Resistive Exercising Methods
There are significant differences in the manner of
execution of the various resistive training methods. In isotonic exercises, the inertia,
which is the initial resistance, must be overcome before the execution of the movement
progresses. The weight of the resistance cannot be heavier than the maximum strength of
the weakest muscle acting in a particular movement or the movement cannot be completed.
Consequently, the amount of force generated by the muscles during an isotonic contraction
does not maintain maximum tension throughout the entire range of motion. In an
isokinetically loaded muscle, the desired speed of movement occurs almost immediately and
the muscle is able to generate a maximal force under a controlled and specifically
selected speed of contraction. The use of the isokinetic principle for overloading muscles
to attain their maximal power output has direct applications in the fields of sport
medicine and athletic training. Many rehabilitation programs utilize isokinetic training
to recondition injured limbs of athletes to their full range of motion. The unfortunate
drawback to this type of training is that the speed is constant and there are no athletic
activities that are performed at a constant velocity. The same disadvantage applies to
normal human activities.
In isotonic resistive training, if more than one repetition
is to be used, a submaximal load must be selected for the initial contractions in order to
complete the required repetitions. Otherwise, the entire regimen would not be completed,
owing to the inability to perform or to fatigue.
A modality that can adjust the resistance so that it
parallels fatigue to allow a maximum effort for each repetition would be a superior type
of equipment. This function could be accomplished by manually removing weight from the bar
while the subject trained. This is neither convenient nor practical. With the aid of the
modern computer, the function can be performed automatically.
Another drawback with many isotonic types of resistive
exercises is that the inertia resulting from the motion changes the resistance depending
on the acceleration of the weight and of the body segments. In addition, since overload on
the muscle changes due to both biomechanical levers and the length-tension curve, the
muscle is able to achieve maximal overload only in a small portion of the range of motion.
To overcome this shortcoming in resistive training, some strength training devices have
been introduced that have "variable resistance" mechanisms in them. However,
these "variable resistance" systems increase the resistance in a linear fashion
and this linearity may not truly accommodate the individual. When including inertial
forces to the variable resistance mechanism, the accommodating resistance can be canceled
by the velocity of the movement.
There seem to be unlimited training methods and each is
supported and refuted by as many "experts." In the past, the problem of
accurately evaluating the different modes of exercise was rendered impossible because of
the lack of adequate diagnostic tools. For example, with isotonic exercises, the
investigator does not know exactly the muscular effort nor the speed of movement but knows
only the weight that has been lifted. When a static weight is lifted, the force of inertia
provides a significant contribution to the load and cannot be quantified by feel or
observation alone. In the isokinetic mode, the calibration of the velocity is assumed and
has been poorly verified. The rotation of a dial to a specific speed setting does not
guarantee the accuracy of subsequently generated velocity. In fact, discrepancies as great
as 40 percent have been observed when verifying the bar velocity.
Most exercise equipment currently available lack
intelligence. In other words, the equipment is not "aware" that a subject is
performing an exercise or how it is being conducted. Verification of the speed is
impossible since a closed-loop feedback and sensors are absent. However, with the advent
of miniaturized electronics in computers, it became possible to unite exercise equipment
with the computer's artificial intelligence. In other words, it became possible for
exercise equipment to adapt to the user rather than forcing the user to adapt to the