Reading #1 Introduction to Science

Anaerobic Energy: The Immediate and Short-Term Energy Systems

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Anaerobic Energy: The Immediate and Short-Term Energy Systems

Evaluation of the Immediate Energy System

erformance tests that rely on maximal activation of the intramuscular ATP-PCr energy reserves have been developed as “field tests” to evaluate the immediate energy transfer system. These maximal effort performances, generally referred to as power tests, evaluate the time-rate of doing work (i.e., work accomplished per unit time). The following formula computes power output:

where, F equals force generated, D equals distance through which the force moves, and T equals exercise duration.

Watts represents a common expression of power

One watt equals 0.73756 ft-lb•sec–1 or 6.12 kg-m•min–1

Stair-Sprinting Power Tests

Researchers have measured short-term power by sprinting up a flight of stairs. Figure 2 shows a subject running up a staircase as fast as possible taking three steps at a time. The external work performed equals the total vertical distance the body rises up the stairs; for six stairs this distance usually equals about 1.05 meters.

he power output for a 65-kg woman who traverses six steps in 0.52 seconds computes as follows:

F = 65 kg; D = 1.05 m; T = 0.52 s

Power = [65 kg x 1.05 m] ÷ 52 s

Power = 131.3 kg-m•s-1 (1287 watts)

Because body mass greatly influences the power-output score in stair sprinting, a heavier person necessarily generates greater power at the same speed as a lighter person who covers the same vertical distance. Because of the influence of body mass, use caution in interpreting differences in stair-sprinting power scores and making inferences about individual differences in ATP-PCr energy capacity. The test may be better suited for evaluating individuals of similar body mass, or the same people before and after a specific training regimen.

For Your Information

Interchangeable Expressions for Energy and Work

1 foot-pound (ft-lb) = 0.13825 kilogram-meters (kg-m)

1 kg-m = 7.233 ft-lb = 9.8066 joules

1 kilocalorie (kcal) = 3.0874 ft-lb = 426.85 kg-m = 4.186 kilojoules (kJ)

1 Joule (J) = 1 Newton-meter (Nm)

1 kilojoule (kJ) = 1000 J = 0.23889 kcal

Jumping-Power Tests

For years, physical fitness test batteries have included jumping tests such as the jump-and-reach test or a standing broad jump. The jump-and-reach test score equals the difference between a person’s standing reach and the maximum jump-and-touch height. For the broad jump, the score represents the horizontal distance covered in a leap from a semicrouched position. Although both tests purport to measure leg power, they probably fail to achieve this goal. For one thing, with jump tests, power generated in propelling the body from the crouched position occurs only in the time the feet contact the floor's surface. This brief period cannot sufficiently evaluate a person’s ATP and PCr power capacity.

Other Power Tests

A 6 to 8-second performance involving all-out exercise measures the person’s capacity for immediate power from the intramuscular high-energy phosphates (refer to Figure 1). Examples of other such tests include sprint running or cycling, shuttle runs and more localized movements such as arm cranking or simulated stair climbing, rowing, or skiing. In the popular Quebec 10-second test of leg cycling power, the subject performs two all-out 10-second rides at a frictional resistance equal to 0.09 kg per kg of body mass, with 10- minutes rest between exercise bouts. Exercise begins by pedaling as fast as possible as the friction load is applied and continues all-out for 10 seconds. Performance represents the average of the two tests reported in peak joules per kg of body weight, and total joules per kg of body weight.

Power tests may be used to show changes in an athlete’s performance with specific training. Such tests also serve as an excellent means for self-testing and motivation, and provide the actual movement-specific exercise for training the immediate energy system. Many football teams, for example, routinely use the 40-yard dash as a criterion to evaluate a player’s speed. Although many types of “speed” need to be evaluated in football, the 40-yard scores may provide useful information for player evaluation. It should be emphasized, however, that research needs to establish how 40-yard speed in a straight line relates to overall football ability for players at similar positions. A run test of shorter duration (up to 20 yd), or one with frequent changes in direction, may be an equal or more suitable performance measure.

Several physiologic and biochemical measures, in addition to exercise performance, can estimate the energy-generating capacity of the immediate energy system. These include:

  • Size of the intramuscular ATP-PCr pool

  • ATP and PCr depletion rates from all-out exercise of short duration

  • Magnitude of the oxygen deficit calculated from the oxygen uptake curve

  • Magnitude of the alactic (fast component) portion of recovery oxygen uptake

Evaluation of the Short-Term Energy System

As displayed in Figure 1, the anaerobic reactions of glycolysis (short-term energy system) generate increasingly greater energy for ATP resynthesis when all-out exercise continues longer than a few seconds. This does not mean that aerobic metabolism remains unimportant at this stage of exercise, or that the oxygen-consuming reactions have not been “switched-on.” To the contrary, Figure 2 reveals an increase occurs in aerobic energy contribution very early in exercise. However, the energy requirement in all-out exercise significantly exceeds energy generated by hydrogen's oxidation in the respiratory chain. This means that the anaerobic reactions of glycolysis predominate, with large quantities of lactic acid accumulating within the active muscle and ultimately appearing in the blood.

Unlike tests for maximal oxygen uptake, no specific criteria exist to indicate that a person has reached a maximal anaerobic effort. In fact, one's level of self-motivation, including external factors in the test environment, likely influences the test score. Researchers most commonly use the level of blood lactate to indicate the degree of activation of the short-term energy system.

Performance Tests of Glycolytic Power

Activities that require substantial activation of the short-term energy system demand maximal work for up to three minutes. All-out runs and cycling exercise have usually been used, although weight lifting (repetitive lifting of a certain percentage of maximum) and shuttle and agility runs have also been used. Because age, sex, skill, motivation, and body size affect maximal physical performance, difficulty exists selecting a suitable criterion test for developing normative standards for glycolytic energy capacity. A test that maximally uses only the leg muscles cannot adequately assess short-term anaerobic capacity for upper-body exercise such as rowing or swimming. Within the framework of exercise specificity, the performance test must be similar to the activity or sport for which the energy capacity is being evaluated. In most cases, the actual activity serves as the test.

Figure 3 presents the relative contribution of each metabolic pathway during three different duration all-out cycle ergometer tests. The results are shown as a percent of the total work output. Note the progressive change in the percentage contribution of each of the energy systems to the total work output as duration of effort increases.

lood Lactate Levels

Blood lactate levels remain relatively low during steady-rate exercise up to about 55% of the VO2max. Thereafter, blood lactate begins to accumulate, with a precipitous increase noted in the region of the VO2max.

Glycogen Depletion

Because the short-term energy system largely depends on glycogen stored in the specific muscles activated by exercise, these muscles' pattern of glycogen depletion provides an indication of the contribution of glycolysis to exercise.

Figure 4 shows that the rate of glycogen depletion in the quadriceps femoris muscle during bicycle exercise closely parallels exercise intensity. With steady-rate exercise at about 30% of VO2max, a considerable reserve of muscle glycogen remains, even after cycling for 180 minutes. Because relatively light exercise relies mainly on a low level of aerobic metabolism, large quantities of fatty acids provide energy with only moderate use of stored glycogen. The most rapid and pronounced glycogen depletion occurs at the two heaviest workloads. This makes sense from a metabolic standpoint because glycogen provides the only stored nutrient for anaerobic ATP resynthesis. Thus, glycogen has high priority in the “metabolic mill” during strenuous exercise.

Changes in total muscle glycogen as illustrated in Figure 4 may not give a precise indication of the degree of glycogen breakdown in specific muscle fibers, however. Depending on exercise intensity, glycogen depletion occurs selectively in either fast- or slow-twitch fibers. For example, during all-out one-minute sprints on a bicycle ergometer, activation of the fast-twitch fibers provides the predominant power for the exercise. Glycogen content in these fibers becomes almost totally depleted because of the sprint's anaerobic nature. In contrast, slow-twitch fibers become glycogen-depleted early during moderate to heavy prolonged aerobic exercise. Glycogen utilization (and depletion) mainly in specific muscle type fibers makes it difficult to evaluate the degree of glycolytic activation from changes in a muscle’s total glycogen content before and after exercise.

Anaerobic Energy Transfer Capacity

Differences in training level, capacity to buffer acid metabolites produced in heavy exercise, and motivation contribute to individual differences in capacity to generate short-term anaerobic energy.

Effects of Training

Short-term supermaximal exercise on a bicycle ergometer in trained subjects always produces higher levels of blood and muscle lactic acid, and greater muscle glycogen depletion. For all subjects, better performances are usually associated with higher blood lactate levels. These results support the belief that training for brief, all-out exercise enhances the glycolytic system's capacity to generate energy. In sprint and middle-distance activities, individual differences in anaerobic capacity account for much of the variation in exercise performance.

Buffering of Acid Metabolites

Lactic acid accumulates when anaerobic energy transfer predominates. This causes an increase in the muscle's acidity, negatively affecting the intracellular environment. The deleterious intracellular alterations during anaerobic exercise have caused speculation that anaerobic training might enhance short-term energy capacity by increasing the body’s buffering reserve to enable greater lactic acid production through more effective buffering. However, only a small increase in alkaline reserve has been noted in athletes compared to sedentary individuals. Thus, the general consensus is that trained people have similar buffering capability as untrained individuals.


Individuals with greater “pain tolerance,” “toughness,” or ability to “push” beyond the discomforts of fatiguing exercise definitely accomplish more anaerobic work. These people usually generate greater levels of blood lactate and glycogen depletion; they also score higher on tests of short-term energy capacity. Although difficult to categorize and quantify, motivation plays a key role in superior performance at all levels of competition.

Aerobic Energy: The Long-Term Energy System

The data in Figure 5 illustrate that persons who engage in sports that require sustained, high-intensity exercise (i.e., endurance) generally possess a large aerobic energy transfer capacity. Men and women who compete in distance running, swimming, bicycling, and cross-country skiing generally record the highest maximal oxygen uptakes. These athletes have almost twice the aerobic capacity as sedentary individuals. This does not mean that only VO2max determines endurance exercise capacity. Other factors, especially those at the muscle level such as capillary density, enzymes, and fiber type, strongly influence the capacity to sustain a high percentage of VO2max. However, the VO2max does provide useful information about the capacity of the long-term energy system. Attainment of VO2max requires integration of ventilatory, cardiovascular, and neuromuscular systems; this gives significant physiologic “meaning” to this metabolic measure. For these reasons, VO2max represents a fundamental measure in exercise physiology and often serves as the standard against which to compare performance estimates of aerobic capacity and endurance fitness.

Measurement of Maximal Oxygen Uptake

Tests for VO2max use exercise tasks that activate large muscle groups with sufficient intensity and duration to engage maximal aerobic energy transfer. Exercise includes treadmill walking or running, bench stepping, or cycling. VO2max has also been measured during free, tethered, and flume swimming and swim-bench ergometry, and simulated rowing, skiing, stair climbing, as well as ice skating and arm-crank exercise. Considerable research effort has been directed toward (1) development and standardization of tests for VO2max, and (2) establishment of norms related to age, sex, state of training, and body composition.

Criteria for VO2max

A leveling-off, or peaking-over, in oxygen uptake during increasing exercise intensity signifies attainment of maximum capacity for aerobic metabolism (i.e., a “true” VO2max). When this generally accepted criterion is not met, or local muscle fatigue in the arms or legs rather than central circulatory dynamics limits test performance, the term “peak oxygen uptake” (VO2peak) usually describes the highest oxygen uptake value during the test.

Tests of Aerobic Power

Numerous tests have been devised and standardized to measure VO2max. These test performances should be independent of muscle strength, speed, body size, and skill, with the exception of specialized swimming, rowing, and ice skating tests.

The VO2max test may require a continuous 3- to 5-minute “supermaximal” effort, but it usually consists of increments in exercise intensity (referred to as a graded exercise test or GXT) until the subject stops. Some researchers have imprecisely termed this end point “exhaustion,” but it should be kept in mind that the subject terminates the test (for whatever reason). A variety of psychological or motivational factors can influence this decision, and it may not reflect true physiologic exhaustion. It can take considerable urging and prodding to get subjects to the point of acceptable criteria for VO2max, particularly individuals unaccustomed to producing maximal exercise. Children and adults encounter particular difficulty if they have had little prior experience performing strenuous exercise. Practical experience has shown that attaining a plateau in oxygen uptake during the VO2max test requires high motivation and a relatively large anaerobic component.

Factors That Affect Maximal Oxygen Uptake

Of the many factors influencing VO2max, the most important include mode of exercise and the person’s heredity, training state, sex, body composition, and age.

Mode of Exercise

Variations in VO2max during different modes of exercise reflect the quantity of muscle mass activated during the performance. In experiments that determined VO2max on the same subjects during exercise, treadmill exercise produced the highest values. Bench stepping, however, has generated VO2max scores identical to treadmill values and significantly higher than values on a bicycle ergometer. With arm-crank exercise, aerobic capacity reaches only about 70% of one’s treadmill VO2max.

The treadmill represents the laboratory apparatus of choice for determining VO2max in healthy subjects. The treadmill provides easy quantification and regulation of exercise intensity. Compared with other forms of exercise, subjects achieve one or more of the criteria for establishing VO2max more easily on the treadmill. Bench stepping or bicycle exercise is suitable alternatives under non-laboratory “field” conditions.


A question frequently raised concerns the relative contribution of natural endowment to physiologic function and exercise performance. For example, to what extent does heredity determine extremely high aerobic capacities of the endurance athletes? Do these exceptionally high levels of functional capacity reflect more than the training effect? Although the answer remains incomplete, some researchers have focused on the question of how genetic variability accounts for differences between individuals in physiologic and metabolic capacity.

Studies were made of 15 pairs of identical twins (with the same heredity since they came from the same fertilized egg) and 15 pairs of fraternal twins (who do not differ from ordinary siblings because they result from separate fertilization of two eggs) raised in the same city by parents with similar socioeconomic backgrounds. The researchers concluded that heredity alone accounted for up to 93% of the observed differences in aerobic capacity as measured by the VO2max. In addition, genetic determination accounted for 81% of the capacity of the short-term glycolytic energy system and 86% of maximum heart rate. Subsequent investigations of larger groups of brothers, fraternal twins, and identical twins indicate a significant but much smaller effect of inherited factors on aerobic capacity and endurance performance.

Estimates of the genetic effect equal about 20–30% for VO2max, 50% for maximum heart rate, and 70% for physical working capacity. Similar muscle fiber composition occurs for identical twins, whereas wide variation in fiber type exists among fraternal twins and brothers. Future research may determine the upper limit of genetic determination, but currently available data show that inherited factors contribute significantly to both functional capacity and exercise performance. A large genotype-dependency also exists for the potential for improving maximal aerobic and anaerobic power, and the adaptations of most muscle enzymes to training. In other words, members of the same twin-pair generally show the same response to exercise training. Genetic makeup plays such a prominent role in determining training response that it is nearly impossible to predict a specific individual’s response to a given training stimulus.

Training State

VO2max scores must be evaluated relative to the person’s state of training at the time of measurement. Improvements in aerobic capacity with training generally range between 6 and 20%, although increases have been reported as high as 50% above pretraining levels.


VO2max values (mL•kg-1•min-1) for women typically average 15 to 30% below scores for men. Even among trained athletes, this difference ranges between 15 and 20%. Such differences increase considerably when expressing the VO2max as an absolute value (L•min–1) rather than relative to body mass (mL•kg-1•min-1). Between world-class male and female cross-country skiers, for example, a 43% lower VO2max value for women (6.54 vs. 3.75 L•min–1) decreased to 15% (83.8 v 71.2 mL•kg-1•min-1) using the athletes' body mass in the ratio expression of VO2max.

Sex difference in VO2max has generally been attributed to differences in body composition and hemoglobin content. Untrained young adult women generally possess about 25% body fat, whereas the corresponding value for men averages 15%. Although trained athletes have a lower percentage of fat, trained women still possess significantly more body fat than male counterparts. Thus, the male generally generates more total aerobic energy simply because he possesses a relatively large muscle mass and less fat than the female.

Probably due to their higher level of testosterone, men show a 10 to 14% greater concentration of hemoglobin. This difference in the blood's oxygen-carrying capacity potentially enables males to circulate more oxygen during exercise and gives them a slight edge in aerobic capacity.

Although lower body fat and higher hemoglobin provide the male with some advantage in aerobic power, we must look for other factors to fully explain the disparity between the sexes. Differences in normal physical activity level between an “average” male and “average” female provide a possible explanation. Perhaps considerably less opportunities exist for women to become as physically active as men due to social structure and constraints. In fact, even among prepubertal children, boys become more active in daily life than their female counterparts.


Changes in VO2max relate to chronological age. Although limitations exist in drawing inferences form cross-sectional studies of different people at different ages, the available data provide insight into the possible effects of aging on physiologic function. Figure 6 shows the VO2max as a function of age. Note the dramatic increases during the growth years. Longitudinal studies (measuring the same people over a prolonged period) of children’s aerobic capacity show that absolute VO2max increases from about 1.0 L•min-1 at age 6 years to 3.2 L•min-1 at age 16 years. VO2max in girls peaks at about age 14 and declines thereafter. At age 14, the differences in VO2max between boys and girls approximate 25%, with the spread reaching 50% by age 16. Note also the decline in VO2max with increasing age. Beyond age 25, VO2max declines steadily at about 1% per y
ear, so that by age 55 it averages 27% below values reported for 20 year olds.

One’s habitual level of physical activity through middle age determines changes in aerobic capacity to a greater extent than chronological age.

Body Composition

Differences in body mass explain roughly 70% of the differences in VO2max scores among individuals. Thus, meaningful comparisons of exercise performance or the absolute value (L•min-1) for VO2max become difficult among individuals who differ in body size or body composition. This has led to the common practice of expressing oxygen uptake in terms of these components – either related to body surface area (BSA), body mass, fat-free body mass (FFM), or limb volume.

Lecture #7 Study Guide

Define Key Terms and Concepts

  1. Anaerobic capacity

  2. Anaerobic power

  3. Average power

  4. Glycogen depletion

  5. Graded exercise test

  6. Joule

  7. Jumping power tests

  8. Peak VO2max

  9. Power

  10. Relative VO2max

  11. Stair sprinting power test

  12. “True” VO2max

  13. VO2max

  14. VO2max Criteria

  15. Watt

  16. Wingate test

Study Questions

Overview of Energy Transfer Capacity During Exercise

Identify the energy system that primarily supports each of the following activities:

Standing vertical jump and reach

Four hundred meter run

Three mile run

Power = ______________ x _______________ ÷ _______________.

Anaerobic Energy: The Immediate and Short-Term Energy Systems

Evaluation of the Immediate Energy System

What type of tests typically measures the immediate anaerobic energy system?

Stair-Sprinting Power Tests

Compute the power output for a person who weighs 55 kg and traverses nine steps in 0.75 seconds (vertical rise each step equals 0.175 meters).

Jumping-Power Tests

Give one factor that might limit power jumping test scores as measures of the power output capacity of intramuscular high-energy phosphates.

Other Power Tests

List two tests (other than stair-sprinting) to estimate power output capacity of the immediate energy system.



Evaluation of the Short-Term Energy System

What type of test best estimates the power output capacity of the short-term energy system?

Performance Tests of Glycolytic Power

List two tests to measure short-term energy transfer capacity.



List three factors that affect anaerobic power performance.

1. 3.


Other Anaerobic Tests

Name one other exercise performance test to measure anaerobic power and capacity.

Glycogen Depletion

List two factors that determine muscle glycogen depletion in different muscle fiber types within the same muscle.



Buffering of Acid Metabolites

Do athletes have an enhanced buffering capacity compared to non-athletes?


What relationship would you expect between “pain tolerance” and one’s capacity for anaerobic exercise? Explain.

Aerobic Energy: The Long-Term Energy System

List three categories of athletes that typically exhibit high values for VO2max?

1. 3.


Measurement of Maximal Oxygen Uptake

Criteria for VO2max

Describe the “gold standard” to indicate attainment of true VO2max.

Tests of Aerobic Power

List two general criteria for a good test of VO2max.



Factors That Affect Maximal Oxygen Uptake

List six factors that influence VO2max.

1. 4.

2. 5.

3. 6.

Mode of Exercise

Indicate the most common piece of exercise equipment to determine VO2max.


What is the estimated magnitude of heredity in determining VO2max?

Training State

Give the general range for VO2max improvement with training?


Give one reasons for sex-related differences in VO2max.


After age 30 y what happens to VO2max?

Body Composition

How does body size influence VO2max?

What is the “best” way to express VO2max? Explain.

Practice Quiz

  1. Power Output:

    1. F x D / T

    2. D x T / F

    3. work / time

    4. force x work

    5. none of the above

  2. A Watt:

    1. measure of oxygen uptake

    2. measure of glycolysis

    3. measure of power

    4. measure of distance

    5. none of the above

  3. Jumping tests measure:

    1. aerobic power

    2. OBLA

    3. EPOC

    4. localized energy depletion

    5. none of the above

  1. Trained athletes compared to untrained:

    1. have greater buffering capacity

    2. have lower buffering capacity

    3. have the same buffering capacity

    4. have reduced buffering after training

    5. none of the above

  2. Among the following athletes who has the highest VO2max:

    1. fencers

    2. speed skaters

    3. swimmers

    4. cross-country skiers

    5. weight lifters

  1. Women compared to men:

    1. have lower VO2max

    2. have higher VO2max

    3. have about the same VO2max

    4. higher buffering capacities

    5. none of he above

  2. Estimates of genetic effects on VO2max:

    1. no effect

    2. 5%

    3. 20-30%

    4. 60%

    5. none of the above

  3. VO2max decreases about ___% in aging:

    1. 1% per year

    2. 10% per year

    3. 15% per year

    4. 25% per year

    5. none of the above

  4. Body composition can explain about ___of the differences in VO2max:

    1. 10%

    2. 30%

    3. 50%

    4. 70%

    5. none of the above

10. Performance tests of anaerobic power would include:

a. long distance runs

b. flexibility tests

c. stair-sprinting power test

d. walking tests

e. none of the above

Lecture #8

Physiologic support systems and exercise


Most sport, recreational, and occupational activities require a moderately intense yet sustained energy release. The aerobic breakdown of carbohydrates, fats, and proteins generates this energy for ADP phosphorylation to ATP. Without a steady rate between oxidative phosphorylation and the energy requirements of physical activity, an anaerobic-aerobic energy imbalance develops, lactic acid accumulates, tissue acidity increases, and fatigue quickly ensues. Two factors limit an individual’s ability to sustain a high level of exercise intensity without undue fatigue:

  • Capacity for oxygen delivery

  • Capacity of specific muscle cells to generate ATP aerobically

Understanding the role of the ventilatory, circulatory, muscular, and endocrine systems during exercise enables us to appreciate the broad range of individual differences in exercise capacity. Knowing the energy requirements of exercise and the corresponding physiologic adjustments necessary to meet these requirements provides a sound basis to formulate an effective physical fitness program and evaluate one's physiologic and fitness status before and during such a program.

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