Golgi tendon organ

       The Golgi tendon organ (OTG) located on the tendon and is in series with the extrafusal muscle fibers. Essentially, OTG serves as a safety device that helps prevent a generation of excessive force during muscle contraction (POWERS; HOWLEY, 2005).

      Unlike the muscle spindle, Microsoft responds better to the contraction of the muscle that extension. While the tendon demonstrates a low trigger threshold for contraction, one needs a pretty high threshold to respond to stretching (JAMIL, 1992 apud ACHOUR JR, 2006).

      Also according to the authors, the OTG relative insensitivity to the stretching exercise is caused by its location in series with the muscle bundles.

     During muscle contraction, OTG unloads a nerve impulse able to inhibit muscle contraction and causes muscle relaxation. For this reason, the Golgi tendon organ is an afferent inhibitory system, while the muscle spindle is excitatory (Silverthorn, 2003 apud ACHOUR JR, 2006).

      Basically, OTG inhibits contraction of agonist muscle (the agent movement) and stimulates contraction of the antagonist (muscle that opposes agonist) when muscle tension reaches critical levels. In this mechanism gives the name of tendon reflex (TORTORA and GRABOWSKI 2002 apud Di ALENCAR; MATIAS, 2010). This inhibitory process exists to prevent excessive muscle contraction, as this could cause an overload on the tendon and result in injury (MONTEIRO and FARINATTI, 2000). How OTG forces the agonist muscle to relax, this leads to greater difficulty of maximum force generation in that movement.

      Kokkonen. et al. (1998) found deficits in the test 1RM (one repetition maximum test) in subjects who underwent five different stretching exercises for the extensor muscles and knee flexors with a total volume of 20 minutes. The results obtained in the study report that the group submitted to the stretching protocol got a 16% decrease in power generation compared to the values obtained by the same group before the application of stretching.

      This was attributed by the authors to changing answers muscle and joint propioceptores due to stretching.

       According to the authors, OTG would be responsible for responding to the tension caused by stretching, generating an inhibitory reflex in the muscle was being stretched. Also according to Kokkonen et al. (1998) these receptors in the muscles, tendons and joint capsule can also be responsible for neural inhibition of the motor units.

      Some authors suggest that the deficit in muscle performance generated by stretching exercises would be directly proportional to the time kept in extended position (ACHOUR JR, 2006; ZAKAS et al, 2006).

     Order to investigate the influence of stretching volume in the quadriceps muscle performance, Zákas et al. (2006) found that of five and eight minutes protocols caused significant deficit in the isokinetic torque, but no significant difference was found when the protocol only 30 seconds of stretching was applied. Have Brandenburg (2006) found significant deficits in isokinetic performance hamstring after static stretching protocols with volumes of 15 and 30 seconds. Thus, the question of what would be the residence time in the elongated posture enough to compromise the generation of muscle strength is still a very controversial aspect in the literature (GREEK and MANFFRA NETO, 2009).

Image referente: anatomyfacts

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