Running daily actually resulted in leg muscles degenerating in athletes because of the immense energy consumption, reports a new study.
Using a mobile MRI unit, researchers at the University Hospital of Ulm in Germany followed runners for two months along a 4,500-kilometer course to study how their bodies responded to the high-stress conditions of an ultra-long-distance race.
"Much of what we have learned so far can also be applied to the average runner," said Uwe Schutz, a specialist in orthopaedics and trauma surgery.
The results showed that runners lost an average of 5.4 percent body volume during the course of the race, most of which was in the first 2,000 kilometers.
They lost 40 percent of their body fat in the first half of the race and 50 percent over the duration of the race. Loss of muscle volume in the leg averaged 7 percent.
"One of the surprising things we found is that despite the daily running, the leg muscles of the athletes actually degenerated because of the immense energy consumption," Schutz said.
He also found that some leg injuries are safe to "run through." Other overuse injuries, such as joint inflammation, carry more risk of progression, but not always with persistent damage.
Another key finding of the study was that the first tissue affected by running was fat tissue. More importantly, visceral fat loss (mean 70 percent) occurred much earlier in the running process than previously thought. Visceral fat is the most dangerous fat and is linked to cardiovascular disease.
"When you just begin running, the effects of fat reduction are more pronounced than in athletes who have been running their whole life," Dr. Schutz said.
"But you should do this sport constantly over the years. If you stop running for a long time, you need to reduce your caloric input or opt for other aerobic exercises to avoid experiencing weight gain."
The results were presented today at the annual meeting of the Radiological Society of North America.