By Meredith Schneider
Fat burning during exercise depends on intensity. Low-intensity exercise burns a higher percentage of fat from total calories burned when compared to high-intensity exercise. Low-intensity exercise includes walking or strolling, light cycling, steps or light swimming, where your heart rate is at or below 65 percent of your maximum heart rate. High-intensity exercise includes running, sprinting, heavy swimming or cycling, where your heart rate is at or above 85 percent of your maximum heart rate. Fat is the main source of fuel for low-intensity exercise, and carbohydrate stores are the main source of fuel for high-intensity exercise.
Fuel Sources for Exercise
The main sources of energy during exercise of any kind are carbohydrates and fat. Carbohydrate sources in the body include blood glucose, liver glycogen and muscle glycogen. Fat sources include adipose, or fat, tissue and triglycerides. If you have eaten a meal before exercising, the main source of energy to fuel exercise will be the food you've eaten. Therefore, exercising after fasting for eight to 10 hours is best in terms of burning fat tissue and body stores rather than food. You have 50,000 to 100,000 calories of energy stored in your fat tissue, which translates into 500 to 1,000 miles of walking. You have 1,200 to 3,000 calories of carbohydrate stored as
Low-intensity Exercise
Low-intensity exercise is any exercise during which your heart rate is at or below 65 percent of maximum heart rate. Low-intensity exercise can be sustained for longer periods of time than high intensity because the body burns a higher percentage of fat to fuel exercise longer. During low-intensity exercise, the body is able to break down fat and metabolize it for energy. The heart is working at a proper pace to effectively burn and use fat. However, low-intensity exercise does not burn as many total calories as exercising at higher intensities.
High-intensity Exercise
High-intensity exercise is considered exercising at or above 85 percent of maximum heart rate. This type of exercise cannot be sustained as long as low-intensity exercise but does burn more calories per minute than at lower intensities. However, the percentage of fat calories burned decreases with increasing intensity, resulting in greater carbohydrate use at high intensities. When the body is working at high intensity, it cannot break down and use fat tissue for energy fast enough. Oxidizing fat takes too long to provide enough energy to sustain high-intensity exercise. Therefore, the body converts to a greater percentage of carbohydrate use for energy.
Combine Both High- and Low-intensity Exercise
Both low- and high-intensity exercise have benefits. Both types burn fat, but low-intensity exercise burns a higher percentage of fat from total calories burned. High-intensity exercise burns more calories overall and is better for cardiovascular health. It works the heart harder and results in greater adaptations in the cardiovascular system than low-intensity exercise. Low-intensity exercise can be sustained for a longer period of time so you can accumulate more minutes of activity at lower intensities. If time is an issue and your health and body allow you, short bouts of high-intensity exercise might be best for you. Either way, including both high- and low-intensity exercises in your workout routine is the best combination for your health and shape.
Other important points for high intensity training are that it raises fat burning hormones in the blood (so that more calories are burned for upto 24hrs post exercise - basal metabolic rate has been boosted), more growth hormone is released (a major fat burning hormone), develops your aerobic capacity (getting aerobically fitter means that you are able to exercise harder than before therefore can burn more calories), uses up carbohydrates means they need to be replaced (if your existing body fat is used to create carbohydrates) more calories are lost because this is an inefficient process and improves insulin sensitivity. The down side is that too much high intensity training can lead to over training where the body does not have the time to heal itself and this can lead to illness and injury. Also, it is difficult to train for long periods of time at high intensity.
Low intensity exercise is good because it can be practised when you are recovering from injury, illness, short of breathe from high intensity training and on a regular basis for long periods of time with little risk to health.
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