It is no secret that I am a fan of Accelerade sports drink. But lately I have not been using Accelerade in my training. I've been using Accelerade Hydro.

Accelerade Hydro has the same 4:1 carbohydrate-protein ratio as Accelerade but is quite a bit lighter. In fact, it has 30 percent fewer calories and 55 percent less sugar than Gatorade. Unlike other low-calorie sports drinks, however, Accelerade has the same level of efficacy as conventional sports drinks. Thus Accelerade is the perfect product for endurance athletes who are trying to limit their calorie intake but not at the expense of performance. Other low-calorie sports drinks are fine for gym bunnies who are concerned about their calorie intake but for whom maximizing workout performance is not a major priority. But Accelerade Hydro is the first sports drink that allows performance-focused, calorie-conscious endurance athletes to enjoy the best of both worlds.

What proof do I have that Accelerade Hydro is as effective as Gatorade despite having substantially fewer calories and less sugar? I have a study entitled "The Effect of a Low-Carbohydrate-Protein Beverage on Endurance Performance" by researchers at the University of Texas. In this study, the authors note that past research has shown that Accelerade increases endurance performance substantially more than conventional carbohydrate sports drinks. But Accelerade contains the same amount of carbohydrate as conventional sports drinks plus protein, hence more total calories, so skeptics have contended that it's not necessarily fair to credit Accelerade's superiority to its protein content. However, more recent studies in which Accelerade was compared to a carbohydrate sports drink with equal total calories revealed that although the difference was smaller, Accelerade still increased endurance significantly more. Hence it must be something about the protein content of Accelerade that makes it more effective. Exactly what that something is remains unknown, however.

Since Accelerade is more effective than conventional sports drinks matched either for carbohydrate content or total calories, it is plausible that a lighter carbohydrate-protein sports drink (Hydro) with less carbohydrate and total calories might still be as effective as a conventional sports drink, and it is this possibility that the University of Texas researchers tested. Twelve trained cyclists completed an exercise test consisting of 2.5 hours of ergometer riding at 55-50 percent VO2max followed immediately by a ride to exhaustion at 80 percent VO2max on four separate occasions: once with water, once with Gatorade, once with Accelerade and once with Accelerade Hydro. Average time to exhaustion at 80 percent VO2max was 14.7 minutes with water, 26.9 minutes with Gatorade, 28.9 minutes with Accelerade Hydro, and 30.5 minutes with Accelerade. The differences among the three sports drinks were not statistically significant, so the authors of the study concluded:

"Partially substituting PRO protein for CHO carbohydrate in a sports drink did not enhance aerobic endurance, but substitution was able to occur without loss of efficacy. Thus, adding PRO to a low-caloric CHO sports drink may be an effective strategy to enhance endurance performance while limiting caloric consumption."

There is a lot of talk in the media and in the commercial sphere about the desirability of "raising your metabolism".  Raising your metabolism means increasing the rate at which your body consumes energy, or "burns calories", at rest.  The more calories your body burns at rest, the more calories you can consume in food without gaining weight, or the less you have to reduce your calorie intake to lose weight. 

The concept of raising metabolism is especially appealing to overweight men and women who do not wish to exercise.  Their thought process goes like this: "If I can just raise my metabolism enough, I can have the body of my dreams without exercising at all!"  Ironically, though, exercise itself is the single best way to elevate the body's resting metabolism.  Triathletes are likely to see great justice in this cold, hard reality.  We earn our burn.  Why should couch potatoes get it for free?

As endurance athletes, we are motivated to swim, bike and run primarily by our enjoyment of these activities and our desire to achieve personal goals, and only secondarily by vanity.  A secondary motivation is still a motivation, however, and what's more, a lean body composition is good for both appearance and performance.  So it's natural for endurance athletes to want to know how they can optimize their training and diet to raise their metabolism and get leaner.  Keep reading: your curiosity will soon be satisfied.

A Whole New EPOC

Back in the 1920s the legendary British exercise physiologist A. V. Hill first observed that the body's rate of oxygen consumption remains elevated for some time after exercise, and that this phenomenon is indicative of a metabolic rate that, while lower than the metabolic rate during exercise itself, remains above the normal resting metabolic rate.  This phenomenon has come to be known as excess post-exercise oxygen consumption (EPOC).  More recent research has determined that EPOC has two phases-a strong acute phase lasting up to two hours and a weaker long-term phase last 24 hours or more-the sum of which accounts for 6 to 15 percent of the total caloric cost of a workout, depending on its duration and intensity.  Thus, if you burn 1,000 calories during a workout you can expect to burn roughly an extra 100 calories in excess of your normal resting metabolism in the hours after the workout.

Different types of workouts produce different levels of EPOC.  High-intensity cardiovascular exercise (think interval sessions) result in the largest amounts of post-exercise energy consumption.  Indeed, EPOC increases exponentially at exercise intensities exceeding roughly 60 percent of VO2max.  Exercise scientists who performed the earliest studies on the effects of high-intensity intermittent exercise on body weight and composition were shocked by the results.  A recent study from the University of New South Wales, Australia, found that women lost an average of 10.5 percent of their fat mass after 15 weeks on a three-times-a-week program of 20-minute workouts consisting of 8-second stationary bike sprints followed by 12-second passive recoveries.  (Sounds easy but that's 60 all-out sprints-a hellishly hard workout.)  Subjects in a control group that performed traditional endurance workouts lost considerably less fat over the same period despite spending roughly 400 percent more time pedaling. 

Gym exercisers have pounced on results such as these (and other results showing that high-intensity intervals boost aerobic and anaerobic capacity in a far more time-efficient manner than conventional endurance training) to argue that high-intensity intervals are simply "better" than conventional endurance training and to imply that endurance athletes are fools for doing so much steady-state work.  However, workout duration has a big effect on EPOC, as well, and most triathletes routinely ride and run longer than the 40 minutes that the controls in the study cited above rode at the peak of their training-not to mention, we seldom ride and run as slowly as the 60 percent of VO2max at which they rode.  A study conducted by researchers at the University of New Hampshire found that a one-hour workout at 70 percent of VO2max resulted in 55 percent more EPOC than a 40-minute workout at the same intensity (which itself produced only 14 percent more EPOC than a 20-minute workout at the same intensity).

And let's not forget that 85 to 94 percent of the total energy cost of each workout comes during the workout itself, not through EPOC, and it's possible to burn a lot more calories in an exhaustive moderate-intensity workout-due to its far greater duration-than in an exhaustive maximum-intensity interval workout.  In a recent review of the scientific literature on EPOC and body weight management, researchers from University of South Australia concluded that "the earlier research optimism regarding an important role for ... EPOC in weight loss is generally unfounded... The role of exercise in the maintenance of body mass is therefore predominantly mediated via the cumulative effect of the energy expenditure during the actual exercise."  In other words, for the purpose of getting lean, going long trumps going fast-although doing some of both is better still.

The reason you would not want to perform maximum-intensity interval workouts exclusively for the sake of getting as lean as possible is the same as the reason you would not want to do the same for the sake of maximizing your fitness, despite the fact that maximum-intensity interval workouts boost aerobic and anaerobic capacity in a far more time-efficient manner than conventional endurance training.

Suppose we took the subjects in one of these eight-week studies comparing the effects of high-intensity interval training and steady-state aerobic training and asked them to continue doing what they were doing, and not only continue doing it, but to do more and more of it as long as they kept improving.  What would happen?

Well, those in the high-intensity interval group would be able to increase their volume of anaerobic training for a short while, but before long-indeed, probably right around the time they tried training every day-they would hit a wall, beyond which any additional increases would prove counterproductive.

Meanwhile, those in the slow-and-steady group would be able to continue increasing their slow-and-steady workload, and continue getting fitter, for a long, long time. Their total training volume would be vastly greater than that of the interval doers by the time they reached their own plateau, and their performance level would be significantly better in longer performance tests, although probably still worse in shorter ones.

Now let's suppose that each group began to replace their respective core training type with the other group's training to stimulate further improvement, again stopping when they plateaued. When all was said and done, the slow-and-steady folks would have reduced their slow-and-steady training by roughly 20 percent and added a volume of intervals equal to no more than 20 percent of the new, reduced slow-and-steady training volume. But the interval doers would have had to reduce their interval training by no less than 80 percent and added a volume of slow-and-steady training equal to perhaps 400 percent of their original interval volume. Both groups, of course, will now be training in precisely the same way: the way real-world competitive endurance athletes train, with a broad foundation of moderate-intensity "base" work and a thin layer of high-intensity training on top.

The lesson of this thought experiment is that you should not increase your reliance on interval training for the sake of boosting your resting metabolism or your fitness level unless you really aren't doing very much interval training.  Many triathletes do indeed underutilize high-intensity intervals, though.  One set of intervals per week in cycling and running and two to three in swimming are the right amounts.  If you're currently doing less interval training you will undoubtedly experience improvements in your body composition and performance by correcting this training imbalance, even if your training volume is slightly reduced in the process.

Gas-Guzzling Muscle

During exercise, the amount of oxygen you consume depends not only on the intensity of your exercise but also on the amount of muscle mass you carry.  Increased muscle metabolism is the cause of increased oxygen consumption during exercise, so the more muscle mass you have, the more oxygen you consume-hence, also, the more calories you burn at any given work rate.

Elevated muscle metabolism is also the cause of EPOC.  Consequently, the more muscle mass you carry, the more EPOC you will enjoy after workouts.  It's another example of the tendency for the fit to get fitter and the fat to get fatter.  Training increases the percentage of the body's mass that consists of muscle.  This change itself increases the amount of EPOC one experiences after a workout.  In other words, lean individuals get a greater post-exercise fat-burning effect than fatter individuals get from the same workout.

This was shown in a recent study involving 250 Japanese male athletes between 16 and 21 years old. Researchers measured the EPOC of each athlete for 40 minutes after short-duration exhaustive exercise. These values were compared against measurements of body size and composition.  The researchers found that differences in fat-free body mass (which is mainly muscle) accounted for 55 percent of the individual differences in EPOC. 

The lesson of this study is that, with respect to maximizing EPOC, it is best to be large and lean.  Indeed, resting metabolism in general is highest in the most muscle-bound men and women.  Of course, with respect to triathlon performance, it is best to be light and lean.  Therefore I do not recommend that you replace half of your swimming, cycling and running with heavy weightlifting for the sake of maximizing EPOC! 

That said, many age-group endurance athletes could use a little more muscle than they have.  Incorporating some maximum-intensity sprints into your training will increase your power by conditioning your seldom-used fast-twitch muscle fibers.  In addition, incorporating a small amount of strength training into your weekly regimen will further enhance your sport-specific power and reduce your injury risk by improving the stability of your joints.  A slight increase in muscle mass will also result from these changes.  This will increase your EPOC levels after workouts and also elevate your resting metabolism outside of EPOC, as it takes 30 to 50 food calories per day to maintain a pound of muscle.

The Protein Factor

They say you have to spend money to make money.  Similarly, your body has to burn calories to digest and absorb food calories.  Scientists refer to calories burned during digestion and absorption as dietary induced thermogenesis (DIT), because they produce body heat.  The "thermic effect" of different foods and nutrients can be estimated by recording subtle changes in body temperature after eating.  It so happens that protein has about twice the thermic effect of carbohydrates and about triple the thermic effect of fat, meaning protein calories are more likely than fat or carbohydrate calories to be transformed into body heat instead of body fat.

This was shown in a recent study conducted by researchers at the University of Arizona.  A group of young, healthy women were fed two sets of diets. The first diet was high in protein and the second was high in carbohydrate, while both were low in fat.  The thermic effect of the high-protein diet was found to be 100 percent greater than that of the high-carbohydrate diet.

Dietary induced thermogenesis accounts for only a tiny percentage of the body's daily energy expenditure, however.  You won't raise your resting metabolism significantly by switching to a high-protein diet.  But increasing your protein intake will help you preserve calorie-guzzling muscle mass during any period when you reduce your overall calorie intake for the sake of shedding excess body fat.  In one recent study, 158 obese men and women were placed on a diet that contained 500 fewer calories per day than their normal diet.  Half of the subjects consumed a whey protein supplement daily before breakfast and again before dinner.  The remaining subjects consumed a non-protein supplement of equal calories. The study period lasted 12 weeks. Body weight and anthropometric measurements were recorded every four weeks.

Members of both groups lost a significant amount of body weight. Those consuming the whey protein supplement lost slightly more weight, on average, but the difference was not statistically significant. However, members of the whey protein group lost significantly more body fat than controls (6.18 vs. 3.56 lbs) and lost significantly less muscle mass (2.35 vs. 5.3 lbs).

The problem with high-protein diets is that they may not be very well suited to support endurance performance.  Very little research on the effects of high-protein intake on endurance performance has been done, but in one short-term study, New Zealand researchers found that cycling time trial performance was significantly impaired after seven days on a high-protein diet.

The average American is already on a moderately high-protein diet.  A 10-percent protein diet is adequate to meet the needs of endurance athletes and non-athletes alike.  The average American gets 18 percent of his or her calories from protein.  So instead of increasing your protein intake, concentrate on making sure you consume some of your daily protein within an hour after completing each workout.  Research has shown that dietary protein is most efficiently used to synthesize new muscle tissue when consumed after exercise, and that over time athletes build more muscle and lose more fat when they routinely consume protein after exercise than when they do not, even if total daily protein consumption is held equal.

A Big Breakfast

Another dietary tactic that increases resting metabolism slightly is eating more of one's daily calorie allotment before noon and fewer calories after noon.  That's because dietary induced thermogenesis is higher in the morning than in the evening.  This was shown in a study published in the American Journal of Clinical Nutrition, in which volunteers were given an identical 544-calorie meal at one of three times. In subjects fed at 9 am, DIT increased by 16 percent; in those fed at 5 pm, DIT increased by 13.5 percent; and in those fed at 1 am, TEF increased by only 11 percent.  So it's clear that we burn more calories in the morning.

To take advantage of this phenomenon, do a little calorie counting and modify your typical meal menus to ensure that your breakfast has more calories than your lunch, and your lunch has more calories than your dinner.  This is precisely the opposite of how most of us eat, so be prepared for a major overhaul.  Use food labels and resources such as www.nutritiondata.com to get accurate calorie counts.

Supplemental Means

There are many diet supplements that purport to raise resting metabolism and burn off excess body fat.  Most of them do not work at all or have such a small effect on the metabolic rate that they're really not worth the distraction from better ways to get the job done.  Caffeine and green tea extract are on this list.  So is conjugated linoleic acid (CLA), a type of fat that is found in trace amounts in some meats and dairy foods.  It showed promise as a thermogenic fat reducer in early animal studies, but more recent human studies have failed to duplicate such results.

Don't Blame Your Genes

Men and women who struggle to control their weight often blame their genes for giving them a slow metabolism.  It is true that the metabolic rate is largely genetically determined.  However, lifestyle trumps genetic inheritance-in fact, lifestyle largely controls how your metabolism-regulating genes express themselves.  For example, Finish researchers recently compared "discordant" identical twins (one obese, one non-obese) and "concordant" identical twins (both non-obese) and found that, while both twins in the pairs with one obese member were more likely to have certain genes that slowed metabolism, these genes were significantly less active in the non-obese member of the discordant pairs, who tended to have a much higher fitness level.  Exercise switches of some of the genes that want to make you fat, making it almost as though we had not inherited these genes in the first place.

One of the best things you can do to increase your resting metabolism and achieve a lean body composition is to be an endurance athlete.  As an endurance athlete, you can further increase your resting metabolism by regularly engaging in high-intensity interval training and strength training, by consuming protein after workouts, and by eating a large breakfast, a medium-size lunch and a smallish dinner.  But leave the fat-burning supplements alone.

I just got word that Running Times will print an excerpt from my forthcoming book, Run Faster from the 5K to the Marathon, coauthored with Brad Hudson, in its August issue. It's going to be a condensed version of Chapter 2, which discusses the 12 core methods of Brad's training system. Check it out if you can. And in the meantime, check out this brief sneak peak at the same chapter:

General running volume-or how much you run-is the most basic parameter of training and therefore the first parameter that each runner should consider in creating a customized training plan. How many times per week should I run? How many miles per week? How much should my running volume increase from the beginning to the end of my training plan? These are the questions you need to answer before asking any others as you look ahead to your next training cycle.

The running volume that is most appropriate for you depends on your next peak race goal, your capacity to absorb and recover from frequent runs and longer runs, and your training history. As a general rule, I recommend that runners consistently maintain a moderately high running volume relative to these individual considerations.

Some training systems are characterized by extremely high volume rather than mderately high volume. In extreme high-volume systems, runners push themselves to run as many miles each week as they possibly can. Arthur Lydiard was a persuasive proponent of extreme high-volume training. Many of America's top runners of the 1970s and early 1980s-including Frank Shorter, Bill Rodgers, and Alberto Salazar-were strongly influenced by Lydiard's philosophy and achieved great success on high-mileage training (upwards of 150 miles per week in some cases).

Other training systems are known as high-intensity systems. In these systems, training intensity, not training volume, is considered to be the true path to running success. The weekly training schedule is packed with high-speed sessions that leave runners exhausted after relatively few miles compared to the number of miles they could complete at lower intensities. High-intensity training systems are necessarily moderate-volume systems, because the more high-speed running you do each week, the less total running you can do without becoming overtrained or injured. Many great runners have achieved outstanding success on training programs that emphasized quality over quantity. American middle-distance star Alan Webb and former marathon world record holder Steve Jones of Wales are among the most noteworthy runners to have reached the top by doing a lot of high-intensity workouts and less total mileage than most of their peers. Bill Bowerman, the legendary University of Oregon coach and Nike cofounder, also used a high-intensity, moderate-volume system with his athletes.

Based on the proven effectiveness of both approaches, I like to split the difference between the extremes in volume emphasis and intensity emphasis. I believe that high running volume is indispensable for maximal aerobic development. However, high-intensity training clearly provides fitness benefits that moderate-volume training does not. Since the only way to truly maximize running mileage is to forego high-intensity training, I believe that overemphasizing mileage is a mistake. Most runners will get the best results by finding a balance between quality (intensity) and quantity (volume). So the adaptive running approach is to do as much running at various faster speeds as you can do without seriously limiting the total running volume you can absorb, and to do as much total running as you can do without seriously limiting the amount of high-intensity running you can absorb. Naturally, the precise formula is different for each runner and requires experimentation to find.

Another aspect of my philosophy on running volume is consistency. Some training systems entail large fluctuations in running volume throughout the training cycle. But I prefer to keep the overall running volume fairly consistent throughout the training cycle while manipulating other variables to produce fitness gains. Obviously, when an athlete's recent training has been at a low volume it is necessary to gradually increase it to the level that is required for peak fitness. However, once a runner has attained this level, I like to have him or her stay relatively close to that level thereafter, except for brief off-season rest periods.

The rationale for consistency in running volume is, first of all, that it does no harm to maintain a relatively high volume year-round. As long as you take one or two breaks each year and reduce the overall workload of your training when appropriate, you won't wear yourself down. Secondly, having to build your running fitness from a low level to the level required for peak fitness can really bog down a training program, because volume increases must be executed gradually to avoid overtraining and injuries, and it's very risky to increase overall running mileage and high-intensity running mileage simultaneously. You'll be able to build fitness faster and peak at a higher performance level if you start each training cycle with a relatively high volume of running. And the only way to safely start a training cycle at a fairly high volume is to never allow your training volume to drop too low.

A third benefit of maintaining moderately high running mileage more or less year-round is that it reduces injury risk. Injuries tend to occur during periods of increasing running volume. If you keep your mileage relatively high, you will minimize these risky volume ramp-up periods in your training.

Several years ago I developed a nagging pain on the right side of my pelvis, in the crease between the top of my thigh and my pubic area. Clearly an overuse condition related to running, the pain got so bad that I had to stop running completely. It went away for a while and then returned with a vengeance after I resumed full training. Fearing that I had developed a sports hernia, I went to see a doctor about it, but he diagnosed hip flexor tendonitis.

Later, when rehabilitating an unrelated injury, a physical therapist told me I had extremely tight hip flexors (a common problem in runners) and suggested I start an intensive stretching program to lengthen them. Very soon thereafter another physical therapist analyzed my gait and told me that my stride was too short because I was unable to hyperextend my hips normally, probably due to those tight hip flexors. The two therapists (who knew each other) agreed that this muscle imbalance was probably the cause of my tendonitis.

Whether because of the stretching or other changes that I made (most especially to my gait), I was able to control my pelvic pain (which eventually emerged on my left side, as well) enough to train as I pleased, but it was a constant source of discomfort and became borderline debilitating during my heaviest periods of training and in my hardest, longest workouts. Indeed, it nearly took me out of the California International Marathon last year.

Recently, on a hunch, I decided to test whether making a specific change to my stride would ameliorate the problem. Since the first time I saw myself running on videotape as a high school junior I have known that I run in a sort of seated position, with my pelvis tilted forward-a posture that you might expect in someone with very tight hip flexors, which contantly want to fold the trunk toward the thigh, and another very common issue in runners. I wondered what would happen if I forced myelf out of this position by pressing my hips forward, neutralizing the position of my pelvis and thus making it easier to hyperextend my hips to lengthen my stride.

I began playing around with proprioceptive cues that would enable me to sustain this change.  Consciously pressing my hips forward worked well, and so did running tall, or imaging my head being pulled skyward by a wire. Interestingly, in this position I immediately felt my hip flexors being forced to stretch more, as they were having to work from a more lengthened position compared to the contracted position they were used to working in. But while I felt more stretch in these muscles, I actually felt less strain. My hypothesis is that to facilitate my new posture, my brain has relaxed my hip flexors instead of holding tension in them as it normally does. Without this tension, my hip flexors no longer resist the lengthening they must undergo to allow my hips to extend. A tug-o-war has ceased.

This experience strengthens my belief that stride improvements trump stretching and strengthening exercises with respect to overcoming and preventing recurrence of injuries. Tight and weak muscles only cause injuries inasmuch as they alter the stride in bad ways. And no amount of stretching and strengthening will fix stride flaws on their own. There must be a concious effort to run differently.

The physical therapist who told me to stretch my hip flexors was not wrong to do so, but what she did not understand is that muscle tightness is not a matter of a muscle being structurally too short. Muscles can't shrink in that sense any more than bones can shorten. Tightness is, rather, a matter of your brain holding the muscle in a shortened position-keeping it constantly semi-contracted. Traditional stretching exercises are not the best way to train your brain to relax a tight muscle, especially in the context of complex movements such as running.  What you really have to do is trick your brain into letting the tight muscle relax by changing something about the way you move so that your brain sort of forgets to hold tension in the tight muscle and then discovers that no harm is done in the process (as holding tension is essentially a self-protective mechanism) and continues to allow it.

It's only been a few days since I made this discovery. I'm still at the stage where I have to concentrate on pressing my hips forward with every stride or else I fall back into sitting. But I think I'm onto something and I am very eager to see whether the pain in my pelvis slowly diminishes as I continue.  Maybe someday I will no longer wince when I wake up in the middle of the night having to pee and contract my hip flexors to sit up in the bed.

Ever since I moved back to San Diego on February 1 I have been struggling with post-exercise recovery. For a while I was just struggling with my running in general. I've gotten past that period of malaise and am now performing reasonably well in my planned hard workouts, but I am still feeling much crappier and running much more slowly than I am accustomed to doing in the recovery runs that I complete 24 hours after each hard run. Two days ago, however, I stumbled upon an embarrasingly obvious likely explanation for the pattern.

On that day I did a hard session of 300-meter intevals on the track. I started the workout at about 4:30 pm. As soon as I finished, I drove straight home to meet up with my wife and a couple of friends and head out to a restaurant for dinner. By the time I put the first bite of appetizer in my mouth it was nearly 7:30, more than two hours after I had completed my run. This is not good, I thought. If I had a nickel for every time I have written about the importance of consuming protein, carbs and fluid within the first two hoursand ideally within the first hourafter completing a workout I could retire. Research has shown that athletes who wait too long to nourish themselves after training seriously compromise their physiological recovery processes and sabotage their performance in the next day's training. So I kicked myself for failing to drink some Endurox R4 or get some other kind of appropriate post-workout nutrition fix after leaving the track.

In the next moment I suddenly realized that I had been neglecting my recovry nutrition after every weekday run since returning to office work 10 weeks earlier. Before the move I was doing my main workout of the day at 10 or 11 am and eating lunch immediately afterward. My second workout, on days when I doubled up, took place in the evening. But since relocating I had moved my secondary workout to the early morning and pushed my main workout back to the late afternoon. My unthinking routine after these runs has been to commute back home, shower and then eat dinner. Even on a typical day when I eat dinner at home with my wife, I don't eat until 90 minutes after completing my run.

This oversight could easily explain the better part of the sluggishness I have been feeling in my recovery runs. It's not the sort of mistake a person in my position should make. I've been encouraging other endurance athletes to "drink the Kool-Aid" of post-workout nutrition for years. But where has my cup been in the past 10 weeks? Embarrassed as I am, I'm also relieved, because a solution to what had been a mystery problem until two days ago is now at hand. I'm hitting the track again this afternoon and my Endurox R4 is ready to go.

Fat is the muscles' primary fuel for low- to moderate-intensity exercise. Carbohydrate is the muscles' primary fuel for moderately high- to high-intensity exercise. Carbohydrate fuel supplies are very limited in the body, such that carbohydrate fuel depletion is a major cause of fatigue during prolonged exercise at higher intensities (e.g. triathlons and marathons).  Fat fuel supplies are virtually unlimited in the body.  Thus, by increasing their reliance on fat fuel and decreasing their reliance on carbohydrate fuel during race-intensity exercise, endurance athletes could theoretically delay fatigue and perform better.  Endurance training and increased fat consumption are known to increase fat burning during exercise.  But is there solid proof that endurance athletes can actually perform better by training and eating to burn more fat?  Let's explore the question.

Several years ago, researchers from the University of Buffalo published an interesting study on the performance effects of various levels of fat consumption in men and women.  Endurance and VO2max tests were performed at the end of four-week periods in which runners consumed diets of 16 percent, 31 percent, and 44 percent fat.  Time to exhaustion in the endurance test was 14 percent greater at the end of the medium-fat diet than it was at the end of the low-fat diet.  However, there was no change in VO2max.

One major limitation of this study was that the order of the diets was not random, therefore we cannot rule out the possibility that the runners performed better in the second endurance test because they were more familiar with it, or in better shape, not because of their diet.  Also, there was no difference in the rate of fat burning in the second endurance test versus the first.  If higher fat intake was the cause of superior endurance, we would expect increased fat burning during exercise to be the mechanism.

Other research, however, has found that increased fat intake does result in greater fat oxidation during exercise.  Researchers from New Zealand compared the effects of a 14-day high-carbohydrate diet, a 14-day high-fat diet, and an 11.5-day high-fat diet followed by a 2.5-day carbo-loading diet on fat oxidation and performance in a 15-minute cycling test and a 100-km cycling test.  Performance in the 15-minute test was slightly better after the high-carb diet, but not to a statistically significant degree, while performance in the 100-km test was slightly better, but again not to a statistically significant degree, following the high-fat diet.  Fat oxidation was significantly greater during the 100-km test following the high-fat diet.

Like this study, other studies have also suggested that, while increased fat intake may increase endurance, it may also reduce performance in shorter higher-intensity races.  In a recent review of the existing literature, researchers from Kansas State University wrote, "We and others have observed that although fat oxidation may be increased, the ability to maintain high-intensity exercise (above the lactate threshold) seems to be compromised or at least indifferent when compared with consumption of more carbohydrate."

That's why the New Zealand researchers mentioned above thought to include a hybrid diet-a high-fat base diet followed by a short carbohydrate-loading period-in their study.  The rationale for this approach is that a couple of weeks on a high-fat diet will stimulate increases in fat oxidation capacity during exercise, and that following this adaptation period with a couple of days of carbo-loading immediately preceding a race or other maximal endurance effort will maximize muscle glycogen stores, so the athlete has the best of both worlds.

A recent study from University of Cape Town, South Africa, suggests that this strategy just might work.  Researchers examined the effects of a high-fat diet versus a habitual diet prior to carbohydrate loading on fuel metabolism and cycling time-trial performance. Five trained cyclists participated in two 14-day randomized cross-over trials during which they consumed either a 65 percent fat diet or their habitual 30 percent fat diet for 10 days, before switching to a 70 percent carbohydrate diet) for three days.

All subjects then performed a cycling test consisting of 2.5 hours at 70 percent of peak oxygen uptake followed immediately by a 20-km time trial. The high-fat diet resulted in increased total fat oxidation and reduced total carbohydrate oxidation during exercise. Most noteworthy, the high-fat treatment was also associated with improved time trial times.  On average, the cyclists completed the 20-km time trial 4.5 percent faster after the high-fat diet.

The problem with this study is that the design of the exercise test was biased to take advantage of improved fat burning.  The initial 2.5-hour ride at a moderately high intensity ensured that the cyclists' muscles were significantly glycogen depleted before they even started the time trial, forcing a greater reliance on fat, of which the cyclists were more capable after the high-fat diet.  But if this study had instead involved a time trial after a standard warm-up, it is unlikely that the high-fat diet would have been seen to result in better performance.  Indeed, other studies have found that a high-fat diet followed by a carbo-loading phase impairs performance in high-intensity time trials.

What about Training for Fat Burning?

Some endurance sports coaches believe in emphasizing training in the "fat-burning" zone (approximately 60 percent VO2max) to increase fat-burning capacity and thereby increase fat-reliance in races.  Perhaps the best-known advocate of this approach was Phil Maffetone, an endurance sports coach who made his name by developing a training philosophy that was characterized by an extreme emphasis on the importance of fat metabolism. He taught his athletes to do virtually all of their training at a very low intensity to maximize fat metabolism and stimulate physiological adaptations that increased the body's capacity for fat oxidation in subsequent workouts. Over time, Maffetone believed, the athlete would be able to swim, bike or run faster and faster at the same, low, fat-burning intensity.

Research has shown that training in the fat-burning zone does improve fat-burning capacity.  However, it only improves fat-burning capacity within the fat-burning zone itself-that is, at lower exercise intensities.  No matter how fit they are or in what manner they've trained, all runners rely on carbohydrate when racing at intensities that are near or above the lactate threshold.  Indeed, despite being well adapted for fat burning, elite male marathon runners oxidize carbohydrate almost exclusively during competition.  Only slower marathon runners (3:30-plus) and ultramarathon runners are likely to benefit from emphasizing training in their fat-burning zone.

In summary, there is probably nothing special you need to do with your diet or your training to become a fat-burning machine and, as such, a faster racer.  Proper training will automatically increase your fat-burning capacity, but this adaptation will not directly influence your performance in races lasting less than several hours.  If you care to, you may experiment with 10 or 11 days on a high-fat diet followed by two days of carbo-loading before a longer race, as it won't harm you and there's a slight chance it might help.

Currently I'm working on an article for Runner's World entitled "Run Any Race in Four Weeks." This catchy title represents a clever way to hook readers into reading an article on nonlinear periodization. The way I pitched the article to the editors at Runner's World was this: The typical runner allows his base fitness level to fall far below peak level between major races. Volume is sharply reduced, the long run distance comes way down, and high-intensity workouts are all but phased out. Many elite runners, by contrast, maintain a high level of well-rounded fitness year-round by keeping their running volume fairly high and keeping a variety of different workout types in their regular training regimen. This allows them to peak very quickly and effectively for races with a short period of very challenging race-specific training. The typical runner should take a page from the elites and reap the benefits of nonlinear periodization.

Nonlinear periodization may be thought of as a philosophy of staying within shouting distance of the fitness level required to race well at any distance at all times. Training is consistent, balanced, and moderately challenging at most times. Training in this way enables the runner to take on a very high training load with minimal risk of injury or overtraining when it comes time to sharpen for a race and thus to peak at a very high level of performance.

Runners who fail to practice nonlinear periodization have to play catch-up through most of the training process. They have to devote a much longer period of time to focused preparation for a race. This is true even if they have not allowed their training volume to drop very low. Simply cutting back too much on high-intensity training will put them in a similar hole, because they will have to spend large amounts of time working to shore up weaknesses.

As I do so often these days, I relied on Brad Hudson as my expert source for this article. He is a major proponent of nonlinear periodization and practices it very effectively with Dathan Ritzenhein and his other runners. You can learn more about Brad Hudson's training methods on his website and in his forthcoming book, Run Faster, which I coauthored. And be sure to check out my article in the June issueof Runner's World!

Phil Maffetone was an endurance sports coach who made his name by developing a training philosophy that was characterized by an extreme overemphasis on the importance of fat metabolism. He taught his athletes to do virtually all of their training at a very low intensity to maximize fat metabolism and stimulate physiological adaptations that increased the body's capacity for fat oxidation in subsequent workouts. Over time, Maffetone believed, the athlete would be able to swim, bike or run faster and faster at the same, low, fat-burning intensity. (I'm using the past tense not because Maffetone has passed on, but rather because he seems to have reinvented himself as a musician.)

There are a numerous problems with the Maffetone Method. The fact that the body's ability to increase its fat burning capacity is far more limited than Maffetone believed is the smallest of them. A much greater problem is that it's impossible to maximize performance in standard endurance sports events such as half-marathons and Olympic-distance triathlons without doing a fair amount of training at high intensities. Threshold workouts, VO2max intervals and even all-out sprints produce valuable fitness benefits that complement those resulting from slow and steady workouts, which simply cannot replicate these complementary benefits on their own.

Having said this much, I have very recently come to a place where I appreciate the value of exercising at a very low intensityspecifically, of running at a very slow pacemore than I did before. I did not come to this place voluntarily. My body seems to have been seriously disrupted by my recent relocation and return to outside-the-home work for the first time in seven years. I've been running very poorly ever since my return to San Diego. For a while I tried to get through it with the right mixture or patience and pushing, but recently I decided to try another tactic. I cut out all of the threshold runs, interval workouts, and even moderate-intensity base runs that were causing me such misery and replaced them with what I generally consider to be recovery runs, in which I run as slow as necessary to feel comfortable, even if my pace is utterly embarrasing to my ego.

I have found that, by essentially embracing necessity in this way, I am indeed able to "feel good" once again when running, and one should feel good when running most of the time, even when training very hard. I'm also able to spend just as much time running as before, and I've even begun to take advantage of the gentleness of my training by going longer than I had been planning to do before I took evasive action. Yesterday I did my first two-hour run in a while.

My rationale for taking this approach has little to do with fat metabolism and everything to do with the nervous and immune systems. I saw my poor running as a symptom that my body was under stress. I changed my training in a way that heeded my body's message to me yet without sacrificing my desire to maintain (or regain) a high level of fitness. I certainly have not yet reaped benefits that will allow me to once again run faster and comfortably, but I think I'm on my way. In any case, I'm now planning to continue running very slowly longer than is strictly necessary, as a little experiment to see how far the Maffetone Method can take me.