Technically speaking, injuries occur when a task or activity exceeds the body’s current capacity. But what does that actually mean? When we talk about injuries, we often refer to the body’s load tolerance – the ability of the body to cope with the stressors, forces, and activities we are exposed to throughout the day. If we think about the body mechanically, this makes sense – if we pick up something that is too heavy for our body’s current capacity, that we have not trained or prepared the body to do, it is very likely that the load will exceed our capacity and some kind of injury may occur. While this makes sense of injuries that occur while doing unfamiliar or untrained activities, many people still experience injuries as a result of activities that they perform regularly. How does this happen?

Imagine you were to pick up a 20kg box at work, and that you had been doing this day-to-day, for many years. Your body has adjusted and built up the strength to do this over time, and you have never noticed any pain or discomfort doing this activity before. There is nothing inherently dangerous about the activity that you have been doing, but one day you pick the box up, and injure your back. What happened? The weight and the size of the box didn’t change. Your muscles didn’t suddenly shrink and get weaker overnight, and yet an injury still occurred. This is because your capacity to perform an activity is not just based on your physical strength, but on the total resources that your body has for the day. 

For instance, sleeping poorly reduces the amount of energy you have to expend throughout the day. Not eating well or hydrating properly can further reduce your body’s resources. Stress, although we think about it as a psychological phenomenon, activates your fight/flight/freeze response, which requires your entire nervous system to participate – this can be a further drain on your resources. Suddenly, the task that is familiar and usually within your body’s capacity to perform is requiring resources that have been used up elsewhere. Without these resources, your body’s tolerance to load is significantly reduced, and tasks that would usually be easy for you to perform may be more difficult, or require a capacity that your body does not currently have. 

So what does this mean? Injuries are caused by overload – this can be related to physical strength, but also to quality of sleep, nutrition, hydration, stress and any number of things that impact the body. This means that on days where you notice you are more fatigued than usual, or where you haven’t been able to look after your body as well as you normally would, it is important to be aware of what is happening in your body when you go to perform tasks that are a bit more demanding. Listening to your body and being aware that your limits may change day-to-day, or even week-to-week.