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Tuesday, November 17, 2015

Sarcopenia the largely neglected "penia"

There are now at least four classes of medications that have received FDA approach for the treatment of osteoporosis and, according to various guidelines, for certain instances of " high risk"  cases of osteopenia.Family practitioners,internists and gynecologists have all joined the crusade to detect by using a questionnaire based risk tool and by bone  density scans  those patients thought to be at high risk" for fragility fractures and thousands of prescriptions for the bisphosphonate  category of anti osteoporosis drugs have been written.

In regard to the other age related loss of tissue integrity ,sarcopenia, there are no medications proven to help and no popular screening test.Only resistance exercise along with an adequate protein intake have been shown to mitigate the loss and in some relatively short periods of time in clinical trials have actually increased muscle mass and strength.

In regard to quantification of the loss of muscle size and strength a number of clinical papers have been published.Here are the stylized facts: From abut age 40 to age 70 there is about a 1-1.5% annual loss of strength as least as measured by the leg extension tests. Then  things get worse around  age 70 where losses of 2.5% or more per year have been documented. Men have been shown to show a greater proportional loss than women and in one study Afro Americans showing a greater loss than Caucasians.

There is a  proportionally greater loss in type 11, ( fast twitch)  muscle fibers  than the slow twitch type 1 fibers. Some of the muscle loss is due to a loss of anterior horn cells with aging. with more type 11 muscle cell loss.Some of the type 11 are replaced by type 1 cells.There is also evidence of qualitative  changes in muscles in the elderly among which there is the deposition of fat within fibers and possibly changes in the angular or spatial arrangement of fibers. Walking , cycling and other aerobic type exercises are largely powered by the slow twitch fibers and a  reasonable anti sarcopenia regimen would include aerobic and resistance exercises,the latter to try a preserve some type 11 fivers. .

The age related decline in maximal oxygen uptake can also be blamed in part on loss of muscle function. About half of the loss of max 02 is due to stroke volume of  the heart and about half to decrease in  a-v o2 uptake which is driven by loss of muscle mass with the associated decrease in the capillary density and mitochondrial mass.

Sarcopenia and osteopenia are related in several ways.The prevention of sarcopenia by resistance exercises also can increase bone density.The sarcopenic person is more likely to fall and sustain a fracture.No randomized trials  are likely to be done to compare a program with resistance exercise and weight bearing excise versus any one the anti-osteoporosis medications.

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