体育锻炼的原因通常被称为"motivation for exercise"。来源可能包括健康原因、减肥、提高体能、改善心理健康、缓解压力、提升自尊心、增强社交关系等。

例句：

I exercise to improve my health and reduce my risk of developing chronic diseases.
I want to lose weight and tone my body.
I want to increase my strength and endurance.
Exercise helps me improve my mental health and reduce stress.
I exercise to boost my self-esteem and confidence.
I enjoy the social aspect of exercise and the connections I make with others.

翻译：

我锻炼是为了改善我的健康状况，降低患慢性疾病的风险。
我想减肥，让我的身体更健美。
我想提高我的力量和耐力。
锻炼能帮助我改善心理健康，缓解压力。
我锻炼是为了提升自尊心和自信。
我喜欢锻炼的社交方面，和与他人的联系。