Full Title: Affects of Aging on the Hamstring Group
Author: Sharon L. Johnston, RVT
Date of Publication: July 29, 2014
Research Paper Text:
As a dog ages significant changes occur which affect the function of their mind and the form and function of their body. Goldston & Hoskins (1995) wrote “elderly animals seldom have a single disease, but instead have a unique combination of multiple organ disease with varying levels of dysfunction” (pp. 3). (see table 1-2).
One of the most obvious and life altering examples of this process is deterioration of the musculoskeletal system.
Metabolic and degenerative diseases become more prevalent and muscle atrophy; a weakening or wasting away of muscle mass begins. While a small amount of atrophy occurs naturally due to reduced hormone production and changing metabolic rates, the two major causes are disease and disuse.
Diseases such as Cushing’s, neurotrophic atrophy and lactic academia are examples of processes that weaken the muscles and tendons, cause inactivity and hasten muscle atrophy. Painful conditions such as arthritis, hip dysplasia and intervertebral disk disease may also inhibit normal activity such as walking, running or playing. The longer movement is restricted the more detrimental it is to the rest of the body, most importantly the circulatory system.
Muscle tissue has a very high metabolic rate. A long term decrease in blood supply and nutrients seriously compromises the ability of all muscles and groups to function properly. One such group of muscles is the hamstring group.
Lateral muscles of the hip and thigh, the hamstring group is made up of three muscles; the biceps femoris, the semitendinosus and the semimembranosus. (see fig. 1.) A significant weight bearing group of muscles, actions of the hamstring group include extension of the hip joint, flexion or extension of the stifle and extension of the hock. Coupled with the longissimus group located in the front limbs, they are the most important muscle groups in relation to straightaway running.
The muscles of the hamstring group have shared and individual origins, insertions, innervations, blood supplies and actions.
All three muscles originate from the tuber ischiadicum with the biceps femoris also originating from the lower part of the sacrotuberal ligament. The biceps femoris inserts at the cranial portion of the tibia, the patella and the patellar ligament; the semitendinosus at the medial tibia and the semimembranosus at the distal femur and medial tibial condyle. Tendons from the femoral biceps and semitendinosus join tendons of the digital flexor and gastrocnemius to form the common calcanean tendon. Kainer & McCraken (2003), (plate 31).
Both the nerve and blood supplies to the hind limbs are extensive and complex. The nerve supply to the hamstrings arise from the lumbosacral plexus and include the caudal gluteal, common peroneal, tibial and sciatic nerves. The abdominal aorta which branches into the external and internal iliac arteries then to a network of veins is the vascular supply to the pelvis and hind limbs.
While the primary action of the hamstring group is extension of the hip joint, each muscle has its own function and action. The largest muscle of the group, the biceps femoris acts to extend the hind limb when rearing, kicking or propelling the body. The actions of this muscle affect all joints except those of the digit. The semitendinosus extends the hip and hock on a weight bearing limb while flexing the stifle of the non-weight bearing limb. The cranial aspect of the semimbranosus works to extend the stifle while the caudal aspect flexes the stifle. Both aid in hip extension.
When the muscles of the hamstring group are compromised whether due to injury, nervous system disruption or atrophy the impact is often immediately evident. The inability to bear weight on one or both limbs is the most common presentation. This weakness compromises a dogs’ ability to get up and down, climb stairs, walk or run. A stiff or unsteady gait, complete collapse and loss of proprioception are other common occurrences. Without intervention to delay the progression of symptoms, loss of hind limb muscle function greatly decreases a dogs’ lifespan.
Massage is a powerful, appropriate approach to intervene and prevent musculoskeletal damage. Using techniques to increase circulation and eliminate toxins we have the ability to help the dog achieve whole body wellness. While nothing can stop the inevitable decline of health due to aging, massage may provide an increase in our dog’s quality of life and optimistically a longer lifespan. It would be recommended to start massage sessions at early puppyhood and continue throughout their life.
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