If the statistics are correct, many millions of new runners have laced up for the first time in the last few days. If you are one of them, then, as I’ve written elsewhere, you are well on your way to being faster, stronger, more resilient, more intelligent and more empathetic than when you awoke on New Year’s Day nursing little more than a hangover and a firm resolution. So, with such great rewards in the pipeline, why do millions of us fail in those first critical weeks? It’s because, for the body, the first month of new training is so booby-trapped that Lara Croft would find the obstacles tricky to negotiate. Read on and you might just make it safely to February, and beyond.

On your very first run your body will have become suddenly aware that it needs to remodel to match its new training loads. Our muscular system responds to training easily, and can repair and rebuild in a matter of days. And, because the heart and lungs are part of this system they too will improve rapidly. After just a few runs, the cardiorespiratory system will become more efficient making you feel fitter and stronger. And this is at the core of where most new runners get into trouble. The tragedy is that other soft structures, connective tissues like tendons and ligaments, are just as weak as when you stepped out for your very first run. They are slower to repair and remodel than muscles, and about ten days in to your new regime, they will probably have completed the adaptation from only your first run.

The Goldilocks Threshold

For training to work effectively, soft tissues have to be strained and slightly damaged to what I’m going to call a Goldilocks Threshold. If soft tissues are not stressed by training, they will not adapt at all (but this is never the case for new runners). If they are too stressed (almost always the case for new runners) then you will only be as strong as your weakest link, and wherever that is, that will be the first thing to go.

In the first few weeks of a new exercise regime, you need to bear in mind that your tendons and ligaments are at least ten to 14 days behind how strong you might be feeling on any given day.

And if you’ve been careful, and made it through the first fortnight without imposing too many new demands on tendons that are still struggling to adapt, there is another process that is even slower.

Ever since the 19th century, we have had Wolff’s Law to tell us that our bones adapt over time to increased loading. Imposing new demands on bones stimulates them to remodel. Called mechanotransduction, bones convert the physical indicators of the forces and stresses placed upon them into chemical ones that stimulate the bones to repair, first by breaking down their existing structures and then by rebuilding stronger ones. But this is a much slower process than with soft and connective tissues.

While it may be surprising to learn that two weeks into your new training schedule your bones are basically still those of a non-runner, the news is actually worse than this. Bone remodelling requires that some of the structure is destroyed (by a cell called an osteoclast) before it can be rebuilt. So, during your third week of running, feeling fitter and stronger, with some soft tissue adaptation beginning to take place, your bones are for a short period actually weaker than when you first started. By the fourth week, your bones will have succeeded to adapting to your first week’s run and so will be a little stronger. But they are always going to be a few weeks behind because contrary to popular belief running is very good for our bones, but density adaptation is comparatively slow.

With these processes in a constant and unsynchronised cycle, the new jogger has to be vigilant in not running away with their new-found fitness straight into a stress fracture. If you have just taken up running it is worth thinking about the Goldilocks Threshold, and remember that no one has ever given up or got injured because they did too little. The clearest feedback that your body gives you while running is that of your immediate cardiorespiratory experience. And for every run you do, this will improve, but you must avoid entirely the idea that cardiorespiratory ability is an indicator of your overall fitness – it isn’t. It is only the tiniest tip of the iceberg of what is going on in the body.

While you’re just hitting your stride, your body is punishingly hard at work doing some miraculous things under your skin to adapt to your change of lifestyle; so be kind to yourself, take it slow, enjoy it, give your body the time and space that it needs, and you will be much more likely to make it to February.

Author Bio: Vybarr Cregan-Reid is a Reader in Environmental Humanities and Author of ‘Footnotes: How running makes us human’ at the University of Kent