Originally Posted by Moz
I'm a running coach, although mainly distance runners.
Is it better exercise? It depends on your goal.
Slower, longer: Increase your base fitness, better preparation for future intensity, increases in mitochondria and safer injury proofing. Not a short term route to performance fitness.
Shorter, faster: Faster gains in functional fitness, likely increases in vo2 max and possibly lactate threshold. More likelihood of strress induced problems. Not a well designed run - too long for high intensity, a little short for mid term fitness gains.
Better for your health? In theory the longer slower run will have better 'health benefits' in the long term and leave you less susceptible to injury.
Should I alternate? Depends on your goal.
Now that is a good answer!!!!!
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