Originally Posted by toly
I think that Serena doesnít use right arm bicep significantly, because she doesnít bend additionally her elbow around and after impact. See picture below.
[picture deleted - see quoted post above]
About straight linear motion: She applies bend elbow FH technique, because she can use ISR, the fastest motion of the arm, to build translational motion of the ball. In case of straight arm ISR can create spin and practically zero translational speed. Thatís why almost all WTA players use bend elbow FH.
I think you are right, but it becomes complex when you factor in the wrist layback angle, different grips, etc. Best to experiment and choose what works for you!