Previously, we discussed the various heart rate “zones” as a way of categorizing and monitoring your training efforts. As you start to tune in to the beat of your heart during training, you may find that your heart rate does not always correlate with what you would anticipate at a given running pace.. As you start to notice trends and variations overtime, HR tracking can sometimes leave you with more questions. Let’s talk about some of the limitations of heart rate monitoring, and what may be factoring into the variation in your heart rate numbers.
Limitations of Heart Rate Training
An interesting research study monitored recreational athletes during a marathon race, looking at theirVO2max, HR, anaerobic threshold, and gas exchange. For these athletes it was found that while heart rate leveled off in the later stages of the race, (between 88 to 91% of HR max). However, the speed they were able to sustain, and the percentage of vo2max they were able to work at, declined significantly. This indicates that although heart rate is stable, it is not accurately reflecting the body’s decreased ability to clear waste products. The heart rate may be at a stable level, while performance and ventilatory function are declining. Additionally, it is not uncommon for heart rate to decrease over the course of a long race. Thus, when racing a marathon, pacing based on heart rate may not be ideal.
Although heart rate training is a useful tool when training, during a race, it may be better to go by feel and rate of perceived exertion, rather than relying on HR as your sole metric for performance feedback.These findings should be interpreted with caution, as all the subjects in this study were male.
Why is my Heart Rate so High?
After a prolonged break in training, it may be difficult for you to keep your heart rate in zone one or zone two on easier efforts. It is normal for your heart rate to be more elevated on lighter efforts when your aerobic conditioning is low. This is why it is important to build volume (easy miles) before intensity (workouts) when returning to activity. When you are already working harder than usual on easy runs, it does not make sense to add in harder intensity efforts until your heart, lunge, muscles, tendons, ect have had the appropriate time to re-adjust and adapt to the training.
Resting Heart Rate
In addition to monitoring your heart rate during runs and training sessions, we can also monitor trends over time in our resting heart rate. If you are taking your resting heart rate manually, it is best to do so before getting out of bed in the morning. In general, a low resting heart rate, with a greater heart rate variability, is indicative of elevated cardiovascular fitness. (Heart rate variability means there is a bigger difference between your resting heart rate and heart rate max). This monitoring can give you insight over time into your fitness level, and how recovered you are.
Other Factors Affecting Heart Rate
When your heart rate is elevated more than seems appropriate for a given pace or intensity level, it is important to keep in mind other factors that impact heart rate. These factors include, but are not limited to:
Temperature. As discussed in this post, our cardiovascular system works harder to cool us down in warm conditions.
Illness. When your body is working extra hard to fight off infection, heart rate can be elevated.
Sleep/Recovery Status. Heart rate can clue you in to how rested you are. Heart rate is elevated when stress is high, and when sleep is insufficient
Caffeine. Did you drink coffee or have a caffeinated gel before your run? This type of stimulant can certainly cause a HR spike.
Body Position. Heart rate will be lower in a resting position i.e. laying down, compared to sitting or standing. (This is why it is best to record your resting heart rate before gettng out of bed)
Body Size. Those with a high BMI often have a higher resting heart rate.
Smoking. This should be an obvious one. Smoking negatively impacts the health of your blood vessels, and entire cardiovascular system, resulting in an elevated resting HR
Disease. Conditions such as diabetes, cardiovascular disease, and high cholesterol can elevate HR.
Medications. Certain heart medications, such as beta blockers, can artificially lower heart rate, while certain thyroid medications can cause an increase.
No one metric is superior to others when it comes to monitoring training workload. A combination of tools should be used. I would argue that the rate of perceived exertion is one of the most highly valuable indicators of effort, as it entails tuning into your body and how you are feeling in that moment. Other tools such as blood lactate testing, heart rate monitoring, and pace monitoring can work together to inform your training and to help you develop a sense of appropriate effort levels with both easy and hard running days. Whether you are in the thick of training, currently sidelined from training, or working your way back after injury, I am here to help you along the way. At Zenith, we have the knowledge and skills to take you beyond your basic return to run program and can provide you with training guidance unique to you.
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