Lactate Threshold Workout with Power Analysis (Kings Mtn)

2012-02-20 • SEND FEEDBACK •
Related: heart rate, training

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Disclaimer: I am not a cycling coach. What I share here is my own approach to training, presented in a way that I hope will be useful for readers looking for an approachable discussion.

This workout example is an Lactate Threshold workout, defined in TRPM as 91-105% of FTP (functional power threshold).

My FTP according to the TRPM test protocol is 350 watts (perhaps a bit lower at 330 in the winter), therefore a lactate threshold workout for me should be held in the range of 300 - 346 watts (assuming FTP of 330 watts).

Warmup and metrics

Prior to this effort, I rode for 66 minutes at 226 watts, a good solid warmup.

Metrics for the climb graphed below:

Duration: 26:28
Watts: 319.7
Kilojoules: 507
BPM: 150
Distance: 4.17 miles
Ascent: 1531 feet
Speed: 9.44 mph
Temp: 52° F

Workout goal

Play with the intensity such that it oscillates around a sustainable level which should average around where my lactate threshold is (partly by feel of how the legs respond). The pace goal was such that I should be able to maintain this intensity for an hour (regrettably there are no hills anywhere near that high short of an hour’s drive away).

Analysis

The SRM power meter is a great help on any workout where the goal is a consistent effort; it keeps me honest and motivated, with constant biofeedback— not too hard and not too easy for the goal.

While such a workout can be done without a power meter, one is blind to the actual effort over the course of the climb without a power meter whose output can be graphed. The graph below shows exactly what happened— power was consistent, but heart rate rose steadily. In short the heartbeats/watt ratio rose steadily.

Which raises the question: can fitness improvements be made such that the average heart rate does not continue to rise in this way? At the 5-minute mark, heart rate is about ~145, but by the 20 minute mark, heart rate has risen to ~155. Yet power is consistent. This same pattern of heart rate rise is seen on an Old La Honda maximal effort.

Perhaps there is another explanation, but temperature cannot be it, because it was quite cool and became colder with the ascent. Nor can heart rate drift (dehydration) explain it, because 26 minutes is too short a time period for such a large change.

Another possible explanation is depletion of certain energy systems, or adaptation by the body to the power requirements, changes which demand more oxygen as the ride goes on (perhaps for lactate metabolism?), and thus cause the heart rate to rise. This is speculation, but I deem this idea as being most probable.

If the heart rate rise is a reaction to the effort so far (accumulation of waste products, e.g., lactate), perhaps it is fitness itself which can be improved with more such workouts. It would also be interesting to pursue this effort on a climb 1.5X to 2X longer, to determine a steady-state reading— would the heart rate level off, or would it continue to rise towards my max of 171?

The low heart rate at the start is due to a brief stop prior to the ascent.

Click for a larger graph. Red is heart rate, green is power.

Lactate threshold workout graph with power, heart rate, elevation
Goal of 320 watts consistent power

I repeated the same workout the next day, but aimed for a much lower active recovery/endurance pace. Around the 17 minute mark, there is a distinct rise of 3-4 beats per minute after a brief harder effort, even though power stays consistent.

Endurance workout climb with power, heart rate, elevation
Goal of 245 watts consistent power