by Mark Eller

In Running Tough: 75 Challenging Training Runs, Boulder-based writer Michael Sandrock takes the favorite workouts of elite runners and renders them into an entertaining book. Some of the workouts-like Czech legend Emil Zatopek’s “100 X 400 Meters” (that’s 30 miles of track work in one session!)-verge on the superhuman, while other workouts in the book can be easily adapted for mortals.

Chapter 6 of Running Tough is devoted to tempo runs and includes testimonial from University of Colorado cross-country coach Mark Wetmore: “The greatest training effect comes right at your anaerobic threshold. That’s where you get the most stimulus for adaptation.”

The key to these workouts is running at the proper intensity. In short, tempo runs are a sustained effort at a “comfortably hard” pace. Some tempo workouts call for a series of shorter efforts, which makes them easy to mistake for speedwork or anaerobic interval training.

Whether tempo work is divided into blocks or done as one sustained chunk, the goal is quite different from high-intensity intervals. While most interval workouts push into the anaerobic zone, tempo runs are designed to teach your muscles to work aerobically as long as possible. For that reason it’s vital that tempo runs don’t exceed the “comfortably hard” level of exertion.

Avoiding the Anaerobic Plunge
When you run at an easy pace, your muscles convert stored fuel into energy in an almost entirely aerobic state. Increase your pace and you’ll gradually approach the point where your muscles can no longer handle the stress aerobically; to meet the increased demand for energy production, you’re forced to supplement the aerobic effort with anaerobic energy production, or glycolysis. An unfortunate side-effect of glycolysis is buildup of lactic acid, which when produced faster than it can be cleared, impairs muscle-cell contraction-and hurts.

Once you’ve “gone anaerobic,” you’re running on borrowed time. Elite athletes can withstand higher levels of anaerobic activity than less-fit ones, but everyone eventually succumbs to the muscle-seizing onslaught of excess lactic acid. Unless you reduce the workload to the point that your muscles can  clear lactic acid faster than it is produced, you’ll reach a point where the effort becomes impossible to sustain.

During a tempo run, you should push yourself just hard enough that your muscles begin to increase the production of energy from anaerobic metabolism. You should hold this effort for a predetermined amount of time, then wind down the workout with some easy running.

Tempo Runs for All Occasions
The threshold level of exertion is best thought of as a range, not a precise pace or a narrow heart-rate zone. Since your heart is responsible for driving oxygenated blood to your muscles (to keep them functioning aerobically), your heart rate climbs along with your level of exertion. But heart rate isn’t an exact indicator of what’s going on in your muscle cells during a run. For that reason, “going anaerobic” can’t be expressed as a precise number of heart beats per minute, but it will generally fall near the anaerobic, or lactate threshold, pace.

“For most runners, a tempo-run pace will range between 10K and half-marathon race pace,” says Neal Henderson, Coordinator of Sport Science at the Boulder Center for Sports Medicine and a former elite triathlete. “Pushing harder than this level during a tempo run can be counterproductive. Save 5K-race-pace and faster efforts for interval sessions and all-out efforts for races.”

Instead of gauging your tempo runs by a specific heart rate, simply strive to attain a challenging level of effort. Tempo pace means that running just a little faster would require a race-like effort, but running a few notches slower would feel like an average workout.

Going the (Right) Distance
Trail-running guru and Liberty University exercise-physiology professor Dr. David Horton believes in the value of tempo runs and shares this advice: “The duration of the session depends on the length of the event you’re training for. Training for shorter races-anything under an hour-means you should do tempo runs on the high side of anaerobic threshold, at an intensity that’s quite close to what you’ll achieve in the event. But if multi-hour races are your thing, tempo runs should be done at a slightly more comfortable pace.”

Horton suggests that races under an hour call for once-a-week tempo runs lasting 20 to 30 minutes, plus a brief warm-up and cool-down jog. Training for ultra-distance events calls for tempo runs ranging from 45 to 90 minutes, and can be worked into a multi-hour training run. These workouts, he suggests, are best done every other week. “Tempo runs are strong medicine,” warns Horton. “It’s asking for trouble to do more than one long, hard run a week.”

Horton believes that the rolling hills near his Virginia home provide a perfect format for fast-paced workouts. “I look for mountainous runs of eight to 10 miles, and really try to fly on the downhills,” he says.

Vail, Colorado’s Josiah Middaugh-one of the country’s best middle-distance trail runners and a top-ranked off-road triathlete-also relies on tempo runs. Middaugh does a weekly tempo session while he’s building aerobic power during his pre-race season. One month before his key racing schedule gets underway, he changes from tempo runs to interval training, in order to incorporate a higher degree of anaerobic work.
Horton adds, “When you’re working at tempo pace, you’ll feel it equally in your legs and lungs-it’s a great sensation because it lets you know your whole body is being challenged.”

More at trailrunnermag.com

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