Most commercial gyms carry both free weights and machines.  Which ones you should use?  The short answer is that free weights are generally better for muscular development, but machines have certain advantages that can be used to enhance your workouts.  Here’s a breakdown of the advantages of each.

Advantages of Free Weights

• Build more muscle and strength – decades of experience have shown that free weights are more effective than machines at building strength and muscle. The main reason is that all machines have friction which makes it easier to lower the weight than to raise the weight.  The lowering portion of weight training (aka eccentric contraction) is crucial to building muscle, and you get less of an eccentric stimulus on machines due to friction.
• Permits a natural bar bath – with free weights, you are in control of how your body moves rather than being constrained by a machine.  With experience, you can find a bar path on each exercise that feels best on your joints and puts maximum stress on the target muscles.
• Build stabilizers – lifting free weights requires getting them into position and guiding them through space which works the smaller stabilizer muscles in addition to the prime movers. Developing your stabilizers will give you a more complete physique and help prevent injury.
• Build balance and coordination – lifting free weights requires more coordination than pushing weights along a machine track. Exercises like squats, deadlifts, and cleans also have an element of balance to them, and the complexity of those movements can develop significant coordination and body awareness.
• Fits all shapes and sizes – no matter your size or proportions, you can lift free weights without the constraints of a machine with limited adjustability.
• Carryover to everyday life – lifting free weights will better prepare you to pick up or move heavy objects around the house, yard, or work site because those objects are basically odd shaped free weights. The overall strength, muscular coordination, and stabilizer development described above are the same qualities that you need to lift everyday objects without hurting yourself.

Advantages of Machines

• Variety – there are only so many ways you can lift a barbell or dumbbell, so machines are great for adding variety to your program.  With free weights, the resistance is always in one direction (down) while machines can create resistance in any number of directions so exercise variations are practically endless.
• Isolation – machines can do a better of isolating individual muscles. Isolation work can be used to improve a lagging muscle group, to work around injuries, or to perform a workout with less overall stress to the body.
• Better resistance curve – high quality machines incorporate a lever or cam that produces a more even resistance curve than a free weight. For example, lateral raises with dumbbells create a lot of resistance at the top of the movement and very little resistance at the bottom of the movement.  In contrast, a good lateral raise machine creates even resistance so that you build strength through the entire range of motion and your shoulders never get a break during the exercise.
• Handle more weight – on some exercises, machines allow you to handle more weight by removing the weak links of balance, coordination, and stabilization strength. A great example is the leg press, where people can typically handle much more weight than they can squat.  By handling more weight, you’re able to put more stress on the legs, rather than being limited by a weak lower back or poor technique as is often the case on the squat.
• Safety – machines require less practice and coaching to perform correctly than free weight exercises, so in that sense they are safer. Weight lifting is a safe activity compared to other sports, but there’s more risk with free weights of dropping the weight on yourself or straining a muscle by getting out of position on a lift.

Recommendations

For a healthy person who wants to maximize their results in the weight room, I recommend roughly a 50-50 split of workout time between free weights and machines.  The foundation of your routine should be the basic free weight exercises: squats, bench presses, deadlifts, overhead presses, bent over rows, cleans, flyes, curls, and variations of those exercises.  Spend the other half of your time on machines to add variety to your routine and to isolate specific muscles that you want to focus on.  If you have injuries to work around or don’t know how to perform free weight exercises correctly, then it’s OK to spend more time on machines.  It’s certainly possible to build an impressive physique using machines alone.  At the end of the day, hard work, consistency, and avoiding injury are the keys to progress regardless of what tools you choose to use in the gym.