Rahlves bikes or runs, using heart-rate-based training for targeted cardio workouts. For longer aerobic sessions, he mixes in some fun: motocross, mountain biking, wakeboarding.
The goal of Rahlves' cardio workouts is to raise his anaerobic threshold (AT), the heart rate at which the body begins to use glycogen for energy instead of fat. In simple terms, the higher the AT, the more fit you are. Rahlves uses three types of workouts to reach his goal.
The first is "steady-state" training: 20 to 25 minutes of activity at 70 percent of your maximum heart rate (150 beats per minute for Rahlves).
Second is a "threshold" workout: Eight sets of 40-second intervals at 80 percent of the maximum heart rate, with six minutes at 60 percent of max between sets.
Third is a "tolerance" workout: Three sets of 30-second intervals at 90 to 100 percent of max, with two minutes of recovery between intervals and 10 minutes at 40 percent of max between sets.
What it works: lungs, heart.