Endurance athletes, whether recreational or professional, constantly expose themselves to high training loads. The goal with these athletes, is to train the body systems with training stimuli that that result in a fitness response. However, the body can only handle a limited amount of stress at one time, so the question is, how much is too much? Also, why do we get injured during training?
There is ample academic literature that supports the notion that excessive training stimuli are the leading cause of overuse injuries commonly seen in endurance athletes. To accurately measure ‘excessive’ is difficult though. There are numerous methods and theories regarding this, but nothing has been established concretely for what we call ‘optimal loading for injury prevention’. The most common terms used to indicate a high training load are a recent/sudden change in training variables such as volume (e.g. total hours), frequency (e.g. sessions per week), velocity (e.g. run pace), and distance. We commonly look at how much a variable has been increased, and at what intensity has it been increased. These two factors have been studied in depth, and the development of the acute:chronic workload ratio (or the ‘training stress balance’) has become a frequent term used in training load management. In short summary, stress balance scores of less than 0.8 or greater than 1.5, put an athlete at an increased risk for injury. The principles behind this ratio are quite complex, but in short – it considers an athlete’s chronic training load (3-4 weeks) compared to their acute training load (current week). The goal is to gradually build a chronic load over 3-4 weeks, ensuring there is gradual progression, and to make space for de-loading in between.
However, the complexity of training makes this difficult. There is not one best answer to the optimal load question and there is also no set number to reach for in your weekly training load. It is also not an absolute that there will be the risk for injury at a high training stress balance score. Some athletes have developed tolerance to higher training loads (acute and chronic) over time so their relative risk at that level is different to someone who may be new to training. When it comes to increasing your training load, you might have heard about ‘the 10% rule’, where increases in training volume should be limited to 10% per week. However, in many research papers this number has been proven not to be very useful. Again, the risk of injury is relative to an individual, and also reliant on so many other variables. For example, less than 8 hours of sleep has been shown to result in 1.7 times more risk of injury. Another example from published research, is that having less than 2 recovery days in a week of training has shown to result in a 520% increased risk of injury. Mental and emotional fatigue factors also play a big role as part of training load issues.
What we as physios mostly see with endurance athletes are the overuse injuries. These types of injuries usually occur over an extended period, leading to a worsened progression. The location and presentation of injuries varies between the types of sport, but some general patterns do occur. In runners and cyclists, overuse injuries to the knee are more common (iliotibial band syndrome, patellofemoral joint pain, and patella tendinopathy), whereas in swimmers, overuse injuries to the shoulder are more common (rotator cuff syndromes, and biceps tendinopathies).
The consensus on injury prevention in endurance athletes is that training should follow a gradual progression of increasing load (volume, frequency, velocity, and distance). Also, avoiding heavy spikes (highs) and troughs (lows) in any of these variables is a way to protect yourself against injury. Monitoring your training load is also important. This is best done by using training load variables such as volume and the rate of perceived exertion (RPE) score. RPE is very useful as it measures an individual rating of your training load i.e. how hard you feel you worked. Other metrics such as heart rate, power, and velocity are also useful, but are limited due to the fact that these are pure numbers, and do not consider the human element of training load. To end off, simply remember to gradually progress your training load and avoid very high and low spikes of training. Also, have fun while you are at it!