Richard Weil, MEd, CDE, is an exercise physiologist and Certified Diabetes Educator, and is director of the New York Obesity Research Center Weight Loss Program at St. Luke's Roosevelt Hospital Center in
Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.
The simple answer is both, if you have access. Bodybuilders use both, and obviously it works for them. Here's a review to help you understand the advantages and disadvantages of each; plus, I've included information about alternatives to free weights and machines (your own body weight and exercise tubing).
Free Weights (Dumbbells and Barbells)
You can do a variety of exercises for all the muscle groups.
They allow for self-selected movement based on your anatomy (unlike machines which confine the movement). For example, if your shoulder joint is limited in range of movement, you can accommodate naturally to the limitation with a dumbbell.
Free weights help build coordination because it takes skill to move and control the dumbbells. For example, if you're doing dumbbell presses, you must control the motion so that the dumbbells move straight up and not outward. If you're doing a squat, you must be able to steady yourself so that you don't fall.
You may recruit more muscles than just the group you're focused on. Getting back to dumbbell presses, you not only use the pectorals, anterior deltoid (front of the shoulder) and triceps, but you may need other shoulder and back muscles to coordinate and hold your body steady during the exercises. Likewise, if you're doing standing front raises, you will naturally recruit muscles in your abdomen and back to steady your body.
There is a risk of injury from dropped bars or dumbbells. A bench press with a bar can cause serious injury or even death. For this reason, always use a spotter when lifting free weights.
If you are strong and require lots of weight, then you're going to need space to store all the dumbbells. You can get away with plates that load on bars to minimize the number of dumbbells that you need, but it's inconvenient and not much fun to continuously change weight plates while you're working out.
It can get costly, with dumbbells costing 50 cents to more than $1 per pound.
Free weights do require skill and knowledge, so it's a good idea to have a fitness trainer help you get started if you're a beginner.
They are simple to use. Just stick the pin in the weight stack and you're ready to go. If you need more weight, you just take the pin out and put it in the next weight.
They are relatively safe (as long as you don't pick a weight that's too heavy and strain yourself). Even if you drop one, it won't land on you.
They don't require lots of coordination. Simply push or pull on the bar or handles, and you're lifting weights.
They require lots of space.
They are expensive.
Each machine is typically limited to working just one muscle group, so you need lots of machines to cover all the muscle groups. The exception is the cable pulley machines. They are extremely versatile (you can do lots of exercises with them), and they are safe.
If your body doesn't anatomically match the movement of the machine, you might injure a joint with repetitive use over time. For example, the biceps and triceps machines are limited in their range and can cause problems for the shoulder and elbow joints.
I suggest working through the gym and finding the machines and free weights that work best for you. For example, you might prefer cable rows with the machine to bent-over rows with dumbbells. Here's a list of some of the other exercises you can do with machines or free weights (listed as machine/free weight).