Saturday, November 19, 2011

Sarcopenia: Muscle Loss with Aging

Competitive masters athletes, 40 to 81 years old, who trained four to five times per week did not lose any muscle size or significant strength with aging (The Physician and Sportsmedicine, October 2011;39(3):172-8). This shows that loss of muscle size and strength in older people is caused by lack of exercise, not just with aging. The athletes did gain fat in spite of exercising. Those in their 70s had almost as much strength and thigh muscle size as those in their 40s.

MOST PEOPLE LOSE MUSCLE: Recent studies show that after age 40, men lose more than eight percent of their muscle size each decade, and this loss of muscle increases after age 70. The people who lose the most muscle are usually the ones who die earliest. They are also most at risk for falls and broken bones.

HOW EXERCISE PREVENTS MUSCLE LOSS WITH AGING: Muscles are made up of thousands of individual muscle fibers. Each muscle fiber is innervated by a single nerve. With aging, humans lose the nerves that innervate muscle fibers, and with each nerve loss, they lose the associated muscle fiber so muscles become smaller. We used to think this happens because of aging. However, this new study and others show that lifelong competitive athletes do not lose the nerves that innervate their muscles with aging. They retain the nerves and therefore retain most of the muscle fibers that they would have lost if they were inactive.

MESSAGE: If you exercise regularly, continue to do so. If you don't, check with your doctor and then get instructions on how to start an exercise program.

Saturday, November 12, 2011

The Only Mineral Needed by Exercisers

People who are serious exercisers can be harmed by the broad recommendations for all Americans to restrict salt intake. It is true that excess salt intake can cause high blood pressure, but heavy exercise usually helps to protect people from salt causing high blood pressure. The minimum salt requirement is 1,500 mg (1 teaspoon) of sodium a day. The average North American is told not to exceed 2,300 mg per day, but he ingests too much salt, between 3,100 and 4,700 mg of sodium per day.

FITNESS DOES NOT REDUCE SALT LOSS: This month a study from Spain shows that being fit does not reduce the concentration of salt in sweat (European Journal of Applied Physiology, November 2011). A person who exercises in the heat can lose far more than 4000 mg of salt. So in spite of the fact that most serious exercisers get a lot of salt from the massive amounts of foods that they eat, they can still become salt deficient.

SYMPTOMS OF SALT DEFICIENCY: If you are a serious exerciser and you suddenly are not recovering from your workouts as fast as you usually do, a common cause is loss of salt. Symptoms of salt deficiency include muscle weakness, soreness and cramps, loss of strength and tiredness. Get a blood test for sodium on the day after a hard workout. If your blood sodium is below 132 mmol/L, you need more salt.

SALT IS NECESSARY FOR SERIOUS EXERCISERS: In 1942 the US government commissioned James Gamble of Harvard Medical School to set mineral requirements for soldiers fighting in the Pacific. He showed that sodium (table salt) is the only mineral that needed to be replaced. Potassium, magnesium, calcium and the trace minerals were not significant. To this day, nobody has improved on his data and recommendations.

HOW SALT DEFICIENCY HAMPERS PERFORMANCE: Not taking in salt when you exercise for more than two hours can prevent you from retaining the water that you drink. It can also block thirst, so you may not know that you are dehydrated. Thirst is a late sign of dehydration. You lose water during exercise primarily through sweating, and sweat contains a far lower concentration of salt than blood. So during exercise, you lose far more water than salt, causing the concentration of salt in the blood to rise. You will not feel thirsty until the concentration of salt in the blood rises high enough to trip off thirst osmoreceptors in your brain, and it takes a loss of two to four pints of fluid to do that.

SALT BEFORE COMPETITION: Taking salt just before competition improves performance (Medicine and Science in Sports and Exercise, January 2007; Clinical Journal of Sport Medicine, January 2007). Athletes who took extra salt had larger blood volume and greater endurance. Salt makes you thirsty earlier so you drink more, and salt in your body holds water so you have more water available to meet your needs.

ENDURANCE EVENTS LASTING LONGER THAN FOUR HOURS: You can keep yourself fresh during extended exercise by eating foods with salt and drinking frequently, before you feel hungry or thirsty. Once you are weakened by loss of fluid or salt, it becomes very difficult to regain your strength. Commercial sports drinks help increase endurance with their caffeine, sugar, salt, and to a lesser degree, protein content. It is unlikely that any other component improves performance (The Physician and Sportsmedicine, April 2010).

MOST EXERCISERS DO NOT SUFFER FROM SALT DEFICIENCY: The North American diet contains up to 10 times your minimal salt requirements. Salt is added to almost all prepared foods, so if you doubled or tripled your salt losses through sweating, you would still not be deficient because you are already taking in far more salt than you need.

EXERCISE CAN PREVENT RISE IN BLOOD PRESSURE FROM SALT: People who exercise are far less likely to suffer high blood pressure from eating food with excess salt intake (presented at the American Heart Association Scientific Sessions, March 2011). High blood pressure increases risk for heart attacks, strokes, and kidney damage. Many middle-aged people who start an exercise program lose their tendency to develop high blood pressure when they take in extra salt (Journal of Human Hypertension, May 2006).

If you are concerned about your blood pressure, you can buy an inexpensive wrist cuff and check your systolic blood pressure at bedtime. If it is below 120, you probably do not need to restrict salt.