Adaptations to Resistance Training in the Elderly

8/2/2019 Adaptations to Resistance Training in the Elderly

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Skeletal muscleadaptations to resistance

training in the elderlyJeremy Baker, PhD, ATC


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Muscle Structure

Skeletal muscle, composed of muscle cells, organizednetworks of nerves and blood vessels, and anextracellular connective tissue matrix. basic unit of skeletal muscle is the muscle fiber

(myofiber).

The cytoplasm =sarcoplasm,

has a cellular matrix andorganelles A skeletal muscle fiber is derived from the fusion of

multiple myoblasts. The myoblasts fuse into multinucleated myotubes Once the nuclei move to a subsarcolemmal position,

the muscle cells are called myofibers. Each Nucleus is thought to control a certain amount

of sarcoplasm, therefore more nuclei are needed toadd more cytoplasm for increased CSA


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Basic Structure

Skeletal Muscle

Myofibril


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Muscle Fiber Types

Type I muscle fibers (slow-oxidative fibers) (SlowTwitch)

Use cellular respiration - high endurance.

lots of mitochondria and myoglobin appear red

Type II muscle fibers (Fast Twitch)

Use anaerobic metabolism -low endurance.

low levels of mitochondria and myoglobin, appearwhite.

Used for short bursts of strength

Type IIa (Fast-Oxidative) and IIb (Fast-Glycolytic).Type IIb (Fast-Glycolytic) tire the fastest, and arethe prevalent type in sedentary individuals.


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Resistance Exercise Causes

MicrotraumaMechanical trauma ruptures the myofiber plasmamembrane and basal lamina, leading to an influx ofextracellular calcium.Injured myofibers undergo angiogenesis and attractmononuclear cells, activated macrophages, and T

lymphocytes.The lymphocytes secrete cytokines and growth factors.The release of growth factors such as insulin-like growthfactor-1 (IGF-1), hepatocyte growth factor (HGF),epidermal growth factor (EGF), transforming growth

factors (TGF- and TGF-), and platelet-derivedgrowth factors regulate myoblast proliferation anddifferentiationSystemic release of hormones including GH and T


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Satellite Cells and HypertrophyThe satellite cells become activated, proliferate, and differentiateinto multinucleated myotubes and eventually into regenerated

myofibers.Muscle Cell Growth includes:1. satellite cell recruitment, which proliferate & fuse with muscle cellfibers2. pro-growth factors such as IGF-I, and Testosterone whichpromote satellite cell proliferation and cellular protein production

3. growth inhibition factors, such as myostatin block satellite cellgrowth and differentiation


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Changes in Muscle with Aging

Significant loss in maximal force production. 30% declinein strength and 40% decline in muscle area between 20and 80 yrs

Decline in strength from either the loss of muscle mass,

alteration of the muscles capacity to generate force or acombination of the two mechanisms

Reduction in muscle size starts before age 30 yr and byage 50 muscle area may be reduced by 10% After 50 the rate of muscle area decline is faster

Type I fibers are resistant to atrophy until about 60-70yr old

Type II fibers more likely to shrink in size


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Distribution of muscle type was oncethought to change but the most recentdata has found both type I and II affected

equallyLoss of fiber number begins around age25 and by 80 the total number is reducedby about 39% Fibers are lost due to either damage to

muscle cells without regeneration ordeinnervation (which is more likely)


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Deinnervation

Loss of alpha-motorneurons

Axonal sprouting of remaining motorneurons resultsin reinnervation of some of the fibers

Motor unit size is increased with aging

Contractile Properties

Muscle does NOT become intrinsically weaker withage, may be less flexible

Metabolism Oxidative capacity has been shown to decline in

skeletal muscle with age

This is found in only truly sedentary individuals

Decreased activity plays a bigger role than age


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Motor Unit


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Adaptations to Resistance Training

Hypertrophy is mediated by structural changesin muscle fibers

Increased CSA of type I and II, but type II

usually increases moreLiterature shows increases in CSA for TypeII about 20-52%, type I 8-17%

Connective Tissue

Aging may cause a less organized extra-cellular matrix, lowered ability for collagen tostretch


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Young men and women can expect a 20-35+% increasein muscle strength with a standard strength resistancetraining protocol in a matter of months.

Older men and women show increased strength also

Older men show a similar strength gain compared toyoung men

OU study 14 month weight training study (80% 1-Rm), 8 reps, 3 sets) with postmenopausal womenshowed strength improvements of 13-53% dependingon muscle and 19-38% increase in muscle sizes


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GLUT-4 Glucose enters muscle cells via facilitated diffusion, mediated by

glucose transporter proteins

glucose transport is the rate-limiting step for muscle glucosemetabolism.

GLUT-4 glucose transporter is predominate glucose transporterprotein expressed by skeletal muscle

Exercise (aerobic exercise and endurance level resistancetraining) increases GLUT-4 levels in younger and older people

Muscle endurance Ability of the muscle to hold a contraction or maintain force over

repeated contractions Age has little effect on muscle endurance during brief contractile

activity at a given relative workload

Older individuals cannot sustain same absolute work load

Thesis study overall absolute workload for protocol of 3 sets of10 rep 80% of 6 exercises was same for young, middle aged and

older groups. Older men able to do whole protocol.


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Hormonal AdaptationsTestosterone

Total T levels decrease by about 1% each yearbeginning at about the age of fortyA lower production of T in older men =decreasedability for the body to maintain and add leanmuscle mass

Most of the research done on young malesubjects and shows an increase in circulating Tafter and during acute high-volume exercise.Most studies show a muted response in older

men (and women) to acute exercise. Myresearch has shown T response to be same in 3age groups of men.


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Hormonal AdaptationsTestosterone Continued

Factors include intensity, exercise volume,amount of muscle usedWomen do not usually se a rise in T but initiallevels may be correlated to muscle trainability

Studies that follow subjects through a period ofresistance training generally show no increases,regardless of age, in the baseline levels of Tduring the training or after the training period is

over


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Hormonal Adaptations

Growth Hormone Promotes bone and muscle

growth

Mediated by Insulin-like

growth factors (IGFs) andbinding proteins (IGFBP-3)

Young subjects = increasein both GH and IGF-I after

acute exercise Older subjects show

diminished response


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Conclusions

Since older individuals adapt to resistanceexercise in a manner similar to young people,the decline in force producing capacity and

metabolic capacity are not inevitable.Changes may be due to reduction in activitymore than primary effects of aging

Adaptations to exercise training may preventsarcopenia, enhance ADLs, prevent falls,increase BMD, etc

Adaptations to Resistance Training in the Elderly

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