As fall is settling upon the Northern Hemisphere many cyclists are looking forward to both the crux off their off-season and starting to plan for next year. As you look back at the season just passed, and ahead to next year what will you do differently? We routinely make choices about our equipment, our training plan, our coach, and even our diet and nutritional needs, but have you ever really considered the importance of your metabolic efficiency?
By Matt McNamara
A couple of weeks ago I attended Bob Seebohar’s “Metabolic Efficiency Training” webinar and came away with a new perspective. Bob is a well respected sports dietitian who has served as the lead sports dietitian for endurance sports at the U.S. Olympic Committee, and is the author of numerous books, studies, and articles on performance nutrition.
Seebohar has developed a variety of novel approaches to the question of optimizing performance through responsible nutrition management. His “Nutrition Periodization” book is essential reading if you want to learn more about how to organize your nutrition to suit the different phases of the training year. This webinar introduced his new book on metabolic efficiency and continued the outside-the-box thinking that has defined Seebohar’s approach to sports nutrition.
The Theory
What is metabolic efficiency and why does it matter? Metabolic efficiency is simply the process of increasing the use of fat as an energy source and preserving carbohydrate stores during exercise. The average person has over 80,000 calories of fat in their body, but only about 2000 calories of carbohydrate. The goal of metabolic efficiency training is to take maximum advantage of this discrepancy. According to Seebohar, and research across decades, there are only two ways to increase this efficiency – aerobic training and changing your nutrition.
Aerobic training increases both mitochondrial enzymes and the absolute quantity of mitochondria, both of which contribute to better beta oxidation (use of fat). Similarly altering an athlete’s nutrition profile during different training phases by decreasing carbohydrate intake helps blunt the insulin response and allows the athlete to become more efficient at using fat.
The classic method for determining energy use is through “indirect calorimetry,” measuring the volumes of oxygen consumed (O2) and carbon dioxide (CO2) expired. Essentially oxygen uptake and caloric burn rate are interchangeable. It requires 208.06 milliliters of oxygen to burn 1 calorie, always. The relationship between O2 consumption and CO2 production is termed the Respiratory Exchange Ratio, or RER (and is interchangeable with Respiratory Quotient, RQ, for this article).
Typically a graded exercise test, capturing all inspired and expired gases, is used to determine RER. This ratio establishes the percentage of fat (FAT) and carbohydrate (CHO) utilization at different exercise intensities. For example an RER of 0.707 means that 100% of energy is being derived from FAT, while an RER of 1.0 equals 100% CHO.
In this model there is an inevitable “Crossover” point at which substrate utilization reaches a 50/50 balance of FAT and CHO. As intensity rises the percentage of energy derived from CHO continues to rise as well.
Seebohar terms this crossover point as the “Metabolic Efficiency Point”, the point where fat utilization contributes maximally to energy requirements. Ideally, you would like to move this point to the right of the above graph so that the crossover doesn’t occur until higher power outputs. To determine your individual efficiency point you’ll need to get tested.
The Test
In order to determine your current metabolic efficiency you need to have access to a metabolic cart. These carts are usually found in University or hospital settings, though there are an increasing number of gyms and performance centers that provide effective assessments. To be truly effective your metabolic cart must measure the actual oxygen consumed and carbon dioxide produced. This is important as there are several lower cost options that merely estimate the CO2 side of the equation and don’t measure it directly. To be accurate find a location that measures CO2 directly.
The Metabolic Efficiency Point test is fairly straight forward. It is an incremental sub-maximal effort lasting 30 – 60 minutes and can be performed on a treadmill, bicycle ergometer or Computrainer. The athlete is asked to avoid calories and stimulants for 3-4 hours before the test, and will typically warm up for 15-20 minutes while on the metabolic cart. The test is broken into five minute stages with a recommended ramp rate of 0.2 – 0.5 mph on the treadmill and between 15-50 watts per stage on the ergometer. The actual ramp rate will vary due to the relative fitness of the athlete. A fitter athlete can usually handle a faster ramp rate, but you have to be careful not to push too hard too fast. You are looking for a gradual and steady progression of the workload so that the test lasts for at least 30 minutes.
The Analysis
Once you have the data from the test you are looking for a couple of markers on the data sheet. Specifically you should look at the RER value and the percentage of energy derived from fat and carbohydrate. Seebohar defines the Metabolic Efficiency Point as being at an RER of 0.85, meaning that the body is using the highest percentage of fat possible before CHO passes the 50% mark. On an incremental test like this RER need not exceed 0.93, so it is truly a sub-maximal effort. You will also get the actual caloric expenditures for fat and carbohydrates.
By understanding both the total caloric expenditure and the mix of those calories you can begin to construct a training plan to maximize the use of fat and decrease and improve your total caloric expenditure pure hour. This leads directly to an improvement in your carbohydrate storage and subsequent need for external sources of carbs during training and racing.
The Problem
The theory of a metabolic crossover point is well researched and accepted across populations, but it is not a given. Interestingly, in looking at different metabolic efficiency profiles of athletes across time, Seebohar has repeatedly come across a profile where the expected cross over point didn’t happen. Instead these athletes started a graded exercise test already over 50% CHO utilization. He attributed the response to poor nutrition, the intensity of their training phase, or both elements.
Essentially this poor utilization of existing fat stores leads to a direct decrease in performance by forcing the athlete to utilize existing CHO stores more quickly, leading to an increased reliance on carbohydrate supplementation from external sources, and increasing the risks o gastrointestinal distress (GI Distress). Additionally a high carbohydrate diet increases carbohydrate oxidation as the spike in insulin turns off beta oxidation (fat oxidation). This double hit of highly inefficient metabolism and predisposition to GI Distress had a tremendous effect on performance.
The Solution
Now that you have a good grasp of the athletes metabolic efficiency profile, and associated heart rate, power, or pace to achieve the 0.85 RER we can begin to modify training to maximize improvements in beta oxidation. One primary goal is to decrease the hourly demand for CHO, and associated risk of GI distress.
According to Seebohar the process of actually changing your metabolic efficiency takes a couple of focused efforts. First you have to change your nutrition, then you have to change your training. The change in nutrition requires you to dramatically cut the starches and whole grain carbohydrate load in your diet. This is no small feat for endurance athletes and may require up to four or more weeks to accomplish. In addition to changing the total CHO load it is advised that the athlete change their CHO utilization prior to, and during training. In essence you want to avoid dumping a bunch of carbohydrate into your bloodstream in the hour before you start training. This will help manage the insulin response and allow your body to begin using fat more efficiently.
You also have to be willing to eliminate high intensity training for a few weeks. As such this sort of training adaptation is best achieved in the preparation and base periods of a training block. You have to stay aerobic to see the benefits! That means no high intensity, threshold and above efforts for a few weeks, which is why it works so well at the start of a base period. For many of us that is either now, or in the next few weeks.
Summary
Metabolic efficiency is the process of increasing your reliance on stored body fat to fuel your exercise, thereby saving carbohydrate for later in an exercise bout or race when it could provide an essential performance advantage. There are two elements to improving your metabolic efficiency. The first is to train your aerobic system. Focused training at low to moderate intensity is the perfect vehicle to improving your aerobic function and ultimately your fat utilization profile. The second element is nutritional. You have to modify your nutrition profile to allow your body to begin optimizing beta oxidation and metabolic efficiency.
If this all seems like a lot to figure out there is hope! Seebohar’s next book is all about the metabolic efficiency training and should be available at retailers within the next month or so!
References
Brooks & Fahey Exercise Physiology Human Bioenergetics and its Applications
Podolin, Exercise Physiology Lab Techniques
Seebohar, Bob. Metabolic Efficiency Training Webinar
Seebohar, Bob. Nutrition Periodization for Endurance Athletes
Goedecke, St Clair Gibson, et al - Determinants of the variability in respiratory exchange ratio at rest and during exercise in trained athletes Am J Physiol Endocrinol Metab 279: E1325-E1334, 2000
About Matt McNamara: Matt is a USA Cycling Level 1 coach with over 20 years of racing, coaching and team management experience. He is the founder and president of Sterling Sports Group, a performance coaching company focused on creating a seamless interface between athlete and coach, technology and personal attention. Learn more by visiting his website at www.sterlingwins.com.
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