Endurance Performance variables

The main factors that determine level of performance in Endurance exercise are:

• VO2 max - your maximum ability to use oxygen when exercising. Or  perhaps more useful, your speed at VO2max. (v-Vo2max or sometimes called VDOT) 

•  Lactate Threshold - the first lactate "threshold" LT1 or VT1 (first Ventilatory threshold)

•  Exercise Economy- Metabolic and mechanical

• Oxygen uptake kinetics- How reactive your aerobic system is start of exercise and efficiency during continuous exercise

•  Critical Power or Critical Speed- (Similar intensity to the second Lactate Threshold  LT2 or Ventilatory Threshold VT2 

It is very unlikely that anyone can maximise all these factors at the same time. To improve one factor can cause one or more of the others to deteriorate. The aim of training is to try and optimise the factors to produce the best combination for the specific requirements and timing of the target event. 

 Why do we see training Zones talked about in training plans and sports watches and where do they come about and how to use them?

Schematic Lactate/Running Intensity Chart  

The above chart shows an idealised graph of the rise of Lactate sampled in the blood as the level of exercise intensity increases. The lactate levels follow typical pattern with a fairly steady lactate concentration at low intensity ( up the LT1); an progressive increase between LT1 and LT2 ; and a sudden increase after LT2. This is a reflection the operation of the changes in the use of the three energy systems described in earlier posts. For typical athletes the LT1 occurs at when La levels start to rise above 1  mmol/litre; and LT@2 when Lactate passes the 4 mmol/litres concentration. However this differs from individual to individual and moves with training status. 

In the literature Zone 1 is called Moderate Intensity; Zone 2 is Heavy intensity; and Zone 3 is Severe Intensity. This intensity distribution has been divided up into smaller chunks to aid training prescription. So we typically see 5 zone models with Zone 1 and 2 covering the Moderate Zone; Zone 3 and 4  the Heavy Zone; and Zone 5 the Severe Zone. So if you see some one referring to Zone 2 you need to be sure which model they are referring to.

These inflection points are therefore markers of changes in metabolic status and the bodies production and use of energy and are the basis of the "Three Zone" training model. 

I would point out here that Lactate has been the traditional scientists substance of interest for over 50 years from the study of why we experience fatigue during running over different durations and intensities. During early experiments, Lactate was found to appear in the blood as shown above and was assume to be the main cause of fatigue and so got a bad name. However it is now becoming clear that it is not the lactate that causes the fatigue but other metabolites that are produced at the same time such as the H+ ions that are produced as part of the same process (glycolysis). Partly because it was relatively easy to measure in the lab during exercise with simple prick of the finger or earlobe, it is continued to be used in exercise measurements in the lab. is in fact not a waste product but an important fuel which is used to produce more ATP in the muscle where it is produced or transported via the blood to other places in the body such as the heart, brain and liver to be used or converted back into glycogen to feed glycolysis again. However it continues to be the go to marker of our metabolic state during exercise.

Of course the majority of us recreational athletes don't have routine access to or wish to pay sums of money to undergo regular Lactate or Ventilatory testing in a lab so we rely on identifying these metabolic markers of LT1, LT2 and VO2max from actual performance in training and racing. 

*percentage of Power/Velocity @ VO2max
RPE Borg scale 1-10

Of the three markers, perhaps the most difficult to define by performance is  LT1. But there are various guides to define these as a percentage of either Power or Velocity at VO2max. The table give a typical range. Recently attempts to define LT1 has been produced which involves the use of Heart Rate Variability measurement using a smart phone App and a suitable Heart Rate monitor. (measuring something called DFA(alpha1). This calculates your heart rate when exercising at Aerobic threshold (equivalent to LT1 and can be done either on a treadmill or outside)

Critical Power or Critical Velocity can be calculated from maximum efforts over a suitable range of durations and plugging the numbers into a spreadsheet or software model. 

A surrogate for VO2max is similarly calculated as the best effort average power or Velocity of a 5min Time trial carried out with optimal pacing strategy.

Most sports watches use heart rate data from you training history to estimate Heart rate LT2 to set their boundaries of the training zones. Provided you are using a reliable chest strap based monitor you can use percentages of HR max to set values for all three of the markers.

The main problem with using pace and heart rate to set training zones for running is that these factors are greatly impacted by how hilly your runs are;  by the weather conditions (heat, cold and especially how windy); and daily variations in how you are feeling.

Hence the appearance of power being used in monitoring training and racing in running. The Stryd powermeter is a small footpod that attaches to your shoe laces and calculates your running power in real time while taking into account the rise and fall of the terrain and the effect of wind on every run. The associated App does all the background calculations and continually updates you Power/Duration curve to assist with training intensity and race pacing. The Stryd links to your Garmin or other sports watch to provide the real time information as you run.

Stryd Power Duration Curve

The software among other things continually updates your training zones to match your current fitness.

Stryd's 5 Zone system

A more traditional and established training system is the one developed by Jack Daniels back in 1998. He was involved in testing endurance athletes VO2max.  A problem with VO2 max values is they don't always correlate very well with actual race performance. Although you need a good VO2max to be a good endurance athlete,  it is not always the athlete with the highest value that wins the race. This can be related to differences in the two athletes LT2 or CP, or on how efficient  and economical we are in using the oxygen we take in. So Daniels and his associate Jimmy Gilbert, produced a set of tables which introduced the term VDOT as a surrogate to VO2max by taking into account actual performance at different race distance and in so doing, the efficiency/economy factor. So by either racing or doing a time trial over one or several race distances you can look up your VDOT in a set of tables (old school) or by inputting you results into an App. This then provides relative training paces for your different workout types. The draw backs are that the VDOT value will  differ depending over what distance you are doing the test, and the paces assume similar conditions from the test to training and racing in terms of hills and wind. In my opinion, the use of VDOT is much more reliable and applicable information than any of the VO2max estimates produced by the algorithm in you sports watch.

The values for LT1, LT2/CP and VO2max/VDOT are considered the three pillars of intensity training and allow you to set the training zones for which ever training method you decide to follow.

It is then just a case of determining your strengths and weakness; you target event/s, how much time you have available to train; and to draft out plan. The next step is to follow the plan as best as you can; adjust as you go; monitor training and test progress and review the plan towards target event.

The next post will examine why and how to Warm up for Endurance events.

Any Comments or questions just leave a comment or get in touch.