Which technique divides one set into three parts, commonly used for bicep curls?

The correct technique that divides one set into three parts is referred to as '21s'. This method is specifically designed for exercises like bicep curls and consists of performing seven repetitions of the lower half of the range of motion, followed by seven repetitions of the upper half, and finally concluding with seven full-range repetitions. This approach not only helps in targeting different areas of the muscle throughout its range of motion but also increases the overall volume and intensity of the workout for the biceps.

In contrast, Time Under Tension (TUT) involves manipulating the duration muscles are under load during an exercise, but does not specifically segment the set into parts. A Giant Set entails performing multiple exercises sequentially without rest, typically targeting different muscle groups, rather than splitting one exercise into parts. Drop Sets involve reducing the weight after reaching muscle fatigue and continuing to perform more repetitions, which also does not fit the description of dividing one set into three segments. These differences highlight why '21s' stands out as the correct choice for the specific technique mentioned in the question.