The Envelope of Function

I wanted to introduce a concept that I speak to patients about regularly within my clinical practice. It's a concept which underpins their training and/or rehab programming, as well as an ongoing underpinning philosophy for their health and performance. It’s called the ‘Envelope of Function’.

We all have an envelope of function’ Simply put, it means what your structure (eg hip/knee, quadriceps etc) is physiologically capable of. If you work above this threshold then we may experience pain or injury, if we never push the boundaries of the envelope then no progress is made.

Figure 1 A graphical representation of the Envelope of Function (ref. BFitter Performance)

Injuries occur when the activities we perform exceeds our tissues capacity. The envelope of function is a zone of homeostasis or balance, which is the amount of activity and load we can tolerate or manage without any pain-related symptoms or injuries. If we provide our bodies with just enough stress and load, then we are able to adapt and get stronger. Although if we exceed this range with too much stress then we may see injuries and reactive responses such as swelling and pain. This can occur due to a one off, large load or an aggressive increase of load via training or exercise frequency/volume. It’s important to also note other factors can influence our bodies ability to tolerate and manage load such as life stress, poor sleep, illness and nutrition on a day-to-day basis, but this will be looked into another time.

After sustaining an injury – for example a lateral ankle sprain, your normal 10km capacity may be reduced to only being able to 5km. Anything beyond the 5km is pushing the new ‘reduced’ envelope of function (homeostatis in figure 1) and could lead to symptoms such as pain and swelling.
Figure 2 The three possible outcomes with loading strategy

Why should you be aware of the Envelope of Function? In an industry that is primarily reactive in nature, we often address body aches, and pains when an acute injury is sustained. Previous injury and surgery reduces your envelope of function, this is important to be aware of and the job of you medical professional to guide you through. Even with surgical intervention, there will be a great deal of scar tissue around the affected structures and this will reduce its previous function and structural capacity. In turn this alteration of length, strength and elasticity has the potential to influence the joints and limbs that rely on this repaired or injured structure. In turn, this can result in further injury, or compensatory patterns of movement.

As with all physiotherapy management, it’s important that a detailed clinical assessment is conducted, as there are other, less obvious factors that require investigating. Such as environmental, physiological and/or systemic issues that may be present, which may be a driver for the issue at hand. If this is the case, then further investigation or referral may be needed as an initial port of call. When the cause of concern has been established and diagnosed, then you can address the envelope of function and management plan.

With rehab, our goal is to increase your Envelope of Function and expand your 'manageable zone’. We can do this with programmed conditioning, aiming to increase the amount of activity and load you can tolerate.

We will delve further into this topic, but I hope you enjoyed this introduction into your Envelope of Function. If you enjoyed this, then have a read of our post on the ‘Future Impact on your Injury History

Thanks for taking the time to read

Sophie

@sophielanephysio