Most combat sport athletes do not have big biceps, and bicep size does not correspond with the fighting skill.
However, bicep strains are common in both striking and grappling.
They can happen while punching, they can happen from joint locks, and they have a tendency to become chronic if not addressed, many fights have been canceled because boxers injure their biceps during the training camp.
Training your biceps directly is functional, the stronger your biceps muscle, the less likely you are to strain it.
Incline bicep curls are my favorite exercise for training bicep strength and flexibility
The slight incline and sitting upright fully stretches the bicep muscle. You could use a deeper incline if you want, this high incline works for me
Doing even one set of the exercise to positive failure each week would have benefits.
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