Final answer:
The statement is true; muscles only store enough ATP to initiate a contraction, which lasts about three seconds. Afterwards, the body must quickly regenerate ATP using various metabolic pathways to sustain muscle contractions.
Step-by-step explanation:
The statement that muscles store only enough energy to start a contraction is True. Muscles use adenosine triphosphate (ATP) as the source of energy for muscle contractions, which includes power for cross-bridge formation and filament sliding.
A muscle cell contains a small amount of ATP that can be used immediately, but it only lasts for about three seconds. Consequently, muscles must rapidly regenerate ATP through creatine phosphate metabolism, anaerobic glycolysis, and aerobic respiration to sustain contractions.
During intense activities, like heavy lifting or sprinting, the body recruits the maximum number of motor units for a powerful contraction, but this is not sustainable for long periods due to the high energy expenditure and the risk of complete muscle fatigue.
Muscle cells are designed to efficiently generate force and prevent this fatigue by alternating which motor units are active, thereby allowing for longer durations of muscle contraction.