Sunday, 27 February 2011

Is Marathon Good for Health ?

By Syed K Haque, MD
Image Credit: KJohansson
The Fresh Air Fund is inviting runners to 13.1-mile marathon that takes you through beautiful Central Park, action-packed Times Square and ends with breathtaking finish-line views of the New York City harbor. So the question is, " Is it Good for health?".

Role in Weight Loss

In a study, published in Journal Obesity, researchers followed 6406 runners over 7.4 years. What they found would be useful in motivating many to take to running.
They found that when initially sedentary men and women started running regularly, they lost weight at the rate of 0.017 kg/km per week in case of men and 0.023 kg/km per week in case of women(1). Should this now be used to decide how much to run per week to achieve our desired weight loss goal in a short time ?

American Heart Association recommends, "..perform any moderate-to-vigorous-intensity aerobic activity for at least 30 minutes on most days of the week at 50–85 percent of your maximum heart rate". They caution, "...But don't overdo it. Too much exercise can give you sore muscles and increase the risk of injury." According to them, the maximum heart rate is 220 minus your age(2).

What after having achieved your desired weight loss goal ?

The above study on 6406 runners, having found weight loss with regular running, also found that those who quit running gained weight at a rate of 0.005 kg/km per week in men and 0.018 kg/km per week in women. So to maintain weight, it suggests regular exercise.

How to avoid dehydration ?

Another study has found that during a marathon the maximum weight loss occurs in the first 4 hours (3). This suggests proper fluid intake right from the start to avoid dehydration.Some people suggest taking weight before and after a marathon, and making up for the loss through drinking water.

Could rehydration, the solution to dehydration, be harmful ?

Sometimes, athletes consume too much water leading to low sodium in the blood. While researchers have argued on what causes low sodium in marathon runners ? They generally believe that it's overdrinking which dilutes the blood, and blame the global sports drink industry for continuing to promote overdrinking. Some also believe in the role of loss of sodium in sweat(4). Many sports specialist recommend fluid intake ad libitum ( "at one's pleasure"). So listening to the body's own alarm "thirst","thirst","thirst" should be a useful guide to fluid intake .

What should we do ?

Measure your weight before and after exercise. Drink in moderation. Consult your physician if you have headache, confusion or any other new symptom. Follow the advice of American Heart Association regarding physical activity.


1.Williams PT, Thompson PD.Dose-dependent effects of training and detraining on weight in 6406 runners during 7.4 years.Obesity (Silver Spring). 2006 Nov;14(11):1975-84.

2. Physical Activity-American Heart Association. Feb 19,2011.

3.Kao WF, Shyu CL, Yang XW et al.Athletic performance and serial weight changes during 12- and 24-hour ultra-marathons.Clin J Sport Med. 2008 Mar;18(2):155-8.

4.Yoram Epstein and Yoav Cohen‐Sivan.Exercise‐associated hyponatraemia: facts and myths.Br J Sports Med. 2007 February; 41(2): 111.

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