Question

For the first 45-90 seconds of moderate to heavy exercise, skeletal muscles obtain energy:

Answer 1

Skeletal muscles gain energy from anaerobic glycolysis, using stored ATP and creatine phosphate initially, transitioning to muscle glycogen for sustained activity, all while not requiring immediate oxygen, thus leading to lactic acid production and post-exercise oxygen debt.

Step-by-step explanation:

For the first 45-90 seconds of moderate to heavy exercise, skeletal muscles obtain energy primarily through anaerobic glycolysis. This process involves the breakdown of muscle glycogen to produce glucose, which is then used to make ATP. This system kicks in because the high demands of intense muscle activity cannot be met quickly enough by aerobic respiration, which requires a steady supply of oxygen and is a slower process.

Initially, the muscles use ATP stored in the muscles, then they quickly shift to generating ATP from creatine phosphate for about 8-10 seconds. As the exercise continues, the muscles predominantly use the glycogen reserves to produce energy through glycolysis, creating ATP without the need of oxygen. However, a by-product of this anaerobic process is lactic acid, which can cause muscle fatigue and soreness. Oxygen debt accumulates during this kind of exercise, which the body repays after exercise, increasing breathing rates to restore ATP and creatine phosphate levels and convert lactic acid back to pyruvic acid.