Let’s think about your knee, and a term called your envelope of function. Your “knee joint” is made up of a variety of things including bone, muscle, ligaments and connective tissue which work together to accept, transfer and dissipate load. Your envelope of function refers to the amount of load or force your knee is able to accept, transfer and dissipate within a given time period without getting an injury. Look at this graph below, there are three zones that we will look at. First is the zone of homeostasis (1), second is the zone of supraphysiologic overload (2) and third is the zone of structural failure or injury (3) with the darkened line being your envelope of function.

Let’s use two examples: person A is someone with an active lifestyle who follows the Canadian fitness guidelines and person B is largely sedentary not meeting these guidelines. Person A has an envelope of function that is higher in the graph because their body has adapted to their lifestyle and is now able to withstand higher amounts of load. Person B has an envelope of function that is lower, in other words their knee joint may not be able to withstand as much force prior to injury compared to person A.

To Increase your envelope of function you need to train your body gradually to avoid injury. Resistance training with things like gym equipment, weights and bands is a great way to do this. With your physiotherapist it is best to start slow, the changes will be gradual but with consistent work you will start to see changes. Remember it can take at least 6 to 8 weeks of consistent exercise to see noticeable strength differences!

References

Dye, Scott. (1996). The Knee as a Biologic Transmission With an Envelope of Function: A Theory. Clinical Orthopaedics & Related Research, 325, 10-18. Retrieved from http://ovidsp.ovid.com/ovidweb.cgi?T=JS&PAGE=reference&D=ovftb&NEWS=N&AN=00003086-199604000-00003.