McMaster University (Canada) studies on the effectiveness of high intensity interval workouts.
Sprint Results Set the Stage
The 2005 study and others (links provided above), published in the Journal of Applied Physiology and , showed that three to seven all-out sprints on a stationary bicycle (250% of VO2 max), 30-seconds each, with four-minute rest periods, six times over two weeks, are as effective as 90 to 120 minutes of cycling at moderate intensity (65% of VO2 max) six times over two weeks. Both workouts improved endurance capacity by almost 100%, increasing time to fatigue at 80% effort from 26 minutes to 51 minutes. In short, about 15 minutes of hard sprints spread over two weeks produced the same results as nine to 12 hours of moderate intensity effort.
Both the sprinters and the traditional riders showed a substantial increase in citrate synthase, a mitochondrial enzyme that indicates the power to use oxygen, along with increased glycogen (muscle sugar) content. Neither group, however, showed a change in maximum oxygen uptake (VO2 Max, or the ability to utilize oxygen per kg of body weight in liters per minute; it can be approximated to % max heart rate with the formula %MHR = 0.64 × %VO2max + 37) or anaerobic work capacity (ability to produce lactate, a byproduct of anaerobic metabolism).
The interesting thing about this study, is that the high intensity exercise group should have produced more anaerobic work (ie more lactate) and probably did BUT were able to clear it faster because of the short duration of the exercise. Remember that the 1st few seconds of the 30 second sprint would have been using creatine phosphate stores, before tapping into the glycogen stores.
The lower intensity exercise at 65% VO2 Max works predominantly the aerobic system (incidently, 65% of VO2 Max is probably a “moderate exercise” and is probably less demanding); thus these folks would be better able to recycle lactic acid, should the levels rise to levels requiring it. Changes in VO2Max would be able to be changed much less (3-5%) in trained individuals than untrained (up to 20%), so the findings are not that surprising.
The bottom line is that high intensity training offers some gains that are similar to traditional aerobic training with less time, and should probably be included in your training regimen.
Shawn and Ivo……..Striving to increase your knowledge base more efficiently