With challenging workouts from ultra-marathons to endurance events on obstacle courses all the rage, fitness experts say more and more weekend warriors are leaping into extreme activities before looking into the perils of overdoing it.

The drive to push the body too far too fast can backfire in most unpleasant ways. Recent research studies suggest extreme over-exercising can cause conditions like sleeplessness, blood poisoning, fractures or heart damage.

“Massive jumps in activity level, that’s how you get stress fractures,” said Dr. Derek Ochiai, an orthopedic surgeon specializing in sports medicine.

Overuse injuries, ranging from rotator cuff damage to tendonitis, comprise a significant part of his practice in Arlington, Virginia.

“Pain tells you you’re injuring something,” he said. "Instead of pounding a treadmill for 90 minutes through severe shin pain, (and) bench pressing with intense shoulder pain, stop. Rest it. Then go back at a lighter level.”

Elite athlete and running coach Tom Holland said he has seen an explosion in the number of extreme fitness events over the last decade.

“Many people who might never have competed in an organized event in the past are jumping right into these extreme races," said Holland, the author of “Swim, Bike, Run – Eat,” who has run more than 60 marathons.

“When it feels like it’s too much, it’s too much,” he said. “There is absolutely a point of diminishing returns.”

Disorientation, severe muscle cramps, cessation of sweating and dizziness are among the warning signs, he added.

A recent Australian study of ultra-marathoners found that extreme exercise may trigger blood poisoning in people who haven't trained properly.

The research, published in the International Journal of Sports Medicine, showed that pushing the body too far can cause intestinal bacteria to leak into the bloodstream, causing blood poisoning.

A 2012 study also showed long-term endurance running may cause heart muscle scarring.

Anthony Wall of the American Council on Exercise said continual fatigue, decrease in performance, a sense of apathy or distraction are subtle signs of overtraining.

"It isn’t about going hard all the time,” he said. “Professional athletes spend a tremendous amount of time in recovery and low-impact activity.”

Ochiai said the cardiovascular benefits of moderate exercise far outweigh the risk of injury.

“It’s far better to be exercising than not, but you don’t have to see results the day you start,” he said. “It’s a marathon, not a sprint.”