What is the purpose of a lunge line in training?

The purpose of a lunge line in training is primarily to exercise a horse without a rider. When using a lunge line, the horse is free to move in a circle around the handler, which allows for the development of the horse's balance, strength, and responsiveness. This method of training is beneficial for evaluating the horse's movement, attitude, and overall fitness. It provides an opportunity for the trainer to work on the horse's gaits, transitions, and basic groundwork commands, all of which contribute to the horse's training and development.

While the other options describe activities that may involve a horse, they do not accurately reflect the specific purpose of a lunge line. Teaching horses to jump typically involves different training techniques and equipment. Leading horses for grooming is best achieved with a regular lead rope, and performing dressage movements generally requires a rider on the horse, which is not facilitated by a lunge line. Thus, the use of a lunge line is distinctly focused on exercising the horse independently, promoting both physical fitness and skill development.