Runners love running, and it is often difficult for a non-runner to understand the desire to run, even when injured. A big fear for our patients who run regularly is to be told to ‘give up ’, which may explain why runners struggle on, delaying seeking advice.
Thankfully, there is a great deal we can do to help if we spot the problem early. Stress fractures and ‘stress responses’ (when the softening of bones occur prior to an actual fracture occurring) are very common, Yet the perception is that they are uncommon. Why do we overlook them? Well it might be because consciously or subconsciously, we can tend to stereotype our patients, and be under the impression that stress fractures only occur in elite level, underweight females. The reality is that any runner is susceptible to a stress fracture, particularly if they are relatively new to the sport, have gone through a rapid increase in mileage, or have poor biomechanics or muscular conditioning.
Trouble doesn’t just occur in the exercise newbies. If a person comes from a previous sporting background requiring high levels of CV fitness (e.g. road cycling or football), and they decide to switch to running, they can push themselves into bony injury because their skeletal system hasn’t been able to keep up with their CV motor. Add in a sudden change of footwear choice, along with a recent trend in running shoe manufactures to make big changes in their heel-height-to-forefoot-height ratios, and you’ve got the perfect recipe for dramatic loading change in the body.
When we think about it, bony stress injury is really a series of micro-fractures within bone, created either through impact (which focally overloads a discrete area, e.g. a metatarsal), or through the force created when muscles traction against bone, or compress it (e.g. the fibula). Bone constantly remodels itself to be more effective at enduring forces placed upon it, and on a cellular level, osteoclasts breakdown bone cells and osteoblasts lay down new ones.
When we’re exercising appropriately, and not excessively loading our bones, this adaptive remodelling process actually makes our bones stronger. If we’re completely sedentary, or we have an immobilised limb, our bones atrophy. We’re not entirely sure how bone cellular activity change is switched on or off in different areas of a bone, but it’s thought that there may be a piezoelectric effect happening when bones are tensioned, making them relatively electropositive. This increased focus of positive charge in a particular bony location is thought to stimulate osteoclasts to start munching. When too many osteoclasts, and not enough osteoblasts are getting busy, this leads to a gradually weakened bone, an inevitable trouble – sometimes ridiculously quickly. Military recruits have been known to generate stress fractures in just a week of high intensity training, but three weeks of excessive loading may be a more common history in our general distance running population.
But it’s not only about mechanical forces.
Sure, duff biomechanics may explain why a fracture happened in a certain area, but we now know that stress fracture causation is multifactorial, and energy balance in particular, has a huge role to play.
We’re all familiar with the concept of the ‘female athlete triad’, but we know that stress fractures also affect huge numbers of men, so our thinking and our ‘labels’ are shifting. ‘Female athlete triad’ has now be upgraded to the grand title of ‘Relative Energy Deficiency in Sport’- ‘RED-S’.
To understand energy deficiency, we first need to think of energy balance. Energy balance is a simple case of maths – the amount of daily food energy you take in, minus your total energy expenditure. Energy expenditure means all the exercise activities you carry out, plus the normal physiological processes that occur in the body (such as breathing, gut activity, even thinking). Energy availability is what’s left in the energy kitty for these physiological and health restorative processes, after athletes have done all their running around. It’s as if exercise gets ‘first dibs’ on the energy pot, and our physiological system has to ‘make do’ with what’s left.
If we end up in negative equity on a regular basis, we can swiftly become ‘relatively energy deficient’. Our energy kitty determines how happy our hormonal system is. Specifically, our hypothalamic pituitary axis becomes upset by poor energy availability, and this is why in women we see menstrual cycle changes. These hormonal effects are less easy to spot in men, but they still lead to the same consequences of poor health and athletic performance, affecting many systems other than just bones.
What kind of figures are we thinking about when considering RED-S? We know that damage can occur if we fall below a finite number, which is determined by our lean body mass, the exercise energy that we expend, and the amount of food calories that we consume. In other words, to prevent injury, there is an absolute bottom level calorie number that needs to be in the kitty at the end of each day. Get that wrong for more than five days in a row, and you’re in trouble.
When we reflect on these figures, it’s easy to see how many of our patients are unaware of their ‘under-fuelling’, whilst striving to be healthy. Of course not everyone who develops a stress fracture will have ‘RED-S’, but we need to be more pro-active in asking questions relating to RED-S.
So the next time you have a stress fractured patient, consider making a quick guestimate about their calorie intake and expenditure, and ask yourself if they might be falling prey of the energy trap.