Is the Weight Lifted on a Smith Machine the Same As Free Weights?

Advantages

The major advantage of a Smith machine is safety: the limited plane of movement means you can’t fall backward or forward. Also, most Smith machines have safety features that prevent the bar from falling too low. So, for example, if you’re doing an overhead shoulder press, you don’t have to worry about the bar crashing down if you should slip or collapse.

Spring Mechanism and Weight

Some Smith machines also feature a spring mechanism that neutralizes the weight of the bar, which is typically 20 kg, or about 44 pounds. If you don’t account for this weight difference when switching to free weights, you might make the mistake of thinking you can lift the same number of weight plates with a free-standing barbell. For example, on a Smith machine with a spring mechanism, adding 100 pounds of weight plates to the bar might mean you're lifting 100 pounds. But 100 pounds of weight plates on a barbell might mean you’re lifting a total of 140 pounds because you must factor in the bar’s weight.

Equal Weights, Different Movements

Another potential issue is that lifting a heavy weight on a Smith machine might be too easy compared to a free-weight version of the exercise, even when the weights involved are equal. The smooth, stable and linear movement that a Smith machine provides does not challenge your muscles in the same ways barbell lifting does, which often involves curving movements that challenge many more muscle groups. So, for example, a weightlifter who can bench press 150 pounds on a Smith machine might not be able to replicate her performance during a barbell bench press, even with identical amounts of weight.

Considerations

If you don’t have access to a Smith machine, or if you want to obtain the benefits only free weights can offer, ask spotters to assist you and prevent accidents. This way, you can lift challenging weights on barbells but with less risk. Spotters also can motivate you to work harder and achieve more.