CrossFit does not use the typical single body part exercise machines that you find at a standard gym. There is a good reason for this. Those machines limit you to exercising one body part – single joint movements. When you lift a bag of groceries is there only one body part (such as bicep) involved? No, you use your legs to bend, and your biceps to lift. If the bag is heavy, you might even be engaging your back during the lift.
CrossFit’s intention is to train you for living. We want to train you the way your body moves – in multi-joint movements. We want you prepared for anything – lifting boxes up onto a high shelf in a closet, lifting a child or groceries, helping a disabled spouse out of bed, and so much more. Regular gym machines are effective for building bigger, stronger muscles, but they do not work your body the way it works in everyday living.
Why spend an entire hour working maybe 4 body parts and doing nothing aerobic, when you can spend just 10-20 minutes working your entire body including your lungs and heart?