Let’s be clear: Not all machines are created equal.

Exercise machines were invented to provide a safe alternative to free weights, but sometimes they’re anything but. As a matter of fact, they can put your body into unnatural positions and take your joints through dangerous ranges of motion. Over time, this can lead to muscle strain and even serious injuries.

So to make the most of your next sweat session, avoid these nine machines, and instead use the alternative exercises shown in each slide for safer, more effective training.