One of the keys to the modern tennis game is topspin production. In order to hit a heavy ball with consistency, topspin helps to keep the ball in. During its travel through the air, topspin pushes the ball towards the ground due to the Magnus effect.
That is why ambitious tennis players seek to increase their topspin production. But how can one create topspin, and what is the most important factor?
Tennis coaches often tell their students to “brush upward” the backside of the ball with the racquet. However, “brushing upward” is not easy, especially if the ball is hit fast. The quicker one “brushes upward”, the narrower the time window for a centered shot becomes.
There is another problem with the “brushing upward” metaphor. To “brush” suggests the ball should be hit with that brushy sound which is created when strings literally brush the ball. One can also hear that sound when juggling the ball with the racquet in front of oneself while trying to apply sidespin to the ball by moving the racquet mostly sideways.
That sound is no good. It arises when the strings do not bite into the ball but instead “brush” it. Science teaches us that topspin is mostly created if the strings bite into the ball, which makes the strings move in the direction the ball pushes them, and then they snap back. The “snapping back” causes much of the modern topspin. But for this to happen the strings have to bite into the ball! There is a very good article about this at Tennis Warehouse University.
While “brushing upward” is at most a bad metaphor, the “upward” part is certainly heading the right direction. Though it is possible to hit topspin with a downward movement (think of an easy put-away), the general idea of moving upward is good.
But moving “upward” is not the only thing that matters. In fact, there is something more fundamental to topspin production. Moving “upward” is just one aspect of three main properties that matter:
- The speed and angle of the incoming ball (i.e. is the ball rising or falling)
- The speed and the upward motion of the racquet head
- The racquet head tilt (i.e. at what angle does the racquet head lean forward)
You can see the three aspects in this picture, which is a blend of two frames of a slow motion video of a famous tennis player.
The yellow arrow shows the incoming ball trajectory (1). The grey arrow is the movement of the racquet head (2). The blue arrow is the racquet forward tilt (2). You can see the entire video here and the time of ball impact here.
The above stroke results in quite some topspin. It is difficult to say how much, because I do not know the exact speed the video is shot at. I guess it is around 250 frames per second, which means there is a frame every 0.004sec. Counting the frames between a full ball rotation, I get 10 frames. This would result in one full ball revolution every 0.04 second, equalling 25 revolutions per second, which is 1500rpm. This is very reasonable, as the average topspin production of Roger Federer is way above 2000rpm according to many sources, for instance this one.
From the picture above we can clearly see that the upward motion is not extreme. It measures about 15 degrees, which corresponds to 25 centimeters upward for every meter forward.
But notice the racquet head forward tilt, which is also about 15 degrees (compared to a vertical line toward the sky). As we will see in another post, Roger Federer could have achieved the same amount of topspin by rising his racquet movement angle to 30 degrees while applying no racquet head tilt. But then he would have had a hard time hitting a centered shot, as the upward velocity would have doubled and thus the time window for an acceptable shot would have halved. In addition to that, ball forward speed would have declined by about 10% and the trajectory of the ball would have been much higher over the net. The higher trajectory could easily have resulted in hitting the ball long, so he would have lowered racquet head speed, which in turn would have lowered topspin.
This makes it obvious that the racquet head tilt is very important. How everything is connected will be shown in the next post.
So, what is the bottom line? This is how we can increase topspin:
- Do not brush the ball, but make it bite into the strings
- Do not only focus on racquet head upward movement, focus on racquet head forward tilt as well!