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03
06
2019

Workload, Range of Motion, and Early Season Injuries

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Spring training is usually a happy time of year. Everyone gets to look forward to baseball being played after a long winter. Unfortunately for the players, early season also corresponds with the highest chance of injury.

Source: Epidemiology of Major League Baseball Injuries

The above study shows a spike in total injuries at the beginning of the year. While another looked at UCL injuries from 2007-2014 found a significantly larger number of tears occurred in the first 3 months of the season. (DeFroda et al., 2016)

This may be a surprise to some considering overuse is a commonly cited reason for injuries in pitchers, but this data shows that professionals see more injuries earlier in the year.

Today, we look specifically at range-of-motion research and workload-related research to see if we can get a better sense of direction for why so many injuries may be occurring in the early part of the year. The research will be able to tell us “what” they found, while we try to piece together a hypothesis for “why.”

Ideally, this should give us a better idea of how some issues may be connected. with the hope of reducing overall injury rates in pitchers.

For the sake of this discussion, we assume that these pitchers were healthy before being injured in the spring. We already know that one of the biggest predictors of injury is previous injury. Plus, it’s theoretically possible for players to have small injuries crop up at the end of the year, resulting in their trying to manage it in the off-season and then have it get worse in spring training, thus qualifying as a spring injury when it may have been a longer-term problem involving a relatively smaller previous injury that lead to a bigger injury.

But today, we focus on the question, What could be the cause of otherwise healthy pitchers being hurt in the beginning of the year?

To answer that, we first dive into an explanation of the basics of workload, followed by range-of-motion research, to set a baseline of information before trying to see how they may tie together.

A Quick Description of Workload Research

In research, workload is generally split into an athlete’s acute or chronic workload. Acute workload is the “workload” that occurs over a week’s time, while chronic workload is the rolling measure of “workload” over 28 days.

You can then take the acute workload (intended to measure fatigue) and divide it by the chronic workload (intended to measure fitness) and get your acute-chronic workload.

While there is not a large amount of baseball-related workload research, there is a good amount of research in cricket and other sports, which we can take some themes from. Broadly speaking, there are some recommended ranges that athletes are suggested to stay within (0.8-1.3 is often broadly recommended, though it’s shown to differ between sports), and while more research can and should be done for baseball-specific workload, this research gives us a solid starting point.

The big idea of workload measurements is that there is a sweet spot that athletes can be in, a balance between acute and chronic workloads, that can reduce their risk of injury.

In the case of a pitcher, this means he could be both undertrained or overtrained and be at a higher risk of injury. He could have a low chronic workload and see a big spike too soon, or he could have a relatively high chronic load but have frequent big spikes in workload, meaning both undertraining and overtraining can cause injury, similar to what’s seen in cricket (Hulin et al., 2014).

When we’re talking about early-season workload issues, the main issue is having a low chronic workload (from taking time off) and then seeing a sharp increase in workload, which highlights the importance of what we call on-ramping.

Note: Throwing workload is also something that the Motus sleeve monitors, if you use their sleeve. They also factor in the intensity of the throw, which undoubtedly matters as a throw at 99% of a pitcher’s peak torque should be accounted for differently than a throw at 55% of a pitcher’s peak torque.

Early Season Throwing: On-Ramping

While baseball has generally done a good job of being more aware of overuse injuries and taking time off, there is one area in particular that it isn’t very good at: getting back into throwing. This is going to be especially relevant to the time of year that we are talking about: spring training.

Not only are professional athletes starting to compete, colleges are also starting to play games, and high school teams are either starting to practice or play games depending on where they are in the US.

At Driveline, we qualify the time that athletes go from either no throwing or low-medium intent to high-intent throwing as on-ramping. It’s the period of time where they are throwing, but they are throwing to build workload capacity and prepare for high-intent throwing. High-intent throwing includes bullpens, pull downs, plyo velos—anything that is at max intent.

This period of time, on-ramping, needs to be more specifically discussed in baseball because of its relevance to throwing workload.

We want to steadily increase an athlete’s chronic workload without seeing drastic spikes. What happens too often is athletes come back from a period of time off and then see a spike in workload (generally bullpens) that is too high.

Even in spring training, pitchers report and almost immediately have to throw multiple bullpens, which quickly turns into simulated games and then spring-training games. While the overall volume may try to stay low, the intensity can still spike.

Somewhat complicating the relationship between workload and injury, besides intensity playing a role alongside volume, is that there can be delayed effects.

Some cricket research has seen that an increase of acute workload over chronic workload can result in a high chance of injury a week after (Hulin et al., 2014). Other cricket research has seen delays of 3-4 weeks (citation).

In tying this together, there seems there may be a link between mismanaging acute/chronic workloads and early season injuries, but the possible correlation might not be immediately apparent due to the possibility of delayed effects.

A Quick Look at Range of Motion

Throwing athletes tend to have less internal rotation but more external rotation in their dominant (throwing) arms when compared to their non-dominant arms.

This is likely an adaptation to throwing, but it has been shown that there can be some small differences in ROM between arms that can end up making a big difference for chance of injury.

Total Range of motion is generally similar between arms. Picture Source

Though, when we look at ROM measurements, such as the ones provided above, it is important to consider that ROM is a fluid measure that constantly changes over time for each individual athlete. For example, there are differences between measurements before and after a pitcher has pitched: either losing internal rotation, gaining external rotation, or both (Kibler, Sciascia & Moore, 2012; Freehill et al., 2014; Case et al., 2015).

Furthermore, it has been shown that there can be ROM effects that are seen after pitching in the following days (Kibler, Sciascia & Moore, 2012). This means that a pitcher can gain external rotation and lose internal rotation immediately after a start, and the lack of internal rotation can still be seen days later.

This goes to show that there seems to be an adaptation of the body where the throwing arm has less internal and more external rotation, but there are still fluctuations in range of motion that can occur based on throwing volume and intensity.

Early Season Range-of-Motion Research

Now, we are going to look at three studies in particular that both measured a number of pitcher’s ROM measurements before the season and analyzed various deficits that were seen to be related to future injuries. Now, all three studies didn’t find the exact same results, but they did all conclude that lacking range of motion before the season may be an issue.

Below are the studies and their key points:

Decreased Shoulder External Rotation and Flexion and Greater Predictors of Injury than Internal Rotation Deficits: Analysis of 132 Pitcher-Seasons in Professional Baseball

“For continuous variables, the risk of elbow injury increased by 7% for each degree of increased shoulder ER deficit and 9% for each degree of decreased shoulder flexion.”

Deficits in Glenohumeral Passive Range of Motion Increase Risk of Elbow Injury in Professional Baseball Pitchers: A Prospective Study

Neither glenohumeral internal-rotation deficit nor external-rotation insufficiency was correlated with elbow injuries. Pitchers with deficits of >5 degrees in total rotation in their throwing shoulders had a 2.6 times greater risk for injury. Pitchers with deficits of >5 (or equal to) in flexion of the throwing shoulder had a 2.8 times greater risk for injury.

Deficits in Glenohumeral Passive Range of Motion Increase Risk of Shoulder Injury in Professional Baseball Pitchers: A Prospective Study

Pitchers with insufficient external rotation (<5 greater external rotation in the throwing shoulder) were 2.2 times more likely to be placed on the disabled list for a shoulder injury and were 4.0 times more likely to require shoulder surgery.

Note: The last two studies both lasted for 8 seasons, but researchers combined the measurements of pitchers who have multiple seasons because they didn’t find a statistical difference in between year measurements. The first study also lasted multiple seasons, but if a pitcher had multiple measurements, they counted them as separate individual seasons. Those researchers cited prior evidence showing that ROM can change between seasons. (Shanley et al., 2012)

So, we see either lacking flexion, lacking external rotation, or having less total range of motion as possible red flags.

Now, these studies only link ROM deficiencies with injury risk and do not explain why these deficiencies occurred in the first place. However, one can reasonably hypothesize that these ROM deficiencies found in higher level throwers early in the season could be related to throwing volume, or a pitcher’s early-season workload.

As mentioned above, there have been studies that have shown an increase in external rotation and decrease in internal rotation when comparing before and after measurements of pitching. This makes sense given how pitching is a very dynamic action, especially when you’re asked to throw at high velocities for long periods of time (100 or so pitches) or frequently as a reliever.

So, if some players are taking time off and limiting their workloads during the off-season, they may not have thrown enough to get their dominant arm back to a “normal” level of range of motion by the start of spring training (whatever normal level that may be.) This movement deficiency coupled with throwing too much, and at too high of an intensity too soon, may be part of the reason why we see injuries early in the year.

We don’t know exactly how this would affect throwing mechanics (if at all), but what we could be seeing is an increase in dynamic external rotation without enough passive range of motion, which may be putting an athlete’s arm at risk.

We are essentially making a few assumptions:

  • Players will have some change in range of motion by taking time off from throwing. Because throwing is overhead and dynamic, this likely means a possible loss of flexion, external rotation, or an overall decrease in total range of motion.
  • If you go from no throw to high intent too soon, a pitcher might have arm issues because the passive rotation hasn’t “caught up” to the dynamic rotation.
  • These differences in range of motion may be a reason why acute spikes in workload are dangerous for overhead throwers.

We also need to mention that there is a difference between passive and dynamically measured range of motion. We have been discussing passive range of motion, generally measured by some sort of practitioner on a table, whereas dynamic range of motion is what would be measured in a biomechanics report.

There are differences between the two, but in one analysis that aimed to compare how closely each lined up with one another, a moderate correlation of 0.46 was found between the two measurements (Miyashita et al., 2008). The main takeaway is that there is some overlap between passive and dynamic external rotation, but it’s likely that more research is needed to fully understand the relationship between the two measurements.

It may be reasonable to hypothesize that a piece of the early-injury spike may be caused by more significant differences between passive and dynamic range of motion, specifically looking at external rotation when a pitcher starts throwing. But again, more research is needed before we can confirm this.

In theory, increasing the intensity of throwing too soon could stretch passive structures beyond what the pitchers are comfortable adjusting to. This may be especially relevant for pitchers who are lacking passive external rotation, because they may be experiencing a greater than normal difference between their passive and dynamic measurements, Which hypothesizes that range of motion plays a role in early season workload injuries specifically for pitchers.

Trying to Piece Things Together

So here’s what an answer to the previously asked question, What could be the cause of otherwise healthy pitchers being hurt in the beginning of the year?”, may be:

  • A pitcher reports to spring training, having lost some range of motion in his throwing arm, enough to cause his dominant arm to measure a less passive range of motion than his non-dominant arm. This is caused by a lack of throwing workload and mobility during the off-season.
  • He gets to spring training and starts throwing bullpens 2-3 times a week in preparation for the season.
  • Because of the decrease in passive range of motion and increase in throwing, he experiences a bigger than “normal” (defining “normal” as what he would experience in-season) differences between his passive and dynamic external rotation.
  • Because of a decrease of off-season work and sharp increase in bullpens, the pitcher also experiences a sharper than expected increase in workload.
  • The effects of differences in larger passive and dynamic external rotation are unknown, but we have seen delayed effects of increases in workload, meaning the pitcher may be at risk of an injury due in part to a lack of external rotation or flexion and what may be more appropriately termed a workload error.
  • All of this leads to a pitcher being at a higher risk of injury because of a poor combination of multiple variables that have been seen to put pitchers at risk.

Limitations in Finding the Root Causes of Injuries

If this sounds too simple and too perfect to be true, it probably is. There are, of course, other reasons why a pitcher could see changes in ROM that are not caused by a lack of throwing.

For example, we’ve seen that an athlete’s non-dominant arm can see changes as well, complicating how reliable comparisons between arms are.

We also cannot rule out anatomical issues, as a pitcher could be generally more “stiff” or have more muscular tightness that restricts range of motion. 

Furthermore, injuries are multifaceted problems, and we’re only looking at a few variables: range-of-motion measures and throwing workloads. We may also be making assumptions on the relationship between passive and dynamic range of motion beyond what we have evidence for.

Lastly, the injuries mentioned during the ROM studies didn’t report the time of year when the injuries occured. However, in this article we’re making the case that ROM discrepancies in pitchers increase the risk of experiencing an early season injury based on the evidence provided in the very first study that we looked at above.

To truly see if there is a relationship between the two, we need to see some research that’s able to consistently monitor throwing workload and measure range of motion. This is a relatively tough task because it would require a longer period of time and consistent tracking.

Suppressing Early Season Injury Rate in the Future

First, there should be a closer look at the workload of pitchers who are coming off of a no-throw or little-throwing period. Second, regarding range-of-motion research, findings that see a relationship between injury and range of motion should include time of year to get a more specific view of how strong the relationship is.

So are workload injuries definitely related to range-of-motion deficits? Maybe, but there isn’t much workload research on pitchers, much less workload research paired with range of motion, but baseball is also different from other sports. The specific demands of throwing are unique compared to running or cricket, where a bowler needs to keep a straight arm.

One thing we do know is that pitchers and coaches need to spend more time focusing on how they go from not throwing to being able to start pitching again in a game.

This article was written by Technical Project Manager Michael O’Connell

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