You can do anything with statistics, but here are some fun numbers.
In 1979 the fastest serve in the world was Roscoe Tanner 136mph
In 2019 the fastest serve in the world is Sam Groth 163mph
That’s a 20% increase!
In 1979 the 100m World Record was Steve Williams 9.9 seconds
In 2019 the 100m World Record is Usain Bolt 9.58 seconds
A 32% increase!
In 1979 the 1500m World record was Sebastian Coe 3,32
In 2019 the 1500m World Record is Hicham El Guerrouj 3,26
A 28% increase!
So in respect of the Serve, tennis has not matched the speed increases that athletics has achieved.
When we examine the Forehand though, we have a very different story:
In 1979 the fastest forehand was the very flat stroke of Jimmy Connors at 58mph
In 2019 the fastest forehand is Andy Murray at 124mph
A staggering 113% increase!
We have improvements in equipment, size and physique and yet the service and forehand have improved at totally different rates.
Clearly, something has changed in the technique of the Forehand Stroke.
The changes in technique to achieve this radical improvement is complex;
Improved use of the torso and therefore rotational force.
Pronation and the dynamic force created through the shoulder, arm and wrist.
The segmentation of the component parts of the stroke creating torque and therefore energy.
I am sure like most coaches I could continue with this list, however, none of this knowledge helps students learn the Modern Forehand. In fact, often the more the players try to understand the strokes the worse they become.