The exercises are designed to strengthen your stomach muscles.
这些活动目的`在于增强你的腹部肌肉。
Muscles contract and relax during physical activity.
身体活动时肌肉收缩放松。
He didn't move a muscle.
他一动不动地站着。
The heart muscles contract to expel the blood.
心脏肌肉收缩以挤压出血液。
The exercise consists of stretching and contracting the leg muscles.
此项训练包括伸展和收缩腿部肌肉。