For more than 40 years scientists have studied the effects of both concentric and eccentric contractions on building muscle size and muscle strength and in rehabilitation following an injury. Study after study found that the eccentric or “negative” phase of muscle contraction resulted in greater strength gains than concentric contraction alone. It has been demonstrated that elastic components of the muscle contribute to a more forceful eccentric contraction than is seen with the concentric contraction, which involves muscle elements alone. It is a combination of concentric and eccentric contraction that is best.
An eccentric muscle action occurs when muscle fibers lengthen, yet at the same time contract, to lower a load as in the downward movement of a biceps curl. The concentric phase is the upward movement of the weight as in the biceps curl. Another example is the squat maneuver with the eccentric contraction while lowering the hips and the concentric when moving to an erect position.
Forces generated during eccentric movements have ranged from 20% to 146% greater than concentric contractions. Yet, both metabolic requirements and muscle fatigue are lower with eccentric contractions than with concentric contractions. This finding is of importance in using the method in rehabilitation and in strength training for older adults.
The evolution in the development of strength training and rehabilitation equipment capable of permitting both concentric and eccentric action begins with Arthur Jones’ Nautilus equipment, followed through the years by other equipment including Kin Com, Cybex, Biodex, Lido, and X-Force . Yet it was not until the development of Exerbotics that a safe, efficient, effective and truly user friendly apparatus became available.
Thomas W. Allen, DO MPH