Energy Systems in Muscle - Anatomy and Physiology
- Which skeletal muscle fiber type relies mainly on aerobic metabolism, with many mitochondria and much myoglobin?
- Type I (slow oxidative) fibers. They resist fatigue and suit endurance activity.
- When oxygen supply is insufficient, what is pyruvate converted to in muscle, and why?
- Lactate (lactic acid). The conversion regenerates NAD+ so glycolysis can keep producing ATP.
- Which enzyme catalyzes the transfer of phosphate from creatine phosphate to ADP?
- Creatine kinase.
- For about how long can stored ATP plus creatine phosphate power maximal muscle effort?
- About 10 to 15 seconds, enough for a short sprint or a heavy lift.
- About how many ATP does complete aerobic respiration of one glucose molecule yield?
- About 30 to 32 ATP, produced mainly by oxidative phosphorylation in the mitochondria.
- What is excess post-exercise oxygen consumption (EPOC)?
- Elevated oxygen use after exercise that restores creatine phosphate and ATP, reloads myoglobin with O2, and helps convert lactate back to pyruvate and glucose.
- What is the net ATP yield per glucose molecule from anaerobic glycolysis?
- 2 ATP. It is fast but inefficient compared with aerobic respiration.
- Which compound regenerates ATP fastest at the onset of intense exercise?
- Creatine phosphate, which transfers its phosphate group directly to ADP.
- Which energy system supplies most of the ATP for exercise lasting longer than a few minutes, such as a 10 km run?
- Aerobic (oxidative) respiration in the mitochondria, using glucose and fatty acids.
- Which muscle protein binds and stores oxygen within muscle fibers?
- Myoglobin. It releases oxygen to the mitochondria during contraction.
- Why must muscle fibers continuously regenerate ATP during sustained contraction?
- Stored ATP is very limited and powers maximal contraction for only a few seconds, so other pathways must rebuild it from ADP.