As our dogs age some of them lose body mass. Their muscles appear to waste or atrophy. This condition is called sarcopenia which is literally translated as “poverty of flesh” but more accurately describes the loss of muscle mass and strength with age.

Why does muscle wasting occur in older dogs?

There appears to be two factors that affect muscle atrophy in older people and dogs. They are

• loss of muscle mass

• decline in muscle function

Loss of muscle mass

Loss of muscle mass occurs with changes in the metabolism of muscle protein. It is thought that a combination of muscle protein synthesis declining and an increase in muscle protein degradation leads to a reduction in the number of muscle fibres.

As dogs age, the rate of protein degradation through the normal programmed ageing processes increases.

Ageing also leads to a build up of dysfunctional mitochondria, the portion of a cell that converts food to energy, which is vulnerable to oxidative stress. The body’s “normal” function to remove dysfunctional mitochondria is impaired with age which in turn increases the level of oxidative stress in cells. Increased oxidative stress and dysfunctional mitochondria upregulates autophagy (the process for removing destroyed cells as a result of stress of protein degradation) and leads to a decline in the number and size of muscle fibres.

As muscle protein degradation accelerates with age, muscle protein generation slows. The number of satellite cells which are the precursors to skeletal muscle cells and the substrate required to regenerate muscle cells decrease with age in both humans and animals.

Muscle function

While muscle mass decreases as dogs age so too does muscle function – strength and performance. Loss of muscle function is associated with a decrease in muscle fibres and motor neurons. This can be attributed to a permanent loss of contact between the nerves and muscle fibres, thus, reducing the number of functioning motor units and causing a loss of function and disability.

Human and canine studies show that muscle atrophy selectively affects Type II “fast twitch” muscle fibres which may account for the decline in speed or performance in older dogs.

Another factor that affects aging dogs’ muscle function is the increase in pro-inflammatory substances in their circulatory system. These substances mediate the effect of insulin-like growth factor (IGE-1). IGE-1’s role is to repair muscle fibres that have lost nerve supply and damaged axons.

In animal studies, age related lesions on axons are more prevalent on ventral (underside) and peripheral nerves of the lumbar spine (compared with the cervical region) suggesting that lower limb muscles are more affected by age-related denervation (nerve supply loss).

How to treat muscle atrophy in older dogs?

In human and animal studies, there is evidence that a combination of diet and exercise is effective in managing age related muscle atrophy.

Diet

Amino acids are required to maintain muscle mass and provide sufficient energy for the dog to exercise. Specifically, the amino acid leucine increases protein synthesis to maintain muscle mass. Foods that are rich in leucine are beef, tuna, chicken and eggs.

For energy, creatine in the form of phosphocreatine is required as an energy store for muscle contractions, Creatine is synthesized from several amino acids including arginine, glycine, and methionine.

Exercise

Strength training is effective in reducing the rate of functional decline in humans and animals. In humans, it has been shown that the neuromuscular system responds positively to heavy loading training by facilitating changes in the central nervous system to compensate for the loss of motor neurons. This type of training was also shown to reduce inflammation, increase mitochondrial function and improve satellite cell activity.

Aerobic exercise also conserves muscle mass by improving blood flow and decreasing oxidative stress.

Key messages for carers of older dogs:

• Age related muscle atrophy is part of the normal ageing process.

• It is likely to affect the hind limbs more than other parts of the dog’s body.

• A diet with adequate, high quality protein can maintain protein synthesis and provide sufficient energy for exercise.

• Strength training reduces the rate of decline in older dogs.

Full Stride provides canine therapeutic massage and physical therapy to conserve muscle mass and function. I also tailor diet plans to suit each dog’s stage of life and owner’s lifestyle.
For more information please contact me at jlconlon@fullstride.com.au.

You can also stay up to date by following Full Stride on Facebook – https://www.facebook.com/FullStrideCanineMassageTherapy/

Until next time, enjoy your dogs.

Sources:

Aagaard, P, Suetta, C, Caserotti, P, Manusson, S.P, & Kjaer, M 2010 “Role of the nervous system in sarcopenia and muscle atrophy with aging: strength training as a counter measure” Scandanavian Journal of Medicine and Science in Sports 20: 49-64

Buford, T.W. Anton, S.D. Judge, A.R. Marzetti, E. Wohlgemuth, S.E. Carter, C.S. Leewenburgh, C. Pahor, M. & Manini, T.M. 2010 “Models of accelerated sarcopenia: Critical pieces for solving the puzzle of age-related muscle atrophy”

Evans, H & de Lahunta, A, 2013, Miller’s Anatomy of the Dog (4th ed), Elsevier Saunders, Missouri.

Freeman, L.M 2012 “Cachexia and Sarcopenia: Emerging syndromes of importance to cats and dogs” Journal of Veterinary Internal Medicine 26:3-17

Lexell, J, Taylor, C.C. & Sjostrom, M 1988 “What is the cause of the ageing atrophy: Total number, size and proportion of different fiber types studied in whole vastus lateralis muscle from 15 – 83 year old men” Journal of Neurological Sciences 84:275 – 294

Morley, J.E 2012 “Sarcopenia in the elderly” Family Practice 29:i44-i48

Pagano, T.B. Wojcik, S. Cosatgliola, A, De Biase, D. Iovino, S. Iovane, V. Russo, V. Papparella, S. & Paciello, O. 2015 “Age related skeletal muscle atrophy and upregulation of autophagy in dogs” The Veterinary Journal July 2015

Sandri, M 2008 “Signaling in Muscle Atrophy and Hypertrophy” Physiology 23: 160–170

Wall, B.T. Dirks, M.L. van Loon, L.J.C 2013 “Skeletal muscle atrophy during short term disuse: Implications for age related sarcopenia” Ageing Research Reviews