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Endurance Workout with Power Analysis

2012-02-03 • SEND FEEDBACK
Related: heart rate, tilt shift, training

Legal disclaimer: Since we are not doctors, never follow anything based on health-related or training topics on this or related sites without first consulting with your doctor or other trusted health professional.

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 Endurance workout, defined in TRPM as 56-75% 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 an endurance workout for me should be held in the range of 190 - 262 watts.

Excluding the ~20 minute warmup, I targeted 260 watts, using my SRM 7950 power meter to hold myself to the target, which mainly meant restricting my exertion most of the time, so as not to overtax myself for this long a workout; I wanted a consistent ~260 watts for the entire portions of the ride where that kind of power input was feasible.

There were two larger climbs (Kings Mtn and Tunitas Creek out of Woodside, CA) and one smaller climb (upper Alpine in Portola Valley) in this workout, with moderate flattish and rolling grades separating them, and of course the downhill sections from the summits.

Duration: 3:54
Watts: 221.7
Kilojoules: 3112 (about 3000 KCal)
BPM: 126
Distance: 63.78 miles
Ascent: 5633'
Speed: 16.3 mph
Temp: 56 - 68° F


In spite of leaving fully hydrated with 2 liters of water, I become dehydrated during this ~4 hour workout. Total riding weight (TRW) including water and calories when leaving was 205.6 pounds, but that had dropped to 196.8 pounds upon my return— and I was quite thirsty.

That’s a loss of 8.6 pounds. Since I drank 4.4 pounds (2 liters of water), that means that I perspired out 8+ pounds of water — a gallon (food and metabolic processes likely account for half a pound or so). That much water loss is worth noting, since most of the ride was around 60° F, quite cool.


Key sections in the 3:54 ride—

Kings Mtn (1580' ascent, 32 min): 258 watts @ 134 bpm (77% max HR)
Tunitas Creek (1735' ascent, 39 min): 262 watts @ 133 bpm (76% max HR)
Mixed stuff (end of ride, 58 min): 252 watts @ 137 bpm (78% max HR)
Average including warmup/cooldown: 221.7 watts @ 126 bpm (72% max HR)

Dehydration clearly played a role in raising heart rate for the last 1/3 of the ride, and it began to degrade my performance at the very end (I had to really concentrate to maintain my watts goal).

My power meter kept me within a few percent of the 260 watt endurance workout goal, making for a very high quality targeted workout. There is nothing I would change, except filling up my water bottle after descending Tunitas!


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

An endurance workout graph with power, heart rate, elevation
Goal of 250-260 watts consistent power (dips are downhill)

Kings Mtn

The data for Kings Mtn ascent. Gray area is elevation profile.

A power meter provides superb biofeedback: note the consistent heart rate, power and rate of ascent (straight line).

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

Kings Mtn Road ascent— targeting 260 watt endurance pace

Tunitas Creek

The data for Tunitas Creek ascent. Gray area is elevation profile.

About about 50% of the way up, the rate of ascent lessens; the grade slackens and so speed increases (lower line, magenta). The power meter kept me on track for wattage.

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

Tunitas Creek ascent — targeting 260 watt endurance pace

Last 68 minutes

Heart rate in the last hour is about 6 beats faster than the first 3/4 of the workout, even though power output is slightly lower; this is almost certainly heart rate drift due to dehydration. My feeling of thirst started in the last hour and became quite strong by the end.

Beware of a feeling of higher exertion (which was the case for me in the last 30 minutes); it might not be fatigue, but simply dehydration.

Once one is in the “hole” of dehydration, it’s too late to fix it during a sustained workout; drink enough fluid all along, being thirsty is a sign that it’s too late to recover hydration in any meaningful way (for that workout).

The issue I face is very few water sources, so I must ponder the hydration issue and perhaps take on water sooner than I’d like (e.g. at the Bike Hut), so that I have enough for later use.

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

Tunitas Creek ascent — targeting 260 watt endurance pace

Repeating the workout 2 days later

I took an active recovery day (Feb 3) on the day following the workout above (Feb 2), then repeated the first 3/4 of the workout on Feb 4.

My hunch on Feb was that I was 90% recovered from Feb 2, but not fully recovered, since my legs still felt slightly stiff. Nevertheless they felt good, and I resolved to target ~270 watts on the climbs instead of ~260 watts.

The results were very consistent; I was within one (1) watt on both climbs! Compared to the 2-days-prior endurance workout discussed above:

  • On the Kings Mtn climb, I increased wattage from 258 to 271 watts (+13 watts) and cut off 1:12 from the ascent time.
  • On the Tunitas Creek climb, I increased wattage from 262 to 272 watts (+10 watts) and cut off 1:07 from the ascent time.

It was on the return trip that I felt more fatigued than on the 2 day prior workout, so I cut out some extra distance and about an hour of riding, and ended up with 4370' of ascent, versus 5630. While I was able to hold good wattage to home, it was clear that my legs did not have the full get-up-and-go they had felt two days prior.

A couple of things are worth of consideration in future workouts—

  • My hunch about recovery was probably right— less than full recovery after a 4-hour endurance workout might not show up right away in wattage, but it is likely to influence endurance.
  • Increasing power just slightly might be significantly more stressful as an aerobic boundary is crossed.
  • Both of these might have been the case. Perhaps it would have been better to target the same wattage the 2nd time around, to ferret out the recovery issue.
  • The level of exertion on this workouts is a ripe target for improvement: given my Everest Challenge goal (6+ hours the first day with more climbing), it seems advisable to aim for a level of fitnesss that would allow a minimum of three (3) consecutive 4-hour endurance workouts (3 workouts in 3 days) with consistent results all 3 days.
  • Exploring the 260 - 300 watt range for endurance is a ripe area for investigation and training: can endurance power be raised towards the 300 watt level?
An endurance workout graph with power, heart rate, elevation
Goal of 270 watts consistent power (dips are downhill)


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