Doctors in Windsor, Ont., have noticed an increase in a condition called rhabdomyolysis, which is the breakdown of skeletal muscle.
Historically, the condition was most common during basic training in the military, where bodies are pushed to their physical limits. According to Ontario's Ministry of Health, it can also be the result of West Nile virus.
However, with extreme workouts and exercise boot camps growing in popularity and New Year's resolutions of better physical fitness in full swing, the condition is cropping up in the general public.
During rhabdomyolysis, muscle fibers break down and enter the bloodstream.
According to Health Canada, symptoms include muscle pain, weakness, tenderness, fever, dark urine, nausea, and vomiting. In severe cases, rhabdomyolysis can lead to kidney failure and be life-threatening.
"It has the potential to be very serious, potentially even life threatening, because if there's enough muscle breakdown, multiple other organs - the one that's of greatest severity is the kidneys -can cause the kidneys to fail completely requiring dialysis," warned Dr. Amit Bagga, director of the Regional Kidney Clinic in Windsor.
Bagga says too much extreme exercise too fast can be dangerous.
"Most studies show that consistent and persistent exercise, gradually over years, is better than these extreme versions of exercise for short periods," Bagga said.
Dan Bosco, who owns Windsor CrossFit, said several people want the quick fix and immediate results.
"That's why I have to come in and make sure these people aren't pushing too hard so that they don't hit those levels of intensity that could induce rhabdo.[rhabdomyolysis]," Bosco said.
Bosco said his club gained several new members early in the new year.
Those new to high-intensity workouts are already hooked.
"It's working all muscles every time, it's totally different compared to the style of workouts I used to do," Kyle Cant said. "This is totally different and I love it."