If you want to lose fat, you have to train a certain way in addition to being in a deficit. First, let’s talk about what not to do while on a diet:
Maintain a sedentary lifestyle. Do hours of cardio a week. Do cardio and very light weight training (20-30 reps or more) that does not take you to failure.
You will lose weight if you choose one or a combination of those three options. However, it will not be just fat, meaning you have a higher probability of losing lean mass. This has become known as “skinny fat”. You will weigh less, but you’ll still be flabby. Skinny people look good in clothes, fit people look good naked. If you don’t care how you look naked, then you can stop reading here and go back to whatever else you were doing. However, if aesthetics is a concern… it is important to focus on losing fat, not just weight. In addition to looking better fat loss also improves your bad cholesterol and glucose tolerance, brings blood pressure down and reduces risk for cardiovascular disease.
Glycogen Stores 101
When you eat a meal, the carbohydrates are converted to glucose and used for energy. Excess carbohydrates are converted into glycogen and stored in the liver, muscles, and a tiny amount in the blood stream.
When your body needs energy (to fuel a workout or because you haven’t eaten in four to six hours), it converts that glycogen back to glucose and starts to deplete your stores. According to research, the more glycogen you have stored in your body, the less fat you burn during your workout and at rest. Therefore, by depleting your glycogen and manipulating your diet, you can maximize fat burning.
The Energy Systems
In order to lower glycogen stores you have to train a certain way. During the first ten seconds of a muscular contraction your body is using its phosphate system, also known as the ATP-CP energy pathway. ATP stands for adenosine phosphate which is stored in the muscle. CP stands for creatine phosphate which resynthesizes ATP. The body then moves to aerobic metabolism or anaerobic metabolism depending on your intensity.
The anaerobic pathway or glycolysis creates ATP from carbohydrates (glycogen). This pathway is used during high intensity work, like weight lifting or sprinting and can last up to two minutes. Lactic acid is a by-product of glycolysis. And after that two minute mark, you start to feel a muscular burn caused by lactic acid’s accompanying hydrogen ions. This is what forces you to take a rest period before you start again. Glycolysis can only fuel about two hours of work… but this is the pathway that will lower your glycogen storage. After that, you will have to lower your exercise intensity to keep going.
At that point you will be dipping into your aerobic metabolism. It uses oxygen to convert carbohydrates, proteins, and most importantly fats to ATP. This is primarily what your body uses during endurance exercise, like running, biking, and dancing. But, this is also the pathway you use at rest which is an important point I will bring up later.
The body doesn’t exclusively start one pathway, then stop and go onto the next. They all run together and work harder or pull back depending on exercise intensity. The harder the intensity, the more your body is going to call upon the anaerobic pathway. When you lower the intensity your body is going to get a higher percentage of fuel from the aerobic pathway.
How to Deplete Glycogen
1. Metabolic Training
Metabolic Training has several pseudonyms: interval training, circuit training, turbulence training and more. They all accomplish the same thing and are carried out on relatively the same principal. You perform (on average) 12 to 15 reps of an exercise with only 30 to 60 seconds of rest in-between sets. Usually, you do three to four sets of an exercise before moving onto the next. This type of training is forcing your muscles to use the anaerobic pathway. When exercising this way at the right intensity, you will “start to feel the burn” towards the end of your set. That’s the lactic acid and hydrogen ions. It’s also the reason why you need a brief rest between sets—to clear it out—so you can go again.
2. Lift to Failure
To use glycogen, you need to lift heavy. I recommend staying within the 8 to 12 repetition range. That means, that you physically cannot lift the weight anymore somewhere between the 8th and 12th rep. In the last three years, a handful of studies have called into question whether light weight can induce as much muscle hypertrophy as heavier weights. But, your focus here is to deplete glycogen. You want to work in the anaerobic pathway as much as possible.
Achieving failure is a lot easier said than done. Exercise beginners are afraid of burn. Even some experienced exercisers don’t like to push themselves to that point and stop too soon. No matter what weight you choose, you need to work to failure.
3. Lift first
If fat loss is your goal, it makes sense to lift first. By performing resistance exercise for at least 30 minutes, you are using up glycogen. By the time you get to cardio, your body you will be using more of your aerobic metabolism. Remember, it will not be relying completely on aerobic metabolism if you still have glycogen. To help increase the percentage coming from aerobic metabolism, do 5 to 10 minutes of sprints followed by 20 to 30 minutes of lower intensity exercise. As the duration of the cardio goes up, the more of the aerobic pathway you use.
4. Fasted Workouts
When you sleep, your body needs fuel to maintain all of its bodily functions, so it uses glycogen. If you work out in the morning, you can get into aerobic metabolism a lot faster because there is less glycogen to deplete. Remember, you can create ATP from fat metabolism, it is just slower and you will not be able to lift as heavy. Aerobic metabolism is also what your body uses all day long: as you sit in your car, work in the office, etc. It will operate at a lower percentage when there are carbohydrates available for fuel and increase as available glucose drops off.
This means the best time to train might be after you wake up before you eat when your body is already drawing upon fat stores for fuel.
In the last few years, many studies have come out in support of this. One such study asked participants to fast for 12 to 14 hours and then perform moderate intensity exercise during the fast. On average, participants did about 60 minutes of walking. Over 12 weeks, the study subjects lost around nine pounds of weight, but measured 16 pounds of fat loss; meaning they gained muscle while losing fat.
Basically, what researchers confirmed in this study (and many others like it) are the benefits of intermittent fasting. You can perform a fasted workout in the morning, or fast during the day and perform a workout in the afternoon, properly fueling your body after exercise. Since you are going to be strength training and not just walking, you may want to look into Martin Berkhan’s intermittent fasting protocol. He has laid out specific recommendations for branch chain amino acid consumption pre-workout and meal consumption post-workout.
The rules set above apply to experienced exercisers. If you are new to a program and fueling your body correctly, you have a short window whereby almost anything you do is going to promote muscle growth while reducing fat.
You need to have a nutrition plan in place. You want to fuel your body correctly before and after exercise but not completely refill your glycogen stores. This is a complex piece of the puzzle. You want to eat enough and consume the right foods to repair your muscles but not undo all of your hard work. Some basics are laid out in this article.
Finally, do not workout at high intensities all the time. You are setting yourself up for all sorts of hormonal problems. The point of glycogen depletion is to train smart: time your workouts and meals to give you the best fat burning advantage. Questions, comments? Email the author at firstname.lastname@example.org
Michelle Fiscus writes a regular column for fredericknewspost.com. Michelle and her husband own a personal training and nutrition business based in Frederick County and hold industry certifications and credentials.