Meeting the load

Physiological control systems - hypertrophy and atrophy

Running a 'fast' marathon requires a body prepared for the stresses that arise during the race. The order and extent of the stresses depends upon the relative effort expended by the runner. Training is usually considered to be the best way of adapting the physiological systems such that they do not fail dramatically during the race. The degree to which different elements of training prepare the body is often considered to be highly individualistic - Everyone is different - is a common refrain. The underlying idea being that what makes one person fast will not necessarily work for another.
Or, to put it another way, if one applies the same set of stresses to a group of humans there will be a diversity of training responses that prevents generalized trends from being seen. The idea presumably being that some people are destined to be slow runners and others fast by virtue of their 'train-ability'. The complexity of training often makes it hard to investigate whether this is actually the case. However, the question has some important consequences for athletes trying to become fast. If we believe that we are entirely unique then we can only progress by experimenting with our own training since what will work for one runner will not necessarily work for another. But, if we share some general training characteristics with others then we can apply the same successful ideas that they have used to make themselves faster to also make ourselves faster. Instinctively we know that this must be true. Training improves performance and more training improves performance more. Our entire system of education and science is based upon the knowledge that systems arise through interactions and those interactions are subject to certain rules.

Physiological systems tend to adapt to stresses that are applied to them. Usually the response does not involve producing a greater adaptation than the stress requires. If you look at the size of someone's leg muscles, they are usually in proportion to their body weight (as long as they are not doing some special form of exercise training). Biology is quite clever - rarely does it allow excess or inadequate amounts of muscle to exist. We are in a balance of hypertrophy (growth) and atrophy (shrinkage) such that we have 'just the right amount of stuff'. It allows us to cope with the normal loads without consuming an excess of energy. This ability of our body to match the response to the load is central to physiology.

The same principles apply to run training. If we increase the load the body produces a greater adaptation - if we remove the load the adaptations reduce. This is what is referred to as a control system. Whilst the adaptations are insufficient hypertrophy continues, once the adaptations are sufficient to meet the load then there is no longer a stimulus to drive further adaptations. The effect of this control is that the same training load applied to different individuals should result in similar levels of adaptation - an adaptation capable of coping with the load. In this case the differences between individuals may appear as either an inability to adapt to the load or the speed with which the adaptations occur.

Specifically with regard to running a fast marathon, there are two obvious extremes for producing the necessary load. One could either attempt to run at the same target speed of the marathon one is aiming for, but over progressively longer distances to force the adaptations, or one could run the same distance as the marathon and then gradually increase the speed. The question is; "With which technique can one achieve that best results?". To consider this fully we must also remain open to the possibility that the systems that limit our marathon performance might be adapted by other stresses than running alone.  This is critical since we have a limited capacity for run training. To force the maximum amount of adaptation one needs to apply the greatest load possible. However, as the load increases one tends towards the point at which the rate of damage caused by the load first matches the rate of the repair and hypertrophy process before eventually exceeding it. At this point we effectively lose the ability to increase the training load. The very structures we are attempting to adapt are incapable of producing a greater load. It is thus minimizing the rate of damage accumulation with respect to the training benefit that limits the size of the adaptation that can be produced.

This points at the need for a virtuous cycle within training whereby the hypertrophy induced by a load allows for a progressive rise in the load (training to train). The hypertrophy in this case is a combination of many systems not just skeletal muscle. However, where speed is an essential driver of the increase in load then skeletal muscle hypertrophy together with the ability of the legs to cope with the stress is critical. Where distance is the key driver for the load increases other factors than simple muscle strength are likely to dominate.

Next: What is a training load?