Estimation of Muscle Mass

1
Estimation of Muscle Mass

• Limited availability of approaches and techniques
  to assess muscle mass.

2
Estimation of Muscle Mass

• Anthropometry alone does not provide accurate
  predictions of regional muscle mass
• The more appropriate techniques are
• CT
• MRI
• DXA

3
Estimation of Muscle Mass

• Muscles
• Cardiac
• Smooth
• Skeletal
• Represents 30 of body weight in female and 40
  in male.

4
Location of Muscle Mass

• Majority is found in the legs, with lesser
  amounts in the head, trunk, and arms

5
Estimation of Muscle Mass

• Applications
• Monitor changes in relation to growth and
  development
• Relation to aerobic and anaerobic training on
  performance.
• Evaluate the progression of catabolic disease and
  possible intervention.

6
Anthropometric Indicators

• A site-specific physical measurement will reflect
  the mass of that muscle, and the mass of the
  estimated muscle group is directly proportional
  to the whole-body skeletal muscle mass.

7
Estimation of Regional Muscle Mass

• Upper arm
• arm circumference corrected for subcutaneous
  adipose tissue thickness,
• muscle cross-sectional area estimated from the
  corrected circumference.

8
Estimation of Regional Muscle Mass

• Validity
• In adult body weights ranging from 60 to 120 of
  ideal body weights, predictive error was 7-8.
• In adult body weights above 150 of ideal body
  weight, predictive error was gt50.
• Gender specific equation have been derived to
  account for errors.

9
Muscle Metabolites

• Two metabolites specific to skeletal muscles
  include
• Creatinine.
• 3-Methylhistidine

10
Creatinine

• The precursor of creatine found in the liver and
  kidney.
• Related to FFM and skeletal muscle mass.
• One gram of creatinine excreted was 18 kg - 20
  kg of muscle mass.

11
Creatinine

• Limitations
• Large individual variability in daily creatinine
  excretion because of dietary intake.
• Other factors that may invalidate the results
  include
• age,
• gender,
• maturity,
• physical training,
• metabolic state

12
3-Methylhistidine

• An amino acid that has been suggested as a
  measure of muscle protein breakdown.
• The concentration of 3-MH in human muscle is
  relatively constant between the ages of 4 to 65,
  but decreases with urinary excretion.

13
3-MH

• A reduction in 3-MH output might reflect a
  decreased muscle mass with age.

14
3-MH

• The use of 3-MH as a marker of muscle mass has
  been criticized because of the potential
  influence of non-skeletal protein turnover on its
  excretion rate.
• The general use of urinary 3-MH excretion may be
  reasonable in conditions of physical trauma in
  which accelerated rates of protein degradation
  occur, especially in skeletal muscle.

15
Limitation to the use of Metabolites

• Although creatinine and 3-MH arise primarily from
  muscle, their relationship to skeletal muscle
  mass needs further examination with respect to
  factors that affect their pool sizes and turnover
  rates.

16
Radiographic Methods

• Several radiographic methods have been used to
  estimate muscle mass
• Computed tomography.
• Magnetic resonance imaging.
• Dual X-ray Absorptiometry.

17
Limitations of CT

• Cost per study limits the percentage of healthy
  people that can be studied.
• Exposure to radiation.
• Validity studies have yet to be completed.

18
Limitations of MRI

• Time 45 minutes for whole-body test.
• Validity studies have yet to be completed.

19
Limitations of DXA

• Cost
• Radiation exposure.
• DXA cannot distinguish between intra- and
  extra-cellular fluid.
• Ingestion of fluid and/or regional accumulation
  of water and salts will change the readings.

20
BIA

• BIA is another approach for assessing the
  regional muscle mass.

21
BIA

• The areas of adipose tissue and muscle in the
  upper arm for CT are related to those estimated
  by BIA.

22
BIA

• The type of electrodes and their placements have
  not been defined in reference to minimizing the
  error of this technique.

23
Summary

• Techniques with the best precision cost more.
• Selection of a method may depend on the resources
  available and the purpose of the test.