If you're getting ready for a running event, I got some bad news: You're getting slower. Most people train by doing everything at once. Long runs! Sprints! Intervals! Weight training! But that's a recipe for burnout. A recent study even found "American runners have never been slower." There's a smarter way to slash time off your miles.

Your body has two ways to use energy: "aerobic" and "anaerobic." The aerobic energy system is built for hours of endurance, while the anaerobic system is built for intense activities and only lasts a minute or so. (Your body generally transitions from aerobic to anaerobic after reaching 150-160bpm.) To make gains in one energy system, your body has to sacrifice the other. If you take a "kitchen sink" approach with your training, you won't improve much in either.

Instead, focus on one energy system at a time for 4 to 6 weeks, which is called a training "block" or "phase." When you improve one correctly, those gains last for a long time—even as you shift focus to the other system. But you have to do it just right. Here's your guide.

For the First Training Block:

Start by boosting your aerobic side. Why? Because it's the foundation for everything. On endurance runs, you rely on your aerobic system. When you do a hard sprint (which is anaerobic), you still need your aerobic system to recharge your batteries afterward so you can sprint again without puking. It also helps build a bigger and stronger heart so you can pump more blood, and it makes your muscles better at absorbing oxygen.

Bottom-line: To run the best race of your life, you have to improve how hard you can push yourself before crossing the line into anaerobic. Here's how:

  • During runs: Keep your heart rate between 130-150bpm (the aerobic range). Focus on increasing your speed or distance while staying in this range.
  • Use Fartlek runs: Run in your aerobic range and periodically sprint for a few seconds. This increases how hard you run while staying aerobic.
  • In the weight room: Do heavy exercises like squats, lunges, and deadlifts while keeping your reps low to increase your basic strength and muscular endurance.

For the Second Training Block:

Once you have a strong heart and aerobic system, it's time to gently increase the speed and distance of your runs. The second block is where you start targeting your anaerobic system by adding intervals to your training. Here's how:

  • For runs: Do 30-second sprints, and take as much time as you need to completely recover between them. Gradually add more sets.
  • In the weight room: Replace your strength work with plyometric and explosive exercises—box jumps, power cleans, jump squats, kettle bell swings, etc.—to improve the endurance of your fast-twitch muscle fibers, which are responsible for speed and power.

For the Third Training Block:

In the third block, put everything together to hit your target speed and distance. This is where you peak, so start this block a few weeks before your race so you hit the peak at the right time. Stop your strength training and focus entirely on getting to where you want with your race times. As race day gets closer, gradually reduce how often you run so your body and legs are fresh for the big day.

Now, enjoy the race of your life.

Anthony J. Yeung, CSCS, is a fitness expert and founder of unlockyourfitness.com.

From: Esquire US