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Post by godzulla on Feb 11, 2010 19:50:50 GMT -5
Hope this isn't a boring topic. But, I've been riding for about 25 yrs and it seems like people have used L.T. and A.T. interchangably. From a Conconi Test my A.T. for example would be 230W, but from an 8 min effort it would be 270 Watts and from a blood sample maybe 240.. It seems over the years I have heard those terms used in place of one another. I would think my lower number would be my L.T. and not my A.T. What's the scoop you pysiology guru's?  I always thought that L.T. was the point of deflection where your body is switching from an aerobic state to anaerobic. I thought A.T. was something you could hold for 10 - 20 min??? Very confused? |
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Post by Josh Whitmore on Feb 12, 2010 12:46:20 GMT -5
It is common to use LT and AT interchangeably. They should describe roughly the same process but in different ways. LT is the point in which the body can no longer metabolize lactate in the blood (remove it) and it starts to build. AT is the point in which the body's ability to keep up with oxygen demands is surpassed and muscles move to an Anaerobic process to produce energy. Both of these things are describing different aspects of the same process.
Doing a blood lactate test - basically a ramp-up test where wattage is increased in increments every min till failure while taking blood samples - is a very accurate way to measure where this "threshold" occurs. It is also the most expensive to test.
Another way to test threshold would be to do the same ramp test or "conconi" test and track heart rate and respiration. If you graph these numbers, you will see an abrupt turn in the graph where the HR and Respirations suddenly go exponential instead of linear. This turning point is usually a good indicator of what your wattage at threshold is. This still requires a fairly sophisticated lab test to complete.
More common these days is to measure what has been deemed "functional threshold power" as developed by Coggins. This method is very doable by anyone with a power meter. It is basically a time trial test. The gold standard of this would be your average power in a 60min or roughly 40k time trial under perfect conditions and motivation. It is extremely difficult to achieve your true max for an hour, even for seasoned pros, so some other substitutes are also usable:
1. 30min all out Time Trial in training (not an event) = 100% of average power. The only time this does not work is if the individual is hyper motivated and absolutely crushes themselves - which rarely happens in training.
2. 20 min all out time trail - subtract %5 from average power
3. 2x8min all out time trials with 5min rest between each. Take average of both 8mins and subtract %10
For the numbers you give, they all seem pretty similar. Keep in mind that your threshold power will change throughout the year as your fitness changes, but it will also change from day to day depending on training fatigue, rest, temperature, motivation, etc. So, your 230-240w from your conconi test and blood samples are close enough to be accurate. The 270w from an 8min test is about the same. 270-%10 = 240w
Of course in order to compare your threshold wattage to someone else, you need to account for weight, watts per kilogram. So if you weighed 165lbs or 75kg, you would be at 240/75=3.2 watts per kg. Just for comparison, George Hincapie comes in at 6.2 or more watts/kg, That's 165lbs and 470w at threshold!
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Post by godzulla on Feb 12, 2010 13:50:26 GMT -5
great way to explain all that. It makes more sense now. All the numbers jive. Although, occasionally, I creep over to this site (http://americanroadcycling.org/TheBook/PowerToWeightCalculator.aspx) and compare my strength to weight ratio. It is quite depressing. My friends coach switched him from some zone chart to the Coggins zones to sync with training peaks. That is how all this talk started. He is having a hard time now completing his workouts on the Coggins zones though.
BTW I just bought a book called Faster , Better, Stronger by Eric Heiden,Max Testa. Great book so far. Amazon $7
Good read
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I always thought that L.T. was the point of deflection where your body is switching from an aerobic state to anaerobic. I thought A.T. was something you could hold for 10 - 20 min??? 
