Time to Exhaustion Test – 80/20 Endurance

Time to Exhaustion Test

The latest edition of the International Journal of Sport Nutrition and Exercise Metabolism features a study that will be of interest to any runner seeking to perfect his or her race fueling practices. Conducted by scientists at the University of Bath and the University of Nottingham, the study compared the performance effects of consuming carbohydrate in small doses at high frequency and consuming an equal amount of carbs in one big lump at a crucial juncture during a treadmill run to exhaustion.

The subjects were six well-trained runners who ran as long as they could at a moderately high intensity on two separate occasions. On one occasion, the runners consumed 5 grams of sucrose every five minutes until they had taken in a total of 75 grams. On the other occasion, they consumed 75 grams of sucrose in a single dose 75 minutes into the run. Now, I know what you’re thinking: What runner in their right mind would gobble 75 grams of carbs all at once? Of course the first fueling protocol is going to yield better performance! But from an abstract physiological perspective, there’s no reason to make this assumption. That’s because the body of a well-trained runner stores enough carbohydrate to last more than 75 minutes at a moderately high intensity. So, in theory, the runners were getting that big lump of sucrose in time to preserve their ability to keep going at the same intensity.

Nevertheless, your assumption is correct: On average, the subjects lasted 105.6 minutes when given small, frequent doses of carbs compared to just 96.4 minutes when they had to wait 75 minutes for one big lump. But not all of the runners benefitted equally from the “carbohydrate drip” fueling approach. The researchers found that performance was most positively affected in those runners whose rate of stored carbohydrate use was reduced the most by frequent carb intake. This finding suggests that glycogen sparing was the mechanism by which frequent carb intake improved performance. But other research has shown that consuming carbs also boosts endurance performance by reducing perceived effort, so I’m sure this was a factor as well.

Granted, there is quite a bit of space between 5 grams of carbs every 5 minutes and 75 grams of carbs after 75 minutes. In the real world, runners are more likely to consume a gel packet containing 20 to 25 grams of carbs every 30 minutes or so. It would be interesting to see how this real-world fueling schedule compares to the carbohydrate drip approach. My hunch is that the closer a runner can get to a continuous, slow infusion of carbs during a race, the better. That’s why, when I take a crack at running a 2:38 marathon on March 29th, I will practice my version of the carbohydrate drip approach.

Here’s how it works: The Modesto Marathon (which is the event I’m competing in) has 13 aid stations, or one every 2 miles, give or take. I will grab a cup of Gatorade at each of them. Between aid stations, I will sip from one of two small flasks (as pictured above) containing a mix of Hammer Gel and water. These sips will be small and frequent—every 5 minutes or so. Between the Gatorade and the Hammer Gel I will take in 160 grams of carbs over the course of the race, or approximately 60 grams per hour. By executing this fueling plan, I should get more out of this amount of energy intake than I would if I took in the same amount in larger, less frequent doses, thanks to both glycogen sparing and a reduction in perceived effort. I have also found that the carbohydrate drip approach minimizes the GI discomfort that commonly attends energy intake during intense and prolonged running. What’s more, with the flasks I don’t have to worry about carrying sticky empty gel packets in my hand until I reach the next garbage can.

I should note that I am treating Modesto as a kamikaze marathon, meaning I intend to sustain my goal pace (6:04 per mile) until I reach the finish line or keel over. There will be no adjusting the pace based on how I feel as in a normal race. This makes it effectively a time-to-exhaustion test not unlike the one that was done in the study I described at the beginning of this article. It’s also the same strategy Eliud Kipchoge employed in his two sub-two-hour marathon attempts. Wish me luck!

In last week’s post, I addressed a fundamental question: What are the major objectives of an endurance athlete’s diet? In this post I would like to tackle an even more basic question, which I’ve already given away in the title. Namely: Which is most important for endurance fitness and performance—training, diet, or sleep?

As you’re about to see, there’s no simple answer to this question. But attempting to answer it is nevertheless a worthwhile exercise, because it yields clarity on the role of each of these three factors in relation to your athletic ambitions.

The All-or-Nothing Angle

Sleep is a mysterious phenomenon that has long eluded scientists’ efforts to fully explain it. As neuroscientist Michael Halassa confessed in a 2017 article published on livescience.com, “It’s sort of embarrassing. It’s obvious why we need to eat, for example, and reproduce . . . but it’s not clear why we need to sleep at all.” What isclear is that we literally can’t live without sleep. The longest any human has been known to survive without sleep is just 11 days.

Arguably, this makes sleep even more important than food. The average person can go about 40 days without eating before succumbing to starvation. 

As for training (i.e., exercise), it is, of course, not required for survival, though a case can be made that some amount of physical activity is needed to achieve a normal lifespan, as people who are unable to move their bodies (i.e., sufferers of paralysis) don’t live as long as people who are.

In light of these facts, we can say definitively that if you were going to attempt to complete an endurance race either without training, without eating, or without sleeping, your best move would be to skip the training in favor of eating and sleeping.

The Realistic Angle

Thankfully, you will never have to make the choice I just presented. We live in a relatively stable society in which most people have plenty of food to eat and a comfortable bed to sleep in. So, let’s now approach the question of whether training, diet, or sleep is most important for endurance fitness and performance from a more realistic angle. 

Although I just got through saying that in our society most people have a comfortable bed to sleep in, the modern lifestyle is such that a large fraction of us do not spend enough time in bed and do not get enough sleep. Research suggests that the kind of chronic, mild sleep deprivation that is so common in our society has a bad effect on endurance performance. A 2016 study by researchers at UC San Francisco, for example, found that cyclists whose sleep was restricted to four hours per night for three nights experienced a 2.9 percent decrease in maximal aerobic power and a 10.7 percent decrease in time to exhaustion at VO2max. True, few athletes get only four hours of sleep per night as a matter of habit, but it’s reasonable to assume that longer periods of milder sleep deprivation probably have a similar effect.

Similarly, although most athletes get enough to eat overall, a majority of athletes also fall well short of eating optimally to support their fitness and performance. Common mistakes include poor diet quality, overeating, and within-day energy deficiencies, all of which are proven to negatively affect endurance fitness and performance.

And then there’s training. What’s different about training, from the realistic perspective, is that, whereas everyone sleeps and eats, only a minority of adults in our society exercise regularly. This makes the transition from sedentariness to endurance training a rather common phenomenon. Thus, in the case of training, the realistic scenario isn’t all that different from the all-or-nothing scenario.

There’s plenty of research on how the transition from sedentariness to endurance training affects endurance performance. One example is a 2019 study by Spanish and German researchers, which found that 12 weeks of endurance training increased VO2max by 11 percent and time to exhaustion by 14 percent in a group of previously sedentary adults. Those are big numbers. And it should be noted that sedentary individuals can’t exactly leap straight into heavy training workloads right off the couch. The subjects in this study completed just three low-intensity sessions per week totaling 2.5 hours. Given what we know about the dose-response relationship between endurance training and fitness and performance, it’s safe to say that these folks would have experienced vastly greater improvements over time if they had continued to train in a progressive manner.

Indeed, studies investigating the effects of different training programs in already-fit athletes show tremendous potential for improvement in going from imperfect training to optimized training. A 2014 study conducted at Salzburg Universityreported improvements ranging from 6.2 percent and 17.4 percent in time to exhaustion among experienced endurance athletes placed on one of four different training programs for nine weeks.

Comparing the above-referenced data on sleep, diet, and training leads us to the conclusion that, in the realistic scenario, training offers far greater potential for improvement in endurance fitness and performance than does either sleep or diet. In other words, if you are a typical athlete who doesn’t get quite enough sleep, has a mediocre diet, and trains less than optimally, and you can only change one of these things, your best move is to optimize your training.

The Bottom Line

So, which is most important: diet, sleep, or training? The answer, we now see, is that training, on the one hand, and diet and sleep, on the other hand, are important in different ways. Most athletes place greater emphasis on training, and they are right to do so in the sense that, realistically, getting the training piece right will have a greater impact than getting either the diet or the sleep piece right.

However, as we saw in exploring the all-or-nothing angle, diet and sleep are more foundational than training. Fitness is really just an extension of health, and diet and sleep are more important to basic health than training is. Therefore, any athlete who wishes to get the most out of optimized training should make every effort to get the diet and sleep pieces right as well.

Exercise scientists have two basic ways of measuring performance in their studies. One is a time trial, where subjects are asked to cover a specified distance in as little time as possible (or cover as much distance as possible in a specified amount of time). The other is a time to exhaustion test, where subjects are required to sustain a fixed work rate (speed or power output) as long as possible.

In the real world, most runners approach most marathons as time trials. In my coaching role, I generally advise runners to take this approach because it offers the best odds of a satisfying outcome. The idea is to choose a time/pace goal that is challenging but realistic, start the race at this pace, and then make adjustments along the way based on how you’re feeling. The advantage of this strategy is that it limits the risk of hitting the wall. When a runner is even slightly too aggressive in the early part of a marathon, he is likely to slow down precipitously in the later part and consequently fall not seconds but minutes short of finishing the race in the least time possible—if he finishes at all. To avoid “wasting” a marathon (not to mention the months of preparation leading up to it), a runner must be a little conservative, choosing a target pace that he’s very confident of being able to sustain for the full distance and relying on a fast finish to avoid leaving time on the table if it turns out that the target pace is a tad too conservative.

This fall, Eliud Kipchoge will make a second attempt to break the hallowed two-hour marathon barrier. He got very close in his first attempt, covering 26 miles, 385 yards in a time of 2:00:25 in Italy in 2017. Of necessity, Kipchoge approached this bid to make history not as a time trial but as a time to exhaustion test. Aided by a phalanx of pacers, he set out at 4:34.5 per mile (1:59:59 pace) and held on as long as he could, which turned out to be about 18 miles, at which point he began to slow involuntarily, despite his best efforts to hold the required tempo.

In his second sub-two bid, which will take place in late September or early October, Kipchoge will take the same approach, as indeed he must, for such an ambitious goal cannot be achieved in any other way. Avoiding the wall is not a concern, because anything short of sub-two is failure. Whether Kipchoge hangs on almost all the way and ends up clocking an excruciating 2:00:01 or blows up at 35K and literally crawls to the finish line, the two-hour barrier will remain in the realm of the impossible for the time being. Thus it makes no sense for Kipchoge to adjust his pace as he goes based on how he feels. If 1:59:59 (or better) is indeed possible for him, he will only get there by forcing himself to hold that 4:34.5/mile pace no matter what.

My (possibly politically incorrect) term for a marathon that is run as a time to exhaustion test is kamikaze marathon. Inspired by Eliud Kipchoge, I have decided to run a kamikaze marathon of my own this fall. A sub-two-hour marathon being slightly out of my reach, I will attempt to sustain a pace of 6:04 per mile as long as I can in the context of the Pacific Northwest Marathon on September 21. The fastest pace I’ve ever sustained for the full marathon distance is 6:05 per mile, at the 2017 Chicago Marathon. I was 46 years old then and am 48 now, a difference that is far more consequential as it relates to performance decline than is, say, the difference between 36 and 38. What’s more, I spent the summer of 2017 living in Flagstaff and training with Northern Arizona Elite, a huge advantage that I will be lacking this time around. In consideration of these facts, I think I’ve got about as much chance of achieving my goal as Kipchoge has of achieving his, which is to say close to none. But that’s the whole point of a kamikaze marathon. You choose a goal time that you think is probably-not-definitely impossible for you and go for it! If you plan and execute appropriately, there’s about a 90 percent chance you will implode painfully in the late miles of your chosen race and a 10 percent chance, give or take, that you’ll achieve something special that you would not have been able to achieve with the usual time-trial approach.

So, what do you say—are you in? Before you blurt, “Hell, yeah!”, understand that Kamikaze marathons are appropriate only for seasoned marathoners who don’t mind possibly “wasting” a marathon. But if you fit this description, do consider joining Eliud Kipchoge and me in running a kamikaze marathon this fall. Put some thought into coming up with a time/pace that is probably-not-definitely impossible for you and then find an appropriate event. (I chose Pacific Northwest because the course is net downhill and mostly flat and the weather is reliably perfect every year—oh, and because my brother Josh is running it). Also consider recruiting a pacer who can easily run the time you’re hoping to run. Tommy Rivers Puzey, a 2:16 marathoner, has agreed to serve as my pacer (though there’s a chance he’ll have to bail out at the last minute due to sponsor obligations).

If you accept the kamikaze marathon challenge—and I hope you do—be sure to share the journey (Strava, Twitter, etc.) as I will be doing in the months ahead. Let’s make this a thing!

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