# understanding fatigue



## stevesbike (Jun 3, 2002)

Since training is based on the notion of adaptive stress, it seems like one of the key concepts to understand and quantify is fatigue. Yet, fatigue often seems to be treated monolithically in training articles. This forum seems like a great place to discuss theories of fatigue, their impact on training schedules, and whether current training tools such as powermeter/HRMs can be used to help quantify and track fatigue. Here are some initial questions I've been wondering about as a competitive cyclist and scientist (biological but not exercise-related) who dabbles in the exercise physiology literature with an interest in optimizing training time (given job/family commitments). These are just some semi-random thoughts to initiate discussion.

It seems as though fatigue is still poorly understood in the exercise physiology literature. Even the role of lactic acid in fatigue seems uncertain. How many different types of fatigue would a cyclist likely experience over the course of a season, what substrates underlie each, what timecourses are involved in recovery, and what factors improve/impede recovery (nutrition, supplementation etc)? A quick pass through the literature suggests at least:

metabolic fatigue: glycogen depletion. timecourse for recovery?

muscle fatigue: disturbance to any of the steps in excitation-contraction (EC) coupling. Also, factors like reductions in tissue oxidative capacity as opposed to hemoglobin-mediated decrease in oxygen carrying capacity ( iron-dependent mitochondrial oxidative enzymes and electron transport chain cytochromes). timecourse/recovery?

cardiovascular fatigue: hemoglobin-mediated decrease in oxygen carrying capacity? timecourse/recovery? Is this the primary cause of chronic fatigue/overtraining?

central fatigue: e.g., Noakes' central governor model (neurobiological theory)

structural muscle fatigue: damage/remodeling to the muscle ultra structure, inflammation and delayed onset muscle soreness. Heavy legs often taken by cyclists to be signal of fatigue and to recover, but does second-bout effect suggest that in fact no further damage is done exercising during DOMS? 

immune system fatigue: maybe more secondary, but immune system fatigue's effect seems big as it underlies vulnerability to viruses etc that limit training.

Intuitively, it seems like these can be decoupled (as when the legs feel good but it's impossible to get heartrate up). Are there ways to analyze powermeter/HRM data to quantify fatigue/recovery to different systems? 

If these have different timecourses, how would one structure training to induce appropriate levels of fatigue across systems and what would be the appropriate recovery period? E.g., is there evidence for blocking consecutive intense training days followed by multiple days of recovery as in high intensity training? The notion of a restday per week seems a bit old school-is there any evidence for a 24 hour period of recovery versus more consecutive days of intense training followed by longer periods of recovery?


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## goldsbar (Apr 24, 2002)

Whoa, this is way too scientific. Most advice is given based on "so and so who coached what's his name said so". Only 5 minute intervals will work, 7 are garbage; 20 minutes seems to matter a lot for no apparent reason. Even most serious studies involve 5 or so random untrained drunken college students.

Good luck!!!

On a more serious note, I've heard that certain schizophrenics have incredible endurance. This seems to indicate that consciousness plays some role in fatigue.


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## goldsbar (Apr 24, 2002)

Forgot to mention that I agree with your last paragraph. One day of rest is biblical in age and totally unsupported evidence (i.e. myself) makes me believe that it leads all but the most gifted to at least mental burnout.


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## Sub (Feb 13, 2004)

This is a pretty heavy question, but I get the general Idea of what your asking. One thing I can say is that each individual is different and you have to look at many different factors. You can correlate HR Date and Power Date to see if there is some developing fatigue. This is where coaches like myself come in. Reading a book and getting the general idea how to train is great, but each individual is different and trarining needs to be adjusted accordingly.


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## terzo rene (Mar 23, 2002)

I think the best measure is the ratio of RPE to average or normalized power. Increases indicate you are close to going over the edge (working harder for the same result), and it shows impending doom before power actually starts dropping. It's a catch all fatigue measure based on your body's own sense of how things are going inside, so you don't have to worry about what sort of fatigue you have or even whether any of the current theories are correct.


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## STARNUT (Jun 19, 2005)

Fatigue is not a zero sum game. When you wake up in the morning you fatigue is not at "0". You build upon previous days to accumulate fatigue.

The best estimation I've seen of the fatigue issue is the ISS and IF scores in trainingpeaks powermeter softwear.

I think what your really asking is how can you be most effective with the least amount of time spent. Actually, you did ask that  . The softwear and the scores are a good place to start. Second, look to kj/time.

I'm a self-coacher and I plan my weeks around how much time I have to spend training. I then figure out how much "stress" or kj I need to burn that week in training to get a desired result in fitness and stress.

I was tring to firgure out what "form" ment in the context of training and racing. I always hear people mention that so and so is on form and I'm on form and etc.............the best anwser I've seen for what "form" is, is the best combination between fitness (accumlated stress over time) and freshness (lack of stress over time). This is why we taper prior to a big event or we take time off when we become over trained.

Starnut


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## OldEndicottHiway (Jul 16, 2007)

Stevesbike, 

I'm liking your subject matter here...below is a "highly compressed" article I posted on another forum, somewhat related to the subject at hand. Would be curious as to your thoughts on it. Controls were in place, and as Sub said, there are so many variables to take into acoount esp. in athletes. The testing was done on what I'm assuming to be non-atheletes, but it's interesting at least to me.

I'd be curious to understand more of what is entailed in "hgb-mediated decrease in 02 carrying capacity". I'm assuming this covers a wide range of issues incl. iron deficiency anemia and blood dyscrasias, conditions causing erythropoeitin-resistance etc. Where I'm losing you is how electron transport comes into play here realtive to hgb and 02 carrying capacity: heme groups? Ability to release/uptake 02 molecules? Way rusty here apparently.

Anyway, here's the blurb from Journal of Applied Phys:

Eccentric exercise-induced muscle damage impairs muscle glycogen repletion
K. P. O'Reilly, M. J. Warhol, R. A. Fielding, W. R. Frontera, C. N. Meredith and W. J. Evans 


Five healthy untrained young male subjects were studied before, immediately after, and 10 days after a 45-min bout of eccentric exercise on a cycle ergometer (201 W). The subjects were sedentary at all other times and consumed a eucaloric meat-free diet. Needle biopsies of the vastus lateralis muscle were examined for intracellular damage and glycogen content. Immediately after exercise, muscle samples showed myofibrillar tearing and edema. At 10 days, there was myofibrillar necrosis, inflammatory cell infiltration, and no evidence of myofibrillar regeneration. Glycogen utilization during the exercise bout was 33 mmol glycosyl units/kg muscle, consistent with the metabolic intensity of 44% of maximal O2 uptake; however, the significant glycogen use by type II fibers contrasted with concentric exercise performed at this intensity. At 10 days after exercise, muscle glycogen was still depleted, in both type I and II fibers. It is possible that the alterations in muscle ultrastructures were related to the lack of repletion of muscle glycogen. Damage produced by eccentric exercise was more persistent than previously reported, indicating that more than 10 days may be necessary for recovery of muscle ultrastructure and carbohydrate reserves.


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## wfrogge (Mar 5, 2007)

Ill make this simple 

Fatigue is part of any endurance sport. Your body sends signals to your brain telling you to stop the activity due to stress. I think you are asking the wrong questions......


This is where the old saying comes into play "Cycling is 90% mental". Its not about your fatigue level... its about how you react and adjust to your bodies signals. Do you know our body well enough to push through it risking injury? Do you know when the signals mean something is really wrong and you should stop?


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## OldEndicottHiway (Jul 16, 2007)

Wfrogge,

They are not "wrong" questions. Simply questions you have little interest in. 

There's nothing "wrong" per se, with your approach either. But, one can take a broad generalisation such as, "Your body sends signals telling the brain to stop the activity due to stress" as you put it, and some of us are just not naturally satisfied at stopping there.

That curiosity thing...


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