By John Downes, D.C., CCEP
Photography by Guy D’Alema
The benefits of exercise are well documented, and the outcomes usually vary in direct proportion to your goals and objectives. Some individuals desire an increase in cardiovascular endurance, while others concentrate on muscle hypertrophy. If you have decided that weight lifting is going to be a part of your exercise plan, the question often asked is, “What equipment is best for me?” The answer is based on your goals, but for the average person usually a combination of free weights and machines produces the desired outcome. The most important component in any program is safety. There is nothing more discouraging than suffering an injury as you start your exercise program. This is where the design and principles resistance training machines (RTM) may be of prime benefit, or a hidden menace.
Pay a visit to any gym, sports equipment store or fitness center and what catches your eye? The machines! How much of your selection process is determined by the advertising, the svelte salesperson or personal trainer, the look or how it will fit in your home or color scheme? None of these “reasons” have anything to do with the science of exercise.
What matters most is what the machine is intended to accomplish and its effectiveness. Some of the mechanical issues that should be considered are: axis of rotation, type of lever, path of motion, range of motion and strength curve versus resistance profile. There is an infinite selection of designs to choose from, but the basis of using a machine is that the path of motion closely replicates the motion of the body part you are exercising. By selecting properly and then using the equipment correctly, a safe and effective result occurs.
Axis of rotation: When using a machine in which the primary joint action takes place at a single joint, the machine must replicate the motion of the body. If it does not or if the “form” (method of using the equipment) is improper, then the pain of exercise may actually be injury-based rather than sore muscles from a good workout. For example, when exercising the shoulder area some of the popular exercises are “pull over,” “lateral raise,” and “fly.” When exercising the shoulder complex both the scapulothoracic area and the glenohumeral area must move through a range of motion that produces a complex series of changes. The RTMs are “fixed plane” devices, thus there is no way that the axis of rotation of the machine can match the instant axis of the shoulder throughout the exercise. Observing a person performing the “fly” or “reverse fly” will drop their elbows below the horizontal plane in order to increase the weight or feel more comfortable in the exercise. This change in form can overload the anterior capsule and stabilizing musculature of the glenohumeral joint. In the lower extremity the most common area that cannot be adjusted on the machines is hip/pelvis design. A typical by-product of trying to adapt to poor design is low back pain when exercising the hip region.
Type of lever: There are three types of lever systems: first, second and third class. A lever system is composed of bar, two forces and a fulcrum. The difference in the classes is where the forces (weights) and fulcrum (pivot) are located. In a first class system the axis is in the middle. The second-class system has the weight (forces) in the middle, such as the Thrustaway System. The third-class fulcrum and weights are at each end and the force exerted is in the middle. Each of these designs has advantages, but remember the action should replicate the motion of the body part you are exercising.
Path of motion: It makes sense that the path of motion should be the same as the joint you are exercising. An easy way to do a quick check is to take the joint through a full range of motion on the machine and see if you “sense” any shift or slide that occurs. A prime example is the biceps curl machine. If the handles are not “floating” it would appear that the hands should move in a straight line, e.g. parallel as the elbow flexes. The hands actually rotate slightly internal, therefore the arc of the elbow may be good, but you will start to develop elbow pain as you are working to strengthen the biceps.
Range
of motion: A muscle tends to be strongest around its normal resting length.
When using a RTM the muscle will be weaker at either extreme of shortening or
lengthening, thus the design of the machine should assist the efficiency as
well as increase the load to produce strength improvement. Signs that the design
is not right for you is if the joints are at the extremes of your range of motion
and you are unable to maintain mechanical and neurological control. Unfortunately,
most people discover this after a “fatigue failure” that never seems
to recover as you continue to use equipment with the same design.Strength curves and resistance profiles: This is where we have to compare pulley designs to cam-based designs. The purpose of the cam is to change how heavy the weight feels, not the actual weight to vary the resistance throughout the range of motion of the joint. The pulley system simply allows different angles of load, but does not vary the resistance. The cam design has been a dominate product for over 30 years in the RTM business, but most people don’t even question the function or design.
So,
which machine is best for you? Good question. To answer it, study the design
and match it with your goals and objectives. Remember, the advantage of using
RTMs is the isolation of specific muscle groups without producing a large load
on the central nervous system. If you begin a program and find that joint “stiffness”
rather than muscle “soreness” is the predominant problem, then consider
that you may be doing too much, too soon. The solution is to take some time
off and begin again at a slower rate of increase. Or, the design of the machine
may not be best for you and the solution could be to find a machine with a better
design. Either way, your problem is likely fixable—and your exercise days
just beginning!About the author: Dr. John Downes is the Acting Dean of the Life University College of the Chiropractic. He previously instructed in the Sport Health Science Department of Life University and leads the university’s sports chiropractic program. He lectures nationally and internationally as a post-graduate faculty member and is in private practice at
Performance
for Life.