How to use the seated calf isometric test to assess calf function and injury risk

Calf injuries among athletes are on the rise. So what do we need to do to better understand what is going on and try and reduce injury risk? We spoke to Physiotherapist at Munster Rugby, David Breen who has been working as part of a group within Irish Rugby to refine a protocol to assess calf function and fatigue through an isometric test. We spoke to David and asked him six questions to learn more about it.

Speaking to a number of podcast guests, there seems to be an increase in the amount of calf injuries in rugby and football. Why do you think this is?

Over the past 10 years, there has been a move to reduce overall running load in training in an effort to reduce hamstring injuries, with a focus on controlled exposure to very high speed running (Z5) and total sprint distance (Z6). This makes sense if your focus is on robustness of the more proximal hip muscles: hamstrings, quads and hip flexors. Additionally, most of the muscle injury research has focused on the hamstrings, so this is most likely to influence practice.

However, the calf is working hard across all speeds, especially during high speed running (Z4), which are cruising speeds of 5.5 – 7 m/s ^[2]. Reduce your exposure to these speeds and perhaps you’re reducing your calves’ overall power endurance capacity.

There also isn’t the same culture around programming localised strength training for the calves as there is for the hamstrings or quads.

Perhaps some coaches feel that the calves get all the loading they need from running. But without targeted strength training, the muscle will never be as robust as it can be. Combine this with the ever increasing game demands of both football and rugby, and it may explain the rise in these injuries.

What is the purpose of the seated calf isometric test, what is it telling you and how often do you perform it with your athletes?

It has a number of functions, from monitoring local calf muscle fatigue or recovery to tracking soleus strength or RFD changes over time. It all depends on how and when you use it.

On a squad basis, we use the gym session on the first training day of the week to monitor calf strength (peak force) across the season. We test approximately 10 players during the session and cycle through a different 10 players each week. We look to combine this with a measure of reactive strength for the foot / ankle, e.g., a repeated hop test. This allows us to build a more rounded profile of calf performance on both a squad and individual level over the course of the season.

Any deviation from a player’s norm is a flag for a one-to-one conversation, and possibly an intervention or training modification depending on what we’re dealing with.

What is the setup of the test and are there any tips that could help practitioners get the best quality data?

The two main options are securing a ratchet strap over the thigh to keep the leg fixed in position, or wedging the thigh under a fixed bar and pushing into it ^[4,5]. We use the ratchet strap approach.

Approximate angles are 90° hip flexion, 100° knee flexion and 10° ankle dorsiflexion. Although, if you ask the athlete to get into the position in which they feel strongest, they will probably find the same position ^[3].

Here are the three best tips to ensure quality testing:

1. Comfort. Whether you use the strap or bar approach, it needs to be comfortable. Unless you’re using an extremely wide strap, padding is a must. However, use too thick a padding and it will affect your RFD output, if that is something you are measuring ^[1]. Use the minimum thickness padding to achieve comfort.

Check in with the athlete to ensure they are giving their true max effort, not just their max before it gets too sore.

2. Positioning. Put more tension in the strap than you think. We go 90% of the way and allow the athlete to do their warm-up reps. Then add another 10% for their testing reps to ensure there is no movement through the ankle, thereby allowing them get their best score.

We find that the athletes who cramp at the hip flexor are mostly weak in this test or are seated too low (<90° hip flexion). We adjust the seat height and trunk position to help reduce that cramping.

3. Feedback. These are competitive beasts. If you tell them what score they hit last time and whether they’ve hit that score again this time, they will be sure to give you their “true” best effort.

Is this test a part of a bigger picture when it comes to understanding calf injuries at Munster and within the IRFU? If so, what does that bigger picture involve?

I think to understand muscle injury in any sport we need to quantify performance. Strength underpins functional performance of the calf. The soleus is the most frequently injured and reinjured muscle in the calf. It is a powerhouse of a muscle in terms of lower limb function in athletes, so this test offers a quick and easy way to measure its isometric strength.

For testing of this nature, one-off screening has limited value. At a very basic level it tells you who is weak in this position compared to squad and positional averages. However, greater value comes from serial testing / monitoring throughout the season to obtain multiple data points for each athlete. This allows you to establish a bandwidth of normal variability.

Once an athlete scores below this bandwidth, you may have evidence of local muscle fatigue similar to what we see in hamstring research ^[6]. Combine this with a measure of reactive strength for the foot and ankle, such as a hopping test, and you have a good indication of calf and Achilles performance.

The ideal would be to put the same calf testing device in each of the Irish Rugby Football Union provincial and national teams to establish normative data across the union, while also collecting prospective data for injury. We have seen a number of players with a history of injury in the ankle or knee show significant asymmetries on this test, either in maximal strength or relative RFD. This informs our strength and plyometric programming for these players and puts them on the watch list.

Do you have any normative data for this test that coaches can benchmark against?

Our peak force squad average currently sits at approximately 1.8 x BW for this test, approximately 190 kg. There is some positional variation. Our lighter backs will be closer to 2 x BW and our heavier forwards (particularly front five) will be closer to 1.6 x BW.

Seth O’Neill and colleagues have research coming out in this area in both Premiership football and rugby players, with averages around 2 x BW. Adam Mattiussi from the Royal Ballet of London is currently publishing his PhD. work profiling their dancers, and has average scores of 2.3 x BW in this test.

There is value in assessing calf strength while standing because being strong in a dorsiflexed position doesn’t necessarily mean you’ll be strong in neutral or plantargrade. When we isometrically tested our squad in standing, our averages were approximately 3 x BW. This is a test we tend to do more frequently on an individual basis in a rehab setting, just due to logistics.

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

The most common mistake I see is practitioners trying to assess seated calf strength without a proper testing device. This usually results in them trying to wedge the athlete’s knee under a barbell and getting all kinds of inconsistencies in effort, comfort and testing angles each time they test.

Whatever you use, the testing setup has to be consistent and reliable.

Another common mistake we made with this test was our use of language.

In the early days, any time we used the words “calf testing,” players tended to avoid doing the test thinking they were going to go out and “pull a calf” on the pitch after doing it. We replaced the word “test” with “scores” or “ISOs”, and programmed it into their squad gym sessions.

Soon it became a pretty normal part of their weekly training schedule without the fear associated with”‘calf testing.”