Intervals vs. long runs

I’m back home from a fascinating couple of weeks in India — many thanks to the athletes, coaches and scientists who shared their time with me. More articles to come, which I’ll link to in future posts.

In the meantime, the blog will get back to its bread-and-butter: reporting on new research related to exercise, fitness and sports. For starters, a study in the current Medicine & Science in Sports & Exercise adding to the debate on the benefits and shortcomings of short, intense interval training for cardiovascular and other health benefits, from Lars Nybo’s group in Denmark. (The full text is freely available online.)

The study: four groups of nine untrained men did a 12-week training program:

1) Interval group: 5 min jog warm-up; 5 x 2 min HARD (getting HR above 95% of max); 1 min break between intervals (not clear from the paper, but I assume they just rested between intervals); 3 workouts per week, but they only completed an average of 2.0 due to factors such as injury (more on that below).

2) Endurance group: 1 hr of running at 80% max HR; 3 workouts per week, though they only completed 2.5 sessions on average.

3) Strength training: this group did three weights sessions a week. Not that interesting — they managed to confirm the well-known fact that running doesn’t give you bigger muscles, and lifting weights doesn’t improve aerobic fitness. (They probably should have to used these subjects to increase the size of the other groups…)

4) Controls who did nothing.

The key results are that (a) interval training produced double the increase in cardiorespiratory fitness that endurance training did (14% boost in VO2max compared to 7%); and (b) interval training was much less effective at lowering resting HR, body fat and bad cholesterol.

This is all good — we can all agree, I think, that different workouts do different things. Unfortuanately, you can’t cram all the benefits of an hour-long endurance session into 20 minutes. The big pitch for HIT (high-intensity interval training) is that it’s so much more time-efficient than the standard slog-on-the-treadmill-or-bike-or-elliptical workout. This is true. But the revised message of the last couple of years’ research is that you can adjust part of your weekly routine to HIT, not all of it. And in fact, you’re actually better off doing, say, 1-2 HIT sessions and 2-3 longer, slower runs per week than just doing four of the slower sessions. High-intensity has some major benefits beyond simple time-efficiency.

The one point that I wanted to circle back to is the injury question. The subjects in this study apparently hadn’t “participated in any type of regular physical training for at least 2 yr.” I don’t see any reference to a breaking-in period or a gradual ramping-up period — so it’s remarkable to me that ANY of the subjects made it through this study alive! Running for an hour continuously is a pretty tough task for an untrained subject, let alone a hard interval session. As it is, of the nine interval subjects, three missed sessions with shin splints, another got plantar fasciitis, and a fifth had “bilateral unspecific knee pain.” In the endurance group, two subjects had overuse injuries.

To me, that’s a pretty important point. If more than half of the subjects in an experimental group get injured, that’s a relevant detail when you’re talking about public health advice. The subjects in this study presumably had access to experts who could tell them how to deal with their injuries. For the average person outside the lab, encountering shin splints, plantar fasciitis or unidentified knee pain could easily spell the end of their attempt to get in shape.

Don’t get me wrong — I’m a big fan of interval training as a powerful and efficient way of getting in shape. But it’s an approach that does carry some higher risks, so I’d prefer to see it advocated as part of a well-balanced exercise regimen, rather than a revolutionary approach that should replace your current one.