Professional runners and hobbyists join a marathon to stay fit, but what if the activity that is supposed to keep you healthy cost you your life?

Joining a marathon takes lots of effort and time, but to ensure the runner is in top shape during the run, he or she should be highly hydrated.

St. Luke's Orthopedic Surgeon, Dr. George Canlas, said to avoid fainting and heat stroke during marathons, hydration is key.

A hydration plan should be formulated during the preparation and training phase. While training, runners should monitor the percent of weight they have lost after running and convert that to its water loss equivalent. With that, runners could estimate how much fluid they will be needing during the actual marathons, Canlas said.

For activities below one hour, Canlas said drinking water is enough. But for distance events lasting above an hour, electrolytes, sports drinks are needed.

Drinking in intervals during a marathon is also required, with runners personally determining when they already need to take a sip or gulp.

Canlas added that shivering after a marathon is the body's mechanism to compensate for the lack of fluids.

Lastly, he advised runners, specially those 35 years old and above, to have a complete check up with their cardiologist before going the distance.