Marathon Mania: What's best in the long run?
Logically, if running is good for your health, then more must be better. But experts have discovered a point where the benefits are outweighed by the wear and tear on your heart - and research suggests it's about half of what training for a marathon requires.
The threshold is 32 kilometres a week. Running more than that does not improve your chance of living any longer than someone who doesn't run at all, say American researchers who analysed the data of more than 50,000 people who were tracked for up to 30 years.
Presenting their findings at the American College of Sports Medicine (ACSM) annual meeting in June last year, the researchers revealed that the 14,000 runners in the study were linked with a 19 per cent lower risk of death compared to non-runners. A U-shaped relationship between running and mortality was observed. The largest benefit was observed in those who ran 16 to 24 kilometres weekly.
Similarly, the researchers found an optimal pace and frequency. Running at between 9.7 kilometres and 11.3 kilometres per hour was linked with up to 27 per cent lower risk of death; a pace faster than 12.8 kilometres per hour had only a 7 per cent lower risk of death. Running two to five days per week produced the most benefit.
The Copenhagen City Heart Study, published last year in the European Heart Journal, showed similar results. Researchers who followed 20,000 Danes since 1976 found that the runners lived about six years longer than the non-runners, with a 44 per cent lower risk of death during the study. The optimum: jogging at a slow to average pace, for a total of one to 2½-hours per week over two or three sessions.
Marathon training, however, requires running on most days, with a weekly mileage of 60 kilometres or more, says Michael Tse, director of the Active Health Clinic at University of Hong Kong's Institute of Human Performance. Putting your body under periods of stress and running at high speeds is vital to improving performance, he says.
Cardiologist Dr James O'Keefe of Saint Luke's Hospital in Kansas City, Missouri, led a study published last year in Mayo Clinic Proceedings that suggests constant training for and competing in extreme endurance exercise such as marathons, ironman-distance triathlons, and very long distance bicycle races may cause structural changes to the heart and large arteries, leading to myocardial injury.
At rest, the heart pumps about five litres of blood per minute, increasing to up to 35 litres during strenuous exercise. While the heart is designed to handle increased volumes in short bursts, doing so for more than an hour overloads its thin-walled chambers, causing micro tears.
The good news is these abnormalities tend to return to normal within one week, according to O'Keefe's study. But in some people, over months and years of repetitive injury, this process can lead to the development of patchy myocardial fibrosis (scarring of the heart muscle).
"The take-home message for most is to limit one's vigorous exercise to 30 to 50 minutes per day," wrote O'Keefe in an editorial published recently in the journal Heart. "If one really wants to do a marathon or full-distance triathlon, and so on, it may be best to do just one or a few and then proceed to safer and healthier exercise patterns."
But not all scientists agree. Concerns over the effect of endurance exercise are overblown, according to cardiologist Dr Benjamin Levine of the University of Texas Southwestern Medical Centre in Dallas. Levine's studies of both young and old elite endurance athletes have suggested a physiological adaptation to exercise. He has found no evidence of fibrosis in these athletes.
Dr Carl Lavie, a researcher involved in the ACSM study, acknowledged that other factors may have led to a reduction in the mortality of the endurance runners in the study, such as poor diet.
"There is always a danger with too much of anything, even 'good' stuff," says Tse. Taking on too much too early may do more harm than good. Beginners should only run every other day before working up to a daily regime. Tse also recommends mixing in some cross training and alternating between high intensity training days and days of easier running with less volume.
Apart from hurting the heart, there's also the possibility of other musculoskeletal injuries. David Garrick, a physiotherapist from Physio Central, suggests at least three months' preparation for a marathon - and that's if you're already a runner. "A beginner would need probably closer to 12 months to build up to such a level without injury risk," he says. "The best rule is the 10 per cent rule: increase total mileage from the week before by only 10 per cent."
These days, distance running is becoming the norm. Hippocrates, the father of medicine, said: "The right amount of nourishment and exercise, not too much, not too little, is the safest way to health." While I'd prefer to live out my days running, I don't want to run too fast to an early finish line.
Marathon Mania is a 12-week series leading up to the Hong Kong Marathon on February 24. For more preparation tips, go to facebook.com/hkmarathon