Overtraining and Underfueling Can Feel the Same. Here’s How to Tell the Difference, According to a Run Coach and Dietitian

Fatigue plays a part in long-distance running and racing, but it shouldn’t be the overall theme of your training. If it starts showing up regularly, finding you on every workout and easy run, and hanging on your heels like a competitor that you just can’t shake, you’re likely dealing with an energy imbalance in your training. In short, you’re asking your body to do more work than it has the resources to support.The solution doesn’t come from pushing through the fatigue. Instead, you’ll want to examine your daily routine for two major suspects: training too much and fueling too little.The answer isn’t necessarily one or the other. Much of the time, overtraining and underfueling are two sides of the same coin.“In some way, they’re kind of the same thing: a mismatch of input versus output,” explains Cortney Berling, RD, a registered dietitian, certified run coach, and founder of Eat Well Run Better.In both situations, your energy output exceeds your recovery input. Input includes nutrition, but also sleep and activities that help reduce overall stress, such as yoga and mindfulness meditation. “So in the big picture, it can be hard to tell the difference”—especially because the signs and symptoms of both overtraining and underfueling can overlap, Berling says.But if you know what to pay attention to, the root cause of your fatigue can become much clearer, Berling says.Here’s how to tell whether you need to scale back on mileage and intensity, add more fuel throughout your training, or do a little bit of both to see improvements in your overall energy, recovery, and running performance.Signs of Overtraining and UnderfuelingAccording to Berling, the duration of your fatigue can help you determine whether you’re feeling wiped out from overdoing it in a workout or underfueling. “If you’re overtraining, you might feel especially rundown after a big workout or a hard race for a few days after, specifically in your legs,” Berling explains. “Fatigue from underfueling is going to last for much longer; it’s not going to go away as quickly.”While overtraining and underfueling can share symptoms like fatigue and poor performance, underfueling is more likely to come with signs that your body isn’t getting enough energy overall. These symptoms can affect cognitive health and functioning, Berling says, and include brain fog, difficulty forming thoughts, irritability, and anxiety. Many athletes also notice a significant change in appetite; while some may feel ravenous, others may suddenly find they’re never hungry.“You might be losing motivation to run or even feeling like you can’t get out of bed in the morning,” Berling explains. “It’s more than just feeling exhausted after a hard session; it has a full-body effect that you’ll start to notice on a day-to-day basis.”In short, Berling says that while underfueling and overtraining can look remarkably similar, true overtraining is significantly less common. If you’ve been dealing with persistent physical and mental fatigue, it’s worth taking a close look at whether you’re eating enough to support your training. In fact, a narrative review published in Sports Medicine found evidence of low energy or low carbohydrate availability in 86 percent of overtraining studies, leading the authors to suggest that many cases attributed to overtraining may actually reflect underfueling.If you’re confident that you’re eating enough—which includes prioritizing carbohydrates and taking in energy before, during, and after workouts—you may be pushing your training too hard, Berling says. This happens more frequently with new runners who do too much too soon.“If a novice runner went from running once or twice a week to starting a marathon training cycle, layering on mileage and intensity really quickly, their muscles might not be able to adapt to it because the stimulus would be too high, too fast,” Berling says. If that’s the case, a runner might feel fatigue and soreness that don’t resolve as long as their training load remains elevated.How to Fix Fatigue Caused by Overtraining The quickest way to resolve this is to scale back on training, and ensure that you’re following established recovery guidelines and practical rules for increasing your weekly running volume.For example, Berling says that runners should take a deload week at least every four to six weeks. This not only gives your body the opportunity to consolidate the training gains over the previous month of running, but it also creates some variation in your routine. “You can’t be going full throttle and increasing mileage all the time,” she says. “It’s stress, plus the rest, that equals growth.”Berling also says that it’s important to increase mileage gradually to avoid fatigue from overtraining. Research shows that increasing the distance of each run by no more than 10 percent of any previous effort in the week can help minimize your risk of injury. Likewise, following this 10 percent rule can decrease the chance that you’ll increase your training load faster than your body can adapt to it, she explains.A simple rule of thumb that can help ensure you’re getting adequate recovery? Give yourself at least one full rest day per week, adds Berling.How to Fix Fatigue Caused by UnderfuelingFor many athletes, resolving underfueling isn’t just a matter of eating more. “You can be eating enough overall calories, but if it’s the wrong proportions of macros, your body is going to interpret that as a form of underfueling,” Berling explains.For example, she says that maybe a runner has really leaned into the current high-protein craze and is consuming more protein than they really need, but they aren’t getting enough carbohydrates. Their overall caloric intake might be adequate if you crunch the numbers, but they’re missing those carbs that are essential for providing readily available energy to the muscles. “Your body needs the right calories for the job that it’s trying to do,” says Berling.The timing of your nutrition can also lead to underfueling. “If you’re eating the bulk of your calories at the end of the day, that can mean you’ve missed the most important fueling opportunities: before, during, and after your training run,” Berling says.Those are the times when your body needs fuel the most, she explains. So even if you are consuming enough calories overall, you’re not getting the same recovery benefits if you don’t time that fuel around your workouts.If you suspect underfueling is the cause of your fatigue, Berling says getting in fuel around your runs is the first place to start. She tells her athletes to always eat a carb-forward meal or snack before runs. For a run shorter than an hour, you’ll want to consume about 30 grams of simple and easy-to-digest carbohydrates at least 10 minutes before you head out. Her morning prerun snack of choice? One banana or two graham crackers. Both are right around 30 grams of carbs.The longer the run, the more carbs you need and the more time you need for digestion, Berling explains. Aim for 0.5 grams of carbohydrate per pound of your bodyweight when running longer than an hour, and 1 gram of carbohydrate per pound if your run is two hours or longer. Try to finish your meal one to two hours before your run, and keep in mind that some runners need more time to digest, she adds. Before a long run, Berling likes a bagel with peanut butter and honey and drinks her water with a serving of Liquid IV electrolytes.Make sure you fuel during your runs, as well, with at least 30 to 60 grams of carbohydrate per hour during efforts lasting 60 minutes or more, especially if you’re including intensity.When you finish your workout, don’t delay your postrun meal. “Your body wants those carbs and protein immediately after the workout—that’s when it’s going to most readily absorb and utilize them,” she says. The sooner you refuel, the sooner your body can use that energy to kick-start the recovery process.Berling says to aim for a 3:1 carbs-to-protein ratio in that recovery meal or snack. A good ballpark range is about 60 grams of carbs and 20 grams of protein, but these amounts don’t have to be exact. If you find yourself without an appetite after a hard effort, try Berling’s go-to postrun smoothie: one cup of fruit, milk, Greek yogurt, and a scoop of whey protein powder. Give it a spin in the blender, and top with one-third cup of granola.The one skill you need to resolve underfueling? Consistency. Berling explains that the key to success is making these nutrition practices a habit. They should become part of our daily routines—not what we do just once in a while when we remember, she says. “Every time we eat, it’s an opportunity to fuel our bodies,” she explains. And to stay resilient through the ups and downs of training, we need to capitalize on every opportunity we get.Morgan is a gear editor who has been with Runner’s World since 2017. She started as an intern ghostwriting The Warmup, a bygone version of the daily RW newsletter. Now, she tests and reviews anything you might find on runners’ feet-from crew socks and compression boots to carbon-plated super shoes. A lifelong runner and shoe geek, Morgan has been chasing the perfect pair of kicks since she joined her grade school cross-country team. Since then, she ran as a Division I walk-on for the cross-country and track & field teams at the University of Delaware, where she studied English and Biology. She has one full marathon under her belt, and has raced more halfs and 5Ks than she can count.