Have you had difficulty performing up to your potential in endurance racing and suspected nutrition as the culprit? Found yourself bonking out when consuming the "recommended" number calories over the course of your marathon or century race?
Unfortunately, the formulas we rely on to determine our baseline and exercise caloric needs are only generic estimates that can be off by hundreds of calories, and which tell us little about the fuel sources that our individual physiologies utilize at various work outputs. Harris-Benedict - the most common estimate of basal metabolic rate - has a margin of error of 1000 calories.
Before going further, lets define some important terms:
Basal (or Resting) Metabolic Rate (BMR or RMR): The number of calories your body consumes to support baseline physiologic function over the course of the day. We think of this as the number of calories you would require to survive if you laid in bed all day staring at the ceiling.
Daily Caloric Expenditure (DCE): The total number of calories you burn each day. This number includes your BMR, any calories you burn through movement and training, and the thermogenic effect of the food you consume (very small percentage of DCE).
Exercise Metabolic Rate: The rate of calories you burn during exercise. This rate varies according to the type and intensity of exercise. As an example, the old "rule of thumb" is that you burn about 100 calories per mile of running. However, upon testing you might find that you burn 4.8 kcal/min at a 12:00 min/mile pace (57.6 cal/mile), 7.6 at a 9:00 min/mile pace (68.4 cal/mile) and 12.4 at a 7:00 min/mile pace (86.8). So if you've been assuming you burn 500 calories on a moderate 5 mile run, you'd be about 158 calories off.
Fuel Recruitment: The mixture of fuels (% fat versus % sugar) that you burn at rest and during exercises of different intensities. I'll discuss this in more detail in a coming post, but the specific mixture that you burn has important ramifications for your approach to eating, training and racing.
All of these natural variations in BMR, EME, and fuel recruitment can contribute to the frustrations that many individuals and athletes experience as they try to optimize their body compositions and fuel for races. However, the good news is that once you learn what YOUR true numbers are you are well positioned to make the changes that will finally be effective in helping you attain success - whether in losing weight, racing to your potential, or both.
But how do you find out what your BMR and EMR really are? Metabolic testing.
Metabolism is the biochemical process of combining nutrients with oxygen to release the energy needed for the body to function. This energy is measured in calories (Kcal). By measuring the volume of oxygen consumed and corbon dioxide produced by an individual both at rest and during exercise, we can determine both amount of energy use and the mixture of fuel sources (fats and sugars) being used.
During exercise testing, it is also possible to determine VO2Max and the threshold at which your body begins to sharply limit the amount of energy it draws from its large resources of free fatty acids, and begins to primarily use your very limited glycogen stores as its energy source. This is what we think of at "threshold" and knowing the pace, HR, or work output with which it is associated is key. Stay just below it, and you can hold that pace for a very long time (from an energy standpoint). Go above it, and your time is quite limited before you run out of fuel if you don't consume AND ABSORB calories (hard for your GI system at such intensities). The result is the dreaded bonk, and in ultra-endurance events, can often also be a DNF.
To perform metabolic testing, we use a mask and tubing system that has sensors connected to assessment equipment that measures the individual's respiratory gases input and output. The data, along with HR, fuel sources, and other biomarkers, are displayed on the computer screeen for the test administrator to observe and monitor. The system looks something like this:
We are very lucky that Seaside Cycle has invested in such a testing unit for use with the elite cyclists and triathletes that it sponsors. Seaside's owner, Scott Bumpus, is also allowing Janda Ricci-Munn and I to offer testing to our clients and the general public.
If you are interested in testing you can email april @ trainingmeetstlc.com or call (978) 729-9048 for more information or to schedule a testing date. You can also visit my website at www.TrainingMeetsTLC.com or Seaside's at www.SeasideCycle.com to learn more.
0 comments:
Post a Comment