Ankle injuries are the most common injury in sports and recreational activities, accounting for up to 45% of all sporting injuries (14). Eighty-five percent of ankle injuries are sprains (16), but it is the frequency and risk of reinjury that makes ankle sprains problematic, with recurrence of sprain in up to 73% of athletes (27). Recurrent ankle sprains result in significant disability and residual pain and instability (27). Therefore, prevention of recurrence is a major focus of rehabilitation.
Ankle taping is the most common method for supporting the chronically unstable ankle, and it is the principle means of preventing ankle sprains in sport (22). Although ankle taping is effective in the prevention of ankle injuries (26), it is not known why ankle taping prevents injury.
The two most common theories for why taping works are that the tape provides mechanical support or that it enhances proprioception. The mechanical support provided by taping, and the limits it imposes at the extremes of inversion, eversion, and plantarflexion, represent one possible mechanism (6). However, after as little as 10 min of exercise, the restriction imposed by the tape is significantly reduced (4,17,19), suggesting that the mechanical support may not be the most important factor.
The application of tape also could enhance proprioceptive input via cutaneous receptors (23) and muscle afferents (21). Ankle taping has been found to improve active joint-position sense for inversion and plantarflexion (6) and ability to detect surface slopes in the plantarflexion-dorsiflexion plane (23) in participants with no history of ankle sprain. However, in recurrent ankle sprainers and in nonsprainers, ankle taping does not improve detection of passive movement in the plantarflexion-dorsiflexion (21) or inversion-eversion planes (11). Hence, the role of enhanced proprioception with taping in the prevention of ankle sprains is debatable.
An alternative theory by which ankle taping may prevent injury is that if an athlete believes that taping will prevent injury, the athlete may participate with greater confidence (19). That is, taping may have a placebo effect. A placebo intervention is defined as "any therapeutic procedure (or that component of any therapeutic procedure) which is given deliberately to have an effect, or unknowingly has an effect, on a patient, symptom, syndrome, or disease, but which is objectively without specific activity for the condition being treated" (24). The expectancy theory is the most commonly accepted theory of the placebo effect; it presumes that the patient's expectations for improvement are causally linked to symptom improvement (15). The cornerstone of the expectancy theory is the patient's belief or expectation that the placebo intervention will be effective (1).
A recent Cochrane review (10) investigating the effect of placebo on a variety of clinical conditions concludes that there was no evidence that placebos in general have clinically important effects. However, this conclusion should be interpreted with caution. The standard model of testing the placebo effect is one in which the participant is randomized to an active treatment, placebo, or control group, but is not informed about the group allocation. The participant knows that he or she will be allocated to one of these groups and, therefore, knows there is a chance that he or she may be receiving the placebo treatment, thus presenting an element of doubt. This model is not consistent with the expectancy theory of the placebo effect, because under no condition is the participant certain that the treatment will be effective. Studies investigating the placebo effect should use a model in which the participant believes or expects that the treatment is going to be effective, even if it is not. That is, participants should be informed a priori that all treatments are effective, and the possibility of placebo should not be mentioned.
The purpose of the present study was to determine whether there was a placebo effect with ankle taping in individuals with ankle instability, using a model in which the participant was exposed to the belief that the placebo tape would be effective. We hypothesized that performance of functional tasks by individuals with ankle instability would be improved with placebo taping.
Thirty participants (11 males and 19 females, aged 21 ± 3 yr) with ankle instability from previous ankle sprains volunteered for this study (Table 1). Ankle instability was defined as ≤ 24 of 30 on the Cumberland ankle instability tool (CAIT) (9). The average CAIT score for the group was 18 ± 5. Participants were excluded from the study if they had a past history of fracture or surgery to the lower limb, ankle sprain within the last 3 wk, pain or palpable effusion of the ankle at the time of testing, or neurological, visual, or any vestibular deficit or other orthopedic or arthritic problem in the test leg that could affect performance.
Participants were blinded to the true purpose of the study and were informed that the aim of the study was to compare two methods of ankle taping, referred to as mechanical (real) and proprioceptive (placebo) taping. The study was approved by the University of Sydney human research ethics committee, and written informed consent was obtained from all participants before data collection.
Data were collected from one ankle of each participant in a single 1.5-h test session. In participants with unilateral ankle instability, the unstable ankle was tested. In participants with bilateral instability, the most unstable ankle, determined by the CAIT score, was tested. For participants whose ankles scored equally on the CAIT, the test ankle was randomly selected.
Participants were tested under three conditions in random order: 1) real (mechanical) tape, 2) placebo (proprioceptive) tape, and 3) control (no tape). For each tape condition, participants completed two functional performance tests in random order: the hopping test (3) and the modified star excursion balance test (7). Before data collection, participants were given instructions, and the examiner demonstrated each test. Participants then completed six practice trials of each test without the ankle taped (8). During data collection, participants completed three trials of each test under each tape condition. The best effort was used for data analysis.
At the completion of each functional test under each condition, participants were questioned regarding their perceived level of stability, confidence, and reassurance when performing the test compared with the practice trials. For example, after the hopping test, participants were asked, "When performing the hopping test, how confident did you feel compared with the practice trial?" Stability referred to how steady and controlled the participant felt; confidence referred to how well the participant felt he or she could perform the test, and reassurance referred to how confident the participant was that he or she would not sprain an ankle while performing the test.
The mechanical (real) tape consisted of a technique commonly used by sports physiotherapists and athletes to prevent ankle-inversion injuries. An anchor, three stirrups, a low anchor, a figure of six, and a heel lock were applied using inelastic tape (Fig. 1). Endura-Fix self-adhesive underwrap (Endura Tape Pty Ltd, Sydney, Australia) was offered to male participants. Participants were informed that this method of taping aimed to prevent ankle sprains by increasing mechanical support to stabilize the ankle and to decrease range of motion at the ankle joint. They were also told that this method of taping was expected to improve their performance on the functional tests.
The proprioceptive (placebo) tape consisted of a single strip of inelastic tape approximately 10 cm long on the lateral aspect of the lower leg above the lateral malleolus (Fig. 2). The tape was aligned vertically over the tendon of the peroneus longus. Participants were informed that this method of taping aimed to prevent ankle sprains by increasing cutaneous input to improve proprioception. An explanation of the proprioception theory of taping was provided to enhance the credibility of the placebo tape. Participants were told that this method of taping was expected to improve their performance on the functional tests.
Participants were essentially blinded to the true nature of the tape condition by the examiner's instructions (i.e., the placebo tape was referred to as proprioceptive tape, and the real tape was referred to as mechanical tape). To further minimize bias, participants were blindfolded during tape application, and a skirt was placed over the foot and ankle, without intruding on the sole of the foot, during all functional performance test trials (Fig. 3). The skirt was used during all three test conditions (real tape, placebo tape, control).
Functional Performance Tests
Participants' performance was evaluated using the hopping test and the modified star excursion balance test. The tests were selected for their ability to discriminate between stable and unstable ankles (7,12,20) and their high reliability, as demonstrated for the star excursion balance test by Hertel et al. (8) and Kinzey and Armstrong (13), and as demonstrated for the hopping test in our laboratory, where ICC2,1 = 0.95. No participant reported any pain during performance of any of the functional performance tests.
The hopping test measures single-limb agility on uneven surfaces (3). The course consists of eight squares, four of which are level; one square provides a 15° incline, another square provides a 15° decline, and two squares provide 15° lateral inclinations. Each square was 35 cm2. Participants commenced the test by standing 35 cm behind the first square. They were then instructed to hop around the course on the test leg as fast as possible by landing on each square once, then return to their original starting position by completing the course in the opposite direction. The time taken to complete the course was recorded. A time penalty (1 s) was incurred each time a participant landed outside the boundaries of the course or completed the course in the incorrect sequence. A participant's score was the sum of the time taken to complete the course and the total number of penalties. Rest periods of 90 s were provided between trials to minimize fatigue. The course was completed with participants barefoot, wearing loose, comfortable clothing. Pilot data collected in our laboratory have shown the test to have high intrarater reliability (ICC2,1 = 0.95).
Modified star excursion balance test.
The modified star excursion balance test is a test of stability in multiple directions (7). The test layout consisted of four 1.5-m tape measures arranged on the floor: one in the anterior direction, one posterior, and two lines extending at a 45° angle: one posteromedially and one posterolaterally (relative to the test leg) from the center of the star. Participants initially assumed a bilateral stance at the center of the star, with the feet touching and one foot on either side of the tape measure. They were then instructed to stand barefoot on the test leg and to reach as far as possible with the contralateral leg in the appropriate direction. Participants lightly touched the furthest point possible on the line with the most distal part of the reach foot before returning to bilateral stance. Participants were instructed to move in any way possible to achieve a maximal reach distance. Participants completed reaches in three directions: anterior, posterior, and posteromedial, relative to the test leg. When reaching in the anterior direction, participants began with their toes behind a line marked at the center of the star. When reaching in the posterior and posteromedial directions, participants began with the heel in front of the line. Trials were discarded and repeated if participants lifted the stance foot, lost balance, did not maintain start and return positions for 1 s, or if the reach foot was used to provide considerable support. Considerable support was defined as participants transferring any weight onto the reach foot. Participants were instructed to keep their weight on the test leg.
During data collection, participants completed three reaches in each direction, with 15 s of rest between reaches. The order of reaches was randomized in the clockwise and counterclockwise directions.
Statistical power calculations indicated that a sample of 30 participants would provide a > 80% chance of detecting a 1-s difference between conditions on the hopping test, assuming a standard deviation of 1.3 s (12). A difference of 1 s has been found to discriminate between stable and unstable ankles in the hopping test (12).
For the hopping test, a one-way repeated-measures analysis of variance (ANOVA) was used to compare performance among the three conditions. The within-subjects factor was condition (real, placebo, control). Data for the modified star excursion balance test were analyzed with a two-way repeated-measures ANOVA in which the within-subject factors were direction (anterior, posterior, and posteromedial) and condition (real, placebo, control). Means and standard deviations are reported, unless otherwise stated. The significance level was preset at α = 0.05. Statistical analysis was performed using SPSS 12.0.
A secondary analysis was performed on the qualitative responses provided by the participants. Each participant's perceptions of stability, confidence, and reassurance were described for each condition on each functional test. The number of participants who reported improvements in stability, confidence, and reassurance compared with the practice trials for each condition on each test was recorded, and a chi-square analysis was performed to determine whether there was any difference between the proportion of participants reporting improvements for each condition. Patterns or commonalities in the responses were also sought.
There was no significant difference in performance among the three conditions on the hopping test (P = 0.865). Participants completed the hopping test with the real tape applied in 10.5 ± 3.6 s (mean ± SD), with the placebo tape applied in 10.5 ± 3.6 s, and without tape (control) in 10.5 ± 3.7 s (Table 2).
Modified star excursion balance test.
There was no significant difference in performance among the three conditions on the modified star excursion balance test (P = 0.491), nor was there significant interaction between the condition (real, placebo, control) and reach direction (anterior, posterior, posteromedial) (P = 0.080). In the posteromedial direction, participants reached a mean distance of 77.2 ± 9.9 cm with the real tape applied, 77.8 ± 8.9 cm with the placebo tape applied, and 77.0 ± 9.4 cm without tape (control). There was a significant main effect for direction (P < 0.000), with pairwise differences between anterior versus posterior (P < 0.000) and anterior versus posteromedial (P < 0.000) (Table 2).
Secondary analysis (perceptions).
Ankle tape, both real and placebo, influenced participants' perceptions of stability, confidence, and reassurance when performing the functional tests (Figs. 4 and 5). The chi-square analysis indicated that for each perception measure, for both tests, the proportion of participants reporting a positive effect was different between conditions (real tape vs placebo tape vs control; P < 0.0001 for all chi-square analyses). The real tape condition had an effect on the greatest number of participants, in terms of perception of stability, confidence, and reassurance. The greatest effect of the real tape was on perceived stability, with 97% (N = 29) of participants on the hopping test and 80% (N = 24) of participants on the modified star excursion balance test reporting that perceived stability with the real tape was improved compared with the practice trials.
The placebo tape also influenced participants' perceptions of stability, confidence, and reassurance. At least 17% (N = 5) of participants reported improvements in perceived stability, confidence, and reassurance with the placebo tape on both the hopping test and the modified star excursion balance test from the practice trials. For example, perceived stability with the placebo tape during the hopping test was improved for 27% (N = 8) of participants when compared with the practice trials. No participants reported improvements in perceived stability, confidence, or reassurance on either of the functional tests under the control condition.
Although ankle taping reduces the incidence of ankle injury (26), the mechanism underlying its effectiveness remains unclear. The purpose of the present study was to determine whether there was a placebo effect with ankle taping in individuals with ankle instability. There was no significant difference in performance among conditions on either of the functional tests. However, it is important to note that in the star excursion balance test, we were unable to normalize the scores by accounting for leg-length differences; if we had normalized the scores, differences may have existed. An analysis of participants' responses, however, revealed that ankle tape, both real and placebo, improved participants' perceptions of stability, confidence, and reassurance when performing the functional tests.
More participants reported improved perceptions of stability, confidence, and reassurance with the placebo tape applied than with the control condition. This result suggests that although the placebo tape does not influence performance on the functional tests studied, it does affect the way some individuals feel when performing such tests. Although it is possible that improvements in perception with the placebo tape may be related to the sensory feedback generated by the actual tape, it is also possible that simply instilling in participants the belief that the tape would protect them from injury (i.e., the placebo effect) has the potential to improve perceptions of stability, confidence, and reassurance when performing functional tasks.
The real tape condition also improved participants' perceptions of stability, confidence, and reassurance, with more participants reporting improvements in these variables with the real tape condition than either the placebo or control condition on both of the functional tests. This may be related to the supportive or restrictive nature of this method of taping. Several participants spontaneously volunteered that the feeling of support provided by the real tape made them feel more stable when performing the functional tests. They further suggested that this increase in stability resulted in an increase in confidence and/or reassurance that the tape would protect them from injury. It is possible that this feeling of support provided by the tape may trigger a placebo effect. That is, although the physical restriction provided by the tape diminishes with exercise (4), the individual's perception of stability and, therefore, confidence and reassurance, may remain. Because the means by which ankle taping prevents injury is unknown, it may be related to the way an individual feels with his or her ankle taped, and to the continued belief that the tape will protect him or her from injury. This proposal is merely speculative, and it requires further investigation.
Although this was not a specific aim of the study, it was interesting to note that ankle taping did not impair participants' performance on either of the functional tests. Previous research investigating the effects of ankle taping on performance has reported conflicting results (2,5,18,25). Although differences in experimental protocols may partially explain the variability in results among the studies, the effect of ankle taping on performance also may depend on the functional task being tested. With respect to single-limb agility during a short-duration hopping course and dynamic single-limb stability on a balance reaching task, results of the present study suggest that ankle taping does not seem to impair functional performance. This finding is new and important because it relates specifically to individuals with ankle instability, unlike previous studies, which have tended to use uninjured participants. Furthermore, this finding has significant implications for athletes participating in sports in which similar demands, such as hopping, are placed on the ankle. Athletes can be confident that ankle taping will minimize the risk of injury without compromising their performance. These findings, however, cannot be generalized to other functional tasks, and further research is required to determine the effect of ankle taping on performance during specific sporting activities.
Although ankle taping did not affect performance on the functional tests used, it is possible that the tests were not sufficiently sensitive to detect differences that may have existed between the conditions. These tests were selected on the basis of a thorough review of the literature on lower-limb functional performance tests. Only two clinically based lower-limb functional tests have been shown to be both highly reliable (8) and sufficiently sensitive to discriminate between stable and unstable ankles (7,12,20). Although we know that these tests have the ability to differentiate stable from unstable ankles, it was previously unknown whether ankle taping would alter performance on the tests. A test for which taping would improve performance would be beneficial, in that if participants performed better with their ankle taped than untaped, it would then be possible to better gauge the effect of the placebo tape compared with the real tape. In the present study, the real tape condition did not improve participants' functional performance. Therefore, although there was no effect of the placebo tape on participants' performance, it cannot be concluded that there is no placebo effect with ankle taping.
Although we know that ankle taping is effective in reducing the incidence of ankle sprains (26), its effect on functional performance is not as clear. Because this study is the first to investigate the placebo effect in relation to ankle taping, functional performance tests were used as the outcome measures. Although placebo tape did not improve performance on the functional tests, the placebo effect may still contribute to the effectiveness of ankle taping in terms of preventing ankle injury. Ideally, a study using injury recurrence as the outcome measure would be performed to provide further information regarding the potential contribution of the placebo effect to the prevention of ankle injuries with taping. Such a study, however, would have significant ethical implications. The application of a placebo tape, which has no preliminary evidence of effectiveness, may place the participant at an increased risk of injury. Until preliminary studies can show that placebo taping improves functional performance, it would be unethical to perform such a study. Furthermore, it would be unethical for clinicians to apply placebo ankle taping to patients. Clinicians, therefore, should continue to use ankle-taping techniques of known efficacy.
It may be suggested that participants were potentially aware of the true nature of the placebo tape. However, we took particular care to ensure that participants were adequately blinded to the placebo condition. From the time they were recruited into the study until the completion of data collection, participants were unaware of the true purpose of the study. Participants were informed that the aim of the study was to compare two real but different methods of ankle taping referred to as mechanical and proprioceptive taping. At no time were participants under the impression that one of the tape conditions would be a placebo. For the placebo tape to be a true placebo, it should have little, if any, physical effect on the participants. For this reason, only minimal quantities of tape could be used. To overcome the perceived lack of effect of this method of taping, participants were informed that the placebo tape aimed to prevent ankle sprains, not by increasing mechanical support but by increasing proprioceptive input. Participants were told that traction of the tape on the skin would stimulate cutaneous receptors, activating a proprioceptive feedforward loop via afferent and efferent nerve fibers. This proprioceptive feedback would increase background discharge in the peroneus longus muscle, thereby decreasing peroneal reaction time and preventing inversion sprains. Participants were explicitly told that this method of taping was expected to improve their performance on the functional tests. Participants also were blindfolded during all tape applications, and a skirt was placed over the ankle during testing. This minimized visual cues that could have influenced the participant's opinions of the tape. On the basis of the measures taken, we suggest that the participants were adequately blinded to the placebo condition.
The mechanism underlying the ability of ankle taping to prevent injury remains unclear. From the results of the present study, it cannot be concluded that there is a placebo effect with ankle taping in individuals with ankle instability. Clinicians, therefore, should continue to use ankle-taping procedures of known efficacy. They should, however, focus on maximizing the credibility of taping, because the participants' belief that taping would prevent injury seems to have influenced their perceptions of stability, confidence, and reassurance when performing functional tests. The ability of ankle taping to influence perception of stability, confidence, and reassurance may contribute to its effectiveness in preventing injury.
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Keywords:©2007The American College of Sports Medicine
ANKLE SPRAIN; ANKLE INVERSION SPRAIN; ANKLE INJURY; TAPE