The Signs of Pain
Horses behave badly mostly because they are in pain, and the humans responsible are usually unaware there is a problem, or they believe it is a training issue. Before pain becomes obvious, horses suffer in silence. The most common cause of pain is their bridles, bits, saddle, and rider imbalance. In addition to the original cause of pain, there will be several layers of compensatory pain.
The minimal muscle strain is small enough to go clinically unnoticed. Signs of muscle strain consist of subtle intermittent lameness, reactive to palpation, unwillingness to engage the hind end, mechanical lameness (mostly seen at slower gaits), heat, and swelling. Never have "all the checks" been done if the source of the problem has not been identified and eradicated. There is a reason horses are irritable and distracted. Check your saddle; poor saddle fit causes discomfort, pain, and possible permanent damage, according to Jochen Schleese, CMS, CEE, CSFT, saddle ergonomist.
Tightness and tension in the shoulders spell trouble for the tendons. The muscles of the foreleg make the tendon work. Tendons are the extension of the muscles to the joints which engage the leg to move. When the shoulder muscles are tight, they do not release completely; therefore, the flexibility is lessened. Because all muscles work together, tightness in one area transmits compensation to another muscle group, then another group, then another. The body functions as a unit and the wellbeing of one part depend essentially on the efficiency of the neighboring parts.
According to Erica C. McKenzie, BSc, Ph. D, Dipl. ACVIM, ACVSMR, an associate professor of large animal medicine at Oregon State University states, "Equine athletes have proportionally greater muscle mass than comparable athletic species..." "Thus, muscle problems can have a profound impact on performance quality."
Jack Meagher, Sports Therapist affirms, "...it is the modus operandi of covering up minor causes which leads to severe problems somewhere down the road." "Until it is realized that the muscular system (sixty percent of the horse's total body weight and the system responsible for motion) is a predominant cause of motion problems, many things will remain a mystery that shouldn't be mysterious at all." The mystery problems do not happen without a reason. If your horse is off, be sure to have a veterinarian check first. However, the failure to recognize the problem may be because it lies in the muscular system.
Bell, Catherine CHBC (Fall 2019) The IAABC Journal. Reflections of Pain in Equine Behavior. https://fall2019.iaabcjournal.org/
Larson, Erica. (2012, July 5). Muscle Problems Can Cause Poor Equine Performance. The Horse. Retrieved July 5, 2016, from http://www.thehorse.com/articles/29363/muscle-problems-can-cause-poor-equine-performance
Meagher, Jack (1985) Beating Muscle Injuries for Horses. Hamilton, MA. Hamilton Horse Associates.