text: Physiology
  OXIDATIVE PHOSPHORYLATION
  4-9. This pathway is the predominant source of energy for low-intensity, sustained exercise lasting for more
  than three minutes. This pathway supports aerobic performance. The presence of oxygen allows pyruvate in
  the muscle cell to be converted into much more adenosine triphosphate than the other two energy systems.
  Both fat and carbohydrate are converted into energy in this system. The process for fat metabolism is called
  beta oxidation. Leaders typically use prolonged, low-intensity training such as Foot Marches, Release Runs,
  and Ability Group Runs to increase aerobic endurance. This type of training encourages the metabolism of
  fat for fuel. Its use of training uses much shorter rest intervals than the phosphagen pathway. Rests of as little
  as 5 to 10 seconds are common during low-intensity intervals.
  4-10. Carbohydrates, the body’s main fuel source, are broken down into glucose and stored as glycogen.
  Glycogen stores supply about 3,000 kcal in the typical Soldier and are rapidly depleted as exercise intensity
  increases. Soldiers may burn 1–3 grams of glycogen per minute during exercise and most will run out of
  glycogen after 1 1/2–2 hours of activity. When glycogen stores are depleted, it results in the condition
  sometimes called “hitting the wall.” Soldiers must pay careful attention to nutrition before and during
  prolonged aerobic activity. For example, to avoid degrading their performance on the 2-Mile Run event,
  Soldiers avoid depleting glycogen caused by the anaerobic effort of the Sprint-Drag-Carry.
  VO MAX
  2
  4-11. The highest amount of oxygen that can be used during maximal aerobic effort—endurance training—
  is called the maximal oxygen consumption, or VO max. It is measured as volume (V) in milliliters of oxygen
  2
  (O ) consumed per kilogram of body weight per minute, abbreviated to mL/kg/min. A recruit who scores
  2
  black on the OPAT has a predicted VO max of 33 mL/kg/min. Over time and with progressive training, that
  2
  recruit could improve his or her maximal aerobic capacity. Strength training typically results in little or no
  change in VO max unless the Soldier uses longer sessions of circuit-type strength training with shorter rest
  2
  intervals between exercises. Strength training improves physical performance by increasing relative work
  capacity through increases in muscle mass and the improved strength of support structures (see paragraph 4-
  23). Strength training coupled with circuit training directly increases muscular strength and power, while
  supporting the further development of aerobic endurance, anaerobic speed, and muscular endurance.
  ANATOMY
  4-12. Anatomy refers to the physical structure of the body. Understanding the bones, muscles, and different
  systems that form the body helps Soldiers and leaders build better training programs that improve
  performance while preventing injuries.
  BONE
  4-13. The 206 bones in the human skeleton form both a chassis for muscles to attach to and enclosures to
  protect vital structures such as the brain, heart, and spinal cord. Bones store deposits of minerals such as
  calcium and phosphorus. Although bones vary in size and shape, some typical features compose a bone’s
  function and bone injury. The outer, hard surface of the bone is the cortex. This strong and stiff tissue is lined
  by a fibrous layer called periosteum (“around the bone”). The periosteum conveys blood vessels and nerves
  to the bone and signals pain when bumped or irritated and excruciating pain when fractured.
  4-14. The softer inner tissue of the bone is the marrow. Bone marrow generates red and white blood cells
  and platelets. Wherever two bones meet to form a moveable joint in the body (an articulation), the contact
  surface of the bone is covered in cartilage. Cartilage is a softer, more fibrous material than the bone cortex
  and is made of cells that produce collagen. Its purpose is to cushion the bones, especially in weight-bearing
  joints like the hip, knee, and ankle, and to allow the bones to move more smoothly against each other.
  Cartilage does not have nerve supply, nor as many blood vessels as the rest of the bone. Once it is damaged,
  it does not repair well. This can lead to pain and inflammation in the joint, otherwise known as arthritis.
  4-15. Bones are living tissue. They grow larger and longer up to adulthood. Throughout adulthood bones
  remodel when physical activity stimulates the bone to thicken and strengthen. In response to physical stress,