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Intervals for Everyone

All healthy people can benefit from some form of interval training. They can pick up the pace for a few seconds while walking, running, cycling, swimming, skiing or skating, and then slow down when they feel the least discomfort. When they regain their breath and their muscles feel comfortable, they can pick up the pace again, and alternate these pickups and rests until their legs start to feel heavy or stiff. Then they should stop for the day. On the next day, their muscles will probably feel sore, so they should go at a slow, easy pace. When their muscles feel fresh again, they can try another interval workout.

This interval training technique has been used in all endurance sports since the early 1900's, but it wasn't until a couple decades ago that George Brooks of the University of California at Berkeley showed how interval training can make anyone more fit and a better athlete (American Journal of Physiology-Endocrinology and Metabolism, June 2006).

Fuel for Your Muscles
Your muscles burn sugar, fat and protein for energy, but sugar is the most efficient fuel of the three since less oxygen is used to convert sugar to energy. The limiting factor to how fast you can move is the time it takes to move oxygen into muscles. Sugar is the major fuel for your muscles during intense exercise. In a series of chemical reactions, the sugar, glucose, is broken down step by step, with each step releasing energy. When enough oxygen is available, the glucose releases all of its energy until only water and carbon dioxide remain and the carbon dioxide is blown off through your lungs.

If your heart cannot pump enough oxygen to your muscles to meet their needs for energy, the chemical reactions stop at lactic acid which accumulates in the muscles and spills over into the bloodstream. Lactic acid makes muscles acidic, causing a burning feeling in muscles that makes you slow down. However, if you can get rid of the lactic acid and convert it to energy to power your muscles, the burning disappears and you feel better.

Lactic Acid, the Most Efficient Fuel
Since the cause of the muscle burning and shortness of breath is lack of oxygen, slowing down allows you to catch up on your oxygen debt, which in turn coverts lactic acid all the way to carbon dioxide and water and supplies a tremendous amount of energy to power your muscles. The exciting news is that lactic acid requires less oxygen even than sugar does to be converted to energy and that means that when you clear lactic acid from your bloodstream, you can go much faster. Anything that helps muscles to break down lactic acid faster will make you a better athlete because it will allow you to exercise more intensely to increase your endurance and allow you to move faster when you are tired (Sports Medicine, 2006;36).

Inside each muscle cell are hundreds of mitochondria, the little furnaces that burn fuel for energy. Lactic acid is burned for energy in the mitochondria, and anything that enlarges the mitochondria builds a bigger furnace and helps to increase endurance. Lactic acid is carried from the cells into the mitochondria by special proteins called lactate transporter molecules, so anything that increases these molecules will build endurance. An enzyme called lactic acid dehydrogenase is needed to start the reaction, so anything that increases this enzyme will also help. Interval training does all three: it enlarges the furnace (mitochondria), increases lactic acid transporter molecules, and increases the amount of lactic acid dehydrogenase.

Lactic Acid Aids Muscle Contraction
Muscles contract more efficiently when lactic acid accumulates in them. Electric currents cause muscles to contract. This electricity is generated by cell membranes causing potassium to move inside cells and chloride ions to stay outside. With vigorous exercise, potassium ions accumulate outside cells. As large amounts of potassium ions accumulate outside cells, electricity is not generated and the cells cannot contract. Another ion called chloride accumulates outside cells and prevents potassium from getting back inside cells. Lactic acid removes the chloride, so it is easier for potassium to get back inside cells. Therefore lactic acid increases the ratio of potassium inside cells to the amount outside, and this helps the muscle contract with more efficiency.

Burning in Muscles
Competitive athletes are supposed to exercise vigorously and feel a burn in their muscles during exercise, which signifies buildup of lactic acid in muscles. However, the muscle burning caused by lactic acid buildup disappears almost immediately as soon as you slow down. However, a few hours after you finish exercising your muscles start to feel sore. This soreness continues into the next day and is caused by the hard force on muscles from interval training that damages the muscle fibers themselves. Therefore athletes usually take easy less-intense workouts on that day and for as many days as it takes for muscles to feel fresh again. Most athletes set up their training programs so that they alternate hard and easy workout days. This is called the hard-easy principle in which you exercise so intensely on one day that you damage your muscles, feel sore on the next day, and then go easy for as many days as it takes for the soreness to go away.
Interval Training Helps Your Heart
Intervals Lower Blood Sugar
Interval Training for Sports
Short Intervals are Best

CAUTION:People with blocked arteries leading to their hearts can suffer heart attacks with intense exercise. Check with your doctor before starting a new program of intense exercise or increasing the intensity of your current program.

October 15th, 2017
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About the Author: Gabe Mirkin, MD

Sports medicine doctor, fitness guru and long-time radio host Gabe Mirkin, M.D., brings you news and tips for your healthful lifestyle. A practicing physician for more than 50 years and a radio talk show host for 25 years, Dr. Mirkin is a graduate of Harvard University and Baylor University College of Medicine. He is board-certified in four specialties: Sports Medicine, Allergy and Immunology, Pediatrics and Pediatric Immunology. The Dr. Mirkin Show, his call-in show on fitness and health, was syndicated in more than 120 cities. Read More
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