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Pacing During Hard Exercise:
Brain Versus Body?
Written by Dr. SkibaIs the flesh willing but the will weak, or vice-versa? This month’s newsletter centers on an interesting line of research coming from Dr. Timothy Noakes and company. Most of you are probably familiar with his work and theories from his popular tome “Lore of Running”, which has almost become required reading for serious endurance athletes. In recent years, Dr. Noakes has caused a stir in the field of exercise physiology because of his somewhat unorthodox theories regarding exercise performance. His contention is limited not by the abilities of the muscles and heart, but by the mind; that there is a “central governor” which orchestrates performance.
Athletes generally have some sort of pacing strategy for whatever their particular exercise task is. One common strategy is an initial peak in power output, followed by a period of time during which power decreases for a time, followed by a period where power output begins to climb again towards the finish. You may have noticed this behavior in your own training files. The physiologic reasons for this behavior are less clear.
Noakes and associates designed some experiments to investigate whether this behavior could be explained by the central governor hypothesis; that is, that the exercise is limited by the brain, possibly as a self protective or performance optimization measure. The first experiment involved well trained cyclists. The cyclists were asked to perform 3 time trial efforts of 4 km each on an ergometer, separated by 17 minutes between them which involved rest and a warm up before the next effort. The cyclists were not informed of the time during the trials, only of the distance covered. The investigators tracked changes in work output, blood lactate, and oxygen uptake. The athletes were monitored by electromyography (EMG), which involves placing small electrodes on muscles and monitoring the electrical activity as they fire. Typically, the higher the workload, the more muscle cells must be recruited to do the work, and the higher the measured electrical activity.
Interestingly, average power output for each interval was not different, and each took roughly the same amount of time, although the highest peak power was seen in the first interval. In each trial, power output spiked, lowered to a plateau level, and then increased again as the end of the trial neared. More interesting was the observation that EMG activity coincided with power output. Taken together, these facts would seem to suggest that the brain was directing the activity of the muscles. In other words, it wasn’t that the cyclists were trying as hard as they could and the muscles were not responding, but that the brain was seemingly figuring out what kind of work the body could maintain, and was directing it accordingly.
The next interesting observation was that EMG activity did not increase from trial to trial, which you would expect if the firing muscle cells were fatiguing significantly and more needed to be recruited. Again, Noakes uses this data to argue that the exercise tasks were regulated by central (i.e. brain), and not by peripheral (i.e. muscle) fatigue. In other words, it isn’t that the muscle cells themselves were getting tired, but that a central controller was telling them what to do for its own reasons.
Put that experiment in the back of your mind for a moment as we consider another. Noakes’ group examined the Wingate test, whereby a cyclist is told to cycle as hard as is possible against a constant resistance for 30 seconds. What they did was tell the cyclists that they were going to do 4 trials at 30 seconds, 1 at 33 seconds and 1 at 36 seconds. However, the trials were actually set up as follows: 2 of 30 seconds, 2 of 33 seconds, and 2 of 36 seconds. They manipulated the clock that the cyclists watched so that they were not aware of the real time: As far as the clocks were concerned, the trial was going on exactly the length it should. The power output always peaked early, and fell as the test progressed, which we would expect as the athlete tired out.
Something interesting happened in the 36 second trials. When the cyclist knew that the trial was 36 seconds long, there was a steady fall in power output until the end. When the cyclist believed the trial was 30 seconds long, but it actually was 36 seconds long, power output dropped significantly in the last 3 seconds. Noakes argues again that this is indicative of a central regulator. The central governor was aware of how long the trial was supposed to take, and was not fooled by the fact that clock read wrong. Thus, power drop was not related to the actual fatigue of the muscle, but that the brain had decided the best strategy to get the maximal work for exactly 30 seconds and had carried it out. In short, Noakes argues that the brain tries to program an optimum strategy based on the length and type of the perceived task. Other supporting data includes studies that indicate that the EMG activity decreases at the end of a maximal cycling test, indicating that fatigue at the end of the task is at least in part due to a shutdown on the part of the nervous system, rather than simply a failure of the muscle cells.
Our question should always be, “Does this have any effect on how we should be training or racing?” While I am not ready to put all my eggs in Noakes’ basket in terms of all aspects of the central governor hypothesis, I do see a rather simple application of his theories. If the brain really does program our effort to optimize our performance on both conscious and subconscious levels, it is to our advantage to know precisely the task we are to accomplish. In other words, we should always be sure to at least drive, or preferably ride/run our race courses as appropriate if we want to have our best performance. Even on an intuitive basis, this is obvious. You would consciously measure your efforts early on in a race if you knew the final mile was up the side of a mountain, never mind the unconscious adjustments you might make. We don’t lose anything by following this strategy, and we may gain a lot, even if we do not subscribe to a central governor theory. Recall that in the 2003 Tour de France, Lance Armstrong reviewed the final time trial course by car before the race. He knew where the slippery spots on the road would be. His main rival Jan Ullrich did not, and preferred to view a video tape of the course. Ullrich would later skid and fall on a corner, effectively ending his bid to de-throne Armstrong. Would a little reconnaissance work have made a difference? I have no doubt that very question will occur to Jan Ullrich many times over the years.
Until next month, stay strong and keep training smart!
References:
Ansley et al. Regulation of pacing strategies in successive 4km Time Trials. Med. Sci. Sports Exerc. 36(10): 1819-1825. 2004.Ansley et al. Anticipatory pacing strategies during supramaximal exercise lasting longer than 30 s. Med. Sci. Sports Exerc. 36(2): 309-314. 2004.
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