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The Forgotten Role of Heart Rate in Athlete Load Monitoring

Heart rate monitoring has widely fallen out of favour as tracking technologies have gained attention in sports science. This post delves into the benefits of incorporating heart rate technology and why this benefits athlete load monitoring.


This post is a follow-up from a recent webinar I joined by JOHAN Sports titled 'Hard Work needs Heart Rate'. I joined Niels van der Linden, Tjerk Bijlsma, and David van der Meijde to discuss the theoretical, technical, and practical aspects of integrating heart rate data to monitor team sport athletes. Is heart rate data still relevant? Are we missing crucial insights into athlete performance by neglecting heart rate monitoring?


You can watch the webinar back via the video further below from the Global Performance Insights YouTube channel. We had such great engagement from the attendees that we wanted to follow up with a post to discuss some of the questions and address those we did not get to on the day.



Training Theory and Load Monitoring


In my presentation for the webinar (below), I presented the theoretical basis of training load. While external load, so commonly captured nowadays by player tracking technologies, represents the work done, the internal load represents the physiological cost to carry out the work.


Such internal load can be measured subjectively via Rating of Perceived Exertion (RPE) and objectively with heart rate. Combining internal load measures with external load can reveal a holistic picture of an athlete's health and performance, by tracking their fitness-fatigue status.



During the webinar , I presented examples to illustrate how heart rate data can serve as an ongoing fitness test, particularly when combined with external load. We also discussed the appeal of submaximal fitness tests (SMFT), which can integrate seamlessly into training and offer valuable insights into an athlete's status. More on SMFT can be found in this post.



Usability and Compliance Challenges


Of course, it would be remiss not to address the most common concerns with heart rate monitoring: the practicalities and compliance. Heart rate belts can be awkward, cumbersome, and often face compliance issues with athletes, as well as technical issues with data dropout.


As we discussed in the webinar, equipment reliability, player compliance, and the fact that heart rate can be influenced by external factors such as hydration, caffeine, sleep, stress, and environmental conditions are potential downsides. Conversley, you can argue its for the influence of these factors that heart rate should be monitored, as these influences are not represented via external load measures.


I'll admit I've worked in environments both where we did, and did not use heart rate belts. In certain settings at that time, we felt these practicality challenges were too great. Yet, it is important to revisit these practicalities and question whether the insights gained from heart rate data justify overcoming these hurdles.


The team from JOHAN detailed how their technology solves for a number of the technical challenges with heart rate data collection, including its integration with GPS in a single device. Niels added that ensuring accurate heart rate data collection can be as simple as establishing protocols like dampening the heart rate belts/vests prior to each session.



Practical Implementation of Heart Rate Data Collection


In the Q&A portion of the webinar, there were numerous questions around the implementation of heart rate in the applied setting. For example, one participant asked whether it is recommended to monitor heart rate every session or pick specific sessions where the benefit is clear (i.e. sessions with a SMFT). As so often is the case, the answer is "it depends" and I've been involved in environments that have taken both approaches as I detailed in the video.


We were asked about the specifics of what zones and TRIMP (Training Impulse) formula to use. As I discussed (~24:06), there are many options available of which there is not necessarily a "correct" answer, much like we've previously discussed with velocity, acceleration, and deceleration zones.


One recent open-access systematic review by Gardner et al., (2023) in Technologies identified ten papers that studied TRIMP measured via wearable technologies with collegiate and/or professional soccer players. They identified and discussed the following TRIMP methodologies: Edward's, Bannister's, Individualized, Lucia, and modified TRIMP (also known as Stagno's TRIMP). Access that review here to read more.


Along with David van der Meijde in the panel discussion, we emphasised the importance of comparing heart rate data trends over multiple sessions and the individual variability among athletes. Heart rate responses should generally be compared within an athlete rather than across different athletes.



Population Specific Questions


We were also asked population-specific questions. For instance, we discussed at what age one should start monitoring heart rate. I suggested that an educational approach could be taken with the younger athletes, around 13, 14 years old, just on occasion to expose them to the technology. It is most likely to be of most value once the athletes are in a full-time training programme with you, say from 16 years old. But I'd be interested to hear thoughts o this; what approach are those working in academies currently taking?


We were also asked about heart rate monitoring with female athletes. For me, the theoretical basis of training remains the same regardless of sex. Internal load is just as much of interest in female athletes, and combining it in a holistic load monitoring programme with external load and training response measures is valuable. Yet, as we summarised in a recent narrative review on monitoring readiness in female footballers, our current practices are based heavily on research conducted in male athletes and more female-specific research is necessary.


One consideration with female athletes is the impact of the menstrual cycle on heart rate. Resting heart rate can be significantly higher in different phases, in this study for example specifically in both ovulatory and luteal phases (Moran et al., 2000). This reaffirms the importance of having different data streams integrated so that, in this case, heart rate data can be assessed alongside menstrual cycle tracking.


Niels from JOHAN also mentioned they provide female-specific vests with their system. This is an interesting area of developing in sports apparel and technology, and I'm interested to see how such items develop to be more suitable for the female athlete. For further reading on this, read the 2022 invited article on 'Ten questions in sports engineering: technology in elite women's football' led by Kat Okholm Kryger.



Unanswered Questions on Heart Rate


Further below I have answered further questions posed by the attendees that we did not get chance to discuss on the day. If you have any further questions or comments, please do not hesitate to get in touch!


What is the influence of cardiac drift on the interpretation of HR?

For context, cardiovascular (CV) drift is a phenomenon in which CV responses undergo a time-dependent change ("drift") after approximately 10 minutes of prolonged moderate-intensity exercise in a neutral or warm environment. It is characterised by a progressive decline in stroke volume and arterial pressures with a increase in heart rate in parallel (Coyle and Gonzalez-Alonso, 2001).


While CV drift can occur in the absence of dehydration, it is certainly exacerbated by dehydration. So I would interpret heart rate alongside any hydration status measures collected (e.g., urine osmolality, body weight pre- and post-training). I would certainly apply greater focus and caution on such interpretation when working in hot environments. Again, I would combine internal and external training data to try to identify if such drift was occurring (i.e. an increasing heart rate without a corresponding increase in work completed).


What assessment do you propose to use as a "good" Heart Rate Recovery %? Do you use different levels of % according to the time that passed by i.e. 30sec, 60sec, 90sec, 120sec?

I prefer to compare athletes to themselves to interpret their outcome in the context of their individual dataset, as opposed to absolute reference values. As we discussed in the webinar, there can be wide individual variability in heart rate responses so with all of these measures I focus on within-athlete changes, as opposed to between-athlete differences.


Just to expand further on Heart Rate Recovery (HRR), it has been recommended in Tzlil Shushan's work on SMFT to use Heart Rate Exercise (HRex) rather than HRR. This is the heart rate during the final 30 or 60 seconds of the test, as opposed to after the test. From my own experience, this is also practically easier than trying to control athletes movements in the minute or so immediately after the test.


What are your thoughts on using Zone 2 training in football?

Martin Buchheit and colleagues recently published a paper entitled 'Aerobic Conditioning in Football: Is Zone 2 Training Outdated' on the Sports Performance and Science Reports site, available open access here. They argue that high-intensity interval training (HIIT) is a superior method of training professional footballers, owing to similar if not, enhanced physiological benefits compared to Zone 2, achieved in a more time-efficient manner and in greater alignment with the dynamic nature of football.


What about the reaction/load at a physiological level for players with a lot of fast fibre/explosive players, in comparison to those "long running - slow fibre" players?

In team sport environments, we work athletes who differ in their skeletal muscle fibre typology, and this has implications for their responses to training. Athletes with a fast typology can experience more pronounced fatigue and slower time to recover following high intensity exercise (Lievens et al., 2020).


In my opinion, such between-athlete differences reiterate the importance of 1. capturing physiological stress via heart rate and 2. focussing on comparing individual athletes to themselves rather than across the group.



Final Thoughts and Further Reading


While heart rate monitoring may pose some practical challenges, the potential insights it offers make it a valuable tool for sports scientists. We've arguably become distracted by the endless metrics captured by athlete tracking technologies but these do not tell the whole story. By combining heart rate data with measures of external load, sports scientists and coaches can develop a more holistic understanding of athlete training response, to aid in the planning, monitoring, and adjustment of training programmes for better performance outcomes.


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The sports technology company, JOHAN Sports logo, which is the word JOHAN in white text on navy blue background, except the O is in bright green.

This article is supported by JOHAN Sports. For more information about their technology, visit their website.

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