Muscle Contraction When Doing Exercise
- force of gravity
- isokinetic apparatus
- fixed resistance
- electrical stimulation
1. The force of gravity
DEFEATING THE/FORCE OF GRAVITY results in a type of contraction which is commonly called concentric (Latin corn-centrum means having a common centre) and denotes the case -where the muscle length shortens. Concentric contraction or defeating the force of gravity is the common training technique employed by most athletes using free weights.
RESISTING THE FORCE OF GRAVITY is a means of developing strength which is less frequently used, although extremely effective. This simply means that instead of lifting a weight (defeating the force of gravity) one lowers it, slowly yielding to the force of gravity. During such an eccentric contraction the muscles actually lengthen during the phase of stimulation. Such is the case when the shock of impact is absorbed after jumping down from a high object.
2. Isokinetic apparatus
Several types of machines (Nautilus, mini-gym, Cybex) have recently been developed and used for strength development. In all cases an isokinetic (equal or constant movement) contraction occurs, during which the resistance of the apparatus is held constant throughout a full range of movement. During the movement which combines both concentric and eccentric contractions, the machine provides a resistance which is equal to the force performed by the athlete.
3. Fixed resistance
A muscle can develop tension, often higher than that developed during a dynamic contraction, via static or isometric condition. The application of an athlete’s force against specially built immobile frames or objects that will not yield to the force generated by the athlete, make the muscle develop high tension without altering its length.
4. Electrical stimulation
Although not yet adequately investigated, it seems that electrical stimulation could lead to gains in a muscle’s strength. Sources suggesting such improvements are mostly from Russia (Webster, 1975; Kots, 1977) and Japan (Ikai and Yabe 1909). According to Webster, Russian weight lifters improved their maximum strength as a result of employing electrical stimulation. Kots (1977) claims that the use of electrical stimulation increases the muscle’s hypertrophy and that gains were found to be not only in strength but also in endurance. Ikai and Yabe used a frequency of stimulation three time higher (up to 150 impulses/second) than the physiological frequency (1-50 in> pulses/second) claimed that strength increases were found to be 31% higher than those realized through voluntary maximum contractions.