Academic journal article
By Fisher, Michele
JOPERD--The Journal of Physical Education, Recreation & Dance , Vol. 80, No. 4
The promotion of physical activity and physical fitness are central tenets of physical education. It is often assumed that these two concepts go hand in hand, in that those who participate in regular physical activity are physically fit. However, in children, the relationship between habitual activity and fitness is not particularly strong (Payne & Morrow, 1993). Much of the disparity between activity levels and physical fitness in children can be attributed to varying rates of growth and development (Corbin, 2004). Maturation (or lack thereof) has a significant effect on how children respond to exercise. In other words, when it comes to exercise, children should not be treated as miniature adults (Corbin, 2002). An understanding of how growth and development during childhood affect fitness, of physiological responses to exercise, and of exercise programming is particularly important for physical educators working in an elementary school setting. Therefore, the purpose of this article is to review concepts of pediatric exercise physiology that are essential to physical education programs for children in grades K-6.
Influence of Growth on Fitness
Growth and development during childhood are largely mediated by the actions of growth hormones and an "insulin-like growth factor." These factors work together to produce skeletal growth and muscle hypertrophy (increase in muscle size), as well as increased size and function of the heart and lungs (Rowland, 2005). At the onset of puberty, the effects of these growth factors are augmented and supplemented by reproductive hormones, initiating an adolescent growth spurt and the development of secondary sex characteristics. There is a great deal of interindividual variability in the timing (age of onset) and rate of progression (tempo) of pubertal development. Gender differences are also evident, with girls exhibiting the onset of puberty at about 10 to 11 years of age, approximately two years earlier than boys (Malina, Bouchard, & Bar-Or, 2004; Rowland). This article focuses on the impact of growth and development of fitness and exercise programming in children between the ages of five and 12 years. The assumption is most students in this age bracket are prepubescent, however girls in the upper portion of this age range are likely to be in the early stages of puberty.
Cardiorespiratory endurance--also known as aerobic capacity--is defined as the ability of the entire body to sustain prolonged rhythmical exercise. Aerobic capacity is related to the efficiency of the respiratory and circulatory systems, as well as the ability of skeletal muscle to utilize the oxidative (aerobic) energy pathway. Absolute (whole body) measures of aerobic fitness are lower in children than in adults. However, when body size is taken into account, values for aerobic capacity are similar between children and adults (Wilmore & Costill, 2004). Although children are proficient in using the aerobic energy system, they have a tendency to fatigue sooner than adults for a given activity. This phenomenon is related to economy of effort, which refers to the mechanical efficiency of the body in locomotion and in the execution of motor skills. According to Sallis, Buono, and Freedson (1991), children at the age of five expend 37 percent more energy in locomotion than adults. Thus, although children are quite capable of using the aerobic energy pathway, their performance in aerobic activities is limited by their low mechanical efficiency. Both absolute aerobic capacity and mechanical efficiency for performing aerobic activities gradually improve throughout childhood and into adolescence with the maturation of the body relative to body size, and the function of the cardiorespiratory, neuromuscular, and metabolic systems (Rowland, 2005).
Another issue is whether children have the capacity to improve their cardiorespiratory endurance, beyond what is attributed to growth, in response to exercise training. …