Speed, Power, Heart Rate and Fitness

One of the best measures of fitness change is your output-input ratio. That may sound quite technical but you use this a lot when talking about your car. You call it “miles per gallon” or “kilometers per liter.” That’s a nice way of measuring how economical your automobile is. In this case, high numbers are good and low numbers are bad. Your wallet likes it when mpg/kpl is a high number. Of course, “high” and “low” are relative terms. High or low compared to what? If your old car got 18 mpg and you buy a new one that gets 25 mpg you’re happy. But if the old one got 32 then 25 isn’t so great.

It’s the same for your fitness. For performance, one way of using output-input ratio is to express how fast you are going relative to how much effort it takes to go that fast. Output can be measured with speed using a GPS device or power using a power meter. Input can be measured with a heart rate monitor.

So, for example, in running if you average 10 miles per hour (6 minutes per mile) in a 5km race and your heart rate averaged 160 then your output-input ratio is 0.063 (10 ÷ 160 = 0.0625). If in a 40km time trial in a bike race your average power was 280 watts and your heart rate was 150 then your output-input ratio was 1.87 (280 ÷ 150 = 1.8667). In either case what you’d like to see happen in future races is that you run faster or your power goes up but there is little change in your heart rate. Aside from the faster times, that would be an indicator of increasing fitness.

But it doesn’t have to be a race to use O-I ratio. This can be done with any standard workout, but works best with steady, as opposed to highly variable, outputs. And it also works best with relatively long efforts due to the lag in heart rate change when output increases. With intervals, for example, it works best when the work interval is around 5 minutes or longer.

Let me describe how I’ve used the O-I ratio myself recently.

You may recall that on April 9 while at a camp in Spain I crashed on my bike and fractured my pelvis. I commented on this in an earlier post.  I was lucky in that the bone was not displaced so it just took some time for everything to heal. For the first 11 days I pretty much did nothing other than whine and moan so my wife would feel sorry for me. Then on April 20 I decided the pitty party was over and got back on my bike, albeit on a trainer in the garage. Basically, all I did was turn the pedals with no concern for output or input. This was for my head, not by body. On May 3 I started using my power meter and heart rate monitor again. It had been 23 days since the crash so a lot of fitness was lost.

The first order of business was to rebuild aerobic endurance, the most basic ability for endurance athletes. Beginning on May 3 I rode with as much time as I could manage at my aerobic threshold heart rate of 120-125 bpm. For the most part it was an hour a day, although some were as short as 15 minutes and others, more recently, up to 90 minutes. Every day I observed what happened to power at that HR range and recorded the daily output-input ratio. The accompanying chart illustrates the changes that happened to the ratio over a 17 day period.

 

On April 3, 6 days before the crash, I had done a 98-minute aerobic threshold (AeT) maintenance ride. My average power then was 175 watts with an average HR of 120 for an output-input ratio of 1.50. After 23 days of doing almost nothing (other than issuing proclamations to my wife-nurse) my first AeT O-I ratio was 0.68 (84w and 123 bpm) – a 55% decrease. Pathetic. It probably wasn’t all fitness loss, however, at least in the traditional sense. When there is an injury the muscles in that area of the body are inhibited from working normally. This is a protective measure. There is no doubt, however, that there was a lot of aerobic fitness lost in addition to the muscle inhibition.

During this period I rode every day doing the same AeT workout except for one (day #7 was a complete day of rest). Notice the steady climb in the ratio on the chart since my first AeT ride. This is an extreme example of fitness change given my situation. Someone who is in moderately good shape will see much less change over the course of several weeks as training ramps up, and there will likely be a large number of downturns due to fatigue and other confounding variables.

If you only measure input using a heart rate monitor and have no gauge of output then you are limited in how to determine changes in fitness other than by racing, which isn’t always an option. Races also don’t tell you much about specific intensities such as aerobic threshold. Of course, you could pay to have a VO2max test done every month. Or, lacking GPS or a power meter you could run on a track or ride on a velodrome. You could also do a workout on a measured section of road or hill at given heart rates comparing time with HR, but this certainly limits your training options. (Speed isn't a good measure of performance on a bike due to the exponentially increasing wind drag as speed increases linearly. This affects running to a lesser extent since the speeds are so much lower. Excessive, head- and tail-winds also affect both considerably.)

Having output-measuring devices gives you a lot of options for workout venues and, essentially, makes every workout a test of your fitness progress.

Comments

[Matt]

Coach Friel, when returning to fitness after injury/illness, would you always recommend focusing on getting the HR under control *before* worrying about things like cadence? Or is it better to get used to operating at the "right" cadence again, before targeting a particular HR/power range?

[Michael]

Thanks for the post on this topic, Joe. Is there a way to visualize and track this easily using either WKO or training peaks on the chalkboard to track ones fitness?

[Seiji Ishii]

Good words Joe. Glad you're OK. I tell everyone in my field that you open your mouth and I learn something.

[Joe Friel]

Michael--Have to do it manually, I'm afraid.

[Joe Friel]

Matt--Skill trumps everything. If technique is poor then "fitness" means little.

[Pieter]

Hi Joe,

mathematically it seems to me that you can do this more accurately. instead of dividing Watts by Heartrate.

In fact, at 0watts you do not have 0 heart rate, but e.g. at 90 bpm you have 120W. Adapt this numbers to your own situation. Then I would do the following : (Watts - 120W) / (BPM - 90). This would allow to compare not only level2 to level2 workouts, but also level3 and level4 workouts. I'm collecting some statistics on this myself (as it's not the first time you write about W/bpm), and it seems nicely fitting.

[Mike in Boulder]

If power meters were less expensive, I would own one. Therefore, i do use Flagstaff mountain and HR for gauge. I can avg. 170 HR the entire way up, and time plus perception plus gear selection plus wind gives me a 90% idea of my fitness. I do the Gateway ride, and I don't think a power meter will make me go faster. Sure, power meters make it more scientific, but seeing a number won't make me faster...will it?

[Chuck Nguyen]

Joe,
I have just started biking while recovering from shoulder recovery. My AeT heart rate is 135 bpm with a puny output power of 93 W. However, I could go on for more than an hour without any decoupling. Does this mean I won't see an improvement in power unless I increase either intensity or duration?
Thanks for a great blog.
Chuck

[Joe Friel]

Chuck Nguyen--At some point you will plateau, meaning fitness changes little if at all. At this point the best course of action is _usually_ to increase intensity.

[Joe Friel]

Mike--As mentioned, you can use a hill. The results just aren't quite as accurate.

[William]

Coach Friel: Love your blog. Very insightful. In charting this, is there any way to chart it to take account of the fact that I do rides of different durations? Sometimes my rides are an hour, sometimes 3 or more. I would assume my watts/HR ratio would be higher for shorter rides than longer rides. (Is this right?) But I would not assume it is a 1 to 1 ratio, such that my normalized watts/avg HR number on a 3 hour ride would not be one-third the ratio of a 1 hour ride. Is there any way to adjust the formula to take account of the duration changes? (I.e. could i calculate joules/per hour and then divide that number by avg HR or something?)

Many thanks.

[Anne Findlay]

cool. just today I was watching my HR at different cadences and same power. At a lower cadence (90), my heart rate was a bit lower than at 100 RPM (162 vs 166 respectively). But I felt it more in my legs so I think sustaining it over a longer period of time might be harder. 95 seemed to be a good balance, which is not a surprise since this is the cadence I have targetted for the past 5-6 years.

[Chuck Nguyen]

Is there a way to determine if I have reached a plateau by looking at HR vs. Power from a ride instead of testing repeatedly over time? Secondly, if I move on to Z3,4 or higher, should I expect to see an improvement in power at AeT? What is your take on the effectiveness of training at high intensity in boosting aerobic fitness (or more specifically, power at AeT heart rate)?

Before my surgery, I rode a lot above Z4 fartlek-like mainly because I live in a very hilly area. My Z2 would be at around 8 MPH, most of the time. Now on a trainer, I wonder if I am better off putting in a lot of time at AeT instead of doing intervals. The fun factor is about the same for both.

[Madeleine]

Hi Joe,

I am very glad to see your P:HR rising, and am also glad to see you draw attention to the way in which it can used in assessing recovery from injury. In addition to injury-induced muscular inhibition and general loss of fitness, I would throw out the possibility of acute anemia as a contributor to reduced P:HR. If your injury is severe enough to keep you off the bike for a while, it is possible that it was severe enough to cause some blood loss – e.g. into the soft tissues of the thigh and pelvis, where one can ‘hide’ significant amounts of bleeding. The heart beats faster to accommodate the lower level of oxygen-carrying-capacity of the blood at rest and with exertion.

On the input-output subject, though – don’t you think this ‘supply-and-demand’ relationship is between cadiac output (HR x stroke volume) and power, not HR and power? I’ve been trying to figure out why some people’s actual HR falls below their calculated HR zones, and it seems likely to me that their heart has a greater dynamic range of stroke volume than the average (genetics ? years of aerobic conditioning?). This is why I remain agnostic about using heart rate zones in training - and maybe that is what Pieter is writing about too, though I am not sure I understand his math.

Madeleine

[Ed Schaffer]

Joe, I asked this last time you posted on this topic. I see that you can only do this manually now but are you going to add this to TP or even WKO+? I'd really love it and it seems such a simple, relevant measure. Thanks!

[Daly]

Joe,

Thank you for the blog post. The numbers from my workouts will be more meaningful and I can measure the progress I'm making towards increasing my fitness.

[Joe Friel]

William--Best to compare apples with apples.

[mitch]

Joe,

This question is a bit off-topic, but I've been waiting to ask it. It's about what the input/output relationship seems to vary based on external factors, such as terrain and resistance. It's making it hard for me to figure out how to translate training from one setting (i.e. the trainer) to rolling terrain to climbing.

Like many, I find a significant gap in power output inside and on the road (CycleOps 300PT stationary with felt resistance pads). For a set of 5x7 min intervals with 2 min recovery, I routinely average 350-360 watts outside, with heart rate ramping up to about 166 by the end. It's extremely hard to match that inside. There's definitely a psychological element, but the interesting thing is my legs just kind of give out while I still have headroom with heart rate, etc., compared to the road.

I recently experienced the same thing in a long road race. Because of where I train, I don't regularly do much real climbing, and this had a 4 mile climb averaging about 6%. On the climb, the same perceived effort, heart rate and cadence that would produce about 320 watts on flatter terrain was only producing about 250 watts. Again, my legs seemed to be producing less power, which puzzled me since PE, HR, cadence etc. were the same.

This got me wondering whether the type of resistance affects power output. Specifically, gravity (climbing) resistance is completely constant and requires constant acceleration to overcome. Flatter road resistance and acceleration probably varies a lot more instantaneously due to terrain, surface, airflow, etc. (The trainer resistance is a lot more even, like gravity.) So could it be that my muscles have to work completely differently against these types of resistance as well, explaining the different input/output relationships I experience?

If this is the case, how would I incorporate this into training, both to deal more efficiently with both types of resistance and also to train consistently across the different environments?

[Joe Friel]

mitch--Good point. Terrain has a lot to do with training. I always specify the type of course i want my athletes to use for a given workout--down the grade of the hill. And in order to compare workouts with some degree of accuracy the workouts must have been done on similar terrain.

[Personal Training Leamington]

Congratulations on your recovery from your accident Joel. Keep Training hard!

[Rodrigo Loureiro]

Just discovered this post today !!!!
Great post, this protocol works great, as you mention, coming back from injury, but... I've used it this year to come back after months off the bike (and gaining 30 pounds), and came back from CTL about 6 to 40 (and shedding 20 pounds in the process).
Awesome post, and I'll try not to miss any posts in the future.

Thanks !!!!