Four cases of subtle neuromuscular weakness in horses and how to asses and correct them using kinesiology.

Subtle neuromuscular weakness is common in horses. It may go undetected except perhaps as a non-lameness performance or training problem that persists despite efforts to address nutrition, saddle fit, training regimen, conditioning, etc. Once identified, many of these weaknesses can be easily corrected, sometimes in a single treatment. The material presented here is based largely on human Applied Kinesiology (AK) techniques.

I have adapted AK to horses over the last four years and have collected data and observations from approximately 150 Thoroughbred racehorses between the ages of one and four, as well as sport, pleasure, and rescue horses of different ages and breeds. A number of these techniques require the use of a surrogate, knowledge of manual muscle testing (MMT),^1,2 surrogate muscle testing (SMT)³ or a “strong/weak” testing technique.

Lower motor neuron dysfunction

Neuromuscular weakness can result from either upper motor neuron (UMN) or lower motor neuron (LMN) dysfunction. This article focuses on LMN-related weakness. LMN cell bodies, also called ventral horn motor neurons, are located in the ventral horn of the spinal cord. These neurons form part of the ventral nerve root of spinal nerves and travel via spinal nerve dorsal and ventral branches to provide motor innervation and trophic factors to specific muscles, as well as receiving sensory input from joints, proprioceptors, and a variety of superficial and deep cutaneous receptors. They contain two types of motor nerve fibers: alpha and gamma. Alpha motor neuron (AMN) fibers are large, heavily myelinated, and innervate the extrafusal muscle fibers of skeletal muscle. Gamma motor neurons are smaller, less myelinated and specifi c for the spindle cells.

1. Neurologic disorganization or “switching”

The most common neuromuscular weakness I encounter is related to neurologic disorganization, more commonly called “switching”. This problem often appears as a disruption in left to right communication within the brain. Switching can be demonstrated as a regular or cyclical fluctuation in muscle strength of (and presumably LMN input to) the left and right sides of the body, or different regions of the body, with observed periodicities from approximately five to more than 60 seconds. Using direct manual muscle testing (MMT) and surrogate muscle testing (SMT), it is possible to observe several different patterns. Nearly 100% of horses I’ve tested in the last four years have been positive for switching.

Neurologic disorganization or switching is most often caused by shifting of the skull bones, called a cranial fault. This changes pressure along, and mobility of, the skull sutures. It can easily occur when the head is bumped or hit, or when excess pressure is applied to an area. Even mild pressure, applied at the right angle, can cause a cranial fault. Dental issues, TMJ problems, a shift in the position of the hyoid apparatus, heavy metal toxicity, and sacral issues may also cause switching. Most horses I have examined had one or more cranial faults; of those, most had a sagittal suture fault on the midline at the poll, involving the suture between the left and right parietal bones. This cranial fault is specifically associated with weakness of the rectus abdominus muscles. In horses with dropped back, sway back, or poor engagement of the abdominal muscles (and potentially those with overriding spinous process – “kissing spines”) the rectus abdominus may be neuromuscularly inhibited. Correcting the sagittal suture fault will often restore normal muscle function with improvements seen immediately or in a short period of time.

Assessment: Using MMT or SMT (see below), first check for switching, usually a five-second pattern. Test for a strong muscle, then touch (therapy localize, TL) the midline at the poll and see if the indicator muscle goes weak, indicating a problem at that location. Also check both the left and right rectus abdominus.

Correction: Put finger and thumb on either side of the midline at the poll, straddling the sagittal suture. Very gently, using light tension, check whether opening (lateral) or closing (medial) tension makes the weak indicator strong (usually the suture needs opening tension). Maintain light tension for three to five seconds, then release. Check your indicators to make sure switching is resolved and TL is strong.

2. Weakness related to previous injuries

The injury recall technique (IRT) was created by podiatrist Dr. Robert Crotty, and further developed by Walter Schmitt, DC, DICAK, DABCN, as a means of finding and addressing a local or remote area of previous trauma that’s creating neuromuscular weakness and/or pain at a specific site. The mechanoreceptors of the foot, ankle, and neck are particularly important in supplying afferent information to the brain for postural balance and equilibrium. Extension of the head and neck is one of the reflex responses to trauma. Memory encoding of head and neck trauma appears to reside in a cervical extensor reflex pattern.4 In the horse, the IRT neck correction works well for injury on any part of the body, provided the horse is standing.

Assessment: Using SMT or other strong/weak muscle test (see below), test a muscle at the problem or suspected problem area. If the muscle tests weak/inhibited, activate the muscle spindle cells by stretching the fibers in the middle third of the muscle belly using both hands, along the long axis opposite the direction of contraction. This technique is called autogenic facilitation (AF). If the AMN control mechanisms are functioning normally, a weak muscle will strengthen after AF. If it does not, then IRT is needed.

Correction: The basics of IRT are to find and connect the neurologically active area of injury (NAAI) with the affected muscle, while reversing the head and neck extension trauma reflex. This is done by touching (therapy localizing, TL) the problem area, which should test weak, then over the whole body to identify locations that when touched make the weak muscle test strong. TL identifies neurologic connections between two things but not the nature of those connections. Once the NAAI is mapped out, the horse is asked by way of treats or gentle encouragement to several times fl ex the head and neck, particularly the occipital-atlantic (O-A) joint, while the cutaneous receptors of the skin overlying the weak muscle and the NAAI are stimulated simultaneously by light snatches or pincering with the fingertips. Retest the original muscle afterwards. It should now be strong. In most cases, only a single treatment with IRT is needed unless there is repeated injury, a deeper layer of trauma, or other issues involved.

In some cases, particularly involving head or neck injuries, surgical procedures, scars, IV catheterization, injection site issues, TMJ, hyoid or dental issues, the muscles of the surrounding area may all test strong. In this case, put the horse’s head and upper cervical vertebrae into extension (particularly the O-A joint) by raising the head and extending the nose forward. With the horse’s head in this position, recheck the muscles and see if there is now one that is weak or inhibited (positive test). TL the entire area thoroughly to find the NAAI, then fl ex the horse’s head and neck while stimulating the two areas, as above.

IRT can be done sequentially over days, weeks or months, as new areas with an IRT spindle cell pattern will usually continue to surface for quite some time. This technique is also excellent for helping or resolving many chronic pain and scar issues.

3. Weakness association with vaccination injection sites

In evaluating and detoxifying almost 150 yearling and two-year- old racehorses, it became apparent that the area(s) on the neck around the site for vaccines and other injections was almost universally a site of apparent muscle atrophy and neuromuscular inhibition. Further (unpublished) work has shown that muscles outside the immediate area of the neck injection site can also be affected. This raises the question of an association between the injection of inflammatory chemicals such as formaldehyde, aluminum hydroxide, thimerosal, and chronic chiropractic problems and/or bony inflammatory lesions of the lower cervical vertebrae.

Assessment: With the flat of the hand, carefully palpate the sides of the neck from cranial to caudal to assess muscle tone and thickness. If there are areas of muscle atrophy, use SMT or one of the other methods described to assess neuromuscular status in the affected area.

Correction: IRT at the site can often improve or even resolve neuromuscular inhibition, as well as apparently improve local blood or lymphatic circulation. This is evidenced shortly afterwards by visual and palpatory changes in the character of the muscles at that site.

4. Paired muscle weakness: patterns associated with organs of detoxification 

Paired or bilateral muscle atrophy can frequently be observed in equine sport/racehorses as well as pleasure horses, and often involves muscles of the shoulders (deltoids, supraspinatus and infraspinatus), withers (trapezius), and particularly the dorsal hindquarters (gluteals and long head of the biceps femoris). The degree of muscle loss is sometimes surprising, considering the level of training and conditioning in some affected individuals, plus the fact that the gluteal muscles are the most powerful for running and jumping. If a neuromuscular circuit is inhibited, however, conditioning alone may not be sufficient to stimulate muscle development.

In human AK, muscle-organ and muscle-gland relationships have been identified by manual muscle testing of individual muscles and by finding the reflex point or tissue extract that counteracts weakness of the specific muscle. This suggests that at least some paired muscle weaknesses may be related to stress, dysfunction and/or toxicity of major organs of detoxification. Frequently encountered specific paired muscle weaknesses and their associated organs are: deltoids and lungs, pectorals (deep) and liver, caudal trapezius and spleen, psoas and kidneys, popliteals and gallbladder (horses lack a gall bladder but still produce bile and have a Gall Bladder meridian involved in liver and lateral hindquarter muscle function), gluteals and reproductive organs (removed in geldings and some mares). The spleen may have a role in detoxification because red blood cells sequestering lead, cadmium, mercury, zinc and other heavy metals are taken out of circulation in the spleen⁵, suggesting that some of these metals may accumulate or have local effects there.

A multiple muscle-to-gland relationship exists between the medial stabilizer muscles of the hindquarters and the adrenal glands. These muscles include the inner thigh muscles (adductors, gracilis and sartorius), the gastrocnemius and soleus, and the posterior tibial muscle, which becomes part of the deep digital flexor tendon, with an apparent functional association with the suspensory (interosseous) ligament (my unpublished observation). This association means that a problem with the adrenal glands, such as stress from shipping, hard training and showing, inadequate nutrition, or environmental chemicals, affects those specific muscles, causing dysfunction leading to weakness. The reverse is also true: weak muscles from injury or another cause can also impact the associated gland or tissue.

When organ-muscle association is the main reason for neuromuscular weakness, circular rubbing of the associated neurolymphatic reflex point can often bring immediate improvement. Neurolymphatic reflex points were discovered by oeteopath Dr. Frank Chapman in the 1930s. When stimulated, they were observed to cause rapid improvements in organ or gland function in human patients. Later, Dr. Goodheart found he was able to cause dramatic improvement in the associated muscle’s strength and function by rubbing the points.

In horses, similar improvement in muscle strength and nervemuscle function occurs when the appropriate neuro-lymphatic reflex is stimulated by circular rubbing. These points can be rubbed daily for three to five minutes as part of treatment or routine management of equine athletes, or in cases of severe organ, gland, or metabolic stress/dysfunction.

AK as a diagnostic tool

Applied Kinesiology is a diagnostic and therapeutic discipline that combines knowledge of muscle and nervous system function with biochemistry, anatomy, neuroanatomy, nutrition, cellular physiology and other biomedical fields. It can be described as functional neurology, providing a means to detect and correct a wide range of neuromuscular functional abnormalities stemming from previous injury or nutritional, biochemical, metabolic, or emotional factors. AK was initially developed 50 years ago by chiropractor Dr. George Goodheart. It’s now an international discipline primarily practiced by chiropractors, physicians, acupuncture physicians, and some veterinarians.

AK utilizes manual muscle testing (MMT) as a “window into the nervous system”. It tests the functionality of the AMN as a means of testing muscle strength and ability to respond to increasing force challenge.

The ends of a muscle are apposed by positioning the limb or body so that the origin and insertion are closer to each other and the muscle is in a relaxed but slightly shortened position prior to testing. The muscle is challenged by a gradually increasing force over three to five seconds and opposing the normal action of the muscle. A “strong” muscle resists the challenge; a “weak” or neuromuscularly inhibited muscle is not able to maintain the contracted position against the challenge.

Loss of input (“weak test”), or deafferentation, can be caused by trauma, both accidental and surgical, chemical toxins, nutritional imbalances or deficiencies, structural issues such as subluxations, or even emotional and psychological factors. Partial deafferentation of AMN impulses results in muscle weakness with or without significant atrophy and may be reversible; complete deafferentation results in paralysis and may be permanent. After corrections, the muscle will test “strong”.

References for AK techniques

Cuthbert SC, Rosner AL, McDowall D. “Association of manual muscle tests and mechanical neck pain: results from a prospective pilot study”. J Bodyw Mov Ther., 2011, Apr 15(2):192-200.

Pollard HP, Bablis P, Bonello R. “Can the ileocecal valve point predict low back pain using manual muscle testing?” Chiropr Aust, 2006, 36:58-62;

Jacobs, G, Franks, T, Gilman, G. “Diagnosis of thyroid dysfunction: applied kinesiology compared to clinical observations and laboratory tests”. J Manipulative Physiol Ther., 7(2):99-104.

Conclusion

Using these techniques is very often clinically rewarding and may help resolve chronic issues related to muscle weakness and dysfunction in horses.

References