The theory used to be that shorter people should play with a double-handed backhand and the taller players, because they are often less mobile but have a better reach, should play single handed.
A good example of this theory is Pete Sampras compared with Andre Agassi, but of course there are always exceptions to the rule – the 6ft 6in Todd Martin had a really good double-handed backhand, and Jim Courier was quite a big guy and his double-hander was quite an unusual technique. It was almost like a baseball shot the way he batted the ball, but of course it was very successful.
Nowadays it is more about what feels most comfortable. A double-handed backhand (for a right-hander) is mainly controlled with the left hand, it is almost like a left-handed forehand. The racket takeback is controlled with the left hand for both types of forehand, but the closer you get to the point of contact the technique differs greatly. For a double-hander the left hand follows through and overtakes the right hand on the right shoulder, whereas for a single-handed player the left hand goes back and acts as a counter point to keep the balance.
In theory the slice should be better for single handers but, to be honest, at the top level there is no difference. Andy Murray’s sliced approach shot or backhand volley might not be quite as good as Roger Federer, Stan Wawrinka or even Grigor Dimitrov's, but it is certainly not a weakness.
Another advantage of the single-handed backhand is that you have a bit more reach, but it is tougher on the return; you need a really strong core to maintain that balance and be able to return well. Most of the juniors coming through seem to be playing two-handed – the likes of Dimitrov and Dominic Thiem are rare as single handers.
It is really tough to say who should hit with one hand or two – ultimately it should be down to what an individual feels comfortable with. My father is a tennis coach and he tried to teach me to play two-handed but he quickly realised that I am a one-hander because I was too slow and my co-ordination wasn’t good enough at that age. Maybe I should have tried again at some point.
Sometimes it is simply down to how a player is taught, other times it is fate. I was teaching a young 13 or 14-year-old in Germany but he broke a bone in his left wrist in a mountain bike accident and had his arm in a cast. I suggested he tried playing with a single-handed backhand and he was really comfortable doing it from the start. It often happens that as a young player grows, their co-ordination changes and the left hand is not doing what it is supposed to, or the timing might be out.
I’ve had times when I’ve suggested a player switches to a one-handed backhand but we ended up changing back because we realised it wasn’t going to work. Making such a major change to your technique is best done at an early age. It is a big step because you don’t know if it is going to work or not. You cannot turn back time; it’s a risk but that is the beauty of the game – you never know the outcome in advance. It’s like playing the lottery.
Sometimes it can just click and the transition phase is very quick, for others it will take longer. But no matter what, it just takes repetition; hitting balls over and over again until it feels natural.