Multiple choice

The heart keeps on beating throughout life without fatigue because

  1. it contracts slowly

  2. it has a resting or recovery period

  3. it can use lactic acid as an extra source of energy

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The heart muscle (myocardium) has a long refractory period, which acts as a recovery phase, preventing the muscle from entering a state of sustained contraction (tetanus) and allowing it to rest between beats.

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