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Muscle mass and strength. Muscle mass is the primary determinant of strength Obese individuals have higher lean mass therefore are stronger than thinner people Men have proportionally more lean than women thus are stronger at the same weight

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muscle mass and strength
Muscle mass and strength
  • Muscle mass is the primary determinant of strength
    • Obese individuals have higher lean mass therefore are stronger than thinner people
    • Men have proportionally more lean than women thus are stronger at the same weight
    • Sarcopenia, the loss of muscle mass is the major determinant of the loss of strength with age.
changes in muscle with age
Changes in muscle with age
  • Loss of muscle fibers
  • Loss of motor neurons at the spinal cord level
  • Reduction in type II fibers from 60% to 30%
  • Increased infiltration of muscle with fat
changes in muscle metabolism with age
Changes in muscle metabolism with age
  • Increase in mitochondrial DNA mutation
  • Decline in muscle mitochondrial protein synthesis (40%)
    • Decreased oxidative phosphorylation and ATP generation
    • Results in fatigability
  • Decline in myosin heavy chain synthesis
    • Major protein involved in ATP and conversion of chemical to mechanical energy
sarcopenia what is driving the process
Sarcopenia: What is driving the process?
  • Chronic inflammation?
    • Acute inflammation: anorexic - catabolic state
    • Relationship to cancer and cardiac cachexia?
  • Decline in anabolic hormones?
    • GH/IGF-1
    • Decline in sex steroid hormones
      • Free testosterone
      • DHEA
    • Fading effectiveness of insulin
  • Loss of innervation?
muscle quality loss of strength greater than loss in muscle mass health abc
Muscle Quality – Loss of strength greater than loss in muscle mass (Health ABC)

Nm of torqueper cm2 muscle area

Age

muscle quality
Muscle quality

Strength

Function

Lean mass/muscle

+

?

_

Fat mass

slide9

Skeletal Muscle fat

Less More Most

slide11

Muscle area and attenuation are both inversely associated with age: The Health ABC Study

50

Men

180

Women

160

45

140

40

Mid-thigh attenuation (HU)

Mid-thigh CSA (cm2)

120

35

100

30

80

60

25

<71

71-72

73-74

75-76

77-78

79-80

<71

71-72

73-74

75-76

77-78

79-80

Age (y)

Age (y)

Goodpaster, BH. J Appl Physiol 2001;90:2157-2165.

what about the quality of muscle

Men

Women

What About the Quality of Muscle?

1.3

1.2

1.1

Specific force (Nm•cm-2)

1.0

0.9

0.8

0.7

< 30.9

31.0-35.5

35.6-40.

> 40.4

Muscle Attenuation (HU)

slide13
“Metabolic Obesity”Intermuscular fat and Visceral fat:Associations with Fasting Insulin by BMI strata

Women

Men

Standardizedbeta

BMI

BMI

slide14

Lower extremity function is worse with higher fat and lower muscle area – Health ABC

*

*

*

*P<0.01

*

*

Lower-extremity performance

*

Tertiles

of total

body fat

Tertiles of mid-thigh muscle area

Visser M, et al, JAGS, in press

what is the prevalence of sarcopenia
What is the prevalence of sarcopenia?
  • No standardized definition to define an individual as sarcopenic
  • Several proposed methods
    • Lean mass
    • Lean mass relative to healthy young adult
    • Lean mass adjusted for height or height squared
    • Lean/fat ratio
    • Lean for fat mass and height
slide16
Prevalence of sarcopenia and sarcopenic obesity in Health ABC - lean mass adjusted for height and fat mass
risk factors for sarcopenia
Risk factors for Sarcopenia
  • Likely multifactorial and complex
    • Both behavioral and biological factors probably important
  • Few identified
    • New Mexico Elder Health Survey:
      • Age, income, low activity, smoking, lung disease (Baumgartner, 1998)
      • Higher SHBG ( Baumgartner, 2001)
    • Health ABC:
      • Age, physical activity, smoking; in men, cancer and number of chronic conditions
prevention approaches
Prevention approaches
  • Maintain or increase lean mass
    • Avoid weight loss
    • Anabolic hormones (GH - IGF-1, Testosterone, DHEA’s)
    • Block cytokines (TNF alpha, Il-6?)
    • Nutritional approaches - ranging from creatine to caloric restriction
  • Maintain or increase muscle quality
    • Improve metabolic capacity of muscle
    • Decrease loss of type 2 fibers
    • Strength training
clinical trials to prevent sarcopenia
Clinical trials to prevent sarcopenia
  • Testosterone, DHEA
    • Both result in very small increases in lean mass and strength with side effects limiting use
  • GH, GH secretagogues
    • Slight increase in mass without increase in strength
  • Exercise
    • Minimal increase in mass, but large increase in strength
the role of exercise in the prevention of sarcopenia

pre

Extension

post

Flexion

The role of exercise in the prevention of sarcopenia

50

150

45

40

140

35

30

130

Knee Strength (kg)

25

Area (cm2)

20

120

15

10

110

5

0

100

Right Left

0 12

Weeksof Resistance Training

Frontera et al. J. Appl. Physiol., 1988

lessons from observations of regarding sarcopenia and muscle quality
Lessons from observations of regarding sarcopenia and muscle quality
  • Preserving lean mass is likely the major key to preserving strength
  • The quality of the muscle is also important - fat infiltration impairs muscle quality
  • Both quantity and quality are important targets for the preservation of function in older age
conclusions
Conclusions
  • Methodologic advances in the ability to quantify muscle mass and fat distribution have been key to progress
  • More work is now needed to determine risk factors
  • Preventive interventions will be depend in part on these findings
  • Current strategies
    • Avoid weight loss
    • Exercise
slide23
End
  • Anne B. Newman, MD, MPH
  • Sarcopenia in Older Adults
  • August 19th
  • University of Pittsburgh School of Medicine
  • Pittsburgh, PA, 15213
  • 412-624-4012
  • anewman@pitt.edu