Muscle Function: Effects of Aging

Introduction

As we age our muscles undergo progressive changes, primarily involving loss of muscle mass and strength.

The age-related loss of muscle function is known as Sarcopenia[1], derived from the Greek words for flesh (sarcos) and loss (penia) and its definition includes loss of muscle strength and power, as well as reduced function[2]. It occurs with increasing age, and is a major component in the development of frailty.

The loss of muscle mass during the aging process is important clinically as it reduces strength and exercise capacity, both which are needed to perform activities of daily living. The video below gives a good summary of the changes and effects on performance and health.

[3]

Sarcopenia - consequences

Sarcopenia is not a disease but rather refers specifically to the universal, involuntary decline in lean body mass that occurs with age, primarily due to the loss of skeletal muscle. Sarcopenia has important consequences.

  • The loss of lean body mass reduces function, and loss of approximately 40% of lean body mass is fatal[4].
  • It has been attributed to a reduction of muscle size as well as a reduction in satellite cells (a stem cell that lies adjacent to a skeletal muscle fiber and plays a role in muscle growth, repair, and regeneration[5]), mitochondrial numbers, and elasticity.
  • Sarcopenia is seen in increasing numbers with advancing age but is not universal.
  • Sarcopenia varies in degree of physical activity, gender, and race[6].
  • Sarcopenia has a marked effect on function in all activities of daily living, contributing (along with reduction in balance) to reduced gait speed, falls, and fractures. The combination of osteoporosis and sarcopenia results in the frailty which frequently occurs in the elderly population.

Age-related Changes in Muscle Structure

With increasing age, we lose muscle mass: lean muscle mass contributes up to 50% of total body weight in young adults, but this decreases to 25% by 75 to 80 years[7]. Typical muscle changes with age:
Gross Muscle changes:

Reduced muscle mass (replaced by increased fat mass)

Reduction in lower limb muscle cross-sectional area have been observed to begin in early adulthood and accelerate beyond 50 years of age.This reduction in muscle cross-sectional area associated with decreases in contractile structures accompanied by increases in non contractile structures such as fat and connective tissue.[8] A cross-sectional study[9] suggested that the older inpatient showed an increase in the intramuscular quadricep muscle adipose tissue approx 1.7 times that of the healthy older individuals. Also, the study observed increased intramuscular adipose tissue with older inpatients who were unable to walk independently as compared to older inpatients who were able to walk freely.

Reduced muscle strength

The total number of muscle fibers is significantly reduced with age, beginning at about 25 years and progressing at an accelerated rate thereafter The decline in muscle cross-sectional area is most likely due to decreases in total fiber number, especially type II fast-twitch glycolytic fibers. This results in reduced muscle power.[8] A study examining 1-year changes in the physical functioning of older people using the ICF framework showed a significant decrease in muscle strength (both hip abductors and knee extensors) walking capacity, speed, mobility, sit-to-stand performance, upper extremity function, and balance performance at the end of 1 year[10].

Muscle Fibre changes:

  1. Changes in Muscle Fiber Size

Elderly individuals often fall because of poor muscle strength and reduced balancing ability related to muscle aging. Types IIA and IIB muscle fibers decrease with age in the area percentage, fiber number percentage, and mean fiber area, whereas Type I fibers increase in area and number but not in size. Morphologically, Type II fibers appeared smaller and flatter. Investigations suggest deterioration in muscle quality and balancing coordination in elderly patients. A research done provided data to help determine treatments for reversing muscle fiber changes and reducing the number of falls and related fractures in patients.[11]The reduction in number of muscle fibers contributes more to the decrease of whole muscle cross-sectional area than does the reduction in area of individual fibers. The individual fast-twitch type II fibers decrease in cross-sectional area suggest that the relative contribution of fast-twitch type II fibers to force generation is less in the older adult.

2. Motor Unit Number and Size

The majority of the literature indicates that muscle fiber loss is due to a loss in motor neurons. There is consistent denervation and reinervation of the muscle fiber throughout one’s lifespan, but in the aged, denervation appears to outpace reinveration. Data indicate that a 60-year-old has approximately 25-50% fewer motor neurons than a 20-year-old, with the greatest losses in distal fast twitch motor neurons With the loss of the motor neuron, the denervated fast twitch muscle fibers that were attached to it are either permanently denervated and undergo apoptosis, or are reinverated with a different motor neuron most likely that of a slow-twitch neuron, potentially making the fiber take on slow twitch characteristics[12]

Effects of Endocrine Changes on Muscle

With increased age, the following changes in endocrine function result in sarcopenia:

  • Increased insulin resistance[13]
  • Decreased growth hormone[14]
  • Reduction in oestrogen and testosterone[15]
  • Vitamin D deficiency[16]
  • Increased parathyroid hormone[17]

Conditions Associated with Impairment of Skeletal Function

Physiotherapy Interventions to Minimise or Reverse Sarcopenia

Resistance exercise training :

The effects of resisted exercise on ageing muscles are the same as for young muscles:

  • improved muscle strength
  • increased muscle power - power is a product of both strength and speed. Optimal power reflects how quickly you can exert force to produce the desired movement
  • improved muscle composition

Evidence:

Population studies

Resistance or weight training has been demonstrated to produce increases in muscle strength and power, and also mobility function, in older people living in the following settings:

  1. independently in the community[18][8][19]
  2. in nursing homes[20][21]
  3. hospitalised elderly people[22][23]

A Systematic Review of Randomized Controlled Trials suggested that a low dose of creatine monohydrate along with resisted exercises may improve upper and lower extremities strength in healthy older adults[24].

Gender differences

Increased muscle quality from resistance training is a common finding in older adults, and in men there appears to be no difference in young versus old[25], but there is a study that suggests that older women have a blunted response relative to younger women[26].

Frequency of resistance training

Studies have demonstrated that resistance training regimes performed once, twice or even three times a week all result in strength improvements[19].

Length of training programme

There are many studies which clearly demonstrate that older people who participate in resistance training programs lasting at least 6 to 12 weeks will show increase in both strength and mobility function[27][28][29].

Cochrane Review

The authors collated the results from 121 RCTs examining the effects of resistance strength training exercises, and came to the following conclusions:

"This review provides evidence that PRT (Progressive resistance strength training) is an effective intervention for improving physical functioning in older people, including improving strength and the performance of some simple and complex activities. However, some caution is needed with transferring these exercises for use with clinical populations because adverse events are not adequately reported."[30]

Dietary Advice

The Society for Sarcopenia, Cachexia, and Wasting convened an expert panel to develop nutritional recommendations for sarcopenia prevention and management.This panel concluded that for preventing and treating this condition key components are

  • protein and energy intake
  • both resistance and aerobic exercise

Is there a role for supplements?

There is some evidence suggesting that additional supplementation with the amino acid Leucine (or its metabolite HMB) could potentially increase the effects of resistance training to combat sarcopenia[31][32].

Resources

References

  1. Rosenberg IH. Sarcopenia: origins and clinical relevance. J Nutr. 1997;127(suppl 5):990S-991S.
  2. Rolland Y, Czerwinski S, Abellan Van Kan G, Morley JE, Cesari M, Onder G et al: Sarcopenia: its assessment, etiology, pathogenesis, consequences and future perspectives. J Nutr Health Aging. 2008;12(7):433-450.
  3. Mayo clinic. Muscle loss and aging. Available from: https://www.youtube.com/watch?v=ymcFS1tQrsk [last accessed 11.5.2019]
  4. Roubenoff R, Castaneda C. Sarcopenia—understanding the dynamics of aging muscle. Jama. 2001 Sep 12;286(10):1230-1.Available from:https://jamanetwork.com/journals/jama/article-abstract/194167 (last accessed 8.1.2020)
  5. Merriam Webster Satellite cell Available from:https://www.merriam-webster.com/medical/satellite%20cell (last accessed 8.1.2020)
  6. Noto RE, Edens MA. Physiology, Muscle. InStatPearls [Internet] 2018 Oct 27. StatPearls Publishing.Available from:https://www.ncbi.nlm.nih.gov/books/NBK532258/ (last accessed 8.1.2020)
  7. Short KR, Nair KS. The effect of age on protein metabolism. Curr Opin Clin Nutr Metab Care.2000; 3(1):39-44
  8. 8.0 8.1 8.2 Henwood TR, Riek S, Taaffe DR. Strength versus muscle power-specific resistance training in community-dwelling older adults. J Gerontol A Biol Sci Med Sci. 2008; 63(1):83-91.
  9. Akazawa N, Okawa N, Kishi M, Hino T, Tsuji R, Tamura K, Moriyama H. Quantitative features of intramuscular adipose tissue of the quadriceps and their association with gait independence in older inpatients: A cross-sectional study. Nutrition. 2020 Mar 1;71:110600.
  10. Kahraman T, Çekok FK, Üğüt BO, Keskinoğlu P, Genç A. One-Year Change in the Physical Functioning of Older People According to the International Classification of Functioning Domains. Journal of geriatric physical therapy (2001). 2019 Mar.
  11. Lee WS, Cheung WH, Qin L, Tang N, Leung KS. Age-associated decrease of type IIA/B human skeletal muscle fibers. Clin Orthop Relat Res. 2006;450:231-7.
  12. Bunn JA. Aging and the Motor Unit. J Sport Medic Doping Studie. 2012; S1:e001. doi:10.4172/2161-0673.S1-e001
  13. Refaie MR, Sayed-Ahmed NA, Bakr AM, Aziz MY, El Kannishi MH, Abdel-Gawad SS. Aging is an inevitable risk factor for insulin resistance. Journal of Taibah University Medical Sciences. 2006;1(1):30-41.
  14. Toogood AA. Growth hormone (GH) status and body composition in normal ageing and in elderly adults with GH deficiency. Horm Res. 2003; 60(Suppl 1):105-111.
  15. Gower BA, Nyman L. Associations among oral estrogen use, free testosterone concentration, and lean body mass among postmenopausal women. J Clin Endocrinol Metab. 2000; 85(12):4476-4480.
  16. Wicherts IS, van Schoor NM, Boeke AJ, Visser M, Deeg DJ, Smit J, et al. Vitamin D status predicts physical performance and its decline in older persons. J Clin Endocrinol Metab. 2007; 92(6):2058-2065.
  17. Visser M, Deeg DJ, Lips P. Low vitamin D and high parathyroid hormone levels as determinants of loss of muscle strength and muscle mass (sarcopenia): the Longitudinal Aging Study Amsterdam. J Clin Endocrinol Metab. 2003;88(12):5766-5772.
  18. Beneka A, Malliou P, Fatouros I, Jamurtas A, Gioftsidou A, Godolias G, et al: Resistance training effects on muscular strength of elderly are related to intensity and gender. J Sci Med Sport. 2005;8(3):274-283.
  19. 19.0 19.1 Taaffe DR, Duret C, Wheeler S, Marcus R. Once-weekly resistance exercise improves muscle strength and neuromuscular performance in older adults. J Am Geriatr Soc. 1999; 47(10):1208-1214, 1999
  20. Beyer N, Simonsen L, Bulow J, Lorenzen T, Jensen DV, Larsen L, et al. Old women with a recent fall history show improved muscle strength and function sustained for six months after finishing training. Aging Clin Exp Res. 2007;19(4):300-309.
  21. Harridge SD, Kryger A, Stensgaard A. Knee extensor strength, activation, and size in very elderly people following strength training. Muscle Nerve. 1999; 22(7):831-839.
  22. Hauer K, Specht N, Schuler M, Bärtsch P, Oster P. Intensive physical training in geriatric patients after severe falls and hip surgery. Age Ageing. 2002; 31(1):49-57
  23. Suetta C, Magnusson SP, Rosted A, Aagaard P, Jakobsen AK, Larsen LH, et al. Resistance training in the early postoperative phase reduces hospitalization and leads to muscle hypertrophy in elderly hip surgery patients—a controlled, randomized study. J Am Geriatr Soc. 2004;52(12):2016-2022
  24. Stares A, Bains M. The Additive Effects of Creatine Supplementation and Exercise Training in an Aging Population: A Systematic Review of Randomized Controlled Trials. Journal of geriatric physical therapy (2001). 2019 Feb.
  25. Ivey FM, Tracy BL, Lemmer JT, NessAiver M, Metter EJ, Fozard JL, et al Effects of strength training and detraining on muscle quality: age and gender comparisons. J Gerontol A Biol Sci Med Sci. 2000; 55(3):B152-B157; discussion B8-B9
  26. Hakkinen K, Alen M, Kallinen M,  Newton RU, Kraemer WJ. Neuromuscular adaptation during prolonged strength training, detraining and re-strength-training in middle-aged and elderly people. Eur J Appl Physiol. 2000;83(1):51-62
  27. Galvao DA, Newton RU, Taaffe DR Anabolic responses to resistance training in older men and women: a brief review. J Aging Phys Act. 2005;13(3):343-358
  28. Hunter GR, McCarthy JP, Bamman MM. Effects of resistance training on older adults. Sports Med. 2004;34(5):329-348, 2004
  29. Phillips SM. Resistance exercise: good for more than just Grandma and Grandpa’s muscles. Appl Physiol Nutr Metab. 2007;32(6):1198-1205
  30. Liu CJ, Latham NK. Progressive resistance strength training for improving physical function in older adults (Cochrane review). Cochrane Database Syst Rev 2009; (3):CD002759. doi: 10.1002/14651858.CD002759.
  31. Anthony JC, Anthony TG, Kimball SR, Vary TC, Jefferson LS. Orally administered leucine stimulates protein synthesis in skeletal muscle of postabsorptive rats in association with increased elF4F formation. J Nutr. 2000;130(2):139–145
  32. Vukovich MD, Stubbs NB, Bohlken RM. Body composition in 70-year-old adults responds to dietary beta-hydroxy-beta-methylbutyrate similarly to that of young adults. J Nutr. 2001;131(7):2049–2052