While this study yielded interesting results, and answered the calls for both research on mindfulness-based biofeedback interventions in sport, and single-subject research in sport psychology, there were some limitations worth addressing. The main limitation concerned scheduling and timing of study meetings. Participants were high school student athletes, with full days of school and extracurricular activities, resulting in limited availability. In addition, the high school environment offered limited availability of space to an outside researcher. Obtaining and maintaining both classroom and gym
space for study use posed significant challenges and required constant monitoring on the part of the researcher. Given these restraints, most of the study meetings took place before the participants started school, typically 7:00am - 8:00am.
Due to this timing, a variety of factors could have affected the outcome
measurements, and the results. For instance, concern for the participants’ need to get to their first class on time, required brevity during study meetings. The fast pace, both physically and mentally in the morning could have altered both the physiology and psychology of the participants. The environment may have contributed to results on physiological and psychological measures that did not accurately reflect the state of the participant if they had been recorded at a different time, and under different
circumstances.
Although there are no standards for the period of time needed for the participant to acclimate to the environment before recording physiological data (Schwartz, & Andrasik, 2015), researchers have used intervals of three to five minutes (Dziembowska
et al., 2016; Gross et al., 2017). Due to time constraints in the current study, athletes were
acclimatized for only about two to three minutes, as they entered the room, removed their
jackets and placed belongings on the side, and were fitted with the physiological sensors.
Although the researcher attempted to move slowly, and talk calmly with each participant,
the procedures may have felt rushed. The pace needed to begin the recording each session
may have impacted the results.
Additionally, performing study meetings before school may have contributed to
high school students’ day may contribute to deleterious effects on their health and well- being (Wahlstrom, & Owens, 2017). The unique physical characteristics of adolescents
may have contributed to results that are not typical due to the inherently problematic
early morning physiological and psychological state of high school students. It should be
noted, however, that the students did have some choice in study meeting times.
Therefore, participants may have preferred the early morning not just because of
availability but because their unique chronotype allows for morning performance which
is atypical of most high school students.
A further limitation could have been an increased level of anxiety in the
participants brought about by the environment of the study meetings. Two main factors
could have affected results. First, the study meetings occurred in a closed classroom with
only the participant and the researcher. The researcher, an adult male, relatively unknown
to the female teenager could have contributed to uncomfortable thoughts and feelings in
the participant which may have affected both physiological and psychological measures.
Second, although the rooms used were private, they were not locked or restricted access.
With this, the study meetings could have been interrupted by outsiders (teachers or other
students), and were on a few occasions. This uncertainty of disturbance could have
affected participant attention and anxiety, and again altered physiology or psychology.
A further limitation was the homogenous participant pool. All participants were
adolescent, female soccer players. Although a goal of the study was to examine soccer
performance optimization using a single-subject design, restrictions on generalizability
and sport performance measures were seen for this limited population. However, future
studies should consider male athletes, differing age ranges, and expand beyond the sport
of soccer.
5.3 Future Directions
The fields of biofeedback and mindfulness have each provided effective intervention strategies for athletes (Morgan, & Mora, 2017; Bühlmayer, 2017). Only recently have suggestions been made to combine these two training options in an effort to maximize efficient and effective building of self-awareness, and learning of self-
regulation skills. With this recent suggestion, a call was made to advance empirical investigation into mindfulness-based biofeedback interventions in sport (Khazan, 2016). Although this study was the first to respond to this call, continued work examining this unique strategy is needed.
Future research should continue the empirical examination of using mindfulness- based biofeedback for enhancing sport performance and athlete well-being. Two main threads should be considered. First, the current study recruited a limited population of female, high school soccer athletes. Future work could broaden the field by examining mindfulness-based biofeedback techniques across a range of ages as well as with male athletes. Second, research is needed that evaluates these interventions in other sports, at both the individual and team level.
As this study is the only known research that examines MBT with athletes to date, it is recommended that several aspects of the protocol be explored in more detail. The current study consisted of an intensive five-day introduction to both mindfulness and
biofeedback. Over those five days the two techniques were integrated, and following that integration a seven-week intervention period proceeded. Weekly meetings with
biofeedback refresher training, coupled with daily at-home meditation practice was used to elicit increased self-awareness and self-regulation skills. Future research should assess the timing of the intervention, looking at both total length, and frequency of training. In addition, the amount of at-home meditation practice should be explored more fully, including an evaluation of the type of guided meditations used.
The current study tracked the entire array of outcome measures: physiological, psychological, and sport performance. Generally, previous research on biofeedback has shown changes in physiological measures such as HR and HRV, or muscle tension; or in psychological measures such as anxiety, while mindfulness studies have primarily tracked changes in psychological dimensions such as anxiety or stress. While both
physiological and psychological dimensions have a relationship to sport performance, the relationship is indirect. Therefore, future research should consider measuring changes in sport performance, in addition to physiological and psychological parameters. It is advised that future studies consider emulating the current study and use physiological, psychological, and sport performance measures as all three are relevant and informative to intervention effectiveness and athlete improvement.
More broadly, there is a lack of research on mindfulness interventions that explore participant physiology. As discussed earlier much of the work on mindfulness in athletes considers psychological outcomes. Within sport, and even more extensively, future research should examine physiological changes that occur with delivery of
mindfulness interventions. Measuring features such as HR, HRV, RESP, SC, and TEMP would greatly contribute to an ever-growing body of evidence supporting the assorted benefits of mindfulness training. Although much work exists showing neural changes related to mindfulness (Fox et al., 2014; Hölzel et al., 2011; Luders et al., 2012; Murakami et al., 2012; Tang, Hölzel, & Posner, 2015), the rest of the body has been largely ignored to date. As mindfulness is concerned with the present moment, both thoughts and emotions, and the state of the body, future research on mindfulness should explore physiological outcomes.
5.4 Conclusion
The current study sought to examine the effects of a mindfulness-based
biofeedback intervention with high school soccer athletes. The research answered calls for more empirical support for MBT interventions in sport, as well as long-standing requests for more single-subject design within sport psychology. Furthermore, in carrying out this research three types of outcome measures addressing changes in physiology, psychology, and sport performance were explored. Results were variable across measures and participants, with only a few variables showing statistical significance. However, when examining the measures holistically, beneficial changes were demonstrated. All participants improved soccer passing skill post-intervention. Additionally, all participants generally showed improvements in physiological variables, demonstrating increased levels of self-awareness, and learned self-regulation strategies. Although psychological measures were variable, with some slightly suboptimal effects, these changes may have actually been caused by improvements in self-awareness brought about by the MBT. As
this study was the first to explore a MBT in a sport setting, the stage has been to set to more fully examine this potentially promising athlete mental training technique.
Appendix A Recruitment Flyer