When researchers at France's National Institute of Sport asked a group of triathletes to ramp up their training by 40 percent and maintain that volume for three weeks, the results were predictable—at first. By the end of week one, the athletes showed signs of overtraining, like excessive fatigue and an inability to get their heart rate up to its max, and they began to run more and more slowly. But after the three weeks and a week of easy training to recover, their performance rebounded. They ended up running faster than the athletes in the control group, who had trained at their usual levels.
Pushing yourself beyond your limits for a few weeks—a tactic coaches call "functional overreaching"—can force your body to adapt and build fitness more quickly than the usual slow-and-steady approach. Be warned: Training through heavy fatigue is a high-risk approach that can progress to full-blown overtraining if you don't pull back in time, and it's not easy to get the timing just right. But if you've been stuck at a performance plateau for a few seasons despite consistent training, the gamble may be worthwhile.
Ramp Up the Volume
Increasing either volume or pace can push you into the overreaching zone, but volume is the safer bet. Speeding up makes it hard to control exactly how much extra fatigue you get, and you risk turning aerobic workouts into anaerobic ones. For the first week, increase your mileage by 15 percent by lengthening easy, long and tempo runs; spread out the extra miles over a few days, and don't change your high-intensity workouts.
If you're struggling to recover after the first week, simply maintain this mileage increase. If you still feel "normal," increase volume by another 10 percent, adding 1 or 2 double runs if necessary. In either case, as soon as you start feeling unusually fatigued, you know you've entered the overreaching zone. Hold the higher volume for two weeks from that point, and then back off. (BEWARE: Are you making these Top 5 Training Mistakes?)