During PNF stretching, three muscle actions are used to facilitate passive stretching. The isometric and concentric muscular actions of the antagonist (the muscle is stretched) are used before passive stretching to achieve autogenous inhibition. Isometric muscle action is called maintenance and concentric action is called contraction. A concentric muscular action of the agonist called agonist contraction is used during passive stretching of the antagonist to achieve mutual inhibition. Each of these techniques also involves passive and static stretches called relaxation. There are three types of techniques for PNF stretching: The mechanism of PNF mentioned above is how TM and its antagonistic muscles work together. When one contracts, the other relaxes and becomes inhibited to prevent the muscles from working against each other (Neuroscience Online, 2011). This may explain some of what happens during PNF`s CRAC method. In the CRAC method, the contracting muscle in the “antagonistic contract” part of the technique causes this reflex and inhibits TM. This inhibition of TM, along with the shortening of antagonist muscle contraction, allows the muscle fibers of TM to stretch even more, creating a greater stretching force for TM and creating a greater inhibitory influence on TM (Etnyre and Abraham, 1986; Sharman et al., 2006). The interneuron that innervates the alpha motor neuron, which synapses to TM, causes a decrease in neuronal activity in TM, resulting in greater stretching of TM (Rowlands et al., 2003). Further research on how long this reflex affects TM needs to be done to prove that mutual inhibition is behind the effects of PNF stretching. Hold-relax with agonist contraction is the most effective PNF stretching technique due to the relief provided by reciprocal and autogenic inhibition.
Wallin et al. (1985) conducted a study of 47 male subjects who were randomly assigned to four treatment groups. These four groups represented each group of TMs that were stretched; gastrocnemius, ankle spine flexors, hip adductors or thighs. The gastrocnemius, hamstring and adductor groups received 14 attacks of treatment with the cr method of PNF, while the ankle dysflexor group received a BS method. The dorsiflexor group of the ankle was then replaced by the CR method. Flexibility has been increased more with the CR method than with the BS method for this group. Thus, we can see that the “hold-relax” technique refers to an isometric muscle contraction (STATIC), and the athlete or therapist does not attempt movement while performing the technique. The contraction is built gradually.
Stretching has long been considered beneficial for improving performance and reducing the risk of injury during exercise, as well as for improving ROM and function after injury (McCarthy et al., 1997). It has been found that PNF stretching before exercise decreases performance when maximum muscular effort is required. B for example, during sprinting, plyometrics, cutting, weightlifting and other high-intensity exercises (Bradley et al., 2007; Mikolajec et al., 2012). Marek et al. (2005) showed a decrease in strength, power output and muscle activation. Similar studies have shown a significant decrease in the height and power of vertical jumps, as well as a decrease in ground reaction time and jump height in fall jumps after PNF stretching (Bradley et al., 2007; Mikolajec et al., 2012). The Contract Relax technique is very similar to the Hold Relax technique. Passive stretching is maintained for 20 seconds and then contracted. The difference between contract relax and hold relax is that in the contract relax technique the muscle is contracted concentrically. This means that the muscle is moved in such a way that it temporarily shortens.
The contraction is released for a few seconds, and then the passive stretch is repeated for another 20 seconds. I just thought I was sharing a typo that could confuse readers. The chips list the 3 types of PNF before going into details. It is called: Hold-relax with antagonistic contraction, but in detail it is said that the agonist is contracted. I think the ball should be: Hold-relax with contraction agonist Thank you for sharing this information as it was very helpful in a project I`m working on! Stress relief is what occurs when the musculo-tendon unit (MTM), which affects the connected muscles and tendons, is under constant stress (Sharman et al., 2006). Muscles and tendons have viscoelastic properties in which they have properties of viscous and elastic materials. A viscoelastic material resists both linear shear and deformation when stress is applied, and returns to its original shape once the stress is removed from the MTU. As already mentioned, a phenomenon called “stress relaxation” occurs during a constant tension of the MTU. This reduces the force generated by the viscous material when it resists the stretching stimulus caused by stretching in the MTU.
As the viscous material loses its ability to withstand deformation over time, MTU slowly increases in length, a property MTU calls creep (Sharman et al., 2006). There is a limit to the distance at which a muscle can “crawl” because the longer an MTU becomes, the higher the passive torque (resistance of the MTU to stretching) and the stiffness of the muscle (Sharman et al., 2006). Although, when stretching is maintained, stress relaxation occurs and there is a decrease in passive torque and muscle stiffness that lasts for a short time (Sharman et al., 2006). It is a protective mechanism to prevent muscle tearing and maintain a healthy relationship between the contractile units of muscle sarcoma. When the CR method is used in PNF stretching, the contraction of the TM increases the traction load of the MTU and promotes the “creep” of the muscle fibers in an elongated orientation. This is similar to the CRAC method, except that the contraction of the antagonist muscle exerts more tensile force on the TM. Feland and Marin (2004) studied 72 subjects to determine whether submaximal contractions during the CR method of PNF on the thighs would provide flexibility gains comparable to MVIC. 60 of the subjects were randomly assigned to one of three treatment groups, which included 20% MVIC, 60% MVIC and 100% MVIC, while the remaining 12 were placed in the control group. Each subject in the first three groups performed three six-second sections of the CR method, all in their respective intensity, with 10-second breaks between each contraction for five days. .