Resistance exercise develops muscle mass, which provides for greater muscle strength and endurance. Resistance training also makes your bones stronger and improves your body's ability to regulate blood sugar. Free weights and machines are both used to perform resistance exercise. Each offers specific advantages.
Compound and Isolation Exercises
Resistance exercises can be classified depending upon the number of joints at which movement takes place. During compound exercises, movement occurs at multiple joints and involves a number of different muscle groups. Conversely, single-joint exercises are also known as isolation exercises because they target muscles that cross only one joint. It is often easier to perform single-joint exercises that isolate small muscle groups when using resistance machines.
Loading Pattern
When you perform resistance exercise, the muscles you target must always be contracting in the opposite direction from the line of pull of the load you are working against. If you lift free weights, the line of pull of the load is always directed downward. This can be problematic when exercising some muscle groups. For example, if you're trying to work your back and arm muscles by performing rows with a barbell, you have no choice but to bend forward at the hips so that your torso is parallel to the floor. This places stress on delicate structures of the lower spine. For resistance training machines, the line of pull is altered by pulleys that guide a cable attached to the machine's weight stack. For example, rows can be performed in a seated position on a resistance machine because a pulley changes the downward pull of the weights on the stack by 90 degrees. Two pulleys on a pulldown machine change the line of pull by 180 degrees, which is necessary to work the back muscles that draw your arm down without having to pull your entire body weight up to an overhead bar.
Technique
Generally speaking, it's more difficult to learn proper technique when lifting free weights compared to machines. When you're performing a free-weight exercise, movement must be controlled in multiple planes, which requires coordination and balance. Resistance machines dictate the range of motion you'll follow, which means learning how to use them is far less involved. For this reason, machines might be more suited for beginners, especially those lacking the supervision necessary for learning to lift safely and effectively. Free weights can also be intimidating to people who lack confidence in their athletic ability.
Spotter
Even experienced lifters require a spotter when lifting free weights. For example, when you perform a barbell bench press while lying supine, an inability to complete a repetition will result in the bar being stuck on your chest. This is why a spotter typically stands behind the lifter to provide assistance. Performing a similar movement on a machine requires no such help because the weight on the stack is not free to fall on your body. For example, on a seated bench press machine, if you are unable to complete a repetition, you can simply return the handles to the starting position beside your body and exit the machine.
Adjusting Weight
When performing resistance exercise, the load you work against is an important determinant of the results you will achieve. Working against a load that is lighter than what is required to create metabolite build up is unlikely to bring an adaptive response and using a weight that is too heavy can result in injury. Figuring out the correct weight to lift requires trial and error and it's easier to adjust weights on resistance machines that have weight stacks because all you have to do is insert a pin. Free-weight exercises with barbells require adding and removing various sized plates.
References
- "Strength and Conditioning: Biological Principles and Practical Applications"; M. Cardinale, R. Newton and K. Nosaka; 2011
- "Strength and Conditioning Journal"; Roundtable Discussion: Machines vs. Free Weights; G.G. Haff; Dec. 2000
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