B4 Exercise and Respiration

B.4.1  Define VO2 and VO2 max

VO2:  The volume of oxygen that is absorbed by the body per minute and supplied to the tissues (i.e. oxygen consumption)

VO2 max:  The maximum rate at which oxygen can be absorbed and supplied to the tissues (i.e. maximum capacity of oxygen consumption)

B.4.2  Outline the roles of glycogen and myoglobin in muscle fibres

Glycogen:  Involved in glucose storage (polymeric form allows for improved storage of glucose in muscles)

Myoglobin:  Involved in oxygen storage (binds O2 when levels are high and releases when low, allowing muscles to respire aerobically for longer)

B.4.3  Outline the method of ATP production used by muscle fibres during exercise of varying intensity and duration

Short Duration:

  • Creatine phosphate can be used to regenerate ATP for 8 - 10 seconds of intense exercise
  • Creatine phosphate can be hydrolysed to produce a free phosphate, with a net release of energy that is used to regenerate ATP from ADP
  • Creatine phosphate acts as a high energy reserve and can be regenerated from excess ATP during periods of rest

Long Duration:

  • Beyond 10 seconds, supplies of creatine phosphate are exhausted and ATP is produced entirely by cell respiration
  • At high intensities, oxygen supplies are insufficient and muscles will respire anaerobically, producing lactic acid as a waste product
  • At low intensities, oxygen supplies are adequate for muscles to respire aerobically
  • As intensity of exercise decreases and the duration increases, the percentage of anaerobic respiration decreases and aerobic respiration increases

Comparison of Energy System Usage at Different Durations of Exercise

energy system durations

Overview of Energy Systems

B.4.4  Evaluate the effectiveness of dietary supplements containing creatine phosphate in enhancing performance

  • Supplementation is aimed at increasing the upper limit to the amount of creatine phosphate the body can store
  • High intensity anaerobic sports participants have reported performance enhancement (e.g. sprinting, lifting, wrestling)
  • It is of questionable benefit to other forms of athletic performance (results are inconclusive for runners, swimmers, etc.)
  • It has been taken by body builders as it is reputed to increase muscle mass, however some suggest mass gains are due to increased water retention
  • Supplementation is not recommended for adolescents or people with kidney dysfunction
  • Supplementation can cause health concerns (e.g. high blood pressure, diarrhoea, cramps, etc.)
  • It has been suggested that supplementation may function to suppress the body's natural synthesis of creatine phosphate
  • It is only really effective in individuals that possess naturally low concentrations of creatine phosphate

B.4.5  Outline the relationship between the intensity of exercise, VO2 and the proportions of carbohydrate and fat used in respiration

  • The body requires more oxygen to generate a set amount of energy when metabolising fats as compared to metabolising carbohydrates
  • At lower exercise intensities (below 50% of VO2 max), more oxygen is available for aerobic respiration and stored fats will supply the energy source
  • As exercise intensity increases (above 50% of VO2 max), less oxygen is available for aerobic respiration and carbohydrates need to be used
  • As exercise intensity increases towards the VO2 max, anaerobic respiration occurs and carbohydrates are used exclusively
  • So as exercise intensity increases and oxygen availability decreases, there is an increase in carbohydrate use and a decrease in fat metabolism

B.4.6  State that lactate produced by anaerobic cell respiration is passed to the liver and creates an oxygen debt

  • An oxygen debt describes the additional oxygen the body requires after exercise to restore body systems to their normal state
  • Lactic acid produced during anaerobic respiration is passed to the liver and requires oxygen to be reconverted back to pyruvate

B.4.7  Outline how oxygen debt is repaid

  • Lactate can be converted into pyruvate within the liver
  • The pyruvate can either be used for aerobic respiration or converted into glucose for later use (via the Cori cycle)
  • This repayment of the oxygen debt occurs using oxygen taken in during deep ventilations after exercise
  • Other events that occur when the oxygen debt is repaid include restoring myoglobin to oxymyoglobin and restoring creatine phosphate levels

Oxygen Uptake During Steady State Exercise

oxygen debt