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Aging and the effects of exercise on muscle mass and function. Stephen P. Sayers, PhD, Department of Physical Therapy, University of Missouri. Outline. I. Changes in Muscle Mass with Aging. Sarcopenia. II. Changes in Muscle Performance with Aging. Strength, Power.

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aging and the effects of exercise on muscle mass and function

Aging and the effects of exercise on muscle mass and function

Stephen P. Sayers, PhD, Department of Physical Therapy, University of Missouri

slide2

Outline

I. Changes in Muscle Mass with Aging

Sarcopenia

II. Changes in Muscle Performance with Aging

Strength, Power

III. Factors Responsible for Age-Related Changes in Muscle Mass and Function

IV. Does Exercise Restore Muscle Mass and Function?

slide3

Changes in Muscle Mass with Aging

40% loss in muscle mass from 20-70 years of age

Rogers & Evans, 1993

6% decline in muscle mass per decade from age 30-70

Fleg & Lakatta, 1988

1.4 –2.5% decline in muscle mass per year after age 60

Frontera et al., 2000

sarcopenia
Sarcopenia

age-associated decline in muscle mass

  • “Sarco” flesh (muscle).
  • “penia” deficiency.
  • Sarcopenia is associated with increased mortality and functional decline

Roubenoff, 2003

sarcopenia6

21 year old Female (BMI = 24.3 kg/m2)

73 year old Female (BMI = 24.5 kg/m2)

Sarcopenia

age-associated decline in muscle mass

sarcopenia7
Sarcopenia
  • Muscle Fiber Changes with Aging:
  • Decreased muscle fiber size (atrophy)
  • 2) Decreased number of muscle fibers
sarcopenia8
Sarcopenia

Muscle Fiber Changes with Aging:

1) Atrophy

Men: 20-29 and 60-65

Type I - no change

Type II - 25% decrease

Men: 19-84

Type I - 6% decrease

Type II - 35% decrease

Larsson et al., 1978

Lexell, 1991

slide9

Sarcopenia

  • Muscle Fiber Changes with Aging:
  • Atrophy
  • By age 85, Type II fiber CSA may be less than 50% of that for Type I fibers

Type I

Type II

slide10

Sarcopenia

  • Muscle Fiber Changes with Aging:
  • Atrophy
  • Maintenance of Type I fiber size may be compensatory hypertrophy
  • Lexell, 1991
  • Disuse of Type II fibers?
sarcopenia11
Sarcopenia

Muscle Fiber Changes with Aging:

2) Decreased number of fibers

25% loss in men ages 19-37 to 70-73 (110,000 difference)

Muscle of 20 yr old - 70% fibers

Muscle of 80 yr old - 50% fibers

Lexell et al., 1983

Lexell et al., 1988

sarcopenia12
Sarcopenia

Muscle Fiber Changes with Aging:

2) Decreased number of fibers

Selective loss of Type II fibers:

Type I fiber % increased from 40 to 55 in men ages 20-30 and 60-65

Larsson, 1982

• Loss of Type II fibers?

• Acquiring more Type I fibers?

sarcopenia13

Sarcopenia

“No single feature of age-related decline can more dramatically affect nutritional status, ambulation, mobility, and functional independence.”*

*Rosenberg 1989

prevalence of sarcopenia

Age group

(years)

Males

(n=205)

Females

(n=173)

<70

13.5

23.1

70 – 74

19.8

33.3

75 – 80

26.7

35.9

>80

52.6

43.2

Prevalence (%) of Sarcopenia*

*New Mexico Elder Health Survey, Baumgartner et al. 1998

slide16

Muscle Strength

  • Maximum capacity to generate force or tension.
  • Muscle CSA
  • Intrinsic factors
  • MU recruitment / Firing rate
upper extremity strength
Upper extremity strength

% of 20 yr

old group

Metter et al., 1997

J. Gerontol.

Age

slide18

Strength Loss with Aging

8% loss per decade after age 45 -

Brooks, 1995

Strength increases up to age 30

Plateaus from age 30 – 50

Declines 24-36% between 50-70Larsson, 1979

# women unable to life 4.5 kg (10 lbs) increased from 40% in 55-64 yr olds to 65% in those age 75-84.Jette & Branch, 1981

slide19

Strength Loss with Aging

Most precipitous loss after age 70:

35% loss over 11 year period in 80 year old subjects

Grabiner & Enoka 1995

15% loss per decade up to 6th and 7th decades of life, 30% loss per decade thereafterEvans, 1997

slide20

Strength loss does not always parallel loss in muscle mass

  • Specific Strength (Force per CSA) may be lower in older compared to younger men
  • Quadriceps CSA decreased 21% (65-80)
  • Force production decreased 39%

Jubrias et al. (1997)

  • Quantitative and qualitative changes
slide21

Muscle Power

  • Power: Maximum rate of work performance

Power = Force x Velocity

power vs strength over time
Power vs. strength over time

% of 20 yr

old group

Metter et al., 1997

J. Gerontol.

Age

slide23

Muscle Power

  • Men and women in their 70s compared to 20s:

Vertical JumpForce 50% lower

Vertical Jump Power 70-75% lower

Bosco & Komi, 1980

  • Strength loss 1-2% per year after 60
  • Power loss is ~3.5% per year

Skelton et al., 1994

slide24

How do changes in strength and power impact function?

% MVC/Power needed to perform ADLs

*Diminished reserve capacity

sarcopenia26
Sarcopenia*

age-associated decline in muscle mass

  • etiology related to changes in:

hormone status

neural factors

Inflammation

protein/energy intake

disuse atrophy

Age-related

Behavioral

*Rosenberg 1989

slide27

Sarcopenia

Roubenoff, 2003

slide28

What factors are responsible for decreased strength in older men and women?

  • Changes in force producing capability of muscle tissue
  • Changes in neural activation of muscles
slide29

1.Changes in force producing capabilities of muscle

1.Decrease In

Specific Tension of

Individual Fibers

2. Relative Increase in

Type I

Fiber Characteristics

Death of –motor

neurons

(spinal cord)

-Multiple MHC isoforms

(hormones)

Death of Some

Muscle Fibers

-Re-innervation of

Some fibers

-Motor Unit Remodeling

(Fewer, larger MUs)

3. Muscle Atrophy

Barry & Carson, J Gerontol 2004

slide30

2. Changes in neural activation of muscles

“The ability to develop maximal force… is dependent upon the capacity of the nervous system to maximally activate individual muscles, and to coordinate appropriately the activation of groups of muscles.”

Barry & Carson, J Gerontol 2004

2 changes in neural activation of muscles
2. Changes in neural activation of muscles

1.Inability to maximally

activate individual

muscles

2. Inability to coordinate

groups of muscles

•Increased co-activation of

agonist/antagonist

•Increased antagonist activation

•Reduced cortical drive

•Altered –motor neuron excitability

Reduces net maximal

joint torque

Limits rate of force

development

•NMJ Degradation

•Impaired E-C Coupling

•Distrupted agonist/synergist

activation

Barry & Carson, J Gerontol 2004

slide32

Factors responsible for decreases in power

Skeletal muscle mass

“Sarcopenia”

Neural Factors

Fiber number,

Cross-sectional area,

Selective type II atrophy

Larsson, 1979

Loss of Motor units

(47% decrease 20-65)

Doherty, 1993

MU remodeling (Type I)

Specific tension,

in vitro shortening velocity

Larsson, 1997

Reduced MU firing rates,

Asynchronous MU firing,

Slowed nerve CV

Contraction velocity:

E-C coupling impairment

SR impairment

Actin slowing (18-25%)

resistance training in older adults
Resistance Training in Older Adults
  • Landmark RT Studies:

Moritani & DeVries (1980)

Aniansson et al. (1980)

First studies to demonstrate safety and potential for increases in strength in older men

Little hypertrophy response

slide36

Resistance Training in Older Adults

  • Landmark Studies:
  • Resistance training and strength:
  • Men 60-72 (12 weeks): 107-226% increase
  • Frontera et al., 1988
  • Women 64-86 (12 weeks): 28-115% increase
  • Charette et al., 1991
  • Men & Women 86-96 (8 weeks): 174% increase
  • Fiatarone et al., 1990
slide37

Resistance Training in Older Adults

  • Landmark Studies

Resistance training and hypertrophy:

Men 60-72 (12 weeks): Type I – 33.5% increase

Type II – 27.6% increase

Frontera et al., 1988

Women 64-86 (12 weeks): Type I – 7.3% increase (NS)

Type II – 20% increase

Charette et a., 1991

Men & Women 86-96 (8 weeks): Muscle CSA (8.4-11%)

Fiatarone et al., 1990

slide39

Power Training in Older Adults

Fielding et al. (2002)

Power training in older women (N=25; Age = 73.2 years)

Power Training: High-intensity high velocity RT

Strength Training: High-intensity low velocity RT

LP and KE: 3 x 8, 3x/wk, 16-wks @ 70% 1RM

slide40

The Disablement Pathway (Nagi, 1965; Verbrugge & Jette, 1994)

Pathology

Impairment

?

Strength

Power

Functional Limitation

?

Disability

resistance training in older adults41
Resistance Training in Older Adults
  • Effects on Function and Disability are Questionable:

Latham et al., 2003

Small to moderate effect on Function

Little to no effect on Physical Disability

slide42

Functional Threshold

Threshold

Healthy Elderly

Motor Impaired “Pre-Frail”

Functionally Limited (Frail)

Function

Strength/Power

slide43

The Disablement Pathway (Nagi, 1965; Verbrugge & Jette, 1994)

Pathology

Impairment

Functional Limitation

Correcting “strength” impairments has been primary focus

Disability

What about other impairments?

slide44

Muscle Power

  • Maximum rate of work performance

Power = F x V

Key component of success in athletics

slide46

Muscle Power and Function

Studies have shown that lower extremity muscle power is a stronger predictor of functional limitations and disability than muscle strength in older men and women

Bean et al.,2002; Suzuki et al., 2001; Foldvari et al., 2000

Muscle power declines sooner and more rapidly than strength

slide47

The Disablement Pathway (Nagi, 1965; Verbrugge & Jette, 1994)

Pathology

Impairment

Functional Limitation

*Power may be a more critical variable on which to focus resistance training protocols

Disability

slide48

Low and High Velocity Power and Function

Muscle power at high or low velocity may be more important to certain functional tasks than muscle strength

Speed at which we generate power is critical to lower intensity functional tasks

Cuoco A, Callahan DM, Sayers SP, et al. J. Am. Geriatr. Soc. 2004

slide49

Contraction Velocity and Function

Contraction velocity alone was more important to walking speed than muscle strength in older adults

Sayers SP, et al. J. Am. Geriatr. Soc. 2005

slide50

The Disablement Pathway (Nagi, 1965; Verbrugge & Jette, 1994)

Pathology

Impairment

Functional Limitation

*Contraction velocity (speed) may also be a critical variable on which to focus resistance training protocols

Disability

current study sayers
Current Study - Sayers

53(12 currently)older men and women > 65 years of age will perform 12 weeks of RT 3x/week

Velocity Training: 3 x 14 @40% 1RM "as fast as possible"

Strength Training: 3 x 8 @80% 1RM over 2 seconds

Control

Functional Tasks: Stair Climb, Chair rise, Timed Up and Go, Balance, Short and long walking tasks

preliminary conclusions
Preliminary Conclusions
  • Muscle strength and power both appear to be improved with velocity training
  • Some functional tasks appear to be improved by training at lower resistances and higher speeds
  • Too soon to tell