Why Distance Doesn’t Tell the Full Story During Hop Testing

Over the last year or so, I’ve taken a keen interest in how rehabilitation professionals qualify athletes to resume sports participation following injuries (“return to play”). It’s a natural area of research for me, as it’s essentially the bridge between rehabilitation and performance training.

One of the biggest conundrums in rehabilitation is the high rates of re-injury -- and whether current return to play testing protocols are even helpful for reducing re-injury risk.

One injury with alarmingly high re-injury rates is the ACL, or anterior cruciate ligament. Return to play testing protocols during ACL rehab typically consist of measures of range of motion, single-leg strength, and hops for distance.

Four different hops for distance

Much of the debate centers on which hop tests should go into the testing battery, as there are about a million and one options: single hop, triple hop, triple crossover hop, six-meter timed hop, side hop, etc.

But there’s relatively little talk of a simple way to derive way more information out of whichever hop tests are used.

My friend Tim Rowland and I teamed up to shed light on this subtle addition to testing procedures that we believe can have a major payoff for return to play decision-making:

https://www.physio-network.com/why-distance-doesnt-tell-the-full-story-during-hop-testing/

The Two Most Common Misconceptions about the FMS

Over the past three years as part of my PhD, I’ve been researching the relationship between movement and injury. A recent Twitter discussion reminded me that people on either side of the great FMS social media debate are still confused. I figured I’d put my research efforts to good use to clear up a couple of common misconceptions.

Misconception #1: The FMS composite score can predict injury.

When the FMS first became popular in the late 2000s, its creators touted it as an injury prediction tool [1,2]. The trouble was, at the time they had zero scientific evidence to back that claim up.

It turns out scoring low on the FMS does increase a person’s risk of injury slightly [3,4], but it doesn’t guarantee it. In other words, while low scores are associated with injury, the FMS does not predict injury on an individual basis. Big difference [5].

Specifically, when the FMS is conducted on a large group of people, as in a scientific study, we tend to see a lot of false negatives (people who score high but still get injured).

The fact that the FMS can’t predict injury actually isn’t that surprising. There’s no one thing that predicts injury [6]. This is because injuries aren’t caused by just one factor. Instead, they’re the result of a complicated web of interrelating factors -- a web that’s different for every person based on the types of activities they do [7].

Bittencourt NFN, et al. Br J Sports Med 2016;50:1309–1314.

The (Inconvenient) Truth About the FMS and Injury Rates

The Functional Movement Screen (FMS) is a series of seven bodyweight tests designed to rate human movement quality/competency. Each test on the FMS is scored on a 0-3 scale. A perfect total or "composite score" would be 21 points.

The FMS's relationship with injury has been studied extensively in athletes. The thinking is that scoring low on the FMS (usually 14 points or lower) puts an athlete at increased risk for injury, which the research bears out to an extent.

When all the studies were pooled together (in 2015), scoring 14 or below did increase injury risk by about 50%. However, for every 100 athletes that got injured, the FMS only managed to correctly identify about 25 of them as being at risk. For this reason, the FMS should not be used to predict which athletes will get injured on an individual basis.

Despite the fairly conclusive evidence against the FMS's ability to predict injury, new studies keep coming out investigating this same tired research question. In the past two years alone there have been at least nine such studies on rugby, soccer, cricket, handball, volleyball, and basketball players.

Based on this continued proliferation of research, clearly not everyone has gotten the memo about the FMS's inability to predict injury. For this reason - and in an attempt to help put this issue to rest - my colleagues and I just published a critical review of the FMS. I break down the results of our review below.

Is Some Injury Risk Factor Research Worthless?

I recently read an interesting 2016 paper by Clifton et al. in the Journal of Athletic Training called Predicting Injury: Challenges in Prospective Injury Risk Factor Identification.

The premise of the paper is that some researchers screw up when concluding they've identified risk factors for injury. In the paper, the authors describe two of the most common screwups and how to address them.

Before I get to the screwups, a quick explanation is in order regarding the correct way to identify risk factors for injury, which is through a prospective study. It can be summed up in three steps:

Step 1. Examine a group of uninjured athletes at baseline (i.e. in the pre-season). 

Step 2. Track their injuries prospectively (i.e. over a period of time, usually a competitive season). 

Step 3. At the end of the study, break the sample into two groups -- the athletes who got injured and the athletes who didn’t -- and look for differences between the groups in their baseline measures.

And now for the common screwups, as per Clifton et al.:

Common Screwup #1) Retrospective Study Design

Prospective injury studies are difficult to do because they require careful and consistent follow-up regarding injury. A much easier approach is a “retrospective” one. With this type of study, you simply assess a group of athletes with and without injuries and compare the groups based on these previous injuries. With this design, there’s no need to follow the athletes over time.

The mistake that’s commonly made comes with the interpretation of the retrospective study. Researchers will often state that measures on which the injured athletes performed worse are risk factors for injury. The trouble is, there’s no way to know whether those factors were present prior to the injury OR if they are actually the result of the injury.

This isn’t to say retrospective research is worthless. It’s just that follow-up studies with prospective designs are needed to determine whether the differences seen in retrospect are true risk factors for injury prospectively.

5 Ridiculous Claims About the FMS

Let me start by saying I’m actually a proponent of movement screening. I even recommend the Functional Movement Screen (FMS) for new personal trainers.

But that doesn’t mean the FMS is blameless -- far from it. When it comes to marketing their product, they put the cart before the horse. They sold certifications and made claims about the screen before they had any evidence to back them up. That’s not good science, and for this people have a right to be peeved.

A new Facebook video by Dr. Greg Rose of Functional Movement Systems (watch it here) is yet another great example of why people get so frustrated with the FMS. Let’s break it down point-by-point, shall we?