High repetitions (11 or more)

When you use higher reps, your muscles have to contract for long periods of time. This increases the number of mitochondria in your muscle fibers. Your mitochondria are energy producing structures that not only burn fat (the more the better!) but also lead to greater muscle endurance and cardiovascular fitness. What's more, these structural changes boost the fluid volume in your fibers, adding size to your muscles!

Low Repetitions

Low repetitions (1 to 5): This rep range allows you to use the heaviest weights, which puts your muscles under the highest amounts of tension. This increases the number of myfibrils in your muscle fibers. What the heck is myofibril? It's the part of your muscle fiber that contains the contractile proteins. Think of it this way: When there are more of these proteins to contract, your muscles can generate greater force. That is why 1 to 5 is an ideal rep range for building strength. And, of course, more myofibrils increase the size of your fibers, making your muscles bigger!

There is no such thing as a bad rep... 3 part series

Trainers don't just randomly choose the number of repetitions a person does. Well at least the good ones don't. That is because the rep range you use dictates how your muscles adapt to your routine. In fact,by knowing the benefits of three key rep ranges, you can choose the strategy that's best for the results you want. Keep in mind that these rep ranges don't work like an on-off button; they're more like a dimmer switch. As you move up and down in reps, you're simply dialing back the benefits of one and emphasizing those of another. I will post 3 more posts that will cover each rep range and what they do.