1. Age-related Muscle Changes Kerstin Palombaro, PT, PhD, CAPS Guccione, Ch. 3

2. Anatomical Changes Source: http://www.shoppingtrolley.net/how%20a%20muscle%20cont racts_clip_image002_0000.jpg Guccione, Ch. 3

3. Reductions in Muscle Mass  Decreases in total muscle cross sectional area  Accompanied by increases in non-contractile structures such as fat and connective tissue  Maintenance of muscle mass is due to a balance between protein synthesis and degradation.  Rates of skeletal muscle protein synthesis decline with age Guccione, Ch. 3

4. Reduction in muscle fiber number  Total number of muscle fibers is significantly reduced with age  Declines in muscle CSA most likely due to decreases in total fiber number, especially Type II fast twitch fibers  Loss of muscle fibers is followed by a replacement with fat and fibrous tissue and a gradual increase in non-muscle tissue Guccione, Ch. 3

5. Changes in muscle fiber size  Size of individual fast-twitch Type II fibers decreases with age  Slow twitch type I fiber size does not change.  Reduction in number of muscle fibers contributes more to the decrease of whole muscle CSA than does the reduction in area of individual fibers Guccione, Ch. 3

6. Motor unit number and size  Decrease in total number of motor units with age  Accompanied by an increase in size or innervation ratio so each motor unit innervates more muscle fibers in the older adult.  Reduced number of functioning motor units with age. Guccione, Ch. 3

7. Axon  Reduction in the numbers and diameters of motor axons  See changes in both duration and amplitude of motor unit action potentials  Axonal nerve conduction velocities are slowed with aging Guccione, Ch. 3

8. Neuromuscular junction  Number of preterminal axons entering an end plate increases  Increased branches  Convolutions of motor endplate decreases  Sarcolemma becomes smoother Guccione, Ch. 3

9. Altered Motor Unit remodeling  Type II fibers selectively denervated and reinervated by axonal sprouting of slow motor units  Terminal sprouting decreases with advancing age Guccione, Ch. 3

10. Age-related changes in motor neurons  Reduction in number of lumbosacral spinal cord motor neurons  Size of the slow motor units increases  Number of fibers and the total fiber area in a given motor unit also increases  Muscle undergoes continuous denervation and reinnervation due to accelerating reduction of functioning motor units Guccione, Ch. 3

11. Sarcoplasmic reticulum  Age-related slowing of isometric twitch  Decreases in receptors related to excitation coupling Guccione, Ch. 3

12. Sarcopenia  Sarcopenia, in which muscle tissue is lost with aging and results in diminished muscle mass and strength. (Rosenberg,1997)  Sarcopenia has been described as a universal aging phenomenon that is characterized by progressive loss of skeletal muscle fibers and fat free mass and is operationally defined as skeletal muscle mass > 2 standard deviations below the healthy young adult mean. (Leveille, 2004)  Some degree of sarcopenia appears to be inevitable with age, as older athletes also experience strength declines as compared to younger athletes. (Deschenes, 2004)  As sarcopenia progresses from normal to greater than two standard deviations below normal, the likelihood of functional impairment increased. (Janssen et al, 2002) Guccione, Ch. 3

13. Changes in Muscle Performance Guccione, Ch. 3

14. Strength  Reductions in isometric and dynamic voluntary strength decline starting at 3 rd decade  Weakness due to a decline in the ability to activate existing muscle mass.  Weakness could be due to decreased central drive resulting in decreased ability to voluntarily activate a muscle  Weakness could be due to loss of muscle mass and thus reduction in the number of force generating cross bridges between actin and myosin Guccione, Ch. 3

15. Power  Aging reduces peak forces that can be generated by muscles at fast contraction speeds resulting in a decrease in peak power output  LE power output reduction and functional ability such as stairs or max walking speed are related  can also result in impaired ability to recover balance Guccione, Ch. 3

16. Endurance  Contractile and metabolic changes result in impaired endurance Guccione, Ch. 3

17. Glucose Uptake  Aging is associated with decreased glucose tolerance and increased incidence of Type 2 diabetes Guccione, Ch. 3

18. Enzyme activity  Glycolytic enzymes have no changes  Decreased oxidative enzyme activities among other changes Guccione, Ch. 3

19. Blood flow and capillarity  Decreased endurance capacity of muscle with age reflects decreased blood flow and decreased oxidative capacity Guccione, Ch. 3

20. Journal Club Discussion  Marcus et al, 2012 Guccione, Ch. 3

21. References  Bassey EJ. Longitudinal changes in selected physical capabilities: Muscle strength, flexibility and body size. Age Ageing. 1998;27 Suppl 3:12-16.  Carmeli E, Coleman R, Reznick AZ. The biochemistry of aging muscle. Exp Gerontol. 2002;37:477-489.  Deschenes MR. Effects of aging on muscle fibre type and size. Sports Med. 2004;34:809-824.  Janssen I, Heymsfield SB, Ross R. Low relative skeletal muscle mass (sarcopenia) in older persons is associated with functional impairment and physical disability. J Am Geriatr Soc. 2002;50:889-896.  Rosenberg IH. Sarcopenia: Origins and clinical relevance. J Nutr. 1997;127:990S-991S.  Thompson LV. Physiological Changes Associated with Aging. In: Guccione AA, ed. Geriatric Physical Therapy. Mosby; St. Louis, MO; 2000:28-55. Guccione, Ch. 3