To maximize its beneficial effect, any training program must develop the specific physiological capabilities required to perform a given sport or activity (see Chapter 2). The most important physiological capability to be enhanced is the ability to supply energy (adenosine triphosphate [ATP] and the substrate phosphocreatine [PC]) to working muscles. ATP can be supplied in any of following three ways to the muscles:

As illustrated in Table 6A.1, the capacity and the rate at which energy (ATP) can be supplied by these three systems in the body differ. The rate of supply can be referred to as “power.” The predominant energy source will be a function of the total amount and rate of energy demanded by that exercise (see Table 6A.2). When a training/conditioning program is constructed, such a regimen logically should specifically increase the capacity of the energy system used most often in that particular sport.

Factors to consider for achieving maximal benefits from a training program include the following:

Four major principles should be applied to any training/conditioning program:

Necessary steps in the construction of a conditioning program should include the following:

For an in-depth justification of the recommendations given here, please refer to the American College of Sports Medicine (ACSM) statement on quality and quantity of exercise (Appendix 5A). As mentioned earlier, the four major training components of conditioning are frequency, intensity, duration, and mode of activity.

Unique physiological characteristics of the young athlete include the following:

A summary of pertinent questions that might be asked of a physician about prepubescent training regimens include the following:

It has long been suspected that the ultimate limit for physiological performance is set by genetic makeup. The contribution of genetic potential to the adaptation to conditioning is major. Heredity has been shown to account for anywhere between 81% and 93% of the observed differences in cardiorespiratory endurance. Researchers who have studied the phenomenon of puberty state that certain yet-to-be-known organic adaptations involving endocrine functions must be present for puberty to occur. The trigger hypothesis (see Figure 6B.3) represents a parallel assumption that for organic adaptations for training and conditioning to occur, certain necessary conditions must precede those adaptations. An increase in lean to fat body ratio, maturation of the neuromuscular system, and increase in the levels of endocrine function must precede any significant training effect in children (17).

Both androgen and growth hormone are thought to play a part in the development of functional capacity in the pubescent individual. Androgen levels determine muscular response to resistance exercise. That response is minimal in a prepubertal youngster (18). Should a 9-year-old boy weight train? The risk (injury)–benefit (minimal muscle growth) ratio would say, “No.” Because of its many functions throughout the body, growth hormone is believed to be the prime agent working in the presence of physical conditioning to induce organic adaptations. Prepubertal athletes and nonathletes differ little in their metabolic adaptation processes, yet they can be remarkably different in athletic performance. It appears that athletic performance in this age group is more dependent upon the level of skill development than on physiological conditioning. This principle should guide the practitioner in advising prepubertal athletes on constructing an athletic training program. Additionally, the primary care physician should be well versed in the clinical use of physical maturity staging to allow for accurate assessment of the stage of puberty before formulating any exercise program (see Chapter 4, Figure 4.3).

Postpubertal children require physiological conditioning along with skill training for optimal athletic performance. There does not appear to be a definitive answer about whether conditioned prepubertal children will demonstrate greater physiological changes after puberty, but there is evidence to suggest that prepubertal conditioning may prime the body to accept changes occurring in the postpubertal individual because of training. Any postpubertal individual follows predictable adult patterns concerning exercise-induced adaptations from training and conditioning.

When working with a postpubertal individual, the concept of initial level of fitness at the beginning of an exercise program is important. An individual who starts at a low level of functioning should have room for considerable improvement. For many children who are beginning their first serious exercise training, the previous consideration is important. Aerobic fitness improvements of 5% to 25% can be expected from systematic training by postpubertal individuals. In strength training, it is not unusual to see 100% to 200% improvement during the adolescent years. Physiological adaptations to exercise in the postpubescent period may be dependent upon initial levels of strength and endurance, but they can be demonstrated within 1 to 2 weeks after starting a conditioning program if the intensity is sufficient. Optimal physical conditioning in the postpubescent individual also depends upon the frequency, intensity, and duration of exercise, just as it does with adults. Most changes seen in this group result from the intensity of the training overload. Wilmore (19) indicates
that the greater the relative training intensity, the greater the training adaptation. There probably is a “minimal” threshold intensity below which training effects will not occur, as well as a possible “ceiling” threshold above which there are no further gains in adaptation. Studies of the frequency of activity in the postpubertal individual have shown that training more than 3 to 4 days a week yields very little additional change in physiological function. It appears that rest between exercise sessions is an important component in producing biological adaptations in this age group. The duration of exercise to build endurance requires a minimum of 25 to 30 minutes and an approximate 300 kcal expenditure for adaptations to take place. Strength training workouts need not exceed 40 minutes at maximum intensity levels.

Habitual level of activity, not gender or age, is the primary determinant of an individual’s cardiovascular fitness. Male and female athletes who participate in the same sport are more similar in aerobic power (VO_2max) than athletes of the same sex in different sports. The elite male athlete has a higher VO_2max than the elite female athlete. The lower oxygen carrying capacity of a woman, a reflection of lower hemoglobin levels, is probably the major factor in this difference. Absolute levels of VO_2max usually are higher for men because males have a larger body mass than females and VO_2max is directly related to body size. This presents a problem for women only in the sports or activities in which both sexes must perform at the same absolute work rate.

One of the most important concepts in all descriptive research studies is the fact that female athletes can obtain high levels of cardiovascular fitness. They are physiologically capable of undergoing the physical stress of endurance sports and they do not, as many texts imply, reach their peak fitness levels at age 15 (20). Older female athletes generally possess cardiovascular fitness levels equivalent to those of sedentary women a decade younger, whereas older women trained specifically for endurance events, gain two decades or more in fitness levels. Women who were inactive during their early adult years but now are actively engaged in physical fitness programs show significant training effects, which may improve longevity and general fitness.

Gender per se is not the factor that must be considered when prescribing exercise for women. The female’s initial level of fitness, her previous exercise experience, and her level of knowledge and skill are more important. The younger female with no previous experience in sports who wants to be in a regular exercise program will require much more guidance than a woman with prior competitive experience. The basic principles of exercise prescription outlined in this chapter apply equally to men and women. It is likely, however, that there will be greater variation in the background and experience of women seeking advice regarding exercise.

The potential of female athletes to develop strength has been greatly underestimated. Women benefit from strength training and demonstrate improved athletic performance and prevention of injury. The female athlete can obtain approximately the same kind of increase in strength as men with only a fraction of the male athlete’s increase in bulk. Increased muscle mass in men gives the male athletes a strength advantage that most women are unlikely to overcome. The anabolic properties of testosterone account for the major difference in muscle size between the sexes. In general, the overall strength of women is approximately 67% that of men. Upper body strength of the female
athletes averages approximately 65% of the male athletes, whereas leg strength is almost identical when expressed relative to body mass. The major gender differences lie in the size of the muscle fiber. Although fiber area can be increased with strength training, men still maintain an advantage in fiber size because of biological differences between the sexes.

Female athletes should not be discouraged from developing the muscular strength to meet the demands of their sport. Development of upper and lower body strength should be a priority for most female athletes. Female athletes should be encouraged to strengthen their quadriceps and hamstring muscles to prevent knee injuries.