What are the main energy systems used for muscle contraction and when are they predominant?

• A. Aerobic oxidative metabolism dominates longer durations.
• B. Immediate ATP-CP system (0–10 s) predominates early; anaerobic glycolysis (10–60 s); aerobic oxidative metabolism dominates longer durations.
• C. Anaerobic glycolysis is not used in short-term effort.
• D. ATP-CP is only used after 1 minute.

Answer: (B)

Muscle contraction draws on ATP produced by three energy systems that take turns depending on how long and how intensely you’re working. The quickest source is the immediate ATP-CP (phosphagen) system, which uses stored ATP and phosphocreatine to power very fast, powerful actions for about the first 10 seconds. Once those stores run down, the body relies on anaerobic glycolysis, which breaks down glucose to make ATP without using oxygen and can sustain high-intensity effort roughly from 10 seconds up to around a minute or two. For longer, continuous activity, the aerobic oxidative metabolism uses oxygen to generate ATP from carbohydrates and fats, supporting energy production for extended durations. It’s normal for these systems to overlap a bit, and the exact time ranges can vary with fitness level and the specific task, but this sequence reflects how energy is supplied as duration increases.