You know what it feels like to run comfortably -- comfortable! -- and you're likely also familiar with the burn of going all-out. But what about the range of paces that lie in between these two extremes?

Workouts that target that middle ground -- often referred to as "tempo runs" -- should be part of your weekly routine, whether you're running for fitness or looking to set a personal record. They build both slow- and fast-twitch muscle fibers, which leads to gains in speed and endurance, says Samantha Clayton, Olympic sprinter and former women's sprint coach at Pepperdine University in Malibu, California. And in-between runs develop capillary beds (which provide oxygen to working muscles) better than easy or hard runs do, says Ryan Warrenburg, head coach for ZAP Fitness-Reebok Coaching and USATF Level 1-certified coach in Blowing Rock, North Carolina.

Middle-ground runs also benefit your brain. These workouts help you understand how different paces feel, putting you more in tune with your abilities (and limits), Clayton says. They also build mental endurance and toughness, an asset whenever you're pushing yourself to go longer or faster than you've gone before. With all these perks, it's wise to spend some time running between easy and all-out.

MORE from Runner’s World: Find Your Tempo

Here are a few ways to do it.

Lactate-Threshold Run

What It Is: A workout at the pace at which your body produces and clears lactate (a metabolic by-product of exercise) at a close-to-equal rate. Many runners erroneously blame lactate, a substance the body clears fairly quickly, for postrun soreness, says Alicia Shay, a Flagstaff, Arizona-based runner for the Nike Elite Trail Team, coach for the Run SMART Project, and coach and nutrition consultant for Hypo2 Sport Performance Center. In fact, your body can use lactate as fuel for muscle cells. You start to slow when it accumulates faster in the blood than your body is able to clear it. (Lactate itself does not cause fatigue, but it builds up in tandem with by-products that do.) When you run at lactate-threshold pace (what most people mean by "tempo-run pace"), you're training your body to hold the fastest speed at which your blood lactate levels stay fairly steady for a longer period of time.

The Workout: Warm up with 15 to 20 minutes of easy running. Run 20 minutes at a pace you could sustain for an hour-long race. (You're doing it right if you can barely talk, Warrenburg says.) Cool down with five to 10 minutes of easy running.

MORE from Runner’s World: More Than Half of Americans Limit Activity Because of Foot Pain

Race-Pace Run

What It Is: A workout in which you practice the pace you're hoping to hit during a marathon or half-marathon. If you're prepping for one of these races, these workouts are a crucial way to rehearse. "You're teaching your body how to efficiently utilize fats and carbohydrates at your desired pace on race day," says Chris Heuisler, RunWestin Concierge and RRCA-certified coach in Boston. Plus, race-pace training lets you practice fueling at goal pace, which helps you learn what goes down smoothly.

The Workout: Every three weeks, sub out your normal, easy-paced long run for one with a race-pace segment. If you're training for a half-marathon, warm up for two miles, run at race pace for six to eight miles (depending on where you are in your training plan), then cool down for a mile. If you're training for a marathon, work a race-pace block of six to 14 miles (after a two-mile warmup) into your long run.

MORE from Runner’s World: How to Prevent Marathon Fatigue

Progression Run

What It Is: A run that starts easy but gradually increases in speed. These workouts teach you to be mindful of your pacing, which can help you avoid going out too fast (and burning up precious glycogen stores too early) in a race, Warrenburg says. Whether you're planning to race or not, the occasional progression session can bust everyday-run boredom--stepping up the pace at regular increments keeps your body challenged and your mind engaged.

The Workout: Warm up 15 minutes. Then, start a 30-minute progression run: Speed up by 10 to 15 seconds per mile every six minutes until you're running at about threshold pace by the last six minutes. Cool down five to 10 minutes.

MORE from Runner's World: How to Survive a Tempo Run in the Heat

Like us on facebook, follow us on twitter, and subscribe to our YouTube channel.

1939 Dodge Still Runs -- As A Grill