Is a weak looking upper limb performance always due to weakness?

This past week during one of my seminars, I observed a pair of course participants struggling to improve a basic exercise together. The exercise in question was the low load, global proprioceptive task of a standing wall press. The task is simple: the starting body posture is maintained as the body moves towards the wall through bending arms, and then away from the wall as the arms straighten. It helps us to see whether an individual really can feel and control the relationships between upper, central and lower body without the compensatory feedback or “fixing” of high muscle activity.

The young and physically substantial looking young healthcare professional attempting this just couldn’t respond to the cues of his partner. He was unable to maintain his central axis throughout the movement, making the movement appear weak and incoordinated, yet he was surely strong enough. What was going on?

The movement pattern that he was exhibiting was consistent, and appeared to be driven by his head in both directions. His head would drop forward, associating neck flexion with elbow bending as he moved towards the ball, and then he would drive his head back as he straightened his arms. Ah – the symmetrical tonic neck reflex (STNR).

What is an STNR?

This takes us back to our early development. The STNR is a transitional reflex which helps a baby to progress from lying on the floor to vertical positions in order to allow new, purposeful motor activity. It is necessary for postural development, and is generally thought to emerge at somewhere between 6-9 months of age. It allows a child to get up on all fours, but then to creep or crawl successfully, it needs to be integrated so that the limbs can move independently of head position. In the standard paediatric literature this is said to occur at around 11 months.

How does an STNR work?

The STNR is driven by head position. When the head drops forward, the movement impulse is for the arms to bend and the legs to relatively straighten. When the head moves back, the impulse is for the arms to straighten and the legs to bend.

What does this have to do with a normal, healthy young man?

Well, in this case, and in a surprising number of perfectly normal people, the STNR is still present. I usually see it provoked by press up/out type activities, or in loaded upper limb activities. Sometimes, as in this case, the reflex is the driver for the movement. i.e. the head moves and the limbs respond. In others, where the task involves supporting the body on straight arms, particularly in horizontal positions, as soon as the head drops, the arms bend. This is often interpreted as arm weakness, but in fact it is the reflex in play.

This type of presentation often accompanies neck, shoulder and thoracic pain in adults, as they are unable to achieve sound, supported force management throughout their body.

But surely the reflex is integrated in an adult?

Well, actually not necessarily. Sometimes a sensory processing hiccup interrupts the process. Those who skip the creeping and crawling stage may not have managed to integrate the STNR.  Even if that stage had been successfully completed, the reflex never actually disappears, but becomes integrated with the rest of our nervous system. Trauma, either physical or emotional, sustained stress triggering unmodulated sympathetic nervous system activity, or an over or under reactive sensory state can all cause the STNR to re-emerge.

What do I do if I spot this with a client?

The first thing to understand is that the primary driver for the movement dysfunction is not weakness, but appears as weakness

The next thing is to add lots of sensory input, and focus on a more open, lengthened posture. This young man was capable of squatting a good amount of weight, but without the sensory stimulus of loading, was unbalanced and not at all grounded. People like this will gravitate towards quite static loaded exercises, but are not good at dynamic motion, or have stopped this type of activity due to injury.

It is important to increase the amount of proprioceptive and balance work in their programmes, and to shake out the excessive limb muscle tension that they frequently carry as a compensatory feedback mechanism. Limb shaking itself can be a useful source of sensory input.

Be disciplined about head position – cue to stay long through the back of the neck to avoid posterior compression. The head should be balanced in line with the body. Challenge this in different body orientations: mix up positions that are face up, face down or vertical. Alternating cross body patterns for arms and legs on the floor or in standing, and tasks such as reciprocal arms movements with pulleys in a standing position with hips and knees soft and a balanced head position would also be appropriate.

If you’ve read this far, I salute you – many will have switched off once I started talking about baby development, but once you spot your first STNR in the gym or clinic, it will make sense of a number of clients’ presentations!

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