Fatigue Forensic: What really slow you down!

Traditionally, cyclists have viewed fatigue as an inescapably muscular event – a situation in which muscles are simply unable to function with a desired level of force production. However, new research indicates that fatigue can – and often does – occur when muscles are humming along quite nicely. This fatigue is produced by a neural regulator, and it is the cyclist’s task to fine-tune his/her regulating system.

If you carry out challenging interval workouts during your cycling training, you are studying the true nature of fatigue. After all, you have probably had the following experience: You decide on a workout at 40-K pace, say 10 X 2K in 3:23 each (we’ve selected a standard training session and a reasonable distance and velocity – and thus time – for each work interval; in this case, the speed is 35.5 kilometers per hour, or about 22 miles per hour). Your warm-up goes well, and you’re off and cycling!

The pace you have chosen is an ambitious one, but you are feeling great the first time through the 2-K distance, and you cover the initial 2000 meters in 3:15. The second one is 3:18, the third 3:21, and from the fourth one on you are struggling a bit to hit your target of 3:23 each time. For the most part, you stay on track, but one interval, we’ll say the eighth, slides up to 3:29.

The ninth feels really tough, but you hang in there and produce a 3:23. You have reached the point in the workout at which fatigue should be close to maximal. After all, you are a believer in the traditional concept of fatigue. You know that as you continue to cycle quickly, for one work interval after another, your intramuscular pH is dropping fast, reflecting the tide of hydrogen ions which are flooding your muscle cells (1). That devastating fall in pH is interfering with the release of calcium ions into your muscles’ sarcoplasmic areas (2), making it much-more difficult for your muscle fibers to contract forcefully (3). As a result, adhering to planned pace is becoming a major undertaking. 

And then, something magical happens! At the point when muscular fatigue is greatest, when pH has bottomed out, when calcium ions have been locked away for the day, when muscle contractility has ebbed, you uncork your best 2K of the day – a 3:12! Who said that cycling does not have its magical moments?

Huh? If muscle fatigue is truly a function of metabolic events happening inside muscles, that last 2000 should have been the slowest, not the fastest interval of the day. Our views of fatigue – and of what determines cycling velocity during workouts and races – must be wrong!

Indeed, that is what recent research carried out by Tim Noakes and colleagues at the University of Cape Town, the University of Stellenbosch, and the Sports Science Institute of South Africa is telling us. In this new investigation, eight healthy males (average age = 22 years) completed “anaerobic capacity” tests in the laboratory on a Monark friction braked cycle ergometer (4). To gain a better understanding of the nature of fatigue and of pacing strategies during high-power exertions, South-African researchers used an element of deception with the subjects. Specifically, the young men were informed that they would be completing four 30-second maximal trials, as well as one 33-second and one 36-second maximal effort on the bike. In reality, they completed two trials of 30 seconds, two tests of 33 seconds, and a duo of 36-second exams.

The deception took place in the following way: Prior to one of the 33-second tests, the cyclists were told that it was actually a 30-second exertion, and the same was true for one of the 36-second affairs. The researchers hoped to determine whether the subjects would subconsciously alter pace or strategy during the “informed’ 36-second trial (when they were told that the trial would last for 36 seconds), for example, compared with the “deception” 36-second trial, when the cyclists thought they would only be cycling for 30 seconds. The cyclists were allowed to watch a clock during all of their maximal exertions, but – ingeniously – the scientists had programmed the clock to run more slowly during the deception 36-second trial, so that it would tick 30 “seconds” during what was really a 36-second time frame.

You might expect that the cyclists would ride with more power, at least initially, during the deception-36 trial, compared with the informed-36 trial (since they thought that the deception-36 trial was going to be shorter in duration), but the results were more interesting than that. As it turned out, power output was exactly the same in the informed and deception 36-second trials, right up until the 33-second point, but then power fell significantly over the last three seconds of the deception trial!

How should we interpret that? Since the cyclists were able to perform more work when they were reliably informed about the duration of exercise, compared with when they had been deceived, some internal factor, not located in the muscles, must have controlled power output. If “peripheral fatigue” (fatigue centered in the muscles, as according to traditional theory) was the true factor controlling performance, then power outputs should have been exactly the same in the informed and deceived 36-second trials (because the extent of muscle fatigue would have been the same in these two trials of equal duration).

Source http://cyclingresearchnews.com/News_And_Events.php?cid=3&iid=92

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