The piece cited this study — the first-ever comprehensive analysis of medical emergencies related to snow shoveling from 1990 to 2006 and published in the American Journal of Emergency Medicine — which found that: "U.S. hospitals treat on average about 11,500 injuries and medical emergencies a year related to shoveling snow." Moreover, shoveling:
...places extraordinary demands on the cardiovascular system and can raise heart rates above recommended upper limits after only two minutes. Freezing temperatures also constrict peripheral blood vessels, further stressing the heart. Two-thirds of shoveling injuries occurred in men, and 15% of injuries were in children under 18 years old. More than half of injuries resulted from acute musculoskeletal exertion, 20% from slips and falls, and nearly 7% from cardiac problems, such as heart attack.
The study said most shovels contribute to injuries because of their non-ergonomic design, which hasn't changed in over a century. Researchers recommend shovelers under 18 be supervised, people should warm up with light exercise before shoveling and sedentary individuals should consider hiring someone for the task.
I think their advice about warming up before shoveling (and considering hiring someone better fit for the task) should also apply to taking your 5-year-old sledding in blizzard conditions when not another soul is around to call 911 if necessary.
This program aired on January 12, 2011. The audio for this program is not available.