Biking uphill

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Find Nature's Resistance Button
You already: Ride your bike (305 calories for 30 minutes at 12 mph to 13.9 mph, or with moderate effort).

You should also: Plan a route that will take you headfirst into the wind for at least part of the ride, says Bob, because this force of nature can make work almost 100 percent harder. One easy way to find the resistance: If you feel the wind at your back during your ride, reverse course.

Bonus tip: Bob says that the most challenging routes involve rolling hills that take you into the wind, and these can often be found near the ocean or large lakes, or on country roads that aren't protected by lots of trees.
As a reminder, always consult your doctor for medical advice and treatment before starting any program.