to swim rapidly and gracefully, using only those muscle fibres required to execute the stroke effectively. Neuromuscular skill obviously plays a great role in determining the mechanical efficiency in swimming.

The swimmer should always consider the advice of their coach who can explain how movement patterns should be altered to become more skilful. Often the coach can rely upon personal experience and observations to make critical improvements in a swimmer’s technique.

Video analysis of the swimmer’s performance can provide clues about changes in movement patterns that can be made to improve efficiency. The assistance of a biomechanist or a coach well-educated in biomechanics could be important in this phase of the swimmer’s preparation. The swimmer must repeat the appropriate movement patterns in a skilful manner many thousands of times during practice so the nervous system learns to perform the movement correctly every time.

There is no substitute for good technique.

SUMMARY

In physical terms, the fastest swimmer sustains the greatest power output to overcome resistance or drag.

It may not be sufficient to simply have the ability to produce great power. The successful swimmer must be able to sustain power output in an efficient and skilful manner for the entire race distance.

During maximal intensity sprint swimming (up to 50m), the anaerobic breakdown of phosphocreatine and glycogen in muscles provides energy at rates many times greater than can be supplied by the aerobic breakdown of carbohydrate and fat. This high rate of anaerobic energy production cannot be sustained for more than about 20 seconds.

In the 800 and 1500 m events the swimmer who has a high lactate threshold [produces a large amount of energy aerobically without a major accumulation of lactic acid in the blood] will be better able to sustain a higher rate of energy expenditure than a swimmer with a lower lactate threshold.

A high level of mechanical efficiency [the ratio of the mechanical power output to the total energy expended to produce that power] is vital if a swimmer is to make the most of their sustainable rate of energy expenditure. Mechanical efficiency depends upon the extent to which the swimmer can recruit slow-twitch muscle fibres, which are more efficient at converting chemical energy into muscle contraction than are fast-twitch fibres.

Neuromuscular skill is critical to mechanical efficiency because the more skilful swimmer will activate only those muscle fibres required to produce the appropriate movements. Uncontrolled muscle contractions require more energy expenditure and may not contribute effectively to swimming speed.