Like every machine ever invented, from the Cuisinart to the iPhone, weight machines provide advantages over the low-tech contraptions that came before. Here are some of the ways that weight machines can top dumbbells and barbells:
Weight machines are safe. Your movement range is limited and the intended pattern is preset, so you need less instruction and supervision than you do with free weights.
Weight machines are easy to use. Machines don’t require much balance or coordination, so you can get the hang of an exercise more quickly. Also, you’re more likely to use proper form because the machine provides so much guidance.
Machines don’t guarantee good form. You can still butcher an exercise on a machine, which can lead to injury or at the very least cheat your muscles out of a good workout.
Weight machines enable you to isolate a muscle group. In other words, machines enable you to home in on one muscle group to the exclusion of all others. For example, very few free weight exercises isolate your hamstrings (your rear thigh muscles). Usually, you can’t exclude other muscles — such as your front thighs, butt, or lower back — from getting involved.
On the other hand, numerous machines can isolate your hamstrings. This feature of weight machines is helpful if you have a particular weakness or you’re trying to build up one body part.
Weight machines help you move through your workout in minutes. You put in the pin, do the exercise, and then move to the next machine. This process also makes working out with a friend, who is stronger or weaker, easier — you don’t have to load or unload weight plates off a bar. But keep in mind that you do need to adjust each machine to fit your body.
Weight machines challenge your muscles throughout the entire motion of an exercise. Many (although not all) modern-day weight machines compensate for the fact that your muscles aren’t equally strong throughout a particular motion. Consider the triceps kickback exercise. This exercise is relatively easy at the start, but by the time your arm is halfway straightened out, your muscle is being challenged a lot more. By the end, your triceps again have better leverage, so you finish feeling strong.
Use a kidney-shaped gizmo called a cam to manipulate the resistance at various points throughout your exercise. When you’re at a weak point during the exercise, the cam lightens the load. When your muscle has good mechanical advantage, the cam gives it more work to do. This way, your muscles are working to their fullest throughout the motion. Otherwise, you’re limited to a weight you can move only at your weakest point, as you are with free weights.