How does a running martingale differ from a standing martingale?

The correct answer highlights an important functional aspect of a running martingale in its design and application. A running martingale adds leverage to the bit, allowing for more effective communication and control between the rider and the horse during movement. This device features a strap that attaches to the horse's girth, with two smaller straps that connect to the reins. As a result, when the horse elevates its head, the running martingale exerts pressure on the reins, which encourages the horse to lower its head and maintain a more balanced frame. This leverage can be particularly beneficial in disciplines requiring a horse to be responsive and well-rounded in its movements.

In contrast, while a standing martingale also serves the purpose of preventing the horse from raising its head excessively, it does not provide the same level of leverage since it remains fixed in place and doesn’t change with the horse’s movements. As a result, it limits the horse's ability to raise their head but doesn't exert the adjustable control offered by a running martingale. The other options either mischaracterize the function and purpose of these devices or apply restrictions that do not universally reflect their use in equestrian practices.