Let’s do an experiment with your arm muscles. First, stand with your arms at your side. Bend your right arm at the elbow, touching your fingers to your shoulder and then returning your arm to its starting position. Repeat the movement 10 times. Your arm isn’t tired, is it? The reason is that your arm muscles didn’t have to work very hard to lift your arm up and down.
Now, repeat the exercise holding a bottle of water in your right hand. This time your arm muscles feel tired. The reason is resistance. To lift the water bottle, your arm muscles had to overcome (resist) the weight of the water bottle. The heavier the bottle, the more resistance, and the harder your muscles have to work.
Resistance exercise is anaerobic, meaning it is “without oxygen.” Anaerobic exercise, like weight lifting and sprinting, uses muscles at high intensity for short periods of time (2 to 3 minutes), as opposed to aerobic exercise, which is low intensity for long periods of time (15 or more minutes). The energy for anaerobic exercise comes from glycogen stored in your muscles.
Now, let’s take a look at your voluntary muscles: the ones you use to do resistance exercises. Different exercises work different muscle groups. Here some good exercises for different parts of your body:
As you make a list of the resistance exercises you’re going to do, be sure to include at least one exercise from each major muscle group on your list. Start your exercise sessions with compound exercises that involve two or more joint movements and work several muscle groups at once, like bench presses and squats.
Work toward isolation exercises that primarily involve just one joint movement and one muscle group, like biceps curls and leg extensions. This approach allows you to do the most demanding exercises when your muscles are the least tired. For example, you’ll use better form on your bench presses if you do them before exhausting your triceps doing triceps extensions.
More fitness and health information at The Boy's Fitness Guide: Expert Coaching for Young Men