The low-impact, easy-on-the-joints nature of cycling lets you go for hours.
Quads, hamstrings, calves, glutes, and core work in concert.
Amp It Up
Determine your cadence by counting how many times one of your legs rises in 15 seconds; multiply that number by 4. Berlinger suggests you ride at a 90-100 cadence for four minutes in an easy gear. Kick it up a gear and maintain the cadence for another minute. Do another four minutes at the original gear before going up two gears for another minute at 90-100. Keep pushing until you can't do a full minute at that pace.