Final answer:
The training regimen that starts with rapid eccentric muscle action followed by concentric action is known as a plyometric exercise, which enhances explosive muscle power.
Step-by-step explanation:
The training regimen described, which involves a rapid eccentric contraction followed by a concentric action of the same muscle, is commonly referred to as a plyometric exercise. These exercises focus on increasing muscular power by first lengthening the muscle (eccentric phase) and then contracting it (concentric phase). For example, the eccentric action occurs when a muscle actively resists a force, leading to muscle lengthening, as seen when slowly lowering a weight during a bicep curl. This is followed by a concentric action where the same muscle shortens to produce a force, as in lifting the weight back up.
Plyometrics are often used to enhance explosive athletic performance and involve a pattern of physical exercise that can include various intensities and durations of muscular work. All muscle activities, including plyometric exercises, are under the control of the nervous system, which regulates muscle contractions, fiber recruitment, and muscle tone through motor units.