Proper training pace.

giving thought to what pace you should be running on any given day enables you to shape your training to meet specific goals. It also helps cut down on mileage that offers little or inefficient training effect. This takes an understanding of what various running paces do for you aerobically, mechanically and chemically.

Perhaps the easiest way to be sure you're running at the desired pace is to use a heart rate monitor, but many people simply learn over time how their bodies feel at certain training paces. The following will help you become accustomed to the feel of each type of running, and provide an overview of the various factors in play at a given running pace.

Easy Pace. Easy running occurs at about 60 to 70% of your maximal oxygen consumption (VO2max), or 70 to 75% of your maximal heart rate (MHR). It is a good recovery pace in between faster workout days, and so in this sense it is your "normal" training pace. When this pace is held for longer runs, it's a useful way to attenuate your body's glycogen depletion and rely more on fat for energy. These runs are more about putting in the time than pushing the intensity. They will help you become accustomed to fluid loss and other cellular stresses. Easy pace is the one at which any training regimen begins and should remain for three weeks before introducing faster running. Focus on light turnover and rhythmic breathing.

Threshold Pace. At around 88% of VO2max or 90% of MHR, this pace provides quality training with limited stress. For many runners, it's slower than 5K race pace by about 24 seconds per mile. These are the "tempo runs" we incorporate into our training, and they should feel comfortably hard. You can use threshold pace for other running, too, such as mile repeats with 1-minute rests in between. The pace is best for improving the body's ability to clear lactic acid from the blood during exercise. The importance of this increases with distance. Also note that, at 20 to 30 seconds per mile slower than threshold running, there is a useful pace for long-distance runners we'll refer to as "marathon pace". Use this as an effective alternative to the typical easy run. Just avoid any non-specific training intensity that falls elsewhere on the continuum between your easy and threshold paces.

Interval Pace. This is hard running over short distances. The goal is to eventually achieve 98% of MHR for brief periods of time. Intervals should never be longer than five minutes, and they are usually much shorter. Intervals train the body to carry on through prolonged periods at VO2max. As a guide, your pace should approximate one that you could not keep up for longer than 15 minutes. This is not all-out running. Running intervals faster than this pace will introduce fatigue and possibly injury; it will certainly compromise your next training day. Remember that you're not running at MHR for 15 minutes. (If you were to actually perform a 15-minute run at this pace as a test, you would not be running at MHR the entire time.)

Repetition Pace. This is faster than interval pace, but does not improve VO2max as effectively. It's used to get your body moving smoothly at a fast pace. A runner training for a 10K will have the same interval and threshold paces as a runner training for 1500 meters. But because one runner is training for a faster race than the other, their repetition paces would differ. Racing requires running economy and speed, both of which this pace improves by forcing the mechanical aspect of the training to mirror race-day running. Unlike interval training, fully recover in between repetition workbouts. You should be able to run the sixth 400 meters as fast as the first. Once you understand the benefits of each pace, you can begin to sculpt a training regimen over many weeks that meets your specific distance goals in the most efficient way possible, while remaining interesting and varied at the same time. For a middle-distance runner (racing between 5 and 15K), long runs should generally not make up more than 25% of total weekly mileage, threshold running 8 to 10%, intervals 6 to 8% and repetition pace 5%.

(Adapted from Daniels' Running Formula by Jack Daniels, PhD, Human Kinetics, Champaign, IL, 1998, 287 pp. $18.95)