Expected physiological, psychological and performance outcomes FOLLOWING BIOFEEDBACK INTERVENTIONS8/24/2020
If you are new to HRV Biofeedback, start from part one to learn more about the foundations or part two to learn more about the important metrics to keep track of both during and outside of HRV Biofeedback sessions. In part three, you can learn more about the most common protocols In this last part of our introductory series on HRV Biofeedback, we will provide an overview of the main outcomes of HRV Biofeedback interventions, in terms of performance changes as well as physiological or psychological changes. We will first report on early explorations, then move towards higher-quality studies and finally cover recent attempts to investigate HRV Biofeedback interventions in more applied and practical settings The issue with performance measuresBefore we start, I believe there is an important point to cover, concerning performance measures In elite sport settings, performance is often the outcome of interest. However, in many sports (e.g. in teams settings), performance cannot be unambiguously measured (Cannon-Bowers and Salas, 1997; Richard et al., 1999; Wiseman et al., 2014), and is often estimated using different approaches For example, in many situations, athletic performance is measured during isolated tasks (e.g. sprinting ability), which might have low fidelity with respect to the complexity of an actual game. Even when sport-specific tests are used (e.g. a passing test in soccer), it is difficult to extrapolate test results to in-game performance, as often shown by research on talent identification (Den Hartigh et al., 2018; Bergkamp et al., 2019). For these reasons, focusing only on studies that clearly report changes in performance can be limiting. On the other hand, it follows from the previous considerations on HRV Biofeedback (see parts 1–3 of this guide) that physiological and psychological parameters might be mediating the relation between HRV Biofeedback and performance For example, HRV Biofeedback could increase parasympathetic activity at rest or improve emotional self-regulation during high anxiety tasks (Lehrer et al., 2003, Deschodt-Arsac et al., 2018), which might be beneficial for performance, as further discussed in the next sections. Hence, my goal here is to provide an overview of the effects resulting from the implementation of HRV Biofeedback methods in athletes. In particular, while it makes a lot of sense to first investigate sport-specific changes in athletic performance measures, I will also look at physiological and psychological changes that have been documented in the literature and can mediate athletic performance In other words, in this post, I aim at answering the following questions: what is the effect of HRVB on athletic performance? How do physiological and psychological measures change following HRVB interventions in athletes? A summary of the studies and outcomes can be found in the table below, while a thorough analysis of the studies organized by type of outcome (performance, physiological or psychological), is provided in the second part of this blog post Early studies and conflicting outcomesOne of the first studies to use the standard HRV Biofeedback protocol previously introduced (Lehrer, Vaschillo, and Vaschillo, 2000) was carried out by Lagos et al. (2008). This was a case study of a junior competitive golfer where sport-specific performance measures improved after the HRV Biofeedback intervention (number of strokes required to complete a 18-hole competition). Additionally, the authors reported improvements for both physiological (increase in HF, a marker of parasympathetic activity) and psychological measures (Profile of Mood States (POMS) and Competitive State Anxiety Inventory (CSAI-2)). On the other hand, the same year, Tanis (2008) investigated the effect of HRV Biofeedback on volleyball performance, psychophysiological regulation and perception, with less promising results. In this case, sport-specific performance was defined as the individual rating of four sport-specific skills during each game, as determined by a coach. Psychophysiological regulation was measured as coherence, an artificial construct relating to an individual’s performance during biofeedback. From a physiological point of view, higher coherence should be reflected in higher HRV at the resonant frequency or higher overall HRV. The authors found no improvement in performance after six weeks of HRVB in a team of 13 athletes. Coherence (or HRV) as measured at baseline before each session, also did not improve during the intervention but only at the end of each session, highlighting a possible acute effect. In terms of psychological outcomes, athletes reported perceived improved mental performance Additional studies in the following years were again able to show positive outcomes for HRV Biofeedback interventions. In particular, in Perry, Shaw, and Zaichkowsky (2011) the authors reported performance improvements both in gymnasts and hockey players following a 8–10 sessions biofeedback intervention. Anecdotal evidence on the positive psychological effects of biofeedback are reported also in two studies targeting elite athletes preparing for the Olympic games (Dupee and Werthner, 2011; Beauchamp, Harvey, and Beauchamp, 2012). In both studies however, no performance, physiological or psychological measures were quantified, and only anecdotal results were reported (two gold medals won and improved team ranking, Beauchamp, Harvey, and Beauchamp, 2012) A common issue with studies targeting elite athletes is that often several interventions are carried out at the same time, as reported for example in Olympic speed-skaters undergoing a multi-year program targeting psychological training (e.g. PST), neurofeedback, as well as HRV Biofeedback (Beauchamp, Harvey, and Beauchamp, 2012). As a result, it can be difficult to isolate the effect of HRV Biofeedback To sum up, most of these early studies reported positive outcomes in terms of psychological measures, and mixed findings in terms of physiological measures and performance improvements (Tanis, 2008). However, none of these studies included a control group, and some of the reported improvements in performance were either anecdotal (Beauchamp, Harvey, and Beauchamp, 2012) or involved a single athlete (Lagos et al., 2008) Higher-quality studies: control groups and follow-upsIn recent years, more and more studies have started including control groups to better account for the effect of HRV Biofeedback independently of other changes that might be occurring as training progresses Two studies in particular (Pusenjak et al., 2015; Deschodt-Arsac et al., 2018), evaluated physiological responses to stress tests (STROOP and math tests as well as university exams), in high level and elite athletes of various sports. In both cases, control groups were present, and only the intervention group showed improved physiological responses during the stress tests, for example reduced heart rate, reduced breathing rate and increased HRV. Changes in physiological parameters during stress tests are not commonly measured, but might highlight improved emotional self-regulation due to HRV Biofeedback Psychological measures also improved following the intervention, as reported in terms of standard tests (State-Trait Anxiety Inventory, STAI) or in short questionnaires evaluating subjectively the positive impact of the intervention Unfortunately, none of the studies reported performance measures, which is a common issue especially when targeting athletes of different disciplines. Similar findings were also reported in another intervention targeting athletes of various sports (Dziembowska et al., 2016). In this case there were no measurements during stress tests, but HRV was measured before and after biofeedback training, showing improvements in the experimental group. In terms of psychological measures, both self-esteem (Rosenbert Self-Esteem Scale (SES)) and state anxiety (STAI) improved after the intervention in the experimental group, while no changes were reported in the control group Other studies in more homogeneous populations (e.g. including athletes of a single sport), provide more insights in terms of performance outcomes (Paul, Garg, and Sandhu, 2012; Paul and Garg, 2012; Choudhary, Trivedi, and Choudhary, 2016; Wakefield and Shipherd, 2017). Wakefield and Shipherd (2017 measured performance in a strength task (one repetition maximum) following an HRV Biofeedback intervention. In this case, performance was improved but was no different than the improvement in the control and alternate groups. This study clearly shows the importance of a control group, as improvements in performance can occur independently of HRV Biofeedback. On the other hand, other studies reported performance improvements only in the intervention group. For example, in Paul, Garg, and Sandhu (2012), the authors performed an intervention in basketball players and included placebo (watching motivational videos) and control (no intervention) groups, reporting improved reaction time, movement time and shooting performance in the HRV Biofeedback group. The control group also improved performance, but to a lesser extent. Similarly, physiological (HRV features and respiration rate) and psychological (concentration) parameters improved only in the HRV Biofeedback group. The same authors carried out an additional study but with an interesting twist, selecting only players with high trait anxiety (Paul and Garg, 2012). This is particularly relevant as the HRV Biofeedback intervention might have a different effect based on personal traits. In this second study, all measures (performance, psychological and physiological) improved following the intervention. The two studies just mentioned are also among the few that included follow-up analysis (Paul, Garg, and Sandhu, 2012; Paul and Garg, 2012). In particular, the authors re-assessed all measures one month post-intervention, and found consistent results. Performance improvements were also found in another study looking at HRV Biofeedback in track athletes (Choudhary, Trivedi, and Choudhary, 2016) Towards more practical settingsNeedless to say, standard HRV Biofeedback protocols requiring athletes to spend significant time at the laboratory each week, and can be impractical for time-crunched elite or recreational athletes. As a result, sustained practice can become a challenge. Thus, in very recent studies, a variety of different approaches and methods have been employed in order to make HRV Biofeedback more practical, for example using mobile apps and mostly home-based practice as well as sessions as short as 3 minutes. However, mixed results have been reported In a first study, HRV Biofeedback was used in professional soccer players (Rijken et al., 2016). In this case there was no control group, but interestingly various measures were reported not only post-intervention but also at 5 weeks follow-up. In terms of performance, each player self-reported performance using a numeric scale, and reported no change throughout the study or at follow-up. Physiological measures (HRV analysis in the frequency domain) showed results consistent with previous literature (Dziembowska et al., 2016), such as increased LF and reduced HF. Among a series of psychological parameters collected with standard questionnaires (Recovery-Stress questionnaire for athletes and Sport Improvement Measurement-60), improvements were reported for emotional stability and concentration capacity only. In a recent study (Perry, 2018) used a combined HRV Biofeedback and mindfulness protocol in 4 junior soccer players. Performance was assessed using a sport-specific test (Loughborough Soccer Passing Test), and improved over time. No changes were reported in physiological (heart rate, respiration rate, skin conductance and HRV) and psychological (CSAI-2) parameters Finally, Mueller et al. (2019), carried out a HRV Biofeedback intervention on an elite triathlete and provides additional insights on baseline changes in HRV. In particular, in this study for the first time resting physiology (heart rate, HRV) was measured in unsupervised free-living settings using a commercially available mobile phone app. Performance was assessed in terms of time spent training as well as subjectively, and improved during the study. Morning HRV, a marker of parasympathetic activity and overall physiological stress was improved during the intervention. In terms of psychological measures, school stress was assessed with a numerical scale and remained unchanged Where does this leave us?General issues typical of early exploratory studies in sport science such as small sample size, lack of an active control group, and difficulties in assessing performance are also present in most of the HRV Biofeedback literature. Thus, in this section I will try to generalize from pooled findings and discuss in more detail effects and potential issues in terms of performance outcomes as well as changes in physiological and psychological parameters. Finally, I will provide recommendations for future research and for practitioners working in applied settings Performance outcomesResults in terms of performance outcomes have been conflicting so far. Part of the issue has to do with the difficulties of measuring performance. While for certain sports, in particular individual endurance sports, performance testing is often done routinely, this is not the case for team settings where performance testing is hardly performed or standardized. Additionally, when performance testing is carried out with a test that aims at simulating certain skills required during a game, it is debatable how such tests relate to in-game performance (Den Hartigh et al., 2018; Bergkamp et al., 2019). Another issue with standard tests, especially if the athletes have not performed them before the study, is the learning effect that would make them better at the task regardless of the intervention. This is the case in a few studies that showed improved performance in literature (Perry, Shaw, and Zaichkowsky, 2011; Paul, Garg, and Sandhu, 2012; Perry, 2018) In elite settings where a control group was lacking (e.g. Canadian Olympic athletes), anecdotal evidence has been positive, but it is difficult to determine if HRV Biofeedback was particularly beneficial in the athlete’s quest for a gold medal. Other studies that have shown improvements also relied on subjective assessment of athletic performance, or on metrics that might have little to do with performance, for example time spent training in an elite triathlete (Mueller et al., 2019). Similar criticisms can be made for studies that showed no improvements (Tanis, 2008; Rijken et al., 2016), as performance was assessed subjectively in both volleyball players (from their coaches) and elite soccer players (self-assessed) From the performance outcomes reported in HRV Biofeedback interventions so far, it seems difficult to determine if there is any direct positive effect of HRV Biofeedback on performance. While some of the aspects just covered can be better accounted for (e.g. including an active control group, using standard performance tests or preferably in-game performance, as well as using standard protocols for interventions), in certain sports it can still be very challenging to effectively determine performance changes following an intervention, for example in team sports or sports with a strong tactical component (Cannon-Bowers and Salas, 1997; Richard et al., 1999; Wiseman et al., 2014; Den Hartigh et al., 2018; Bergkamp et al., 2019) For these reasons, and considering the important physiological and psychological changes that can be impacted by HRV Biofeedback, and how physiological and psychological changes can mediate performance, it can be particularly interesting to determine if there are more consistent findings when it comes to such measures Psychological and physiological outcomesPsychological measures following HRV Biofeedback interventions are probably the most consistent in terms of positive outcomes. In particular, the various studies investigating effects on anxiety (both trait and state) as well as on self-esteem and self-efficacy, often found improvements in most measures (Lagos et al., 2008; Paul, Garg, and Sandhu, 2012; Paul and Garg, 2012; Dziembowska et al., 2016) with only one study reporting no changes in a small sample of younger athletes (Perry, 2018). While a few studies reported only anecdotal evidence or qualitative feedback from the athletes, a number of studies used standard questionnaires to assess anxiety, stress and mood In general, psychological parameters seem to benefit from HRV Biofeedback interventions, especially for what concerns anxiety, similarly to what has been reported in literature outside of sports In terms of physiological measures, results are also quite consistent across studies. However, an important caveat here needs to be considered. In particular, I have stressed before how physiology can be measured at different times, and in the case of HRV Biofeedback, how measurements taken during the session are reflective of acute changes as a result of deep breathing and RSA, and how these changes are not necessarily linked to baseline physiological changes in parasympathetic activity. Hence, while various studies have consistently shown increases in HRV, and in particular in the LF band (due to breathing at 0.1Hz), these changes do not imply any adaptation in the ANS (Dziembowska et al., 2016; Rijken et al., 2016). These are important aspects to consider as results differ greatly, as we can see from the few studies that measured both before and during HRV Biofeedback, and often found no improvement in HRV before the session, but increases during and right after each session (Tanis, 2008) When it comes to baseline changes, very few studies have investigated HRV outside of the HRV Biofeedback session In a few cases, baseline measurements were taken before the session, resulting in conflicting results (Tanis, 2008; Lagos et al., 2008). While this protocol might not be ideal, as other confounding factors are most likely present (e.g. physical activity beforehand, food or caffeine intake, etc.), a pre-session measurement is at least not affected by RSA as much as the actual HRV Biofeedback session. In this case, the study that found no change was shorter (6 weeks instead of 10), which might point to a required minimum dose for baseline physiological changes to take place. Only one study has measured changes in resting HRV from data collected first thing in the morning, showing an increase over time. However, this was a case study with only one participant, no control, and the change in HRV was associated with a change in training load, hence it is not possible to determine causality In other studies HRV is reported as improved, similarly to respiration rate being reduced, but it is often unclear when these parameters were measured (Paul, Garg, and Sandhu, 2012, Choudhary, Trivedi, and Choudhary, 2016). Given how short some of these studies were (down to 10 days), it seems unlikely that baseline changes in physiology were assessed. It is also highly unlikely that a person would modify respiration rate from an average of 12–14 breaths/minute to exactly 6, again highlighting how despite the lack of clarity in terms of the protocol, changes reported are most likely acute changes during the HRV Biofeedback intervention, and not baseline assessments of ANS activity While these acute changes are unrelated to baseline effects, they are still very important. In particular, consistent results form a variety of studies show that athletes are able to learn HRV Biofeedback and that breathing at their resonant frequency does synchronize breathing and heart rate in a way that is quantifiable and can have beneficial effects. I have introduced earlier the various pathways that try to explain the relation between HRV Biofeedback and positive changes in physiological and psychological variables (see part 1 of this guide), and we have seen how certain psychological aspects are consistently improved following HRV Biofeedback interventions, for example anxiety. Reduced anxiety could be a beneficial effect of HRV Biofeedback due to deep breathing and changes in baroreflexes regardless of baseline changes in the ANS. Yet, the relationship between acute changes in HRV, baseline changes in HRV, and psychological measures following an intervention is complex and requires further investigation Wrap UpIn this series of posts, we have provided an overview of research on HRV Biofeedback and athletic performance, as well as of the main effects on physiological and psychological parameters that can mediate performance outcomes
While researchers have been quite active in the last two decades, trying to determine if there is a positive impact on performance due to HRV Biofeedback interventions, the quality of most studies is fairly low and methodology is inconsistent. Case studies or anecdotal evidence is often reported, with very few studies using active control groups. Additionally, performance is almost always quantified subjectively or using simple tests that might not be reflective of actual performance Based on the available evidence, HRV Biofeedback can be considered an effective tool to reduce anxiety as well as acutely improve HRV, and therefore can be considered valuable in the context of emotional self-regulation even in an athletic population Hopefully, the availability of tools such as HRV4Biofeedback will make it easier for scientists, athletes and coaches to further investigated these aspects Comments are closed.
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