Sports Medicine: Just the Facts

CHAPTER 13 • BASIC PRINCIPLES OF EXERCISE TRAINING AND CONDITIONING 75

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of Family Physicians, American Academy of Pediatrics,
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13 BASIC PRINCIPLES OF EXERCISE

TRAINING AND CONDITIONING

Craig K Seto, MD, FAAFP

INTRODUCTION

• Regular physical activity is an important component
  of a healthy lifestyle. Increases in physical activity
  and cardiorespiratory fitness have been shown to
  reduce the risk of death from coronary heart disease as
  well as from all causes. There is increasing evidence
  showing that regular participation in moderate-inten-
  sity physical activity is associated with health bene-
  fits, even when aerobic fitness remains unchanged. To
  reflect this evidence, the Centers for Disease Control
  and Prevention (CDC) and the American College of
  Sports Medicine (ACSM) are now recommending that
  every US adult accumulate 30 min or more of moderate-
  intensity physical activity on most—and preferably
  all—days of the week. Those who follow these recom-
  mendations will experience many of the health-related
  benefits of physical activity, and if they are interested in
  achieving higher levels of fitness, will be ready to do
  so (Whaley and Kaminsky, 2001; Franklin et al,
  2000 a; 2000b).

OVERVIEW OF EXERCISE

PHYSIOLOGY

METABOLIC ENERGY SYSTEMS

• At rest, a 70-kg human has an energy expenditure of
  about 1.2 kcal/min with less than 20% of resting
  energy expenditure attributed to skeletal muscle; how-
  ever, during intense exercise, total energy expenditure
  may increase 15–25 times above resting values, result-
  ing in a caloric expenditure between 18 and 30
  kcal/min. Most of this increase is used to provide
  energy to the exercising muscles, which may increase
  energy requirements by a factor of 200 (Demaree et al,
  2001; Rupp, 2001).

ROLE OFADENOSINETRIPHOSPHATE

• The energy used to fuel biological processes comes
  from the breakdown of adenosine triphosphate(ATP),
  specifically from the chemical energy stored in the
  bonds of the last two phosphates of the ATP molecules.
  When work is performed, the bond between the last
  two phosphates is broken, producing energy and heat.
  ATP –––––––AT Pase→ADP +Pi +energy


• The limited stores of ATP in skeletal muscles can fuel
  approximately 5–10 s of high-intensity work. Therefore,
  ATP must be continuously resynthesized from adeno-
  sine diphosphate(ADP) to allow exercise to continue
  (Demaree et al, 2001; Rupp, 2001). Muscle fibers con-
  tain three metabolic pathways for producing ATP: crea-
  tine phosphate, rapid glycolysis, and aerobic oxidation
  (Demaree et al, 2001; Rupp, 2001).

THREEENERGYSYSTEMS ARERESPONSIBLE

FOR THERESYNTHESIS OFAT P

Creatine Phosphate System

• When limited stores of ATP are nearly depleted
  during high-intensity exercise (5–10 s), the creatine
  phosphate (CP) system transfers a high-energy phos-
  phate from CP to rephosphorylate ATP from ADP.
  Since it involves a single reaction, this system can
  provide ATP at a very rapid rate; however, as there is
  a limited supply of CP in the muscle the amount of
  ATP that can be produced is also limited.
  ADP +CP –––––––––creatine kinase→ATP + C


• There is enough CP stored in skeletal muscle for approx-
  imately 25 s of high-intensity work. Therefore, the ATP-
  CP system will last for about 30 s (5 s for the stored ATP,
  and 25 s for CP). This will provide energy for activities
  such as sprinting and weight lifting. The CP system is
  considered an anaerobic system since oxygen is not
  required (Demaree et al, 2001; Rupp, 2001).