Oxygen Kinetics (and the Warm up)

What do we mean by "Oxygen Kinetics" ?

When we start exercising from rest say in a race or a workout our muscles require energy to perform the work. The three main energy supply systems we draw upon can't all turn on to full capacity immediately as we saw in Energy Systems - Part 2.

In particular the aerobic system can take over 2 minutes to reach maximum capacity. 

The following chart shows how aerobic system reacts to this initial demand for energy.

from Mark Burnley and Andrew Jones 02 August 2007

Note in particular the three Intensity Domains - Moderate, Heavy and Severe. The Moderate domain is when you are exercising at an intensity or effort lower than LT1 ie up to 65-70% of your VO2max or 1500m pace; the Heavy Domain somewhere between the LT1 and LT2 (or Critical Power/Speed (about 87-90% of 10km pace); and Severe which is above LT2 and Critical Power and extends to beyond VO2 max. 

It shows three different Heavy Domain intensity runs with the black full circles being one at a  intensity between 5km to 10km pace/power; the open circles at and intensity of about 3km pace /power; and the third at an intensity of about 800m pace/power. They show the differing rates of the uptake of oxygen from starting to run a time 0 until 12 minutes. From time -2min to 0min is the base rate of oxygen uptake; then there is reasonably fast increase in oxygen uptake (the Fast Component)  until 2min before it either levels out if exercise is below LT2 or a much slower rise (Slow Component) from 2min until it reaches your VO2 max, at which time you are either forced to stop or slow down considerably.  The black triangles would be the most intense of the three runs. 

The following Chart shows a simplified picture of the VO2 response to Heavy domain exercise with the muscle O2 demand superimposed. The area between the demand curve and the supplied O2 curve has been erroneously called Oxygen Debt. The body has to dig into its limited fast energy sources- the Alactic CP and the Anaerobic Lactic systems. This debt has to be “paid back” either during the remainder of the run or in recovery by recharging the Alactic battery or removing the fatiguing waste products associated with the production of lactate. 

So the ability to speed up the fast component and/or slow down the slow component will lead to improved performance. 

From Andrew Hamilton "Sports Performance Bulletin"

This is where the benefit of carrying out appropriate warm up comes in. 

There hasn’t been a lot of science studies carried out on optimal warmup procedures. It being left to individual athletes or coaches  to use what seemed to work best for the individual and the event. The warmup will differ for faster sprinting type events; the fast 3-10km events; and longer slower events Half marathon upwards. 

However things to consider are:

To stretch or not to stretch

Static or dynamic stretch/mobility

Passive warmup ( hot or cold application)

Muscle massage

Low intensity or high intensity running or low intensity with some faster strides

How long to warmup and how close to start time

However let’s consider the case of warmup for 5km race. This will be a race carried out in your severe domain ie above your Critical Power / LT2. 

Some work done by Mark Burnley and Andrew Jones (i) has shown that by performing a 6 min warmup in the Heavy intensity domain followed by 6-20min passive recovery improved performance in a Heavy/Severe intensity race. This is provided the warmup doesn’t reduce the Anaerobic Capacity excessively in relation to the duration of the race. Easy paced warmups in the moderate domain don’t however show any improvement. Sprint warmups can can have a detrimental impact on subsequent performance presumably related to reducing the Anaerobic capacity and high energy phosphate battery stores.

The heavy domain warmup appears to speed up the fast component in subsequent heavy/sever intensity exercise to reach a higher VO2  sooner and slow down the Slow component (the VO2 rate curve follows the yellow dashed line). This combination effectively reduces the “Oxygen debt.” You are therefore able to utilise a greater proportion of Aerobic energy, sparing anaerobic energy for later in race and reduced production of fatiguing metabolites and improve race performance.

From Andrew Hamilton "Sports Performance Bulletin"

To summarise the Warm Up needs to be specific to the event, weather conditions, current fitness, the circumstances of the actual event. A warmup in the Heavy to Severe intensity domain (60 - 80%Vo@max) lasting between 6 and 10 min with a passive recovery before the event of between 5 and 15 min "primes" the Aerobic system while allowing the recovery of the Alactic system without significant muscle temperature drops. It may also be beneficial to include some short strides above race pace to remind the neurological system to wake up. More is not better however, as there is the danger of drawing down your Alactic system and/or adding unnecessary fatigue before the race. Because of all these considerations it is down to the individual athlete to try what works for them at their intended event. 

It is important to note that routine, appropriate endurance training changes the shape of the curve over time. However this can't be achieved overnight or even within one season but takes many years of activity. So using a effective warmup is an efficient way to optimise your race performance.

References:

(i) Oxygen uptake kinetics as a determinant of sports performance 

(ii) Slowcoach Endurance Webpage