In HPP, we introduced the basic tenets of sport science - the adaptation process, progressive overload, the principles of specificity, variation & individuality along with other factors related to the training process. Those should always be considered whenever prescribing any type of training item to an elite player. It may be useful to review those concepts again before proceeding.
Once these principles are well grasped, I believe it’s vital that coaches have a general understanding of the force-velocity (F-V) relationship. Gaining more insight into the F-V relationship (or curve, as it’s often called), will give you a better sense of why elite off-court training is organized in such a manner (and why the program at the end of this guide is structured the way it is).
THE F-V CURVE EXPLAINED
The force velocity relationship underpins all muscle contractions and joint movements. Its premise being that muscle force and velocity are inversely related. In other words, when high forces are generated, the velocity of the associated movement is very low. On the flip side, when movement velocities are high, force outputs will be low.
For instance, lifting very heavy, like a 1RM back squat, produces very high forces, at very low velocities. Thus, maximum strength training would fall onto the high-force, low-velocity end of the curve (Figure 1 below depicts a theoretical version of the F-V curve and associated physical qualities). On the complete other end of the spectrum you have tasks like sprinting, or hitting the movement of the racquet on a groundstroke - high velocities, low forces.
Hill (1938) has been attributed for the discovery of the force-velocity relationship, almost 80 years ago. Today, strength & conditioning coaches and sport scientists use the F-V curve to guide training programs. This is so as it’s theorized that an upwards shift in the curve will improve muscle function and athletic performance. Because now, at any given velocity, more force can be generated. And if we recall from basic physics:
Force x Velocity = Power
In practical terms, think of it this way. If a player can impart more absolute force into the ground, they’ll be able to generate more power. Imagine the benefit when loading the rear leg on a forehand groundstroke, or when re-accelerating after a change in direction.
**insert MP branded F-V curves
FIGURE 1 - THEORETICAL FORCE-VELOCITY CURVE & ASSOCIATED POWER CURVE
Here’s a more specific example of the F-V curve during a serve. During the service motion, the shoulder internal rotators can reach velocities of 3000 degrees/s (that’s fast!). The internal rotators must produce up to 200 N (Newtons) of force to reach these speeds. Now, consider an a player of yours has gone through a specific velocity training program (the velocity/low end of the F-V curve) - one which targets the rotators. After completing this program, they’ve increased the velocity output of that motion and are able to reach 3250 degrees/s for the same given force output. This is a velocity specific adaptation - and will therefore increases power output for that specific action.
A MORE DETAILED LOOK AT HOW THE F-V CURVE AFFECTS TENNIS
Every stroke and every movement in tennis doesn’t fall perfectly into one specific part of the F-V curve - training would be a lot simpler if it did. Remember, the F-V curve applies to muscles and joints (??). We should therefore look at it as part of a continuum. Within one tennis stroke, many (and perhaps all) parts of the curve could be involved as human movement is complex (contraction types, speeds & angles are different and are affected by many variables). Below, we will break down the various parts of the F-V relationship and attempt to place various movements along the curve.
Maximum Strength and The Force-Velocity Curve
Maximum strength can also be referred to as absolute force or absolute strength. It’s concern is with maximum force generation of a muscle, or a group of muscles. To develop maximum force, you need to lift maximum loads - this doesn’t mean doing a 1RM every time you're in the gym but it does mean lifting somewhere above 85% of your 1RM - reps will usually range between 1 and 5. You’ll find max strength at the very top of the F-V curve, where higher forces are generated at concomitantly lower velocities.
In tennis, max strength is critical to both absorb high forces and to generate high forces. When referring to the absorption of forces, the most common scenario in tennis is deceleration. The higher the running speed before setting up for a ball, the faster will be the rate of deceleration and the more force the lower body must absorb. The deceleration phase is also referred to as the braking phase of a change-in-direction movement. During the braking phase, research has revealed the force being imparted on the body (specifically the lower-body) can be as high as 2-3 times an individual’s bodyweight. If our musculature cannot dissipate and handle that type of force, imagine the impact it’s having on our tendons, ligaments and joints overall.
Thus, eccentric strength is vital in this scenario. If you think about decelerating when tracking down a ball, you can associate that with the deceleration phase of a heavy squat, heavy deadlift or heavy single-leg lunge variation. Now of course brute strength is not the only concern here - proper braking mechanics are also important so that excessive forces aren’t being isolated in one area. But that doesn’t excuse players from being strong.
Strength adaptations are joint specific, contraction specific and speed specific - which is why a specific prep program will place players into more targeted position to handle the appropriate forces.
Example video of a slow, heavy, eccentric movement.
The landing portion of the serve is another example of force absorption in action. When serving, there are large forces and torques (another term for force but in a rotational manner) created. Kovacs & Ellenbecker (2011) observed that these forces can be as much as 2 times your bodyweight after a serve. If we don’t have the eccentric strength to land efficiently on our front leg after the serve, that force will crush us and impede the next movement.
Insert landing GIF here
Let’s use the serve again to outline the force generation portion of the F-V curve. Upon landing after the serve, to initiate the subsequent movement, a player must overcome a high amount of inertia (or resistance). To do so, a high level of force must be imparted into the ground, to facilitate the next movement (generally a backwards recovery step).
Two other examples include the re-acceleration (or propulsion phase) of a movement change-of-direction. This occurs after basically every groundstroke - note that the forces needed differ and are dependant on the type of shot that was executed. Running down a tough wide ball that forces an acute angle at the knee, will require greater propulsive forces. Lastly, the very early stages of a big groundstroke - planting the foot and using ground reaction forces - may require high force generation (again, depends on the shot type and intention).
Insert MP branded curve
Figure 2 - Theoretical Force-Velocity Curve After High Force Training
It is critical to remember that the higher the inertia (or resistance) the more important max strength becomes. Research also suggests that you cannot have high levels of power without first being relatively strong (Cormie et al 2011). Stronger athletes have greater neuromuscular characteristics - greater size of type 2 muscle fibres, enhanced neural recruitment, superior inter & intramuscular coordination. Because of these neural factors, max strength potentiates the remainder of the F-V curve. That means that at any given velocity, you’ll produce more force and hence, more power (remember...P = F x V).
Lastly, while absolute strength is not correlated with COD ability, relative strength is - in terms of its association with an individual’s bodyweight. But, and it’s a big but, max strength training has a smaller influence on muscle hypertrophy, compared to other types of resistance training. Usually what happens when we lift heavy - we get strong AND improve body composition which ultimately, improves relative strength. Keep in mind, it’s all connected.
Strength-Speed and The Force-Velocity Curve
When compared to max strength, during strength-speed activities - which are one step down on the curve - there is still high amounts of force being generated, but at greater velocities. This occurs when performing explosive strength exercises like the clean & jerk or snatch (Olympic weightlifting movements). Again, here, the loads must be quite high (between 80%-90% of 1RM?) which puts this quality just below max strength on the F-V curve.
In tennis, strength-speed qualities are important during various parts of groundstrokes and serves. More specifically, the leg drive and take off phases of these strokes. Another example is movement qualities. After the initial acceleration phase, high levels of explosive strength need to be generated to propel the body in the direction of the oncoming ball. Remember, at different moments of a movement, the characteristics of a muscular contraction differ. Within an individual muscle, one fibre may be acting in a fast concentric manner while another may be acting in a slower concentric manner. This is based on the length-tension relationship - i.e. when a muscle fibre is very long or very short, it cannot produce a lot of force while somewhere in between those lengths, the highest forces (and muscle contraction speeds) are produced.
Insert length-tension relationship graph (or link to wiki)
Strength-speed is primarily developed through Olympic weightlifting movements. These movements generate higher power outputs compared to traditional strength training exercises because the bar (and body) are propelled throughout the entire acceleration phase of a lift. In other words, there is no deceleration until you have to catch the bar (either on your shoulders in the clean OR overhead in the snatch). This deceleration helps with braking forces in tennis, especially when the requirement are to decelerate VERY quickly.
Staggered snatch video
Furthermore, Olympic weightlifting exercises have similar movement kinetics (joint angles, recruitment patterns etc??) to movements that occur in sport. This includes jumping, accelerating and changing direction.
It's never too early to start prepping young juniors with Olympic weightlifting movements. Here's a video example of an 11 yr old performing snatches with a light load.
Video of juliette
Speed-Strength, Reactive Strength and the Force-Velocity Curve
One quick thought before we move on to speed strength. To better understand the difference between strength-speed and speed-strength (I know it can be confusing), just remember that the first word in each of the terms is the quality that’s being emphasized to a greater degree AND both refer to what many coaches call, power. Meaning, strength-speed uses heavier load power training and the adaptations, therefore, will be more on the strength side (because of higher forces). While speed-strength is more on the lighter side of power training and the adaptations are more speed focused (because of higher velocities).
With speed-strength, we’re now starting to move our way down the F-V curve and into ranges of 30-60% of 1RM. In tennis, the acceleration phases of serves and groundstrokes require high levels of speed strength. In other words, you must be able to produce very high velocities under lighter force demands. Bigger shots and serves will be seen if one can produce higher velocities at a given force, which is the goal of this type of training. Speed-strength is primarily targeted through medicine ball (MB) exercises, loaded jumps, and other ballistic type movements (lighter load Olympic lifts work too).
Couple video examples here
Furthermore, speed-strength qualities are important during the use of elastic/reactive strength on most change-of-direction (COD) actions, strokes, split-steps etc. This is where our plyometric training and reactive abilities come into action (we will explore the specifics in section ??). These exercises are seen further down on the F-V curve as there is no external resistance added (i.e. unloaded).
Again, the further down the curve you go, the more sport specific the exercises become - so when it comes to speed-strength, in some cases, there is still an added resistance to the exercise, but because it’s lighter, you’ll be able to produce more velocity. The adaptations are similar to those seen with strength-speed (neural) along with an increase in RFD (rate of force development).
Essentially, speed-strength can be lightly loaded (barbell jumps etc), plyometric focused (either with upper body MB work or lower body jumping drills) and plyometric/reactive (fast SSC jumps).
Figure 3 - Theoretical Force-Velocity Curve After High Velocity Training
Lastly, at the bottom of the F-V curve, we have maximum speed. This is emphasized during training drills that can generate very high speeds. An example is certain phases of a throw or a sprint (but not all phases and muscle actions). Some sport scientists argue that loads are usually less than 30% of 1RM - but I believe this is too difficult to quantify as movements here are more specific to sport, and occur at higher velocities.
In tennis, max speed can be seen through arm speed (and hence, racquet speed) on all serves and groundstrokes. The highest velocities occur just before contact. Also, high speeds can occur with the rotational components of these shots, especially during (and just after) the acceleration phases.
Max speed, to an extent, can also occur during sprinting movements in tennis. More specifically, when running down drop shots, serving & volleying, retrieving wide balls, on the run etc. It’s nearly impossible to truly reach top speeds in tennis, but high running speeds still have a place in the training of elite players for the previously mentioned scenarios - but not greater than 30m for tennis as it’s irrelevant and could lead to injury.
Furthermore, research has proven that increases in power and force in high-velocity movements occur with high-velocity training. Meaning that the F-V curve at the velocity end will shift upwards (Figure 3 above).
Figure 4 - Theoretical Force-Velocity Curve After a Multi-Faceted Training Program
I know that was a lot to digest but knowing the basics provides us with a foundation when it comes to programming. Coaches can start looking at each drill, exercise etc. from an F-V perspective. Why? Because each area of the force-curve, starting from highest force and moving downwards, potentiates the subsequent area of the curve. Look at figure 4 above - when training incorporates all areas of the curve, there's a shift upwards and to the right. That means, at any force, there will be an increased velocity response and vice versa.
For sure, in tennis, more time will be spent on the bottom areas of the curve. But I believe - and the science backs it up - that athletes should be hitting all areas of the curve during training. When it comes to tennis, this type of multi-faceted approach has yet to find its way into the training regimes of most players, until now. From a performance perspective, failing to target specific areas of the curve may hinder a player’s ability to move more explosively, hit bigger shots and remain injury-free.
Type IIX FIBERS
Video explaining the F-V curve?