Building your endurance is not only the central focus of many training plans, it is a process that has widespread benefits in most of your body's systems. By understanding and applying the science of building endurance, you can design a program that will optimize your progress, develop your oxygen transport system and bring your one step closer to your goals.
How Endurance Training Works
The central idea of endurance training is that it enhances the transport system your body uses to get oxygen from the environment to the muscle cells where it is used to create energy. When you put stress on your muscles, heart and lungs by pushing them through activities like running for periods of time that are longer than they are used to, you stimulate adaptation in the system and make it more efficient.
The superstar of your transport systems is the red blood cell which carries oxygen to the muscles. Endurance exercise improves your red blood cells in two ways. The first effect is that EPO (erythropoietin), which is responsible for red blood cell production, is naturally increased with endurance training. The second change is that exercise breaks down old red blood cells and stimulates your body to produce new ones. The newer red blood cells may be more effective at picking up and carrying oxygen than the older cells. To help your body build new and better red blood cells, you need to focus on eating foods that are high in iron. Oxygen binds to hemoglobin in the blood and iron is a key component of the hemoglobin molecule. Foods that are high in iron include red meat – especially organ meats like liver and kidney, dark green vegetables, quinoa, beans, lentils, nuts and seeds. You should also consume foods with a high vitamin C content because it helps your body absorb iron.
The primary method for runners to improve endurance is "Long Slow Distance" or LSD, a form of training that has widespread benefits. To begin with, forcing your heart to beat more frequently causes the same change in your heart muscles that occurs in any muscle you use regularly – it gets stronger and can pump blood through the body more easily. You are also increasing the rate at which oxygen is absorbed into your body by your tissues. This happens because you induce a process called "angiogenesis" which increases the density of the capillary beds that surround your muscle fibres. Capillaries are the tiny tissues at the end of the chain of blood vessels that begins with your heart and arteries. There are between 3 and 5 capillaries around each muscle fibre in your body and endurance activity ensures that your body will be at the upper end of this range.
On top of this improved capillary density, you also encourage the growth and development of mitochondria. Mitochondria are little organelles inside your cells that produce energy. Exercise stimulates mitochondria to grow, replicate and improve their ability to make use of carbohydrates, proteins and fats in order to generate energy. Endurance training also trains your muscle fibres to store more glycogen (the stored form of glucose) and become more efficient at burning fats, which is helpful because your carbohydrate stores are finite.
What the Research Tells Us
Much of the science related to endurance focuses on measuring cardiovascular performance using tests like VO2max and resting heart rate. For the purposes of your training, you can use your heart rate to measure your exertion level and ensure that your training is optimal. Since taking your pulse while running is like trying to knit on a roller coaster, many runners use a heart rate monitor to track their pulse, but you can also learn how to monitor your breathing as an indicator of how hard your body is working. Dr. Robert Goode from the University of Toronto recommends exercising at an intensity that is strong enough to increase your ventilation to a level where you can hear yourself breathing, but not so intensely that you can't carry on a conversation.
Research has found that for athletes aiming to increase their endurance, the recommended training target is to exercise between 70 and 80 % of your maximum heart rate. This means that the typical 40 year old whose maximum heart rate is around 180 bpm should exercise at a pace that requires between 125 and 145 bpm. We also know that endurance training is not just about improving the strength of your heart. It also teaches your body to increase the volume of blood in your system.
Heart rate is the key to gauging your aerobic intensity and building endurance. The most important investment you can make to monitor your aerobic training is a heart-rate monitor. If you don't have one, you can easily check your heart rate during exercise. Place your fingers between the trachea and the long muscle that runs next to your windpipe, feel for your pulse and then calculate your heart rate in beats per minute. The next step is to calculate your maximum heart rate (HRmax). You can estimate your maximum heart rate by subtracting 0.85 times your age from 217: Maximum heart rate =?217 – ____ [0.85 × your age] = ____ beats/minute (b/m) This is just an estimate - the method will produce reasonable estimates in about 70% of the population. You can also have your maximum heart rate measured accurately by a physiologist or doctor. Consult your physician or trainer to have this test conducted if you want more accurate results. Once you know your maximum heart rate, you can calculate your aerobic cardiovascular training zones to help improve your endurance and health.
The amount of blood that moves through your body with each beat of your heart is called "stroke volume" and researchers have found that athletes' bodies make amazing adaptations in this area. In one study, researchers found that while elite athletes and non exercisers alike saw an increase in their heart rate during a workout, the elite athletes were moving 10 litres more blood per minute through their system.* That is a huge difference in the amount of oxygen getting to the muscles!
Improve your Performance
Things to consider related to endurance training:
• Endurance training programs should involve a long run or walk to build endurance on a weekly basis. Your LSD run needs to stress your muscles enough so that your body will adapt and increase its endurance.
• Build your mileage slowly so that your system has time to adjust to the new demands – aim for increases of no more than 10% per week until you reach your target mileage goal. Don't forget to give yourself a recovery week with lower mileage on a regular basis, for example every 4th or 5th week.
• Long workouts should be performed at a slower pace but you need to make sure that your heart rate is at least 50 % of your maximum but not higher than 85%.
• Make sure you learn a proper recovery process including cooling down, refueling and rehydrating to help your body regenerate effectively
Long runs require a different mindset than typical exercise. You can't be looking at your watch or wondering when it will end – you need to just get into the groove and go. Most runners find that doing their long runs in a group setting is helpful. Many also report that the mental state that is achieved during extended sessions has a meditative effect. Either way, you will find that endurance training makes you a more efficient runner, improves your overall health and gives you a kind of mental strength that will influence almost every aspect of your life.
* Zhou B, Conlee RK, Jensen R, Fellingham GW, George JD, Fisher AG. Stroke volume does not plateau during graded exercise in elite male distance runners. Med Sci Sports Exerc 2001: 33: 1849–1854.
Greg Wells Ph.D. (www.drgregwells.com, @drgregwells) is an Assistant Professor at the University of Toronto in the Faculties of Medicine and Kinesiology. He was the sport science analyst for the Olympic Broadcast Consortium during the 2010 & 2012 Games, and is the author of Superbodies: Peak Performance Secrets from the World's Best Athletes. Jessica Caterini is a member of the Human Physiology Research Unit in the Faculty of Kinesiology at the University of Toronto.