You need to be strong to have good style, look at the photos below and try to assume the body positions that these surfers are in and you will soon realize just how strong these athletes are. Take special note of the awkward looking position of the knee and foot of the back leg. If you struggle to assume these postures on dry land then good luck on a wave.
In a way surfing is a lot like dance; we wish to express ourselves through our bodies in a rhythmic and stylish manner in tune with the environment. To allow full and creative self expression requires a strong and supple body – able to assume the desired positions and movements demanded.
If you want to lean back onto your back foot, let the knee fold in and have a relaxed upper body like in the pic below of Alex Knost then you need to develop the strength to do so.
These positions and movements of the pro surfers are natural and primal – what we used to do as children in the playground. If, like these surfers you started young and have kept surfing then you will have maintained the functional strength and mobility needed to surf with style. If you started a little later in life or have been stuck at a desk for some time then you have probably reverted to surfing in postures that are day-day familiar i.e. the chair shaped position we see in the beginner.
There is a solution, regain your natural range of motion and functional strength by daily, smart and progressive exercise. Start by working your way through the Squatting Series.