Topic approved.

It's quite common with incorrect riding posture. Typically happens to a lot of riders after long hours on the saddle when we slack off a little and unknowingly start putting more weight on the handlebars and end up with hurt wrists and shoulders.

The correct way to sit on the bike is tighten your core slightly, keep your back straight and grab the tank with lower body. The grip on the handlebars should be light but firm. Shoulders, wrists relaxed and elbows slightly bent. When riding, lower body & torso needs to do a lot more work than upper body.

Fitness is also necessary to ride a bike for long hours. Regularly working on squats, planks, back stretches, shoulder/wrists mobility will increase your tolerance and make riding more pleasurable.