Cross education (CE) is a phenomenon that’s fascinated me for a number of years now. And while I don’t have any clear answers for you (mostly because it seems like the scientific and medical worlds don’t seem to really understand it either), I do think it’s worth keeping in our peripheral consciousness, particularly because…when was the last time you injured both limbs symmetrically? Buckle into your anecdotal-report mobiles, and let’s just have a chat about something that I find really cool and don’t understand in the slightest.
Back in late 2015, I came out of a 12-year retirement from tennis and decided to go hit some balls around with a friend. Within the first 15 minutes of warming up, I managed to sprain my ankle really badly. I pigheadedly insisted on playing through (I suppose I probably wasn’t aware at the time of its severity), and I ended up with partial tears in four of the ligaments in my right ankle.
I’ve talked a little in the past about how to train around (some kinds of) illness, but injuries are a slightly trickier subject. Some injuries may be pretty easy to work around (e.g. a peripheral lower-body injury like a broken toe could simply mean you’re training your upper body with non-load-bearing exercises, and potentially leave you able to make use of machines to hit up your quads and hamstrings), while others can impair your ability to work unaffected body parts (e.g. stitches on your finger could rule out ‘lower body’ exercises like deadlifts, or anything where grip comes into play). As such, I’m not gonna be able to make any blanket recommendations for how to train around every injury, but I can talk about one strategy I’ve used since The Great Ankle Shredding of 2015, and — personally, and entirely anecdotally — seem to have had great success with.
I first came across a similar mechanism to CE when reading an article about mirror therapy in the management of phantom limb pain in amputees and stroke patients. When I sustained that injury (which technically should have benched me from any lower body training for a good 8 to 10 weeks), I told my coach I wanted to try and keep training my unaffected leg unilaterally, in part because I needed something to motivate myself to keep pushing through the disappointment of an injury, but also because if there was even the slightest chance this mitigated any losses in strength and or muscle atrophy, I was all in.
So what is CE? It’s a neurophysiological phenomenon where training one limb has been shown to result in an increase in strength and/or skill of the other untrained limb. Part of this results in how repetitive strength training has not just muscular but also neural adaptations (which can also be observed in how someone who lifts is likely to have some pretty sweet linear strength gains when they’re new to the style of training — nobody grows 5lbs upon 5lbs of strength capacity in each lift, week after week). Some earlier studies have found the effect of CE to result in 7 to 8% increases in initial strength in the contralateral untrained side, or around a quarter of the trained side’s gains. While a more recent meta-analysis is suggesting the number may be higher (almost 12%), what’s really cool about this is the fairly consistently observed effect that unilateral training can help to preserve muscle mass and strength while the contralateral limb is immobilised, such as in the case of injury.
Back to 2015 and this sample size of 1: prior to shredding my ankle, I’d just started working towards the goal of unassisted pistol squats. I’d gotten about as far as unassisted eccentric squat-to-bench, but was pretty wobbly on my way up. Based on my barbell back squat numbers at the time, I should have had the strength to stand up, single-legged, from a bench, but damn if those little stability muscles weren’t taking their time to get their act together. By the time I was allowed to resume non-rehab training on my injured leg, I’d worked my way up to about 8 unassisted pistol squats on the good side. The first time I attempted a pistol squat, post-injury, on my bad leg, well. I promptly fell over, because bye balance. But within about a week or so, I was up to 5 unassisted pistols. On my bad leg.
Fast forward to 2017 — I sustained (yet another) injury to my left knee this time (partial tears of the MCL and PCL, for those who care, and no, it was unrelated to training or any sport for that matter). Within 2 to 3 weeks of crutching around, there was a visible difference in quad size between my right and left legs, way worse than back in 2015, since I wasn’t even able to use machines like the quad extension or hamstring curl to isolate my upper leg muscles. I still trained my right leg like a boss though. And once I was able to resume bilateral training, I regained more than 80% of the lean mass I’d lost (according to DEXA scans) within 2 weeks.
While, again, this is an incredibly unscientific and reviewed by exactly zero peers ‘study’ of a sample size of 1 (with no control, to boot!), and while the mechanisms through which neural adaptations contribute to CE remain unclear, multiple studies have shown (or at least observed) that strength, muscle, and even muscle activation have been preserved via CE.
My best guess is that it’s got to do with the brain being…not quite as smart as we often give it credit for (there’s a lot of wires in there that can easily get crossed, so this is one way to make use of that), but also that it probably has to do with the way the desire to eat “well” and the ability to train in the way that you enjoy are often tightly correlated: smash out a great workout and you’re likely to want to fuel your body in a way that will support optimal recovery and performance; overdo it on a series of crappy decisions and the likelihood of those subpar nutritional choices extending into skipped workouts skyrockets. Chances are, if you’re training with intent, even (or especially!) in recovery from an injury, you’ll also be more mindful of food choices, particularly protein, which may help to combat loss of muscle mass due to a decline in postprandial muscle protein synthesis rates.
As for how I went from not-quite-standing-up-unassisted-from-a-bench to multiple reps of unassisted pistol squats, via a serious ankle injury? Who knows, really? And, to be perfectly honest, I don’t even really care, as long as this remains a viable option for whenever I next do something ridiculous like…drop a 20kg weight plate on my big toe, or…close my hand around a falling knife. Don’t worry — I’ve broken up with tennis for once and for all (I think a couple dozen ankle sprains, 3 shoulder dislocations, and various other niggling random injuries are plenty for one lifetime!) so fingers crossed my (properly rehabbed) ankles are safe (for now).