Athletes and injuries are like oil and water.

 

Athletes will do anything they can to avoid having to rest, because they know there’s a cost to doing so if forced to rest for too long.  But in some instances, there’s no way around it.  We reach a point that we just need to rest and give that injury time to heal.

 

One significant cost is that we lose muscle strength and muscle size in the region of our body that is rested or immobilized.  It’s inevitable and unfortunately it can start happening very quickly.  Disuse muscle atrophy has been shown to start in as little as just a few days of immobilization with the most rapid rate of loss happening in the initial period of disuse.  

 

This atrophy happens faster with strict immobilization versus just rest from training.  And the effect seems to occur slightly faster in the legs versus the arms, and is more rapid and significant when the whole body is immobilized (ie. bed ridden) versus a limb or portion of the limb.

 

A systematic review found that immobilizing an upper limb has been shown to decrease the total triceps muscle volume by approximately 11% after 28 days and immobilizing a lower limb can decrease the quadriceps muscle volume by approximately 9% after 28 days.

 

If you’ve been training for years and forced to suddenly rest or immobilize, this is frustrating and maybe even devastating to look down at your soft shrunken quad, pec, calf or insert any other favourite muscle of yours that wilted away after an injury.  

 

So what can you do to battle this inevitable loss of muscle strength and size?

 

Cross Education for Strength

 

Cross education or the cross-training effect refers to the transference of the training effects from one limb to the opposite limb.  It’s a simple concept: if you injure a part of your upper or lower limb, by strength training the same muscles of the uninjured side you can minimize the loss of strength or muscles size on the injured side.

 

Cross education theories have roots in the scientific literature dated way way back to 1897.  It is a low risk, low cost rehabilitation strategy but for some reason it gets very little attention in the rehabilitation world.  In fact I’m willing to wager most of you reading this article have never had a physician or surgeon recommend this while under their guidance and care.  Even amongst strength coaches and therapists this is a largely untapped resource for rehabilitation.

 

As little as 4-5 weeks of progressive unilateral training has been shown to INCREASE strength by as much as 13% in an untrained arm. 

 

Read that last sentence again… 13% improvements in strength by not even training the area getting tested.

 

How is this happening?  This is what experts have decided recently should be called crossed education for strength.  You may have heard this being referred to as a different term (we used to call it the crossover effect).  Cross education is largely as a result of specific effects to the nervous system.  A recent consensus statement from experts in the field primarily attribute this phenomenon to stimulation of the motor cortex of the brain.   There likely are some effects to regions of the spinal cord and possibly some systemic hormonal effects at play from the generalized effect of strength training as well.

 

But can we harness this phenomenon after surgery or a significant injury?  Can we increase strength while injured??  In short, no, but we can decrease the rate of strength loss and improve the rate of strength recovery.

 

A study on ACL reconstruction patients found subjects randomized to a concentric only or eccentric only training group of their uninjured side’s quadriceps muscle had 20-25% greater isometric strength in their injured (surgical side) at 12 and 24 weeks compared to controls.  

 

Again these are not insignificant effects being captured in clinical populations.  Another clear signal of the cross education effect for strength at play.

 

There is still lots to sort out in specific clinical populations.  How much does pain and swelling factor in?  Are there areas of the body that are resistant to this cross training effect?  The research will continue, but your injury can’t wait for the academics.  And the worst case is that you maintain or build strength and muscle size on the unaffected side.  Doesn’t seem like much of a downside.

 

What type of strength training is best for cross education?

 

A recent scoping review of the existing literature concluded that traditional resistance training frequencies (ie., 2-3d/wk) at high intensities are most effective at promoting cross education of strength.  The experts in this review conclude that eccentric muscle actions also show additive benefits. 

 

The majority of research in this field is taken from subjects with untrained or artificially immobilized parts of their body (ie 8 hrs of induced immobility a day) not from injured or post surgical populations. 

 

So we have to be a little bit cautious in placing expectations on the magnitude of effect we can have.  But again there is only upside to this strategy.

 

And if we stick to strength training principles we know work in normal circumstances we can be flexible and leave room for individualization for how we prescribe it for cross education.  

 

A pivotal 2021 paper by Brad Schoenfeld and team challenged the dogma that certain repetition ranges are required for strength vs hypertrophy vs endurance.  Strength gains, hypertrophy gains and endurance gains are not confined to narrow repetition ranges they argue, but instead are stimulated primarily by the intensity of muscular effort.  

 

A very specific athletic or muscular function the training may need more nuanced consideration, but in most cases pick a weight that represents more than 30% of your 1 RM (repetition max) and build your own rep and set scheme that pushes you HARD.  

 

If you like lifting heavy, go for it: 75-80% of your 1RM (rep max) in the 6-12 rep range and 3-4 sets will certainly work.  

 

But if you don’t have access to heavier weights or prefer lighter weight and higher rep style training you can work deep into a muscle burn and get a similar effect when it comes to muscle hypertrophy.  Even a single set to failure approach can work for building muscle and can be a great time effective protocol. 

 

Unless you have a very specific post surgical concern, working the muscle or movement on the uninjured side hard in your preferred rep and set scheme will yield you some benefit to your injured side.  

 

Take Home notes to preserve muscle size and strength on your injured side:

-train the same muscle groups of movements you want to preserve on the uninjured side

-start cross education training for strength right away as disuse atrophy sets in early

-focus on training those muscles or movements hard to build strength

-work in some eccentric exercises where possible

–2-3 sessions a week for as little as 4 weeks can help