This a great workout to improve V02 max and aerobic capacity. Warm up for 1-3 miles (depending on fitness level) and then begin the 4 x 2 miles at a pace close to your fastest half marathon speed. Jog 2 minutes between sets. Be strict on the rest. Finish with another 1-3 easy miles to complete the workout. Cycle this workout in every 3-4 weeks in your training block. You’ll see huge improvements in your long distance speed.