With the bicep curl

, the concentric (work) phase occurs when the dumbbell is raised towards the shoulders, and the eccentric phase is when the dumbbell is lowered back down.

Which joint action occurs if the biceps contract eccentrically?

it contracts. This is usually associated with controlling or slowing down a movement. When the biceps concentrically contracts to cause flexion at the elbow, the triceps eccentrically contracts (lengthens) to control the movement.

Are biceps concentric or eccentric?

The best example of both concentric and eccentric movements is the biceps curl. When you curl your arm up toward your shoulder, your arm muscles contract (a concentric movement). When you lower the weight back toward your waistline, your arm muscles lengthen (an eccentric movement).