Talking about too much of a good thing, a trio of athletes recently completed a task many experts would consider impossible: Crossing the Sahara Desert's 4,000 miles by running the equivalent of two marathons a day for 111 days!

If it's hard for you comprehend how far that really is, these runners, from Taiwan, Canada and America, crossed six countries during their nearly four-month journey, starting at the Senegal River and ending at the Red Sea. That also included the 560-mile detour they had to make, just to avoid contracting malaria and dysentery.

On top of temperatures above 100 degrees during the day (that dropped to below freezing at night), these super-athletes often ran on unpaved roads, endured all kinds of unbelievable physical aches and pains and had to dodge landmines for their trouble. By the way, a documentary of this epic trek across the desert, called Running the Sahara, will debut later this year at a film festival in Toronto.

All this makes me wonder, however, how much damage those men, as fit as they were, did to their bodies in the long run. Will all that running harm them as it did Olympic medal-winner Grete Waitz who has been struggling to fight cancer? It's always wise to treat exercise like a drug that must be prescribed precisely -- not too much or too little -- to do the most good.