Online. Tools to assist measurement and training of human fitness and exercise levelsPublished on Friday, August 9, 1996 by Gideon Ariel
Tools To Assist Measurement and Training of Human Fitness and Exercise Levels
For centuries, many devices have been created specifically for strength development. These devices include treadmills, bicycle ergometers, rowing machines, skiing simulators, as well as many of the more traditional resistive exercises with dumb bells, bar bells, and commercially available weight equipment. Each type of exercise has some advantages but none are designed to cope with the difficulties inherent with the gravitational effects which affect the multi-linked human body performing on various exercise equipment.
All systems that employ weights as the mechanism for resistance have major drawbacks in four or more areas, as follows: (1) biomechanical considerations, (2) inertia, (3) risk of injury, and (4) uni-directional resistance. The biomechanical parameters are extremely important for human performance and should be incorporated into exercise equipment. The biomechanical factors were discussed previously. Inertia is the resistance to changes in motion. In other words, a greater force is required to begin moving weights than is necessary to keep them moving. Similarly, when the exercising person slows at the end of a movement, the weights tend to keep moving until slowed by gravity. This phenomenon reduces the force needed at the end of a motion sequence. Inertia becomes especially pronounced as acceleration and deceleration increase, effectively reducing the useful range of motion of weight-based exercise equipment. The risk of injury is obvious in most weight-based exercise equipment. When weights are raised during the performance of an exercise, they must be lowered to their original resting position before the person using the equipment can release the equipment and stop exercising. If the person exercising loses his/her grip, or is unable to hold the weights owing to exhaustion or imbalance, the weights fall back to their resting position serious injuries can and have occurred. Finally, while being raised or lowered, weights, whether on exercise equipment or free standing, offer resistance only in the direction opposite to that of gravity. This resistance can be redirected by pulleys and gears but still remains unidirectional. In almost every exercise performed, the muscle or muscles being trained by resistance in one direction are balanced by a corresponding muscle or muscles that could be trained by resistance in the opposite direction. With weight-based systems, a different exercise, and often a different mechanism, is necessary to train these opposing muscles.
Exercise mechanisms which employ springs, torsion bars, and the like are able to overcome the inertia problem of weight-based mechanisms and, partially, to compensate the unidirectional force restriction by both expanding and compressing the springs. However, the serious problem of safety remains. An additional problem is the fixed, nonlinear resistance that is characteristic of springs and is usually unacceptable to most exercise equipment users.
The third resistive mechanism commonly employed in existing exercise equipment is a hydraulic mechanism. Hydraulic devices are able to overcome the inertial problem of weights, the safety problem of both weights and springs, and, with the appropriate selection or configuration, the unidirectional problem. However, previous applications of the hydraulic principle have demonstrated a serious deficiency that has limited their popularity in resistive training. This deficiency is that of a fixed or a preselected flow rate through the hydraulic system. With a fixed flow rate, it is a well established fact that resistance is a function of the velocity of the piston and, in fact, varies quite rapidly with changes in velocity. It becomes difficult for a person exercising to select a given resistance for training due to the constraint of moving either slower or faster than desired in order to maintain the resistance. Additionally, at any given moment, the user is unsure of just what the performing force or velocity actually is.
In the field of rehabilitation (54) especially, isokinetic or constant velocity training equipment is a relatively new fitness technology that has enjoyed wide acceptance. These mechanisms typically utilize active or passive hydraulics or electric motors and velocity-controlling circuitry. The user or practitioner selects a constant level of velocity for exercise and the mechanism maintains this velocity while measuring the force exerted by the subject. Although demonstrating significant advantages over weight-based systems, isokinetic systems possess a serious limitation. There are virtually no human activities that are performed at a constant velocity. Normal human movement consists of patterns of acceleration and deceleration. When a person learns to run, ride a bike, or write, an acceleration/deceleration sequence is established that may be repeated at different rates and with different levels of force, but always with the pattern unique to that activity. To train, rehabilitate, or diagnose at a constant velocity is to change the very nature of the activity being performed and to violate most biomechanical performance principles.