Muscle contraction is the tightening, shortening, or lengthening of muscles when you do some activity. It can happen when you hold or pick up something, or when you stretch or exercise with weights.
Repeated exercise, or wasting, can change the way key genes work.
14don MSN
What’s the difference between ‘lean’ and ‘bulk’ muscle — and which should you aim for?
There's a lot of talk about lean muscle compared to bulk muscle, but experts say it's not worth differentiating the two.
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