How can rider weight affect a horse's conditioning?

When considering how rider weight affects a horse's conditioning, it is important to understand that excess weight can indeed hinder performance. A heavier rider places additional physical demands on the horse, which can impact its ability to move efficiently and effectively. This extra load can lead to increased fatigue, slower response times, and a greater risk of injury for the horse during training and competition.

Moreover, a horse's conditioning program is designed to build strength, endurance, and agility. When a horse is carrying more weight than it is conditioned to handle, it may struggle to perform at its best, especially in disciplines that require agility and quick movements. This can also affect the horse's overall fitness levels as it expends more energy than usual to accommodate the extra weight, which can slow the progress in conditioning.

The other options suggest that excess weight could have either neutral or beneficial effects on the horse and rider's performance, which does not align with the understanding that the horse's ability to perform efficiently is typically supported by a rider who maintains a weight that’s proportional to the horse's size and fitness level.