Murray kicks his legs up in the air and as his legs fall to the ground he pushes his upper body off the ground. Which muscles are taking the strain?
1: Pectorals (the chest)
2: Deltoids (front of shoulders)
4: Transversus abdominis (part of the core muscle group)
Hidden from view, the serratus anterior under the armpit is also being worked
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Andy Murray was pictured doing a strange kind of exercise as he prepared for his Wimbledon quarter-final, what looked like a press-up with a kick. What was the point of it?
Much has been made of Andy Murray's improved speed and endurance on the court, and his new, more honed physique.
Plyometric exercise that builds power in the muscles
It mainly works the chest and triceps
And seeing the pictures of the Scot's face, contorted in agony as he tried to execute a series of complicated press-ups under the guidance of his personal trainer Jez Green, it wasn't hard to see how he's got there. Through pain and hard work.
Although the photographs showed him appearing to defy gravity by elevating his legs while doing a press-up, Murray was in fact kicking his legs up in the air as he pushed his body away from the ground.
So what was he doing?
How to do a Murray press-up
It's commonly known as the "donkey-kick" press-up, says Simon Richman, a physical training instructor with British Military Fitness.
"It's quite an explosive movement. You do the kick when you're down, then push up as your legs are coming back down to the ground.
I wouldn't recommend it for beginners
"It's much more intense than a normal press-up. You need much more strength to support yourself, so it's a much more advanced press-up."
The pectorals (chest) and the triceps do most of the work, he says, but the deltoids (front of the shoulders) and the core muscles - a large group of deep-lying muscles in the torso helpful for balance - are also being exercised.
The explosive strength of the donkey-kick can be replicated by clapping your hands as you press upwards, and doing the clap behind your back is even harder, he says.
In 2008, Murray's physique showed signs of improvement
The Army tends to use a variety of press-ups in its training, and there are many variations, such as "the frog" and "the seal" (also known as the Hindu or the dive bomber), says Mr Richman.
"We wouldn't use the donkey-kick that much because the kick up in the air arches the back and can put pressure on the spine.
"It's not a controlled press-up and you can get the same power in a clap press-up. If done incorrectly, you're unstable for a fraction so I wouldn't recommend it for beginners."
No pain no gain
This kind of exercise is called plyometrics, says personal trainer Ryan Bull. "It involves shortening and lengthening the muscles at speed to generate power and create more force.
"It's normally used on lower body exercises, so for example footballers do plyometrics for their legs.
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"You can use it on the upper body but it's a very difficult movement to perform. These guys are training at a very high level and Andy Murray has obviously been doing these exercises for a while."
One of the benefits for him would be creating power in his serve, says Mr Bull, although his training would also include normal press ups, because these tone the muscle and help with endurance.
"I don't think he's playing for the cameras here. It makes sense that he's doing plyometric exercises like this on a day when he doesn't have a match, because he doesn't want to exhaust the muscles on days when he's playing. Rest is important to get the benefit from the exercise.
"There are lots of different plyometric exercises he could do, like lying on his back and catching a medicine ball thrown by his trainer, then throwing it back at him."
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