JHH Physiotherapy Research Digest: spotlight on multifidus of the equine spine

Question: does active exercise improve the size and symmetry of the deep stability muscle of the equine spine, multifidus?

Short answer, yes it does!

Long answer, read on!

Stubbs and others completed a key study evaluating the effect of particular exercises on the size and symmetry of a very important muscle in the equine spine called multifidus. This paper was published in the Equine Veterinary Journal in 2011.

 

Why is this research important?

Multifidus is a muscle which is found in the human spine as well as the equine spine and other vertebrate species. Studies on humans experiencing spinal pain have shown that this muscle can atrophy (get smaller in size) on the affected side and become asymmetrical between either side of the body. In addition, multifidus atrophy and asymmetry is also seen in conditions such as spondylolisthesis, facet joint osteoarthritis and disc injury. Keep in mind the term ‘use it or lose it’ when considering muscle function and structure – when we don’t use a muscle effectively enough or often enough, it will decrease in size and become less effective at its job, which may be to stabilise a joint or to mobilise a joint. Interestingly, in the situation of spinal pain, this atrophy is very specific to this particular muscle and doesn’t tend affect other spinal muscles. Typically neighbouring spinal muscles will become overactive in an attempt to compensate for a weakened multifidus muscle. For humans and animals suffering from back pain, the more superficial erector spinal muscles will often be tense and tender on palpation. In the case of longstanding pain and movement dysfunction, these muscles may hypertrophy and become larger as a result of working overtime for prolonged periods of time.

Research on pigs has shown that a similar process occurs in this species as per the human species. After experimentally induced disc injuries, changes to the multifidus muscle were seen within three days - illustrating just how quickly muscles can change as a result of injury, pain and changes in movement patterns. Furthermore, research on humans has demonstrated that even when pain resolves post injury, multifidus doesn’t naturally return back to its former condition without focused rehabilitation.  This may lead to reduced spinal strength and stability and is likely to increase the risk of re-injury in the future. This explains why recurrence of back pain is so common in both human and horses – particularly for those who don’t see a qualified physiotherapist post injury, or don’t do their home exercise program!

On a more positive note, research on humans has shown that performance of specific motor control exercises incorporating both dynamic (move) and static (hold) components to the exercise improves both muscle bulk (size) as well as symmetry.

The purpose of this study was to evaluate if dynamic mobilisation exercises have a similar effect in the horse as is seen in the human species.

Multifidi wikipedia.png

Multifidus of the human spine

Image source: Wikipedia

Multifidus in focus…

Multifidus is an important muscle in providing active stability for the spine, linking together two or more vertebrae. Ligaments, joint capsules and interlocking vertebral joints provide passive stability to the spine and the musculotendinous unit provides active stability.

The deep fibres of multifidus will tense before movement, acting in a preparatory manner to help tense the spine and prepare the body for movement of the limbs. This preparatory muscle activation has been demonstrated in human studies. The more superficial fibres which typically span multiple vertebrae have a greater role in controlling the small movements which occur at each intervertebral joint in the spine.

Multifidus is an important deep stability muscle of the spine.

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Multifidus of the equine spine

Image source: Veteriankey

 
Baited stretches

Baited stretch

Image source: practicalhorsemanmag

Study methodology – so what did they do?

Eight healthy Arabian riding horses were used in the study. They were confined to a stable overnight and a small dry lot during the day, throughout the study. The size and symmetry of each horse’s multifidus was evaluated at specific levels in each horse’s thoracolumbar spine using ultrasonography. Each horse participated in an exercise routine which involved cervical spine movement in several directions – three different flexion positions, three different lateral flexion movements and one extension movement. 

The ‘chin to tarsus’ (chin to hock) is shown in the image here from practicalhorsemanmag. Each exercise involved a dynamic (moving) component and a static (hold) component. The exercises were performed a specific number of times daily, five days per week over a three-month period.

 

Results

Results of this study showed that the muscles of the horse’s spine respond to dynamic exercises in a similar manner to the human spine. The size of multifidus increased at the measured points throughout the thoracolumbar spine. In addition to this, symmetry of the muscles on either side of the spine improved at each of the six levels of the spine which were measured.

 

 

What does this mean?

This study showed that performing specific dynamic mobilisation exercises in the horse had a positive effect on the thoracolumbar muscles, an important deep stability muscle in the spine.

Human research shows that we need to allow ten to twelve weeks of rehabilitation to have an effect on muscle size and strength. This study provided ample time for muscles to develop and hypertrophy (grow in size / bulk) in response to exercise.

As we know from human research, there is an association between atrophy and asymmetry of the multifidus muscle and spinal pathology and potentially pain in the human species. Human research has also shown that the multifidus muscle responds positively to specific exercises which includes a dynamic and static component.

This study shows that specific dynamic mobilisation exercises, when performed at a specific intensity, frequency and duration of time, improve the size and symmetry of the deep stability muscle multifidus in the equine spine.


From a physiotherapists perspective…

 From my physiotherapy perspective, these exercises can be used intensively as a rehabilitative strategy or every few days as a means of maintaining strength, symmetry, function and performance of the horse’s spinal musculature.

In addition, running through these exercises is an excellent way to identify any asymmetry in your horse’s range of motion of the spine. If you identify that your horse has lost mobility in a particular direction or is unable to perform the exercise to the standard which he or she has in the past, it may well be an early warning sign of musculoskeletal issues. This is a good time to seek the assistance of your local qualified equestrian physiotherapist, before more significant issues arise which may negatively impact on your horse’s health and performance.

Remember the saying, ‘move it or lose it’! Research shows that it doesn’t just apply to our own spines, but our horse’s spine too. And, perhaps your hound’s spine also!

Reference

STUBBS, N. C., KAISER, L. J., HAUPTMAN, J. and CLAYTON, H. M. (2011), Dynamic mobilisation exercises increase cross sectional area of musculus multifidus. Equine Veterinary Journal, 43: 522-529.