I have a question on this topic:  How much do you think a persons goal would affect whether they use power, virtual power, or HR?

If ones goal was to maximize results in a time trial, I could see being more interested in building power.  However, if the goal is more endurance related (such as in a mid-distance or longer triathlon), I'd think that HR would be the measurement of choice to ensure staying in an aerobic zone (except for those cases where you might intentionally want to go above that).

So when taking HR drift into account, my concern would be that a longer interval designed to push back lactate threshold would end up getting well into the anaerobic zone for the sake of maintaining power, which would start to defeat the purpose of the workout.

Just curious if there is something about power training that I may be missing, and that perhaps my concern is unfounded.

Thanks!

Heart rate is a useful metric mostly in terms of recovery. A responsive heart rate, one that quickly reaches LTHR during LT intervals, for instance, and then promptly returns to a pre-interval HR indicates an adequate level of recovery while one that is slight retarded - maybe 5-10 bpm - during the work interval and then recedes slowly during the rest interval  is a good indicator of fatigue. A consistently lower-than-LTHR heart rate during said LT intervals can lend insight into a rider's ability to recover from previous days' workouts in that further recovery - perhaps an additional day - will bring the HR back within its usual bounds. But, pushing forward at this lower HR can potentially set a rider up for eventual overtraining if carried too far. In a case like this, a rider can use HR to recognize continued fatigue and adjust his training schedule (or more specifically, recovery schedule) in order to reap a better return on the workouts by performing them in a more recovered state.

On the other side of this coin, a rider might interpret this lower-than-usual HR as an immediate need for further recovery and skip what could prove to be a breakthrough, or at the very least, valuable workout and reduce the workload (or skip the workout altogether) when recovery wasn't necessary and the further training stimulus could have brought with it a new level of post-recovery performance. Remember, we achieve new heights by breaking old boundaries, and pushing through fatigue is often one of those boundaries. Just because you're tired and your HR is a little low doesn't always mean you won't have a great workout in terms of meeting your workout requirements, i.e. power output/duration/repetition.

In the case of this low HR, power would have shown a rider that his capabilities were being pushed but not completely overwhelmed assuming he could hit his targeted power numbers. Had he been shooting for a targe HR, this same workout would have been incredibly hard because his level of fatigue would have required suprathreshold efforts to elevate his HR to only threshold levels, assuming he could reach them at all - the ultimate in HR-training frustration. So HR would have expressed fatigue, but power would have shown that this level of fatigue wasn't so high that it would prevent a productive workout.

HR alone shows how hard our bodies are working but power shows how much work we're doing. Couple them and we can see how much work even somewhat fatigued bodies are capable of and allow us to achieve a very high level of training stimulus, one that is very likely higher than what we're accustomed to when using HR as the defining metric. This greater stimulus will lead to higher performance capacity following adequate recovery.

With this in mind, your goal should be to maximize training stiumlus in order to maximize performance capability, all this regardless of the type of event you're training for. Being faster for a 40k TT means that you'll be faster for 112-mile bike leg of an IM, plain and simple. So why not make the most out of your training sessions by using all available metrics, i.e. HR, power, and RPE?

Finally, I think you might have the idea of cardiac drift backwards. As long intervals and workouts progress, HR climbs for the same level of output due to fatigue and/or dehydration. So in your example you would actually start to work at subthreshold output levels because your HR would be climbing due to fatigue/dehydration, you'd consequently reduce your effort to bring your HR back down to LTHR, and you'd then be training at a lower than targeted work level and potentially miss some/much of your workout's intended stress.

So in response to your question, power would tell you that you're too tired to hold LT power during that day's workout and steer you toward modifying (steady state, sweet spot) or skipping your workout whereas HR alone could force you into overdoing the intervals by putting out suprathreshold wattage in an effort to achieve threshold HR with a fatigued body.

-Chad T

"Just because I say it doesn't make it so - be a skeptic."

Thanks for the response - it looks like it probably took you a while to type that all out, and I appreciate it.

Coming from a running background, I have it ingrained in my head that a base-building period must first occur, and that base building period is comprised of low intensity activity for some period of time.  During this base building phase, one of the things the body learns is how to metabolize fat more efficiently as a  fuel, as opposed to glycogen - and HR is the way to make sure that is happening (ie, the lower the HR, the higher % of fuel comes from fat).  So my question was coming from that point of view - if I'm relatively new to cycling (< 2k miles) and wanting to establish a base for this particular activity, I was thinking I'd need to keep my HR within a certain zone to stay aerobic.  Then, during interval workouts, the idea is to push just enough to elicit benefit, but not so much as to hamper recovery by so much that significant workout time is missed - and again HR is usually used to measure that.  For what it's worth, I generally follow the Jack Daniels approach to run training, and he can be very specific with HR zones.  However, it is possible that I've misinterpreted the importance of those ranges - treating them more as rules as opposed to 'guidelines'.  That is where my concern about HR drift came in - that a higher-than-intended HR may mean pushing beyond what is necessary to get the desired benefit.

So I guess my followup question is just clarifcation on whether what you've described above is applicable for both base building and interval-type training, or just interval-type?  Or does base building not really exist in the cycling world?

Thanks again!

After digesting what you posted above, I think I have a clearer picture of things.  It seems like power on a bike is very similar to pace in running - if I start off at 5k race pace, I know I won't be able to hold that for a full marathon, even though my instantaneous HR doesn't indicate that due to lag.  In the same sense, power can tell me a similar story on the bike.

And after rereading my initial inquiry, I realized that in my attempts to keep things brief, I left a lot of things out regarding my specific concerns.

Thanks a bunch for helping to clarify where power vs HR fit into the whole equation of training!

First off, you're very welcome. In response to the follow-up questions, base building is integral to cycling (any endurance sport will benefit from base training, really) for a number of reasons, e.g. metabolic shifts in fuel preference (sugar vs fat), physiological adaptations at the cellular level  (increased mitochondrial proliferation/density & improved enzyme activity), improvements in fuel delivery (cardiac adaptation, increased capillarization), improvements at the muscular level (fiber type adaptation, connective tissue strengthening), and very simply time in the saddle which offers opportunities to work on form, toughen up the ol' undercarriage, and learn how to ride relaxed and comfortably to name just a few of the adaptations to base-work.

What many new riders might not realize is that nearly all of these adaptations can be achieved through intensity as well. So in a related post, when I talked about building a base through VO2max intervals, just not as wide a base as LSD (long, slow distance) might afford, I was referring to intervals as a time-constrained substitute for long, steady base-intensity rides.

With all this in mind, recognize that there is an associated HR with every power level and its associated adaptations & benefits. Where the problem lies with training exclusively by HR is in your heart rate's sensitivity to numerous factors, e.g. dehydration, poor and/or reduced sleep, training load, and the stress pyramid - physical, mental, & emotional - to name the most obvious influences on HR. Power, however, is a more stable metric in that you either have it or you don't, you can hit your numbers or you can't.

For example, I've found that most riders remain aerobic up to about 70% of threshold power, i.e. 70%FT. So imagine you're tired, your aerobic ceiling for HR has been established at 140bpm, your aerobic power ceiling is 180 watts (nevermind the fact that changes in fitness will alter both numbers) and you have a 3-hour, aerobic endurance ride scheduled. Do you get out there and push until your HR is close to 140bpm even though it feels exceptionally difficult and you're nearly convinced it's too much exertion for an aerobic ride? Or, do you look at your power meter and see that you're comfortably meeting your wattage requirement but at a lower than usual HR indicating that you're tired but capable of an easy ride if you ditch the HR concern and ease off the gas a bit?

Finally, HR is very subjective from rider to rider and the "220 minus your age" standard is downright dangerous in terms of establishing training zones. Do many people fit that equation's recommendations, sure, but far too many riders fall well outside of its prescribed bounds for it to be universally, or even widely, useful. Add to that how HR changes with fitness and the HR waters get really muddy.

Nutshell: HR is a very subjective metric, power is king.

-Chad T