Identifying the Fatigue Villain
Fatigue is a universal symptom. It may result from literally hundreds of different causes in athletes and non-athletes. But in otherwise healthy endurance athletes, persistent fatigue coupled with poor workout performance most often indicates one of two problems: overtraining or undernourishment.
Overtraining, or inadequate rest, is more common. Thus, if you begin to experience nagging fatigue and training staleness during a period of increasing training, the first thing you should do is reduce your training for a few days and then try ramping up more conservatively. If the problem doesn't return, it was a matter of overtraining. If it does return, you're probably running an energy deficit.
More: 5 Signs of Overtraining
When you suspect an energy deficit, your best course of action is the two-step process Paul Goldberg went through with Stephanie. First, make any dietary changes that may be needed to ensure that your body is well supplied with energy during workouts and for recovery afterwards.
Ideally, you will eat a full, high-carbohydrate meal three to four hours before your workout and consume a sports drink during the workout. In the first hour after the workout, take in plenty more carbs, a little protein and fluid for rehydration.
If these changes fail to cure your fatigue completely, try adding slightly more calories to your regular meals, but without forcing yourself to eat more than you're comfortable eating. This measure will put an end to your fatigue if an energy deficit is indeed the root cause.
Listen to Your Body
Energy needs naturally fluctuate as your training workload changes. Your appetite should automatically adjust for these fluctuations. Research has shown that ultra-endurance athletes who burn upwards of 5,000 calories a day, day after day, experience a level of hunger that drives them to consume an equal number of calories. Thus, they remain in perfect energy balance without having to think about it. Appetite is intelligent.
More: Eating for Endurance
An energy deficit is not always a bad thing, of course. If you could stand to lose a few pounds and you increase your training, you will probably experience an energy deficit that causes you to shed body fat. This deficit will not render you under-fueled for workouts because your shrinking fat stores themselves make up the energy gap between the calories supplied by your diet and the calories your body burns in workouts and throughout the day.
Even lean, high-level endurance athletes may experience a non-problematic energy deficit of this sort during peak training. A recent study found that a group of Kenyan runners consumed fewer calories than they burned during the final weeks of training before a marathon. This was surely not a matter of under-fueling. Rather, their bodies simply "chose" to become even leaner in preparation for peak performance on race day.
Due to the intelligence of appetite, endurance athletes seldom experience the bad sort of energy deficit unless they control their food intake too strictly. So, if you're an already-lean, competitive runner, my advice for you is this: Stop thinking like a couch potato and eat!race.