Depending on how "wildly" you ride, the act of balancing and gripping handlebars can be very intense and can burn many calories (as opposed to simply sitting). In fact, motocross is the 2nd most physically enduring sport (soccer being the first).

Therefore it is possible that your calorie burn is very high during your stated activity-although we're not sure about the lawnmower - that may be vibration related. Otherwise the vibration of the machine may be misleading the armband into thinking you are doing something else (see the science information below) and giving you a skewed reading. But keep in mind in the big picture of weight control, because the bodybugg is so accurate, an occasional miscalculation means very little.

Generally, if the bodybugg underestimates or overestimates a certain type of exercise/activity it has a minor effect on one's entire week because it's not something you perform during a large portion of the week/day.