Hi, Thank you for providing the brief history of you. A thorough clinical examination is advised. As you are good at your exercise and now facing pain in legs while climbing the stairs, one thing should be understood that too much of anything is not good. This is the first thing in the fitness training. Also, gym injuries are more common and may come with any movement as well. If the pain in the leg is tingling, numbness, etc than it could be related to the spine issue for which a thorough assessment is advised. Also, you need to give a break in your exercise plan, as too much of anything will land up into injury. Going slow and steady will help improve the overall health and fitness. In my clinical practice most patients come having gym injuries and after thorough assessment, they respond well to the new exercise plan to be followed in the gym. Regards Jay Indravadan Patel