The lowest risk to high burn ratio is probably swimming in a non-heated pool. Whether a person can burn that many calories doing that, depends on the lenght of

The lowest risk to high burn ratio is probably swimming in a non-heated pool. Whether a person can burn that many calories doing that, depends on the lenght of the session, and their body and muscle mass. The heavier a person is, the more calories they burn just by breathing. Same with muscle. Thanks to some people, a calorie as defined in the SI is 1/1000 a CAL as written in food packaging. So people keep saying calories when actually talking about kilocalories. So by breathing for a couple of minutes an adult burns about a 1000 calories (or 1 CAL or 1 kcal). There is no completely safe activity. You can pull a muscle just by laying on a sofa, or get back pain from sitting incorrectly. Exercise mitigates these risks and increases others. The sweet spot for adults, as per the WHO, is between 2.5 to 5 hours of aerobic exercise per week, and about 2 hpk of strength exercise. More than that and injuries outweigh benefits. Can anyone lose a 1000 kcal per day extra by exercising? Probably. Can anyone spend two or three hours doing laps at the pool, daily, for the foreseeable future? Doubtful.