To break the bar, the person applies a torque (moment). This torque is generated by the pair of forces exerted by the palm and fingers at opposite ends of the fist grip.

If the maximum force the hand muscles can exert is \( F \), and the width of the grip is \( b \), the applied torque is roughly:

\[ \tau \approx F \times b \]

To break the bar most easily, one needs to maximize this torque \( \tau \). Since the muscular force \( F \) is limited by the person’s strength, the only geometric parameter that directly amplifies the torque is the lever arm, which in this case is the width of the fist, \( b \).