HES 383 - Physical Dimensions of Aging PDF

HES 383 – PHYSICAL DIMENSIONS OF AGING NEUROMUSCULAR CHANGES WITH AGING Prof Gina Whitaker, BSc Kin, PhD Oct 3rd, 2023 The UBC Okanagan Campus and the City of Kelowna are located on the traditional, ancestral, and unceded territory of the Syilx Okanagan Nation. DECLINE IN MUSCLE MASS & STRENGTH WI...

HES 383 – PHYSICAL DIMENSIONS OF AGING NEUROMUSCULAR CHANGES WITH AGING Prof Gina Whitaker, BSc Kin, PhD Oct 3rd, 2023 The UBC Okanagan Campus and the City of Kelowna are located on the traditional, ancestral, and unceded territory of the Syilx Okanagan Nation. DECLINE IN MUSCLE MASS & STRENGTH WITH AGING • Muscle Mass peaks at ~30YO, followed by gradual decline of 3-8% per decade, increasing after 65YO • 20-40% loss by 70YO • Decline in muscle volume + Fat surrounds and infiltrates muscle (Myosteatosis) • Can lead to Sarcopenia Clinical loss of skeletal muscle mass and strength Sayer AA, et al. (2013) New horizons in the pathogenesis, diagnosis and management of sarcopenia. Age Ageing 42(2) 145-150 AGE-RELATED SKELETAL MUSCLE WEAKNESS LEADS TO • Impaired mobility, decreased walking speed • Poor balance • Impaired functional performance (ADLs, IADLs) • Loss of independence • Pathological consequences: Sarcopenia, Dynapenia, Physical Frailty ADLs = activities of daily living: basic self-care tasks (e.g. bathing, dressing, toileting, transferring, feeding) IADLs = instrumental activities of daily living – the things you do daily to take care of yourself and your home (e.g. shopping, transport, food prep, housekeeping, laundry) AGE-RELATED DECLINE IN MUSCLE FUNCTION IS A RESULT OF: • Changes in muscle mechanics (the muscle-tendon unit) • Changes in neuromuscular function (individual motor neurons and motor units) Some of these changes are interconnected • Intrinsic changes within individual muscle fibers (cell senescence) • Changes to the muscle ultrastructure (e.g. myosteatosis & fibrosis) Aversa, Z., Zhang, X., Fielding, R. A., Lanza, I., & LeBrasseur, N. K. (2019).The clinical impact and biological mechanisms of skeletal muscle aging. Bone, 127, 26– 36. https://doi.org/10.1016/j.bone.2019.05.021 AGE-RELATED MECHANICAL FACTORS Wu, R., De Vito, G., Delahunt, E., & Ditroilo, M. (2020). Age-related Changes in Motor Function (I). Mechanical and Neuromuscular Factors. International journal of sports medicine, 41(11), 709–719. https://doi.org/10.1055/a-1144-3408 DECLINE IN MUSCLE SIZE & QUALITY WITH AGE • Cross sectional area (CSA) of whole muscle decreases ~3-8% per decade after 30 years (muscle-dependent) • Accelerating after ~50 years. (~1.5% CSA loss per year) Tibialis anterior CSA McNeil et al., 2007; 2005 Vastus lateralis CSA Aagaard et al., 2010 AGE-RELATED NEUROMUSCULAR FACTORS • Loss and remodelling of motor units • Fiber type regrouping • Neuromuscular junction: decreased transmission & junctional instability • Atrophy and death of muscle fibres (preferential loss of type II muscle fibers) REVIEW: THE MOTOR UNIT & MUSCLE FORCE Motor Unit: One alpha motor neuron and all the muscle fibers it innervates • One motor neuron innervates multiple fibers at once via collaterals. • The total force produced during a muscle contraction is controlled by varying the number of motor units recruited AND the discharge rate of the action potentials that innervate each active motor unit • Motor units undergo a normal process of remodelling throughout lifespan • A process of denervation and re-innervation AGE-RELATED NEUROMUSCULAR DECLINE Wu, R., De Vito, G., Delahunt, E., & Ditroilo, M. (2020). Age-related Changes in Motor Function (I). Mechanical and Neuromuscular Factors. International journal of sports medicine, 41(11), 709–719. https://doi.org/10.1055/a-1144-3408 MOTOR UNIT (MU) LOSS & REMODELLING Motor neurons die with age (estimated rate of 1% per year from 30 – 70YO, then faster rate thereafter) Other Motor neurons grow collaterals to some of the newly orphaned muscle fibres Result: • Fewer, larger motor units • Fiber-type grouping • Muscle fibres that remain orphaned will atrophy and die off It is thought that motorneuron death preferentially occurs among large fastconducting motorneurons that innervate fasttwitch muscle fibres Consequence: re-innervated muscle fibres adapt to slower nerve supply MOTOR UNIT NUMBER ESTIMATES (MUNES) IN YOUNG VS. OLD MALES  Measured in tibialis anterior muscle (25YO) (65YO) POWER, GEOFFREY A.1; DALTON, BRIAN H.1; BEHM, DAVID G.2;VANDERVOORT, ANTHONY A.1,3; DOHERTY, TIMOTHY J.1,4; RICE, CHARLES L.1,5 Motor Unit Number Estimates in Masters Runners: Use It or Lose It?, Medicine & Science in Sports & Exercise: September 2010 - Volume 42 - Issue 9 - p 1644-1650 doi: 10.1249/MSS.0b013e3181d6f9e9 AGE-RELATED NEUROMUSCULAR DECLINE Wu, R., De Vito, G., Delahunt, E., & Ditroilo, M. (2020). Age-related Changes in Motor Function (I). Mechanical and Neuromuscular Factors. International journal of sports medicine, 41(11), 709–719. https://doi.org/10.1055/a-1144-3408 AGE-RELATED CHANGES TO MUSCLE FIBERS • Denervation due to motor neuron death results in atrophy and dying off of muscle fibers • ~5% fibre loss from 24-50YO (preferential loss of fast-twitch type II) • Up to 35% loss of muscle fibres from 50-75YO • Surviving muscle fibers get smaller in size (Atrophy) • Decreased force production • Surviving muscle fibers exhibit slower contractile properties • Contributing intrinsic factors: Decreased mitochondrial function, Myosin ATPase activity, SR Ca2+ handling, Development of Anabolic Resistance (See next slide) ANABOLIC RESISTANCE IN AGING MUSCLE Development of Anabolic Resistance in innervated muscle fibres • Decreased muscle protein synthesis (MPS) relative to breakdown (MPB) Wilkinson DJ, Piasecki M, Atherton PJ. The age-related loss of skeletal muscle mass and function: Measurement and physiology of muscle fibre atrophy and muscle fibre loss in humans. Ageing Res Rev. 2018;47:123–132. doi:10.1016/j.arr.2018.07.005 AGE-RELATED CHANGES WITHIN MUSCLE FIBRES CONTRIBUTING TO DECLINE IN MUSCLE STRENGTH AND FUNCTION • Decreased mitochondrial function & ATP production • Decreased fatty acid metabolism and increased glycolysis • Decreased overall glucose uptake into cells, insulin resistance • Reduced ATPase activity of myosin • Impaired ability to store and release Ca • • • • Decreased velocity of contraction Decreased rate of force development Decreased peak force and power Increased fatigability Wu, R., De Vito, G., Delahunt, E., & Ditroilo, M. (2020). Age-related Changes in Motor Function (I). Mechanical and Neuromuscular Factors. International journal of sports medicine, 41(11), 709–719. https://doi.org/10.1055/a-1144-3408 AGE-RELATED CHANGES IN MOTOR PERFORMANCE • Decreased muscle strength • Decreased max isometric strength ~10% per decade starting at 40-50YO (down to ~40% of max by 80 YO) • These reductions in isometric strength tend to be higher in lower limb muscles (compared to upper limb) • Variable decrease in isotonic strength depending on velocity of contraction and muscle group measured. • Decreased maximum power • Decreased rate of force development and relaxation • Reduced force steadiness – especially during light-load tasks (more on this next class) • Variable changes in fatigability • Less fatigable for isometric (individuals <80YO) / More fatigable in isotonic, fast dynamic contractions • More fatigable in lower limbs • Generally females are less fatigable than males ASSESSMENT MODALITIES • Muscle mass • DXA, CT • Muscle strength • Grip strength • Lower limb muscle strength (isometric) • Physical performance (Functional Assessment) • Short Physical Performance Battery • Timed UP and Go test • 4 or 6 minute walking speed tests • Stair climb test • Balance testing • Activities of Daily Living Scales FUNCTIONAL ASSESSMENT: TIMED UP AND GO TEST DECREASE IN MUSCLE STRENGTH WITH AGE (MEASURED GRIP STRENGTH - ISOMETRIC) Dodds RM, Syddall HE, Cooper R, Benzeval M, Deary IJ, Dennison EM, et al. Grip strength across the life course: normative data from twelve British studies. PLoS One. 2014;9(12):e113637. A DECLINE IN FUNCTIONAL RESERVE Figure: Force required to rise from a chair relative to the strength of a person. At 20 years of age, the maximal voluntary contraction (MVC) is much higher than the force required to perform a simple task, such as rising from a chair. Because of the reduction in muscle strength with aging, the same task may represent a maximal effort in an 80-year-old person. Frontera WR. Physiologic Changes of the Musculoskeletal System with Aging: A Brief Review. Phys Med Rehabil Clin N Am. 2017 Nov;28(4):705-711. doi: 10.1016/j.pmr.2017.06.004. FORCE & POWER-VELOCITY RELATIONSHIPS IN YOUNG AND OLD SKELETAL MUSCLES Muscle and exercise physiology (2019) ch 19, p423-432. Degens, H. Human Ageing: Impact on Muscle Force and Power Wu, R., Ditroilo, M., Delahunt, E., & De Vito, G. (2021). Age Related Changes in Motor Function (II). Decline in Motor Performance Outcomes. International journal of sports medicine, 42(3), 215–226. https://doi.org/10.1055/a1265-7073 Young (25YO) Old (65YO) Very Old (80 YO) Comparison of angular velocity (A) and velocity-dependent power (B) At different submaximal loads normalized to a relative percentage of maximum voluntary contraction (MVC). Measured in ankle dosiflexors Young (25YO) Old (65YO) Very Old (80 YO) VARIABILITY IN MUSCLE DECLINE AS A FUNCTION OF EXERCISE FIGURE 3.MRIs taken across the mid region of the thigh Images taken across the mid region of the thigh, showing a sarcopenic muscle (middle) from a sedentary individual with reduced contractile mass, more subcutaneous fat, and infiltration of fat and connective tissue. By contrast, the muscles of a similarly aged master triathlete (bottom) shows little difference to that of a younger athlete (top). From: Harridge S.D.R & Lazarus, N.R. (2017) Physical Activity, Aging and Physiological Function. Physiology 32(2): 152-161 USE IT OR LOSE IT – EXERCISE CAN HELP MAINTAIN MOTOR UNIT NUMBER • Multiple studies showing retention of motor unit number (estimates) among older adult athletes • Specific to the motor unit being chronically activated (the exercised muscle) **Chronic activation is required to protect against rate of motor unit decline with age MA = Master athletes / AC = Age-matched controls Study: 80+YO track and field athletes Power GA, et.al. Motor unit number and transmission stability in octogenarian world class athletes: Can age-related deficits be outrun? J Appl Physiol (2016) 121(4):1013-1020 POWER TRAINING IN OLDER AGE • Age-related decrease in maximal power are even greater than the age-related decreases in max isometric strength • Power training can improve power in older age • 12 week intervention • 43 volunteers aged 70+ • Measured leg extensor power at increasing resistance (pre and post) Two groups: • Walking group (mod intensity, 30 min/day, 6d/week • Power training group (3x/week) Earles DR, Judge JO, Gunnarsson OT. Velocity training induces power-specific adaptations in highly functioning older adults.Arch Phys Med Rehabil. 2001;82(7):872–878