The 4-second Workout
"How to build muscle in 9 minutes"
"In 6 minutes, you can be done with your workout"
"How 1-minute intervals can improve your health"
"The 4-second workout"
Sounds like advertising, right? Maybe clickbait? Those are actually headlines from New York Times articles. Each article was grounded in new research.
I'm a sucker for articles like these, because they promise so much for so little. In fact, the mini-workouts they describe seem so "mini" I wonder sometimes if we're being duped. Can you really benefit from a few minutes – or a few seconds – of exercise? Or is this just the fitness world's version of a get-rich-quick scheme?
I decided to take a look at the most recent of these studies, reported in a September 29 New York Times story entitled "Exercise Vigorously for 4 Seconds. Repeat. Your Muscles May Thank You."
I approached this study with mixed feelings. On the one hand, I wanted to love it. I wanted to show you a quick exercise routine that boosts fitness, and to show how stats helped demonstrate its effectiveness. On the other hand, I was prepared to find deep flaws. (Why the pessimism? Because I'm a cranky old man, and I'm a marathon runner, and if you belong to either category, you tend to assume that the "no pain, no gain" adage applies to just about everything in life, including fitness. My bias is that exercising for 4 seconds couldn't be "painful" enough to do one's body much good. Spending 4 seconds on anything doesn't seem like it could benefit anyone, unless you're handing out cash or compliments.)
Sadly, the findings of the study turned out to be unpersuasive. A little pain may spur moderate gain. Perhaps even a lot of gain. But I don't think that's demonstrated here.
This particular study reflects recent trends in exercise research and athletic training collectively referred to as High-Intensity Interval Training (HIIT). HIIT techniques are characterized by bursts of short, intense anaerobic activity, interspersed with brief rest periods. If you do it right, a HIIT activity will be quite intense and continue to the point of exhaustion, and your fitness, or strength, or whatever, should then improve.
The study was carried out in the lab of exercise physiologist Dr. Edward Coyle at UT Austin. Here's how it played out: 11 UT students visited Dr. Coyle's exercise lab three times per week for 8 weeks. During each visit, students pedaled a stationary bike intensely for 4 seconds, followed by a brief rest. Each 4-second burst of pedaling was repeated 30 times, resulting in exactly 2 minutes of total cycling. The resting period between each 4-second burst decreased from 30 to 15 seconds over the course of the study, so that the total time required for each session (exercise + rest) changed from roughly 17 to roughly 9.5 minutes. The researchers measured physiological as well as performance changes from the beginning to the end of the 8-week period.
To summarize: students pedaled a stationary bike three times per week for 8 weeks. Within each session, the actual time spent pedaling the bike was 2 minutes, divided into 4-second bursts. So, it's not actually a 4-second workout but a 2-minute workout – which is still a lot less activity than we usually think of as "exercise." By week 8, participants showed, on average...
...a 17.2% increase in maximal anaerobic power (crudely, how much power one can exert in a short period of time);
...a 7.6% increase in total blood volume (an indicator of cardiovascular fitness);
...a 13.2% increase in VO2peak (peak oxygen consumption, an indicator of cardiorespiratory fitness);
...a 2.5 centimeter increase in maximum vertical leap (how high one can jump straight up into the air from a standing position).
There were other findings too, but you get the idea: 2 minutes of cycling, three days a week, makes you stronger and more fit. That’s awesome. And, as I said, a little suspicious. (2 minutes...three times a week? Really?)
The study has four methodological limitations, which I'll present here in order of increasing cause for concern.
1. Use of a small, unrepresentative sample.
In Research 101 you learn that large, representative samples are a prerequisite for good quantitative research. Here the participants consisted of 11 healthy, 20 to 21 year old students at UT Austin. This is a small sample, by any standards, and not representative of the general population of young adults. Still, you might consider the sample good enough if you assume that what's being studied are physiological changes that most human beings would exhibit under similar circumstances. The findings do seem to be predictable from current knowledge about physiology, and they're consistent with the findings of similar studies; thus, one could argue that a larger sample wasn't really necessary.
(Note to stats people: Although repeated-measures ANOVAs were used to test for the significance of pre-post changes, and repeated-measures analyses automatically increase statistical power, no power analyses were reported, so we don't know whether the main analyses were adequately powered.)
Ideally, the sample would’ve been larger and more diverse, so that we could know, for example, whether exercise differentially benefits people who vary on dimensions such as gender and health status. I can't speak for the researchers, but they would probably expect any subgroup differences to be small (again, because all human bodies work the same way, physiologically speaking). Thus, knowing about subgroup differences would merely add to rather than change what the researchers learned, and one might conclude that much was gained from studying just 11 people…
2. Unknown individual differences.
This is a statistical concern, but you don't need a background in stats to see it. The main analyses compared means – i.e., average increases in power, blood volume, etc. from week 1 to week 8. With only 11 participants, it's possible that just a few participants improved a lot, thereby inflating the week 8 means. If this were the case, the cycling intervention might not benefit most people.
Possibilities like this are easy to address. You look at frequency statistics (e.g., for each variable, how many participants improved vs. stayed the same vs. declined) and you look at variability (e.g., the range of improvement for each variable, and the standard deviations). Unfortunately, the researchers provided almost no frequency data, and minimal data on variability. What they do provide on variability hints at big differences from one participant to the next in how much they changed across the 8 weeks. (For those of you who took stats, the researchers provided standard errors of the mean, from which you can easily calculate standard deviations. For some variables, the standard deviations look high enough that one could imagine at least a few participants having stayed the same or gotten worse by week 8.)
In sum, participants responded differently to the cycling intervention, and it's not clear to what extent the overall means were driven by changes that only a few participants experienced. It's also unclear how much more some participants benefitted than others. (In statistical terms, we need to know individual-level data, or at least ranges, since standard deviations only tell us about average variability around the mean.)
3. Lack of a control group.
In Research 101 you also learn that control groups are essential in experimental studies. The researchers seem to have broken a sacred rule by not having one. Instead, they treated each participant as their own control by measuring them before and after the 8-week intervention.
The problem with not using a control group is that you can't rule out extraneous effects – that is, effects from variables that weren't part of the intervention. For example, let's imagine one of the study participants. We'll call her Amy. As it turns out, if Amy hadn't agreed to participate in the study, she would've spent the time at her desk studying, mostly sedentary. Instead, she got some extra activity each time she walked to and from the exercise lab. On lab days, Amy was energized by the experience, and she consequently became more active for the rest of the day.
I'm not suggesting that the actual participants had the same experience as Amy – or, if they did, that their extra activity influenced the findings. I'm just saying that, in theory, the benefits of cycling might be due not just to the cycling, but also to extra mental and physical stimulation, which replaced sedentary activities and increased participants’ subsequent activity levels. This is not to say that the cycling wasn't beneficial; it just might not have helped as much as the researchers claimed.
The value of a control group is that you don't have to worry about what I just wrote. If the researchers had asked a separate group of 11 students to visit the lab three times per week for 8 weeks, and spend a comparable amount of time doing something else (e.g., using an interactive software program to learn about fitness), then changes in both groups could be recorded, and we could be confident that any benefits of cycling were due strictly to the cycling and not to any extraneous variables (like walking back and forth from the lab instead of quietly studying).
4. Confounding effects of measurement and warming up.
The fact that this study requires so little exercise makes considerations like how vigorously participants walked to and from the exercise lab worth pondering. More importantly, once they reached the lab, participants did more than just pedal for 2 minutes. Maximum anaerobic power at the beginning and end of the experiment was measured by asking each participant to run three 20-yard, timed sprints, and to complete several intense tests on a stationary bike. Maximum vertical leap at the beginning and end of the experiment was measured by asking each participant to jump as high as they could three or four times on each occasion. And, for the entire 8 weeks, at the outset of each session, participants warmed up on their bikes for 5 minutes (which means that they actually spent a total of 7 minutes cycling rather than 2). It's possible, in theory, that the measurements of anaerobic power and the warm-ups contributed to the benefits attributed to the 4-second cycling activity. After all, if your study is grounded in the assumption that brief activity is beneficial, and you ask participants do a bunch of brief activities that aren't part of your intervention...well... you've just undermined anything you can say about the effects of that intervention.
(Here too, the problem would be completely resolved by the inclusion of a control group. Have 11 undergraduates come to your lab and do the same sprints, the same cycle tests, and the same 5-minute warm ups. Just don't engage them in the intense 4-second cycling activity. Let them read about fitness, or do something else, in place of that activity.)
So, what's the bottom line, methodologically speaking? It's a flawed study. The sample was too small and a control group was desperately needed. At the same time, if you pretend that participants didn't vary much in response to the cycling (see point #2 above), you might not completely discount the findings. Because if participants all showed approximately the same extent of improvement, the worst-case scenario is that the health benefits documented by the researchers are genuine, but you just don't get them unless you walk to and from a building three times a week for 8 weeks, cycle for 7 minutes while you're there (including 2 very intense minutes), and engage in other strenuous activities at the beginning and end of the 8 week period. That still doesn't seem like a great deal of exercise.
Finally, what's the bottom line, practically speaking? I don't think that's knowable. The study suggests that physical activity is beneficial, but we knew this already. On the other hand, I wouldn't translate the specific findings into an exercise routine. Along with the limitations I've already mentioned, there's no context for the statistics. I get what it means that participants were able to jump 2.5 centimeters higher on average. (That's about an inch.) But as for increases in maximal anaerobic power, blood volume, and VO2peak, what do they mean in practical terms? And what else would create similar effects? If I ate a healthier lunch three times per week for 8 weeks, would I see some of the same changes (via direct effects, plus increased energy levels that make me more active)? Also, without knowing who benefitted more vs. less from the cycling (and what the range was), I can't tell whether or not I’m the type of person who’s likely to benefit.
(Side note: I was disappointed that in their September 29 article, the New York Times failed to mention the painfully obvious limitations with the methodology and implications of the study. NYT usually includes a quote from an independent expert, or at least some sort of observation about potential limitations. From a public health perspective, the oversight is problematic.)
Dang. I really wanted to love this study. There seems to be a lot of evidence for the benefits of HIIT, so I don't want to discount an entire field based on a single study. All the same, the next time this cranky old man rides his bike, he plans to go moderate, and go long...
Thanks for reading!