Having recently completed a course in manual muscle testing, which had a focus on assessing the muscle during eccentric loading (while the muscle is lengthening), I was left with a number of questions unanswered or partially answered. For this reason I went away and did some digging around!
Eccentric loading of muscle is very important for a number of reasons. However in this case, of primary importance is the recognition that during this movement the muscle is under more strain and thus is giving more feedback to the nervous system. This has been reflected most practically with resistance training, where there has been a shift toward a greater emphasis on the negative (eccentric) phase of the exercise, thus getting a higher stimulus to the muscle and better adaptive response to the training.
The vast majority of people define proprioception as a sense which allows us to identify what position our body is in. For example, we do not have to look at our hand to be able to know if our fist is clenched or open. However this does not tell the full tale. King (2008) describes proprioception as the continuous feedback of millions of sensors in the skin, muscles, joints, ligaments and tendons as well as our 5 main senses of sight, touch, hearing, taste and smell. This allows us to assess our environment and adapt to its changing nature, ultimately allowing us to move.
Which brings us nicely to reflexes. Again many people have been to their GP and experienced the knee jerk reflex, where by someone (GP) taps you just below the knee cap and in response the leg straightens. During this sequence of events in which the tap below the knee creates the straightening of the leg a number of things occur, which can be seen in the image below:
This however, is an isolated case and as King (2008) rightly points out, we are constantly being stimulated by external forces from the surrounding environment. Every time we move, jump or run we are essentially stimulating the stretch receptors – it is our reflexes which govern our response to those external forces. Again taking King’s (2008) example:
‘Imagine a gymnast landing on a mat after a somersault. With her kegs bent, she is ready for impact. As her feet touch the mat, her knees bend further. The quadriceps muscle on the front of her thighs start to stretch. Sensors within the muscle detect the speed and the force of the stretch, and fire rapidly. The nerve then carries the massively increase rate of firing back to the spinal cord, where a direct connection is made to nerve that control the tone (strength) of the muscle. The massive increase in activity is transmitted straight back to the quadriceps, causing it to contract instantly’.
If this force was not adaptable i.e. the stretch receptors were not there to change the tone of the muscles, the girl in the above example would either crumple to the mat with not enough muscle force or jump straight back up with too much muscle force. Therefore it can be argued that it is the reflexive response to stretch stimulus which protect us from everyday injury.
So we have stretch sensors and reflexes which control muscle tone and movement allowing us to adapt to our ever changing external environment, so why does injury occur if we have this protective mechanism in place? Especially to what appears to be trivial external forces, such as picking a pen up off the floor? Is it loss of strength or flexibility? Probably not as they are a result of long term physiological adaptation, leaving us then, with a loss of control. But where does this loss of control come from?
As we can see from the example above, proprioception drives muscle tone and adaptation to the external environment. Loss of normal proprioceptive input would lead to altered muscle tone and poor adaptation to the external environment, ultimately leading to injury from what appear to be trivial external forces. To state this quite clearly:
‘Aberrant proprioceptive input leads to neurological inhibition of skeletal muscle and results in poor adaptive range’ (Sandstrom, 2012)
Both Sandstrom and King suggest this aberrant proprioceptive input can come from poor joint mechanics (hyper/hypo mobility), muscle hyper/hypo-tonicity, muscle trigger points, fascial adhesions, pain and inflammation.
Looking at the spine, most people know that it is made up of essentially what is a number of blocks all stacked on top of each other. Focusing specifically on the lower back or lumbar spine, we can identify a number of key characteristics which leave this area vulnerable to injury. Firstly if we look below the lumbar spine we have the big solid pelvis. And if we look above there is the big relatively solid rib cage and thoracic spine. These two bony structures offer rigid support to those areas of the spine, however looking again to the lumbar spine the only thing supporting it, are the muscles which surround it. So if these muscles are not working ‘properly’ i.e. having aberrant proprioception, this would leave the back more vulnerable to injury.
Looking more closely at the lumbar spine, it can be said that there are two, well integrated, stabilization systems. There is what I like to call the global stabilization system – the big muscles which run up the back, around the sides and up the front of the body between the pelvis and rib cage. And secondly – the local stabilization system, which consists of the small muscles running between blocks or vertebrae of the spine. Thinking about the above example where by an injury occurs as a result of picking a pen up from the floor. McGill (2001) suggests that an event he refers to a ‘buckling’ occurs within the spine. He suggests that there is a momentary reduction in neural activation to one or more of the deep intervetebral muscles, resulting in this spinal segmental ‘buckling’ (slight rotation of a spinal segment), leading to tissue irritation or injury.
Putting all this together, if we can identify neurologically/proprioceptively inhibited muscles using eccentric manual muscle testing, we can identify those areas of the body vulnerable to injury. As part of the course I undertook we were taught to be able stimulate those inhibit muscles and thus prevent injury. Equally, once stimulated, as McGill (2001) suggests, it is important to continue to maintain and improve muscle tone and control to further reduce the risk of injury.
King, S. (2008) Live without pain, A new theory on what’s wrong with you, and how to fix it. Naturality Press, UK
McGill, S. M. (2001). Low Back Stability: From Formal Description to Issues for Performance and Rehabilitation. Exercise and Sport Science Reviews. 29, 26-31.
Sandstrom, U. (2012) Manual Muscle Testing – a window to the nervous system, Seminar notes