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This is why high intensity cardio intervals should be part of your injury recovery training

Sep 15, 2024

Exercise is quite possibly the most potent drug on the planet. That's what I love most about the field of Physical Therapy. We get to use various forms of exercise to elicit desired changes in the body and mind. 

In this article, I will summarize to you how the prescription of high-intensity cardio training can be an integral part of an injury recovery or long term pain program. The benefits are undeniable, yet often overlooked in the medical world. 


As most of you probably already know, I work in a non-traditional physical therapy setting. I work with military athletes in a role where my job is to not only guide the rehabilitation of musculoskeletal injuries, but also determine left and right parameters of fitness programming that is safe to continue during injury. 

I view this role as part Physical Therapist and part Strength and Conditioning Professional. The reality is that all exercise ad fitness training is on a spectrum with injured at one end and healthy at the other. All we are trying to do with physical therapy is move along the spectrum until we can train at the level of a healthy individual.  We modify, we adapt, and we always continue to push the needle forward along that spectrum.

Sadly, the prescription of cardio training is rarely provided in most typical physical therapy programs, but I have found massive benefit when it comes to helping both the body and the mind push through injury and/or pain. In this article, I want to share with you some of the science behind this as well as some practical applications that you may find useful either with yourself if you are currently injured or with your clients/patients if you are also a rehab/fitness professional. 


First let's define 'high-intensity'

For the purposes of this discussion, we will only be talking about high-intensity cardio training. There is also immense benefit in lower intensity training such as zone 2 but we will leave that for another day.

So generally speaking, let's define 'high-intensity' as interval work at 80-100% max effort.

I would verbalize this effort to a patient/client as "I want you to go hard enough that you are out of breath, unable to chat with someone next to you, and require a rest period at the end of the interval"

And now for the science backed benefits...


Increased capillarization

In a nutshell- high-intensity interval training cues the body to build more capillaries (small blood vessels that bring blood, oxygen, and nutrients throughout the body). 

More capillaries means more better blood flow and oxygenation to your muscles both of which are necessary for tissue healing. 

Improved capillarization also paves the way for muscle hypertrophy (increased strength) which is often a goal of rehabilitation. 

For a real world example- after knee surgery, I start clients on an assault bike program as soon as it is medically safe. In the beginning that may look like only using the arm handles for sprints. Or maybe it means using 1 leg and 2 arms (while the injured leg sits on the foot peg). And then as soon as it is safe for the operative leg to bike, we start using it. We do 2 days a week high-intensity intervals on the bike often doing 30 second sprints at 80-100% effort and then 3 days endurance building up to 12 miles in sub 40 minutes. I believe this biking program increases capillarization in the legs which then carries over to the weight room when we hit the stage in rehab to increase strength of quads, hamstrings, calves, and glutes. 


Increased Dopamine

Dopamine is a hormone and neurotransmitter that, in short, makes us feel happy. And while 'happy' isn't necessarily a direct rehab goals- everyone wants to feel good and dopamine does just that. 

High-intensity cardio training triggers the release of dopamine in our body and the effects are pretty cool. 

First off, dopamine can help decrease our perception of pain. When your brain is happy, it doesn't perceive pain to be as severe or frequent. This is HUGE when we look at physical rehabilitation. Hands down, I would rather someone get high on exercise instead of high on prescription meds. 

Dopamine is also part of our body's internal reward system which affects our motivation to do things. Simply put, you do a task, the body releases dopamine, you like the dopamine so you are more motivated to continue the task. So if a rehab patient is hesitant or fearful of exercise after an injury, this can quite literally get them hooked on getting back into the swing of working out. 

For a real world example- after a back injury, everything hurts. It literally hurts to breathe after throwing your back out. And sometimes people then start to associate any movement with pain. So they move less. But over the days, weeks, months of moving less, they now become stiff and continue to hurt simply because they aren't moving. It's a self-eating cycle. I have found high-intensity training to be immensely beneficial in these circumstances because when we get the dopamine hit- pain decreases, we feel more confident, and we want to keep doing it. The key, is finding the right mode for interval training and that can be a bit of trial and error mixed with what the client/patient is most willing to perform. Any cardio mode will do, just have to find the right method for each individual. 


Metabolic health

What do I mean by this? Metabolic health refers to how your body utilizes energy and is an indicator of your overall health and vitality. 

When it comes to injury recovery, I care about metabolic health primarily when we think about inflammation in the body. Chronic inflammation and poor metabolic health go hand-in-hand. 

High-intensity cardio training can improve metabolic health by helping regulate blood sugar levels as well as increasing insulin sensitivity. While these things are typically only discussed in certain populations such as pre-diabetics, I assure you they are important for all of us. Ultimately, we want to create the most ideal internal environment inside our body to promote healing. 

For a real world example- there is a saying in my world called 'military old'. What that means is that a 40 year old that has been in the military x 20 years may be in much worse health than a 40 year old civilian. And I see it all the time, especially those on the brink of retirement. It often comes with a diagnosis of arthritis, high blood pressure, high cholesterol, and PTSD. All of this is the culmination of a high stress life and career that has taken a toll on both the body and mind.  There are also often lifestyle choices that need to be addressed- smoking, alcohol, diet, coping mechanisms etc... but this is a talk for another day and often requires a multidisciplinary healthcare team. In my domain, we focus simply on the physical. How can we use exercise to move the needle forward. High-intensity interval training is one of those ways. 


 Now, I know what you are thinking...if someone is hurt or in pain how can they tolerate high-intensity intervals. The answer is somewhat complicated. It depends on the person, the injury, and their beliefs. Sometimes we start with lower intensity and build up. Sometimes we use the rest of the body for the intervals while protecting the injured limb. Sometimes we adapt equipment to meet the needs of the client. The point is that we always find an entry point. Getting started (on any new fitness program) if often the hardest part. So we simply find a place to begin and can progress from there. 

To any readers who are currently injured or navigating chronic pain, I encourage you to evaluate your current fitness program. Are you doing any high-intensity work a couple days a week? If no, why not? 

And to my readers who may be fellow rehab or fitness professionals, are you considering the prescription of appropriate high-intensity interval work with your injured clients? If no, why not? 

This is one of those circumstances where we can use exercise to create amazing changes in the body to promote healing of both the body and mind. 

If you have any questions on this topic or want to discuss further, feel free to send me a note at [email protected] 

Yours in health, 

Jamie Mraz

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