Month: August 2020

Journal, Table Tennis

Improve your Ping Pong skills by adding a skilled backhand (shakehand)

Reading Time: 4 minutes

Up until recently, I have never got an effective backhand for my ping pong skills set. It’s been a weakness, to say the least. With such an obvious weakness, my opponent can just continuously press my backhand and my strong forehand never sees the day of light. Since I got a table for me to practice at home, I have been practicing almost daily to get a handle on my backhand, and here is what I learned. If you read Chinese, here is a youtube video. Youtube Video.

  1. Don’t start practicing backhand drive/fast-loop first, even though that’s what the top players are using in matches right now. When I watch the games amongst top players, this is the technique I see the most, during their practice and actual competitions. So naturally, I want to practice this move. But this move is highly dependent on the wrist but equally dependent on the forearm. It’s very easy for a beginner to only use the wrist and forget about the forearm. The result will be the ball is spiny, but it hit the net a lot. Or you are going to miss the ball because the potential contact area between the paddle and the ball is too small. The correct way is to have a foundation in pushing first, using a lot more upper arm.
  2. Start practicing pushing the ball using the upper arm. This is done by holding your wrist to about chest level. Hold the wrist and forearm at the same angle to the chest, and only extend the upper arm back and forth. Start with your paddle touching the chest, as you will need plenty of “runway” to hit the ball with enough force. Remember to bend the wrist slightly, so the surface of the paddle backhand is parallel to the chest. This will become a good foundation for all later moves. Notice by holding the wrist to chest level, your shoulder is going to get tired a lot more frequently. This is fine at this stage because it will form a good habit for you to hit the ball will a higher percentage, as it’s closer to your eye level. The ultimate form will be slightly different as you learn how to relax.
  3. Practice for relaxing during the game. When I started playing ping pong, I was always tense when trying to hit the ball. Muscle tension is a good fight-or-flight response when physical activity is needed, but it’s not good for hitting ping pong balls effectively. Coaches always ask me to relax, but I was never able to do so in a game, same as when anybody tells anybody to “relax”. So you actually need to learn how to relax. Start by grabbing your paddle loosely, as if you are almost going to drop the paddle. But make sure you bend the wrist and make the paddle parallel to the chest. Without moving the wrist, or forearm, find a way to hit the ball by moving the legs, waist, shoulder, and upper arm, all at the same time, to hit the ball. This is against intuition because adults will use the smallest amount of muscle to finish a task. But “hit ball with your body” is good in the long term to make upper body muscle fatigue occur less frequently and reduce the chance of injury. Construct yourself to relax during practice, and if you do this enough times, you will be relaxed during a match. The goal is to relax during most of the match, but tense up when you actually hit the ball.
  4. Once you have enough practice of pushing, and able to draw paddle back to your chest fast enough in advance of hitting the ball, then you can practice drive/fast-loop. The key to this move is you have to hit the ball fast enough in four different aspects. I. You need to get the wrist drawback to your chest, like a spring. This time not by moving the upper arm, but by rotating wrist, so your thumb is 90 degrees with the forearm. This is because you are not going to have time to use the upper arm in a match. II. At the same time, you need to use the elbow as a pivot point and rotate the forearm towards the chest. In the beginning, you paddle will touch your chest, this is perfectly fine. You can hit the ball, by rotating the wrist and forearm at the same time, towards the front right side. Stop swinging when the forearm and hand are 90 degrees with the chest. III. You need to hit the ball when it just bounced off the table before it reaches the highest point, normally much earlier than your other shots. This way you don’t actually need to distinguish whether the ball is no-spin or topspin because the topspin have not started to take effect yet. VI. Also need to actually hit the ball kind of fast, it will hit the net if you hit too slow because your paddle angle is actually more shallow or flatter. Because you are not hitting the ball with the paddle perpendicular to the table, the maximum chance of success is naturally going to be less. So it’s a more risky shot than just push the ball. But because of its high power and spin, your opponent is not likely to return it, even at the world level. The overall effectiveness is high enough to use regularly in matches. The hard requirement is you need good leg movement to get to the ball, with enough time for you to bend knees, rotate the wrist, and hit the ball before it reaches the highest point. Otherwise, it’s going to fly away and miss the table.
  5. If your steps are not fast enough, the alternative is to hit the ball slower, use less forearm strength, when the ball already reached the highest point or started falling. Your return will be spiny but lack the high speed and power in the drive/fast-loop move.

Now you learned the secret of drive/fast loop backhand using shakehand grip, go pratice!

AI, Journal

Causal Inference Book

Reading Time: < 1 minute

Recently started reading the causal inference book, Counterfactuals and Causal Inference, by Stephen Morgan and Christopher Winship. Link to book. This book was recommended by researchers at the ACL conference. I personally found Pearl’s 2009 book to hard to read and his popular book less detailed. This book started with the history and included other researches done in the field. So after I get partly through the backdoor criterion section, I decided to program it using networkx. I have just gone through the part where I check if the backdoor criterion is satisfied. https://github.com/yangliu2/frontal Will implement the part that will recommend variables to condition to prove the causal relationship.