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Holly asked in HealthDiet & Fitness · 10 years ago

Muscle breakdown after 20 mins exercise?

I've heard that if you do cardio exercise for more than 20 mins, the body begins to break down muscle, i always generally assumed this applied to more things like running, treadmill, cross trainer, cylcling etc so does it apply to swimming as well?

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  • Anonymous
    10 years ago
    Favorite Answer

    no this does not happen as your body only uses protein as an energy source after it has used up all its glycogen and fat stores. you would probably only breakdown protein running in ultra marathons etc

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