The exercises are designed to strengthen your stomach muscles.

　　這些活動(dòng)目的在于增強你的腹部肌肉。

　　Muscles contract and relax during physical activity.

　　身體活動(dòng)時(shí)肌肉收縮放松。

　　He didn't move a muscle.

　　他一動(dòng)不動(dòng)地站著(zhù)。

　　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。