Elbow position during topspin

Hi coaches!

When i  try topspin with 90 degree angle at the elbow(at starting position), the  ball is very heavy. Then i must spend huge amount of energy. But when i try topspin with straight angle at the elbow, it is very easy to throw the ball over the net.  Noticed that Ma Long starts with straight angle at the elbow when he loops. What are your thoughts? Since i am re-learning topspin i don't know how to practice correct...

Hi Ardak,

For more power start with the arm straight.  For more control you can start with it more bent.