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How resilient are you? Muscle activation, strength and the nervous system...

Updated: Apr 28, 2020

Physical resilience i.e. preventing injury or build up of pain, is reliant on the body's ability to withstand external forces. Whether that's bending down to pick up a watering can without 'doing your back in', walking on uneven ground without spraining your ankle, jumping down off a wall without injuring your knee, or even sitting at a desk all day in suboptimal posture without gravity increasing the load and fatigue of your neck muscles enough to cause neck pain/headaches.

So, how do we withstand these everyday forces that can lead to injuries or painful conditions?

There are two key points I want to highlight before continuing:

1) Pain itself is often multifactorial (meaning it is not solely one factor that causes it. Psychological/social factors and even other lifestyle factors such as lack of sleep or poor diet may increase our likelihood of being in pain).

2) Structure does not always govern the likelihood of injury/pain. Imaging now shows that the level of tissue damage or degeneration does not always correlate with pain levels experienced.

So if structure is not always a reliable way of predicting pain/injury, what else must we look at...

When looking at the musculoskeletal element of preventing injury/pain and optimizing performance, function is key.

And how do we assess function?

We test how well your muscles can co-ordinate movement and create strength, in response to external forces.

Observation of movement patterns such as bending, walking, squatting or overhead arm movement can be combined with manual muscle testing to work out suboptimal muscle recruitment patterns and areas of inhibition/weakness that may be leading to compensation elsewhere.

Manual muscle testing allows us to test various movements of the lower limbs, upper limbs and trunk. Variables can be changed, such as how much contraction or stretch the muscle is put in when tested at different ranges of motion. This allows us to test the muscle reaction and strength in different positions (because if we fall we're not going to land with every muscle at it's most optimal length- our leg may be stretched on one side and our arm may be contracted on the other!). In terms of performance, when a cricket player bowls the ball his trunk will be rotated and his arm extended... we can use manual muscle testing in these positions to see how strong and effective he is in this position. In each testing position, the practitioner sees whether the patient can activate muscles in a controlled manor, without compensating and without the muscle strength fading away after a couple of seconds.

Why does muscle activation/strength/function matter?

Muscles attach into and help stabilize joints, so inhibition/weakness can lead to poor joint centration and therefore injury. Weakness in one area often leads to compensation elsewhere. Tightness or joint restriction may develop, adding to pain.

We know muscle strength is a key factor in osteoporosis and preventing falls. But the beneficial effects of muscle strength may go beyond just preventing musculoskeletal complaints alone...there have even been studies linking decreased muscle strength with all cause morbidity.

How is muscle activation, co-ordination and subsequent strengthening achieved?

The neurology...

Most of our movement (at least 90%) is done under unconscious control. We do not have to think about taking each step to walk, we just do it! Each muscle produces the exact amount of force or stretch it needs to achieve to allow each individual movement to take place in a coordinated manor.

Many movements do not rely on processing by the brain, they are brought about solely by spinal cord driven reflexes...

  • The stretch / myotatic reflex takes place when a muscle is suddenly stretched, causing a subsequent contraction of the muscle. This is the reflex involved in the knee jerk reflex. The Golgi tendon reflex is the opposite, taking place when a muscle is suddenly contracted, causing relaxation to prevent injury.

  • Reciprocal inhibition takes place when one muscle relaxes to allow it's antagonistic (opposing) muscle to contract.

  • The (flexor) withdrawal reflex takes place in response to painful stimuli, heat/cold or touch. If you touch something hot, you automatically rapidly withdraw your hand from it. This relies on reciprocal inhibition as the flexors contract and extensors relax. Interestingly, at the same time the opposite happens on the other side of the body with the extensors contracting to allow stability e.g. if you stood on a pin, the other leg would need to stay straight to allow you to stay upright! (Crossed extensor reflex).

These reflexes are all key in preventing injury.

It is afferent input (nerve impulses to the Central Nervous System i.e brain and spinal cord) from proprioceptors that supplies the bulk of information that is responsible for these reflexes.

Proprioceptors are found in skin, muscles, tendons and ligaments and help provide position sense. Muscle spindles are the proprioceptors found in skeletal muscle tissue and are responsible for detecting changes in length.

From the spinal cord, our motor neurons then send out efferent input (away from the CNS) to the muscles, causing them to contract.

Even at rest, each motor neuron is firing around 50 times per second! So think how much input is constantly being received and turned into output! (At maximum effort, each is firing around 500 times per second!).

Muscle spindles are constantly sending input to the CNS, based on external conditions and forces. This controls our muscle tone constantly (even when sitting still) and moves/co-ordinates skeletal muscle unconsciously.

So you can see how complex the neurology behind movement and posture is!

Basically, we need good input from the muscles and other tissues to achieve good muscle output!

Sub-optimal sensory input (such as poor proprioception) = sub-optimal motor output (muscle inhibition/weakness) which may lead to compensation elsewhere.

So, the ultimate question is:

How do we actually improve muscle activation and therefore control and strength?

1) Identify areas of muscle or movement inhibition (by manual muscle testing and/or movement control observation). Read my other blog post of 'the fundamentals of exercise progression' to gain more insight into Functional Movement Screening.

2) Work out why they're inhibited / where the inhibition is coming from e.g. locally from the muscle itself? From the spinal joint/nerve that supplies that muscle? From a region distal to the inhibition? From a systemic factor that may be causing generalized inhibition/weakness? From a previous injury? Inhibited just due to current pain?

3) Change the input e.g. by joint manipulation/mobilization/massage/dry needling/kinesiotaping/specific motor control drills.

4) Retest! Often an immediate change can be seen.

5) Continue building strength and cementing optimal movement patterns with resistance training/plyometrics/Pilates/Yoga or whatever floats your boat!

Many Chiropractors including myself, as well as other musculoskeletal experts, use functional testing such as movement screening and manual muscle testing to assess patients. If you feel you could benefit from this type of assessment feel free to ask around to find a practitioner who works in this way.

Keep strong and keep healthy!

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