BikeMonkey Guest PostPalMD, Isis the Scientist and Dr. Charles have been talking a little bit about restarting fitness and dieting regimens, a topic in which I have a small interest. The cover of the August 17, 2009 issue of TIME magazine insists that "Of course it's good for you, but it won't make you lose weight. Why it's what you eat that really counts." Turning to the feature article on Health penned by John Cloud, all I can note is that the stupid not only burns, but it incinerates all logic and sense for a five block radius. I had trouble getting past the second paragraph:
As I write this, tomorrow is Tuesday, which is a cardio day. I'll spend five minutes warming up on the VersaClimber, a towering machine that requires you to move your arms and legs simultaneously. Then I'll do 30 minutes on a stair mill. On Wednesday a personal trainer will work me like a farm animal for an hour, sometimes to the point that I am dizzy -- an abuse for which I pay as much as I spend on groceries in a week. Thursday is "body wedge" class, which involves another exercise contraption, this one a large foam wedge from which I will push myself up in various hateful ways for an hour. Friday will bring a 5.5-mile run, the extra half-mile my grueling expiation of any gastronomical indulgences during the week.
30 minutes? Maybe "an hour"? Four workouts per week for which the only one potentially useful for acute weight regulation purposes is the single 5.5 mile run? And from this the article claims that "exercise" is not useful for weight management?
First let me wear my anecdote hat. The regimen described by John Cloud is just ridiculously small when it comes to calorie burning. Most people don't realize this because they don't regularly engage in exercise to the point at which it becomes overwhelmingly obvious they have burned a boatload of energy. I refer, of course, to the bonk. The hunger knock. I think most serious cyclists (and the longer distance runners) are aware of the point at which the body just shuts down. I'm not talking about questionable fitness levels, illness or unusually hard efforts. In the reasonably well-trained cyclist there is a certain amount of time (modulated by ride difficulty) beyond which one can continue to perform at a high level, only by consuming some sort of calorie source during the ride.
Personally, this duration of time is somewhat over an hour (yup, even after overnight fasting) and no more than about two hours (at peak conditioning). If you know your body, read, have done a lot of accidental experimentation with not eating enough on various rides over the years, you will start to accumulate some idea of the variability of the bonk onset. You will notice that it can hit slowly or extremely rapidly and that the variables seem to have something to do with fitness.
This brings me to two papers on "time to exhaustion" which is in a body of research papers which are more or less directed at the practice of carbo-loading for sustained athletic performance.
Effect of carbohydrate availability on time to exhaustion in exercise performed at two different intensities. Lima-Silva AE, De-Oliveira FR, Nakamura FY, Gevaerd MS. Braz J Med Biol Res. 2009 May;42(5):404-12. [DOI]
Manipulation of dietary carbohydrates after prolonged effort modifies muscle sarcoplasmic reticulum responses in exercising males. Duhamel TA, Perco JG, Green HJ. Am J Physiol Regul Integr Comp Physiol. 2006 Oct;291(4):R1100-10. Epub 2006 May 11.[DOI]
The first study used "seven healthy fit men, but not competitive athletes" and the second used "male volunteers who were recreationally active but not exercising on a regular basis" as research subjects. I will resist the tendency to geek out over VO2max, lactate thresholds and such-like but the important point is that subjects rode a stationary bike in the lab to the point of exhaustion, aka "volitional fatigue" and/or a failure to complete 1 min of exercise at 125% of VO2max (oops, I did it). The protocol was similar for the two studies in that subjects first underwent an exhausting exercise pre-condition followed by two (the first study) or four (second study) days of dietary manipulation of carbohydrate balance. Data come from the post-dietary-manipulation retest.
When performing exercise under the lactate threshold (colloquially you can consider this the aerobic/anaerobic threshold) subjects in the first study lasted about an hour (mean 57 min; SD 25 min) and there was no effect of a 48-hr preceding interval of low carb or moderate carb diet on time to exhaustion. The subjects in the second study lasted a mean of 67 min (SE 6 min) after four days of lo-carb diet and 103 min (SE 9 min) after four days of hi-carb diet. The diet manipulations are not my main point here, I'm just pointing out that experimental laboratory conditions point to the same one-hour threshold for exhausting readily available energy stores as does my anecdotal experience. Some people seem to insist on such verification.
Now, that 60-90 min interval seems to remind me of something or other being bruited about the intertoobz of late...what was it, what was it......oh yes. The good Dr. Isis has been obsessing over:
In order to achieve weight loss, the American College of Sports Medicine recommends 60-90 minutes of exercise five days a week.
Yup. I don't doubt this one bit and I suspect it has everything to do with regularly running the body out of readily available energy stores, i.e., glycogen. This suggests my conceptualization of the real "fat burning zone", not to mention my gut feeling that the TIME author, John Cloud, had no idea what constitutes real exercise. He said "I have exercised like this--obsessively, a bit grimly--for years". Yet apparently he's hitting an hour of sustained aerobic exercise at best twice per week.
Well, no wonder he thinks exercise can't reduce weight...he's not actually exercising in a way that maximizes calorie burning.
Now, before you start slavering away about how stupidz it is for me to join a conversation about mid-life issues in weight-reduction and fitness attainment with unobtainable youth-focused standards which will injure people if they try to reach them immediately, let us not insult anyone's intelligence here. I'm sure you are reading all the posts from Isis and the good doctors Pal and Charles, as well as the following commentary. This is, if you think about it for half a second, coming at the same issue from another direction. Sure it is difficult to find the time to put in 90 minutes of real exercise 5+ days per week. If, however, you expect exercise alone to do the job (holding your current diet fixed) this is what you are going to have to do. The alternative is to cut your dietary intake, no?
Supercompensated glycogen loads persist 5 days in resting trained cyclists. Arnall DA, Nelson AG, Quigley J, Lex S, Dehart T, Fortune P. Eur J Appl Physiol. 2007 Feb;99(3):251-6. Epub 2006 Nov 22. [DOI]