Age and/or neglect can rob your muscles of their fast-twitch fibres, eventually sapping your speed, power and strength. Fortunately, you can fight back with short, super-fast intervals. Summoning fasttwitch fibres to propel you at full tilt trains your brain to recruit them more quickly at any speed – while you might associate these fibres only with fast running, your body can also use them to keep you moving forward when slowtwitch fibres are fatigued, says Mayer. These workouts can even convert some flexible muscle fibres into the fastesttwitch type, says Gaudette, which results in a fluid, more efficient stride.
THE WORKOUT After a long warm-up – two to four miles – run the following series of repeats as fast as you can without
feeling out of control: 3 x 100m, 3 x 150m, 3 x 100m. Take two to three minutes of standing or walking rest to recover between each rep. As you sprint, focus on leaning forward slightly and pawing backward with your hamstrings and glutes. Supplement these workouts with two to three weekly strength sessions for your hips, core and glutes; lower-body weakness can lead to injury at top speed, says Gaudette.
Intervals can boost your efficiency in ways that help you run longer than ever – whether you’re aiming to increase from 5K to 10K or all the way up to a half or full marathon. ‘The more efficient you can be, the less energy you’ll use to run a given pace,’ says Gaudette. ‘That allows you to potentially go a lot farther before you start to break down.’
THE WORKOUT Warm up for 10 minutes, then run half-mile or mile repeats at a comfortably challenging pace (you might be able to speak a few words, but not quote scenes from Shakespeare, says Gaudette). Recover by jogging for half the time the rep takes. Start with three miles or six half miles, and increase every two to three weeks until you’re logging five miles or 10 half miles of fast running.