Exercise taxes the various physiological systems of the body beyond their normal resting level of performance. Two of the most important purposes of training are to increase the rate of energy release during races and to delay fatigue.
Training the ATP-CP System
The energy for muscular contraction comes from ATP, which is the only chemical stored in muscles that can provide that energy. The primary purpose for all other phases of metabolism is to replace the energy in ATP so that contraction can continue. The ATP-CP system can provide energy for muscular contraction more rapidly than any other phase of metabolism, but it can do so for only 4 to 6 seconds.
After ensuring that technique is good, an athlete can improve maximum speed most significantly by 1) increasing the size and strength of the fibres in particular muscle groups so that the fibres can generate more power and 2) improving the rate and pattern of fibre recruitment by the central nervous system so they can be brought into play quickly and in the proper sequence for a particular skill without involving unneeded fibres.
Increasing the quantities of ATP and CP stored in muscle fibres represents another possible training effect that might increase athletic speed. Increases could extend the maximum rate of ATP recycling for an additional few seconds, which in turn may allow athletes to maintain their sprint speed slightly longer. Training has been reported to increase the storage of both ATP and CP by 18% and 35%, respectively (MacDougall et al. 1977).
Besides training, athletes have tried to improve the creatine phosphate supply in their muscles by supplementing their diets with creatine. This procedure has been reported to increase the free creatine in muscle fibres by about the same amount as training does, 20% (Hultman et al. 1996). The results have been equivocal about whether creatine loading can improve the performances of sprint athletes. Some have reported improved performances, but others have not.
Training Anaerobic Metabolism
The anaerobic breakdown of muscle glycogen supplies approximately half the energy for ATP-CP recycling during the first 5 to 6 seconds of a race. Thereafter, the proportion will increase considerably until anaerobic metabolism will be supplying by far the greatest amount of energy for sprinting within 10 to 15 seconds after the race begins.
Because anaerobic glycolysis involves 11 steps, the power available for speed will decline somewhat after the first few seconds of a race. An athlete’s ability to generate muscular power will decrease by approximately 10% after the first 4 to 6 seconds of effort when the muscle’s creatine phosphate supply is partially depleted and anaerobic glycolysis becomes the primary source of energy for ATP recycling. For this reason the rate of anaerobic glycolysis has a greater influence than the ATP-CP system does on how fast athletes can perform in sprint events.
Training appears to increase both the quantity and activity of many of the enzymes of anaerobic glycolysis. Sprints are particularly good for bringing about these increases, whereas endurance training tends to suppress their quantity and rate of activity. In general, training-induced increases of anaerobic enzymes have not been as great as those reported for the enzymes of aerobic metabolism. Most of the increases in anaerobic enzymes have ranged between 2% and 22%.
The major obstacle to increasing the quantities of anaerobic enzymes is the endurance training that athletes must engage in. Endurance training suppresses the activity of most anaerobic enzymes.
The dilemma most athletes face is that they must improve both endurance and speed to improve their performance in many events. But athletes typically do so much endurance training that the best they can do is maintain their innate ability to recycle ATP rapidly through anaerobic metabolism. More often, their rates of muscle contraction and anaerobic metabolism decline during most of the season because of the large volume of endurance training they perform. Lucky athletes manage to regain their speed during the taper. When the loss of speed has been extreme, however, the taper may not be long enough and speed will not return to inherited levels until several weeks after endurance training has been terminated or considerably curtailed.
Training to Delay Acidosis – Training Aerobic Metabolism
The desired training effect is to reduce the rate and severity of acidosis during races. That effect is the result of two factors – reducing the rate of lactic acid production within muscles and increasing the rate of lactate removal from them.
1. Many training adaptations reduce the rate of lactic acid production:
- Increased diffusion of oxygen from the lungs, which results from improved volume of air exchanged each minute and an increase in the capillaries around the alveoli of the lungs
- An increase in blood volume that permits blood to circulate through the body faster
- An increase in red blood cells so that the blood can carry more oxygen
- An increase in cardiac output so that the blood makes a quicker round-trip from the lungs to the muscles
- An increase in capillaries around the muscles so that more oxygen can be made available for diffusion
- Improved blood shunting so that more of the blood supply and its oxygen can reach the working muscles during each minute of exercise
- An increase in myoglobin so that more oxygen can be transported to the mitochondria of the muscles each minute
- An increase in the size and number of mitochondria in muscles so that the receptacles for aerobic metabolism will be larger and more numerous
- An increase in the activity of the aerobic enzymes so that aerobic metabolism can proceed at a faster rate
- An increase in the rate of the glucose-alanine shuttle so that more pyruvate can be removed before it combines with hydrogen ions to form lactic acid
2. Several training adaptations increase the late of lactate removal from working muscle fibres:
- Increased activity of the lactate transporter in working muscle fibres and receptor fibres
- Increased blood volume and improved cardiac output so that more blood can make the trip to and from working muscle fibres in a shorter time, thus transferring more lactate from the working muscle fibres to the blood and then to areas where it is removed during each minute of exercise
- An increase in capillaries around the working and receptor muscle fibres so that more lactate can be transferred into and out of the blood during each minute of exercise
- Improved blood shunting so that more lactate can be carried away from the working muscle fibres with each minute of exercise
Training Effects that improve the Ability to Train
- An increase in the amount of glycogen stored in working muscle fibres so that athletes can train more intensely more often.
- An increase in the rate of fat metabolism so that the muscles use more of this compound for energy and less glycogen, leaving more glycogen for a greater number of intense training sessions.