Not exercising consistently can lead to muscle atrophy, diabetes, bone density loss, and other problems.

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The problem was an old flag-football knee injury that had caused muscle atrophy on the injured side.

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An old flag-football knee injury had hung around too long, which led to muscle atrophy on the injured side.

FORBES: Magazine Article

Although some of the deaths occurred in people with underlying diseases such as atherosclerosis (and therefore could have been coincidental), government researchers who examined otherwise healthy dieters who died of ventricular arrhythmias found that the pattern of deaths suggested "the effects of protein-calorie malnutrition on the heart, " including atrophy of the heart muscle.

CNN: How crash diets harm your health