This is the final part of a series of posts on change-of-direction (COD) in tennis…for now anyway. While we’ve touched on a number of key aspects of COD, researchers are only beginning to uncover the complexities of this athletic quality. This week’s post will briefly highlight why many in the tennis world believe that strength training doesn’t have a place when it comes to improving COD ability - and how the landscape has changed; and why straight line sprinting, although initially proposed as a key factor in COD ability, doesn’t really correlate after all. We’ll finish up with some practical examples of how purposeful strength training means can improve each phase of COD - the deceleration, planting and propulsive phases.

How Has Change-of-Direction's Landscape Changed?

Not long ago, a review article by Brughelli et al (2008) essentially stated that strength qualities were in no way correlated to COD. Brughelli’s review contained 2 primary problems, however. First, many of the articles that were under review to assess COD, incorporated tests that emphasized a substantial amount of straight line sprinting. In fact, many COD tests still do! When this is the case, we’re no longer looking at the specific moments of COD which are so vitally important - like the last few steps of the deceleration phase, the planting and the initial push-off (or propulsion) after planting.

Although still in it’s infancy, we now have a greater understanding of the mechanisms at play during COD tasks. Sophisticated technologies have helped in this matter. Sport scientists (like Nimphius and her colleagues), are now able to look at the forces acting at various joint angles during a variety of COD tasks. They can then correlate these various COD positions with different phases of a squat exercise pattern, for example. The linear component of COD is essentially completely out of the picture. And because of this, what these recent studies have seen is that, when we look at the instantaneous moments of COD, different strength abilities do in fact play a substantial role in COD tasks. These phases we're reviewed in previous articles.

What About Straight Line Sprinting?

Straight sprinting speed isn’t just limiting when looking at correlations between COD and strength. Remember the COD model proposed by Young and Sheppard (image below)? Straight sprinting speed was theorized to be a subcomponent of COD . But is it true? I mean why would running in a straight line have any benefit to changing the direction of movement? This question is of even more interest when looking at it through the lens of tennis match. About 80% of movements in tennis are 3m or less….and 72% of all movements are in the lateral direction. The dimensions of a tennis court don’t even allow a player to reach maximum running velocities - it takes an elite athlete about 30-40m to reach max running speed and from the net to the back of the tennis court, there’s about 20m of running space, if that!

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That being said, some correlational studies (Gabbett et al 2014) have revealed that athletes who run faster in a straight line ALSO perform better on COD tasks. But researchers started asking themselves…do these athletes have good results in COD tests because their COD ability is good? Or are they doing well because they're simply fast when running in a straight line? Remember, many of the tests that assess COD have a large straight line component. So to answer these questions, researchers from Australia developed the COD Deficit Test (Nimphius et al 2015). Essentially, what this test does it take out the linear component of a 505 test and compares it to the 505 test itself. What they found was what we were all thinking; running in a straight line is a completely different quality than changing direction. In other words, there’s no significant correlation between the two abilities. In fact, improving straight line speed in tennis players may be detrimental if we don't also improve their ability to decelerate. 

The 3 Phases of Change-of-Direction - Practical Application

We’ve spoken in great length about reactiveness. But when is reactiveness important versus strength/power qualities? The following image provides an indication. 

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Recall that when entry velocity - the speed at which we enter a COD - is high, this will affect a number of variables. These variables are presented above. From a practical perspective, let’s look at it this way. If we have to run down a wide ball, we’re running faster than if the ball is nearby. This means that forces acting on us will be much higher, so to compensate, we must possess declarative abilities to counteract momentum (which is pushing us into the direction we're running). This requires a tremendous amount of strength. Furthermore, to recover from this type of shot, we must overcome a high amount of inertia. It's like we're a freight train churning at 100mph and then all of a sudden, we stop and want to move in the opposite direction with the same speed. This requires a heck of a lot of isometric and concentric strength - both to transition well and push off our outside foot with aggression.

Furthermore, there are instances where shots require players to get into pretty low positions (a low volley, a lunge, even a deep squat position can be seen). If we lack strength in these ranges, our ability to transition out of them, will be severely limited. To combat these instances, we need to develop the appropriate types of strengths. Below we will provide a number of exercise examples that can be implemented. Take caution as some of these movements are more advanced than others. Players should all be able to do a variety of bodyweight exercises first, before they can advance to more complex movements. To makes things more sensible, we’ll outline each COD phase and link an exercise or 2 with it.


Exercises That Train All 3 COD Phases Simultaneously

Lunge and/or Squat

Simply performing a regular loaded squat or lunge pattern can be an effective way to load all 3 phases of a COD. Recall that a study on female basketball players revealed a very strong correlation between a half back squat 1RM and COD ability. The key here is to make sure the loads are appropriate - at least 85% of an athlete’s 1RM. Furthermore, during a squat or lunge pattern, when the angles at the hip and knee are specific to what a player will encounter during a match, the performance benefits will be heightened. This again, goes back to the principle of specificity.


Tempo Squat or Lunge

Varying tempos is a great way to find so called ‘sticking points’ and problem angles. Using loads that are quite heavy >85% 1RM, and instructing the player to perform the movement in a very controlled manner - in this example, it was a 5-5-5 count (meaning, 5 seconds down, 5 seconds hold and 5 seconds rise) - is the way to go. You’ll soon notice where a player has issues - these areas can be targeted even further by extending the time in a particular phase. While the squat pattern is a tried and tested exercise, and allows for greater loads to be handled, it is by no means the only variation. Single leg variations, deadlifts, lunges and so on, can also be used in similar manners.


Deceleration Phase - Advanced

Power Snatch - Split Squat

While this exercise can help to create a high amount of rate of force development - something quite valuable for the tennis player - it places a tremendous emphasis on braking mechanics. To catch the bar in an overhead position, we must not only coordinate appropriate limb separation, but we must do so in a very rapid manner. Think about the times when a player only needs to take a few steps to meet the ball- to set-up effectively they must rapidly decelerate their lower extremity. We must have both the ability to absorb force and the ability to do so quickly. Oh and there’s also this highly isometric demand through the trunk and upper limb, important in maintaining good postures and whole-body integrity during the transition phases of all COD tasks.


Eccentric Only Squat

This is a very advanced exercise and one I DO NOT recommend to beginner or even intermediate athletes. If you are experienced, already possess a high amount of strength, and you or your coach see value in this lift, it may warrant implementation. As far as a tennis player is concerned, this is an exercise that targets strictly the deceleration component of COD. Recall that there are times when the forces are several times a player’s body weight. With this exercise, add an additional 10% or so of load to the barbell relative to an athlete's 1RM. If they cannot perform the movement in a slow, controlled manner (around 5-6 seconds downward tempo), the load is too heavy. Furthermore, these types of eccentric only lifts can elicit severe muscle damage (more so than other contraction types) and should be implemented sparingly (once a week maximum and perhaps even more spread out than that).


Propulsion Phase

Concentric Only Squat or Lunge

The concentric only squat is extremely valuable from a tennis player’s perspective. It takes out the elastic component of the movement and forces an athlete to use concentric/propulsive strength only. You may wonder why this is important? There are times on a tennis court when we don’t use the elastic component of the SSC. Here’s one example - say you’re on defense and you don’t have time to make a split-step or a drop-step, essentially you’re already in a squat position and the only way to produce movement is through a concentric push of the lower-body. Again, loads must be heavy (>85% of 1RM) and the intent to move the bar must be very high.


Planting Phase - Advanced

Overhead Lunge and/or Squat

COD in tennis differs from other sports. When recovering, a player is almost always doing so after a highly powerful, rotationally demanding task - whether that’s the serve/overhead motion or a groundstroke. We must also be strong through our trunk and upper limb! I mean, there are times when players have to stretch out their arm to hit a shot and then quickly recover afterwards. The follow through of the serve action places a tremendous amount of force through the upper limb and trunk upon landing. Performing overhead squat/lunge variations is can be an effective way to load the upper-body while still working each COD phase. Here are a couple examples.  


Isometric Split Squat

In extreme cases, isometric only positions may also warrant implementation. These are not advocated too frequently for heavy strength adaptations as they are too isolatory in nature. However, problem cases do arise and this is where we can challenge specific angles. For instance, if a player has trouble developing force in a very deep lunge position, we can ask them to contract forcefully (and to try to develop this force rapidly) in that range for about 5-6 seconds. The benefits of isometrics is that they recruit all available motor units, they don’t produce any shearing forces - because no movement occurs during the contraction - and perhaps most importantly, they improve straight in a particular range +/- 15°. What that means is, when we do an isometric hold at 90°, we’ll also get strength adaptations anywhere from 75° and 105° (more or less).


Final Thoughts on COD in Tennis

Remember the theoretical model of COD from above? Technique is a big factor, especially in tennis! The various technical footwork elements are of course dependant on the tactical scenario at hand BUT, along with increases in the physical capacity to perform COD tasks effectively, we also must improve the specific technical footwork patterns associated with elite tennis play. Does your player know how to perform a left-left movement when attacking a short ball? Are they capable of performing a right-right hop when tracking down a wide forehand, instead of running through the shot? While I believe the technical elements of tennis movement are of extreme importance - successful movement execution is a combination of both technical and physical factors. If a player has very high ‘technical proficiency’ when moving on the tennis court, but seems to look ‘slow’ - for lack of a better word - we must target their capacity. It’s this intricate combination of physical capacity and technical proficiency that results in world-class movement abilities.

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