Thank you for your query. I m glad to hear you are taking care of your health. I would like you to clarify a few things for me. 1) how old are you? 2) about the pain- when and how did it start? where is it exactly ( there could be a starting point of maximum pain which also be felt in other areas called radiating pain)? you mentioned muscles, is it just lower body muscles? 3) what makes it better? you mentioned that sitting and walking/ standing for long makes it worse. 4) what other symptoms do you have? - numbness, loss of sensation or burning sensation? 5) any history of a fall or injury to your back? 6) have you lifted weights? anything more than 8 kg ( not just for a workout, even if it is for professional reasons). or lifted weights above you head? Based on what you have described, I would like to rule our nerve compression due to spinal disc prolapse or spondylosis an lumbar spondylitis. your spine is made of a bony cage that protects the spinal cord. the bony cage is further made of several vertebrae with discs ,that act as cushion and improve flexibility, between each pair of vertebrae. the spinal cord gives out nerve branches that supply the sensory and motir( movement) function of the body. these pass through each pair of vertebrae when there is anything putting pressure on the nerves, it can affect you muscles and cause pain, weakness and numbness. causes include a slipped or worn out disc, injury to the vertebrae. narrowing of space between the vertebrae. I would recommend a consult with your physician to assess for spinal nerve compression and further refer you to either a orthopedic surgeon or neurologist based on their findings. If negative for nerve compression, other cause for nerve and muscle damage have to be investigated. hope I ve helped. please let us know if you need any clarification. wish you good health