I usually have a couple of clients get frustrated in the fall and winter that their Heart Rate does not go up as high as they think it SHOULD.
I put the word SHOULD in capitals because that is always a red-flag in training (and life) when we assume things should be a certain way. It is always worth stepping back and asking if there are reasons it SHOULD NOT be that way, or whether you need to be maxing out your heart rate every day, especially in the fall/winter when races are further away. Remember that most workouts have a range for power, heart rate or other metrics and being at the top of the range does not earn bonus points, large trophies or strava kudos.
*check out the book ‘the myth of stress’ for more on this
A first consideration when Heart Rate is low relative to the expected is that a low heart rate with poor performance is to be taken seriously and countered with some very intensity exercise (ie. under 100 bpm) and/or complete time off with only relaxing yoga and other rejuvenating activities. This expected value is usually based on one or both of how we are feeling (RPE) or power (Watts). If you are feeling pretty good for a cold ride outside (you won’t feel as amped as sunny day) and/or your power is in the expected range then a low heart rate is not an issue. Care should be taken not to drive the heart rate higher in the range and risk riding too hard, even pushing watts out of the endurance range. This can ironically result in heart rate depression due to overtraining.
If you are not over-training or tired than you are set to learn more about training in cold weather and troubleshooting some more. You are likely familiar with Heart Rate going higher during warm/hot weather. You may also have seen a higher Heart Rate while at altitude. So environment can make your heart have to work harder, or make the heart rate HIGHER. For hot environments this is due to the shifting of blood to vessels at the skin’s surface to cool core temp. This means more blood to more vessels and so more work for the heart to maintain output to working muscles.
*these situations that challenge the heart can be great training stimuli and should be sought out to increase your fitness.
If we consider this shifting of blood to surface and increase in Heart rate and work for the heart in hot conditions than assuming a decrease in work for the heart and more blood in the vessels in cold weather is a pretty safe assumption. So our Heart Rate will be lower when it is cold.
There are a few other considerations for cold weather heart rate beyond the physiological reasons above. We may wear more clothes, pedal at lower RPM and/or just go slower in these situations so heart rate may just be lower because you aren’t putting out the same workload or changing your cadence and, in both cases, decreasing the work the heart has to do.
A good way to test and overcome these last few reasons for lower HR is to do a periodic sprint or high cadence drill (like a spinup) to get some more activation and ‘wake body up’. You may even find this helps you stay warmer, and perhaps increase the cooling needs to the heart and normalize your heart rate to your expected range.