When a muscle contracts, it shortens. Take the biceps for example. Without getting too technical, the biceps are attached at the forearm and shoulder. When your biceps contract, they shorten and bring those two points closer together. When you rest, the muscle returns to its normal length, and the two points move farther away. Constantly contracting your biceps over a long period of time would cause them to get shorter, even at rest.
As the structure of the back is complex and the reporting of pain is subjective and affected by social factors, the diagnosis of low back pain is not straightforward. While most low back pain is caused by muscle and joint problems, this cause must be separated from neurological problems, spinal tumors, fracture of the spine, and infections, among others.
How to do it: Loop a resistance band around your ankles and lie on your right side, supporting your upper body with your right hand and forearm. Extend both legs out, feet flexed. Brace your abs in tight and lift your top leg up to hip height, rotating your leg to turn your toes down to the floor, keeping tension on the band. Lift your leg slightly higher than hip height, pushing against band, with heel rotated up to the ceiling. Return to hip height. Repeat 20 times quickly and then switch sides.
Some of these red flags are much less red than others, especially depending on the circumstances. For instance, “weight loss” is common and often the sign of successful diet! (Well, at least temporarily successful, anyway. 😃) Obviously, if you know of a harmless reason why you have a red flag symptom, it isn’t really a red flag (duh!). But every single actual red flag — in combination with severe low back pain that’s been going on for several weeks — is definitely a good reason to get yourself checked out.