It Isn't Just Overtraining
There have been many different methods touted to monitor training versus recovery levels. Overtraining as a concept now seems to encompass any regeneration period required from a training load. With the wealth of advice on avoiding overtraining and trying to ensure adequate recovery it appears to me that the pendulum is stuck on the conservative side. The ultimate standard being aimed for seems to being able to recognise when overtraining is about to occur, before it actually does.
The various methods suggested to achieve this mainly try to attempt to make it an objective exercise. Those from the scientific mindset usually like definitive numbers to work with as they are much easier to replicate, measure and compare than are subjective feelings. Methods include making decisions based on variations in resting heart rate, orthostatic heart rate changes, R-R variability, heart rate at set paces, ratings of perceived exertion versus either heart rate or pace, or various predictors from the various heart rate monitors on VO2max, or fitness scores. To go even further, attempts have been made of using blood or saliva analysis to analyse hormone, lactate or other marker levels in the hope to identify the risk of overtraining or even the degree of overtraining.
Unfortunately all the work and study that has gone into the topic, hasn't resulted in any reliable, valid tools to predict when you are training too much. Maybe it is also too difficult to define what exactly training too much is, other than a very general guideline. Do you define it by hormonal changes, how the whole body responds, musculoskeletal damage, drops in performance or other factors. Should we move away from the term overtraining as this implies you are training either too much, too hard or both? Training hard and a lot is after all a big part of improving performance. Taking all of the above into consideration I like to work from the following guideline:
Inappropriate training results in negative results when compared to the goals of training.
Essentially any training is inappropriate if it moves you away from your training goal. This can now encompass, not training enough, performing the wrong type of exercises, doing something that results in an injury. One very important element is recovery.
If the body isn't allowed to adapt to a training stimulus then it cannot improve. A training stimulus involves a stress that results in some interruption to the body's homeostasis. There is a requirement for acute compensation by the body's systems to recover and return to homeostasis. Beyond this, it is hoped that there is a further response of adaptation resulting in improvement. The problems occur when this balance is upset. Either the training stimulus is too great, has a wrong response (ie. promoting anaerobic glycolysis instead of lipid oxidation), or recovery and adaptation cannot occur properly.
With so many factors affecting training, adaption, performance and recovery, maybe the concept of overtraining is incorrect. So many different ways to cause a detrimental effect on training, (which can include nutrition, sleep, work commitments and stress), there probably will never be just one or two objective measurements that can be used to predict or quantify the concept. That isn't to say you can't have a reasonable expectation that performing certain training methods couple with specific recovery techniques will result in a predictable outcome. In fact, training effects are quite predictable if you have some knowledge and experience. In my view, it can't all be summarised into a single objective measure.
Take the time to listen to your body. Learn what different types of pain mean. Take note of the different styles of fatigue you can feel. Focus on the different feelings of muscle versus connective tissue tightness. Compare left versus right. Don't ignore things that feel wrong, there is usually a reason for this. Remember there is an ebb and flow to training. Every day isn't always a good day, but some days a highlights.