What does a running martingale help achieve?

A running martingale is a piece of equipment used in horseback riding to enhance control over the horse's head. It is specifically designed to prevent the horse from raising its head too high, which can be beneficial for maintaining control during various riding activities. By attaching to the horse's reins, the running martingale provides a subtle influence that allows the rider to guide the horse’s head position more effectively without applying constant pressure.

This piece of tack is particularly useful when jumping or during fast-paced riding, where maintaining the horse's balance and responsiveness is crucial. It helps ensure that the rider can communicate effectively with the horse while allowing the horse some freedom of movement in its neck and head. The other options do not accurately represent the primary function of a running martingale, as it is not primarily intended to increase speed, enhance comfort during jumps, or modify the flexibility of the reins.