Presentation on theme: "Muscle mass and strength Muscle mass is the primary determinant of strength –Obese individuals have higher lean mass therefore are stronger than thinner."— Presentation transcript:
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.
Strength declines across age groups 70-79 Health ABC Torque (Nm) 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 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? 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) Nm of torqueper cm 2 muscle area Age
Muscle quality Lean mass/muscle Strength Function Fat mass + ? _
Histochemical Staining of Neutral Fat Content within Skeletal Muscle Fibers
60 80 100 120 140 160 180 Mid-thigh CSA (cm2) 25 30 35 40 45 50 Mid-thigh attenuation (HU) <7171-7273-7475-7677-7879-80 Age (y) <7171-7273-7475-7677-7879-80 Age (y) Men Women Muscle area and attenuation are both inversely associated with age: The Health ABC Study Goodpaster, BH. J Appl Physiol 2001;90:2157-2165.
What About the Quality of Muscle? 0.7 0.8 0.9 1.0 1.1 1.2 1.3 Specific force (Nmcm-2) < 30.931.0-35.535.6-40.> 40.4 Muscle Attenuation (HU) Men Women
MenWomen “Metabolic Obesity” Intermuscular fat and Visceral fat: Associations with Fasting Insulin by BMI strata BMI BMI Standardized betaStandardized betaStandardized betaStandardized beta
Lower-extremity performance * * * * * * Tertiles of total body fat Tertiles of mid-thigh muscle area Lower extremity function is worse with higher fat and lower muscle area – Health ABC Visser M, et al, JAGS, in press * P<0.01
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
Prevalence of sarcopenia and sarcopenic obesity in Health ABC - lean mass adjusted for height and fat mass
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 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 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 Frontera et al. J. Appl. Physiol., 1988 0 5 10 15 20 25 30 35 40 45 50 Flexion Extension Knee Strength (kg) 0 12 Weeks of Resistance Training 100 110 120 130 140 150 pre post Area (cm 2 ) Right Left
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 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
End Anne B. Newman, MD, MPH Sarcopenia in Older Adults August 19th University of Pittsburgh School of Medicine Pittsburgh, PA, 15213 412-624-4012 email@example.com firstname.lastname@example.org
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