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.
Many people eat two or three meals a day and the occasional protein shake (when they remember), and then wonder why they're not putting on weight. To increase muscle mass, you have to have excess energy (calories and protein) in your system - supplied by regular small meals throughout the day. Most people have no idea how many calories they need. Do you? You may find that eating until you're full is not enough, especially if you're eating the wrong sort of calories (i.e. all carbs and no protein!). Protein is the priority followed by carbs then fat, but all are important and play a part in building mass and size.
Visit your doctor. Pain that persists for more than two to three days should be examined by a physician. Your doctor will conduct a medical history, physical exam and possibly, imaging studies to help make a diagnosis. Follow your doctor's instructions carefully -- they may include rest, use of crutches, physical therapy, stretching or anti-inflammatory medications.
If the iliopsoas and other hip flexors are tight, they pull down and forward on the pelvis, which tilts the pelvis forward and compresses the lower back. Picture a man standing with the front of his pelvis tilting forward and his tailbone lifting. To stand upright, he has to overarch his lower back. Anatomically, this is called hyperextension; commonly, it's called "swayback." Prolonged standing or sitting in this position increases pressure on the facet joints of the lower spine, which can contribute to arthritis in those joints.
I HATE that the resistance training community can be so tribal. I have been preaching to bodybuilders for years about the benefits of powerlifting, or Olympic lifting or kettlebells or even Crossfit style conditioning and many have been receptive. Learn from each other and achieve levels of fitness you simply could not have otherwise. Don’t brush off bodybuilding wisdom…it could be the missing factor in your program.