By Teemu Virtanen
“A specific workout that I like is 6 x 6 min running on the treadmill. Nothing makes the heart pump as some good old-fashioned hill intervals,” says last winter’s Vasaloppet winner Tore Bjørseth Berdal, Team Koteng.
This particular kind of workout is one form of interval training. The purpose is to raise your heart rate close to maximum, like in Tore’s case about 95% of his max heart rate. This workout can improve many aspects of human physiology such as lactate threshold and increase VO2 max.
Lactate threshold is naturally a significant factor in determining performance for long distance sports events. An increase in an athlete's VO2 max allows them to intake more oxygen while exercising, enhancing the capability to sustain larger spans of aerobic effort. Interval training can also induce endurance-like adaptations, corresponding to increased capacity for whole body and skeletal muscle lipid oxidation and enhanced peripheral vascular structure and function.
When doing Intervals lasting from 3 to 5 minutes (in Tore’s case 6 min), you are working in your VO2 max zone, or as mentioned above about 95 percent of your max heart rate, for the duration of the interval. The recovery time between intervals depends on your goals. You can also start your intervals slower than 95%, heart rate about 85-90 %, and increase the pace and intensity towards the end, particularly if you aim to do several intervals.
Short intervals are usually paired with equally short or even shorter recovery periods so your body can adapt to repeated maximal efforts. And because your heart rate stays elevated during the recovery periods, your aerobic energy system gets a training benefit as well. In other cases, such as high-intensity sprints, you want each effort to be done at max, so you need to let your body fully recover for four or five minutes between bouts.