Author: Leslie J Bisson, MD
Have you ever struggled to explain to a patient how their activities led to an arthritic flare, or how too rapid a change in training caused an overuse injury? In this blog, I outline a model I’ve used to help patients understand how activity capacity, intensity, novelty, frequency and recovery are inter-related and can be used to optimize function, even in the presence of a musculoskeletal impairment.
The Activity Balloon Experiment
Do this thought experiment: blow up a balloon and write an activity on it, like “running.” The air in the balloon represents the capacity for that activity a part of your body (your knee, for example) allows before it sends a message that leads to pain. Each body part will have an unlimited number of these balloons, which vary in size due to prior activity history, the demands of the activity on that body part and any pathologic conditions. When you perform the activity, air flows out of its balloon.
If a balloon is emptied and the activity continues, you will feel pain, which is typically delayed by a few hours to 1-2 days. Pain is simply a message that capacity has been exceeded. When you stop doing the activity, a pump (representing recovery) reinflates the balloon. If you regularly do an activity that lets air out, followed by sufficient recovery, the pump gets stronger and gradually expands the balloon, and reinflates it more quickly (Figure 1a). However, if you do an activity too frequently, this effect works in reverse. The pump can’t completely reinflate the balloon after each session and with repeated sessions the balloon gradually empties.
The more intense the activity, the faster air flows out of its balloon (Figure 1b). If you don’t do an activity for a while (generally from a few days to a few weeks) air will slowly leak out of its balloon, eventually returning it to its baseline size. Finally, a musculoskeletal condition like arthritis or tendinopathy (or aging) shrinks balloons and makes them harder to expand. Fortunately, they can still be expanded, albeit more slowly.
Injuries shrink balloons but differ from chronic musculoskeletal conditions in that injured body parts generally 1) are painful immediately if any balloons are emptied, and 2) re-expand their balloons over time as healing progresses. However, different activity balloons for an injured body part will re-expand at different rates.
Figure 1a. Expanding an activity balloon.
You can expand a balloon for an activity like walking by regularly deflating and inflating it. The size of the balloon shows the amount of an activity you can do before you get delayed pain. Recovery re-inflates the balloon. You stretch a balloon by gradually increasing the amount of the activity, a little each time, and recovering in between.
Figure 1b. Adding intensity after you’ve expanded a balloon
This shows a walking balloon that has been greatly expanded by gradual increases in the amount of the activity with enough recovery in between. It is now safer to increase the walking intensity (by walking faster, or on sand or an uneven surface, or adding in hills) because it’s harder to empty the balloon even when the air is let out faster.
Activity Balloons in Action
The balloon model for activity capacity can be used to explain multiple clinical phenomena. For example, why are some people with arthritis able to be far more active than others, OR why is there such a disconnect between the amount of arthritis on imaging studies and the amount of functional impairment? Highly functioning people with arthritis have gradually expanded their capacity through the proper relationship between activity and recovery. Why do athletes develop overuse injuries? They have gradually emptied out one or more balloons through an imbalance between activity and recovery. How can I optimally recover from an injury? Slowly advance your activities and monitor how your body responds during the activity as well as in the days afterwards.
Don’t be discouraged if you feel great during and after some activities, but others still cause symptoms. This just means some balloons are expanding faster. Be patient and allow the others to expand. Why did I suddenly wake up with symptoms? You depleted capacity for the affected body part. Review what you’ve done in the prior hours to 1-2 days that would have emptied a balloon. This is typically something that is new (unexpanded balloon), more (let too much air out), more intense (let air out too quickly), or more frequent (gradually deflated a balloon over time) in comparison to what you’ve been doing recently, or you haven’t been doing the activity regularly lately (and air has leaked out of a previously expanded balloon). Why is it easier to get injured doing high-intensity activity? Because the air is let out so quickly, it’s very easy to completely empty a balloon. Expand the balloon by increasing the volume of activity at lower intensity before increasing the intensity. Why is it better to do a wide variety of activities? It keeps many balloons expanded.
There are many ways to expand an activity balloon for a body part with a chronic condition. Here is one example.
- Start by determining the size of the balloon. Perform the desired activity in a relatively small amount at low intensity and monitor the body part for 2 days afterwards. There are three possible outcomes. First, there is no increase in pain. This means the balloon wasn’t emptied. Perform the activity again on day 4 but increase it by 50% or more, again at low intensity, and go through the two-day monitoring process. Second, pain increases somewhat and lasts 2 or fewer days. You’ve determined the approximate size of the balloon. Third, the pain increases substantially or lasts for 3 or more days after the activity. You did too much and emptied the balloon. Wait for the pain to recover and once it’s back to baseline, try the activity again at approximately 50% (or less, depending on how much pain appeared and how long it lasted) of the prior amount. Go through the same two-day monitoring process and adjust/repeat as needed to determine the balloon size.
- Once the balloon size is determined, expand it by gradually increasing the amount of the activity, monitoring for two days afterwards, and increasing the amount quickly if there is no increase in pain, slowly if pain goes up but disappears by day 3, and decrease the activity if pain goes up substantially or lasts 3 or more days. Once you can regularly do the desired amount of the activity with two recovery days, shorten recovery by one day or increase intensity.
I have employed this method with success for patients with arthritis and other musculoskeletal conditions. Many of my patients use the model to self-regulate, expand capacity and avoid trips to see me.
Take home message
I hope this model to incorporate how various activity factors can work together to deplete or expand musculoskeletal capacity helps your patients and athletes. You can use it to show how changes in activity, when thoughtful and intentional, can decrease pain and improve function in those with arthritis or other chronic conditions by expanding capacity. Conversely, you may also employ it to illustrate how recent or long-standing activity changes can cause pain flares or overuse injuries.
GenAI Statement
No GenAI was used in the preparation of this blog.