Reactive movements are motor responses to physical and mental stimuli that are distinct from spontaneous movements. Essentially, reactive movements are based on the stretch-shortening cycle that occurs when muscles are actively lengthened. Reactive force is subject to disturbances in neurogenic lesions of the extrapyramidal system.
What are reactive movements?
Reactive movements usually correspond to rapid successive eccentric and concentric work of the musculature, as in throwing. Neurology recognizes different types of movements of the neuromuscular musculoskeletal system. Every movement basically consists of muscular force and contraction, which is initiated from the central nervous system via efferent motor nerve pathways. Involuntary movements such as fascicular twitching following stimulation of peripheral neurons are referred to as spontaneous movements. The so-called reactive movements are to be distinguished from this. A reactive movement is a movement that responds to a physical or mental stimulus. Reactive movements usually correspond to a rapid succession of eccentric and concentric work of the musculature. The muscle action form of the reactive movement is known as the stretch-shortening cycle. The stretch-shortening cycle occurs during active lengthening of the musculature, which is immediately followed by contraction of the corresponding muscle. The plastic elastic properties of the muscles cause the contraction to occur immediately after the stretch. Thus, the muscle contracts before it adapts to the stretch. The stored energy of the preceding movements makes the cycle energy efficient and fast. The force to perform reactive movements is called reactive force.
Function and task
The combined functioning of the muscles plays a major role in everyday human life. It plays an even greater role in an athletic context. All reactive movements are characterized by rapidly successive, yielding eccentric and overcoming concentric ways of working the muscles. In the eccentric phase of a reactive movement, the tendo-muscular system stores the kinetic energy from the performed movement within its serial elastic and parallel elastic structures. In the subsequent concentric phase of the cycle, the stored energy is released. Thus, there is an increase in force and power compared to the previous concentric contraction. Reactive force depends on several factors, including neuro-muscular factors. In addition, the extensibility of the tendinous structures plays a crucial role. The basis of the performed power increase within a reactive movement is the stretch-shortening cycle, which activates the muscle spindle receptors. The activation of the muscle spindle receptors is thus the stimulus that must precede any reactive movement. The reactive force is precisely the force that realizes the highest possible force impact in the stretch-shortening cycle. The stretch-shortening cycle itself is the phase between eccentrically yielding and concentrically overcoming work of the muscles. Good reactive strength is the result of good maximum strength, reactive appropriate tension ability of the muscles and fast contraction ability. Reactive tension capacity results from passive elasticity forces of muscles and tendons. Reactive strength is required by humans to perform forms of movement such as jumps, sprints or throws. All such movements have essentially reactive character. The extrapyramidal system is an anatomically crucial structure for reactive movements. Control processes of motor activity are then found in this system as soon as they do not run through the pyramidal tracts of the spinal cord. The nerve tracts of the system run from core areas of the cerebral cortex through subcortical basal ganglia, nucleus ruber, and substantia nigra in the midbrain. From there, they continue into the olive nucleus of medulla oblongata and run down the spinal cord. In primates, the extrapyramidal system has some dominance in movement control. However, a functionally clear separation of the pyramidal and extrapyramidal systems basically does not exist even in primates.
Diseases and disorders
Reactive force can be selectively trained.Athletes use so-called plyometric training, for example, to train reactive movements and thus develop a higher reactive strength than average. In the stretch-shortening cycle, and thus the basis of all reactive movements, tendons must be stretched to the limit in order to produce the required movement effects. In this context, high extensibility may have unfavorable effects on the development of the cycle and thus may also show unfavorable consequences for reactive movements. Apart from these connections, reactive movements may be affected by neurogenic lesions. For example, extrapyramidal syndrome is the term used to describe a disturbance in movement that results from such lesions. Due to an increased or decreased state of tension of the musculature, a drastic increase or decrease of movements occurs. The extrapyramidal system is primarily attributed with unconscious involuntary movements that shape automated movement sequences. The system also contributes significantly to the coordination of tone and movement. Because of the extrapyramidal system, the arms are swayed along when walking, for example. In addition, the exrapyramidal system inhibits and controls the voluntary motor function of the pyramidal tract. Disorders of the system are either hypokinetic-hypertonic, such as in Parkinson’s disease, or manifest hyperkinetic-hypotonic as in chorea or ballismus. Corresponding disorders can also occur as a result of medications such as neuroleptics. The consequence of these disturbances are phenomena such as ataxia, tremor or start inhibitions, which correspond to a disturbed initiation of movement. All reactive movements are reduced in the hypokinetic-rigid form of the extrapyramidal syndrome. Patients with this pathology often suffer from a tendency to fall when walking, since walking in particular is associated with reactive movements. Injuries or other pathologic conditions of the muscles may also underlie decreased reactive force.
