OPTOMETRY. An investigation of the effectiveness of Bolle s Competivision sport-glasses on tennis performance

Transcription

1 C L I N I C A L A N D E X P E R I M E N T A L OPTOMETRY An investigation of the effectiveness of Bolle s Competivision sport-glasses on tennis performance Damian Farrow* BEd MAppSc David Southgatet BScOptom * School of Human Movement and Sports Science, University of Ballarat t Private practice Melbourne Accepted for publication: 20 June 2000 Background: Specifically, Boll6 claims the Competivision lens will enhance the ability of a player to visually perceive a tennis ball and may subsequently improve athletic performance. This study examined the impact on tennis performance of wearing Boll6 Competivision tennis sport-glasses. Methods: Twenty subjects of three tennis skill levels were measured in relation to their hitting accuracy and movement initiation speed while hitting ground strokes projected from a sports action machine. Each participant completed 40 test trials under three conditions: wearing Competivision lenses, wearing clear lens glasses (used as a placebo to create an expectancy of improved performance) and not wearing glasses. Result: No significant differences were found between any treatment conditions or skill groups for movement initiation time. There was a significant difference in hitting accuracy between the skill levels, with the advanced and intermediate skill groups being more advanced than the novices, but this difference was independent of treatment condition. Additionally, there was no significant difference in hitting accuracy between the treatment conditions. Discussion: Possible causes of the results include the role of ball flight information for successful hitting performance and the transfer of colour contrast sensitivity to enhanced sports performance. (Clan Exp Optom 2000; 83: 4: ) Key words: colour contrast, perception, sports performance, sports vision, sunglasses, tennis Sporting success is more likely to occur when a performer can quickly and accurately perceive what is occurring in the environment and plan an appropriate response. Perception in the sporting environment tends to be predominantly visual due to the nature of sports played and a human s tendency to be visually dominant. Gavrisky claimed that 85 per cent of sensation is obtained through the visual system. Considerable research attention has been directed at the contribution of visual information for the control of sports skills, sports expertise and subsequently performance enhancement. Researchers within the field of sports optometry have focused on identifying the contribution of selected visual capacities to sports performance (for example, dynamic visual acuity, depth perception and accommodation). Typically, equivocal findings have resulted when the visual capacities of expert athletes have been compared to those of novice^.^ Generally, the intuitively appealing assumption that expert sports performers also have superior visual skills has not been substantiated. Sport science literature has an abundance of expert-novice comparisons between sports performers on visual-perceptual characteristics, such as pattern recognition, anticipation and object detection. This research approach has been more successful in identifylng key differences between expert and novice performers. Typically, experts are faster and more accurate in reading patterns of play and extracting information from an opponent s a~tion.~.~ 226

2 Not surprisingly, research attention has also focused on how the visual system may be trained to accelerate and improve an athlete s performance. Sports scientists and optometrists have advocated a variety of approaches to assist athletes to develop what can be globally called sports vision. Some sports optometrists have advocated the use of visual training programs (for example Eyerobics) that claim to improve visual capacities of athletes (for example dynamic visual acuity) and subsequently improve sports performance.6 However, the majority of suitably controlled research studies have not supported the claims of visual skills training. Alternatively, sports science research has focused on developing athletes visual-perceptual qualities. This approach has proven more fruitful with research suggesting that pattern recognition and anticipation may be trained to alleviate some of the time constraints of fast-ball Over the last decade, athletes have increasingly embraced the wearing of sunglasses, yet this area has received little empirical research by optometrists or sports scientists. In particular, competitors in fast-ball sports, such as cricket and tennis, have reported anecdotally the benefits of wearing sunglasses to reduce direct sunlight and glare while competing. Reducing glare is thought to aid sports performance because the ball is seen more clearly. Another hypothesised but currently untested benefit of reducing glare is the elimination or reduction of squinting and subsequent loss of concentration through visual fatigue. The ability to see clearly and without undue effort is only one aspect of visual performance. However, the ability to understand and interpret visual information is paramount. While wearing sunglasses has obvious protective benefits for the eye by reducing exposure to W rays, the issue of direct sports performance improvement is unsubstantiated. Interestingly, many athletes who have competed while wearing sunglasses report that some sunglasses may actually hamper their performance, if all objects are tinted with the same colour, making it more difficult to distinguish a moving ball from its background. More specifically, visual qualities such as visual acuity and contrast sensitivity may be red~ced.~ In response to these concerns, sunglass manufacturers have developed sunglasses they claim are more suitable for sports performance. Despite the increased release of sports specific sunglasses by the manufacturers, the direct effect of sunglasses on sports performance remains equivocal. In fact, there is a paucity of research addressing this issue. What has been investigated is the effect of various sunglass lenses on specific visual capacities. Boll6 lo reports the existence of two fundamental types of sunglass technologies: 1. neutral density filters (NDFs) 2. tinted or coloured filters. NDFs attenuate all wavelengths in the visible spectrum to the same extent. Boll6 claims that the resultant perceived response of such a lens is reduced light intensity that causes a loss in colour discrimination, although this point is questionable. The spectral transmission peaks of some simple tinted or colour filter sunglasses may in some conditions reduce the colour contrast between the ball and its background and therefore increase the difficulty in differentiating them. Teikari and Lindstromy found that visual acuity of participants decreased when sunglasses were worn. Interestingly, the level of visual acuity (VA) altered depending on the colour of the lenses. Brown lenses reduced the VA the least, followed by grey lenses, with the mirror lens the most detrimental to VA. It must be noted that testing conditions were a standard indoor examination room with 70 candelas per square metre at the surface of the test plates. The above findings correspond to the verbal reports of some athletes who have found that it is more difficult to distinguish between a moving object and its background when wearing sunglasses. Yellow tinted lenses also have been the source of investigation, as it has been reported frequently that they enhance visual performance, particularly in low visibility conditions. For example, Goldberg and Kelly found that yellow lenses did not enhance visual performance in normal subjects for either detection or discrimination. Similarly, Kelly, Goldberg and Banton found that yellow lenses failed to enhance contrast sensitivity, even though subjects preferred yellow over neutral lenses. In response to the needs of athletes wearing sunglasses while competing, BoW3 has recently released Competivision Technology. Competivision lenses provide a specially adapted, selective op tical filter, supported between the participant s eyes and the object that Boll6 claims is visually enhanced. B0ll6 ~ also claims that unlike existing sunglass technologies, most of which reduce the overall percentage of light transmitted to the eye, lessening the perceived colour contrast between a ball or other selected object and the background, the Competivision lens enhances that contrast with its selective op tical filter. In relation to tennis performance, the Competivision lens is proposed to provide an increase in perceived colour contrast between an optic yellow tennis ball and the background. The result, according to Boll6 s press releasek3 is a true competitive advantage on the court and the ability to improve athletic performance. The research described in this project examined empirically the question of whether the Boll6 Competivision lens designed for tennis players, improves the movement initiation speed and hitting accuracy of tennis players. This directly addresses Boll6 s claims that the Competivision lens will enhance the ability of the human eye to visually perceive a selected object, such as a ball, and therefore the opportunity to improve athletic performance. METHODS Subjects Informed consent was obtained from 20 undergraduate students from the University of Ballarat, ranging in age from 18 years to 21 years (11 males and nine females). The subjects were assigned to one of three groups (novice, intermediate or advanced), based on their skill level as determined by their current playing 227

3 Sports glasses Farrow and Southgatr status in local club tennis. This resulted in six novice players (one male and five females) with little tennis skill and no competitive experience, seven intermediate level players (seven males) who played C or B grade club tennis and seven advanced players (three males and four females) who were playing A grade club tennis. It must be noted that the definition of novice, intermediate and advanced skill level is in relation to the local club tennis competition and not reflective of international tennis standards. Experimental design summary The experimental design was a withinsubjects model. Thirty potential subjects were initially pre-tested on a battery of general visual capacities. This pre-test was used to screen out subjects with undetected visual defects (that is, with belownormal vision). Twenty subjects satisfied the criteria and were subsequently included in the second phase of the experiment. The second phase of the experiment involved all subjects hitting 40 ground strokes with the ball being projected from a Sports Action Machine (SAM). Each participant completed 40 test trials under three different conditions: 1. wearing competivision sunglasses 2. wearing clear lens glasses (used as a placebo to create an expectancy of improved performance) 3. not wearing sunglasses. These conditions were presented to subjects in a counterbalanced order. Vision screening pre-test The purpose of the visual screening was primarily to detect any potential subjects who had uncorrected visual defects or ocular disease. The optometric tests selected were chosen on the basis that they were tests of the visual parameters commonly regarded as important to tennis performance.' The battery of tests was derived primarily from items included in the protocol described by Coffey and Reichow,'' but also included tests commonly used by optometrists in general practice or in sports optometry. Failure to reach a minimum standard in any of the tests resulted in the subject being ineligi- ble for the remainder of the experiment. It was reasoned that given the fine perceptual changes that may occur when using the various lenses, all subjects needed to be free of uncorrected visual defects and be at a known level of visual function. This assisted in creating a relatively homogeneous subject population. The visual attributes screened were refraction, static visual acuity, contrast sensitivity, accommodation, phoria (ocular muscle balance), vergence, depth perception, colour vision and visual reaction time. Materials The testing was conducted at a fully-lit indoor tennis centre on a standard tennis court surrounded by an aluminium grey background. A Sports Action Machine capable of projecting tennis balls in a preprogrammed sequence was positioned on one baseline in the centre of the court. A timing beam was mounted across the mouth of the SAM so that as the ball was projected from the SAM, a time coding unit linking the SAM to a Panasonic videocassette recorder (AG7355) was activated. A Panasonic MS-5 video camera sampling at 50 hz was also attached to the videocassette recorder and was used to record the subject's response. This allowed the resultant video footage to be time coded in seconds so that a frame by frame analysis could be conducted in concert with the subject's response to determine a movement initiation time. A research assistant reset the timer for each trial, after the subject's response had been recorded. Test procedure The test involved the subjects hitting 40 randomly projected new tennis balls from the SAM to either the forehand or backhand side of the court (20 forehands and 20 backhands randomly ordered). The 40 trials were divided into two groups of 20 trials with a two-minute rest period between each set of 20 trials. The SAM was preprogrammed using its menu of options at 'drill 2-baseline, skill leveltournament 1' and an inter-trial interval rate of +2.5 seconds ensuring that all subjects received the same randomised pattern of ground strokes. Subjects were required to stand on a designated point in the middle of the baseline and instructed to respond to the projected balls as they would in a game of tennis. In the 2.5 second delay between trials, the participant was instructed to return to the designated starting point. To control for as many extraneous variables as possible, so that the effect of the lenses could be directly related to the perception of the projected ball, the following constraints were imposed. 1. Subjects were required to wear a personal portable cassette player that played noise of the ball machine (not projecting a ball) so that they were unable to use auditory information as a means of anticipating moment of ball release. 2. Any trial where the participant moved early in anticipation of the intended ball flight was considered a mistrial. The subject's movement initiation time was defined as the subject's first definitive movement initiated in response to the direction of the ball. The visual cue used to determine the first definitive movement was the eversion of the outside heel (that is, movement left characterised by eversion of the right heel) in preparation for a push-off in the direction of the ball. The accuracy of response was also recorded as the ball being hit in to or out of the court. A research assistant marked the accuracy component as the testing was being completed. Treatment conditions Before commencing each sequence under a particular treatment condition, subjects were given the appropriate glasses, if required, for an adjustment period of five minutes. In the final minute of this time subjects hit 10 ground-strokes fed to them by a research assistant as a warm-up. All subjects completed 40 test trials under three treatment conditions in a counterbalanced order. Subjects were required to wait a period of 20 minutes between treatment conditions. The conditions were as follows: 1. Wearing Boll6 Competivision sportglass designed to make an 'optic yellow' tennis ball easier to see. 2. Wearing a Boll6 clear lens that had no 228

4 impact on vision with subjects being told it was designed to improve their tennis performance. Hence, it placed an expectancy of improved performance (placebo). 3. Not wearing sport-glasses. There were two presentation orders of the three treatment conditions (10 subjects followed each order): 1. competivision lens, followed by placebo lens and no glasses 2. no glasses, followed by placebo lens and Competivision lens. Skill level Competivislon lens Clear (placebo) lens No sungiesms Novice 0.31 (SD = 0.03) 0.31 (SD = 0.02) 0.30 (SD = 0.02) Intermediate 0.29 (SO = 0.02) 0.28 (SD = 0.02) 0.28 (SD = 0.02) Advanced 0.30 (SD = 0.02) 0.30 (SD = 0.03) 0.29 (SD = 0.02) Irrespective of skill 0.30 (SD = 0.02) 0.29 (SD = 0.03) 0.29 (SD = 0.02) Table 1. Mean and standard deviation movement initiation times (seconds) for treatment only and as a function of skill level RESULTS Initially a multivariate analysis of variance (MANOVA) was used to determine if the treatment order had a significant effect on the results. The order of treatment was found to be non-significant at the 0.05 level. To examine differences between the three treatments, and between the differing skill levels for the dependent variables of movement initiation time and hitting accuracy, a univariate repeated measures formulation was employed. The alpha level of 0.05 was set for all statistical analyses. Sklll level Competivlrion lens Clear (placebo) lens No sunglassos Novice 15.8 (SD = 9.75) 15.6 (SD = 9.96) 15.6 (SD = 8.90) Intermediate (SO = 5.94) (SD = 5.68) (SD = 4.07) Advanced (SD = 5.05) (SO = 6.20) (SD = 4.48) Irrespective of skill (SD = 7.78) (SD = 9.91) (SD =.41) Table 2. Mean and standard deviation hitting accuracy scores out of 40 for treatment only and as a function of skill level Movement initiation time The mean movement initiation times and standard deviations for each treatment condition are displayed (Table 1) both as a function of treatment only and relative to each skill level group. Analysis revealed that there was no significant effect in relation to the type of lens used (F = (2, 34) = 0.698, P = 0.50), the case when the skill level of the participant was considered (F = (2, 17) = 1.961, P = 0.17). There was also no significant interaction between any of the treatment conditions and skill level of the subjects (F = (4, 34) = 0.219, P = 0.93). This result demonstrates that the Competivision lens does not result in superior movement initiation times when compared with a clear lens (placebo) or no glasses at all, irrespective of the skill level of the participant. Hitting accuracy The mean hitting accuracy scores and standard deviations for each treatment condition are displayed (Table 2) both as a function of treatment only and relative to each skill level group. In accordance with movement initiation time findings, analysis revealed that there was no significant effect in relation to the type of lens used (F = (2, 34) = 0.229, P = 0.80). However, there was a significant difference between the skill groups in relation to hitting accuracy irrespective of treatment condition (F = (2, 17) = 6.086, P = 0.01). A repeated contrast model was used to identify individual effects and it demonstrated that there was a significant difference in hitting accuracy of both the advanced and intermediate skill groups relative to the novice skill group (F = (2, 34) = 9.345, P = 0.01). This is not surprising given the background experience levels of the respective groups. Finally, there was no significant interaction between any of the treatment conditions and skill level of the subjects (F = (4, 34) = 0.353, P = 0.84). These results demonstrate that the Competivision lens does not result in improved hitting accuracy, when compared with a clear lens (placebo) or no glasses at all, irrespective of the skill level of the participant. DISCUSSION Despite an increasing number of athletes competing in sunglasses and manufacturers producing sports specific sunglasses, the direct effect of sunglasses on sports performance in a natural setting has not been investigated previously. The primary aim of this research was to determine the effect of BollC s Competivision lens on tennis performance and in particular on the movement initiation time and hitting accuracy across a variety of tennis playing skill levels. Despite sufficient statistical power (in excess of 0.80) to test the main hypothesis, there were no significant differences between any of the treatment conditions for movement initiation time or hitting accuracy. There was no significant difference between the various skill groups for movement initiation time. 229

5 However, there was a significant difference in hitting accuracy between the skill levels, with the advanced or intermediate skill groups being more accurate than the novices, but this difference was independent of treatment condition. Despite a lack of significant interaction between the treatment conditions and skill groups, further research is required to establish more clearly whether the impact of the various lenses transfers across skill groups due to the small number of subjects within each skill level. A number of factors will be highlighted as possible reasons for the non-significant findings pertaining to the treatment conditions. The strongest argument for the lack of differences between the various lenses may relate to the extent that fast-ball sport performers actually observe the ball. A number of researchers investigating the sports of baseball, tennis and table-tennis found players did not see the ball striking the implement. 17 A number of reasons have been proposed to explain this occurrence. First, the ball travels at a velocity greater than is physiologically possible for the eye to continually track the flight of the ball. More importantly, research has demonstrated that pre-ball flight cues such as postural cues of the opponent (trunk, racquet arm angle et cetera) and probability information (opponent preferences, game score et cetera) also provide a large source of anticipatory cues for tennis players., 8 Indeed, examination of the time available for a tennis player to plan and execute a response reveals that there is insufficient time to wait for the ball s flight to use it as anticipatory information.ig Therefore, is not surprising that the Competivision lens did not contribute to the acceleration or refinement of the perceptual processes of tennis players. The importance of pre-ball flight cues on tennis performance is highlighted by the lack of difference between the skill groups present in the study. Despite being at relatively disparate levels of skill and competitive experience when actually playing tennis (particularly the novice subjects compared to the intermediate and advanced players), the advanced and intermediate players demonstrated no sig- nificant advantage over novices in respect of movement initiation time. It is logical to suggest that the lack of postural cues available to the more advanced players rendered their response to the ball as purely reactive like the other skill groups. This was a necessary design intervention to ensure that any changes in performance between the various treatments could be solely attributed to a change in lens and not some other extraneous variable. The significantly better hitting accuracy of the advanced and intermediate skill groups relative to the novice group can be explained by basic stroke mechanics. The novice group had little previous hitting experience and therefore their stroke patterns were significantly less reliable than the other two groups, resulting in their lower accuracy scores (Table 2). Despite the perceptual-motor limitations cited above as primary reasons for the lack of any significant performance advantages, it is worth examining the results of the subjects when wearing the Competivision lenses as opposed to either the placebo lens or no glasses at all. As highlighted by the mean scores for the three conditions, there was no difference in performance. While this demonstrated that the Competivision lens did not directly enhance sports performance, it does support the contention that performance was not degraded. As previously reported, some sunglasses available to sports performers may degrade colour discrimination and contrast sensitivity. Lenses that reduce light intensity by tinting all objects with the same colour or hue, typically cause the degradation of these two visual parameters. In performance terms, this makes it difficult for a performer to distinguish the ball from the background. Competivision lenses may enable an athlete to see the ball more clearly in conditions reflective of the current testing situation. Indirectly, a reduction in the likelihood of visual fatigue may result if players are wearing sunglasses that do not negatively impact playing performance but reduce the need to squint for prolonged periods. As the research was conducted in a field setting, a number of methodological fac- tors may have impacted on the results of the study. First, the testing venue was indoors and required artificial lighting. Although the court was well lit with indoor lighting and roof skylights, the conditions were not exactly the same as outdoors. Despite this limitation, an indoor venue was deemed necessary because the outside weather conditions at the time of testing were too variable in terms of wind, rain, cloud cover and sunlight. Secondly, in an attempt to examine the specific issue of performance enhancement, the lenses were not directly tested in relation to their impact on colour contrast in a clinical setting. This information would have assisted in identifying the specific source of the advantage (if any) of wearing the Competivision lens. For example, if colour contrast is enhanced in a clinical setting by wearing Competivision lenses, yet concurrent improvements in sports performance are not evident, the issue of whether colour contrast enhancement transfers to the sporting environment is more clearly addressed. In conclusion, when considering the effect of lens tints on colour contrast, great care must be taken in generalising from results obtained under specific testing circumstances. Whether a particular tint enhances or degrades colour contrast depends on a number of variables. They include the colours of the object of interest, the background and the ambient lighting, and possibly even the receptor characteristics of individuals performing under those specific conditions. CONCLUSION Typically, research investigating the effect of sunglasses is based on measures of visual performance in a laboratory setting. In contrast, the current study examined the direct impact that sports specific sunglasses have on sports performance in a natural setting. Results demonstrate no direct sports performance advantage for athletes wearing the Boll6 Competivision lens, relative to wearing a clear lens with the expectancy of improved performance or playing without glasses at all. However, it is not possible to infer from the results 230

6 of this study that the Competivision lens will or will not provide an improvement or reduction of colour contrast, and therefore potentially sports performance, in circumstances different from those in which the current investigation was conducted. It is hoped that this initial investigation of the Competivision lens on tennis performance will prove to be a stimulus for more refined and extensive research into the efficacy of sport-glasses on sports performance in a natural setting. ACKNOWLEDGEMENT The authors wish to thank the following for their support in the administration of the experiment and analysis of the videotapes: Grant Duthie, Josh Ebbels, Bridgette Galler, Samantha Hickman, Ray James, Kate Jarvis, Katie Morgan and Paula Ransom. Rod Hall and Haisam Askari gave the technical and computing assistance. Bill Bass Optical (Boll6-Australia) provided the sunglasses and technical reports. A full description of the visual tests can be obtained by contacting the author. REFERENCES 1. Gavrisky VS. The colours and colour vision in sport. J Sports Med Phys Fitness 1969; 9: Abernethy B, Burgess-Limerick R. Visual information for the timing of skilled movements: A review. In: Summers J, ed. Approaches to the Study of Motor Control and Learning. Amsterdam: Elsevier Science Pub lishers BV, 1992: Wood J, Abernethy B. An assessment of the efficacy of sports vision training programs. Optom Vision Sci 1997; 74: Singer RN, Cauraugh JH, Chen D, Steinberg GM, Frehlich SG. Visual search, anticipation, and reactive comparisons between highly-skilled and beginning tennis players. JApp Sports Psychol 1996; 8: Starkes JL. Skill in field hockey: The nature of the cognitive advantage. J Sport Psychol 1987; 9: Revien L. Eyerobics (videotape). Great Neck, Ny: Visual Skills Inc, Farrow D, Chivers P, Hardingham C, Sachse S. The effect of video-based perceptual training on the tennis return of serve. IntJ Sports Psychol 1998; 23: Starkes JL, Lindley S. Can we hasten expertise by video simulations? Quest 1994; 46: Teikari JM, Lindstrom M. Visual acuity, contrast sensitivity and light transmission with the use of sunglasses. IntJSports Vzs 1995; 2: BollC. Competivision Program. Technical Report, Goldberg OD, Kelly S. The effect of yellow tinted lenses upon face detection and discrimination. Paper presented at the annual meeting of the American Academy of Optometry, Philadelphia, Pennsylvania, December, Kelly S, Goldberg SE, Banton, TA. Effect of yellow-tinted lenses on contrast sensitivity. AmerJOptom Phys Optics 1984; 61: Boll6. Competivision by Bollk. Press Release, Coffey B, Reichow AW. Visual performance enhancement in sports optometry. In: Loran DFC, MacEwan CJ, eds. Sports Vision. Oxford: Butterworth-Heinemann, 1995: Hubbard AW, Seng CN. Visual movements of batters. Res Quart 1954; 25: Moen S. Visual skills: Watch the ball? Strutegies 1989; June: Ripoll H, Fleurance P. What does keeping one s eye on the ball mean? Ergonomics 1988; 31: Buckolz E, Prapavesis H, Fairs J. Advance cues and their use in predicting tennis passing shots. Can JSports Sci 1988; 13: Abernethy B, Russell DG. Skill in tennis: Considerations for talent identification and skill development. AustJSports Sci 1983; 3: Author s address: Damien Farrow School of Human Movement Studies University of Queensland St Lucia QLD 4072 AUSTRALIA 231