You can beat age with strength training .

The ageing process is universal. We find it everywhere. Unfortunately, even our skeletal muscles cannot escape the ageing process and muscle mass decreases over time. Why is this so and is it possible to dampen or reverse this process?

Our cells age too. They take damage at the molecular level over time. This is caused by various biochemical interactions. For the cells, it means that the amount of damage is so high that they can no longer divide and stop in the cell cycle. The observations of these processes led to the term cellular senescence, cellular ageing. Ageing can thus be described as a function of the accumulation of senescent cells during life.

Aging cells no longer function as well and can cause disorders in physiological processes and/or tissues. For example, 2 - 4 times more pro-inflammatory factors are found in the blood serum of older people compared to younger people [1-4]. These factors can promote inflammatory reactions and further accelerate the ageing process.

As we age, the stem cells of our muscles, called satellite cells, also decrease significantly [5,6]. It has been observed that older people have a smaller muscle cross-section in the type II fibres and that these fibres additionally have fewer satellite cells. This could indicate impaired function of these cells [7]. However, this is controversial as targeted pharmacological suppression of satellite cell function had no effect on muscle wasting in adult mice [8,9]. Satellite cells therefore do not contribute to the size maintenance of ageing muscle fibres, but only play an important role in regenerative processes [8,10].
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New evidence suggests a key role for mitochondria, our cellular power plants, in the ageing process and age-related diseases [11]. Caloric deficit has been shown to extend lifespan in yeast [12], Caenorhabditis elegans [13] and mammals [14] . This therefore suggests a role for mitochondria in the ageing process, as one of the things our cells do for longevity is to influence the regulation of mitochondria [15]. In contrast, in ageing cells, mitochondrial dysfunction is observed, which negatively affects muscle function and its maintenance [16,17].
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Further, the ageing process can also disrupt signalling pathways and thus affect the build-up and breakdown of muscle mass, unfortunately favouring the breakdown of muscle mass.

Effects of ageing on strength

Skeletal muscles decline over time. From puberty to between the fourth and fifth decades of life, strength and muscle mass remain relatively constant in healthy individuals. It is only between the ages of 40 and 50 that we decline in muscle mass and strength [18]. By the age of 80, we have lost about 30% of our muscle mass [19,20]. However, the loss of muscle mass is not evenly distributed over the body. The rate of muscle mass loss is more than twice as high in the lower limbs compared to the upper limbs [21]. Although men have more muscle mass than women, the loss of muscle mass is similar between the sexes [21,22]. Since men have about 1.5 - 2 times more muscle mass and strength than women, they reach the disability threshold about 1.5 years later compared to women [23,24].
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As mentioned earlier, the ageing process is accompanied by a reduction in the cross-sectional area of type II fibres [25]. Consequently, the proportion and volume of Type I fibres increases [7,25,26]. Between 22 and 74 years, a decrease in cross-sectional area in type II fibres from 58% to 52% was observed in the vastus lateralis (largest muscle of the quadriceps) [25]. Knowing that type II fibres can generate about 1.4 times more tension than type I fibres [27,28], this can at most explain a strength difference of about 2% but never the observed strength loss of 45% that occurs in this age range [29]. Where does this massive loss of strength come from? Among other causes of strength loss, one of the main reasons is that ageing is associated with ultrastructural changes, such as an increase in connective tissue and an infiltration of fat [24,30,31]. Both fat and connective tissue cannot contribute to strength because they are non-contractile tissues. Compared to young men, older men have twice the area of non-contractile tissue [31]. So it is mainly this non-contractile tissue that explains the loss of strength better than the reduction in the cross-sectional area of type II muscle fibres [31].

Not to leave unmentioned the factor that the reduction in strength in the elderly may also be due to a reduced ability to voluntarily target the muscle [32]. In rats, this accounted for up to 11% of the loss of strength in old age [33].

Age and strength training

Long story short: Plasticity, the ability of muscles to adapt to environmental influences, is present into old age. Fiatarone and colleagues [34] subjected ten subjects aged 90 ± 1 years to eight weeks of high-intensity training. The 9 subjects who completed the training had an average strength gain of 174%. The mean thigh muscle area increased by 9 %. Strength training therefore led to an increase in muscle strength and mass even in frail individuals and increased mobility.
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Wroblewski et al. [35] studied the body composition, peak torque and cross-sectional area of the quadriceps of 40 well-trained individuals aged 40 to 81 years. Quantification of mid-thigh muscle cross-sectional area and fat-free mass showed no increase with age, and a significant relationship was found between preservation of mid-thigh muscle area. Furthermore, strength did not decrease significantly with age in these well-trained individuals. The authors therefore concluded that ageing alone cannot explain the generally observed decline in muscle mass and strength, and that disuse of the muscles may be a stronger reason for the decline in muscle mass and strength than ageing. So if there is no difference in muscle cross-sectional area between 81- and 40-year-old well-trained athletes, regular exercise may "rejuvenate" your muscles by decades.

The plasticity of muscles is not affected by the ageing process, per se. That's why I encourage even the oldest people to incorporate regular strength training into their daily routine. Remember: you decide how you want to age.

References

1. Schaap LA, Pluijm SMF, Deeg DJH, Visser M. Inflammatory markers and loss of muscle mass (sarcopenia) and strength. Am J Med. Elsevier; 2006;119: 526.e9-526.e17. doi:10.1016/j.amjmed.2005.10.049
2. Marzetti E, Picca A, Marini F, Biancolillo A, Coelho-Junior HJ, Gervasoni J, et al. Inflammatory signatures in older persons with physical frailty and sarcopenia: The frailty "cytokinome" at its core. Exp Gerontol. Elsevier Inc; 2019;122: 129-138. doi:10.1016/j.exger.2019.04.019
3. Bian AL, Hu HY, Rong YD, Wang J, Wang JX, Zhou XZ. A study on relationship between elderly sarcopenia and inflammatory factors IL-6 and TNF-α. Eur J Med Res. BioMed Central Ltd; 2017;22: 25. doi:10.1186/s40001-017-0266-9.
4. Can B, Kara O, Kizilarslanoglu MC, Arik G, Aycicek GS, Sumer F, et al. Serum markers of inflammation and oxidative stress in sarcopenia. Aging Clin Exp Res. Springer International Publishing; 2017;29: 745-752. doi:10.1007/s40520-016-0626-2.
5. García-Prat L, Sousa-Victor P, Muñoz-Cánoves P. Functional dysregulation of stem cells during aging: a focus on skeletal muscle stem cells. FEBS J. John Wiley & Sons, Ltd; 2013;280: 4051-4062. doi:10.1111/febs.12221
6. Boldrin L, Muntoni F, Morgan JE. Are human and mouse satellite cells really the same? [Internet]. Journal of Histochemistry and Cytochemistry. SAGE PublicationsSage CA: Los Angeles, CA; 2010. pp. 941–955. doi:10.1369/jhc.2010.956201
7. Verdijk LB, Koopman R, Schaart G, Meijer K, Savelberg HHCM, Van Loon LJC. Satellite cell content is specifically reduced in type II skeletal muscle fibers in the elderly. Am J Physiol - Endocrinol Metab. American Physiological Society; 2007;292: 151–157. doi:10.1152/ajpendo.00278.2006
8. Fry CS, Lee JD, Mula J, Kirby TJ, Jackson JR, Liu F, et al. Inducible depletion of satellite cells in adult, sedentary mice impairs muscle regenerative capacity without affecting sarcopenia. Nat Med. Nature Publishing Group; 2015;21: 76-80. doi:10.1038/nm.3710
9. Jackson JR, Mula J, Kirby TJ, Fry CS, Lee JD, Ubele MF, et al. Satellite cell depletion does not inhibit adult skeletal muscle regrowth following unloading-induced atrophy. Am J Physiol - Cell Physiol. American Physiological Society Bethesda, MD; 2012;303: 854-861. doi:10.1152/ajpcell.00207.2012
10. Murach KA, Fry CS, Kirby TJ, Jackson JR, Lee JD, White SH, et al. Starring or supporting role? Satellite cells and skeletal muscle fiber size regulation [Internet]. Physiology. American Physiological Society; 2018. pp. 26–38. doi:10.1152/physiol.00019.2017
11. Amorim JA, Coppotelli G, Rolo AP, Palmeira CM, Ross JM, Sinclair DA. Mitochondrial and metabolic dysfunction in ageing and age-related diseases. Nat Rev Endocrinol 2022 184. nature publishing group; 2022;18: 243-258. doi:10.1038/s41574-021-00626-7.
12. Lin SJ, Kaeberlein M, Andalis AA, Sturtz LA, Defossez PA, Culotta VC, et al. Calorie restriction extends Saccharomyces cerevisiae lifespan by increasing respiration. Nat 2002 4186895. nature publishing group; 2002;418: 344-348. doi:10.1038/nature00829.
13. Schulz TJ, Zarse K, Voigt A, Urban N, Birringer M, Ristow M. Glucose Restriction Extends Caenorhabditis elegans Life Span by Inducing Mitochondrial Respiration and Increasing Oxidative Stress. Cell Metab. Elsevier; 2007;6: 280-293. doi:10.1016/j.cmet.2007.08.011
14. Nisoli E, Tonello C, Cardile A, Cozzi V, Bracale R, Tedesco L, et al. Cell biology: calorie restriction promotes mitochondrial biogenesis by inducing the expression of eNOS. Science (80- ). American Association for the Advancement of Science ; 2005;310: 314-317. doi:10.1126/SCIENCE.1117728/SUPPL_FILE/NISOLI.SOM.PDF.
15. López-Lluch G, Navas P. Calorie restriction as an intervention in ageing. J Physiol. John Wiley & Sons, Ltd; 2016;594: 2043-2060. doi:10.1113/JP270543
16. Favaro G, Romanello V, Varanita T, Andrea Desbats M, Morbidoni V, Tezze C, et al. DRP1-mediated mitochondrial shape controls calcium homeostasis and muscle mass. Nat Commun. Nature Publishing Group; 2019;10: 1-17. doi:10.1038/s41467-019-10226-9.
17. Huang DD, Fan SD, Chen XY, Yan XL, Zhang XZ, Ma BW, et al. Nrf2 deficiency exacerbates frailty and sarcopenia by impairing skeletal muscle mitochondrial biogenesis and dynamics in an age-dependent manner. Exp Gerontol. Elsevier Inc; 2019;119: 61-73. doi:10.1016/j.exger.2019.01.022
18. Williams GN, Higgins MJ, Lewek MD. Aging skeletal muscle: physiologic changes and the effects of training. Phys Ther. American Physical Therapy Association; 2002;82: 62-68. doi:10.1093/ptj/82.1.62
19. Janssen I, Heymsfield SB, Wang Z, Ross R. Skeletal muscle mass and distribution in 468 men and women aged 18-88 yr. J Appl Physiol. 2000;89: 81-88. doi:10.1152/jappl.2000.89.1.81
20. Topinková E. Aging, disability and frailty. Ann Nutr Metab. Karger Publishers; 2008;52: 6-11. doi:10.1159/000115340.
21. Janssen I, Heymsfield SB, Wang Z, Ross R. Skeletal muscle mass and distribution in 468 men and women aged 18-88 yr. J Appl Physiol. 2000;89: 81-88. doi:10.1152/jappl.2000.89.1.81
22. Silva AM, Shen W, Heo M, Gallagher D, Wang Z, Sardinha LB, et al. Ethnicity-related skeletal muscle differences across the lifespan. Am J Hum Biol. John Wiley & Sons, Ltd; 2010;22: 76-82. doi:10.1002/AJHB.20956.
23. Miller AEJJ, MacDougall JD, Tarnopolsky MA, Sale DG. Gender differences in strength and muscle fibre characteristics. Eur J Appl Physiol Occup Physiol. Springer-Verlag; 1993;66: 254-262. doi:10.1007/BF00235103.
24. Goodpaster BH, Carlson CL, Visser M, Kelley DE, Scherzinger A, Harris TB, et al. Attenuation of skeletal muscle and strength in the elderly: the health ABC study. J Appl Physiol. American Physiological Society; 2001;90: 2157-2165. doi:10.1152/jappl.2001.90.6.2157.
25. Barnouin Y, McPhee JS, Butler-Browne G, Bosutti A, De Vito G, Jones DA, et al. Coupling between skeletal muscle fiber size and capillarization is maintained during healthy aging. J Cachexia Sarcopenia Muscle. Wiley Blackwell; 2017;8: 647-659. doi:10.1002/jcsm.12194
26. Andersen JL. Muscle fibre type adaptation in the elderly human muscle. Scand J Med Sci Sports. John Wiley & Sons, Ltd; 2003;13: 40-47. doi:10.1034/j.1600-0838.2003.00299.x
27. Bottinelli R, Canepari M, Pellegrino MA, Reggiani C. Force-velocity properties of human skeletal muscle fibres: myosin heavy chain isoform and temperature dependence. J Physiol. John Wiley & Sons, Ltd; 1996;495: 573-586. doi:10.1113/JPHYSIOL.1996.SP021617.
28. Widrick JJ, Trappe SW, Blaser CA, Costill DL, Fitts RH. Isometric force and maximal shortening velocity of single muscle fibers from elite master runners. https://doi.org/101152/ajpcell19962712C666. American Physiological Society Bethesda, MD; 1996;271. doi:10.1152/AJPCELL.1996.271.2.C666
29. Degens H, Erskine RM, Morse CI. Disproportionate changes in skeletal muscle strength and size with resistance training and ageing. Journal of Musculoskeletal Neuronal Interactions. 2009. pp. 123-129.
30. Degens H, McPhee JS. Muscle Wasting, Dysfunction, and Inflammaging. Inflammation, Advancing Age and Nutrition: Research and Clinical Interventions. Elsevier Inc; 2013. pp. 247–254. doi:10.1016/B978-0-12-397803-5.00020-4
31. Power GA, Allen MD, Booth WJ, Thompson RT, Marsh GD, Rice CL. The influence on sarcopenia of muscle quality and quantity derived from magnetic resonance imaging and neuromuscular properties. Age (Omaha). Kluwer Academic Publishers; 2014;36: 1377-1388. doi:10.1007/s11357-014-9642-3.
32. Morse CI, Thom JM, Davis MG, Fox KR, Birch KM, Narici M V. Reduced plantarflexor specific torque in the elderly is associated with a lower activation capacity. Eur J Appl Physiol. Springer; 2004;92: 219-226. doi:10.1007/s00421-004-1056-y
33. Urbanchek MG, Picken EB, Kalliainen LK, Kuzon WM. Specific Force Deficit in Skeletal Muscles of Old Rats Is Partially Explained by the Existence of Denervated Muscle Fibers. Journals Gerontol Ser A Biol Sci Med Sci. Oxford Academic; 2001;56: B191-B197. doi:10.1093/gerona/56.5.B191.
34. Fiatarone MA, Marks EC, Ryan ND, Meredith CN, Lipsitz LA, Evans WJ. High-intensity strength training in nonagenarians: effects on skeletal muscle. JAMA J Am Med Assoc. 1990;263: 3029-3034. doi:10.1001/jama.1990.03440220053029.
35. Wroblewski AP, Amati F, Smiley MA, Goodpaster B, Wright V. Chronic Exercise Preserves Lean Muscle Mass in Masters Athletes. Phys Sportsmed. 2011;39: 172-178. doi:10.3810/psm.2011.09.1933.