S1, L8: Domains of exercise

What is critical power?

The highest power output that can be maintained over time

What is there a steady state in at the critical power? (5)

• VO₂

• Blood lactate concentration

• Heart rate

• Muscle cell physiology

• Fatigue products

What is critical power related to?

Maximal lactate steady state

What is W’ (W prime)?

• A fixed energy store that mainly represents anaerobic capacity

• It is essentially an anaerobic battery that can fuel for high power, low time or low power, high time

What is the equation for W’ (W prime)

W’ = power x time

What athletes benefit from a high W’ (W prime)?

Sprint athletes or those that heavily rely on anaerobic capacity

Which athletes benefit from a high critical power?

Endurance athletes

What is critical power used for in practice? (3)

• Characterisation of athletes

• Power zones for training prescription

• Athlete tracking over a season or training cycle

What are the domains of exercise? (3)

• Low intensity domain - below lactate threshold, [Bla] < 2mmol/L, VO_{2 max} < 70%, steady state achieved in less than 3 minutes

• Moderate intensity domain - between lactate threshold and lactate turnpoint, [Bla] is elevated but stable at 2-8 mmol/L, 70-90% VO_{2 max}, steady state is delayed

• Severe intensity domain - above MLSS/critical power, [Bla] > 2-8 mmol/L, VO_{2 max} > 90%, steady state is not attainable

What is oxygen uptake kinetics?

Breath by breath analysis of oxygen uptake

Describe the 3 phases of oxygen uptake kinetics

• Phase 1 - cardiodynamic component (~20s) - oxygen uptake increases as exercise begins and then there is a small dip, transit time of blood between the exercising muscles and lungs

• Phase 2 - primary component (~2-3 minutes) - steep and smooth increase in oxygen uptake until the beginning of a plateau, pulmonary VO₂ rises in a mono-exponential fashion to meet the muscle oxygen demand

• Phase 3 - slow component (>3 minutes) - very gradual increase in oxygen uptake over time, slow rise in VO₂

Why is the slow component of oxygen uptake kinetics only seen during high power outputs?

A growing number of fast motor units (fast twitch fibres) have to be recruited to maintain the power output