Flexibility is the capability to bend, stretch, and twist. All of these can occur in a surfing session. If a surfer gets thrown off the surfboard or finds himself somersaulting above or below water he doesn’t want to have an injury. A pulled muscle could be dangerous in rough conditions.
I ask students to see if they can put their palms on the ground without bending their knees. This is just an elementary test of elasticity but most people cannot do it. This means they will have a problem putting their foot flat on the surfboard during the pop up to stand up.
One problem for people who are sedentary is the muscles of the hamstrings, buttocks, and lower back get tight. People who exercise including running and triathlons are often tight because those exercises tighten the muscles adn the participants don’t take time to stretch afterward.
I find that three of the best exercises for mobility are burpies, deadlifts, and squats. These reach the biggest muscles and add strength to the core. They allow me to put my palms on the floor and do great pop ups without doing stretches. Yet stretching and twisting at different angles can help prevent injuries from bad falls. I see students do flips and ugly falls I can’t believe they could perform.