Exercise Prescription

Steven J. Keteyian

OVERVIEW

Exercise is now touted as a treatment for many types of disease; in fact, lack of exercise and physical activity leads to disease and increases morbidity in many conditions. As society becomes more automated and modern conveniences make exercise less incidental to daily life, the depth of this problem will continue to grow. The body depends on motion and exercise to maximize healthy function. For example, lymphatics in the extremities depend on muscle contraction to pump lymph throughout the body. Joint motion aids in distributing nutrition to its cartilage and synovium, while an immobile joint quickly stiffens and loses range of motion.

Exercise is also important in helping athletes deal with chronic somatic dysfunction. In manual medicine, a common question a patient asks after treatment is “How do I prevent this from happening again?” Whether it is cervical dysfunction, sacral torsion, or other malalignments, exercise is the answer. Flexibility and muscle strengthening are the two most important aspects of dysfunction that go untreated. Many individuals just get manipulations repeatedly, thinking that the dysfunctional segment will eventually be forced into staying in place by the clinician’s manipulations. Without exercises to specifically stabilize the region, the dysfunction will likely recur. After all, when a region is put back into alignment, it is the muscle group that keeps it aligned. Muscles have memory, and if the muscle believes that a dysfunctional position is correct, then the muscle will always fire dysfunctionally, unless it is retrained through exercise. Therefore, manual medicine should always incorporate an exercise prescription, either through a trainer or rehabilitation center, or with a home program the athlete maintains for himself or herself.

The task of prescribing exercise in high-performance athletes, in sedentary healthy people, and in patients with clinically manifest disease is more similar than one might think. Despite any obvious differences in performance level between the three groups or despite concerns one may have about exercise-related complications, there are two basic tenets that apply to everyone when establishing an exercise training program. These are specificity of training (e.g., mode of training) and progressive overload (i.e., intensity, duration, and frequency of training).

Before discussing each of these two tenets in detail, it is necessary to first identify and briefly discuss the major components or types of physical fitness. They include aerobic power or endurance, peak anaerobic power, anaerobic endurance or capacity, muscular strength, muscular endurance, body composition, and flexibility.

COMPONENTS OF PHYSICAL FITNESS

Table 11.1 summarizes various common methods for measuring the primary types of fitness in progression from the least costly and least complex to those of greater cost and complexity. In almost every case, in moving from lower cost and lesser complexity to higher cost and greater complexity, validity and measurement accuracy improve. For the physician routinely involved with sports medicine, having access to many of the more valid methods listed in
Table 11.1 is important. However, before ordering any of these tests it is always prudent to consider whether the need to more accurately quantify fitness level or training effect offsets any increased cost.

TABLE 11.1. METHODS OF ASSESSING COMMON FITNESS PARAMETERS

Complexity of Measure			Anaerobic		Muscular		Body Composition
Complexity of Measure	Cost	Aerobic Power	Power	Capacity	Power	Endurance	Body Composition	Flexibility
Simple	Low	Submaximal test to predict Vo₂ max	—	—	Maximal (kg) using hand grip dynamometer	Repetitions to muscle fatigue	Skinfolds	Sit and reach
		Submaximal test to predict Vo₂ max						Bioelectrical impedance
Moderate	Moderate	Maximal test to predict Vo₂	Margaria-Kalmen power test	—	One repetition maximum (isotonic)	—	Skinfolds	Gravity-dependent flexometer
							Bioelectrical impedance
Complex	High	Direct measure of gas exchange for Vo₂ max and pace at ventilatory threshold	Wingate test for peak power (hp)	Wingate test for anaerobic capacity or total work (joules) and fatigue index (%)	Isokinetic analysis of force/velocity curves	Isokinetic analysis of fatigue index at specific speeds	Hydrostatic weighing for body density	Radiography
							Dual x-ray absorptiometry	Biomechanical analysis
Table developed courtesy of Steven J. Karageanes, DO, Henry Ford Health System.

Aerobic Power

An approximation of peak aerobic power or oxygen consumption (VO₂) can be easily accomplished using a submaximal or maximal bike or treadmill test. Previously established prediction equations are typically used to estimate peak VO₂, and such data are useful when either categorizing one’s fitness level or roughly assessing change in exercise capacity due to training. However, providing an estimate of peak VO₂ may not be helpful for highly competitive athletes interested in quantifying peak aerobic capacity or heart rate or pace at ventilatory threshold. Generally, submaximal and maximal tests tend to overestimate measured peak VO₂ by as much as 15% to 25% (1).

One accurate method for measuring peak VO₂ involves using open circuit, indirect spirometry. Because testing mode or type of exercise ergometer can influence results among highly trained athletes, it is appropriate to test the athlete using the mode that best simulates her or his activity—the principle of specificity of testing (2). Therefore, competitive cyclists should be tested on a cycle ergometer, swimmers in a swim flume, and runners on a treadmill. Among healthy untrained and less competitive individuals, treadmill testing is satisfactory and usually results in a higher peak VO₂, by about 5% to 15%, when compared to testing performed using other ergometers.

Typically, peak VO₂ is reported in mL · kg^-1 · min^-1 and, assuming normal pulmonary function and the absence of clinically meaningful anemia or a skeletal muscle disorder, it reflects the ability of the body to transport and utilize oxygen. A simple rearrangement of the Fick equation (Adolph Fick, 1870) provides a nice illustration of this concept:

VO₂ = Q × a-vO₂ diff

where VO₂ is oxygen consumption in L · min⁻¹, Q is cardiac output in L · min⁻¹, and a-vO₂ difference is arterial-mixed venous O₂ difference in mL · L⁻¹.

In this equation, exercise cardiac output represents the transport of blood to the metabolically more active skeletal muscles and a-vO₂ difference represents the extraction and utilization of oxygen within the muscle. Typical values for peak VO₂ are shown in Figure 11.1.

Interestingly, at-rest cardiac output is the same in both healthy untrained and endurancetrained athletes, about 5 L · min⁻¹. However, atpeak exercise cardiac output may reach 22 to 25 L · min⁻¹ in the nonathlete, and exceed 35 L · min⁻¹ in the athlete. In general, this difference in the ability to maximally transport oxygen to the active tissues is due to a greater stroke volume during exercise in the athlete versus the nonathlete (˜170 mL · beat⁻¹ versus ˜120 mL · beat⁻¹, respectively). In contrast, peak heart rate is influenced little by exercise training, and peak a-vO₂ difference is only slightly greater in the athlete (15.5 mL of O₂ · 100 mL of blood⁻¹) versus the nonathlete (˜13.8 mL of O₂ · 100 mL of blood⁻¹).

Anaerobic Power and Capacity

Whereas the ability to generate adenosine triphosphate (ATP) over a long period of time in the skeletal muscle relates to chemical reactions within the aerobic metabolic pathways (i.e., Krebs cycle, oxidative phosphorylation, and beta-oxidation), a person’s ability to generate ATP during sudden, short-duration and all-out tasks is related to the amount and rate of ATP produced via anaerobic pathways [i.e., phosphocreatine (PC) system and anaerobic glycolysis]. For example, the highly accomplished male 800-m college runner will complete his event in less than 1 minute and 50 seconds, requiring a high level of anaerobic fitness in the muscles of his legs to do so.

Tests that reflect or quantify one’s ability to produce ATP through the ATP-PC system and anaerobic glycolysis have changed greatly over the past 40 years. In the 1960s, the common method for assessing anaerobic power involved
the Margaria-Kalmen power test (1,3). In this test, a subject runs up a flight of stairs as rapidly as possible, taking three steps at a time. Using electronic switch timer plates placed on the third and ninth steps and knowing the rise of each step, power is then calculated using the mass of the subject moved over the vertical distance between step 3 and step 9 and the elapsed period of time to do so.

FIGURE 11.1. Typical values for peak Vo₂.

The aforementioned method has given way over the years to the Wingate anaerobic test (4), which involves pedaling a cycle ergometer for 30 seconds using maximal effort against a fixed braking force that is set at two to four times a previously determined maximum. Peak power is determined in watts or horsepower, usually attained in the first 5 seconds of the test. Mean power represents the average power over the full 30-second test.

To appreciate the magnitude of the power generated in elite anaerobic athletes, consider the Olympic 1-km track cycling event that is conducted outdoors using an aerodynamically enhanced bicycle on a track called a velodrome. This event is often called the “killermeter” because it is an all-out sprint that typically takes 62 to 65 seconds to complete. Approximate Wingate test results for these athletes may approach 1385 W, 940 W, and 285 kJ for peak power, mean power, and total work, respectively. This is enough power to illuminate 100 light bulbs (each 60 W) for almost 5 seconds. Typical values for other athletes and nonathletes are shown in Figure 11.2.

Higher peak and mean power values among various athletes during testing are associated with the ability to achieve higher rates of ATP production through anaerobic pathways and higher concentration of muscle and blood lactate. Also, as one might guess, both of these variables are significantly correlated to the percentage of type II (fast-twitch) muscle fibers (5). However, although the Wingate test does identify people with increased capabilities for
anaerobic performance, it does not always relate well to athletic performance. This is because other factors such as strategy, prior racing experience, and intrinsic motivation often differentiate success.

FIGURE 11.2. Typical values for power generated by different types of male athletes.

Muscle Strength and Endurance

Measures of muscle strength and endurance have long been performed, and established norms exist for boys and girls, men and women, and athletes and nonathletes. Generally, the more simple and inexpensive tests of muscle strength (e.g., hand dynamometer for grip strength, cable tensiometer for quadriceps strength) and muscle endurance [e.g., number of sit-ups or push-ups in 1 minute or until fatigue (3); flexed arm hang (girls) or pull-ups (boys)] do not necessarily correlate well with on-ice or on-field performance.

Another common method for assessing muscle function, more so for muscle strength than muscle endurance, is the one repetition maximum (1 RM). Using either free weights or fixed bar resistance machines, isotonic or concentric muscle strength is then measured as the maximum amount of weight that can be lifted during one repetition, thus 1 RM. Because multiple joints and muscles are involved in muscle strength testing when using free weights, this testing may be better for sport-specific movements or athletic performance. Conversely, fixed bar and isokinetic resistance machines better isolate specific muscles or muscle groups and as a result, often serve for evaluating treatment or rehabilitation outcomes.

Recent work by Robergs and Keteyian summarized grip strength and age-specific chest press norms in men and women using grip dynamometer and bench press, respectively (3). Similar information, expressed as percentiles, is available for upper body strength (bench press) and leg strength (leg press) (6). When 1 RM is not advised or available for whatever reason, equations exist to predict 1 RM for leg press and chest press using submaximal effort (3).

Over the past 30 years, the use of isokinetic or other accommodating resistance devices have
flourished because of their ability to quantify muscle power, force, or torque across a wide range of fixed joint movement speeds—from 0 to 300 degrees per second. With this methodology, the tester can identify points of high and low force output that may occur throughout a limb’s measured range of motion. Such information is generally advantageous for clinical evaluation and research aimed at monitoring training progress or rehabilitation.

Additionally, with isokinetic devices muscle endurance can be assessed using a testing approach that provides a fatigue index. This variable represents the loss of maximally generated force at a given joint movement speed and over a given period of time (e.g., 20 to 30 seconds). Generally, the smaller the difference in mean force when comparing the first five repetitions in a test to the last five repetitions, the greater the muscle endurance. Restoring to less than 10% any differences in fatigue index (loss of power) that exists when comparing a previously injured limb to a healthy limb is often used as a guide when providing return-to-play recommendations among competitive athletes.

Body Composition

Although often more true for athletes than nonathletes, determining the percentage of body mass that is fat versus fat-free tissue (lean body mass) is sometimes included when evaluating physical fitness. This is partly due to the strong relationship between muscle mass or cross-sectional size and muscle performance (i.e., strength and endurance). Likewise, a lower percentage of body fat favors athletes involved in activities that demand balance, agility, and moving their body mass through space (e.g., jumping).

TABLE 11.2. COMMON VALUES FOR PERCENT BODY FAT IN ENDURANCE ATHLETES AND APPARENTLY HEALTHY PEOPLE

	Endurance Athlete	Health Maintenance
	Endurance Athlete	Excellent	Good	Average	Fair	Poor
Men	5-9	10-14	14-18	18-22	22-25	>25
Women	10-16	17-20	20-23	24-30	30-34	>34

Among competitive runners, less fat is also associated with improved performance. In fact, differences in body fat between elite male and female runners partly account for genderatributed differences in running performance. On the other hand, performance in swimming, especially women swimmers, seems to be the exception relative to the relationship between body fat and performance. Current thoughts are that a slightly greater percentage of body fat in swimmers aids buoyancy, which leads to reduced drag and metabolic cost and an improved ability to keep one’s body on the surface of the water. Table 11.2 depicts common findings for percent body fat among endurance athletes and apparently healthy people.

The measurement of body composition is prone to a variety of technical and instrument errors. Therefore, it is important that both tester experience and laboratory reliability be ascertained before accepting results. As mentioned in Table 11.1, one inexpensive and simple method for body fat determination is the use of skinfold measures. In highly trained hands this approach estimates body density, which is then used to compute body fat using existing equations, to within ±3% to 4% (6). If correctly performed, this approach is usually sufficient when setting performance goals and categorizing athletic participation (e.g., weight classes in wrestling). One advantage of skinfold measures is that numerous prediction equations have been developed to estimate body density for a variety of groups including the general population, athletes and nonathletes, men and women, and children and older adults. Another obvious advantage is its lower cost and ease of testing. Subjects can be tested in just about any setting.

Unlike skinfold measurement, and despite its simplicity and popularity for use at health fairs and in fitness centers, bioelectrical impedance analysis is not recommended for the routine measurement of body fat. Technically, this methodology is based on the passing of an undetectable current from electrodes placed on a hand and foot to electrodes placed on an ankle and wrist. Unlike body fat, fat-free tissue contains most of the body’s water and electrolytes and is therefore a good electrical conductor. Thus, the amount of current flow through tissue reflects the amount of fat and fat-free tissue.

It should be noted that body fat determined from bioelectrical impedance (or conductivity) analysis is often underestimated in nonathletic people and overestimated in lean athletic people. One reason for this is that correct pretest instructions aimed at controlling confounding variables are often either not stated or followed. Specifically, the influence of prior alcohol, diuretics, and caffeine consumption; prior exercise; avoiding fluids for 4 hours; voiding before testing; and phase of menstrual cycle on total body water should be addressed. Given the above concerns and the often improper fitting of one population-specific prediction equation to people of different race, gender, age, and ethnicity, body composition determinations using bioelectrical impedance should be viewed with caution. It is important to point out, however, that with proper pretest instruction and the use of the correct population-specific equation, bioelectrical impedance is reasonably accurate.

Although newer and generally accurate commercially available systems are now available to measure body volume using plethysmography, the gold standard two-component method for determining body density remains hydrostatic or underwater weighing. Like skinfold testing, this approach is also subject to tester error. However, if performed correctly it can be used to determine body density and, therefore, body fat to within 1% to 2.5%. Measuring body density using hydrostatic weighing, when done in conjunction with the newer formula meant to convert body density to body fat in a variety of ages, gender, and ethnicity, is quite valid (7).

Another highly sophisticated method for determining body composition, one that represents a three-component model (i.e., bone mineral content, body fat, and lean body mass), is dual energy x-ray absorptiometry, or DEXA. This methodology is accurate, is safe, requires little pretest subject preparation, and provides little subject discomfort. Its only drawback, due to its price, is availability, which is becoming less of an issue as more and more units are purchased by clinics and hospitals.

Flexibility

Important for performance in both athletic activities (e.g., gymnastics, wrestling) and routine activities of daily living, joint flexibility is influenced by variables such as distensibility of joint capsule, adequacy of warm-up, muscle viscosity, and any pain or discomfort due to acute or chronic injury. Just as no single exercise can measure total body muscular strength or endurance, no single exercise can evaluate total body flexibility. Typical instruments for measuring joint flexibility include tape measures, the Leighton flexometer, and goniometers. In the fitness center setting, static flexibility of the hips and lower back (i.e., trunk flexion) is routinely measured using the sit and reach test (i.e., trunk flexion), both with and without the use of a sit and reach box.

PRESCRIBING EXERCISE

As mentioned at the beginning of this chapter, improving an individual’s capacity to perform a certain task involves working specific muscles or organ systems at a progressively increased resistance. The two key training principles to accomplish this are specificity of training and progressive overload or resistance. These principles apply to both anaerobic and aerobic activities.

Specificity of Training

To develop the predominant energy or organ system(s) needed to perform a sport, one must first identify its associated performance time.
For example, near-world-caliber time for the men’s 5000-m ice speed skate is approximately 6 minutes and 33 seconds. Similarly, a nearrecord time for the men’s 3000-m run is about 7 minutes and 10 seconds. Although these two forms of locomotion are different, skating versus running, they both have similar performance times. As a result, the energy contributions from the muscle’s energy systems are similar as well. Specifically, for both events approximately 35% of training time should be spent developing the anaerobic glycolysis system, with the balance spent in training the aerobic metabolic pathways.

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