Did you think we weren’t going to address this after top Games’ athlete, Julie Foucher, tore her achilles while doing box jumps this past weekend? 😉 To avoid sounding cliché, I won’t jump on every anti-high rep box jump bandwagon. What I will do is shed light on the anatomical side of things and why this tends to be a consistent topic of discussion. Time to get nerdy and anatomical with y’all! 😉
Let’s look at the movement itself. A box jump is a plyometric exercise where there’s a powerful eccentric contraction (lengthening) quickly followed by a concentric contraction (shortening). When we land, The Achilles tendon is in the eccentric phase. It’s being stretched at the same time the calf muscles are contracting. The lengthening phase (eccentric) of the Achilles stores energy for the start of the next jump.
The acceleration of lengthening/shortening of muscles under stress is what helps the effectiveness of plyometric exercises and developing strength. It’s also what makes them risky based on the degree at which the muscle and tendon are being tensed. The role of the Achilles tendon during a box jump can be compared to a rubber band. When stretched it stores energy that it uses to return back to its shortened state. Pull too hard and it snaps.
Most exercises create small tears inside tendons. Nothing to be scared of as this is how we build strength. However, in the case of the Achilles, high rep box jumps can cause injuries because the repetitiveness of eccentric loading causes enough micro tears that it no longer has the strength to absorb the forces; leading to a macro tear or complete rupture of the tendon.
I’m certainly not here to tell you to stop rebounding off the floor. We’re adults, you can make that decision. However, I can shed light on where you fall.
If you have:
- Poor ankle mobility (stiff ankles or limited calf flexibility)—stick with the jump up, step down method. You’ll thank us.
- Foot pronation (ankle collapses inward and you aren’t working in a straight line)—again, step down method until we find a way to develop better ankle stability.
- Trained frequently w/ explosive movements and haven’t allowed enough time for rest (i.e. sore/tight calves, tenderness in ankle)—think carefully about rebounding. It may be a good idea to give more time to recover with the step down method.
If your goals include:
- Day to day health and fitness—by all means, if they’re in a workout, STEP DOWN. You’ll gain more from it and will certainly decrease this risk.
- Improving movement quality—go with the step up/down method. Better glute engagement and overall positioning
- Competing—you can’t avoid these in your training but use progression here. Smaller boxes to train rebounding but use as strength sets. You should never use these in workouts if you haven’t built the strength to handle the force the rebounding places on the Achilles. If you’ve been competing for a while, use them as conditioning sets between exercises but never under fatigue/towards the end of a workout. I’d save rebounding for game day.
The Achilles is a tricky beast as no one is sure why it starts to degenerate. It gives no signs and even well trained athletes are at risk for rupture. But with proper training and understanding your own movement patterns, you can certainly minimize your risk for this. Yes, it’s a one in a million injury but it has become the ‘Achilles heel’ ☺ within the crossfit world. I’d like for all our members to have healthy ones!
Train smart, live smarter, CFA!