Mason joined the water polo team at his school. As part of his conditioning, Mason's coach requires a 25-minute run during practice. Mason's heart rate reaches 125 beats per minute, but his target heart rate zone is 138—183 beats per minute. What should Mason do to get the most benefit for his heart?

Increase the amount of time he runs
Increase the speed at which he runs
Decrease the amount of time he runs
Decrease the speed at which he runs