Aging and the effects of exercise on muscle mass and function

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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

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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?
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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
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Changes in Muscle Mass with Aging
Lexell et al., 1988
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Sarcopenia
age-associated decline in muscle mass

• Sarco flesh (muscle).
• penia deficiency.
• Sarcopenia is associated with increased mortality
  and functional decline
• Roubenoff, 2003

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Sarcopenia
age-associated decline in muscle mass
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Sarcopenia

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

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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
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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
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Sarcopenia

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

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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
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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?
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Sarcopenia

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

Rosenberg 1989
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Prevalence () of Sarcopenia
New Mexico Elder Health Survey, Baumgartner et
al. 1998
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II. Changes in Muscle Performance with Aging
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Muscle Strength

• Maximum capacity to generate force or tension.

• Muscle CSA
• Intrinsic factors
• MU recruitment / Firing rate

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Upper extremity strength
of 20 yr old group
Metter et al., 1997 J. Gerontol.
Age
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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
50-70 Larsson, 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
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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 thereafter Evans, 1997
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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

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Muscle Power

• Power Maximum rate of work performance
• Power Force x Velocity

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Power vs. strength over time
of 20 yr old group
Metter et al., 1997 J. Gerontol.
Age
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Muscle Power

• Men and women in their 70s compared to 20s
• Vertical Jump Force 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

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How do changes in strength and power impact
function?
MVC/Power needed to perform ADLs
Diminished reserve capacity
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III. Factors Responsible for Age-Related Changes
in Muscle Mass and Function
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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
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Sarcopenia
Roubenoff, 2003
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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

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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
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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
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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 I
ncreased 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
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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)
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IV. Does Exercise Restore Muscle Mass and
Function?
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Muscle and Neural Adaptations with Resistance
Training
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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

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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
• 
  
  

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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
  
  
  

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Resistance Training in Older Adults
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Power Training in Older Adults
Fielding et al. (2002) Power training in older
women (N25 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 _at_ 70 1RM
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The Disablement Pathway (Nagi, 1965 Verbrugge
Jette, 1994)
Pathology
Impairment
?
Strength Power
Functional Limitation
?
Disability
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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
  
  
  

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Functional Threshold
Threshold
Healthy Elderly
Motor Impaired Pre-Frail
Functionally Limited (Frail)
Function
Strength/Power
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The Disablement Pathway (Nagi, 1965 Verbrugge
Jette, 1994)
Pathology
Impairment
Functional Limitation
Correcting strength impairments has been
primary focus
Disability
What about other impairments?
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Muscle Power

• Maximum rate of work performance
• Power F x V

Key component of success in athletics
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Is Muscle Power and Contraction Velocity
Important in Older Adults?
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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
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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
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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
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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
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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
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Current Study - Sayers

• 53 (12 currently) older men and women gt 65 years
  of age will perform 12 weeks of RT 3x/week
• Velocity Training 3 x 14 _at_40 1RM "as fast as
  possible"
• Strength Training 3 x 8 _at_80 1RM over 2 seconds
• Control
• Functional Tasks Stair Climb, Chair rise, Timed
  Up and Go, Balance, Short and long walking tasks

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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