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Don't Depend on Maximum Heart Rate Formulae

The standard maximum heart rate formula (MHR=220-age) is supposed to predict the fastest your heart can beat and still pump blood through your body. It is not accurate. This month, researchers at Northwestern Medicine announced that the formula for women should be 206 minus 88 percent of a woman's age (Circulation, July 2010). However, this formula is also inaccurate.

In 1970, Dr. Sam Fox, one of the most respected heart specialists in the world, was on a plane with a young researcher named William Haskell. They put together several studies comparing maximum heart rate and age. Dr. Fox plotted a graph of age verses maximum heart rate and noticed that maximum heart rate appeared to equal to 220 minus a person's age. Since they reported this formula, it has been taught in physical education courses and used to test heart function and athletic fitness.

The formula is wrong because your legs drive your heart rate; your heart does not drive your legs. Maximum heart rate depends on the strength of your legs, not the strength of your heart. When you contract your leg muscles, they squeeze against the blood vessels near them to pump blood from your leg veins toward your heart. When your leg muscles relax, your leg veins fill with blood. So your leg muscles pump increased amounts of blood toward your heart. This increased blood fills the heart and causes your heart to be faster and with more force. This is called the Bainbridge reflex. The stronger your legs are, the more blood they can pump, which causes your heart to beat faster.

In 2002, a study of 43 different formulae for MHR concluded that "no acceptable formula currently exists." The formula that fits better than others is: HRmax=205.8-(0.685 × age). It has a standard deviation of 6.4 beats per minute, which is very large (Journal of Exercise Physiology, May 2002). A study from Liverpool, England showed that the maximum heart rate for athletes is lower than for aged-matched sedentary people. The maximum heart rate of male athletes was calculated to be 202 - 0.55 × age, and for female athletes, 216 - 1.09 × age. Weight lifters and runners had similar maximum heart rates, which were significantly lower than the age-matched sedentary people. The athletes have hearts that can pump more blood with each beat than the hearts of sedentary people, so they do not beat as often (International Journal of Sports Medicine, January 2008).

All MHR formulae are based on averages. They can be used to help you plan and monitor your exercise program, but should not be interpreted as absolute limits or goals. If you want to train to become fast, use the following: Three times a week, never on consecutive days, either race or push the pace so that you are at your anaerobic threshold and then use bursts to exceed it to become short of breath. On the other four days, take it easy and do not put pressure on your muscles. The standard Maximum Heart Rate formula (MHR = 220 - age) does not apply to highly fit athletes.

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Dear Dr. Mirkin: Am I harming my health by eating a high sugar and protein meal immediately after a hard workout?

No! You are referring to recent research that shows that avoiding sugar and other carbohydrates after working out causes your cells to respond to insulin better than depriving yourself of calories or loading with extra sugar (Journal of Applied Physiology, December 2009). This study shows that restricting carbohydrates after a hard workout helps cells to respond better to insulin, which lowers both insulin and blood sugar levels, which should help prevent high rises in blood sugar after meals that cause diabetes and its many complications. Increasing insulin sensitivity also reduces your chances of suffering a heart attack.

Knowledgeable athletes train by taking a hard workout that damages muscles, feeling sore the next day and then taking easier workouts for as many days as it takes for muscles to heal. They can tell their muscles are healed when the soreness goes away. Obviously, the faster they can recover from their hard workouts, the sooner they can take their next hard workout and the greater their gain in endurance, speed and strength. Athletes eat a very high sugar and protein meal immediately after their hard workouts to help them recover faster. The sugar and other carbohydrates cause a high rise in insulin which drives the protein building block amino acids into damaged muscle cells to help them heal faster so they can take their next hard workout sooner.

Now for the good news. When you exercise, contracting muscles remove sugar from the bloodstream rapidly without needing insulin, and the harder you exercise, the more effective your muscles are in removing sugar from the bloodstream and the longer they can continue to remove sugar from the bloodstream (Circulation, July 2008). Intense exercise is far more effective in preventing and controlling diabetes than exercising at a leisurely pace (Journal of Applied Physiology, January 2006). The more intensely and the longer you exercise, the greater the increase in insulin sensitivity and control of blood sugar rises (Journal of Strength and Conditioning Research, April 2010). Furthermore, high intensity exercise maximally improves every conceivable measure of heart function and heart strength (Exercise and Sports Sciences Reviews, July 2009).

The combination of an intense workout and faster recovery for your next intense workout helps to prevent blood sugar levels from rising too high. The key is to take your sugar-protein meal when your muscles are most sensitive to insulin: during the last part of your intense workout or no longer than one hour after you finish that workout.

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Dear Dr. Mirkin: Please explain the recent study showing that calcium pills increase heart attack risk.

Calcium in pills, unlike calcium in foods, causes a rise in blood calcium levels that could damage arteries. Also, excess calcium in the blood blocks the conversion of inactive vitamin D to active vitamin D, and lack of active vitamin D increases risk for heart attacks. A review of 11 controlled studies involving about 12,000 patients found that taking calcium pills (at least 500 mg/day) without also taking vitamin D is associated with an almost 30 percent increase in heart attack risk (British Medical Journal, published online July 29, 2010). Furthermore, most people take calcium supplements to help prevent or treat osteoporosis. Taking calcium pills without vitamin D has not been shown to prevent bone fractures.

I recommend that you get your calcium in food; I do not recommend calcium pills. If you feel that you need to take them, take 1000 IU of vitamin D with each 1000 mg of calcium.

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June 21st, 2013
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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