The Fatigue Curve

A big part of understanding the training process comes down to understanding all there is to know about being tired. After all, in order to ‘supercompensate’ to a level of fitness above the ‘norm’ requires the athlete to take on more work and become more fatigued than they would ordinarily submit themselves to.

However, fatigue in and of itself isn’t enough. If the athlete doesn’t allow sufficient time to supercompensate from a given training session, in other words, if the athlete decides to ‘kick himself while he’s down’, all he or she will do is get more tired rather than more fit.

To complicate matters, there are all kinds of ways of getting both tired and fit and to train effectively, the coach or athlete needs to have some rudimentary understanding of them all. For example, no serious athlete can afford to wait for full structural recovery (repair of muscle fibers and functionally disturbed mitochondria) between sessions. To do so would mean that the athlete would be reduced to performing about a session a month. Even the fast responder must concede that it takes more than 6 miles of running a month to achieve anything in endurance sport!! And so the athlete is left to only allow partial recovery between most sessions. This brings us to the concepts of ‘residual tiredness’ & the ‘fatigue curve’(below).



We can ostensibly divide the recovery from fatigue into 4 key periods.

Phase 0: High-Energy Recovery:

Refers to recovery within the session, i.e. the recovery of muscle ATP and Creatine Phosphate stores, resaturation of muscle myoglobin stores with O2 and general repayment of the classic ‘O2 debt’ that comes with vigorous exercise and enables us to repeat this vigorous exercise with relatively short rest. This is the basis of interval training.

Phase 1: Metabolic Recovery

However, even allowing for recompensation of the body’s O2 needs, if sufficient steady-state training or a sufficient number of intervals is completed, eventually the athlete will begin to run low on glycogen. This phase of fatigue (phase 1) requires longer to recover from - 24-96hrs depending on the level of fatigue, the muscle fibers involved and the content of the athlete’s diet. This is the basis of ‘hard-easy’ training within the microcycle or week.

Phase 2: Structural Recovery

Yet, even applying an intelligent approach to structuring your weekly training isn’t sufficient when it comes to recovery. With every one of these tough sessions, a residual muscular damage is carried over from session to session. In other words, the 48-72hrs between hard sessions, while sufficient for supercompensation of the body’s glycogen stores is insufficient for repair and supercompensation of the muscle fibers and intramuscular components which represent a large part of the long term performance improvement in endurance sport. It is both desirable and necessary to do structural damage that will eventually compromise performance within the mesocycle or loading block. This is providing these ‘beat down’ cycles are accompanied by a ‘worthwhile break’ at the completion of the cycle. This period may be 7 days, 10 days or 14 days or more depending on the recovery needs of the athlete. The important thing is that the athlete recovers their performance potential once each cycle. You may notice that this aspect of fatigue comprises about 50% of the fatigue curve. Therefore this aspect of recovery is the key component in the training response.

Phase 3: Neuro-Endocrine Recovery

And, still, even the use of appropriate recovery between sessions and between cycles is not enough to prevent an eventual performance plateau in long term training. In addition to the issue of residual damage, the athlete must also deal with the habituation to stress that comes with long term load cycles. In the interests of protection from stress, in an organism who is perpetually involved in the stress response, the body will eventually habituate itself to higher stress levels so that it literally doesn’t wear itself out. Eventually the body will ‘run out’ of stress hormones or the body’s stress receptors will become less receptive to these hormones (Lehman et al. 1993). This represents the poorly understood fatigue of the neuro-endocrine system. Therefore the response to training is blunted. When performance begins to plateau, the smart athlete rests. This represents the final phase of the fatigue curve. Periodically, a multi-month recovery period will be needed to avoid carrying this small amount of habitual fatigue from one training year to the next.

If we accept Gordo’s saying that, when it comes to training, getting tired is the point then surely a big part of being an intelligent coach and athlete is about understanding what it really means to be tired. Hopefully, in addition to helping to better elucidate the concepts of periodization, in the same way that Eskimos have 100words to describe snow, this article has added to your vocabulary of being able to define your own tiredness :-)

Train Smart.

AC