Variety is one of the cornerstones of an effective and interesting exercise program, but variety sometimes provides room for uncertainty. One way this uncertainty manifests is with questions such as, "which exercise is better A or B." Or statements like, "I don't bother doing A, because I do B." It is usually the case that every exercise has its own inherent value and the important thing is matching that value with your goals.
I was asked recently while designing a client's home gym, "What's better, Smith
Machine bench press or barbell bench presses?"
I don't like saying one exercise is "better" than the other. They both have strengths and weaknesses and they are varying ways of working essentially the same muscles: the pectoralis, deltoids, and triceps. I am always surprised by the loyalty that some people will attach to certain exercises, and the area of bench pressing is at the top of the list.
The Smith Machine is a weight bar with hooks attached which is on a guide rod system. This assembly is mounted on a cage with notches for the hooks to catch. The primary benefit of a Smith Machine is that the use of the hooks allows you to exercise alone with relatively little risk of dropping a weight on your chest or face. This is a good thing, allowing you to push for one or two more reps with confidence.
The primary shortfall of the rod system is its linear nature. The rods are vertical, but the natural path of a bench press is not. As the bar rises from your chest to fully extended position it travels in an arc. This arc is ergonomically dictated by your shoulder joint, and the mechanical advantage of your chest and shoulder muscles. When this arc is flattened, the movement is unnatural and your strength gains will be affected. A 2005 study published in the Journal of Strength & Conditioning Research compared the one-rep max of trained weight lifters on the barbell bench press and Smith-machine bench press and reported that the lifters were about 16% stronger on the free weight press.
Also as you gain safety and stability from the rod system you loose the instability that forces many small stabilizing muscles such as the deltoids and the pectoralis minor to balance and keep you on track. One of the primary benefits of free weight training is the development of these stabilizing muscles.
On the other hand, the inherent weakness of the bench press with a free weight bar or with a Smith-machine is that the hands are necessarily separated at the extension of the movement. The pectoralis (chest) muscle is responsible mainly for horizontal adduction. If you spread your hands out really wide and bring them in as if to clap together, this is horizontal adduction. If you bring your hands in half way, (about as far apart as they are on a bench press grip) you only complete half of the chest's available range. This inherent weakness is fodder for another article, but is easily solved with the use of dumbbells or a chest fly machine. As I said above each exercise has its strengths and weaknesses and one should not be considered "better" than another, they are all "different."
If you exercise in a home or private setting where no one is available to assist you, a Smith-machine can be an excellent choice. Also, the relatively new development of the "ProSpot" equipment is a vast improvement. Undoubtedly, the best recipe for your continued success is to have a variety of choices available to you. Along with a bar set-up, dumbbells make a nice addition, also body weight exercises such as push-ups and dips are very valuable. If you workout in a gym you may be guilty of stalling your progress by not varying the workouts enough and becoming too loyal to certain exercises. Try to change your path in the gym. Go to different stations in a different order and you may be surprised with the result.