It explains the difference between these two seemingly-identical moves: in the dumbbell exercise, the most resistance occurs when the arm is almost straight. At the beginning of the movement, when the arm is bent there is actually no load on the triceps.

During the cable exercise, the most resistance is when the elbow is bent to 90 degrees. Essentially, what is easiest in one exercise is hardest in another. And that very simple tweak can challenge the muscles in important ways.

Why does switching up strength exercises matter?

Studies back up the impact of loading the muscles differently. For example, research from 2019 found that varying joint angles during a workout can enhance muscle activation. The study involved a group of participants performing nine sets of bicep curls in a neutral shoulder position. The other group performed three sets in the same neutral position, three in shoulder extension and three sets in flexion. The latter group had significantly higher activation despite not doing any more work, suggesting that using different angles can increase muscle damage and growth with more efficiency.

Mixing up your workouts: small tweaks can improve muscle and strength