September 15, 2020 at 3:39 am #8557
Usually I run in the morning before breakfast because this way I am getting fresh for the day. Sometimes I run in the afternoon. Comparing these workouts I can see that I consistently have higher heart rates during morning runs:
Morning: 8.8 km, ø pace 7:20 min/km, ø heart rate 135 bpm
Afternoon: 8.8 km, ø pace 6:53 min/km, ø heart rate 117 bpm
Although I run faster in the afternoon, I can maintain a higher pace while staying in zone 2 even with the peak heart rate. In the morning I have a few minutes in zone X. My zones are:
Zone 1 (72% – 80%) 115 bpm – 130 bpm
Zone 2 (81% – 89%) 131 bpm – 144 bpm
Is this a known, typical phenomenon? How does it affect my training success that most runs are in the morning with higher heart rates? Should I better run in the afternoon?
OliverSeptember 15, 2020 at 4:18 am #firstname.lastname@example.orgParticipant
I have noticed this happening to me too. The same speed in the evening could be 10-15 bpm lower than in the morning, which is quite frustrating.
I’ve put it down to being more hydrated in the evening as I have drunk water throughout the day, in effect helping my heart push blood around the body.
Would be interested to see if there are any others who have noticed this and what they have done to address the difference.
PaddySeptember 15, 2020 at 5:15 am #8560
Hydration (or the lack of it) might certainly have an effect. Although I drink half a litre of water before my morning runs that is likely not enough to compensate for the night’s loss of water.
OliverSeptember 15, 2020 at 9:55 am #8563
Great observation, and one that many athletes never notice. AM and PM HR variations by athletes is a very normal phenomenon. It usually manifests itself as lower HR in the AM and higher in the PM, but the opposite is true for many athletes. In fact, here is a list of other ways HR is influenced by external factors:
– For a given pace, HR will rise by about 1 beat per degree Fahrenheit between 70 and 95 degrees. The ramifications to zone training from this alone is staggering.
– HR is 5-10 beats lower indoors than outdoors for a given pace.
– HR will be 5 beats higher 2 hours after eating a large meal for a given pace
– Caffeine intake will dramatically impact HR for hours afterwords.
For veterans of the Forums (do we have veterans? we’ve only had the forums since February of this year!), this is a common theme from me: HR is cheap, easy, but unreliable relative to Pace and Power. HR is not an output. It is an indicator of how your body is adjusting to the environment, of which intensity is only one factor. Pace and Power are outcomes and outputs, which in most cases are more reliable than HR.
So, what is your solution? Continuing to use HR is fine, if you recognize the disadvantages and unique manifestations to you as an athlete. You’ll just have to adjust based on what you know about your AM and PM HR. In your case, you clearly have Pace data as well. Consider switching to Pace and using HR as a secondary measure.
DavidSeptember 15, 2020 at 12:02 pm #8566CharlesParticipant
Even during 80/20 the prescribed warmup my HR was often racing even at the slowest paces; it would eventually settle, but not until I was well into a workout.
Adding a relaxed mobilization warmup session for 5-10 minutes seems to be the cure for me. Just opening up the thoracic area and hip flexors and I can start workouts without the morning tightness and the elevated HR phenomena has disappeared.
I guess that aligns with the 80/20 philosophy – sometimes you have to slow down to get faster…September 17, 2020 at 8:34 am #8583
Thank you for your comprehensive answer. I also asked the same question in the FB group. Most runners who answered have the same experience as I have, some the opposite. I realise that heart rate depends on many factors and decided to invest in a Stryd power meter.
However, do you expect that I have the same power output and pace in the morning and in the afternoon considering the quite different heart rates? Let’s assume I run with the same power but am considerably slower in the morning than in the afternoon. Would it be better for the training effect to switch to afternoon training?
OliverSeptember 17, 2020 at 5:54 pm #8585
Oliver, in general, yes. I recommend relying on power independent of HR, except in extreme situation such as temperature and extended workout (2 hours run and 4 hours bike). Whether it’s AM or PM, whether HR says 140 or 150 for the same watts, use the reliable output that power provides over the sketchy feedback of HR.
It’s not a perfect analogy, but let me refer back to the automobile comparison from our document Intensity Guidelines for Running:
There are four ways to measure intensity: pace, heart rate, power, and perceived effort. The testing protocols for all four types are listed below. Each metric has different applications among the three triathlon disciplines. Each metric also has certain advantages and disadvantages. Power is an output, pace is an outcome, and heart rate is an indicator. Let’s use an automobile as an example. Horsepower (power) is the output, and represents actual work performed regardless of terrain, grade, or environmental factors. Your speedometer (pace) indicates the speed, or outcome. Your engine temperature (heart rate) represents how the car is responding to the output and environment. During a hilly ascent, the output (power) might be high, but the outcome (speed) might be low. On a hot day, the engine temperature (heart rate) might be very high even when stopped at a light with almost no output and zero outcome. For this reason, power is considered superior to pace, and pace superior to heart rate to measure intensity. There are some exceptions, such as hills, where HR can be superior to Pace to measure intensity. The recommended best-practice is to use Power or Pace as your primary measure, with HR as a secondary measure.
How often do you check your engine temperature when driving? Probably only when it exceeds a certain threshold. If you have Power, HR should be the same. Rely on Power and only use HR it it is flashing a warning sign, like Zone 3 HR when your Power says Zone 2.
Consider this test: run with power for 4 weeks, capture HR, but don’t actually look at HR for 4 weeks of running. Let yourself learn to trust power. After 4 weeks, analyze your AM and PM runs and find the Power:HR ratio for each run. I’ll bet you’ll find it won’t be more than about 5 beats off.
I understand this reluctance as athlete move from HR to Power. In the early 2000s, when cycling power meters were just coming out, there was this same hesitation. It was almost a grieving period as athletes “broke up” with HR and committed to Power. Now that running power meters are mainstream, I’m seeing the same hesitation with runners.
My mentor, Joe Friel, said it best to me when he said “introducing training with power was like getting glasses. I didn’t know I was blind until I got glasses.”
Any (ok, that’s hyperbole, almost any) athlete who trains with Power will quickly realize how powerful it is relative to Pace and HR, and you’ll soon let go of those other options.
DavidSeptember 18, 2020 at 3:34 am #8586
Is your “in general, yes” the answer to my first question: “Do you expect that I have the same power output and pace in the morning and in the afternoon considering the quite different heart rates?” or my second question: “Let’s assume I run with the same power but am considerably slower in the morning than in the afternoon. Would it be better for the training effect to switch to afternoon training?”
BTW, I am not reluctant at all. Otherwise I would not have bought an expensive Stryd. I just want to get the best possible benefit out of my workouts.
OliverSeptember 18, 2020 at 7:52 am #8587
Yes, I would expect power:pace ratio to be the same AM or PM, regardless of the difference in HR.
I can think of only one scenario where, for a given course and conditions, a set power output would equal different pace, and that is athlete weight. No other internal factors would change the power:pace ratio, only external factors like wind, temperature or terrain. Unless your weight is significantly different AM to PM, you won’t see a change in power:pace ratio.
Your raw power output might be lower AM vs PM for other reasons, but the power:pace ratio won’t change.
There are other reasons to prioritize workouts in the morning, independent of what we have discussed here. Morning workouts are more likely to get done, morning workouts trigger metabolic advantages for the remainder of the day, training late in the day can interfere with sleep… outside of HR or power:pace ratio considerations, AM training has more advantages over PM training.
You’re also really asking: where will I get the best training effect? AM or PM? In terms of direct fitness benefits, there is no difference. In terms of auxiliary advantages, morning is recommended.
Apologies for implying you were hesitant on switching to power, you’re clearly on -board and want to get the most out of it. What I observe with athletes is the reluctance to let go of heart rate, even after switching to power.
DavidSeptember 21, 2020 at 5:17 am #8610
Thanks again for your helpful answer. On Friday I received my Stryd, on Saturday I did the 3/6 lap test, on Sunday I rested, and today I did my first power zone run. In the hilly terrain where I live it is not easy to stay in one zone, as power changes instantaneously – but I guess I will get used to it 😉
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