Dear Seated Leg Extension Machine,
I understand where you come from. The mind of your creator Arthur Jones was brilliant. Not only would you isolate muscles or muscle groups individually, but you would also provide variable resistance through a series of cams. For each and every repetition, where the moving joint had the least leverage, less force was required, and more force was demanded where the joint was strongest.
With regular use of you and your cousin machines, we would all easily achieve previously unattainable levels of strength and muscle size.
But it turns out that the genius of Arthur was really more in the realm of marketing. In this, he was truly a man before his time, who hired physically massive celebrities and invented an entire training magazine to help sale the idea of you. In truth, Arthur was loose with the facts and crummy as a scientist.
Seated Leg Extension Machine, you exist in the name of health and/or fitness. Yet you are culpable in the needless damage done to hundreds of thousands of knees.
It turns out that most muscles are social creatures, and the quadriceps were not designed to function in isolation. Intense, isolated use of the quadriceps in a seated position literally shears some parts of our knee apart, and grinds other parts together. Kneecaps must glide across the femur every time the leg bends and straightens. The only thing that helps them to stand a chance, over time, is co-contraction of stabilizing muscles and fine tuning accessory movement of the tibia and femur that naturally occur in functional movements.
Seated Leg Extension Machine, although your appearance and engineering are impressive, you are cumbersome and expensive. Before the advent of popular programs like Crossfit and P90X, you had generations of us believing that a large room full of big chrome machines was required to be strong and fit. You had everyone taking a lot of time and effort to train body parts individually.
Seated knee extension, seated knee flexion, seated hip abduction, seated hip adduction, on it goes. And who has time for that? The body is a unit and almost always benefits more from training as a unit. We recieve more benefit from picking up a pet dog and a few gallons of water and performing a well executed set of lunges.
And as your name implies, Seated Knee Extension Machine, you and the whole lot of your cousins cause humans to…sit. Did you not notice that we already sit for far too long, too often? We have an epidemic of tight hip flexors and poor lumbopelvic control, and yet you entice humans to fill the limited minutes they devote to their health and fitness with…more sitting.
Sure, this is an act of omission, but you are guilty nonetheless. As trainer Daniel John often points out, those older than 55 are statistically more likely to die from complication of a fall than from cancer.
You strengthen a muscle group, and this is likely better than no exercise at all. But the real-world application of such “isolated” strength is limited and does not translate to dealing with gravity and ground reaction forces. Seated Leg Extension Machine, your seatedness provides no natural balance demand, no integrative strength demand, and no proprioceptive-rich environment from which an entire human system may improve its functional strength and sense of balance.
At one point you were recommended for high level athletes looking to achieve an edge in performance. But now we have studies and showed what we’ve known all along: The amount of effort put into an activity nearly always dictates what we get out of it. And only so much effort can be poured into using one joint in a seated position.
A set of well executed single leg squats or hip hinge deadlift with a $50 dumbbell or kettle bell better prepares us for real world athletic performance. Generating power on the athletic field is a highly coordinated effort of some joints staying stable while other joints generate high force, high speed movement. This must all be fine-tuned by the nervous system. In all of this you are severely lacking.
In summary, you would make a better coat hanger than piece of fitness equipment. I would suggest that your owners move you to the back parking lot or yard in order to allow more…beautiful…free space for movement. But then you’re cluttering up the great cathedral of the outdoors.
Seated Leg Extension Machine, I have beef with you. Your too cumbersome to carry, too heavy to drag, and too wide to use as a hurdle. So I don’t know what to recommend for you.