When you perform a split step and take that small hop, you aren't looking to get a ton of air. You only want to get about an inch high off the tennis court. What's critically important is that when you land, your weight needs to come down and load up in your legs. When you come down from your split step, you want the weight to equally compress both of your legs like springs so that you can push off explosively in the direction of the tennis ball. This is much more effective than being flat-footed when your opponent hits you the tennis ball.
Now that we know the split step is mechanically just a small hop, let's talk about when you want to split step and how you time your split. You want to split step every single time your opponent is about to make contact with the tennis ball. Since you don't know where your opponent is going to hit it, you need to be able to move in any direction as explosively as possible, and performing a split step is going to allow you to do that.
Timing the split step correctly is slightly tougher than just performing the motion. The key is that you want to be back on the ground, with your weight down and your legs loaded up (so you are at your most explosive) at the exact moment that you realize where your opponent has hit the tennis ball. This of course means that the ball will be well off his strings. Depending on your own reaction time and how hard your opponent has hit the tennis ball, it may be crossing the net toward you by the time you realize where it is going. Knowing that you want to be down and loaded up after your opponent has hit can and should help you time the rest of the motion. Practically speaking, you will generally be just coming off the ground, or in midair, at the precise moment your opponent is making contact with the ball.
?Articles の中の、More efficient movement in tennis
http://www.jezgreen.com/articles/more-efficient-movement%20in%20tennis.htm
“hip opening”が凄く重要なことを説明している。(リターンではそれが唯一の肝!とまで言っているぞ)
“hip opening”というのは、日本語に直すと「股関節を外旋させる」になると思う。
外旋というと、むつかしく聞こえそうなので、「股関節を開く」と言うことにする。
股関節を開いてから、骨盤を回転させる のが、正しい(効果的な)順番のようだ。
このJez Green という人は、November 2007 - 2008にかけて
Andy Murray の Physical Conditioner を担当し、去年の全米あたりからマレーが非常
に好調なこと、マレーのフットワークが Jez Green の教え通りに見えることから、
Jez Green の教えの正しさが証明されているのではないかと思う。