Pauses between meals create space for maximum physical and mental performance. Fasting provides the organism with sufficient energy and nutrients for anabolic (muscle building activities) and metabolic (calorie burning) exercises, without the distraction of digestion, which comes directly after a meal.
People who practice intermittent fasting have a schedule that is more accommodating to fasted training, and many believe that "fasted" workouts are better for you and could actually burn more fat ( increasing the fat utilization -- the use of fat as a fuel source )
Most common forms of fasted workouts are often bike, HIIT sessions, elliptical or running sessions.
Consume water before and during the session for optimal hydration
- Exercising during a fasting state increases lipolysis in adipose tissue while also stimulating peripheral fat oxidation, resulting in increased fat utilization and weight loss. Basically, fasting lowers circulating insulin levels and increases hepatic glycogen breakdown, suggesting that endurance training during this state leads to greater fat utilization compared to the fed state
The benefits of a fasted workout include:
Enhanced fat utilization: This effect, remember, only holds for low-intensity exercise.
Better endurance: Multiple studies have shown that fasted cardio leads to an increase, over time, in VO2 max—a measure of endurance capacity. (VO2 max is your maximum oxygen usage during exercise). In one study, researchers from New Zealand found that both men and women had significant bumps in VO2 max after four weeks of fasted cycling.
More growth hormone: Both fasting and exercise increase human growth hormone (HGH). Two days of fasting, in fact, has been shown to increase HGH by a factor of five. But here’s the thing - despite the name of the hormone, the purpose of HGH is really not to “grow muscle”, but rather to use stored fatty acids and glucose as energy, and in extreme cases shed aminos from your muscles and redistribute them to the organs that are necessary for life: heart, lungs, kidneys, liver, etc. If you lift weights fasted, at most you will tell your body to maintain some of the muscle you have, but HGH by itself and in physiological amounts won’t help you gain muscle. In fact, a good deal of evidence suggests that supplemental HGH doesn’t help adults build muscle. To gain lean muscle mass, you need the material (protein) and the stimulus (strength training).
Anabolic signaling: One study found that fasted strength training led to increased phosphorylation in muscle tissue (a muscle growth response) during the post-exercise recovery period. To be clear, however, the participants ate a protein / carb supplement fairly soon after working out.
Ketosis: When you fast, blood sugar and insulin levels stay low, which sends the ketosis bat signal. To maximize the fat-burning, ketogenic potential of fasted exercise, focus on low-intensity exercise. This kind of exercise may be a useful tool to help type 2 diabetics improve blood sugar levels. But I’ll add again - if you are already doing a low carb or ketogenic diet, you may not really need to train fasted - you are already getting most of its benefits in the first place.
What Not Exercising During Fasting Does With Your Fitness Condition: It tells your body that you are too weak to handle a fast. In ancestral humans, fasting precedes eating. You didn't go to the fridge for a meal. You worked for it. You hunted and gathered to eat. You struggled to fill your empty stomach. Simply lying down during a fast meant that you would die. Don't tell yourself that you are too weak to handle fasting.
It tells your body that you don't need all that muscle tissue. If you don't use your muscles during a fast, your body will deem them unnecessary. These muscles can provide a large dose of amino acids that convert to glucose, and if you're not using them, you'll lose them to make glucose. "This guy obviously doesn't need those biceps, let's burn!"
In fact, one of the reasons people lose muscle when cutting calories and losing weight is that they don't pull iron. Another big reason is that they don't get enough protein, of course – but simply by lifting weights during the caloric deficit, we can retain muscle mass. As fasting is, by definition, an extreme reduction in calories, exercise becomes even more important. Okay, so exercising on an empty stomach is a good move. How should you exercise?
The short story is that for short fasts (of the 24-hour to 36-hour reduced meal window variety), you should exercise the way you always do. For long fasts, from 48 hours to a week or more, you should still exercise, but a little different from "normal". Let's get into it: How to exercise during a longer fast 1. Walk as much as possible.
The simplest form of exercise that everyone should do while fasting is walking. There is no trick or science to walking fasting. You just walk while you don't eat. You can do as much walking as you can, because walking fasting is not just easy or stressful – it's anti-stress. It keeps you busy when you can't think of anything but eating, when fasting is becoming a chore. Research indicates that walking on a fast is no more stressful than walking on eating days; in fact, fasting individuals spontaneously maintain their daily step count without affecting the benefits. What are the benefits?
If you have trouble adhering to a fast – if you are the type who wants to eat because you are bored and can't think of anything else to do, you need to walk as much as possible during a fast. For those who are already very thin but want to be very thin, walking on an empty stomach can be effective. The classic weight training trick to cut body fat is the morning walk on an empty stomach. Wake up, don't consume calories and go for a brisk 20-30 minute walk while the fat is mobilized in your body. This is the most difficult transition in body composition – from thin to very thin. Thin is what the body “wants”, and trying to cut it involves overcoming the natural tendency to keep body fat stores low. A fasted walking, jogging, or cycling session in the aerobic zone almost forces the body fat into circulation. Insulin is low. Sensitivity is high. The stage is perfect, in theory.
2. Lift weights to preserve muscle. On a prolonged fast, it is essential to lift weights. On a short-term fast, lifting weights is a great way to break the fast and increase the anabolic response to food. Your strategies for both will be different. If you are in the middle of a long-term fast and want to avoid muscle loss: Lift weights at a higher intensity with fewer repetitions. Don't go to failure. Don't give it your all. On a scale of 1 to 10, with 1 being “easy” and 10 being “total effort”, stay around 6 to 8. Keep multiple reps in the “spare tank”. Stick to full-body compound movements rather than isolating muscles. You want to reach the entire body with a powerful stimulus. You want to send a message to your entire body, not just your biceps or glutes. This will provide a stimulus strong enough to maintain muscle mass without being so stressful that you start breaking down more muscle mass than you can keep.
3. Do “easy” cardio. If you're going to do aerobic or resistance exercise during an extended fast, keep the intensity low to stay in the “aerobic zone” – the heart rate zone where you're mostly burning body fat. A fasting human should be able to stay active in this zone almost indefinitely without needing much or no food. To determine your aerobic heart rate, subtract the chronological age from 180: If you're 20 years old, your aerobic heart rate zone would be 160 beats per minute. Do not exceed 160 BPM when fasting resistance training. If you are 50 years old, your aerobic heart rate zone would be 130 BPM. Do not exceed 150 BPM when fasting resistance training. This will look “easy”, and that's exactly the point. You're not wasting your glycogen or increasing your sugar cravings because you're not burning a lot of sugar. You are burning (mostly) your own body fat.
In a recent study, men with a restricted mealtime increased to 8-12 repetitions for four sets and consumed 650kcal less than the non-fasting group, but maintained all their muscle mass and achieved gains in muscle strength and endurance. . That said, the non-fasting group made the most gains in size. Another study in women found that resistance training with a restricted eating schedule was good and led to muscle gains as long as calorie and protein intake was maintained.
A 2009 study found that, compared to athletes who lifted weights after breakfast, athletes who lifted weights in the morning on an empty stomach had an increased anabolic response to a post-workout protein and carbohydrate shake.
There is also merit in fasting for a few more hours after training. This will actually increase the release of growth hormone – which is great for fat burning and tissue maintenance. I do this about half the time I'm fasting.
There are no strict rules for exercising while fasting. After all, you are still you. You know what works for you. Most people on a longer fast will do better by walking every day and getting up at least once or twice. And you guys? How do you exercise fasting? Be careful and stay well.
Klempel MC, Bhutani S, Fitzgibbon M, Freels S, Varady KA. Adaptations of diet and physical activity to modified fasts on alternate days: implications for optimal weight loss. Nutr J. 2010; 9:35.
Tinsley GM, Forsse JS, Butler NK, et al. Time-Restricted Feeding in Young Men Performing Resistance Training: A Randomized Controlled Study. Eur J Sport Sci. 2017; 17(2): 200-207.