There's no doubt about it: High-intensity training sharpens your speed and improves your running economy. Unfortunately, conventional wisdom says that upbeat running also increases your risk of injury, overtraining, and "burn-out." Fast running also enhances the breakdown of carbohydrate - not fat - for fuel, and high-velocity workouts are of shorter duration than long, slow runs, leading to less calorie burning. For those reasons, speedy running isn't supposed to be as good as long, slow ambling at trimming excess corpulence from the body. Training

Those knocks on upscale training seem logical enough, but hold on! Recent research demonstrates that fast training is far better than inchmeal pacing at boosting blood levels of an important chemical called human growth hormone (GH). Produced by the pituitary gland, GH also helps break down fat and heightens body leanness. Since swift training sessions amplify GH levels, it may be time to bring on the speed!!

In recent growth-hormone research carried out at the University of Virginia, 16 healthy female runners gradually expanded their training mileage from five to 40 weekly miles over a 12-month time span. Nine of the woman ran six times per week and completed all of their training at or below their lactate threshold running speed (LTRS), the velocity above which large amounts of lactic acids begin to accumulate in the blood. Generally, LTRS corresponds with a heart rate of 80-88 percent of maximum and a running pace which is 10 to 15 seconds per mile slower than 10K race pace.

The seven other women also trained six times weekly, but three of their sessions were conducted at much higher speeds. In fact, up to one-half of their weekly mileage, not to exceed five miles per workout or 15 miles per week, was completed at above-LTRS velocities. Usually, the above-LTRS workouts consisted of intervals run on the track at a speed about half-way between LTRS and two-mile race pace. Although training speeds differed, total weekly mileage was the same for the two groups ("Endurance Training Amplifies the Pulsatile Release of Growth Hormone: Effects of Training Intensity," journal of Applied Physiology. Training

After one year of training, both groups improved maximal aerobic capacity (VO2max), but the improvements were significantly greater in the above-LTRS runners. The higher intensity trainees boosted their average VO2max from 44.2 to 50.1 ml/kg/min, a 13-percent advance which is comparable to lowering 10K times from 45:58 to only 41:16. Both groups of athletes also increased lean body mass, but the above-LTRS runners tended to achieve greater reductions in fat weight and percent body fat.

                                                     Pulses of Growth Hormone

The biggest difference between the groups, though, was in the growth hormone production. Above-LTRS trainers nearly doubled the average amount of growth hormone in their blood, and their "pulsatile" release of GH was also dramatically heightened (The pituitary gland releases growth hormone not continuously but in sudden "pulses," or surges, at various times of the day). Since muscles and bones are especially responsive to abrupt increases in GH levels, this improved pulsatility could greatly enhance bone and muscle repair.

Prior studies had suggested that endurance training might gradually diminish the amount of growth hormone released from the pituitary gland, but the Virginia research indicates that at-the-below-LTRS training maintains GH levels while above-threshold intensities might - because of heightened GH - recover more quickly from strenuous workouts and races, uses fuel more efficiently during exercise, and amplify body leanness.

Also, since growth hormone stimulates the formation of new bony tissue, master's runners who want to fend off age-related decline in bone mass might profit from an increased frequency of above LTRS sessions. Chunkier runners who train slowly tend to produce miserly amounts of growth hormone, so above LTRS exercise should help heavier harriers break down fat and become leaner. Although it's unrealistic to expect masters or overweight runners to spend huge amounts of time exercising at above-threshold intensities, the Virginia scientists suggest that a schedule of three times a week for 20-30 minutes at slightly above threshold should be enough to jump-start GH production.

However, it takes time for the above-threshold training to promote growth-hormone levels. In the Virginia research, which utilized subjects who were initially untrained, growth hormone levels didn't begin to increase dramatically until eight months of above-threshold running had been completed. It's possible that training above threshold for only six months of the year - and training easily for the other six months - might not spike blood concentrations of GH: Fairly regular "doses" of upscale running may be required.

                                                                Speed Kills?

The link between chronic above-threshold training and enhanced blood-GH levels suggests that experienced runners might want to revamp their "base" training and that novice joggers should consider adjusting their initial workouts. Runners doing base or beginning training often rely almost exclusively on slow, steady miles, but it may be far better to mix moderate quantities of above- LTRS intervals with the easier runs. Inclusion of speed into base training won't lead to surges in injury rates; in fact, it might lower the frequency of injuries because the augmented GH could do a better job of fortifying bones, muscles, tendons, and ligaments. Recent research in Holland confirms that early, up-tempo training actually tends to downgrade - not increase - average injury rates. In the Virginia study, above threshold runners were not injured more often than the slower trainees, even though as much as 38 percent of their weekly miles were completed at above-threshold intensities. Generally, scientific surveys have been able to link higher total mileage - but not faster training speeds - with a greater risk of injury. Speed seems to produce problems primarily when it is combined with unusually high mileages or when large amounts of speed are added to a training program too quickly. Even beginning runners are ready for reasonable doses of speed. Training

If you decide to increase your above-LTRS training, it makes sense to add the speed in amounts which your body can tolerate easily. One sensible rule is to tag on no more than an additional half-mile of above-threshold work each week. How fast should you run? An easy way to accrue more above-LTRS miles is simply to run at your current 10K-race speed, which is usually two to three percent faster than LTRS. For example, during a few of your easy runs, cruise along for a half-mile at 10K speed midway through the run and then scoot through another half-mile at 10K intensity near the end of the workout. Or, instead of doing a three-mile easy run, jog two miles easily and then complete two 400-meter intervals at 10K tempo, with 400 meters of easy running after each interval. Even neophyte runners can insert several fast 100-meter intervals inside their short, easy runs.

"Strides" - 20 to 30-seconds bursts at current one-mile race pace - represent another great way to add more above threshold running to a training program. Most runners can ultimately attach four to eight 150-meter strides to three or four of their usual weekly workouts without risking excess fatigue, injury, or mental burnout. Although the strides are short, stride mileage can add up surprisingly quickly: Just 10 strides - five on one day and five on another - add nearly a full mile of above threshold running to a weekly training schedule. In addition, an experienced runner who currently logs 40 miles per week, including 10 miles at above-threshold speed, can increase his/her percentage of above-threshold miles from 25 percent to 31 percent - comparable to the levels reached by the above-threshold trainers in the Virginia study - simply by adding a total of 22 150-meter strides to your usual training too abruptly; about five additional strides per week represent the maximal allowable increase.

Although intense running is claimed to increase the risk of "burnout" and overtraining, it's more likely that a gradually-increased quantity of above-LTRS sessions will boost your growth hormone production, bolster your speed, strengthen your muscles and connective tissues, optimize fat breakdown, and help you develop the ability to recover from tough training sessions and hard races more quickly. Training