Understanding Atrophy Muscle atrophy—or muscle wasting—is a medical term defined in its most simple terms as a decrease in muscle mass. There are generally two forms of muscle atrophy; disuse atrophy and neurogenic atrophy. Both present themselves in a similar fashion but have signifi- cant differences in their cause. The former is a loss of muscle due to lack of physical activity while the latter is due to a problem with the nerves that connect to the muscle itself. Muscle definition can actually be a form of atro-
phy—but it is negative definition in this sense. Positive definition is development of muscular conformation as expected during proper training; negative defini- tion happens when defensive contraction occurs to counteract a poorly fitting saddle. This negative muscle definition is considered ‘hypertonic,’ which means the contraction phase of the muscle(s) is unnaturally long and in a state of abnormal tension. This results in tight, cramped and painful muscle development—which can look like atrophy. Disuse muscular atrophy is the most common type of
muscle wasting. Neurogenic muscular atrophy, often the result of injury to or disease of the nerves that connect to the muscle, is much less common but far more diffi- cult to treat. Neurogenic muscular atrophy can develop when
interruptions occur in peripheral motor nerve function. Usually not all the motor fibers supplied by the nerve undergo atrophy; some remain relatively normal. A severe prolonged neuromuscular blockade can induce neurogenic muscle atrophy. Although atrophic cells may have diminished function, they are not dead initially. However, atrophy may progress to the point at which cells are injured and die. Ischemia is the medical term for an inadequate blood
supply to an organ or part of the body and occurs due to the reduction of blood flow to the capillaries because of pressure—as is often the case with a pinching saddle that is too small in the gullet channel, or too tight over the withers and shoulder because of a tree that has an incorrect angle and width. In ischemic tissues, if the blood supply is inadequate even to maintain the life of shrunken cells, cell injury and cell death may result. Muscle atrophy in the shoulder area of the horse
even has a common name “Sweeney shoulder.” It is caused by damage to the suprascapular nerve that controls the supraspinatus, infraspinatus and triceps muscles. This condition may also be caused by a sudden movement or weight change from the front end of the horse to the hind end of the horse, such as in polo or jumping events. Over 100 years ago, when horses were the primary
source of transportation, Sweeney shoulder was caused by the heavy harnesses horses had to wear while pull- ing carts and buggies. These harnesses would pinch
An incorrectly fitted gullet plate puts constant pressure on the side of the withers, resulting in the formation of this stress line due to the ‘defensive’ contraction of the trapeziums muscle.
Warmbloods Today 51
The trapezius muscle can be inflamed from an incorrectly angled tree point/gullet, resulting in this bulge and nearby hollow behind the withers.
Somewhere in this horse’s past an ill-fitting saddle caused damage noted by the white hairs.
Example of muscle atrophy behind the saddle.
Photos courtesy Schleese Saddlery
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