Heart Rate Recovery: An Underutilized Metric for Identifying Fitness and Fatigue in Athletes

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Heart Rate Recovery: An Underutilized Metric for Identifying Fitness and Fatigue in Athletes

 

Evaluating athlete preparedness for competition demands, and understanding how prescribed training affects fitness and fatigue parameters, is of utmost importance for applied sport professionals. Routinely assessing heart rate recovery can provide pragmatic, cost-effective insights for these evaluations.

What is Heart Rate Recovery?

Heart-rate recovery (HRR) can be defined as the rate at which heart rate declines after the cessation of physical exercise [1]. HRR can be calculated over different time frames, classically between 30 seconds and 3 minutes post-exercise, by subtracting the heart rate (HR) value obtained after the chosen time frame from the final HR value observed during the exercise [2-5]. Assessments of HRR over shorter durations (i.e. 30 seconds, 1 minute) are frequently used in the literature and are the most practical, particularly in the elite sport setting.

Since there appears to be increased reliability of HRR measurements when assessed over shorter durations [6], and the outcome of a systematic review by Daanen et al. (2012) suggests that the measurement of HRR should occur within one minute to better detect meaningful differences over time, HRR assessment over the 30-60 seconds following exercise is recommended [1]. Therefore, most of this article will focus on shorter-duration HRR assessment, its indications, and applicability for assessing fitness and fatigue.

Heart-rate recovery (HRR) is defined as the rate at which heart rate declines after the cessation of physical exercise.

What Can Heart Rate Recovery Signify?

I’ve observed that many people find the concept of heart rate recovery (HRR) to be confusing, so I’ll begin with a brief explanation of HRR and what it may indicate.

A high or elevated HRR typically indicates a high or elevated level of cardiovascular fitness. However, just because a high or elevated fitness level exists, does not mean that its presence will be readily apparent; this is because fatigue can mask the display of fitness. You could be in peak cardiovascular shape but, if you’re also fatigued from the high stress of previous training, you will not be able to demonstrate your robust level of fitness. This is important to understand when considering a potential relationship between performance outcomes and HRR. While HRR indicates a high or elevated level of fitness, performance may actually be reduced at this time due to the presence of fatigue, or overreaching. Also, one should not expect a change in HRR to indicate improvement in power or strength-related parameters.

Associations with Fitness

Significantly higher rates of post-exercise heart rate recovery (HRR) are observed in the population of athletes, compared with the general population [7-11]. The recovery of the heart rate is, initially (during the first minute of the recovery), predominantly conditioned by the activation of the parasympathetic part of the autonomic nervous system [12]. Since the cohort of elite athletes typically has higher parasympathetic tone, we expect to observe faster heart rate recovery in this population, compared with the general population [12]. Another indicator of parasympethic activity in the autonomic nervous system is heart rate variability (HRV); HRV is beyond the scope of this article andyou can learn more about HRV here.

Increases in training status have coincided with increased heart rate recovery (HRR), in both the general population [13], and in athletes [14-16]. Furthermore, fitter and more elite-level athletes have faster HRR rates, compared with their less fit and less-elite counterparts [17-21]. This notion holds true in the general population, as well; individuals with higher levels of fitness, as determined by VO2max, have faster rates of heart rate recovery, compared with those with lower levels of cardiovascular fitness [22-24], independent of gender [24].

Buchheit et al. (2012) observed coinciding increased HRR rates and enhanced fitness (via improved repeated sprint performance), in trained soccer players [16]. However, there was no association between HRR and improvements in maximal running velocity during an incremental running test, countermovement jump performance, or acceleration and maximal sprinting speed obtained during a 40-m sprint [16]. As alluded to previously, the lack of relationship here is expected, since these assessments primarily elucidate outcomes relating to power and strength. In a previous study using young handball and basketball athletes, Buchheit (2008) found a meaningful relationship between performance during an intermittent running test and HRR metrics [17]. Rodríguez-Fernández et al. (2017) also observed a relationship between HRR during a sport-specific fitness test inclusive of repeated and progressive maximal efforts, and repeated sprint performance [18]. Watson et al. (2017) recently found a relationship between HRR 30 seconds post-exercise and VO2max in 84 collegiate intermittent sport athletes [19]. In line with previous research [19], there was no difference between sexes [24].

The aforementioned findings appear promising, but it’s important to note that the research in athletes is limited, and the methodologies used to collect the HRR data are heterogeneous (i.e. diverse).

For example, let’s investigate subject positioning. Although there are a few other intriguing studies assessing relationships between fitness and HRR in athletes, the HRR measurements were obtained during a post-exercise active recovery period, rather than passively [25, 26]. It’s well-known that the positioning of the athlete during HRR data collection, particularly during active movement, can substantially impact the results, which makes the outcomes from these studies difficult to interpret alongside the studies assessing HRR during passive recovery [26-29]. The impact of athlete positioning during HRR data collection is illuminated by recent work of Michaelson et al. (2019). In their study with collegiate female soccer players performing high-intensity interval training, there were substantial differences in HRR rates when the athletes recovered with their hands on head, compared with hands on knees [29]. Recovering with hands on the knees resulted in a significantly faster HRR (by 22 beats per minute, on average), compared with hands on head [29].

Therefore, if heart rate recovery (HRR) is to be assessed, what the athlete is doing during HRR data collection, as well as how the athlete is positioned during that time, must be considered. I can appreciate that it may be difficult to control for these variables, particularly in team sport contexts. Collaboration with the athletes and coaches may vastly improve protocol standardization and the potential for valid and reliable HRR data collection.

Implications for Assessment: Exercise Intensity

The intensity of the exercise may affect the heart rate recovery (HRR) response.

Mann et al. (2014) investigated heart rate recovery rates in response to different exercise intensities in middle-aged runners. Heart rate recovery (HRR) assessed 60 seconds following exercise was more rapid after exercise at higher intensities, but only up to a certain point, after which recovery rates leveled off. A significant increase in HRR between 60 and 70 % VO2max trials was observed, with no further increase between 70 and 80% VO2max [30].

When experimenting with different step test protocols, Huchu (2016) found increasing HRR rates with step tests which elicited higher maximum heart rate values [31]. HRR was substantially faster following achievement of 80% HRMax, compared with 70% HRMax [31]. Although not statistically analyzed, Al Haddad et al. (2011) observed variable HRR rates between sub-maximal and supra-maximal exercise [32]. Higher reliability of HRR values was observed with higher exercise intensity [32], which is in agreement with Lamberts et al. (2004), [6].

Overall, it appears that higher-intensity exercise induces faster HRR and higher reliability of HRR values [6, 31-34].

Implications for Assessment: Exercise Type and Duration

In addition to the intensity of exercise, consideration must be given to the type and duration of exercise.

For example, do Nascimento Salvador et al. (2016) found that heart rate recovery (HRR), measured 60 seconds post-exercise, was greatest following a single bout of continuous exercise, compared with both (1) two successive bouts of continuous exercise, and (2) a continuous bout of exercise preceded by repeated sprints, in amateur male futsol players [35]. Furthermore, two successive bouts of continuous exercise resulted in a faster HRR, compared with a continuous bout of exercise preceded by repeated sprints [35].

In a study involving 22 international soccer players participating in UEFA Champion’s League, Dellal et al. (2015) observed similar HRmax values from a continuous test (Vameval) and an intermittent test (Yo-Yo IE2). However, HRR rates measured 1-minute post-testing were faster following the intermittent test (Yo-Yo IE2), compared with the continuous test [36].

It may be relevant to consider the duration and type of exercise that was performed when assessing post-exercise HRR resultsAdditionally, the type and duration of the acute exercise that preceded the exercise for HRR collection (if any) should be appreciated. A pragmatic way to control for these variables in the team sport setting is to collaborate with the coaching staff to structure a consistent and repeatable sequence of practice drills that can be prescribed on an incremental basis. This will allow for longitudinal HRR assessment using a standardized exercise type, duration, and acute preceding exercise.

Implications for Assessment: Environmental Conditions

The environment, including the exercise-specific situation and temperature, also warrant consideration when evaluating HRR. In their study, Dellal et al. (2015) observed that the number of players and the presence of the goalkeepers during small sided games can alter the exercise intensity, which affects subsequent HRR [36]. Furthermore, the presence of a ball [37] and coach encouragement [38], as well as tactical and technical game-play environments, can impact the HR response [39-41]. Reviewing all of the factors that can affect heart rate (HR) response is beyond the scope of this article; I am bringing up a few things that impact the HR response because it’s important to understand factors that can influence the intensity and duration of exercise, which impacts HRR. We will re-focus, now, to HRR.

Kilgour et al. (1994) found HRR rates to be slower in high ambient temperature than in moderate conditions, likely due to increased vasodilation and consequential increase in heart rate (HR) caused by heat [42]. This notion is supported by Coker et al. (2018), who showed that NCAA Division I male soccer players spent more time >85% HRMax during matches throughout the course of a season when playing in hot and humid environments, compared with less humid and cooler environments [43]. The reduced rate of HRR in the presence of heat stress has been reported elsewhere, as well [44, 45].

Various sport-specific factors can influence heart rate response, which ultimately influences HRR. Some of these factors include the presence of goalkeepers, presence of a ball, level of coach encouragement, and technical and tactical gameplay environments (size of the allotted space, defender placement, etc.). Reduced HRR is observed in hot and humid environments, likely due to the coinciding increased vasodilation and heart rate.

A Brief Review on Functional Overreaching and Fatigue

Adaptations that benefit athletic performance revolve around the relationship between training stress and recovery. I can’t put it any better than Vern Gambetta did in his book “Athletic Development,” which is quoted below [46]:

“The body is always seeking to maintain a state of homeostasis so it will constantly adapt to the stress from its environment. Training is simply the manipulation of the application of stress and the body’s subsequent adaptation to that stress to maintain homeostasis. The adaptation that occurs is fairly predictable. In training the desired adaptive response is called supercompensation.”

Heart rate recovery (HRR) may be a tool that can be used to identify athletes who are experiencing an imbalance between their training stress and recovery [47]. As Vern suggests, some imbalance is required to elicit supercompensation, or adaptive responses to training, whereas too much of an imbalance can elicit maladaptation. Here are a few general terms, or classifications, that have been defined to represent the relationship between training stress and recovery [48, 49]:

Condition Definition Duration Overall Outcome
Undertraining Not enough training stimulus for positive adaptation As long as too little training persists Negative due to lack of application of sufficient stimuli to induce adaptive response
Functional overreaching Increased training leading to temporary (day to weeks) performance decrements, and with improved performance after rest Days to weeks Positive due to supercompensation effect
Nonfunctional overreaching Intense training leading to a longer performance decrement (weeks to months), but with full recovery after rest. Accompanied by increased psychologic and/or neuroendocrinologic symptoms Weeks to months Negative due to symptoms and loss of training time
Overtraining Consistent with extreme nonfunctional overreaching, with (1) longer performance decrement, (2) more severe symptomatology & maladapted physiology, (3) accompanied by an additional stressor, and (4) not explained by other diseases Months to years Negative due to symptoms and possible end to athletic career

Associations with Fatigue

It has been suggested that changes in heart rate recovery can indicate an imbalance between appropriate training stress and adequate recovery [50]. Historically, faster heart rate recovery following near-maximal exercise bouts has been associated with functional overreaching, which is a state of short-term performance reduction due to a combination of increased training and/or inadequate recovery [51-53].

For example, Thomson et al. (2016) observed increased HRR 60 seconds (by ~6 bpm) following a 5-minute maximal cycling time trial after a 2-week heavy training period, in 11 well-trained male cyclists and triathletes [53]. After a subsequent 2 days of rest, the HRR 60 seconds following the cycling time trial decreased back to where it was during light training [53].

Recently, Le Meur et al. (2017) found that maximal, or near-maximal, intensity exercise may not be required for HRR to be indicative of functional overreaching [50]. Following a 3-week period of heavy training, HRR 60 seconds after cessation of exercise across a wide range of exercise intensities (~60% to 100% of maximal aerobic speed) were all indicative of functional overreaching, in 20 trained triathletes [50]. It’s important to note that a reduced HRMax should also be expected when in a fatigued state, as observed in the two aforementioned studies [50, 53], as well as in others [54-57].

In any case, increases in HRR in concert with decreases in HRMax may indicate functional overreaching, or a state of fatigue with coinciding performance decrement.

Associations with Demands During Competition

Harry and Booysen (2019) recently examined relationships between in-game demands, heart rate recovery, and performance on physical tests, such as repeated sprint ability (RSA) and repeated high-intensity aerobic capabilities (via a submaximal YoYo IR1 test), in 32 elite female field hockey players [58]. Players with a faster heart rate recovery (HRR) at 10s and 60s during the submaximal YoYo IR1 test also spent a greater percentage of their playing time at running and sprinting speeds during matches. This is a concrete example of how incorporating HRR indices into player evaluation and monitoring can provide a coach or practitioner with a reasonably accurate indication of a player’s physical preparedness for competition [58].

Harry and Booysen (2019). Faster Heart Rate Recovery Correlates With High-Intensity Match Activity in Female Field Hockey Players—Training Implications. The Journal of Strength & Conditioning Research.

 

Summary

It’s becoming increasingly clear that training load influences heart rate recovery (HRR), and that cardiovascular fitness is associated with increased HRR in a non-fatigued state.

HRR is a simple, non-invasive measure that can be used to evaluate both fitness and fatigue qualities and, in my opinion, is a pragmatic approach to assess deviations in both of these qualities in repeated high-intensity sports. For example, in the sport of ice hockey, an athlete is routinely placed in situations that require maximal, or near-maximal cardiovascular exertion, followed by >60 seconds of recovery prior to their next intensive bout, during a practice. Routine quantification of HRR may aid practitioners in evaluating changes in fitness, particularly if they can work with the coaching staff to standardize a drill, or sequence of drills, within a practice structure that repeats itself over the course of a season.

In line with the observations of Harry and Booysen (2019), it’s logical to think that athletes who have faster HRR are better prepared to repeat high-intensity efforts with greater frequency, and for longer duration, compared with athletes who are unable to recover from high-intensity exercise as quickly. Monitoring time-course for HRR and how it fluctuates over days, weeks, months, or years, may allow applied sport professionals to better assess athlete readiness for competition, as well as longitudinal changes in cardiovascular fitness and fatigue.

 

Written by Adam Virgile / @AvSportsSci

Special to HockeyClan

 

FULL ARTICLE and REFERENCES

 

 

In Case You Missed It… Early Sport Specialization Series

Part 1: A review of the research investigating the true odds of becoming a collegiate or professional athlete.

Part 2: Whether or not early sport specialization leads to long-term athletic success.

Part 3: How early sport specialization increases injury risk and can lead to athlete burnout.

Part 4: 5 simple strategies to prevent athlete burnout.

Part 5: Evidence-based sport volume recommendations for youth athletes.

Part 6: How organized youth sport affects family dynamics.

 

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