Unless you’ve been living under a rock, you’ve likely seen countless videos on social media of athletes lifting big weights. And it’s not just athletes from sports like american football, baseball or hockey. Many athletes across various sports - like long distance running, swimming, volleyball - are lifting weights. We're not referring to light dumbbells but rather heavy loads and big lifts. The question is, why? What’s the rationale behind this type of training? Should tennis players learn from these sports?
I’ve briefly spoken about the importance of strength training for tennis. Some factors include the prevention of injury and increases in serve speed. In this post, we’ll dive deeper into the details of maximum strength training and it's relevance to the elite tennis player. Specifically, we’ll outline how max strength development can impact movement characteristics - including explosiveness, first step ability and acceleration.
Before we get into it, I’d like to mention that tennis is characterized mainly by explosive (speed-strength) actions. This basically means that the majority of movements in tennis are quite ballistic and fast - and I strongly believe training should reflect this (both on and off the tennis court). That being said, there’s a place for maximum strength training in the overall program (and development) of an elite tennis player, and hopefully this article will shed some light on this topic. Below we'll explore the mechanisms behind heavy strength training, how max strength affects movement in tennis, research in the area and practical considerations.
Basic Science Behind Maximum Strength Training
What’s Explosiveness Anyway?
Explosiveness - what sport scientists refer to as explosive strength or rate of force development (RFD) - differs from maximal strength. Explosive strength is related to how quickly a muscle or muscle group can develop force to produce a desired movement. In this context, achieving max force is not a requirement. As you would probably suspect, this quality is quite important for tennis players - every time a player initiates movement, they are attempting to be explosive. Explosive strength is generally trained using lighter resistances (barbell jump squats, power snatch/clean etc.) or via traditional plyometric activities (jumps, bounds, sprints etc.). Many would argue that explosive strength is more important than maximum strength in tennis (myself included). If that’s the case, why am I even writing about maximum strength/force development? Why not just focus on explosive strength?
Max Strength, in a Nutshell
Before we answer these questions, let’s quickly define maximum strength and outline it’s mechanisms. Maximum strength is defined as the maximum force a muscle or muscle group can exert during a voluntary contraction. In practical terms, this essentially translates to how much load can one lift for 1 repetition. Depending on your aim, you may use a barbell back squat to assess lower-body max strength or a bench press to assess upper-body max strength. These are merely examples as other exercises can also be used. Our aim is to improve movement in tennis, therefore the focus is primarily on the development of lower-body max strength - although even this is misleading as heavy lower-body strength training also recruits the musculature of the trunk, shoulders, chest, arms etc.
Muscle Size Isn’t Everything - Neural Factors in Strength Development
Over a year ago, I spoke with a colleague of mine who trains top players at a national federation. We talked about their off-court training regime - it included a lot of plyometric type drills, accelerations, loaded jumps - all good stuff. But when I asked about their strength training protocol, he outlined 2 reasons they don't do any heavy lifting: 1) they still have time to build strength (the athletes were between 16-21, more than old enough to lift) and 2) we don’t want them to gain any mass. In contrast, their strength training sessions included higher rep sets with lighter loads - this however, is the exact opposite of what they should be doing. The type of strength training that we're referring to, shouldn’t have much effect on hypertrophy (muscle growth) anyway. Which brings me to the adaptations of max strength training - neuromuscular factors.
When attempting to produce movement, our brain (central nervous system or CNS) sends a signal to the motor units that innervate a particular muscle or muscle group. When it comes to strength training, as the load acting on our muscle begins to increase, more motor units are called upon to sustain the contraction. Above a certain point (about 85% of our max), 2 things happen: 1) we recruit higher threshold motor units which primarily innervate type 2 fast-twitch muscle fibers AND 2) these motor units begin to fire at a greater frequency. Without sufficient load, we won’t recruit type 2 fast-twitch fibers. These fibers are important because they are responsible for producing maximum force AND for producing force quickly (explosive strength, remember). Through heavy strength training, we provide a stimulus to the muscle to fire these motor units more efficiently, and at higher rates, which actually helps to improve explosive abilities - an ability we agreed was important in tennis.
After strength training, we recruit more high threshold motor units, which helps us develop more force (figure 1 above). Increased firing of these motor units further helps with max force development ALONG with an increase in RFD - or explosiveness (figure 2 above & 3 below). And once adaptation has occurred through heavy lifting, whenever we’re performing explosive movements, we call upon these motor units to help develop the necessary force to execute the desired movement. This simplified explanation defines intramuscular coordination and provides context on how to improve it. It’s development is dependant on heavy strength training - loads that are above 85% of maximum with low reps and multiple sets.
This neural factor is related to the ability of different muscles and muscle groups to coordinate between each other by activating appropriate agonist, antagonist and synergist muscles with the goal being the execution of complex movement. When performing heavy loads, like a back squat for example, one must stiffen the trunk muscles, shoulder girdle and grip (for example), otherwise successful execution won’t happen. As an aside, this is why research has seen greater activation of trunk muscles during heavy squats, deadlifts, than with traditional ‘core’ exercises. Something to think about… While intermuscular coordination is also developed through heavy strength training, heavier ballistic exercises - like Olympic lifts, loaded barbell jumps & throws - have a more impactful effect on this quality. This is due to their inherent complex movement sequencing which improve firing rate (figure 3). This increase of RFD through ballistic movement is also due to the specificity principle - adaptations will reflect the demands imposed. In other words, perform explosive actions, gain explosive abilities (figure 4).
What’s nice about training both explosively and with the intention to produce max force is that adaptations are primarily neural. Of course there will be some amount of muscle size increases, but this is merely a by-product, and not the aim of heavy strength training. This is an important point and one that has a big influence on movement in tennis, as we will soon see.
How Does Max Strength Improve Movement in Tennis?
The First-Step, Acceleration and Deceleration
A nice way to highlight the importance of max strength as it relates to acceleration/first step movement in tennis is by quoting world-class sprint coach Stu McMillan (quick note - Stu is the Lead Performance Coach at Altis, a training ground for world class track & field athletes and is the head coach of Olympic bronze medallist in the 100m, Andre De Grasse):
“Acceleration occurs for approximately the first 3-6 seconds of a sprint, has longer ground contacts and is relatively more dependant upon maximum strength qualities, so it only makes sense to pair this with maximum strength exercises”.
Stu’s referring to the build up to maximum speed in sprinting - those first several strides. Similarly in tennis, and many other land based sports, acceleration is characterized by longer ground contact times, which mechanically, have similarities to heavy lower-body weight training. In other words, both require pushing into the ground to develop movement by overcoming inertia.
From previous research (Kovacs et al 2006), we know that players move 3m in any particular direction during a point (on average). Further, based on evidence from Tennis Abstract, at last year’s French Open, players ran a total of about 10m per point. Points that were 5 shots or longer, saw that number increase to 21.5m. Most points (close to 90%), were no more than 8 shots while the majority coming in at 4 shots or less (70%). Based on this info, the majority of movements occur between 0m and 5m. Brief aside - a tennis court, including outside of the lines has a width of about 18m and the length (from net to backdrop) is maybe 20m. Running these distances during a point almost never happens.
The question remains, why is this important? Recall, max strength helps improve our force generating abilities - when movement velocity is zero, which is the case during the first few steps of acceleration (and last few steps of deceleration), force is highest. So when first moving to the ball, after our split step, we’re actually not moving fast at all, but we are generating high forces. The more force we can develop in these first few steps, the faster we can displace ourselves. This is also true when changing direction (i.e. the recovery after a shot in tennis). At some point movement velocity is actually zero (it has to be or else we would just keep moving in one direction). So those first several steps, both when accelerating and then when decelerating, require high force generation/absorption, which are highly dependant on maximum strength ability.
Explosive Actions in Tennis
You may be wondering about the initiation of movement, along with movements that don’t require you to move much at all. This is where the split-step comes into play. I’ve mentioned before that the split-step requires reactive strength. This quality doesn’t necessarily require high force but rather the ability to generate ENOUGH force, extremely rapidly. Remember, this is what we also refer to as explosive strength. Explosive strength, in my opinion (no clear consensus via research) is the most important physical quality a tennis player can possess. Having this ability is vital in almost every movement scenario during tennis play.
We saw earlier that explosive strength CAN increase with maximal strength training. You may be wondering how this is possible considering that when moving a heavy load, the velocity of the movement is quite slow. Recall that heavy loads are above 85% of a person’s 1RM. You may further wonder how this is the case when I tell you that most adaptations to training are specific to the velocity of movement. This contradiction can be explained via a landmark study by Behm and Sale (1993). The intention of movement velocity may be just as important, and in some cases even more important, than the actual movement velocity. Let’s look at a heavy squat as an example. If my aim is to move the bar explosively, even though the resultant speed is slow, my nervous system is effectively sending a signal for high motor unit activation - i.e. increased recruitment of type 2 fibers and increased firing frequency. The movement velocity may be slow but the contraction velocity is fast. And this is how strength training can impact explosiveness.
What Does the Research Tell Us?
Believe it or not, strength training studies in tennis are few and far between. This is a shame as those that do incorporate heavy strength training with tennis players have had tremendous results. For instance, Kraemar et al (2003) saw a 9-month periodized strength training program improve jump height, 1RM leg strength, 1RM upper-body strength, serve and groundstroke velocities along with body composition. But our concern is with movement in tennis. So how did they do? Compared to a non-periodized group and a control group (who practiced tennis and any other activities done on court), the periodized strength training group did improve both 10m and 20m speed times over the course of the 9-month period, although the results weren’t significant. As mentioned previously, 10m and 20m distances are quite long for a tennis player, so it may not be that relevant anyway. While a review (Seitz et al 2014) on maximal strength training and sprinting revealed that both 10m accelerations and 20m sprints are positively correlated with heavy lifting, it may be useful to look at shorter distances.
When adjusted for body mass and strength, a study of athletes and recreationally active men (Comfort et al 2012) revealed a strong positive correlation between 5m sprints and relative squat strength. In elite first league soccer players (Wilsoff et al 2004), max strength half squats were highly correlated with both increases in agility, 10m acceleration times and vertical jump height. Vertical jump height is an indirect measure of power and explosive ability, providing evidence that being able to generate high forces ALSO helps generate explosive forces. Although vertical jump height is a good indicator of RFD abilities, when looking at the principle of specificity, movement doesn’t occur vertically - it does help on the serve and when loading to hit groundies, but that’s another topic for another day - but rather horizontally (and to the laterally, in reverse etc.). Perhaps a better indicator of explosive abilities as it relates to tennis is horizontal jump distance - often referred to in the literature as a broad jump. In collegiate athletes (Peterson et al 2006), broad jump distance was highly correlated to 1RM squat strength. An even higher correlation to 1RM squat when adjusted to the athlete’s body mass.
Based on the above science & research, we get a better picture of how movement can be improved via heavy strength training. More specifically, when strength is high relative to body weight, we see correlations increase. Peterson et al (2006) concluded that “Relative muscular strength may actually be more applicable to most explosive performance measures than absolute lower-body muscular strength”. Great news as heavy strength training is often increased WITHOUT increases in muscle size. Specific hypertrophy protocols are what cause increases in muscle size, and could very well contribute to decreases in explosive qualities in tennis players.
How NOT to Develop Explosiveness in Tennis
Developing max strength therefore, is arguably critical in the development of successful first step/acceleration ability in tennis and to increase explosiveness through neuromuscular adaptations. That means, fast ladder drills, which are seen as ‘footwork’ drills, have very little to do with first-step/acceleration. Perhaps there are other benefits to ladder drills (coordinative, warm-up, low-level plyometrics) but they DO NOT develop explosive tennis players. Similarly, when performing exercises on a stability ball, force generation capabilities greatly diminish - both maximally and the rate at which it’s developed. These training types lend themselves to criticism as they have very little (if any) benefit from a neural activation perspective. And when looking at the enhancement of movement on court, we must therefore look at training means that favor neuromuscular characteristics.
Each movement/contraction that our muscles produce on a tennis court cannot be seen in a vacuum. Movement is too complex. When initiating the first step for example, there may be certain muscles (or muscle groups) requiring high maximal force while others that require high rate of force. There may even be certain areas of the body acting isometrically to limit movement of a particular limb - stiffening of the trunk for example - while the arm may need to produce high power (a combination of speed and strength) to help propel the body in the direction of the ball. To train the modern tennis player, one must therefore look at both the needs of today’s sport and the limiting factors of the player in question. Other factors to consider include the time of year, the window of adaptability, maturity of the athlete and so on.
In another post, we’ll look at how to implement strength training with players across different ages and levels. For the time being, I will say that the improvement of explosiveness and acceleration in tennis through strength training will differ depending on where the athlete stands developmentally. A young athlete may see great benefits with bodyweight exercises that emphasize explosiveness along with isometric contractions while a more advanced athlete may require heavier loads in exercises like back squats, deadlifts and their derivatives to elicit the desired adaptation. Based on research in older athletes, high correlations exist between maximal half squats and explosive/accelerative abilities. Because players are rarely required to get into a deep squat position, half squats may be more specific to the what an elite player needs. Furthermore, increasing squat strength relative to body mass is likely critical for an elite player to move better on court.
In summary, the player who can produce more force will have a better chance at being explosive and fast....to a point. Remember, I’m not suggesting strength training trump other qualities, but it could play an important role in the overall program of an elite tennis player.