Thursday, January 13, 2011
I used to think I was cool because I was one of a few that used a power meter on my bike. Those days are gone and it now seems everyone has one. Those who have handed over the coin for one of the various models I'm sure quickly realized the benefits and hopefully improved there training once they understood what the numbers (Watts) were all about. Power is a wonderful thing, especially for an exercise physiologist who is addicted to data. Power is essentially energy measured in Watts so if you are putting out 60 watts you could run a standard 60W light bulb, push a little harder and you could possible run your new LED TV for a while!! Interestingly cycling power output is directly related to oxygen consumption. If you correlate the two during an incremental test you can predict oxygen consumption using power with ~96% accuracy. There is also a linear relationship between power and oxygen consumption. If you know the power you can hold for ~4mins you can predict your VO2max using the equation;
Peak Power Output (4min sustainable power) x 0.01141 + 0.435 = VO2max (L/min)
All you need to do then is multiple the VO2max (L/min) by 1000 to get it into milliliters then divide it by your body mass (kg) and you have a number pretty close to your true VO2max (mL/kg/body mass/minute). This value is probably the value you hear everyone talk about if they have had it tested in the lab. For comparison sake a sedentary individual usually has a value around 30-40. A good age group athlete will be 50-60, the guys/girls winning on the weekends will be 60-70 and an elite athlete will have a VO2max of probably >70. Genetic freaks like Cadel and Lance are up around 90. Although VO2max is a good predictor of performance it is not always correct. There are plenty of athletes that I have tested that score lower than me yet smash me on the road or track!!
OK.. Now back to power. Power is good because it is instantaneous unlike heart rate so when prescribing exercise intensities it is far more accurate and easier to use correctly. Anyone who uses programs like Training Peaks will know their highest held power over increments of time. It calculates it for you then allows you to compare your results with others, this is usually done using Watts/kg.body mass because it makes it all relative. Watts/kg also allows a good picture of possible performance for various athlete types. Absolute Watts is often a good predictor of Time trial performance on a flat course, however once gravity is involved W/kg becomes far more important. A good climber should probably be aiming to be able to hold close to >5.5W/kg body mass going up hill for an extended effort (20-30mins). Some of the data over the years from the Tour de'France has shown Lance in 2004 holding close to 6.97W/kg going up Alp de'Huez on a climb lasting close to 1 hour!! Interestingly for a few presentations Ive done I predicted Lance's VO2max using the equation I mentioned earlier. It went something like this;
If Lance is holding 6.97 watts/kg and he weighs 70kg he averaged 488W. Assuming Lance is holding about 80% of his peak power (which I've chosen from observation) then Lance's Peak 4min Power would have been about 610W. Now.. Using the equation (610x0.01141+0.435) we get a VO2max of 7.39L/min. Multiply that by 1000 and divide by his body mass we get 105mL/kg.body mass. As many possibilities for error this prediction has I try to use it to possibly show a superhuman performance
For a typical cyclist monitoring power data is probably the best and easiest way to track performance over a season or lifetime. Ive been striving now for about 2yrs to get my peak power above 400W. Slowly, (but not yet) i am getting closer to this goal. However, looking at it relatively I hit a mile stone leading up to this years Tour of Bright by finally reaching a power to weight ratio of a fraction over 6W/kg. Still by no means comparable to the worlds best but good enough to leave most of my riding buddies struggling to hold a wheel when the road goes up.
All in all power is becoming common place in cycling. If you want to brag about how high your power was at the coffee shop after the bunch ride then you've got to do your time at the front because sitting in will save you somewhere in the vicinity of ~30% when compared to the guys pushing the big numbers on the front!!