Usually, an acute tear happens after some form of forceful move or an eccentric contraction, which means the muscle is contracting at the same time it is being lengthened. For example, when you try to catch a heavy object falling over. The biceps can tear at the lower end where there is only one tendon (distal biceps rupture) or at one of the other muscles at the upper end (proximal biceps rupture). The distal biceps rupture is commonly an acute tear and the proximal biceps rupture is more common with wear over time.