Endurance performance > how to train and what you need
Bulletin No. 51, Endurance Performance
Parrillo Performance Products
(800) 344-3404
The specificity principle states that adaptations to exercise training are specific to the training stimulus applied. 
This means that athletes predominantly interested in muscle size and strength should focus most of their efforts on resistance training, and athletes interested in endurance performance should perform mostly endurance training. However, certain metabolic adaptations occur as a result of endurance training which are of great interest to bodybuilders as well as endurance athletes. These include increased oxidative capacity, increased work output, increased vascular supply to muscles, and increased fat oxidation. Endurance training sessions should be performed a minimum of three days per week for 30-60 minutes at moderate to high intensity to achieve this training benefit. Some authors recommend low intensity aerobic exercise for fat loss, because at low intensity a greater percentage of utilized energy is derived from fat. While this is true, low intensity aerobic exercise is not effective in eliciting the metabolic adaptations which bring about a shift in energy substrate utilization patterns. Furthermore, low intensity aerobic exercise does relatively little to improve cardiovascular and respiratory fitness. While bodybuilders appropriately should focus their training on resistance exercise, they will achieve a higher degree of muscularity and leanness if they also include a component of vigorous aerobic exercise.
Introduction
Optimal endurance training is of great interest not only to endurance athletes but to bodybuilders as well. This series of articles will focus on how to use endurance training to help you achieve your physique goals. Aerobic exercise is the most effective way to lose body fat, and I’ll explain how to train optimally to burn fat without sacrificing muscle. We’ll also talk about ways to maximize your endurance performance.
General Principles
Two general concepts underpin any successful exercise training program. The Overload Principle describes the idea that an exercise stimulus must be of some threshold intensity to bring about a training adaptation (1,2). Exercise represents a form of stress, and the body adapts to that stress by getting stronger. To force the body to continue to adapt, the stimulus must continually become more intense. This is known as Progressive Overload. We can increase the training intensity by increasing the load (the resistance), the workout frequency, the workout duration, or the power output (work performed per unit time). The most effective way to produce increases in muscle size and strength is to increase the load. The most effective way to improve endurance performance is to increase workout duration. The best way to improve speed is to increase power output during the workout. The Overload Principle (sometimes called The Intensity Principle) applies to endurance training as well as to resistance exercise.
The Specificity Principle states that the metabolic adaptations that occur in response to a training stimulus are specific to the type of overload applied (1,2). Resistance training causes increases in muscle size and strength (if it’s intense enough) and aerobic exercise causes improvements in cardiovascular endurance, with surprisingly little carry over between the two (1). Specific exercise elicits specific adaptations creating specific training effects (1).
Metabolic Adaptations
Aerobic conditioning results in metabolic adaptations that improve energy production (1). Mitochondria from skeletal muscle acquire a greatly increased capacity to generate ATP by oxidative phosphorylation. Mitochondria are the small furnaces inside cells where food is burned (oxidized) to produce energy. Oxidative phosphorylation is the biochemical pathway mitochondria use to combine fuel substrate molecules from food with oxygen, resulting in a release of energy which is used to form ATP. Aerobic training makes mitochondria more efficient at this process, which means they can make more ATP to power muscle fiber contractions. This is a benefit of aerobic exercise that you don’t get from weight lifting. Associated with the increased capacity for mitochondrial oxygen uptake is an increase in the size and number of mitochondria and a potential two-fold increase in the level of aerobic energy producing enzyme systems (1). These adaptations are required to sustain a high percentage of aerobic capacity during prolonged exercise sessions. Animal studies have shown that skeletal muscle myoglobin can increase by as much as 80%. Myoglobin is a protein very similar to hemoglobin, except myoglobin is found in muscle cells while hemoglobin is found in red blood cells. Like hemoglobin, the function of myoglobin is to bind oxygen, and an increase in myoglobin can facilitate oxygen delivery to mitochondria.
Aerobic training causes an increase in the muscle’s ability to mobilize and oxidize fat. This occurs by an increase in blood flow within the muscle and in the activity of fat-mobilizing and fat-metabolizing enzymes (1). At any submaximal work rate, a trained individual uses more free fatty acids for energy than an untrained person (1,2). This is a key point and deserves some emphasis. Aerobic exercise training enhances the muscle’s ability to use fat as a fuel source and causes a shift in energy substrate (fuel) selection such that the trained muscle learns to rely more on fat as an energy source and less on carbohydrate. This is important to endurance athletes because increased use of fat as an exercise fuel has a carbohydrate sparing effect - the more fat we can burn the longer the carbs will last. Since carbohydrate (glycogen) depletion is a major factor limiting endurance, this means improved performance. This is also very important to bodybuilders because it offers a way to shift your metabolism into a fat-burning mode. Aerobic training teaches your muscles to burn more fat and less carbs. This happens at rest as well as during submaximal exercise. (During maximal exercise, carbs are still the main fuel.) Notice what happens if you combine this approach with a very low fat diet. The aerobic training shifts your muscle’s fuel selection into fat-burning mode, and your body becomes a fat burning machine. But there’s no fat in your diet. So where does the fat come from to fuel your muscles? From stored body fat. By combining proper training and nutrition techniques you can teach your body to draw on its own stored fat as a primary energy source.
Cardiovascular and Respiratory Adaptations
The weight and volume of the heart increase with long-term aerobic training (1). This is characterized by an increase in the size of the left ventricular chamber and by a thickening of its walls. The left ventricle is the chamber of the heart which pumps blood out to the body, and intense exercise makes it get bigger and stronger, just like any other muscle. This means it can pump harder and deliver a larger volume of blood per minute to working muscles. This in turn means more oxygen delivery, more energy production, and more muscular power output. The heart’s stroke volume increases significantly at rest and during exercise. Stroke volume is the volume of blood the left ventricle can eject in one beat. Since the left ventricle is larger and stronger, it can pump out more blood in a single beat than before training. Resting and submaximal heart rate are decreased during aerobic training. Since the heart can pump more blood with each beat, it doesn’t need to beat as often and heart rate is decreased compared to before training. Plasma volume and total hemoglobin content of the blood increase with endurance training. This also improves oxygen delivery.
One of the most significant changes in cardiovascular function is an increase in maximal cardiac output (1,2). Cardiac output is the volume of blood the heart can pump in one minute. The increased cardiac output is mediated largely by the increase in stroke volume. Training also produces a significant increase in the amount of oxygen extracted from circulating blood (1,2). This is determined by measuring the oxygen concentration in arterial blood supplying a muscle and in venous blood leaving the muscle. The difference is referred to as the arteriovenous oxygen gradient, and it is increased by endurance training because the muscles become more efficient at extracting oxygen from the blood. This is probably due to the increased capillary supply of muscle fibers, as well as their increased myoglobin and mitochondrial content. Regular aerobic training reduces blood pressure. Endurance exercise increases the ventilatory capacity of the lungs by increasing both breathing frequency and tidal volume (the volume of air per breath). In submaximal exercise the trained athlete ventilates less than before training (marathon runners don’t get out of breath from climbing a flight of stairs).
One of the most important adaptations to endurance exercise is an increase in the number of capillaries surrounding each muscle fiber (2). Endurance training can increase capillary density of muscles by 15% (and probably more, I suspect). This allows greater exchange of gases, heat, wastes, and nutrients between the blood and working muscle fibers (2). This facilitates not only energy production, but also fat metabolism and muscular growth. These increases occur within the first few weeks to months of aerobic training. If you want to grow big muscles, you need to deliver nutrients to them. The nutrients are delivered by capillaries. Do your aerobics.
VO2 Max
Endurance is a term that actually describes two separate components: muscular endurance and cardiorespiratory endurance. Muscular endurance is the ability of a muscle or muscle group to sustain high intensity repetitive exercise (2). Muscular endurance is highly related to muscular strength and anaerobic conditioning. An example is how many repetitions you can do with a given weight on the bench press. Technically speaking, strength is defined as your one rep maximum (1RM). Let’s say your one rep max at bench is 225 pounds. That means you can probably do 185 pounds for 8 reps or so. If you train bench for several weeks at 185 pounds, pretty soon you’ll be able to do 9 reps at 185. This is an increase in muscular endurance at 185 pounds. From a strictly technical point of view, this is not an increase in strength. To demonstrate an increase in strength, you need to increase your 1RM. Going from 8 reps at 185 pounds to 9 reps at 185 pounds probably won’t increase your 1RM by much, if any. However, if you keep training soon you’ll be able to do 12 reps at 185, then the next time you test your 1RM you’ll find you can push up 230 with no problem. So while muscular strength and endurance are separate concepts, they are closely related. Another example of muscular endurance is a static muscular contraction, such as a wrestler trying to pin his opponent to the mat (2). Another example would be holding a leg extension in the fully extended position. Let’s say you can hold a leg extension at 150 pounds fully extended for 10 seconds before you start to fail and lower the weight. After several weeks of training you may be able to hold it for 15 seconds. This is an increase in muscular endurance. (This technique, along with forced negatives, is in my bag of tricks for breaking through plateaus.)
Whereas muscular endurance refers to individual muscles, cardiorespiratory endurance refers to the body as a whole (2). It describes your body’s overall ability to sustain prolonged rhythmic exercise. Rather than being limited by the endurance of a particular muscle, your cardiorespiratory endurance is limited by your body’s energy producing ability, which is in turn limited by your ability to deliver oxygen to working muscle tissue, which is in turn limited by your cardiovascular and respiratory systems. Most exercise physiologists regard VO2 Max as the best indicator of cardiorespiratory endurance capacity (2). While strength, defined as the one rep maximum, is the best way to measure performance improvements in resistance training, VO2 Max is the best way to measure aerobic power (2). VO2 Max is defined as the highest rate of oxygen consumption attainable during maximal exhaustive exercise (2). You certainly can exercise at intensities higher than your VO2 Max, but this recruits the anaerobic energy producing pathways. After a minute or two at this intensity fatigue will set in and muscular failure will occur. Your VO2 Max represents the highest level of exercise intensity that you can sustain for a prolonged period of time. The VO2 Max dictates the rate of work or the pace you can sustain (2). Aerobic conditioning results in an average increase of 20% VO2 Max following six months of conditioning. This is brought about by a combination of two factors. An increase in cardiac output results in more blood, and thus more oxygen, being delivered to tissues. Second, an increase in the arteriovenous oxygen gradient means that more of this oxygen is being extracted from the blood by the muscle. This means that more oxygen is being used by the muscle to produce energy, and more energy production means more muscle power and endurance.
Lactate Threshold
When glucose is metabolized anaerobically (without oxygen) it is converted to pyruvate and subsequently into lactate (lactic acid). Lactic acid buildup inside muscle cells is one of the factors that makes your muscles burn when you train a set of biceps curls to failure. At lower intensity exercise, you really don’t recruit the anaerobic energy system because you don’t need it. (Refer back to our series on cellular energy production.) During endurance exercise, your body can supply oxygen fast enough to the muscles so that you can produce all the energy you need from the oxidation of glucose and fat, without producing lactic acid. As exercise intensity increases, you eventually reach a level where the aerobic energy producing pathway is maxed out, and anaerobic energy production begins. At that point, lactate is produced inside muscle tissue and begins to appear in the blood as a waste product. The lactate threshold is the point where blood lactate begins to appear. Like VO2 Max, this is a measure of cardiorespiratory fitness. Endurance training increases the lactate threshold, which means a higher level of energy production can occur by the aerobic pathway before the anaerobic pathway is called into play. Trained endurance athletes can perform exercise at a higher VO2 Max before blood lactate appears. This means that they can exercise at a higher intensity (they can produce more power aerobically) before anaerobic metabolism begins.
At first it might sound like VO2 Max and lactate threshold are really two ways of measuring the same thing, but they’re not. While they both reflect endurance performance, they are looking at different aspects. VO2 Max is a description of the maximal aerobic energy producing ability of an athlete. Lactate threshold describes the percentage of VO2 Max at which the athlete can train before anaerobic metabolism begins. The increase in lactate threshold, at a given percentage of VO2 Max, is probably due to a greater ability to clear lactate produced by the muscle (due to increased capillary density of the muscle tissue bed), an increase in skeletal muscle enzymes involved in aerobic energy production, and a shift in metabolic substrate to a fuel mix involving a higher proportion of energy derived from fat.
These concepts lay the basic ground work you need for a thorough understanding of endurance exercise physiology. Next month we’ll talk about training intensity, respiratory quotient, fat metabolism, and specific strategies on how to incorporate endurance training into your program to maximize fat loss without losing muscle.
Parrillo Performance Products
(800) 344-3404
References
1. McArdle WD, Katch FI, and Katch VL. Exercise Physiology: Energy, Nutrition, and Human Performance. Lea & Febiger, Philadelphia, 1991.
2. Wilmore JH and Costill DL. Physiology of Exercise and Sport. Human Kinetics, Champaign, IL, 1994.
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