If you’ve ever been to New York City in late August, you’ll know that there are two words on everyone’s mind: “US Open.” This year, I had the pleasure of heading over to the Billie Jean King National Tennis Center to watch the top players in tennis hit some balls. TV doesn’t do them proper justice – when I sat in the stands right behind the players on the practice courts, I gained a deeper appreciation of how hard the pros are actually hitting the ball while maintaining a rally.

One player in particular that appears to have mastered this skill is the Jannik Sinner, the current men’s world #1. The rumors are true – his forehands not only sound like gunshots but they look like them too, as the balls fly across the court like bullets. However, Jannik is definitely not the biggest guy on the tour, so there must be something other than pure strength that fuels the power of his shots…

If, like me, you’ve ever wondered how to hit your forehand just like Jannik, it all comes down to something you may have learned in your 9th grade physics class:

*Force = mass * acceleration*

Let’s return to the physics classroom for a moment to hone in on a framework that we’ll use to better understand the science of forehands, and specifically, Jannik’s forehand.

Starting with F = ma; it’s safe to assume that m or the mass of the tennis ball has a fixed value. According to the ITF, we can assume it to be approximately 57.7 grams. Therefore, the formula now becomes:

*F = 57.7g * a*

Acceleration is defined as the change in velocity in a given time period. Velocity is essentially the same as speed, except it has a direction vector. To hit the ball as fast as possible, we want to maximize velocity. Let’s rearrange the formula to isolate velocity:

*F = 57.7g * ( ∆v / ∆t ) *

*∆v = ( F * ∆t ) / 57.7g *

What does this tell us? In plain English, change in velocity is equal to force multiplied by change in time, divided by the mass of the ball. (F * t) is equivalent to another physics term called impulse. As you would expect, impulse is how quickly a force is applied to an object.

So, to put this all together, we can influence two key variables** **to achieve the most powerful forehand possible:

1. **Force** – we want to apply as much force to the ball as possible

2. **Time** – we want to apply this force in as little time as possible

Both are important, but given that contact with the ball is already being made so quickly and the range of values is so narrow (about 5 to 6 milliseconds), time generally has less bearing on the velocity output than force. In other words, if you can apply 1.5x the force to the ball, even if you applied that force over a longer time period, the net impact on velocity will be positive.

Forehands are complicated, and there’s a whole laundry list of skills that players need to precisely execute after getting to the ball to optimize the variables in the formula we derived in order to maximize the power of the shot. Here are a just a few:

• Give the ball some space

• Turn your body perpendicular

• Drop your racket head

• Bend your legs

• Get a nice flick of the wrist

• Accelerate late

• Follow through fully

This is a lot to work with, so let’s focus on just the first item for now — giving the ball some space. This is a skill that casual players struggle with the most due to involving a lot of tiring footwork and fighting against intuition. The reason it’s so important is muscle tension and extension. Tension, also known as flexion, is created when you wind up to hit the forehand, and extension happens when you actually hit it (see below):

During muscle tension, force is generated in your biceps as it contracts. This is due to your muscle fibers shortening in length, pulling myosin filaments over actin filaments. During muscle contraction, the force that was generated is released / transferred. In this case, it is transferred from your biceps to the ball, via your racket.

Lots of research has been done on this topic, and as you would expect, there is an optimal joint angle at which flexor force is maximized:

Therefore, in the wind up, you should aim for just wider than a 90-degree angle between your biceps and forearm. Your biceps are fully relaxed and all the force is released at an 180 degree angle. This is close to what you should be aiming for at contact. Pulling this all together, your body should be positioned such that when your arm is fully extended, the ball is at the racket’s sweet spot. Generally, this means that you should be further away from the ball than your intuition would tell you, and you may need to take a few extra baby steps in the opposite direction to accommodate and retrain your mind.

Let’s take a look at Jannik’s form:

As you can see, his body is in position during flexion, and his elbow joint angle is a little wider than 90 degrees.

Upon extending, the angle is at around 140-150 degrees and the ball is about to make contact with the sweet spot. He has long arms that extend far from his core, yet his awareness of his body allows him to position himself in a way that transfers the force into the shot.

As a concluding aside, according to the ATP, the fastest forehand Jannik has ever hit in an official match was ~166 kph. If we return to the formula from earlier and assume that the ball was in contact with the string for 5 milliseconds, we can substitute more variables to arrive at:

*166 kph = ( F * 5 ms ) / 57.7g *

*F = ( 166 kph * 57.7g ) / 5 ms *

*F = 532 Newtons *

532 Newtons are approximately equivalent to 120 lbs. So, when Jannik hit that shot, he applied the same amount of force to the ball as someone who weighs 120 lbs does to the Earth. Absolutely ridiculous!

Creating power through your shots is no easy feat. As discussed above, it takes a combination of skills to fully maximize the power you’re able to create. While pros like Jannik Sinner have mastered the art of shot power, it's not easy and takes years of practice to not only develop a powerful shot but consistently and confidently use it as a weapon in matches.

Leave a comment below if you enjoyed this read / you would want to see similar deep dives into the countless other elements of a powerful forehand!

**Works Cited**

12kgp-Tennis. (n.d.). *Jannik Sinner - 2024 IW Practice Sessions [Court Level, 4k 60fps]*. YouTube. https://www.youtube.com/watch?v=3m80hWeNLqg

Elliott, B. (2006, May). *Biomechanics and tennis*. British journal of sports medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2577481/

*Flexion and extension vector illustration*. VectorMine. (2022, February 3). https://vectormine.com/item/flexion-and-extension-vector-illustration/?srsltid=AfmBOooXDHQB0OVcJDNBHuJBdxi-RRYsi841kYJ1Iq3cjD_p3_CplVwz

Lee, S., Lee, D., & Park, J. (2014, October). *Effect of the shoulder flexion angle in the sagittal plane on the muscle activities of the upper extremities when performing push-up plus exercises on an unstable surface*. Journal of physical therapy science. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4210405/

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