When designing an exercise program for a child, it is not as simple as applying the same principles you would to designing an adult program. The same rules do not apply. The challenges may appear to be the same, but they are very different. At the same time, you cannot apply the same fitness assessments to a child that you would give an adult. You need to assess the child in the light of the entire growth process. Knowing that the child and adult are very different, both mentally and physically, you need to take several factors into consideration when assessing clients and designing their exercise programs.
When designing a program for a child, you have to take where they are in the growth process into consideration. As a child continues to develop, the physiological processes in the body continue to develop as well. The muscular, skeletal and nervous systems continue to develop as well during the process. However, in an adult, these changes have already been made, and the body has reached its point of homeostasis, and has reached a point of “balance”.
Children have immature regulatory systems and temperature control mechanisms compared to an adult. Temperature control of the cardiovascular system is critical for the exercising participant and is more of a challenge for children and adolescents. Their surface area-to-mass ratio is larger than adults which allows for a greater heat exchange by convection and radiation. When designing an exercise program, the trainer needs to keep intensity in mind since children do not sweat as much as adults due to low surface area of the skin compared to adults. They can acclimate to the heat, but it takes them longer than adults. The tendency is to try to do too much too soon. It is recommended to postpone or recommend strenuous activity when heat and humidity are high and making sure plenty of fluids are ingested before, during and after exercise. Thirst is not an accurate guide for fluid need. As their body temperature increases, they can become susceptible to heat exhaustion easier than adults. Children should not be exposed to hot environments (sauna, hot rooms, etc.) for extended periods due to this.
Children have immature nervous systems compared to the adult counterpart. Myelination of the nerves is not complete until the age of sexual maturity. The child cannot be expected to have high levels of skill, power, and strength until he or she has reached their neural maturity as well. They simply cannot elicit the same response to training or reach the same skill levels as adults.
There are also several differences in the circulatory system between children and adults. As children get older and progress into adolescence, their heart rate progressively declines. However, at childhood, it is normal for a child to have a higher heart rate than an adult if they are performing the same types of exercise. This makes estimation of maximal heart rate by set equations such as 220-age somewhat inaccurate for children and adolescents until the late teenage years. It also means unless there are signs of stress or duress, there is no cause for concern for heart rate values greater than 200 bpm. Healthy individuals should be able to exercise for several minutes at maximal heart rates. In fact, because VO2 max (the greatest amount of oxygen that can be inhaled during aerobic exercise) is relative to the individual’s body weight, VO2 max values are as high as or higher than most adults. Heart rate will return to resting values quicker in children and adolescents than adults. Their maximum heart rate and target heart rates lower due to aging as well. The resting and during exercise systolic blood pressure rises progressively particularly during puberty reaching adult values soon after the growth spurt. Diastolic pressure in both adults and children show very little derivation. When designing aerobic programs for children, you have to take these heart rate differences in consideration.
Exercise capacity also increases gradually throughout childhood. Increases/improvements in endurance capacity occur because of increased muscle mass and enhanced oxygen transport and metabolic capacities. Children will experience a decreased heart rate with endurance training, but not to the same extent as adults do. Children as they get older will be able to handle more activity as they mature due to the increase of capacity, and the decreased heart rate.
When you compare children to adults, the children have immature skeletal systems and less muscle mass. The immature skeletal system causes fragile bone growth (epiphyseal) centers which when put under very heavy stress, can fracture, causing injury to the growth plates. Very young children should avoid very heavy and strenuous resistance training. This does not mean that all children should avoid resistance training. Trainers, parents, and the children should be responsible enough to not allow maximal effort exercises, and practice proper form and technique to avoid these types of injuries. One of the most promising benefits of strength training may be increased bone mass. Bone mass continues to increase throughout growth and development, but a peak in bone mass is reached at a young adult age. Attaining a higher peak bone mass as a young adult may delay the age at which a loss of bone from aging occurs. A loss of bone later in life, especially among menopausal women, can lead to osteoporosis, causing bones to become increasingly porous, brittle and fragile.
As mentioned above, the child contains much less muscle mass than adults. The muscle in adults is stronger as well. Again, the very young should avoid heavy and strenuous resistance training to avoid injury. It has been shown that heavy resistance training will not provide as much value in very young children as in older children. Gains from strength training for preadolescents are generally attributed to neural adaptations and motor learning, rather than circulating androgens. Muscle hypertrophy, or an increase in the cross-sectional area of a muscle, is not usually detected in children as a result of training. Since muscle size has been correlated with strength, studies indicating no increase in muscle hypertrophy implied that strength training was ineffective in younger participants. During the first seven years there is steady growth of the muscles, followed by a slowing trend preceding puberty.
There is also much less hormonal activity in children than adults. Children have very low testosterone levels compared to adults. The amount of testosterone in the child increases along with puberty and levels off slowly after puberty ends. During the time of puberty would be the best time to increase strength training and hypertrophy work due to the increasing testosterone and other hormonal changes.
Adults and children also have very different ventilation patterns. The primary role of the respiratory system is to provide oxygen and to eliminate carbon dioxide from the muscle cells. The amount of air exchanged per minute is called minute ventilation and is the product of the number of breaths (frequency) times the volume of each breath (tidal volume). Children and adolescents exhibit a higher frequency and lower tidal volume than adults at all intensities. Because rapid breathing is readily noticed, it can be upsetting to a well-intentioned adult. The higher frequency and lower tidal volume is normal and no call for alarm. Children reach adult levels of ventilation at 16-18 years old. Younger children who train for endurance will develop adult type ventilation patterns, such as decreasing their breathing frequency, while increasing their tidal volume. Lung diffusion (spontaneous migration of substances from regions where their concentrations are high to regions where their concentrations are low) capacities are also lower in children than adults due to their lungs not being fully developed.