There are a number of fartlek sessions that are effective for the half marathon distance, but the "fitness elevator" fartlek is a standout. The 7-1 workout includes a session of surges of 7:00, 6:00, 5:00, 4:00, 3:00, 2:00 and 1:00. Begin the session at roughly goal half-marathon pace or even a touch slower. Each successive pick-up should be run a hair faster than the previous with the final two surges (2:00 and 1:00) run at roughly 5K race pace. The recovery after each surge is half the time of the piece just completed (after the 7:00 take 3:30, after the 6:00 take 3:00 etc.).
Minus a 10 to 15 minute warm-up and cool down, the workout portion should take 41:30 (including the recovery intervals).
More: 7 Running Drills to Warm Up the Right Way
Split Progression Runs
Progression efforts are moderate-effort runs during which the tempo continually increases throughout the duration of the run. A favorite half-marathon workout at ZAP Fitness is a 4-mile split progression run. After a 10- to 20-minute warm-up, start the first piece of the workout: Run 1 mile at 15 to 20 seconds per mile slower than goal half marathon pace, gradually working up to your goal half marathon pace over 3 miles (so you'd conclude mile 4 at your goal half marathon pace).
After the opening piece, jog easily for 5:00 before starting the second piece: a 3-mile block. Start mile 1 at 10 seconds per mile slower than goal half marathon pace, followed by mile 2 at goal half marathon pace, then 5 to 10 seconds per mile quicker than goal half pace for the final mile.
More: 3 Half Marathon Predictor Workouts
This is a tough session and should be executed two to three times during the final seven to eight weeks of race preparation.
More: 3 Progression Runs to Reach Race-Day Success
Stimulate Anaerobic Threshold
Anaerobic threshold (AT)—also called the lactate threshold—is the effort level that falls between aerobic and anaerobic training. AT is the point during exercise when your body switches from aerobic to anaerobic metabolism. During aerobic metabolism, your body creates energy by burning carbohydrates and fats in the presence of oxygen, and produces carbon dioxide and water as byproducts (breathing and sweating). Most of our daily activities are fueled this way.
