Certified Personal Trainer (NSCA) Practice Exam

Adapting to chronic aerobic exercise positively impacts the body's metabolism, particularly in how it utilizes substrates for energy. One significant adaptation is the increased concentration of GLUT4, a glucose transporter protein. As an individual engages in regular aerobic training, the muscles become more efficient at taking up glucose from the bloodstream. This is essential because, during aerobic activities, the body requires a steady supply of glucose to meet energy demands.

Higher GLUT4 levels enhance the muscles' ability to transport glucose into cells, which supports prolonged exercise and helps improve overall endurance. This adaptation also contributes to improved insulin sensitivity, crucial for metabolic health. With increased GLUT4, the body can better utilize both carbohydrates and fats for energy, but the focus here is on the mechanism that facilitates increased glucose uptake.

The other options do not reflect primary changes that occur specifically due to chronic aerobic training in the same way. For instance, the reliance on carbohydrates or free fatty acids generally varies depending on exercise intensity and duration, while the concentration of hexokinase, an enzyme involved in glucose metabolism, typically does not decrease in response to aerobic training. Thus, the increase in GLUT4 directly aligns with the essential physiological adaptations that occur with continued aerobic exercise.