In the previous blog, we discussed the power of corrective exercise and how it can be an effective solution for pain management. “Corrective exercise can feel like a miracle to those who have experienced troublesome pain due to acute muscle imbalances. When a tight muscle is identified and sufficiently addressed, pain can be IMMEDIATELY reduced.” While the blog went into great detail about corrective exercise, muscle imbalances, what they both are, and how one addresses the other, the blog was an introductory work and requires a follow up entry detailing the magical mechanism behind corrective exercise. This is that follow up.
RECIPROCAL INHIBITION
Reciprocal inhibition is an essential tool used in the field of corrective exercise. Without it, rehabilitation efforts would be prolonged and the pain a client or patient experiences would take longer to subside.
Reciprocal inhibition is an easy concept to understand. In laymens terms, when one muscle contracts, reciprocal inhibition causes the opposite muscle to relax. It does this by means of muscle spindles, the spinal cord, alpha motor neurons, and inhibitory neurons. When a muscle experiences any type of resistance that leads to an increase in length, sensory neurons called muscle spindles send a signal to the spinal cord. In turn, the spinal cord activates alpha motor neurons, sending a signal back to the muscle, telling it to contract. The original impulse from the muscle also activates inhibitory interneurons in the spinal cord, sending a signal to the muscle’s antagonist, telling it to relax. The result of this signaling is force production and movement, depending on the scenario. If reciprocal inhibition did not take place, one may not only have to overcome external resistance but the resistance of the opposing muscle attempting to contract simultaneously. Movement and force production would be hindered and possibly thwarted.
Within the field of corrective exercise, professionals can use reciprocal inhibition as a powerful tool to immediately relax painfully overactive and troublesome muscles. The only problem is that, though reciprocal inhibition is straight forward, it is often misapplied as a treatment and yields less than satisfactory results.
PROPERLY APPLIED RECIPROCAL INHIBITION
When using reciprocal inhibition as a method for immediate relief from a painfully overactive muscle, one must consider exercise selection. It is not enough to arbitrarily pick exercises. Because of motor unit recruitment, not all exercises produce the same amount of reciprocal inhibition. In regard to pain relief, it can be guaranteed that your client will want the maximum amount of reciprocal inhibition so they can achieve the maximum amount of relief. In order to select the best exercise for the job, a professional must understand strength profiles, long and short muscle positions, and resistance profiles.
Strength Profiles
All muscle have a strength profile. A strength profile is the ability of a muscle to produce force throughout its contractile range. This is usually illustrated with a graph and produces the image of a bell curve. Every muscle in the body is weakest at its extreme lengths and strongest at its midrange. In the weaker positions (the absolute shortest position and the absolute longest position), more fibers are likely to be recruited to overcome significant amounts of resistance. The more fibers one can recruit, the greater activation of muscle spindles, the more reciprocal inhibition one will experience. This leaves the practitioner with two positional options to put the painfully tight muscle’s antagonist in: super short or super long.
Short and Long Muscle Positions
To echo my blog, How to: EXERCISE SELECTION, every muscle in the body has a stretched (lengthened) position, a contracted (shortened) position, and a relatively neutral (natural) position. In order to find these positions, one must know the myology of the muscle(s) in question. Let's look at the example from the How to: EXERCISE SELECTION blog (pictures included for visuals). If you are trying to find the long and short position for the hamstrings, you must know what they collectively do. The hamstrings cross over both the knee and the hip joint. If you want the muscle group short (think fully contracted), the hip needs to be in extension and the knee in flexion. If you want the muscle group long (think stretched), the hip needs to be in flexion and the knee in extension. Examples of exercises that illustrate these positions are the prone hamstring curl for the shortest contractile position and stiff leg deadlift or seated hamstring curl for the longest contractile position.
The shortest position the hamstring complex can be in will be the longest position its antagonist muscle, the quadriceps, can be in. The longest position the hamstring complex can be in will be the shortest position for the quadriceps. Do you see where I’m going with this? If you are attempting to gain relief in a painfully overactive and tight muscle, which position do you want that muscle to be in? Do you want it in a seemingly stretched position or a seemingly contracted position? I hope you have correctly chosen the former. The goal is to relax the painful muscle and give it length so the tug is not as great. In order to do that, we need it as relaxed and lengthened as it possible. If you have a patellar tendon pain, your quads are too tight. Using an exercise that puts the hamstrings in the shortest position will give the quads length and produce a significant amount of reciprocal inhibition being that the hamstrings will have to recruit a greater amount of motor units to overcome one of their weakest positions.
Resistance Profiles
Finally, the last thing to consider when choosing an exercise in order to properly apply reciprocal inhibition is the resistance profile. The resistance profile is the measurement of the relative tension in the muscle throughout the whole range of motion in a particular exercise. Basically, it is identifying where a particular exercise is “heaviest” and where it is “easiest.” For example, a banded prone hamstring curl gets heavier as one concentrically contracts through the exercise. This is because the tension in the band increases as you stretch it. This means that the banded prone hamstring curl has a resistance profile that overloads the shortest position of the muscle and then drops off as the hamstrings lengthen eccentrically. The banded prone hamstring curl could potentially be an ideal exercise for patellar tendon issues because the hamstring complex is being asked to do the most work in the position it is weakest in. This, again, will require more fibers to recruit and thus more muscle spindles, sending a whopping inhibitory signal to the quads.
Though overloading the shortest position of a painful muscle’s antagonist may sound favorable, there are some things to keep in mind when choosing a resistance profile. First, know that if a client has a muscle that is painfully overactive, the antagonist muscle is probably extraordinarily weak. This means that if you heavily overload the shortest position of the muscle, it may be too much for the client. Adjusting the resistance profile away from the shortest position may allow them to get further into the position. The second thing to consider is that, if significantly overloaded, the weak muscle may experience some mild to severe cramping during the prescribed exercise. A good rule of thumb is that a tight muscle causes pain and a weak muscle cramps. This occurs because of the lack of contractile efficiency in the weak muscle. Again, adjusting the resistance profile away from the shortest position may be a better option to eliminate the possibility of or the discomfort caused by cramping.
MANUAL RESISTANCE EXERCISES
Considering the above, it may sometimes be more efficient and beneficial for a corrective exercise professional to be the resistance in a treatment exercise. Being the resistance for a client can allow for greater control, more feedback, a wider range of motion, a customized resistance profile, and more precision. In the example of the hamstrings and quads, a manual resistance exercise could look like a prone hamstring curl on a massage table or on the floor. The professional could have the client bend at their knee (knee flexion) and contract their glute max slightly to stabilize the hips in hip extension. In this short hamstring position, the professional could then begin to pull the client’s lower leg out of knee flexion and into a more extended position. Manual resistance exercises could save a professional the time and thought energy used to come up with and set up an adequate treatment exercise.
CONCLUSION
Reciprocal inhibition is a mighty and magical mechanism that can be used to immediately alleviate pain due to an overactive muscle. Because of muscle spindle signaling, an agonist muscle can instantly tell its antagonist to relax. Furthermore, if that agonist muscle is put into its shortest position and then asked to contract considerably, additional muscle spindles will be activated and a greater inhibitory signal will be sent to the antagonist. Understanding that exercise selection matters from a reciprocal inhibition approach will give any professional a greater opportunity to offer relief to a client. The lack of adequately selecting an exercise will not elicit such an effect and pain may linger immediately after the treatment exercise.
After hyping up reciprocal inhibition in this post, it is important to note that, while reciprocal inhibition can offer immediate relief, this does not permanently “solve” the issue. The bottom line is that there is pain because a tight muscle is winning the game of tug-of-war around a joint and the opposite (antagonist) muscle is losing. The tight muscle is overpoweringly strong. Until an ample amount of strength is established in the weak antagonist, pain may come and go. Continually training the weak muscle and emphasizing its shortest contractile position will reduce the frequency of pain and quickly eliminate it all together. In the meantime, muscle activations in the shortest position can be prescribed to clients as “home remedies” to thwart pain in its tracts when it is attempting to creep in.