Later this month, I’ll be speaking at the Women’s Tennis Coaching Association Conference in NYC. The presentation will focus on 'Change-of-Direction Ability in Tennis' - leading up to the event, I'll be posting an article related to COD in tennis. There are still some admission spots open, so If you’d like to attend the event, visit the WTCA site or the conference Facebook page. Hope to see you in NYC!  

Last week we introduced reactive strength and its underpinning qualities. If you haven’t read that post, I strongly encourage you to do so, as it’ll provide a scientific rationale for what’s to come in this article.

Recall that reactive strength is effectively the fast component of the stretch-shortening cycle (SSC) - SSC activity being a rapid change from an eccentric to a concentric contraction that produces more power than would be possible with a concentric only contraction. We also determined that reactive strength is quite important as it relates to change of direction (COD) in tennis. There are 2 reasons for this. First, it’ll improve a player’s split-step ability - effectively allowing for a faster first step initiation - AND it can help with movements - along with recoveries - that are short but require high levels of explosiveness (think of shots that are near you but are coming at you with speed).

Lastly, we mentioned that reactive strength was highly influenced by leg and ankle stiffness. Specifically, the muscles and tendons in the lower-extremity of the leg - essentially, this area act like springs. This spring-like action further heightens the ability to produce force in super short time frames - recall that we’re looking at ground contact times that are less than 250 msecs.

So in this post, we’ll explore some of the research - in particular, training interventions - that show increases in COD through targeted ‘stiffness’ drills. Once that’s established, we’ll present simple progressions that, depending on a player’s unique circumstances, can act as a brief guide to develop this quality while at the same time, mitigating injury.

Training Research on Stiffness

Let’s start from the start. In 2002, Young and his colleagues set out to explore some of the contradictory results on COD ability. What these authors found was that it wasn’t concentric leg power that influenced change-of-direction ability (as this showed virtually no correlation), but it was reactive strength, rather, that had the strongest and most positive correlation to COD. These researchers measured reactive strength via a variety of drop jump tests - both bilaterally and unilaterally (similar to what was presented last week). What was even more interesting was the difference between reactive strength measures of the dominant and non-dominant leg. A topic that requires clarity.

Unilateral Reactive Strength

Muscle imbalances are prevalent in sport, especially in tennis. When it comes to movement, players favor one leg over the other. This is normal. But this could have large implications when moving on the tennis court. In his experiment, Young et al (2002) found that the lateral push off of the outside leg was of greatest importance when changing direction. In fact, it was the dominant leg which was the ONLY side that had a positive correlation between reactive strength and COD. In other words, the non-dominant leg had insufficient reactive strength qualities and it showed - with substantially worse COD results compared to the dominant side.

This is an important finding. Although players hit more forehands than they do backhands, there are still a number of cases where COD ability is necessary when pushing off the non-dominant leg. Let me provide some examples. When landing from a serve, most players land on their non-dominant leg. And I’d argue that recovering after a serve is one of the most critical movement patters an elite player must possess - it’s the beginning of the point, you have the advantage and you better get into a good position to hit your next shot. Here’s another example - an open stance backhand. This type of shot is becoming more prevalent at the higher echelons of our sport. Whether that’s retrieving a wide ball to that side or simply hitting in an open stance because of time constraints, the recovery step after an open stance backhand requires an explosive push-off with the non-dominant leg. And as Young and colleagues found, perhaps it’s this unilateral reactive strength which requires attention - on BOTH dominant and non-dominant sides.

Bilateral Reactive Strength

While recovery in tennis is of paramount importance, it may be the split-step that separates good movers from great ones. Torres-Luque et al (2011) defines the split-step as a “vertical jump or hop commonly used as a preparatory motion for a lateral step when receiving the ball”. I’d argue that it’s not only preparing a player to move laterally, but ALSO in a multitude of directions (forwards, backwards, laterally, at a 62 deg angle etc). Further to that, Smekal et al (2001) found that elite tennis players “used different ankle joint strategies and were able to start the movement faster” than beginners. Remember, it’s the ankle joint that helps transmit force throughout the remainder of the body when performing a reactive type movement. While a player will push off more with one-leg versus the other after landing from the split-step, there's still more bilateral activity with this specific movement pattern than when recovering. One reason using both legs simultaneously in training, still has it's place. 

Uzu et al (2009) examined the split-step in more detail. When comparing a split-step condition to a non split-step condition, this research group observed a significant difference between step time - this was measured as the time from touching the ground after the split to planting the next step. The split condition outperformed the non split condition by 130 msecs. While total reach/response time - the moment one player impacts the ball to the moment his/her opponent makes contact with the ball - is 500-1000 msces (on average). And split-step response time - opponent impact to opposing player split-step - can be as low as 180 msecs to 350 msecs (depends on level of play and tactical position). In any case, I’d say that shaving 130 msecs off your time to respond is rather significant. While decreasing total response time can be done in a variety of ways - improving visual scanning attributes, anticipatory skills and perception skills - step time can only be improved through improvements in stiffness.

How Do We Improve Stiffness? 

Research suggests that there are a variety of ways to improve stiffness - including heavy strength training, Olympic lifting and barbell ballistic training (Brazier et al 2014). While these are worthwhile pursuits (and something we’ll tackle in a later post), we’re going to explore the relationship between plyometric activity and stiffness, as both correlational research and training interventions, seem to confer that this form of work provides the best bang for your buck. For instance, ankle stiffness was 63% higher when performing drop jumps compared to regular hops - the activity patterns extended beyond the triceps surae musculature and were also very high in the Achilles tendon, which has been shown to improve SSC activity (Kubo et al 2007).

Further to that, in a landmark study by Young (1999), after 6 weeks of drop jump training, when the instruction to 'jump as high' as possible AND 'as fast' as possible was compared to simply 'jump as high' as possible, the results differed significantly. The ‘jump high and fast’ group outperformed the ‘jump high’ group in every jumping test that was administered - reactive strength, vertical jump height and run-up jump height. Technique is substantially altered when this type of instruction is given as ground contact times are much lower, joint amplitudes are smaller and eccentric-concentric coupling times are shorter. This leads to long-term neural adaptations that improve the fast SSC component - i.e. the ability to develop force in a very short time frame. The importance of proper cueing when performing this type of training cannot be undervalued - it can make the difference between a reactive split-step (and a great mover), and a split-step that lacks ‘jump’.

Continuous Hops 

There’s another growing body of training knowledge that seems to be pointing to not only improvements in reactive ability but also increases in acute power output. Research calls them ‘repetitive’ or ‘continuous’ hops - some coaches use the term ‘ankling’ - while I’ve been using them for years and call them ‘reactive hops’. The lingo doesn’t matter much. What matters is the importance of these types of hops (video below). Do you remember the term PAP (post-activation potentiation)? Tsonga was performing this type of work in his off-season training. The basic theory is that when performing a neurally demanding movement, any subsequent movement will have a power generating benefit higher than if no movement preceded it.

While I won't discuss the mechanisms in this post, here's some compelling evidence. Maloney et al (2017) found that a combination of ‘reactive’ hops along with drop jumps - prior to performing COD tests - IMPROVED change-of-direction times to a greater extent than performing a traditional warm-up. Furthermore, it was unilateral ‘reactive’ hops and unilateral drop jumps that significantly outperformed their bilateral counterparts. Another study - a 6 week training intervention - found that ‘continuous’ hops increased drop jump height by 12% (Bergmann et al 2013). What does this mean for a tennis player? Two things. First, this type of work is an important starting point when developing stiffness (as we'll soon see). And second, perhaps including ‘reactive’ hops before hitting the court will help augment power output during all COD tasks - including split-steps, recoveries and so on. While the benefits are generally short lived - seconds to minutes - the research is still intriguing. And I’d like to think of that these types of hops are a way to ‘prime’ the nervous system anyway.

Keep in mind that we’re not talking about skipping or performing low-intensity jumps. For this type of work to show benefits, the jumps must be highly reactive - meaning, maximal intent on every jump. But don't start doing these types of jumps before your next match just yet. Make sure you’ve trained this quality and progressed it effectively first. That’s what the next part of this post is all about.

Practical Progressions to Develop Stiffness and Reactive Strength

Before we get ahead of ourselves, I’d like to mention here that reactive strength - and any plyometric activities that target this quality - are highly demanding from a neural perspective. Because of this, proper progressions and programming are of high order. DO NOT, I repeat DO NOT, go out tomorrow and start jumping on and off boxes, over hurdles and so on. Especially, if you’ve never done this kind of training in the past.

Here’s a basic outline of the progressions involved:

Phase 1 - Learn to Land

Focus on proper landing mechanics during sub-maximal bilateral jumps. This includes vertical jumps, horizontal jumps, lateral jumps and anything in between. Once decent mechanics are formed, unilateral landings can be introduced. Some common cues include ‘land quietly’, ‘soft landings’ and ‘freeze’/‘hold’ the landing. At this stage, there shouldn’t be a whole lot of knee or hip flexion when landing but this will depend on the eccentric strength qualities of the athlete (more on this in next week’s post on strength training for improved COD).

Phase 2 - Learn to Develop Force (and continue Landing)

Now it’s time to add maximal jumps into the mix. Start again with double leg jumps and progress to single-leg as you see fit. Maintain good landing mechanics by absorbing forces. The joint amplitudes at this point should increase as the demands are higher. This is ok as long as there aren’t any red flags - these could include dynamic valgus (knees caving inwards), incorrect foot positions on landings, upper-body fragility (i.e. too much bending either forwards or laterall on landings) and poor balance/stability (especially during single-leg landings).

Phase 3 - Prep the Fast SSC

This is where lower intensity ‘reactive hops’ - even skipping - have their place. The emphasis here is on prepping the neuromuscular system for high-intensity reactive work. Common cues include ‘legs like springs’, ‘kangaroo hops’ and ‘stay on the balls of your feet’. There’s no real emphasis yet on jump height but rather on grooving the nervous system and teaching it what it feels like to be reactive. Remember, we’re looking at very short ground contacts and very small joint amplitudes, especially at the knees and hips (first video above).

Phase 4 - Increase Fast SSC Load

Here we add jump height as an objective measure but we DO NOT disregard the reactive components that were established in the previous phase. Jump ‘fast’, ‘high’ and ‘quick off the ground’ is what we’re looking for (video below). The hurdle heights can progress from week to week but not at the expensive of short ground contacts - this is still the key.

Phase 5 - Increase Complexity and Load

This is where drop jumps come into play. Make sure the athlete is able to absorb force when stepping off of a box. If they can’t, regress; otherwise, use drop jumps as an added progression of load. Height and quickness off the ground are still emphasized but now we’re also aiming to feel even stiffer upon contact with the ground (video left below). These can be done in a variety of ways - jumping straight up, onto a box, forwards, laterally over a hurdle etc. You can even turn this into an agility task by calling out a particular side to jump to (video right below) or tossing a ball into a particular direction when the athlete is in the air. As you see in the video example on the right, the athlete makes a couple of mistakes - this should be a goal when designing complex drills, early struggles. If a drill is too easy, it's likely no longer valuable. 

While these are some basic guidelines, there is no ‘one way’ or ‘right way’ to progress. This still depends on the athlete’s needs, the time of the year, day-to-day fatigue levels, along with a host of other variables. Use common sense.

The Importance of Lateral Movements and Final Thoughts

While vertical and horizontal jumps have greater power generating capabilities - and thus should be used extensively, especially early on in the developmental phase - lateral jumps are critical. Remember, the majority of movements in tennis occur in the lateral direction (on average 80%).  Fast/reactive plyometrics need to be the focus when training lateral stiffness. But even this is too simplistic. We must also vary the angles. Do players move 100% laterally with no variation? No. They move in a variety directions - forwards, backwards, into different angles, at different speeds and so on. If we follow the principle of specificity (adaptations are specific to the demands that are imposed), shouldn’t we train all the various possibilities. This would follow a more systems approach to training and something I would highly advocate.

To conclude, I’d like to reiterate that training stiffness should always be done bilaterally before unilaterally - even if the research suggests that unilateral conditions have higher correlations to COD. I’ve seen tremendous results in my own training and that of my athletes (past & present), when performing simple 2-legged reactive drills. But the transfer onto the court isn’t guaranteed. A specific focus on the split-step and recovery - in a reactive manner - is necessary for this quality to transfer onto the tennis court. Which is ultimately what we’re seeking.

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