You burn fewer calories when you exercise in cold weather than you do when it’s hot. The hotter it is, the more extra work your heart has to do to prevent you from overheating. More than 70 percent of the energy produced by your muscles during exercise is lost as heat. So the harder you exercise, the hotter your muscles become. In hot weather, not only must your heart pump extra blood to bring oxygen to your muscles, it must also pump hot blood from your heated muscles to your skin where heat can be dissipated.
On the other hand, in cold weather, your heart only has to pump blood to your muscles and very little extra blood to your skin to dissipate heat. Your muscles produce so much heat during exercise that your body does not need to produce more heat to keep you warm. So your heart works harder and you burn more calories in hot weather. This information should not discourage you from exercising when it’s cold, because staying in shape is a year-round proposition. However, it may help to explain why so many people find the pounds creeping on in the wintertime, even when they stay active.
Dear Dr. Mirkin: What causes dark facial hair on a woman?
Five to ten percent of North American women have hirsutism, or excessive hair on their faces and bodies. Women have the same number of hairs on their bodies and faces as men do, but the male hormone, testosterone, makes hairs thicker, darker and longer, so they are more noticeable. Some women with heavy facial and body hair have normal amounts of testosterone and inherit this tendency. Others have a medical condition that causes their bodies to produce larger amounts of testosterone.
Women with noticeable facial hair should get blood tests for testosterone to measure male hormones made by the ovaries and DHEAS to measure male hormones produced by the adrenal glands. They should also get a sonogram of their ovaries to test for polycystic ovary syndrome (PCOS) in which the ovaries do not release eggs each month. Other PCOS symptoms include storing fat primarily in the belly, irregular periods, acne, or infertility. For more on diagnosis and treatment of PCOS see report #8124.
Dear Dr. Mirkin: Can I exercise after donating blood?
A healthy person should be able to recover completely from donating blood in eight weeks, but you may lose some of your ability to train for a few days. Following a donation of one pint, blood volume is reduced by around ten percent and returns to normal in 48 hours. So, for two days after donating, you should drink lots of fluids and probably exercise at a reduced intensity or not at all. Donating blood markedly reduces competitive performance for three to four weeks as it takes that long for blood hemoglobin levels to return to normal.
You should not donate blood more often than every eight weeks because it takes that long to replace lost nutrients. If you donate blood frequently you need to make sure to replace the B vitamins and iron that you lose with the blood. You can meet your needs for iron by eating meat, fish or chicken or by taking iron supplements; and you can meet your needs for the B vitamins with whole grains and diary products. Donating blood at least four times a year may help to prevent heart attacks by lowering blood cholesterol levels significantly and reducing iron levels. Iron in the bloodstream converts the bad LDL cholesterol to oxidized LDL which can form plaques in arteries.
Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., and his wife, nutritionist Diana Mirkin bring you news and tips for your healthful lifestyle. A practicing physician for 50 years more
The Good Food Book
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