by Robh » Tue Feb 12, 2008 2:14 pm
[quote="huw williams"]Makes perfect sense - even in a 1 hour session on the power tap I can plot a significant 'drift' in HR - the higher the intensity and longer the ride, the greater the drift
It also explains this from PVT - "the first 4 hours seemed so slow that I felt like I'd just been down to the shops, but the last 4 hours at the same pace were incredibly tough."
Slightly simplistically, this is why power training is so much more effective - if you stick to a target HR your power drifts off so you're not training as effectively towards the end of a session - if you stick to a target power value - you'r heart rate will begin to increase over time and the perceived effort will creep up, making the ride progressively harder. After a 5 hour 'endurance' ride a couple of weeks ago I was chewing the bar tape struggling so hard to hold a measly 200w which earlier in the ride I was struggling to stay below
I'd love to see an average power trace for a 12hour TT from one of the really good exponents like Rich V
I've looked @ preiouvs 4hr rides from last year and my heart rate & power in the first half of the ride compared to the 2nd half of the ride was within +/-2 bpm/Watts. The power output for these rides were 205W AV 230NP. I would say these rides were steady state for me. Huw, Your body is tryin gto tell you someting with the drift. I posted this text here earlier from another forum which answres Tok's take on hear rate drift :-
Love his description of Heart Rate being like training with an old friend...I feel the same way. The difference is, I like training with my old friends.
I know I am preaching to the converted, but perhaps your cycling mate will be interested to hear another opinion. Juerg has already written hundreds of pages about using HR and wattage in place of either alone.I will just focus on one part of your friend's comment, the heart rate drift.
So the athlete uses his wattage meter to do a "steady state" ride, and then notices (if he looks at his HR in addition to his wattage), that after some time, his heart rate "drifts" to a new position. Now he makes a choice...keep riding at the same wattage, believing he is still riding at "steady state", or take the information his body is giving him that something has changed.
It may be he is now warmed up, and the arterioles in his leg muscles have dilated, requiring a faster heart rate to supply enough blood to fill the bigger pool of blood being drawn into his legs.
It may be he is producing more lactate, by the process of glycolysis, and his body is trying to distribute it to non-working muscles, or to slow twitch fibers that can better utilize it as a fuel.
It may be that his respiratory system has fatigued, and he is now requiring more breaths to eliminate the rising level of CO2 in his body which resulted from the increase in glycolytic activity.
In any case, his body is certainly no longer experiencing a "steady state" workout. This is not to say, he won;t get benefit form the session...he just won't know which part of his system he worked with to get the benefits he needs.
He is certainly correct in assuming HR monitors are holding amateur athletes back from improving their fitness, especially if they do not understand how they can be used to give very accurate feedback of the bodies current cardiovascular situation, which does change with temperature, effort, nutrition etc.
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