The exercises are designed to strengthen your stomach muscles.
這些活動目的在于增強你的腹部肌肉。
Muscles contract and relax during physical activity.
身體活動時肌肉收縮放松。
He didn't move a muscle.
他一動不動地站著。
The heart muscles contract to expel the blood.
心臟肌肉收縮以擠壓出血液。
The exercise consists of stretching and contracting the leg muscles.
此項訓練包括伸展和收縮腿部肌肉。