Many commuters on public transit carry heavy bags to and from work, lugging meals and changes of clothes, as well as laptops and reading material. An overly heavy bag can have a painful effect on back muscles and the spine, says Charla R. Fischer, MD, spine surgeon at NYU Langone’s Spine Center and associate professor in the Department of Orthopedic Surgery, in an interview with the New York Post.

Dr. Fischer recommends carrying bags weighing no more than three pounds. Anything heavier can put pressure on spine discs, leading to repetitive stress injuries, muscle strain, and even chronic back pain.

To make your bag more commute-friendly, remove things you don’t need from your bag and wallet, and think about lightweight materials like neoprene or canvas for the bag itself. One-shoulder bags can throw off the spine’s alignment, leading to stiffness or soreness, whereas backpacks distribute weight more evenly across your shoulders. “The top of the backpack should line up with the top of the shoulder blades,” says Dr. Fischer.

Read more from the New York Post.