1. Aging and the effects of exercise on muscle mass and function
Stephen P. Sayers, PhD, Department of Physical Therapy, University of Missouri

2. 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?

3. Changes in Muscle Mass with Aging
40% loss in muscle mass from 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

4. Changes in Muscle Mass with Aging
Lexell et al., 1988

5. age-associated decline in muscle mass
Sarcopenia
age-associated decline in muscle mass
“Sarco” flesh (muscle).
“penia” deficiency.
Sarcopenia is associated with increased mortality and functional decline
Roubenoff, 2003

6. age-associated decline in muscle mass
Sarcopenia
age-associated decline in muscle mass
21 year old Female (BMI = 24.3 kg/m2)
73 year old Female (BMI = 24.5 kg/m2)

7. Sarcopenia Muscle Fiber Changes with Aging:
Decreased muscle fiber size (atrophy)
2) Decreased number of muscle fibers

8. Sarcopenia Muscle Fiber Changes with Aging: 1) Atrophy
Men: 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

9. Sarcopenia Type I Type II 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

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

11. Sarcopenia 25% loss in men ages 19-37 to 70-73 (110,000 difference)
Muscle Fiber Changes with Aging:
2) Decreased number of fibers
25% loss in men ages to (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

12. Sarcopenia Selective loss of Type II fibers:
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 and 60-65
Larsson, 1982
• Loss of Type II fibers?
• Acquiring more Type I fibers?

13. Sarcopenia
“No single feature of age-related decline can more dramatically affect nutritional status, ambulation, mobility, and functional independence.”*
*Rosenberg 1989

14. Prevalence (%) of Sarcopenia*
43.2
52.6
>80
35.9
26.7
75 – 80
33.3
19.8
70 – 74
23.1
13.5
<70
Females
(n=173)
Males
(n=205)
Age group
(years)
*New Mexico Elder Health Survey, Baumgartner et al. 1998

15. II. Changes in Muscle Performance with Aging

16. Muscle Strength Maximum capacity to generate force or tension.
Muscle CSA
Intrinsic factors
MU recruitment / Firing rate

17. Upper extremity strength
% of 20 yr
old group
Metter et al., 1997
J. Gerontol.
Age

18. 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 Larsson, 1979
# women unable to life 4.5 kg (10 lbs) increased from 40% in yr olds to 65% in those age Jette & Branch, 1981

19. 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

20. 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

21. Muscle Power Power: Maximum rate of work performance
Power = Force x Velocity

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

23. Muscle Power Bosco & Komi, 1980 Skelton et al., 1994
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

24. How do changes in strength and power impact function?
% MVC/Power needed to perform ADLs
*Diminished reserve capacity

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

26. age-associated decline in muscle mass
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

27. Sarcopenia
Roubenoff, 2003

28. 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

29. Fiber Characteristics -Multiple MHC isoforms -Motor Unit Remodeling
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

30. 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

31. 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

32. 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%)

33. IV. Does Exercise Restore Muscle Mass and Function?

34. Muscle and Neural Adaptations with Resistance Training

35. 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

36. Resistance Training in Older Adults
Landmark Studies:
Resistance training and strength:
Men (12 weeks): % increase
Frontera et al., 1988
Women (12 weeks): % increase
Charette et al., 1991
Men & Women (8 weeks): 174% increase
Fiatarone et al., 1990

37. Resistance Training in Older Adults
Landmark Studies
Resistance training and hypertrophy:
Men (12 weeks): Type I – 33.5% increase
Type II – 27.6% increase
Frontera et al., 1988
Women (12 weeks): Type I – 7.3% increase (NS)
Type II – 20% increase
Charette et a., 1991
Men & Women (8 weeks): Muscle CSA (8.4-11%)
Fiatarone et al., 1990

38. Resistance Training in Older Adults

39. 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, 70% 1RM

40. Functional Limitation
The Disablement Pathway (Nagi, 1965; Verbrugge & Jette, 1994)
Pathology
Impairment ?
Strength
Power
Functional Limitation ?
Disability

41. 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

42. Motor Impaired “Pre-Frail” Functionally Limited (Frail)
Functional Threshold
Threshold
Healthy Elderly
Motor Impaired “Pre-Frail”
Functionally Limited (Frail)
Function
Strength/Power

43. Functional Limitation
The Disablement Pathway (Nagi, 1965; Verbrugge & Jette, 1994)
Pathology
Impairment
Functional Limitation
Correcting “strength” impairments has been primary focus
Disability
What about other impairments?

44. Muscle Power Maximum rate of work performance Power = F x V
Key component of success in athletics

45. Is Muscle Power and Contraction Velocity Important in Older Adults?

46. 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

47. Functional Limitation
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

48. 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

49. 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

50. Functional Limitation
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

51. 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 1RM "as fast as possible"
Strength Training: 3 x 1RM over 2 seconds
Control
Functional Tasks: Stair Climb, Chair rise, Timed Up and Go, Balance, Short and long walking tasks

52. 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