Definition
The reactive force is defined as the force required to achieve the highest possible force impact in the expansion/contraction cycle. The stretching-shortening cycle describes the phase between eccentric (yielding) and concentric (overcoming) working of the muscles.
Structure of the reactive force
A good reactive strength results from the maximum strength, the reactive tensing ability of the muscles and the rapid contraction ability of the muscles.
The reactive voltage capability
The reactive tenseness of the muscles results from the passive elasticity forces of muscles and tendons and the additional neuronal activation. Stretch- shortening cycle:
- Short stretching – shortening cycle (<200ms, partly also <170ms)
- Long stretching – shortening cycle (>200ms)
Recruitment and frequency
Recruitment and frequency are closely related to the reactive force: Recruitment is understood as the ability to involve as many motor units as possible in a contraction. In short: How many muscle fibers are innervated during a contraction? Note: Motor units have different excitation thresholds.
Initially, slow, weak endurance units are activated (slow-twitch):
- Slow Twitch (ST) – fibers (low glycogen content, high mitochondria, high fatigue resistance) – also called red type
- Fast Twitch (FT) – fibers (high glycogen content, easily fatigued) also called white type.
- Fast Twitch oxidative (FTO) – fibers (fast fibers with high fatigue resistance, medium glycogen content) also called intermediate type
Frequency is the ability to innervate the musculature in a sustained and high-frequency manner. From approx. 55 Hertz (Hz) on, maximum power output is possible.
How can the reactive force be measured?
To make the reactive force measurable, a standardized test is required. This can be a Drop Jump, Countermovement Jump or Squat Jump. The Countermovement Jump, one of the most frequently used tests, requires the subject to jump from an elevation to the ground and from there to perform a direct extension jump.
This must be as high as possible. In addition to the jump height, the contact time, jump and landing are also taken into account. If the different factors are put into context, the reactive force capability can be measured.