What is the right amount of stress for our tissues?
Hey all, Matt here from 1HP.
In this thread, I wanted to go over a concept one of my patients shared with me that captures our the approach we take with RSI issues quite well.
The concept is called the envelope of function and it is a way to understand just the PHYSIOLOGIC aspect of an RSI injury quite well. This email and thread is an adapted version of the Kai Sigel from Physiotutors wrote here, considering wrist & hand RSI.
What is the envelope of function?
As you might know after reading content of ours that we consistently reference the concept of the healthbar. And TL:DR it’s the basic idea that tissues can only handle too much. Or that we do too much and our tissues are unable to handle that stress.
The envelope of function adds the dimension of time to hopefully provide a more amplified understanding of the concept. This concept was proposed by an orthopedic surgeon who was looking to highlight the concept of homeostasis. Homeostasis is the body’s natural ability to maintain a stable, balanced internal environment to ensure survival and optimal function in response to changes both externally and internally. If we look further into research this concept has actually been present since 1993 which highlights the idea of allostatic load (but that’s for another conversation).
Adapted from Dye et al. (2005) - Considers Wrist & hand Activities
Here’s the envelope of function from the research article but lets use the wrist & hand instead of the knee so you guys will be able to better relate to this. The black line shows.. what an individual can handle based on their conditioning considering load (y-axis) and frequency (x-axis). You’ll see that for the high loads I created a scenario in which an indivdual catches a 100 lb ball dropped from 3 stories. This would exceed most peoples tissue capacity.
Throwing a 5 lb ball one time is a high load, but doesn’t exceed what you can handle.
And actually for most low repetitive activities of the wrist & hand as you can see they are on the very low load end, but the frequency is really high. Drawing for 2 hours, gaming for 3 hours, typing for 5 hours and or low level typing for 10 hours. All of these are on the low end but depending on how much you do it and how aggressive it can fall in different places of the envelope of function. This can either positively or negatively affect our homeostasis.
Do the right amount underneath the envelope of function? You’re safe and you can even handle more the next time you try it
Do too much above the envelope of function? You temporarily irritate the tissues and you can handle less the next time you try it
Now lets put it in the context of a simple exercise most of us understand: The Bicep Curl
Right amount: Do 10 bicep curls at a weight (lets say 15 lbs) that causes you to fatigue near the last 2 reps? Your muscles will get stronger!
Too little: Do 5 reps of bicep curls of 15 lbs, no fatigue? Our muscles aren’t really challenged, they don’t improve in strength or size!
Too much: Attempt 8 reps of bicep curls of 100 lbs? Your muscle could be damaged if someone helps you actually attempt it by putting it into your arms.
We can visualize how these various situations can impact our tissues by layering on the “zones” in the envelop of function. This parallels the regular concept of the healthbar we consistently reference, yet ads some more nuance.
Grey Zone (Tissue Damage): With high enough load (it has to be excessive) like catching a 50 lb bowling ball dropped form a single story would definitely cause tissue damage. This
Red Zone (Tissue Irritation): Any combination of load and frequency that reaches the red zone will lead to irritation of tissues. And when we spend enough time in this zone it can eventually lead to tissue damage.
The nuance here is that when loads are high there is a higher risk of traumatic injury that can lead to full tears damage that leads to more prolonged disability. The POSITIVE thing about most RSI injuries is that because they are such low load and more of a problem of high frequency (too much) there is less risk of injuries leading to long-term disability. See my article on the fear of “permanent damage”
Blue Zone (Safe Loading Zone): The zone represents the safe where loading at various frequencies will either lead to positive adaptation or keep the tissue where it is at (homeostatic zone). Within the blue zone you can find the right amount of loading that can help individuals progress in their ability to handle function. I like to call this zone the optimal loading zone. You can see the green line is the minimal amount of stress that you can apply to improve your capacity or ability to handle stress. Depending on how close you get to that red line of the “Max Tolerated Dose” you will progress a bit more quickly at the risk of sometimes irritating your tissues.
Working with a physical therapist often allows you to find the “right amount” or “optimal load” more quickly as they are able to help you methodically assess your
- Current Physical Capacity - Through endurance based tests for RSI related problems
- Current Load & Frequency (Activity Dependent) - Through a comprehensive assessment of what activities you are performing and being able to clarify the differences of intensity during the performance of that activity. I’ve alluded to this before in my other content but within a specific activity there are things that cause more stress compared to others. For example playing a solo with a guitar is likely more stressful than playing chords.
- Psychosocial Factors - Assessing your beliefs, fears, understanding of pain and problem which can influence perceived load
Yellow Zone (Too little): This zone represents doing way too little for your tissues, often causing them to weaken and result in the types curve type that you see below. This zone is typically where most traditional interventions fall and is why they often fail in helping the individual return to function. It should be clear as to why - you aren’t doing enough to support improving the tissues ability to handle stress.
And so there are typically two paths that are taken in response to an RSI injury. Unfortunately most people take the left path which leads to the tissues getting more weak and the zone of irritation coming down. The right path is first recognizing what led to the problem in the first place and making the right modifications.
Remember again the X axis is frequency (how much) and Y-axis is load (level of stress). Since the level of loading isn’t typically high with repetitive strain activities there isn’t much we can do on the “load side” except make some minor changes in our posture, ergonomics, input devices etc. But we can reduce activity. We DON’T HAVE TO STOP COMPLETELY. We reduce the right amount to allow us to focus on building up our envelope of function. Or as we have said many times before our health bar or capacity to handle more repetitive strain over time.
How can you use the envelope of function?
I hope you can see now that there is always going to be a relationship between your current symptoms and the specific changes you can make to help you recover. And the “magic” is all in the dose. How well we apply these changes in load (exercises) and frequency (activity management) will directly influence how quickly we recover. So whenever you feel specific symptoms you can always think about whether or not it was a
- Load Stress (exercise or intensity-based) that led to some tissue irritation or..
- Frequency Stress (Activity duration) that led to the irritation
And when you identify what that is, then you can use that as data to guide your decision-making going forward. It seems simple here but the added complexity is layering on your tissue adaptation timeline along with understanding more about pain. In the future I may layer on some psychosocial aspects to these graphs to demonstrate how your beliefs may impact your perception of pain but for now you can recognize that sometimes you may “feel” or “be afraid” that you are going to irritate yourself with a certain combination of load & frequency. In most cases this fear is leading you to feel that increase in pain despite the tissue itself not being irritated. I describe how you can figure out this real line of physiologic irritation in my flare-up management guide. But ultimately it is hard work since you have to learn more about your body and recognize what is real tissue irritation versus increased sensitivity from psychosocial aspects of pain.
The TL:DR here is… your goal is to find the right dose to improve your function. Stop resting, it won’t help since it underloads your tissues but often comes with fears or beliefs that you aren’t able to handle more.
Hope this helped you expand your understanding on the mechanics and resolution of RSI problems!
Best,
Matt
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Resources & References
1-hp.org (website)
Science Behind RSI Injuries & Treatment (VIDEO)
References:
McEwen BS, Stellar E. Stress and the individual. Mechanisms leading to disease. Arch Intern Med. 1993 Sep 27;153(18):2093-101. PMID: 8379800.
Dye SF. The pathophysiology of patellofemoral pain: a tissue homeostasis perspective. Clin Orthop Relat Res. 2005 Jul;(436):100-10. doi: 10.1097/01.blo.0000172303.74414.7d. PMID: 15995427.
Rabey M, Moloney N. "I Don't Know Why I've Got this Pain!" Allostasis as a Possible Explanatory Model. Phys Ther. 2022 May 5;102(5):pzac017. doi: 10.1093/ptj/pzac017. PMID: 35202474.
Feigel ED, Bird MB, Koltun KJ, Lovalekar M, Forse JN, Gage CR, Steele EJ, Kargl CK, Martin BJ, Bannister A, Cruz AV, Doyle TLA, Friedl KE, Nindl BC. Allostatic Load Is Associated with Overuse Musculoskeletal Injury during US Marine Corps Officer Candidates School. Med Sci Sports Exerc. 2024 Nov 1;56(11):2220-2229. doi: 10.1249/MSS.0000000000003507. Epub 2024 Jun 27. PMID: 38934495.
Sigel, K. (2023, April 17). The envelope of function – Overuse injuries explained. Physiotutors. https://www.physiotutors.com/envelope-of-function/
Posted Aug 27, 2025, 4:03 PM UTC