One of the great quandary of practitioners arrangements involving muscle strength, would be indicated stretch preceding the training? In the human body there, according Achour Júnior (2006), contractile tissues (muscles) and not contractile (fascia, tendons and ligaments), both of which have elastic and plastic properties. To achieve the plastic deformation, the voltage applied to the stretching exercise should achieve and remain or even slightly exceed the elastic limit of the tissue. Also according to the author, maintaining the stretching tension causes the increase in size of the fabric.
Currently, muscle stretching before exercise has generated controversy regarding its effects with regard to muscle performance. Shrier (2004) examined, in his critical review, 32 studies related to influence of pre-exercise stretching on muscle performance. Besides not find benefit in either study, the author also found that in 20 of them were reported acute deleterious effects of stretching the capacity to generate muscle strength.
However, there is disagreement among the studies to the subject that would have generated the decrease in strength due to the prior stretching. The ability of muscle tension generation is optimized when the sarcomere is in the rest position, because then the activation is allowed for all possible cross-linking bridges between actin and myosin present in the same (DI ALENCAR; MATIAS, 2010).
When a muscle is much shortened occurs the overlap of the actin and myosin filaments, this results in a reduced number of connections between them, and hence a lower strength development potential contraction (RAMOS; SANTOS; GONÇALVES, 2007). Also, if the muscle is stretched beyond its resting length, the number of cross-bridges also decreases, since the overlap of protein filaments is drastically reduced.
The effects caused by the application of stretching exercises can be divided into acute (immediate) and chronic (over time). Acute result from the flexibility of the elastic component of the muscle-tendon unit. Have the chronic effects are the result of an adaptive remodeling of the muscle, which gives the number of sarcomeres in series the increase in myofibrils, resulting in increased muscle length (HALL; BROD, 2007 apud DI ALENCAR ;MATIAS,2010).
To Shrier and Gossal (2000) apud Di Alencar; Matias (2010), the exercise stretching provide direct decrease in muscle tension through the passive viscoelastic changes or indirect decrease due to reflex inhibition and the consequent change in viscoelasticity arising from the reduction of cross-bridges between actin and myosin. The result of reduced muscle tension and an amplitude greater joint. Another aspect that may negatively influence the generation of muscle strength after stretching is related to neural factors (GREGO NETO, 2007).
The reflex arc in skeletal muscle is presented as an importante adjustment mechanism of muscular contraction level since it maintains the central core constantly informed about the state of muscular tension and stretch (McARDLE, KATCH e KATCH, 2003 apud DI ALENCAR ;MATIAS,2010 ). The main receptors involved in this mechanism are the muscle spindles and Golgi tendo organs.
Image reference: Site Swimex