Research Methods paper (Literature Review & State of problem)

Enhancing Sports Performance With Hypnosis: An Ode for Tiger Woods

Leonard S. Milling and Elizabeth S. Randazzo University of Hartford

We present a comprehensive methodological review of controlled and single-case design studies of the effectiveness of hypnosis for enhancing sports performance. To be included in the review, controlled studies were required to use a between-subjects or mixed model design in which hypnosis was compared with a control condition or alternative intervention to improve sports performance. Single case-design studies were required to incorporate baseline and intervention phases, with multiple assessment points during the baseline phase to establish a stable trend for the target behavior. An exhaustive search of the PsycINFO database identified 17 studies satisfying these criteria. Hypnosis was shown to be effective for improving performance in a variety of sports, with the strongest support for enhancement of basketball, golf, soccer, and badminton skills. Common methodological limitations in the reviewed studies included a failure to fully specify the demographic characteristics of samples, to utilize a treatment manual, and to assess relations between hypnotic suggestibility and outcome. Two hypnotic interventions met criteria as possibly efficacious empirically supported therapies, thereby indicating that hypnosis can be a way of engaging in evidence-based practice in sports psychology. Practitioners who work with athletes may wish to consider the potential of hypnosis for enhancing sports performance.

Keywords: hypnosis, sports performance, effectiveness, methodology, empirically supported therapies

Competitive sports are played mainly on a five-and-a- half-inch court-the space between your ears.

—Bobby Jones, Co-Founder of the Masters Tournament

Since becoming a professional golfer in 1996, Tiger Woods has won 105 tournaments including four Masters Tournaments, four PGA Championships, three U.S. Open Champion- ships, and three British Open Championships, thereby cementing his legacy as one of the greatest golfers in the history of the game and earning him prize money of more than $132 millionworldwide(http://www.tigerwoods.com/ about-tiger). According to Forbes magazine, in

2010–2011, the average annual salaries of pro- fessional athletes were $1.9 million in the Na- tional Football League, $2.4 million in the Na- tional Hockey League, $3.2 million in Major League Baseball, and $5.15 million in the Na- tional Basketball Association (http://www .forbes.com). However, the excitement and challenge of competition are frequently men- tioned as the primary motivations for youth, high school, collegiate, and even elite profes- sional athletes. For example, Lionel Messi, soc- cer forward for FC Barcelona and captain of the Argentina National Team, has said, “my moti- vation comes from playing the game I love. If I was not paid to be a professional footballer, I would willingly play for nothing” (Duda & Treasure, 2015, p. 66). Clearly, the intrinsic and extrinsic rewards for success as an athlete can be substantial.

The pressure on athletes to gain even a small advantage over competitors is often enormous. In the major U.S. sports (e.g., basketball, foot- ball, baseball, hockey, soccer), only about 6% of high school athletes go on to play in college,

This article was published Online First May 25, 2015. Leonard S. Milling and Elizabeth S. Randazzo, Depart-

ment of Psychology, University of Hartford. We thank Taryn Brandt and Dawn Neese for their helpful

suggestions in carrying out this project. Correspondence concerning this article should be ad-

dressed to Leonard S. Milling, Department of Psychology, University of Hartford, 200 Bloomfield Avenue, West Hart- ford, CT 06117. E-mail: [email protected]

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Psychology of Consciousness: Theory, Research, and Practice © 2015 American Psychological Association 2016, Vol. 3, No. 1, 45–60 2326-5523/16/$12.00 http://dx.doi.org/10.1037/cns0000055

45

and less than 2% of NCAA student-athletes later compete at the professional level (http:// www.ncaa.org). The boundary between success and failure is sometimes quite narrow. For ex- ample, at the 2008 Summer Olympics, U.S. swimmer Michael Phelps won an unprece- dented eight gold medals. Across the eight events, his average margin of victory relative to each of the 4th place finishers (who did not receive a medal of any kind) was a mere 3.84 s. Indeed, in the 100 m butterfly, the margin of victory over the 4th place finisher was a razor- thin .55 s. In view of the tremendous incentives for success and the fierce level of competition, it should come as no surprise that athletes often seek out every possible way of maximizing their abilities and performance.

Psychological Skills Training and Sports Performance

A variety of psychological interventions are commonly used to enhance sports perfor- mance, including visualization, self-talk, arousal regulation, and goal setting (Whelan, Mahoney, & Meyers, 1991). Visualization is sometimes referred to as imagery or mental rehearsal. It involves cognitively creating a new experience or recreating a past experi- ence to either practice a specific sport skill or to prepare immediately before competition (Vealey & Forlenza, 2015). Self-talk, or self- instructional training, is concerned with mod- ifying the ongoing thoughts and internal con- versations that athletes experience during preparation and competition, thereby reduc- ing negative cognitions and increasing confi- dence (Williams, Zinsser, & Bunker, 2015). Arousal regulation is a used to produce the optimal level of arousal, which might include arousal energizing techniques to increase arousal levels, as well as relaxation tech- niques to decrease arousal and anxiety (Gould & Udry, 1994). Finally, goal setting involves helping the athlete to establish specific, mea- surable, and realistic performance goals of moderate difficulty that result in improved performance (Gould, 2015). Evidence of the effectiveness of these interventions is mixed, but generally supportive (Gardner & Moore, 2006).

Hypnotic Enhancement of Sports Performance

Another psychological intervention that has been used to enhance sports performance is hypnosis. There are many definitions of hypno- sis, but we prefer the following one because of its clarity: “Hypnosis is a procedure during which a health professional or researcher sug- gests that a client, patient, or subject experience changes in sensations, perceptions, thoughts, or behavior” (Kirsch, 1994, p. 143). Another at- tractive feature of this definition is its neutrality with regard to long-standing, unresolved theo- retical controversies, such as whether people enter an altered state of consciousness when they are hypnotized (Kirsch & Lynn, 1995). According to Hilgard (1965), every hypnotic procedure consists of a hypnotic induction and a suggestion. The induction customarily consists of instructions for relaxation, along with state- ments that the person is becoming hypnotized. Thereafter, a suggestion or suggestions invite the person to experience some imaginary state of affairs (e.g., “you are feeling calm, confident, and powerful as you imagine yourself approach- ing the ball to take the penalty kick”). When a suggestion is delivered without a hypnotic in- duction beforehand, it is referred to as a non- hypnotic or imaginative suggestion (Kirsch, 1997a).

There are numerous anecdotal reports of well-known athletes using hypnosis to enhance sports performance. Undoubtedly, some of these reports involved the use of visualization, which was then inaccurately labeled as hypnosis in the popular media. Although hypnosis and visualization share some common elements, they are not the same. For example, visualiza- tion is not preceded by a hypnotic induction. Thus, visualization would be more similar to use of imaginative suggestions. However, there do appear to be some instances in which well- known athletes used hypnosis to enhance per- formance (e.g., Tiger Woods, Nolan Ryan). For example, in his biography of Tiger Woods, Lon- dino (2010) describes how a sports psychologist worked with Tiger Woods when he was a teen- ager, using hypnosis to sharpen his ability to focus in the moment on the golf course.

Empirical research has shown that hypnosis is a very effective intervention for a variety of problems and symptoms, including pain (Mont-

46 MILLING AND RANDAZZO

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gomery, DuHamel, & Redd, 2000; Patterson & Jensen, 2003), chemotherapy-related nausea and vomiting (Richardson et al., 2007), smok- ing cessation (Green, 2010; Green & Lynn, 2000), weight loss (Kirsch, 1996), and psycho- somatic disorders (Flammer & Alladin, 2007). In this article, we present a comprehensive methodological review of research on the hyp- notic enhancement of sports performance. More specifically, our first goal is to describe the results of all controlled and single-case design studies of the effectiveness of hypnosis for im- proving sports performance. Our second goal is to weigh the methodological strengths and lim- itations of this body of research. Finally, our third goal is to appraise these studies using the criteria for empirically supported therapies ad- vanced by Chambless and Hollon (1998). Over the last 15 years, there have been a number of selective reviews of the use of hypnosis in sport and exercise (Barker, Jones, & Greenlees, 2013; Morgan, 1996; Stegner & Morgan, 2010). How- ever, ours is the first article to comprehensively review all controlled and single-case design out- come studies, to critique the methodology of this literature, and to identify investigations sat- isfying the criteria for empirically supported therapies (Chambless & Hollon, 1998).

Method of Review

To be included in this review, controlled studies were required to use a between- subjects or mixed model design in which a hypnosis intervention was compared with at least one alternative intervention, or a pla- cebo, attention, standard intervention, or no- treatment control condition to enhance sports performance. Single-case design studies were required to incorporate baseline and interven- tion phases, with multiple assessment points during the baseline phase to establish a stable trend for the target behavior. No studies were included that failed to use a performance measure as an outcome variable (e.g., DeVos, Potgieter, & Blaauw, 1999). Finally, studies were required to be published in an English- language journal.

PsycINFO was searched for abstracts meet- ing the stated inclusion criteria through the mid- dle of April, 2015. Search terms were hypnosis in combination with either sports or sports psy- chology. This yielded a total of 142 records. An

additional six records were identified through other sources (e.g., references of relevant re- view articles). This produced a total of 148 records to be screened relative to the inclusion criteria. Of these, 121 records were excluded, leaving 27 records to be examined in greater detail. These 27 articles were read in full and 10 were excluded based on the inclusion criteria. This left a total of 17 articles (i.e., six controlled and 11 single-case design studies) to be in- cluded in the review. Figure 1 details the screening and selection process.

Table 1 summarizes the major characteristics of the controlled studies, including sample size and type of sport, intervention conditions, and key findings. Table 2 summarizes the major characteristics of the single-case design studies. The 17 studies can be grouped based on type of sport into the following seven categories: (a) basketball, (b) golf, (c) soccer, (d) racquet sports, (e) endurance and strength sports, (f) precision sports, and (g) other sports.

Summary of Controlled and Single-Case Design Studies

Basketball

Three studies examined the effects of hypno- sis on basketball shooting. In a controlled study, Schreiber (1991) evaluated the effectiveness of hypnotic suggestions for increased confidence, concentration, and that the basket would appear twice as large as its normal size to improve shooting performance during college basketball games. Athletes in the hypnosis condition achieved higher cumulative scores four weeks into the basketball season than the control con- dition, although inferential statistics for this comparison were not reported.

In a series of single-case design studies, Pates, Maynard, and colleagues utilized a hyp- notic intervention featuring suggestions to re- call a multisensory experience of a best basket- ball performance to successfully improve the jump- and set-shooting (Pates, Maynard, & Westbury, 2001), as well as three-point shoot- ing (Pates, Cummings, & Maynard, 2002) of college players. The findings of these studies suggest hypnosis is an effective intervention for enhancing basketball shooting.

47HYPNOSIS AND SPORTS PERFORMANCE

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Golf

In three single-case design studies, Pates, Maynard, and colleagues examined the effects of hypnosis on golf performance. A hypnotic intervention was used to help golfers evoke a multisensory experience of their best competi- tive golf match in order to successfully improve putting accuracy (Pates, Oliver, & Maynard, 2001), chipping accuracy (Pates & Maynard, 2000), and average stroke performance (Pates, 2013). Results from these three studies support

the effectiveness of this intervention for enhanc- ing golf skills.

Soccer

Two studies by Barker and colleagues exam- ined the effects of hypnosis on soccer ability. Both studies used a hypnotic intervention that included ego-strengthening suggestions to fos- ter feelings of confidence and composure. In a single-case design study, Barker and Jones (2008) utilized this intervention with a profes-

6 additional records identified through

other sources

148 records after duplicates removed

148 records screened

142 records identified through database searching

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121 records excluded: • Review (n=14) • Case study or practice materials (n=18) • Book (n=14) • Commentary or book review (n=5) • Dissertation abstract (n=7) • Not controlled or single-case design

outcome study (n=4) • Not English-language (n=11) • Not relevant to topic (n=48)

27 full-text articles assessed for eligibility

10 full-text articles excluded: • Case study or practice materials (n=1) • Sports performance not an outcome

(n=6) • Not controlled or single-case design

outcome study (n=3)

17 studies included in review

Figure 1. PRISMA flow chart.

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sional soccer player. After receiving the inter- vention, the player self-reported improvements in passing, tackling, heading, ball control, and decision-making. However, the lack of an ob- jective performance measure makes it impossi- ble to know whether there were actual improve- ments in play.

In a controlled study, Barker, Jones, and Greenlees (2010) utilized the hypnosis interven- tion described above to increase accuracy on a wall-volley task in which a soccer ball was repeatedly kicked at a target. Collegiate soccer players who received the hypnosis intervention performed significantly better than those in the attention-control group. These investigations suggest that hypnosis may be an effective inter- vention for improving soccer performance.

Racquet Sports

In a controlled study, Greer and Engs (1986) assigned beginning tennis players to hypnosis, progressive relaxation, or standard instruction conditions. Players in the hypnosis condition experienced suggestions to visualize forehand and backhand drives. There was no difference between conditions on a tennis-rally test. In contrast, in a single-case design study, Pates and

Palmi (2002) used a hypnotic intervention that included suggestions to evoke a multisensory experience of a best badminton performance to successfully improve the serve accuracy of uni- versity badminton players.

Endurance and Strength Sports

In a single-case design study, Heyman (1987) was unable to show that a hypnotic suggestion to silence crowd noise was able to improve the in-fight performance of an amateur boxer. Sim- ilarly, Lindsay, Maynard, and Thomas (2005) used a single-case design to evaluate the effect of hypnosis on the race performance of three elite cyclists. During hypnosis, athletes were asked to recall a multisensory experience of an optimal cycling performance. The intervention was highly similar to the one successfully uti- lized in the studies of basketball (Pates et al., 2002; Pates, Maynard, & Westbury, 2001), golf (Pates, 2013; Pates & Maynard, 2000; Pates, Oliver, & Maynard, 2001), and badminton (Pates & Palmi, 2002) described above. Race performance was positively affected in one cy- clist, sporadically affected in a second cyclist, and not affected in a third cyclist. These results fail to provide clear support for the effective-

Table 1 Characteristics of Controlled Studies of Hypnosis for Enhancing Sports Performance

Study Sample size

(sport) Intervention conditions Summary of key findings

Barker, Jones, & Greenlees (2010)

59 (soccer) Hyp — suggestions for confidence and composure

Hyp improved soccer wall-volley performance more than C

C — video attention control Greer & Engs (1986) 90 (tennis) Hyp — suggestions to visualize

forehand and backhand drives Hyp no different from PR and C on

tennis-rally test PR — Progressive relaxation C — standard instruction

Howard & Reardon (1986)

32 (weight lifting)

CHI — Cognitive hypnotic imagery

Hyp — Hypnosis only CR — Cognitive restructuring C — no-treatment control

CHI improved bench press performance, as well as arm and chest size more than Hyp, CR, and C

Jalene & Wulf (2014)

22 (throwing) Hyp — suggestions for throwing accuracy

Hyp reduced throwing errors more than C

C — no-treatment control Schreiber (1991) 24 (basketball) Hyp — suggestions for confidence

and concentration Hyp may have increased cumulative

points scored more than C C — no-treatment control

Wojcikiewicz & Orlick (1987)

33 (fencing) Hyp — posthypnotic suggestions for confidence and relaxation

Hyp no different from R and C in fencing performance

R — Relaxation C — no-treatment control

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ness of this intervention to enhance cycling performance.

However, in a controlled study, Howard and Reardon (1986) randomly assigned weight lift- ers to cognitive-hypnotic imagery, hypnosis only, cognitive restructuring or control condi- tions. Weight lifters assigned to the cognitive- hypnotic imagery group received suggestions for imagery designed to increase muscular growth and improved bench press performance. Lifters in the hypnosis only group received sug- gestions for relaxation and visualization of a pleasant scene. The cognitive-hypnotic imagery condition produced significantly greater im- provements than the other three conditions in arm and chest size, as well as on bench press performance.

Precision Sports

In a single-case design study, Robazza and Bortoli (1995) utilized a hypnotic intervention

consisting of suggestions to improve body aware- ness during stance, focus during draw and aim, and natural flow of movement to successfully improve the shooting accuracy of an expert archer. Likewise, in a controlled study of throwing accu- racy, Jalene and Wulf (2014) assigned undergrad- uate participants to either hypnosis or control con- ditions. The hypnosis intervention consisted of direct suggestions for throwing accuracy. The hypnosis group demonstrated fewer throwing er- rors than the control group.

Other Sports

In a controlled study, Wojcikiewicz and Or- lick (1987) randomly assigned fencers to hyp- nosis, relaxation, or control conditions. Partici- pants assigned to the hypnosis group were given posthypnotic suggestions for relaxation and confidence. No difference was observed be- tween the three conditions on fencing perfor- mance measures in national-level fencing com-

Table 2 Characteristics of Single-Case Design Studies of Hypnosis for Enhancing Sports Performance

Study Sample size

(sport) Hypnosis intervention Summary of key findings

Barker & Jones (2006) 1 (cricket) Hyp — suggestions for confidence and composure

Hyp improved cricket performance

Barker & Jones (2008) 1 (soccer) Hyp — suggestions for confidence and composure

Hyp improved self-reported soccer performance

Heyman (1987) 1 (boxing) Hyp — suggestions to silence crowd noise

Hyp did not improve in-fight performance

Lindsay, Maynard, & Thomas (2005)

3 (cycling) Hyp — suggestions for multisensory experience of best performance

Hyp improved race performance of 1 out of 3 cyclists

Pates (2013) 1 (golf) Hyp — suggestions for multisensory experience of best performance

Hyp improved golf stroke average

Pates, Cummings, & Maynard (2002)

5 (basketball) Hyp — suggestions for multisensory experience of best performance

Hyp improved three-point shooting accuracy

Pates & Maynard (2000) 3 (golf) Hyp — suggestions for multisensory experience of best performance

Hyp improved golf chipping accuracy

Pates, Maynard, & Westbury (2001)

3 (basketball) Hyp — suggestions for multisensory experience of best performance

Hyp improved jump- and set- shooting accuracy

Pates, Oliver, & Maynard (2001)

5 (golf) Hyp — suggestions for multisensory experience of best performance

Hyp improved golf putting accuracy

Pates & Palmi (2002) 4 (badminton) Hyp — suggestions for multisensory experience of best performance

Hyp improved short serve accuracy

Robazza & Bortoli (1995)

1 (archery) Hyp — suggestions for body awareness, focus, and flow

Hyp improved shooting accuracy

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petition. However, in a single-case design study, Barker and Jones (2006) employed ego- strengthening suggestions to increase feelings of confidence and composure to successfully improve the bowling average, strike rate, and number of wickets taken of a semiprofessional cricket player. The intervention was highly sim- ilar to the one successfully used to enhance soccer wall-volley performance described ear- lier (Barker et al., 2010).

Methodological Considerations

The 17 studies included in this review were appraised relative to six methodological crite- ria: (a) sample size, (b) specification of sample, (c) use of a treatment manual, (d) direct statis- tical comparison of experimental conditions, (e) stable baseline, and (f) assessment of hypnotic suggestibility. Some criteria were selected be- cause they are mentioned in the Chambless and Hollon (1998) framework for empirically sup- ported therapies and others because they reflect general methodological rigor. Only single-case design studies were evaluated according to whether they established a stable baseline across three or more assessment periods. Also, only controlled studies were evaluated as to whether they included a direct statistical com- parison of the experimental conditions. Tables 1 and 2 show the sample size for each of the

controlled and single-case design studies, re- spectively. Table 3 evaluates the 17 studies rel- ative to the other five methodological criteria. Studies are designated by a “Yes” when a par- ticular criterion was satisfied and by a “No” when not satisfied.

Sample Size

According to Chambless and Hollon (1998), for a single-case design study to be designated as empirically supported, there must be at least three participants. Six of the 11 single-case de- sign studies included at least three participants (Lindsay et al., 2005; Pates et al., 2002; Pates & Maynard, 2000; Pates, Maynard, & Westbury, 2001; Pates, Oliver, & Maynard, 2001; Pates & Palmi, 2002). In a controlled study, there must be a sufficient number of participants per ex- perimental condition to provide adequate statis- tical power. As a rule of thumb, we consider 15 participants per condition to represent the min- imum, although it seems likely that many more participants might be necessary to detect an effect of small to moderate size. Of the six controlled studies, four incorporated fewer than 15 participants per condition (Howard & Rear- don, 1986; Jalene & Wulf, 2014; Schreiber, 1991; Wojcikiewicz & Orlick, 1987). In con- trast, only two controlled studies utilized rela- tively large samples, with more than 25 partic-

Table 3 Methodological Criteria

Study Specification

of sample Treatment

manual Statistical comparison

of conditions Stable

baseline Hypnotic

suggestibility

Barker et al. (2010) No Yes Yes No Greer & Engs (1986) No No Yes No Howard & Reardon (1986) No No Yes No Jalene & Wulf (2014) No No Yes No Schreiber (1991) No No No No Wojcikiewicz & Orlick (1987) No No Yes No Barker & Jones (2006) No Yes No No Barker & Jones (2008) No Yes Yes No Heyman (1987) No No No Yes Lindsay et al. (2005) No Yes Yes No Pates (2013) No Yes Yes No Pates et al. (2002) No Yes Yes No Pates & Maynard (2000) No Yes Yes No Pates, Maynard, & Westbury (2001) No Yes Yes No Pates, Oliver, & Maynard (2001) No Yes Yes No Pates & Palmi (2002) No Yes Yes No Robazza & Bortoli (1995) No No No No

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ipants per condition (Barker et al., 2010; Greer & Engs, 1986).

Specification of Sample

To be able to determine the population to which the results of a study generalize, it is important to specify the age, sex, and race of participants. Of the 17 reviewed studies, all but two indicated the sex and age of study partici- pants (Greer & Engs, 1986; Wojcikiewicz & Orlick, 1987). In contrast, none of the 17 studies identified the race of study participants. Be- cause race was not specified in any of the stud- ies, it is difficult to estimate how well the find- ings of this literature generalize to the population of all athletes.

Use of a Treatment Manual

A treatment manual makes it more likely that a treatment or intervention will be delivered consistently within a single research team, or across different research teams. Indeed, to iden- tify a treatment or intervention as empirically supported, a study must utilize a manual, unless the treatment is simple and adequately de- scribed in the journal article (Chambless & Hol- lon, 1998). Ten of the 17 reviewed studies uti- lized the equivalent of a manual (Barker & Jones, 2006; Barker & Jones, 2008; Barker et al., 2010; Lindsay et al., 2005; Pates, 2013; Pates et al., 2002; Pates & Maynard, 2000; Pates, Maynard, & Westbury, 2001; Pates, Ol- iver, & Maynard, 2001; Pates & Palmi, 2002). It is worth noting that these 10 studies were car- ried out by just two research groups.

Statistical Comparison of Experimental Conditions

In a controlled study, the effect of a treatment should be established using a direct statistical test of differences between the treatment and control conditions. Regrettably, one of the six controlled studies did not report inferential sta- tistics (Schreiber, 1991). Another unfortunate statistical practice noted in this literature should be mentioned here. This practice involves cal- culating simple pre/post change scores and then performing multiple within-condition statistical tests to ascertain whether there were differences between conditions (e.g., DeVos et al., 1999). This approach is vulnerable to a regression to

the mean effect and increases alpha beyond .05 by a multiple of the number of tests performed. Appropriate inferential statistical tests such as repeated measures analysis of variance or anal- ysis of covariance should be utilized in a con- trolled study and alpha can be regulated using a Bonferroni correction.

Stable Baseline

According to the Chambless and Hollon (1998) framework for empirically supported therapies, a single-case design study must es- tablish a stable baseline for the behavior of interest across at least three assessment periods. Because the baseline period serves as the equiv- alent of a control condition, a stable or deteri- orating baseline enables a researcher to control for the passage of time and the effects of as- sessment. Only three of the 11 single-case de- sign studies failed to establish a stable baseline across three or more assessment periods.

Hypnotic Suggestibility

In the hypnosis literature, the terms hyp- notic suggestibility, hypnotic susceptibility, hypnotic responsiveness, and hypnotizability are used interchangeably. Hypnotic suggest- ibility is a traitlike individual difference vari- able indicating a person’s general tendency to respond to hypnosis and hypnosis suggestions (Gur, 1978). Hypnotic suggestibility can be assessed with standardized scales consisting of a hypnotic induction and a series of test suggestions. Research with these scales shows there are large individual differences in suggestibility (Gwynn & Spanos, 1996). For example, on the Stanford Hypnotic Suscepti- bility Scale, Form C, widely regarded as the gold standard of suggestibility measures, about 25% of the normative sample scored in the high range of hypnotic suggestibility, about 30% scored in the medium range, and about 45% in the low range (Hilgard, 1965).

Lynn and Shindler (2002) recommend as- sessing hypnotic suggestibility when investigat- ing the effects of hypnosis as a treatment or intervention. In a controlled study, assessing hypnotic suggestibility makes it possible to test whether there is a statistical interaction between suggestibility and treatment outcome. This has to the potential to show that the effects of a hypnotic intervention vary for athletes scoring

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at different suggestibility levels. In a single-case design study, assessing hypnotic suggestibility seems especially crucial because of the very small number of participants. The representa- tion of hypnotic suggestibility in a small sample of one to five athletes could easily be skewed, which might account for a large treatment ef- fect—or none at all. Unfortunately, hypnotic suggestibility was assessed in only one of the 17 reviewed studies (Heyman, 1987).

Empirically Supported Therapies

According to the American Psychological Association (APA), an empirically supported therapy is a psychological intervention that has been identified through research as likely to be helpful for a particular problem and population. In 1995, the APA Division 12 Task Force on Promotion and Dissemination of Psychological Procedures introduced a framework for evalu- ating the results of outcome studies to identify a treatment as empirically supported (Task Force on Promotion and Dissemination of Psycholog- ical Procedures, 1995), which was later refined by Chambless and Hollon (1998).

This framework maintains that to classify a treatment as possibly efficacious, there must be at least one study using a between-groups de- sign showing that the intervention is superior to no treatment, a placebo, or an alternative inter- vention, or the equivalent of an intervention previously identified as possibly efficacious (Chambless & Hollon, 1998). To classify a treatment as efficacious, there must be at least two studies using a between-groups design sat- isfying these criteria carried out by two separate investigative groups. Finally, to classify a treat- ment as efficacious and specific, there must be studies carried out by two separate investigative groups showing the intervention is superior to a placebo or intervention previously identified as efficacious in research controlling for nonspe- cific factors. Such studies must use a treatment manual or its equivalent, clearly describe the sample under investigation, and adhere to the principles of sound research methodology.

According to these criteria, the hypnotic in- tervention utilized by Barker and colleagues (Barker et al., 2010) can be classified as a pos- sibly efficacious therapy for improving soccer wall-volley performance. This intervention was designed to increase efficacy expectations and

consisted of three 45-min small group sessions. Each session was comprised of three phases. The first phase was a question and answer pe- riod about hypnosis intended to facilitate rap- port. The second phase consisted of a hand- clasp suggestion designed to acclimatize participants to hypnosis. The third phase incor- porated progressive relaxation procedures and ego-strengthening suggestions specific to the wall-volley task, emphasizing feelings of con- fidence and composure.

This intervention was more effective than an attention-control condition in improving wall- volley performance immediately after the third intervention session, as well as at follow-up four weeks later. In the attention-control condi- tion, participants watched videos of profes- sional soccer games edited to eliminate the modeling of behaviors that could have en- hanced self-efficacy. The wall-volley task re- quired the athletes to kick a soccer ball at a target 2.7 m wide from a distance of 7.6 m continuously for 90 s, with accuracy of the shots serving as the outcome measure. In a volley, a soccer player kicks a ball in flight without first controlling it using a trap or dribble. The re- searchers utilized a relatively large sample of 59 participants, the equivalent of a treatment man- ual, and clearly described the gender and age characteristics of their sample. Although the racial breakdown of the sample was not re- ported, it was later determined that 92% of participants were White and 8% of participants were Black (J. Barker, personal communication, January 26, 2015).

According to Chambless and Hollon (1998), studies using a single-case design may be used to classify a treatment as empirically supported. To do so, an investigator must establish a stable baseline by showing the behavior targeted for change is stable or demonstrates a pattern of decline for at least three assessment points prior to carrying out the intervention. Acceptable sin- gle-case study designs include (but are not lim- ited to) the ABAB design, in which A is a baseline period and B is an intervention period, as well as the multiple baseline design, in which an intervention is carried out across multiple participants, settings, or behaviors.

In a single-case study design, to classify a treatment as possibly efficacious, an interven- tion must be shown to be effective with at least three participants in research carried out by a

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single investigative group. To classify a treat- ment as efficacious, an intervention must be shown to be useful in at least three studies, with at least three participants each, carried out by at least two separate investigative groups. Finally, to classify a treatment as efficacious and spe- cific, there must be comparable studies showing that the intervention is superior to an alternative treatment controlling for expectancy and atten- tion, as well as assessment effects.

According to these criteria, the hypnosis in- tervention utilized by Pates, Maynard, and col- leagues can be classified as a possibly effica- cious intervention for enhancing performance in golf (Pates & Maynard, 2000; Pates, Oliver, & Maynard, 2001) and basketball (Pates et al., 2002; Pates, Maynard, & Westbury, 2001). The hypnosis intervention used in these studies was designed to increase flow and consisted of four phases: relaxation, hypnotic induction, hypnotic regression, and trigger control.

During the first phase, participants were in- structed to engage in deep breathing and pro- gressive muscle relaxation. During the second phase, participants experienced a staircase in- duction in which they were asked to imagine descending a flight of 20 stairs, opening a door to a room containing a comfortable chair, sitting in the chair, and viewing relaxing scenes on a cinema screen. In the third phase, participants were asked to recall a multisensory (i.e., visual, auditory, tactile, olfactory, and gustatory) expe- rience of a best performance in their sport. In the fourth phase, participants’ recall of a best performance was conditioned to be released by a trigger. Suggestions were given so that the trigger could be used to access associations with the best performance at some point in the future. Triggers included gripping the golf putter (Pates, Oliver, & Maynard, 2001), the basket- ball (Pates et al., 2002), music (Pates & May- nard, 2000), and a word (Pates, Maynard, & Westbury, 2001).

In a series of rigorous single-case design studies each with at least three participants, Pates, Maynard, and colleagues established a stable baseline across at least three assessment periods, utilized the equivalent of a treatment manual, and described the sex and age charac- teristics of their participants. The researchers did not report the racial composition of their samples. However, it was later determined that all three basketball players were White in Pates,

Maynard, & Westbury (2001), whereas four basketball players were White and one player was Black in Pates et al. (2002). In Pates and Maynard (2000), all three golfers were White, whereas in Pates, Oliver, & Maynard (2001), four golfers were White and one golfer was Asian (I. Maynard, personal communication, January 30, 2015). Notably, this intervention could have been designated as a possibly effi- cacious therapy for improving performance in badminton had it been possible to determine the racial composition of the sample in Pates and Palmi (2002).

Discussion

Our review of 17 single-case design and con- trolled studies suggests that hypnosis is an ef- fective intervention for enhancing performance in basketball (Pates et al., 2002; Pates, May- nard, & Westbury, 2001; Schreiber, 1991) and golf (Pates, 2013; Pates & Maynard, 2000; Pates, Oliver, & Maynard, 2001). Hypnosis also appears to show great promise as an interven- tion for improving soccer (Barker et al., 2010) and badminton skills (Pates & Palmi, 2002). Finally, there is preliminary evidence that hyp- nosis may be useful for enhancing performance in cricket (Barker & Jones, 2006), weight- lifting (Howard & Reardon, 1986), as well as precision sports activities like archery (Robazza & Bortoli, 1995) and throwing accuracy (Jalene & Wulf, 2014).

Generally, the methodological rigor of the single-case design studies included in this re- view exceeded that of the controlled studies. Six of the 11 single-case design studies had rela- tively robust samples of at least three partici- pants. Furthermore, approximately three- quarters of these studies established a stable baseline for the target behavior of at least three assessment periods and utilized a treatment manual or its equivalent. In contrast, five of the six controlled studies did not use a treatment manual and one of these studies also failed to perform a direct statistical test of differences between the treatment and control conditions. Moreover, the majority of the controlled studies could be characterized as possessing limited statistical power, with four of the six studies incorporating 15 or fewer participants per ex- perimental condition. Of note, none of the 17

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reviewed studies specified the race of partici- pants.

Another methodological limitation evident throughout this literature involved a failure to assess hypnotic suggestibility. As previously mentioned, assessing hypnotic suggestibility is necessary to establish the representativeness of the small samples characteristic of single-case design studies. In controlled studies, measuring hypnotic suggestibility makes it possible to test whether there is a statistical interaction between suggestibility and treatment outcome. Unfortu- nately, hypnotic suggestibility was assessed in only one of the 17 studies included in this review. Although hypnotic depth (i.e., the de- gree to which the person believes he or she was hypnotized) was measured in a few studies, this construct is distinct from hypnotic suggestibil- ity.

The importance of assessing hypnotic sug- gestibility is highlighted by outcome studies carried out both in the laboratory (Milling, Reardon, & Carosella, 2006) and in clinical settings (see Montgomery, Schnur, & David, 2011 for a meta-analysis) showing that suggest- ibility moderates the treatment effects of hyp- nosis. Indeed, the Montgomery et al. meta- analysis reported that the effect size for the association between suggestibility and hypnotic outcomes for a variety of clinical problems fell in the small to medium range. The relationship between suggestibility and treatment outcome is perhaps clearest in studies of pain. A meta- analysis of the effectiveness of hypnotic pain interventions found that the average effect size for participants scoring in the high range of suggestibility was D � 1.16, which is consid- ered a large effect, and nearly zero for those scoring in the low suggestibility range (Mont- gomery et al., 2000). In view of its potency as a moderator variable, future studies of the use of hypnosis for enhancing sports performance are encouraged to assess hypnotic suggestibility us- ing a standardized scale and to assess its relation to treatment outcome in controlled research us- ing the analytic strategy of Baron and Kenny (1986).

Two hypnotic interventions included in this review satisfied criteria for empirically sup- ported therapies. Specifically, the hypnotic in- tervention developed by Barker et al. (2010) met criteria as a possibly efficacious therapy for improving soccer skills. Likewise, the hypnotic

intervention advanced by Pates, Maynard, and colleagues met criteria as a possibly efficacious therapy for enhancing performance in golf (Pates & Maynard, 2000; Pates, Oliver, & May- nard, 2001) and basketball (Pates et al., 2002; Pates, Maynard, & Westbury, 2001). It is a propitious development that two hypnotic inter- ventions for enhancing sports performance can be classified as possibly efficacious therapies.

Over the last 10 years, there has been a grow- ing emphasis in psychology on evidence-based practice (APA Presidential Task Force on Evi- dence-Based Practice, 2006), including in sports psychology (McArdle & Moore, 2012; Moore, 2007). Identifying an intervention as empirically supported is one way of engaging in evidence-based practice. However, empirically supported therapies and evidence-based prac- tice are not synonymous (Westen, Novotny, & Thompson-Brenner, 2005). According to the APA Presidential Task Force on Evidence- Based Practice, 2006, “evidence-based practice in psychology (EBPP) is the integration of the best available research with clinical expertise in the context of patient characteristics, culture, and preferences” (p. 273). In turn, empirically supported therapies represent some of the best available research evidence that can be utilized in the clinical decision making process (Spring, 2007). Although the interventions used in ap- plied sports psychology are not therapies per se and athletes are not patients, the principles of evidence-based practice are nevertheless ger- mane.

Mechanisms of Empirically Supported Interventions

More research is needed on the mechanisms that could help to explain how the hypnotic interventions developed by Barker, as well as Pates and Maynard work. According to Pates & Maynard (2000), their hypnosis intervention functions by increasing flow (Csikszentmihalyi, 1975), in which the person becomes completely immersed in a challenging activity, loses their sense of self-awareness, and successfully per- forms the activity with a sense of automaticity. An athlete might describe this experience as “being in the zone.” In their rigorous series of single-case design studies, Pates, Maynard, and colleagues consistently showed that this inter- vention produced both higher self-reported flow

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states and better performance in golf (Pates, 2013; Pates & Maynard, 2000; Pates, Oliver, & Maynard, 2001), basketball (Pates et al., 2002), and badminton (Pates & Palmi, 2002). How- ever, as these researchers acknowledge, changes in flow scores did not always mirror changes in performance. Also, because flow was always measured after performance in each of these studies, it becomes difficult to say that changes in flow produced improvements in performance.

Barker (e.g., Barker et al., 2010) contends that his hypnosis intervention works by increas- ing efficacy expectations, or the person’s belief that he or she can successfully execute a specific behavior necessary to bring about a particular outcome (Bandura, 1997). In several rigorous single-case design studies, Barker and Jones demonstrated that this hypnosis intervention produced increases in efficacy expectations in a cricket player (Barker & Jones, 2006) and a professional soccer player (Barker & Jones, 2008). However, the extent to which changes in efficacy expectations played a causal role in producing performance gains is unclear.

Later, in a controlled study, Barker et al. (2010) demonstrated that collegiate soccer play- ers who received this intervention achieved larger increases in self-efficacy and performed better on a wall-volley task than those in a control group. Unfortunately, changes in self- efficacy failed to mediate the effect of hypnosis on wall-volley performance. However, because of the size of the sample in this study (n � 59), the regressions required to test mediation may have lacked sufficient statistical power to detect an effect. Now that the effectiveness of the hypnosis interventions developed by Barker, as well as Pates and Maynard have been demon- strated, large scale controlled studies utilizing Baron and Kenny’s (1986) method of testing mediation would seem desirable to examine whether changes in flow and efficacy expecta- tions are mechanisms of these interventions.

Targeting Specific Sports

The findings of our review suggest the pos- sibility that the hypnosis interventions evalu- ated in this literature may be of greater benefit to sports for which dexterity and coordination are crucial attributes and of less benefit to sports that depend primarily on strength or endurance. For example, the very same intervention that

improved performance in basketball (Pates et al., 2002; Pates, Maynard, & Westbury, 2001), golf (Pates, 2013; Pates & Maynard, 2000; Pates, Oliver, & Maynard, 2001), and badmin- ton (Pates & Palmi, 2002) did not benefit cy- cling (Lindsay et al., 2005). Notably, many of the effective hypnosis interventions in this lit- erature utilized suggestions for increased confi- dence (Barker & Jones, 2008; Schreiber, 1991) or recall of an optimal performance (Pates & Maynard, 2000), which could serve as a buffer against sports performance anxiety.

Sports performance anxiety is conceptualized as a tendency to respond with anxiety to com- petitive sports situations in which the adequacy of the athlete’s performance is evaluated (Smith & Smoll, 1990). Sports performance anxiety can be operationalized along three dimensions: somatic, worry, and concentration disruption (Smith, Smoll, Cumming, & Grossbard, 2006). The Yerkes-Dodson law states there is an in- verted-U relation between arousal and perfor- mance, and that increases in arousal beyond the optimal level results in a deterioration of per- formance (Yerkes & Dodson, 1908). According to Smith (1996), “the more complex the task, the lower is the optimal level of arousal for performing it. Thus, motor tasks that require delicate movements and high demands for tim- ing and coordination such as complex gymnas- tics routines or hitting a golf ball, are more likely to be disrupted by high levels of arousal than are simple tasks such as running or lifting a weight” (p. 270). Indeed, empirical research suggests that performance anxiety is more dis- ruptive to sports emphasizing coordination and fine motors skills than to those depending pri- marily on gross motor skills (Mellalieu, Hanton, & Fletcher, 2006; Smith & Smoll, 1990).

Consequently, by reducing high levels of arousal (i.e., anxiety), hypnosis interventions in- corporating suggestions that increase confidence may be most beneficial to sports for which dex- terity and coordination are key attributes. This position is consistent with the findings of a recent meta-analysis of the effectiveness of self-talk for enhancing sports performance. Specifically, Hatzigeorgiadis, Zourbanos, Galanis, and The- odorakis (2011) reported that self-talk was signif- icantly more effective in improving perfor- mance in sports involving fine motor skills, dexterity, eye-hand coordination, precision, and accuracy (e.g., basketball, golf, dart throwing)

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than those emphasizing endurance, strength, and power (e.g., cycling, long-distance running, shot-put). Of course, it would be premature to conclude that specific kinds of hypnosis inter- ventions are more effective for enhancing per- formance in some sports versus others based on a literature consisting of only 17 studies. More research on this issue would seem warranted.

Implications for Practice

The findings of our review may have useful implications for practice. Psychologists who work with athletes may wish to consider utilizing hyp- nosis and, specifically, the hypnotic interventions developed by Pates and Maynard (Pates & May- nard, 2000) and Barker (Barker & Jones, 2008) as tools for enhancing sports performance. Classi- cally, hypnosis involves direct suggestions for al- terations in sensations, perceptions, thoughts, feel- ings, and behaviors (Hilgard & Hilgard, 1994). Lately, however, some practitioners have de- emphasized the role of direct suggestions and are more likely to provide established cognitive– behavioral techniques in a hypnotic context (Kirsch, Montgomery, & Sapirstein, 1995). From this perspective, interventions such as visualiza- tion and self-talk could be preceded by a hypnotic induction and relabeled as hypnotic visualization and hypnotic self-talk.

It is important to recognize there are large in- dividual differences in hypnotic responding (Gw- ynn & Spanos, 1996). Consequently, hypnosis is unlikely to be an appropriate intervention for ev- ery athlete. On the contrary, there is some evi- dence showing that athletes, as a group, may be more responsive to hypnosis than nonathletes (Dunlap, 2005). Attitudes (Kirsch, Silva, Comey, & Reed, 1995) and expectancies (Kirsch, 1997b) have been shown to be important predictors of hypnotic responding. An athlete who has a posi- tive attitude and expectancies regarding hypnosis may be a good candidate for hypnotic interven- tion. If an athlete has negative beliefs about hyp- nosis, it may make more sense to use nonhypnotic interventions, such as visualization or self-talk. There are many misconceptions about hypnosis (Kirsch & Lynn, 1995), which, if corrected, could help to foster a more positive attitude. At the same time, it is important for athletes to be realistic about the limits of hypnosis. For example, hyp- notic suggestions could not somehow impart an average high school tennis player with the skills of

Serena Williams. Finally, practitioners who pro- vide hypnosis to athletes should have some train- ing and experience in the use of this technique.

Conclusions

Support for the use of hypnosis as a tool for enhancing sports performance once consisted primarily of anecdotal reports (e.g., Tiger Woods) and case histories. However, the evi- dence base has strengthened in recent years, thanks in part to the proliferation of rigorous single-case design studies. Our review of 17 single-case design and controlled studies indi- cates there is very solid evidence of the effec- tiveness of hypnosis for improving sports per- formance, particularly in basketball, golf, soccer, and badminton. Indeed, two hypnosis interventions were classified as possibly effica- cious according to the criteria for empirically supported therapies. To move research to the next level, additional controlled studies, empha- sizing the use of treatment manuals, specifica- tion of study samples, assessment of hypnotic suggestibility, and evaluation of hypothesized mechanisms, are needed. Practitioners who work with athletes may wish to consider hyp- nosis as a useful tool for improving sports per- formance and as a way of engaging in evidence- based practice in sports psychology.

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Received February 1, 2015 Revision received April 23, 2015

Accepted April 27, 2015 �

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