If you’re a regular visitor to SimpliFaster, then you’ll know that one of the objectives of the site is to help coaches get their athletes faster. While linear speed and acceleration are often the focal point, this post will take a look at another physical quality that’s highly valuable in today’s world of elite sport (especially when it comes to court and field sports): change of direction (COD) speed.
The goal of this piece is to present some of the more updated research on COD ability—in particular, what the underlying physical components of COD are and how coaches can organize different training means to enhance this very vital quality.
Before I continue, I’d like to mention something. While I hold a master’s degree in sport science, my practical experience comes from the tennis court. I’ve competed at almost every level—juniors, college, and the equivalent to what other sports would call the “minor leagues.” Over the past decade, I’ve tried to merge my experiences on the court with my experiences off of it. And while tennis is my bread and butter, I believe that the underlying mechanisms that contribute to elite movement outcomes on the tennis court can aptly transfer to other sports. This includes, but is not limited to, basketball, volleyball, soccer, football, and more.
This article reflects my experience both playing and coaching elite tennis for the better part of two decades. I do my best to offer examples from a variety of sporting disciplines, but don’t hold it against me if some examples are biased towards the tennis court.
Agility and COD – An Intro
There are many terms used in today’s sporting environments to define movement. Examples include: “they are quick/agile,” “those are some fast feet,” “good footwork,” and on and on. Coaches from all sports use these terms liberally and interchangeably. While, on the surface, this may not seem like a big deal, with the cutthroat competitiveness of sport today every inch or second matters. For the casual fan or observer, it may not make a difference, but for coaches working in elite settings, knowing the difference between key terms will weigh heavily on how these coaches organize their training programs.
For instance, what does the term “quickness” mean? There are books on the subject but, to be frank, I’ve studied this field for over a decade and I’m still not sure. In fact, prominent researchers in the field (Sheppard and Young 2006) disregard quickness as a sport science term altogether, claiming that it’s simply “too vague.”
Even the term “speed” is misleading. What are we referring to? Is it linear speed? Limb speed? Maximum speed? Or something else? If it’s top running velocity we’re after, you should know that in many field and court sports, athletes rarely reach top running velocities. The dynamics of the game, along with the court/field dimensions, just don’t allow for it.#Agility is often mistaken for #COD speed. They’re closely related, but not the same, says @CoachKuzdub. Click To Tweet
Then there’s agility. “Agility” is a real term and a very critical one at that. While its importance cannot be overlooked, it’s also a term used loosely in sport environments around the world—often mistaken for the main topic of this post, COD speed. For instance, you may think that a simple spider drill is an agility drill (see Video 1 below). If so, you’re wrong. In order for us to better understand COD speed and how training means can improve this quality, we should first differentiate between these two closely related terms, as one is highly dependent on the other.
Video 1: The Spider Drill is a classic change of direction exercise that exposes athletes to different movement patterns that help prime general efficient mechanics. While popular for tennis, athletes in other sports can also do it.
Agility vs. COD: What’s the Difference?
In a recent paper (Huggins et al., 2017), the authors begin with the following sentence: “Agility or COD is a critical physical attribute….” Notice the emphasis on “or.” Or? Really? You don’t have to look very far to know that these terms are not one and the same. To gain deeper insight, let’s briefly define each term, starting with agility. Sheppard and Young (2006) propose the following:
“A rapid whole-body movement with change of velocity or direction in response to a stimulus. This definition respects the cognitive components of visual scanning and decision making that contribute to agility performance in sport.”
Two factors jump out when reading this definition. First, that changing the direction of a movement, in the context of agility, is predicated on the presence of a stimulus. And second, this stimulus acts as a catalyst for an athlete to make a decision as to how they’ll execute the subsequent movement.
In tennis, this is pretty evident. Every time a player makes a movement towards the oncoming ball, several factors are at play. The player may anticipate the oncoming shot based on the tactical scenario, their opponent’s strengths and weaknesses, and the scoreline. Then, they will use various visual scanning cues to better perceive where the ball will end up. Given this info, the player will make a decision, and then execute the movement. This all happens within milliseconds.
Now let’s compare this scenario with the definition of COD ability: “a rapid whole-body movement with change of velocity or direction that is pre-planned.”
See the difference? The former involves a perceptual decision, while the latter does not.
Let’s look outside of tennis to illustrate this distinction. A basketball player, when defending the ball handler, changes the direction of their movements based on what the offensive player is doing—if they cross over to the left, the defender reacts to this (i.e., the stimulus). This is an agility task.
If we look at this same play from the lens of the offensive player, a different story exists. The player likely has an idea beforehand (which is pre-planned) of what play or move they will execute. This movement has layers to it—the player may know their opponent’s weakness (moving to the left) and could try to exploit that or they themself might be stronger/faster when moving to the right and choose to make a play in that direction. Because this is pre-planned (so to speak), it likely falls under the label of “COD” task.
But is it that easy? What about when the defender looks to their right for just a split second to see where their teammates are positioned? In this case, perhaps the offensive player sees a momentary window of opportunity and reacts to it. Is this movement a COD task or an agility task?
The Agility-COD Continuum in Sport
By now, you may be slightly confused. When delving into these concepts, I often am. But there’s a point to all of this; actually, a couple of points. First, movements are rarely just COD-based or just agility-based. There’s likely a continuum that exists. The way I see it, this continuum relates to the open-closed skill continuum in sport.
Gentile (2000) proposed a 16-stage open/closed skill continuum—called “Gentile’s Taxonomy”—to better classify various motor skills. At one end you’ll find skills that are completely closed, while at the other end you’ll find skills that are completely open. Within the two extremes, you’ll find a wide array of skills that may slightly favor one side of the spectrum over the other. Here’s an example of a batter hitting a baseball. (This is taken from Gentile himself. To see all 16 stages, refer to his 2000 study.)
It’s not the aim of this piece to get into the closed to open skill debate, but rather to highlight that COD and agility also act on a similar continuum.
The second point is, while I acknowledge that a continuum exists, training the underlying factors that make up COD, irrespective of agility, is still relevant. Look at Figure 2 below. Although COD doesn’t contain a perceptual component, agility does contain COD. I like the way Sophia Nimphius (associate professor at Edith Cowan) puts it and I’ll paraphrase her here. In essence, COD can occur twice, under “planned” conditions and under “agility” conditions. You can’t have an agility task without the physical, COD side of things.
All this leads us to the following: COD has many sub-components that play significant roles in its successful execution. We will now explore some of these physical qualities to gain further insight into COD speed in elite sport.
In many sports, critical movements of the game occur in incredibly tight spaces. Sport coaches from various disciplines echo similar sentiments, exclaiming thoughts like, “There’s just no space and time out there.” This is obvious in racquet sports where the court dimensions are quite small, but even on the basketball court and the soccer pitch, and in the hockey arena, key plays of a game or match are often decided in these so-called “tight spaces.” Furthermore, it’s typically the player with greater speed—or in this case, COD speed—that seems to win the battle for the puck, ball, or positioning.
Don’t believe me? A recent study (Pereira et al., 2016) took a closer look at movement in professional tennis players, and here are some interesting descriptive results from it. The total distance covered per rally was about 5.5 meters. Lateral movement occurred more than 75% of the time and, when moving to the side, the distances were much shorter. Lastly, and perhaps most intriguing, were the movement velocities. An astonishing 79% of the time, players were moving between 0 km/h and 7 km/h! Another 17% of the time was spent between 7 km/h and 12 km/h, 3% between 12.01 km/h and 18 km/h, and a measly 0.3% between 18.01 km/h and 24 km/h.
In a previous report (Abdelkrim et al 2007), we learned that in men’s basketball, up to 1,000 directional changes may occur during one competitive game. In elite females, a more recent investigation (Conte et al 2015) found that players changed direction 576 times (on average) with a range between 363 and 759. These activities last, on average, between two and four seconds. While 86% of all sprints were less than 10 meters in distance, when analyzing all movements (running, sprinting, jogging, jumping, specific basketball movements, etc.), close to 60% of them occurred in the 1-5 meter distance range.
While the basketball study didn’t analyze movement velocities, it’s safe to say that with the amount of directional changes that take place, and within a specific distance range, full running speeds aren’t reached. To make sense of these stats in terms of training prescriptions, we should look back at sport science basics, and the force-velocity relationship in particular. When movement velocities are low (like the examples above), forces have to be high, otherwise it’ll be a challenge to produce explosive, efficient movement. This leads us into our next topic of discussion, the underpinning physical factors that affect COD in sport.
Change-of-Direction and Sport – Physical Factors
I attended a presentation on COD a couple years back at a tennis federation. While the presentation was well-intentioned, the presenter refuted strength and power training as key components to COD ability. Interestingly, the arguments of the presentation were based on a review paper published in 2006 by Brughelli. Many of us know the results of that paper. If you’ve forgotten, let me refresh your memory: The review found no significant correlation between COD ability and strength or power levels.
Does that mean Sheppard and Young’s model (from above) is completely inaccurate? Or that we should forego strength and power development when attempting to make improvements in COD?!? Here’s the counterargument (Nimphius et al 2017):
“In research and applied practice, the use of total time as a measure of COD performance has been overwhelmingly considered as a ‘valid’ measure of performance. However, recent research has suggested that the use of ‘total time’ from COD and agility tests may be masking actual COD ability, primarily because total time is biased to linear sprint ability in most tests.”
This is the reason Brughelli’s review came to the conclusion it did—up to that point, research on the topic didn’t actually measure what it intended to measure. (In some cases, researchers still make the same mistakes by using T-tests, shuttle runs, etc. that have a large linear component and, in some cases, are more relevant in testing anaerobic capacity than COD ability.)As coaches, we should be more concerned with the various instantaneous moments of COD tasks. Click To Tweet
So when it comes to COD, what are we trying to measure anyway? As I see it, the key to understanding COD ability in terms of the mechanical underpinnings lies in the isolated moments where a COD movement occurs. In other words, as coaches, we should be more concerned with the various instantaneous moments of COD tasks. We can divide these moments into three primary phases:
- The Braking Phase – aka the deceleration phase.
- The Propulsive Phase – aka the re-acceleration phase.
- The Transition Phase – aka as the planting phase.
Based on what we’ve outlined above, in conjunction with Sheppard and Young’s COD model, the remainder of this article focuses primarily on the physical subcomponents that make up COD.
Note: I’m a strong believer that technique and coordination are big drivers when it comes to COD ability in sport. They are heavily influenced by the specific and inherent mechanics of each sport, and even further than that, by very specific movement scenarios within each sport. It’s not the scope of this article to highlight the nuances of the various sporting movements, but for strength and conditioning coaches, I believe it’s worthwhile to analyze every possible movement outcome of the sport in question, as it will likely influence programming.
Leg Muscle Qualities and COD Performance
While research acknowledges the importance of unilateral strength in improving COD ability, I won’t touch on it much here—otherwise this article would turn into a 10,000-word dissertation. I will, however, focus on several physical factors Sheppard and Young (2006) proposed: concentric strength and power, reactive strength, and how anthropometrics influence the discussion. Let’s dive into these in greater detail.
Concentric Strength and Power
Concentric strength and power can be most closely linked to the propulsive phase of COD. In various sport settings, after a deceleration and plant occurs, a re-acceleration in another direction takes place. Because ground contact times are longer during acceleration phases, maximum and explosive strength abilities are critical. In theory, the more force you can impart into the ground and the faster you can generate that force, the more efficient the propulsive phase.
A 2015 study (Spiteri et al.) on female basketball players showed a significant and strong correlation between propulsive force—the amount of force—from zero velocity to initiation of movement, relative to body weight (which we’ll explore in greater detail soon) and exit velocity (along with subsequent 505 test times). This means that generating a high amount of force relative to body mass will essentially improve COD ability. Thus, increases in concentric leg strength may improve first step abilities, whether that’s initiating movement from a starting position or performing a 180-degree COD.
Practically, the concentric portion might be trained in a more traditional manner (heavy explosive squats) or by decreasing and/or eliminating the stretch-shortening cycle’s (SSC) contribution to the lift (concentric or con squats—see Video 2). Con squats may be useful for sports/athletes where there’s a longer-than-normal transition phase, if a swing, kick, jump shot, or some other play is performed between the braking and propulsive phases. In these cases, concentric-only strength would be highly beneficial. Previous research (Nimphius et al 2010) supports this, as stronger athletes are able to apply force at faster rates (RFD) during the propulsive phases of COD tasks.
Video 2: Concentric work is still relevant because of the adaptations to the nervous system and the lowered stress and recovery needs. A mix of eccentric and concentric activities are wise for in-season training.
What Sheppard and Young’s model left out, however, were the two other types of muscle contractions: eccentric and isometric. Both are vital for improved COD ability in sport.
When an athlete begins to decelerate, the braking forces acting on them are quite high. In fact, studies (Delaney et al., 2015) have shown that athletes are exposed to forces that are much higher than their own body weight during this phase. While coaches are often confronted with the question, “How strong is strong enough?,” it’s apparent that we might want to consider the ability to withstand forces that are up to two times the athlete’s own body weight.
Further to that, Spiteri (2013) found that athletes who performed significantly better at a 45-degree cutting task generated significantly higher vertical and horizontal braking forces. In other words, they were better at rapidly decelerating. In a 2015 study, the same research group found that athletes who were stronger eccentrically had a faster and more efficient transition between braking and propelling. Anecdotally, we see this when athletes appear to have a smooth transition between braking and propelling.
Practically, the eccentric phase can be accentuated with supramaximal lifts (Video 3) or by simply performing a variety of slow tempo lifts. But I doubt that’s enough. Athletes must be able to absorb considerably large forces under fast movement velocities. This is where Olympic lifts may warrant implementation—with an emphasis on the catching phase. During a hang power snatch, for instance, you can target the movement to affect bilateral or unilateral force absorption (Video 4).
Video 3: Heavy maximal eccentrics are difficult to implement without the right rack and the properly prescribed load. Eccentrics are above overload in force, not just overload with time under tension.
Video 4: Split snatches are less common than in the past, but they offer a nice blend of bilateral and single leg benefits to athletes. Include scapular strengthening from barbell pulling, and split snatches are a great addition.
Lastly, we have the transition phase. Recall that the transition phase in COD is also known as the plant phase. When looking at instantaneous joint moments, this phase seems to rely on isometric strength abilities (Spiteri et al., 2015). In other words, there’s a transition between braking and propulsion where movement velocity is zero but large forces are still at play.
It seems that athletes who possess higher isometric strength values are better able to maintain a low position when changing direction. This is important for two reasons. If you lack isometric strength, you can’t maintain your body in place. (In essence, you end up fighting against momentum, with it pushing you one way and you wanting to go the other way.)Athletes w/higher #isometric strength values can better keep a low position when changing direction, says @CoachKuzdub. Click To Tweet
Second, staying low when changing direction facilitates a better muscle length-tension relationship. Muscles produce more force at specific lengths. If they are too long (legs fully extended) or too short (legs fully bent), then force output will be diminished, comparatively. Keeping a relatively low stance will enable optimal force production, allowing for greater re-acceleration during the propulsive phase.
Overall, all three muscle contractions have their place when it comes to faster, more explosive, and more efficient transitions between braking, planting, and propelling. And when looking at some of the research on the topic, it seems that each COD phase links with one another. From a practical perspective, it’s likely not necessary to isolate each phase unless a visual assessment from a seasoned coach warrants it. In that case, you may implement an isometric-only exercise that deals with the exact angles of interest (Video 5).
Video 5: Isometrics are very flexible options and split squats are mechanically suited for intense training. Short periods of isometric training can help break through plateaus in strength and power.
Body Mass, Relative Strength, COD, and More
A study by Delaney et al. (2015) assessed professional rugby players on multiple abilities to determine various performance attributes and how they correlate to COD ability. When comparing a 505 COD test to a loaded vertical jump (40kg CMJ—countermovement jump), there was no significant correlation. While peak power from the vertical jump had no bearing on COD ability, when it was converted to relative peak power (based on body mass), everything changed. All of a sudden, there was a large significant correlation between the jump and COD performance.
When it comes to maximum strength in the back squat, the findings are even more telling. Delaney and his colleagues found no correlation between COD and a 3RM full-depth back squat. However, when back squat strength was reported relative to body mass, there was a strong and significant correlation to COD ability. In sub-elite rugby players, relative 1RM back squat strength was the greatest predictor of 505 COD ability. In female basketball players (Spiteri et al., 2015), there was a very strong and significant correlation between relative strength in a half-back squat and 505 COD ability.
Having a lower body mass isn’t the only factor at play here. A lower-percent body fat ratio relative to strength is also linked with faster COD test times (Spiteri et al., 2015). Essentially, lower body fat can have big impacts on an athlete’s ability to change direction rapidly and efficiently, as there is less nonfunctional mass (nonfunctional in this case meaning non-contractile). To my knowledge, strength training is the best way to improve body composition (i.e., lower body fat percentage). Remember, only muscle contracts—fat doesn’t.
A Word on Female Athletes and Specificity
Female athletes seem to consistently show greater correlations in COD ability when compared to relative strength (Nimphius et al., 2010; Spiteri et al., 2013, 2015). In the case of the Spiteri study (2015), one factor contributing to this finding is that the testing used a half squat instead of a full squat. When it comes to training, this is important for two reasons. First, a half-squat elicits angles that are more specific to COD tasks. On a tennis court or soccer pitch, it’s more common for athletes to move and change direction at these smaller angles than very deep ones, which a full squat represents. Second, athletes can tolerate higher loads in these smaller angles, which further increases relative strength values. As we’ve seen before, a conjugate approach that periodizes squats depths appropriately is warranted.
Reactive Strength and COD
Recall the stretch-shortening cycle (SSC) for a moment. The premise is that when performing any type of fast, explosive movement, the involved tissues undergo a rapid eccentric stretch followed by an explosive concentric shortening. Because of this mechanism, the SSC stores and utilizes elastic energy, thereby augmenting power output to levels higher than if we were to perform a concentric-only movement (or if there was a significant lag in eccentric-concentric coupling). There are two components to the SSC, the fast component and the slow component. We’re going to turn our attention to the fast component, as its role is key when reactive strength is in the mix.
I will refer to reactive strength and the fast SSC component synonymously. Movements of this nature are highlighted by short ground contact times (<250 milliseconds), minimal flexion of the hips and knees, and perhaps most relevant to our discussion, a stiffening of the ankle and/or leg.
The Role of Stiffness
Reactive strength possesses one particular sub-component—called stiffness—that enhances the use of the fast SSC. During explosive actions, there is energy exchange between the various tissues of the lower extremity, including muscles, tendons, and ligaments. Stiffness greatly influences this transfer of energy. As the term implies, this literally means a stiffening of the targeted musculature and surrounding tissues. This can occur actively and/or passively. We can see stiffness in the lower extremity as either total leg stiffness—which includes the ankle, knee, and hip joints—or simply ankle stiffness. Stiffness in the ankle is of primary importance due to the activation and rapid contraction (from eccentric to concentric) of the triceps surae musculature, the two heads of the gastrocnemius along with the soleus.
A stiffer spring (to a point) is theorized to rapidly release stored elastic energy. This is exactly what we look for when cutting in football or recovering after a return or serve in tennis. And it begins in the ankle. If the ankle cannot stiffen, not only will ground contact times be higher, but energy may “leak.” This results in diminished stiffness at the knee and hip; both of which are influenced by triceps surae stiffness. Think of the kinetic chain: If there’s a broken link at some point, the rest of the chain suffers. That’s how important ankle stiffness is in generating movement and changing direction.
Researchers (Arampatzis et al., 2001) have found that acute changes in stiffness do, in fact, occur. This tells us two things. First, performing pre-conditioning hops (like the video below) can augment jump height, peak power, and intrinsic ankle stiffness; research has established this on multiple occasions (Kummel et al., 2016; Maloney et al., 2017). Second, having the correct intent may also contribute to increased stiffness, and morphological changes in the muscle-tendon complex are not entirely necessary to achieve stiffness.
Proper exercises and cues, therefore, have a profound effect on establishing this quality, acutely. That said, long-term passive and active morphological adaptations in the muscle-tendon and surrounding tissues may occur. Coaches must assess how much stiffness their sport requires and monitor this diligently.
Video 6: Bilateral reactive jumping is a great way to improve neuromuscular adaptations to the body while sparing the wear and tear that some single leg exercises have. You can use contact grids to measure and monitor lateral movements.
One final note on the notion of proper exercise prescription and cueing. What the aforementioned study revealed was that when athletes performed drop jumps, two things happened. First, there was a greater pre-activation of muscles of the ankle complex before they hit the ground. And second, co-contraction—the ability to contract both the agonist and antagonist musculature simultaneously—increased.It is important to deliberately train stiffness/reactiveness off the field or court, says @CoachKuzdub. Click To Tweet
Both of these factors increase stiffness. This simply highlights the importance of deliberately training stiffness/reactiveness off the field or court. Lastly, there are ways to make these types of drills more “agility” based by using various external cues (whether verbal, hand gestures, or otherwise). For instance, you can prescribe a drop jump exercise in a closed manner (Video 7) or more open (Video 8).
Video 7: Lateral plyos are about redirecting forces, not just moving side to side. Focus on quality landing positions before changing directions, as it’s easy to get lost on the location an athlete moves to instead of how they receive forces off the ground.
Video 8: Athletes can do lateral jumps on the court, field, or pitch. Include hurdles and cones as general guidelines only, not tight zones of movement, so the athlete doesn’t feel restricted.
Don’t Forget About Technique
My objective in this article was twofold. First, it was my belief that making the distinction between agility and COD was key to laying the foundation for these two qualities. While COD deals only with physical/technical factors, agility entails both perceptual/decision-making factors along with COD factors. Second, it was my aim to uncover why strength and power were previously shown as insignificant players in the optimization of COD (in terms of what the previous research revealed). Also, to offer an updated viewpoint towards the underlying mechanical requirements athletes should possess in order to change direction effectively. These can be trained off the court or field.
Lastly, I’d like to reiterate that this analysis only takes into account a fraction of what’s important when attempting to improve agility and COD as a whole. There are a number of schools of thought on this topic, from game-based approaches to constraint-led drills. I’m not trying to disregard the importance of other methods on COD and agility development, but a universal approach to training makes logical sense to me. While I haven’t touched on technique and mechanics, I do believe we shouldn’t neglect their place in the training process. That said, for athletes to express movement efficiently, it’s my belief that they must possess both the technical proficiency and the physical capacity to do so.
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