Understanding the shoulder: Assessing injury risk and maximising performance

When it comes to the shoulder, what methods do we have to assess injury risk and performance?

Evaluating an individual’s injury risk is a developing area. Some of the best published work in shoulder injury risk assessment methods is from handball. Large cohort studies seem to show that a lack of force production capability is the main risk factor, specifically, weakness of the shoulder’s external rotation.

However, given the complex web of factors that relate to shoulder injury risk, I question the importance of assessing individual injury risk markers such as range of motion or even strength in isolation. The best approach attempts to integrate assessments of kinetics, kinematics and tissue health to create a risk profile.

Assessing performance depends on the lens that you are looking through and what we can agree the word “performance” means.

As a strength coach or a physiotherapist working as part of a support team, often we decide that we want an athlete to hit some specific markers that relate to aspects of performance, without questioning their validity. Some of the most interesting rehabilitation case studies that I have been involved in have used actual measures of sports performance to determine success or failure.

For example, I spoke with a performance analyst about a Premier League footballer who is losing more than 70% of aerial duels because he has a shoulder instability and a history of subluxation that limits his confidence. We could use traditional outcome measures to determine whether his performance has improved in terms of physical capacity: how much weight he is moving relative to body weight in upper body strength sessions, how explosive he is via a medicine ball throw, how fast he moves a bar or what his landing forces look like on a force platform. We could also create a “sport specific” defensive header drill against a tackle shield to approximate an aerial duel on the field.

All these markers are appropriate to assessing a player’s ability to go through a return to performance process, and to work out whether there is a specific physical quality driving the player’s inability to perform.

However, ultimately we should be measuring performance within the context of the sport. In this example, on return to sport from bilateral shoulder repairs, the player won 63% of his defensive headers, a measurably impactful performance benefit.

The work to rebuild, prepare and ensure the player is ready to compete should draw on a needs analysis based on the demands and injury risk profile of the specific sport.

The tools we choose to monitor the athlete should assess measures that correspond to the high forces, high risk positions and high repetitions the athlete will encounter during competition. And those tools must be sensitive enough to detect whether the athlete has trainable deficits. Most of the time, the meaningful actions in sport occur in the blink of an eye, and require high force and high rate of force. The assessment tools must be up to that challenge.

In a rugby or NFL player, we might look at a plyometric push up and assess peak landing force asymmetries. If we have access to dynamometers, we can assess whether someone can produce high, balanced forces across the shoulder joint. Along the same lines, there are interesting findings around the relationship between rate of force development in the athletic shoulder (ASH) test and throwing velocity or volleyball spike velocity in Major League Baseball and elite level volleyball players.

We’re still a way off from being able to accurately measure in game shoulder loads using wearables. It’s difficult to place sensors into shoulder pads in collision sports to measure impact forces, and even more challenging to understand shear and distraction forces.

Markerless motion capture systems in throwing athletes can provide insights in terms of kinematics, angular velocities and in-game changes.

In the absence of a better solution, why don’t we just look at a “Shoulder RPE” for the players’ perceptions of the shoulder load they experience in-game? Add in a soreness score as an indicator of their recovery profile on a visual analogue scale so we can start to look at dose response. We can then connect that to, for example, in a rugby context, the number of tackles that player made in the game.

That, in itself, should give us a good guide as to the total demand on that particular player in terms of injury risk.

What influence does the lower limb’s ability to generate force have on injury risk at the shoulder?

The lower limb contributes around 50% of the overall contribution to throwing or punching performance. When an athlete lacks the capability to produce force through their lower limb, they still attempt to throw as fast or punch as hard. They end up overcompensating through the shoulder, resulting in changes in kinematics, shoulder force and range requirements, culminating in shoulder overload.

We can map an athlete’s lower limb ability by measuring an isometric mid-thigh pull, a countermovement jump or an isometric squat, and then match that against upper body ability from the ASH test or external rotation / internal rotation tests of peak force.

If an athlete has high lower body force production but low upper body force production, that, too, can be an issue. A big lower body engine with limited upper body brakes means that the shoulder girdle is unable to cope with the forces being transferred across it.

Force transfer is a critical component of shoulder health and performance. If you lack the ability to produce the optimal amount of force necessary to perform, you are going to have to find it from somewhere else. Over time, that can have an influence on overuse injury, which is what we commonly see in shoulders. Rotator cuff tendon overload and subtle episodes of anterior instability in the shoulder become more significant as they reoccur.

If you think about an athlete in the third set of the final of a tennis competition struggling to change direction because their legs have gone, they are also unable to put themselves or their shoulders in an optimal position to be able to use the shoulder. They end up just swinging at the ball with the arm because they can’t position themselves or generate the force from the ground.

What can ASH test RFD and peak force tell us about an athlete’s risk of injury?

The lower body literature and experience tells us that rate of force development comes back later than peak force after ACL or hamstring injury. The shoulder is the same. We see peak force return earlier than rate of force.

Is an athlete strong or weak (peak force) and explosive or not (RFD)?

We know from ASH tests across a number of sports that athletes who are weak and lack explosive capability are at a higher risk of developing injury (Figure 2).

Before we had anything to quantify rate of force development, peak force assessment was a critical test to pass before return to performance. We are learning a lot more now that we have a tool that can measure RFD.

The ASH test shows us that athletes who pass peak force requirements but fail to produce high enough rates of force development will experience pain or instability when they return to higher intensity, more explosive actions like a rugby tackle, ball release or a tennis serve. We have begun to draw lines in the sand for peak forces and rates of force development in all three ASH test positions (Table 1).

How can we shift an athlete in that quadrant of doom to a healthier quadrant? What exercises would you recommend?

If someone is weak, we want to make them stronger. We need to first of all think about improving force generation capacity. That is simply about exposing that athlete to enough of a stimulus to move the needle on peak force. The exercises we tend to use for that in the context of the ASH test are pretty simple and include bench flyes and long lever isometrics. They could even be something as simple as a well-balanced programme with pushing and pulling in horizontal and vertical planes.

After building a bigger muscle, we progress to exercises that switch it on fast enough. Those include more ballistic actions like cable catches (Video 1), progressing from performing the catch under your own control to a more reactive exercise.

Using the ASH test itself improves an athlete’s capability to produce higher rates of force development over a period of three weeks of daily training exposure (Video 2). We can use exercises that have an intent to move ballistically, as that can improve rate of force development, like with isometrics. That approach might entail more of a neural rather than architectural component of rate of force development capacity.

Once an athlete is within a healthier quadrant, what can they do in season to keep that shoulder healthy?

If it is a baseball pitcher or a volleyball player, their training and competition workload is going to be high, and the shoulder will be taking a hammering. I see too many generic, one size fits all solutions. Where people can get this wrong is not monitoring the adaptations that result from the balance between physical fitness and freshness.

Assuming that there is an impactful, consistent monitoring process in place to identify any changes in balanced peak force (absolute values for isometric rotation, ASH test and ER:IR ratios), frequent doses of load when positioned in the right place can maintain and even improve force and rate of force development.

In someone who has an external rotation deficit, the programme would include longer duration isometric holds (5-10 seconds), accumulating time under tension (1-2 minutes, 2-3 times per day) (Video 3).

A good monitoring system will tell you whether the programme is working or not. You can even use some technologies within a warm up to see whether someone is improving by doing their isometrics, and whether they are able to sustain a consistent level of contraction. This can be positioned in a progressive warm up prior to starting more ballistic actions, like pre-throwing in a baseball context.

If we zoom out from the shoulder, we need to look at all aspects of recovery. During a baseball season, players and coaches need to do all the necessary things to improve recovery in order to manage the high density of competition.

Is a player generally fatigued rather than locally overloaded? Do they need more recovery than additional load doses? Are they moving optimally in terms of their kinematics? Can we change their training in between games to optimally prepare for their next outing?

In season, it’s already too late. Rewinding to when a player arrives from an off season at the start of spring training, we need to know whether they are “tall enough to ride the roller coaster.” By the time you get into the high competition densities of a season, you’re fighting a losing battle. The work needs to happen in the off season, or when a player is rehabilitating from injury, so that when they come back, they are fully ready to tolerate the high demands on the shoulder.

Keeping the shoulder healthy is more complex than just monitoring peak force production.

What are the biggest mistakes you see young practitioners / clinicians making? What advice would you give them to help?

First, be willing to pass the ball. From my own experience, when you are trying to establish yourself as someone who is an important part of the team, there is a tendency to hold onto the ball, to not ask for help.

Don’t be afraid to ask questions, work with others to solve problems and benefit from other viewpoints. I learned that relatively late in my career. By asking for help and working with good people, I feel like I am able to add significantly more value to the people I work with and the athletes and teams I support.

The second point is understanding where you are and where you want to go with your career. I was heavily influenced by the approach Ceri Evans (All Blacks psychologist) shared with us as practitioners at Arsenal, alongside some coaching from experienced colleagues and peers.

Regularly taking some time to reflect, ideally with someone who can help, will keep you on track. Only 10% of people want to move, and only about 10% of those do something about it.

Invest as much in your own behavioural development as you do in improving your technical toolbox. Understand what drives you, the sweet spot between what you’re passionate about, where you can make a difference and what makes you happy. What things do you need to change, whether that be a change of mindset, strategy or technical skill. Being as clear as possible about your direction will help focus the choices you make, like what to say yes to and, perhaps even more importantly, what to say no to.