Runners ask me all the time how fast they should run for various types of workous — easy runs, tempo runs, intervals. Most runners run either too fast or too slow to obtain the desired result. To determine the correct speed, you must know the purpose of each workout. Always remember that the goal of training is to obtain the greatest benefit while incurring the least amount of stress, so you should run only as fast as you need to meet the purpose of the run. And guess what? You only need to run at four speeds. Yup, that’s rght. Just four. From slower to faster, here are the four speeds at which you need to train.
Easy Runs and Long Runs
The purpose of easy and long runs is to stimulate the physiological, biochemical, and molecular adaptations needed for endurance, including the storage of more fuel (glycogen) in your muscles, an increased use of intramuscular fat at the same speed to spare glycogen, an increased number of red blood cells and hemoglobin, a greater capillary network for a more rapid diffusion of oxygen into the muscles, and an increased mitochondrial density and number of aerobic enzymes to enhance your aerobic metabolic capacity. Since many of these adaptations are volume-dependent, not intensity-dependent, the speed of easy runs is not as important as their duration. The single biggest mistake competitive runners make is running too fast on their easy days. By doing so, you add unnecessary stress to your legs without any extra benefit and you won’t be able to run as much quality on your harder days.
Your easy runs should be done at about 1½ to 2 minutes per mile slower than your current 5K race pace, about 70-75 percent maximum heart rate. As you increase your weekly mileage, you may need to run slower to accommodate the extra volume. Speed-type runners (those who are better at shorter races) will have a greater difference between their race pace and easy running pace compared to endurance-type runners (those who are better at longer races). I have always been more of a speed-type runner; my easy runs are much slower than the pace I race at.
Marathon Pace Runs
If you are training for a marathon, I will add a fifth speed to this list because the marathon may be the only race for which it is very valuable to practice specific race pace, for both the value of the pace itself and for the fueling/hydration strategies that you will use in the marathon. Include some long(ish) runs at your realistic marathon pace as you get closer to the marathon.
Lactate Threshold Runs
The lactate threshold (LT), or what I call the acidosis threshold (AT), demarcates the transition between running that is purely aerobic and running that includes significant oxygen-independent (anaerobic) metabolism and the development of acidosis. Therefore, AT is the fastest speed that you can sustain aerobically. The purpose of AT training is to increase the speed at which your AT occurs, which allows you to run faster before anaerobic metabolism and fatigue begin to play a significant role.
I’ve noticed that the AT workout is the most difficult type for runners to run at the correct speed since it requires holding back and not pushing the pace. There’s a comfortably hard feeling to the pace that requires practice. AT pace is about 10 to 15 seconds per mile slower than 5K race pace, or about 10K race pace (75-80% max HR) for recreational runners, and about 25 to 30 seconds per mile slower than 5K race pace, or about 15 to 20 seconds per mile slower than 10K race pace (85-90% max HR) for highly trained runners. The better your endurance, the longer you can sustain your AT pace and the better you’ll be at sustaining any fraction of your AT pace. In other words, if a 15-minute 5K runner can run 30 seconds per mile faster than AT pace (which equals 110% of AT pace) for those 15 minutes, a 25-minute 5K runner is not also going to be able to run 30 seconds per mile faster than AT pace (which equals 106% of AT pace) for 25 minutes, which is 10 minutes (and 66%) longer than the good runner. What matters is how long it takes to run the distance, not the distance itself.
The purpose of VO2max intervals is to increase your VO2max by running at the speed at which VO2max occurs, which corresponds to your max HR, max stroke volume (the volume of blood the heart pumps per beat) and max cardiac output (the volume of blood the heart pumps per minute). Cardiac output = heart rate x stroke volume.
If you can’t get to a laboratory to determine your VO2max pace, either run at close to your maximum heart rate or use your current race performances. Many coaches and runners like to do workouts at 5K or 10K race pace, but there is not much benefit running at 5K or 10K race pace other than to practice that pace since 5K or 10K race pace does not correspond to any physiological variable that affects race performance. For example, 5K race pace is too slow for a VO2max workout and too fast for an AT workout. VO2max pace, which is the fastest speed that can be maintained for about 7-10 minutes, is about 1- to 1½-mile race pace for recreational runners and 3K or 2-mile race pace (10-15 seconds per mile faster than 5K race pace) for highly trained runners.
Interval workouts with reps lasting 3 to 5 minutes are ideal for training VO2max since they provide the greatest cardiovascular load, however research has shown that shorter reps can also improve VO2max as long as the recovery intervals are very short to keep VO2 elevated between reps. An advantage of shorter reps is that you can accumulate a greater distance or total running time at VO2max pace. Regardless of the duration of the reps you choose, the speed should be the same since the goal is the same — to improve VO2max. As you progress, make the workouts harder by adding more reps or decreasing the duration of the recovery intervals rather than by running faster. Only increase the speed of the workouts once your races have shown that you are indeed faster. If running 800-meter reps in 3:15 (6:30 mile pace) elicits VO2max, running them in 3:05 (6:10 mile pace) will also elicit VO2max. But since the key is to run only as fast as you need to obtain the desired result, don’t run each rep in 3:05 when 3:15 will suffice.
Anaerobic Capacity Intervals
The purposes of anaerobic capacity intervals are to cause a high degree of muscle acidosis so that you enhance your buffering capacity, to increase the number of enzymes involved in anaerobic glycolysis, and to increase speed by recruiting fast-twitch muscle fibres. The speed of these reps, which should be 45 seconds to 2 minutes with recovery intervals up to 3 times as long as the time spent running, should therefore be just fast enough to cause acidosis and recruit fast-twitch muscle fibres — 800-meter to mile race pace for competitive runners and 400-meter race pace for recreational runners.
Next time you go out the door to run, ask yourself what is the purpose of the workout. If you run all of your workouts at the correct speeds, not only will you be rewarded with new personal records, you may even be able to tell other runners how fast to run.