Bicep muscle strains happen because of various reasons.
Practicing violin, which requires repetitive low load movements can lead to multiple small bicep muscle strains. Especially if the body is overwhelmed because of long hours of practicing. This high volume of repetitive movements combined with fatigue are a dangerous combination. The risk increases exponentially with every 10 minutes of practice after fatigue starts to set in.
The severe stiffness that you feel after a long session comes from micro-trauma, where a small amount of tears are in the muscle. Now every 10 minutes longer will increase that amount of tearing and the micro-trauma will turn into macro-trauma. This we call a muscle strain or tear.
Doing cross-fit with heavy weights, without being used to the extreme increase in load, can tear your bicep muscle. This could also be from lifting heavy furniture or appliances.
The upper arm will be sensitive to touch and certain localized points may be more tender. Those trigger points can also refer into the shoulder region or down into the elbow or lower arm. A very sensitive spot is right on the knob in the front of the shoulder where the shorter part of the bicep muscle attaches.
The sudden drop of a heavy object after anticipating something light may cause discomfort in your bicep muscle. This is a frustrating way to attain an injury seeing as your muscle can technically bear the weight, it simply didn’t expect the load to be heavy and thus delayed the fiber reaction time. You will be able to tell the exact moment your pain started and the exact area where you felt it. Mostly it is a constant discomfort for a couple of days that should be resolved within a few days. It may also happen at the gym when heavy free weights are used, or during quick movements and especially in eccentric training (i.e. negatives).
After having gymed very hard, your muscles will feel sore and stiff. If you continue training hard under these conditions and try to straighten your elbow quickly, or with a load, without having warmed up properly, the muscle fibers will tear where they were still recovering from the previous work-out. One forceful elbow straightening can also be the reason for an over-stretch, where the triceps (the muscles at the back of your arm) contract stronger than your biceps can control and then this causes the elbow to straighten more than it should. This sort of pain feels like a constant niggle if neglected in Rehab.
A direct blow to the bicep muscle causes the elbow to be forcefully hyper-extended.
The chances of having your bicep muscle torn after an elbow or shoulder fracture is very likely. Sometimes the attention to the fracture overshadows the bicep muscle tear, but when the fracture is healed, you are left with the aftermath of an unhealed tear.