(For video demonstrations as well as reliability and normative data, check out my friend and colleague's page for both the triple jump and single hop for distance)
Hop testing asymmetries have been theorized to predict future 1st time injury as well as predict re-injury, but from the information gathered from this presentation, the current evidence may not support that. It appears to support one leg hop testing usefulness in discriminating between normal and previously injured. As you will see if you click the clink to the presentation above, return to sport is a complex decision (outside the scope of this post). I do believe hop testing can provide value in making this decision, BUT only when used as a part of a battery of tests rather than a stand alone test AND performing the tests in more than simply the sagittal plane. Let's read on...
I bring up hop testing's use in both the rehab and performance world, because the point I'm hoping to make with this post applies to both of these environments...
Why is hop testing only performed in the sagittal plane?
If you look at the battery of hop testing most commonly used, all the tests are only performed in the forward direction. This is a problem, because unless you're a sprinter, sport (and life!) is a multi-planar activity! (The only studies published in a physical therapy journal examining lateral (technically 'medial') hop testing were this one and this one. The Vail Sport Test does incorporate a lateral component as well.)
What got me started on this thought process was reading this study that examined the relationship between change of direction speed in the frontal plane, power, reactive strength, and strength. The authors found "change of direction speed has a greater relationship with power in the frontal plane than with power in the sagittal plane...based on these results, multi-direction athletes should train power in all directions rather than relaying on vertical or sagittal plane power programs."
This study is in agreement with the one above, stating that "training protocols reporting improvements in COD performance have utilized exercises that more closely mimic the demands of a COD, which include horizontal jump training (unilateral and bilateral), lateral jump training (unilateral and bilateral), loaded vertical jump training, sport-specific COD training and general COD training."
Principle of specificity at it's finest. Makes sense.
ANYWAYS, this post is already longer and with more links to research than I initially planned, but my goal is to get folks thinking about single leg testing in more than just the sagittal plane. Not only for performance, but for return to sport decisions as well. I tested myself (n=1) in the single leg hop for distance and triple hop (both forward and medial direction) as you will see in the videos below.
In regards to arm use (I didn't use my arms during testing), I think upper extremities should be allowed if you're assessing athletic performance (uninjured individual) while putting the hands on the hips during return to sport/activity testing (better isolates the lower limbs?).
The highest difference I found was in the single leg medial triple hop (95% LSI. I'd be curious to see a study examining the limb symmetry index for both the forward and medial directions...
I will continue to dig for more research examining tests in the frontal plane, and would love to hear your thoughts in the meantime.
As always, my thoughts are continually evolving...
Single leg hop for distance (sagittal plane)
Single leg hop for distance (frontal plane)
Single leg triple hop (sagittal plane)
Single leg triple hop (frontal plane)