Exercise Prescription and Physiology

Metabolic equivalents (METs): expression of metabolic cost of exercise in terms of oxygen consumption

• Rest defined as 1 MET, which is an oxygenation of 3.5 mL O ₂ /kg/min

• MET chart ( Table 17.1 )

  Table 17.1

  Mets In Common Competitive And Recreational Sports

  Modified from Mead WF, Hartwig R. Fitness evaluation and exercise prescription. J Fam Pract . 1981;13(7):1039–1050.

  Sport	METs
  Basketball (comp)	7–12
  Biking (rec)	3–8
  Dancing	3–7
  Football	6–10
  Golf (cart)	2–3
  Jogging (5–6 mph)	7–15
  Skiing (downhill)	5–8
  Soccer	5–12
  Tennis	4–9
  Volleyball	3–6

VO ₂ max: maximal oxygen utilization

• Gold standard for evaluating cardiorespiratory fitness

• Measured in mL O ₂ /kg/min

Anaerobic threshold: point at which oxygen demand exceeds oxygen availability

Workload: amount of energy required to complete a specific task ( Table 17.2 )

The sarcomere, which is the basic unit of muscle, is composed of actin and myosin filaments ( Fig. 17.1 ).

This linkage between actin and myosin is facilitated via acetylcholine release at the motor endplate, which triggers depolarization and subsequent release of calcium from the sarcoplasmic reticulum; this is followed by a series of reactions, causes formation of an adenosine triphosphate (ATP)–myosin complex, a subsequent change in myosin unit conformation, and ultimately, traction on the actin filament. This pulls on the sarcomere’s connective tissue components, resulting in muscle contraction ( Fig. 17.2 ) and movement.

The motor nerve center directs the timing and sequencing of motor unit recruitment and firing, which facilitates coordinated movement.

Continued muscle contraction relies on an adequate supply of ATP in each sarcomere.

ATP is provided by three interlinked, overlapping energy systems that synthesize ATP for both short periods of intense vigorous activity and longer periods of lower-level sustained activity.

Exercise results in increases in protein synthesis within muscle, with long-term/cumulative changes to the steady-state level of protein synthesis with repetitive exercise.

Body weight and glucose control are influenced by the energy requirements of muscle contraction.

Mitochondrial volume and density may increase up to 40% to accommodate increase in aerobic exercise.

Musculoskeletal and cardiorespiratory systems are highly adaptable to regularly performed exercise.

Adaptation to repetitive exercise can be understood in terms of several factors, which can be represented by the mnemonic P-ROIDS.

• P rogression: Gradual increase in intensity, duration, and difficulty of physical activity to improve strength, endurance, and sport-specific skills

• R eversibility: Training is generally continuous or cyclic in nature, because of the rapid loss of benefits from conditioning when people stop exercising

  • Inactivity for as little as several days can lead to reduction in work capacity secondary to a decrease in protein synthesis from baseline with loss of exercise stimulus

• O verload: Exercising above normal levels through combinations of type of activity, intensity, duration, and/or frequency

• I ndividual D ifferences

• S pecificity: Specific training develops specific adaptations beneficial to a particular sport/activity

Training should focus on energy system that is most important to that sport (e.g., distance runners spend more time working on oxidative system)

Modern training programs typically incorporate cross-training because training focused on optimizing all energy systems can improve sport-specific performance (e.g., dry-land and weight training can improve the performance of skiers)

Concurrent training: integration of both aerobic/endurance and resistance training into the training plan

Lower-volume, high-intensity interval training can improve aerobic fitness in sedentary subjects

Ratio of acute to chronic training load can be used to monitor response to exercise and mitigate injury risk

• Acute training load: workload performed over 7 days

• Chronic training load: 28-day average of acute training load

Aerobic/endurance exercise: fueled by an oxidative energy system and in place when oxygen supply/delivery to tissues is adequate for sustained low- to moderate-intensity exercise

• Increased lipid mobilization and oxidation by skeletal muscle

• Increased number of mitochondria with adaptation

Anaerobic exercise: typically high-intensity, shorter-duration exercise that exceeds capacity of oxidative system and is fueled primarily by phosphagens and glycogen to pyruvate energy systems

Resistance exercise: training for maximal contractile force and muscle hypertrophy

Range of motion/stretching/warm-up/cool-down exercises ( Fig. 17.3 )

Flexibility exercise: increases ability to lengthen muscle–tendon units and improve motion around specific joints

“Lifestyle activity”: cumulative, nonstructured, moderate-intensity physical activities that individuals do during a typical day (e.g., taking stairs and walking from parking lot)

• Ten minutes of moderate-intensity exercise three times a day facilitates changes comparable to health benefits of 30 minutes of continuous exercise

• Increasing lifestyle activity is as effective as structured activity for improving cardiorespiratory fitness and reducing cardiovascular disease (CVD) risk factors.

A tool to teach, coach, and educate patients regarding opportunities to improve overall health and well-being

• Can also enhance exercise and sport-specific performance

Exercise is safe for a majority of patients and has numerous health/fitness benefits

Written exercise prescription has been demonstrated to increase activity levels more compared with verbal advice alone

Prescription should include exercises to improve aerobic fitness, strength, and mobility