Higher weight, lower reps = larger muscles (that doesn't necessarily mean you'll be slower)

lower weight, higher reps = leaner muscles, more endurance (that doesn't necessarily mean they'll be faster)

Alot of people who want speed do explosive exercises. You do the exercise, only you explode out of it. As opposed to slow, deliberate movements. You need to be careful when doing these sorts of exercises though.

So explode on the positive (where the muscle contracts) and then slow on the negative (where the mucle returns to it's starting position)

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