The Science Behind the “Bad Run”

MeaganGeneral3 Comments

On September 13, 2009, Steve and I were spectators at the finish line of the Wisconsin Ironman Triathlon. After first-place finisher Raynard Tissink broke the tape, the MC immediately pulled him aside and asked, “How do you feel? How was your day?”, to which Tissink responded, “This was the worst day of my life.” The MC laughed a bit uncomfortably at this declaration, but after swimming 2.4 miles, biking 112 miles, and running a full marathon with a total time of 08:45:19, you can’t fault the man for brutal honesty. Amazingly, the poor racer spent most of his bike ride with a headache, as well as pulling over periodically to vomit on the side of the road, and yet still managed to go on to run a full marathon and win the race!

Any runner will tell you that there are days when you simply have a “bad run”. It doesn’t matter who you are or what your skill level is—it’s going to happen. You feel sluggish, winded, unfocused, sick, etc., and, sometimes, you might be at a loss to explain why. In the case of Tissink, he clearly experienced what must have been the very essence of the bad run, but what’s really made his story stick with me is the fact that he was able to overcome it. Now that I’ve become a runner myself, I’ve had my own share of days when things don’t quite click and it is definitely frustrating every time it happens. However, being the scientist that I am, I believe that, armed with a better understanding of the science behind what makes a bad run “bad” and increased knowledge of possible causes (and solutions!), I can learn to fight through those dragging-my-feet miles. So, put on your lab coats and read on!

Fatigue and its Causes

No matter how effortless the professionals might make running a marathon look, fatigue is something that every runner at every skill level deals with, especially during a race. It just comes into effect at different distances or speeds for each individual runner. Fatigue is really an essential part of the sport of running. At its core, running is about seeing how far or fast you can go before you feel fatigued and how far you can push yourself through fatigue without stopping. In addition, teaching your body to fight against fatigue is a vital part of training for a race. The causes of fatigue can be classified as both physical and mental, and some debate exists as to which is the controlling aspect.

Lactic acid molecule. Photo courtesy of

There are three main physical processes that contribute to fatigue: neuromuscular fatigue, metabolic fatigue, and energy depletion. Both neuromuscular and metabolic fatigue directly relate to muscles losing their ability to contract powerfully. In neuromuscular fatigue, small fibers within the muscle called myofibrils can lose their ability to contract from the build-up of phosphate ions and a lack of calcium (essential for muscle contraction) due to possible retention of it elsewhere in the body. Metabolic fatigue is the result of the build-up of metabolic substances (metabolites) such as lactic acid, which breaks down into hydrogen ions and lactate. These substances interfere with the body’s use of potassium and other substances that facilitate muscle contraction. Hydrogen ions also raise the acidity of the blood and can be responsible for the burning sensation felt in the muscles due to irritation of nerve endings. Energy depletion comes into play during longer distance runs. When you exercise, your body burns a combination of oxygen, fat, and carbohydrates. On a long run, the body begins to run out of its preferred quick-energy source of carbohydrates and begins to have to rely solely on fat stores for energy, resulting in the feeling of fatigue. This is the reason why many long-distance runners ingest carbohydrate-rich gels during runs.

Ultramarathoner Diane Van Deren. Image courtesy of

There is also a strong mental component to fatigue, and some even argue that fatigue is primarily a mental issue. One of the most striking examples of this is Diane Van Deren, a runner who transformed into a great ultramarathon runner after having part of her right temporal lobe removed at age 37 to try to stop massive, debilitating seizures associated with her epilepsy from occurring. Residual neural damage from the seizures renders her with an inability to keep track of time and also affects her sense of direction and short-term memory. In addition, the part of her brain that was removed deals with how the body processes emotion, meaning that she doesn’t process pain the same way that you or I might. All of this amounts to her being able to run for 10s or even 100s of miles without having any sense of how long she’s been running, or even where she is going, so she doesn’t get tired and isn’t affected by the mental aspect of fatigue as others are.

For the rest of us, we are affected by what is termed Central Nervous System (CNS) fatigue. Your CNS controls everything that goes on in your body, sending out electrical impulses to initiate every muscle contraction and movement you make. In the case of running, your CNS can take protective measures by slowing or inhibiting muscle contractions to try to shield your body from harm when it senses that you are short on carbohydrates or building up metabolites. Thus, the mental aspect of fatigue can take control before the physical aspects do, but you can force your CNS to override these protective measures, making running just as much a mental battle as a physical one.

What factors lead to fatigue during a “bad run”?

Now that we understand some of the physiological and psychological processes that contribute to fatigue, let’s talk about what can actually cause these to become a problem in the first place when you have an unexpected bad run. A bad run can be attributed to a myriad of issues and the following is a list of common causes I’ve come across in my research. Most of them are fairly common sense, but there might be a couple surprises in there for a few of you! One should also keep in mind that sometimes a bad run simply can’t be explained by any of these issues; it just happens!

1. Illness. If you recently recovered from an illness such as the cold or flu or are coming down with something, expect that you might not perform at your highest level when you run. If you have recently been ill, make sure you aren’t jumping back into things too early—rest is important, too!

2. Lack of sleep. Again, this all comes back to being well rested. Sleep is a necessary part of your body’s recovery process and a lack of it can contribute to a whole slew of problems, including preventing your body from working efficiently when you are exercising.

3. Dehydration. Being hydrated is an essential part of running. If you think your bad run is the result of being dehydrated, make sure you get in a few big glasses of water before your next one!

4. Weather. Too hot, too cold, rainy, windy, snowy… If you’re training, it’s definitely good to get out there in all kinds of weather, because you never know what you’ll get on race day, but don’t be surprised if extreme conditions have an effect on the quality of your run.

5. Boredom. Make sure you aren’t getting bored with your training routine! If you’re running the same route, the same distance, the same pace every day, you’re going to tire of it. Do some tempo runs, go to a new location, or mix it up with some cross-training to try and reinvigorate yourself.

6. Overtraining. Rest days or easy days are just as important as the days that you do run. If your muscles are still too tired from a previous training session to function efficiently, you are on track for a bad run.

7. Bad form. This one is especially important for the minimalist/barefoot runners out there who are in the early stages of their transition to the midfoot/forefoot footstrike form. Make sure you pay attention to your cadence (~180 bpm is a good target). You want to remain light on your feet and not increase your fatigue with heavy footfalls and bad form.

Recovering from a Bad Run

Ok, so now you’ve actually had a bad run, or maybe you just want to be prepared for when you do. Here are some helpful tips to help you “recover” so you can get back to being your happy running self again!

Just think of those vultures as the voices in your head during a bad run.

1. Learn to appreciate your bad runs. We all hope that the stars will align on race day and we’ll have the perfect race we’ve been training for. It is, however, more likely that you will encounter some problem or another during your race, whether it be rain, excessive heat or cold, a stomachache, or anything else that might impede your performance. This is where your bad runs of the past will become your best friend. Learn to love them and fight through them, because, chances are they’ll help you push through a tough race in the future!

2. Learn to appreciate your good runs. Don’t take your good runs for granted. You are, after all, training hard to earn them. If you have a bad run, make sure you keep in mind all of the good runs you’ve experienced in order to keep yourself from getting discouraged.

3. Track your bad runs to identify possible triggers. Nike+ GPS has a great system for this, where, with a few screen-touches, you can log how you felt during your run with choices including “Awesome”, “So so”, “Sluggish”, and “Injured”. Be sure to note any specifics in the comments, including changes to your routine (e.g., hillier route, new shoes, weather) to see if you can identify a pattern or possible causes later on. For example, maybe all of your bad runs happen the same day every week after you’ve stayed up late the night before for a weekly Trivia Night at your favorite bar.

4. Run again tomorrow*. After a particularly bad run, it can be tempting to curl up in a ball on the couch and refuse to move for a few days. I mean, obviously, one bad run must mean that you now suck at running forever, right? Wrong! Get yourself out there the next day and I can almost guarantee that you will feel 100% better and, in the process, realize that your bad run was simply a fluke. *That is, unless your bad run is the result of overtraining, in which case, please enjoy a much-needed rest day.

5. Know that it’s OK to stop. Sometimes, you just have to pack it in and turn around early. If you are totally miserable or feel like you might be close to injuring yourself (or already hurting), there’s no shame in not doing as long of a run as you intended. This is especially important for runners who are relatively new to minimalist or barefoot running, as fatigue can contribute to the breakdown of your form and possibly result in an injury. I know I’d rather miss out on the last 20 minutes of my run rather than spend the next month not running at all because of an injury. Take solace in the fact that you still got out there and know that one run is not going to make or break your running career. Remember, you’re still lapping everyone on the couch!