Being a CrossFit trainer and a scientist, I have had a number of members at my box ask me about the science behind CrossFit. They were curious about the published studies, if any, that give credence to the methods. If you ask the folks at CrossFit HQ, they will say the results of the program speak for themselves, and they certainly do. But are there scientific studies out there that support the effectiveness of specific aspects of the program or help us explain why CrossFit gets the results it does? It turns out there are. As such, I will periodically address the science behind CrossFit in a special blog series on this site.
In this first article of the series I address the now famous Tabata interval. In boxes all over the world the workout of the day (WOD) will periodically be some variant of the Tabata interval. For example, take the workout listed below to the left.
The Tabata interval is 20 seconds of intense work followed by 10 seconds of rest. Thus, in the adjacent workout you would do 8 intervals of each exercise. That is, 20 seconds of pull ups and 10 seconds of rest followed by 20 seconds of push ups followed by 10 seconds of rest and so on, repeating the entire list 8 times. Where did this interval come from and why does CrossFit incorporate it as a core training device?
The Tabata interval is named after its creator, Izumi Tabata, who is now a professor at Ritsumeikan University. Although Dr. Tabata has published many papers to date, there are three key studies that form the basis of the Tabata interval:
Tabata et al., 1990 – This is the seminal work where Tabata, as lead author, lays the foundation for his work in training intensity and muscle power. 6 male physical education students were enrolled in the study and required to exercise 5 days a week for 7 weeks. The training was interval training with a cycle ergometer (an ergometer is an instrument that measures mechanical work accomplished, in this case by pedaling a bicycle) such that power output for each subject was 90% of their VO2max (maximum oxygen uptake). Subjects were asked to maintain pedaling at this intensity level. When their intensity dropped, they were given exactly 5 minutes of rest, after which exercising resumed. This cycle was repeated until the subject reached the prescribed quantity of training time for that week. The nature of this endurance training was one of low resistance, moderate speed, muscle training. The results indicated that the increase in isokinetic (at a given speed) muscle power after training was greater if the starting isokinetic muscle power was lower. In other words, subjects with high initial muscle power were less capable of increasing muscle power by means of this aerobic training. The implications of this study were that if one wants to maximize their power output (get more work done in a shorter amount of time), longer, aerobic bouts may not be the most effective approach for muscle training. If so, then what is most effective?
Tabata et al., 1996 – In this next study Tabata again enlists subjects and monitors their power output on cycle ergometers. However, now he compared 6 weeks of moderate endurance training (exertion at only 70% VO2max) to a high-intensity, intermittent training group which performed 7-8 sets of 20 seconds of exercise at a whopping 170% of VO2max followed by 10 seconds of rest. The results showed that the high-intensity group increased their VO2max by 7 ml/kg/min, indicating an increase in aerobic capacity. In addition, maximal accumulated oxygen deficit fell by 28%, which said another way, means a 28% increase in anaerobic capacity for these high-intensity subjects. Anaerobic capacity is a measure of how your body uses energy without oxygen and is thus an accumulation of energy obtainable from existing ATP (adenosine triphosphate) molecules as well as the lactic acid and phospho-creatine pathways. So, what about the moderate intensity subjects? They actually had no gain in anaerobic capacity and, although they did have gains in aerobic capacity, the gains were small, comparable to or less than those of the high-intensity subjects (I can’t say for sure if the gains were the same or less because the actual data values were not presented – only a graph of the data). Thus, in this simple, yet groundbreaking study, Izumi Tabata demonstrated that high intensity interval training gives both an aerobic and anaerobic benefit.
Tabata et al., 1997 – In this follow-up study Tabata compared the previous high-intensity 20/10 interval (20 seconds work/10 seconds rest) to a new interval comprised of 30 seconds of work and 120 seconds of rest (30/120). The goal here was to see just how effective the initial 20/10 interval really is. The results demonstrated that the 20/10 subjects achieved an oxygen deficit that was statistically identical to their maximal oxygen deficit (i.e., their anaerobic capacity). Thus, the 20/10 exercise regimen brought subjects to maximum oxygen debt (quite a workout!). In contrast, the 30/120 subjects did not reach an oxygen debt level near their measured maximum (they could have been working harder or resting less). Further, peak oxygen uptake was statistically identical to VO2max for the 20/10 groups but lower than VO2max for the 30/120 group, indicating that the 30/120 group was not working at maximum aerobic capacity either. Taken together this study indicated that the 20/10 interval worked both the anaerobic and aerobic energy releasing systems better than the 30/120 (and possibly even worked those systems to their maximum). Thus, for the best training of energy exchange and oxygen utilization, the 20/10 interval reigned supreme and the Tabata interval was born.
From this point on Tabata’s work shifted and expanded. Some interesting studies have come out of his lab including two using rats subjected to Tabata swimming intervals. In Terada et al., 2001 the authors showed that high-intensity Tabata training results in maximal levels of glucose uptake into skeletal muscle, suggesting that the long-held belief that maximal glucose uptake was only through low-intensity exercise was incorrect. In Terada et al., 2004 the authors conducted a similar study in swimming rats and showed that high-intensity Tabata training increased citrate synthase (CS) and 3-beta hydroxacyl CoA dehydrogenase (HAD) activity (both markers of increased fat breakdown) just as much as low-intensity training.
The body of work that Tabata has put forth in both humans and animals for over two decades has made a convincing case for choosing high-intensity Tabata interval training as one of the (if not the) optimal means to become a more powerful endurance athlete or simply a fitter individual. For sure, the success of CrossFit wouldn’t be nearly as great without Izumi Tabata’s work. Many thanks, Dr. Tabata.