HIIT it. Swap a leisurely midweek cruise for a short session of high-intensity interval training (HIIT). A slew of studies from the past five years shows that a few brief, gut-busting sessions can improve your endurance as well as much longer rides do. Going hard can prep your muscles to go long. The metabolic magic happens on two fronts. One: Endurance rides tend to hit only your slow-twitch muscle fibers, but HIIT training also recruits your high-speed fibers so you develop a bigger engine. Two: Your body becomes better at tapping into your fat stores to refuel for the next hard effort, so you become a more efficient fat burner.
