Question

1. What are the short- and long-term mechanisms by which the body increases VO₂?
2. Briefly define respiratory exchange ratio and crossover effect; Sketch a graph showing the crossover effect and explain how exercise duration and mass action effect can affect the shape of the curves.

Answer 1

• The Fick equation describes the relationship between cardiovascular function and VO2. Stroke volume is most likely responsible for training-induced changes in VO2 max because it gradually increases as a response to training.

• Treadmill VO2 max results would be higher than bike max test results in an untrained subject. This is highly assumed by excess body weight limiting performance much more than in a bike max test since supporting body mass is very important in this type of exercise. It is also presumed that most subjects would prefer biking over running since it is less challenging.

• Plasma volume is the cause of an increase in VO2 max after only 2 weeks of training. Plasma volume will increase not only VO2 max but increased blood volume.
• It is generally considered the best indicator of cardiorespiratory endurance and aerobic fitness but it does not necessarily mean that if someone who has a higher VO2max will perform better. A person with a lower VO2max can still perform better.
• VO2 max would be normally higher in leg ergometry because legs are a bigger muscle group therefore require more energy. This may not be the case in healthy populations of long distance runner or cyclist, but these groups are conditioned to the stress of working there legs muscle more often.

O2 uptake (VO2) during submaximal exercises in endurance trained and untrained men. Open circles, untrained subjects; solid circles, trained subjects. The tests durations were 4.0, 6.3 and 30.0 min for above LT, within LT and below LT, respectively. LT: lactate threshold. VO2 values are means of one minute taken at the initiation of exercise (1), at the middle of the test (2) and at the end of the test (3). Data are expressed as mean ± SEM, n = 8.

Respiratory exchange ratio (RER) values during submaximal exercises in endurance trained and untrained men. Open circles, untrained subjects; solid circles, trained subjects. The tests durations were 4.0, 6.3 and 30.0 min for above LT, within LT and below LT, respectively. LT: lactate threshold. RER values are means of one minute taken at the initiation of exercise (1), at the middle of the test (2) and at the end of the test (3). Data are expressed as mean ± SEM, n = 8.

Blood lactate concentration during submaximal exercises in endurance trained and untrained men. Open circles, untrained subjects; solid circles, trained subjects. The tests durations were 4.0, 6.3 and 30.0 min for above LT, within LT and below LT, respectively. LT: lactate threshold. Blood lactate was taken at basal (0), the initiation of exercise (1), at the middle of the test (2) and at the end of the test (3). Data are expressed as mean ± SEM, n = 8.