Balance Improvement: Club-Head Velocity Improvement with Custom Orthotics
Effects of Orthotic Intervention and Nine Holes of Simulated Golf on Club-Head Velocity in Experienced Golfers
David E. Stude, DC, and Jeff Gullickson, DC
The scientific literature supports the premise that the function of one body region influences the performance of another, that structural changes in one region of the body can promote compensatory changes in another1-4 and that the human body functions as a whole unit rather than functioning regionally.5-8 In addition, there are studies that demonstrate the global effects of such regional influences.9, 10
Because the spine and lower extremity represent a closed kinetic chain in the upright posture, there is considerable potential for the foundation (i.e., foot and ankle) to influence the function of other regions. There is also evidence to show that shoe selection affects balance performance11-13 and may be very important in reducing the likelihood of overuse injuries, minimizing performance loss from fatigue and impact force from heel strike14 and potentially increasing sports performance capabilities.
In golfers, the foundation upon which the foot rests (i.e outer, inner and mid-sole and heel counter) has a greater impact on lower extremity biomechanics, and overall performance than the upper construction of the shoe.15 Williams and Cavanagh recommend golf shoe design modifications and the use of custom orthotics orthotics to address unique individual differences.16
One performance element that has not received significant attention in the literature is proprioception. Disturbances in the proprioceptive feedback mechanism may cause functional disability.17-20 For example, Leanderson et al. demonstrated an impairment of postural stability in ballet dancers that lasted several weeks after an injury.21 Appropriate rehabilitation improved postural stability that was maintained after professional dancing was resumed. Similar changes have also been documented in basketball players.22 Furthermore, Forkin et al demonstrated a positive relationship between balance training protocols and enhanced proprioception in gymnasts with unilateral ankle sprains.23 This was also supported by Wester et al using åwobble board training after partial sprains of the lateral ligaments of the ankle.24 Proprioception, measured by unilateral postural sway, can be artificially enhanced with the use of an Aircast stirrup in subjects with no history of chronic ankle injuries.25 The use of a knee brace resulted in more consistent tracking of the lower limb when subjects were measured in the seated position on a fixed lower limb dynamometer. This suggests that alterations in proprioception as a result of bracing may be partly responsible for the improvement in knee injury statistics reported in some studies.26
Until recently, research had not been conducted to evaluate whether lower limb proprioception training could be of benefit to those without a history of injury. More recently, Hoffman and Payne investigated the effects of using a Biomechanical Ankle Platform System (BAPS) -- a balance board training device -- on proprioceptive status in 28 healthy subjects.27 The training protocol significantly decreased postural sway in both the sagittal and coronal directions, which suggests a potential reduction in injury occurrence.
Golf is a sport often enjoyed by many members of the senior population. However, several studies have shown a greater risk of falling – and therefore, a greater likelihood of injury -- in this population because of instability.28-30 There have also been many studies demonstrating methods for enhancing balance performance in the senior population.31-35 These studies suggest that loss of balance control occurs gradually and progressively over time, possibly beginning during middle age, and that there may be more than one intervention capable of enhancing proprioception or reducing the speed with which loss of balance occurs. Protocols to objectively measure proprioception and balance parameters have been shown to be reliable and valid in most instances.36-40
Taunton et al demonstrated positive outcomes when introducing a nonsurgical, comprehensive, case-management plan for runners afflicted by cumulative trauma injuries to the knee.41 One of the treatment regimens included in this study was the use of custom-made orthotics. Eng and Pierrynowski demonstrated that flexible orthotics can be an effective intervention for patients with patellofemoral pain syndrome.42 In addition to the use of specific exercise protocols, orthotics can also be used as one element of reducing postural sway.43 According to Baycroft. evidence suggests that the use of custom orthotic devices could be beneficial in the treatment of somatic dysfunctions of the lower limb.44 McCulloch et al showed that, while walking with orthotics, there was a significant decrease in the degree of pronation throughout stance as well as an increase in duration of stance time as measured from heel strike to heel rise.45 Tamara and Burdett showed a statistically significant increase in the active phase of the tibialis anterior muscle after heel strike of subjects wearing custom-fit orthotics, which suggests that more than just local benefits are associated with this form of intervention.46
As described previously, there is evidence to suggest that one region of the body can influence others, either through a positive action or a negative compensatory action. Shoe design can influence lower extremity kinematics and whole body performance.11-14 However, modification of shoe design alone may be inadequate to address unique individual differences.
One assumption made in our study is that no standard manufactured shoe can accommodate individual differences. This is especially true considering the potential benefits of enhanced proprioception in reducing the likelihood for injury.47, 48 The use of custom orthoses may serve as one element in fulfilling this need. Therefore our study measured the effects of orthotic intervention and nine holes of simulated golf on balance and proprioception in experienced golfers. A custom-made flexible orthotic was selected, based on our assumption that rigid orthotics could inhibit normal joint range of motion and potentially produce biomechanical dysfunction.
Materials and Methods
Subject Recruitment: Demographics and Attrition
Potential subjects heard about the study through advertising at the 1995 annual golf exposition held at the Metrodome in the Twin Cities, by word of mouth through students at Northwestern College of Chiropractic (NWCC) and on the “Dr. Golf” radio talk show on AM 1500. Only experienced golfers, some of whom were professional instructors and touring professionals, with a reported handicap of less than 10, were included. This was to minimize a learning curve associated with the golf game and because it was assumed that experienced golfers were more technique consistent. A standard telephone interview script was prepared in advance, and interested subjects were excluded if any of the following criteria were met:
- Use of any form of orthotic within the past 2 years;
- Allopathic health care within the 12 months before participating in the study;
- Chiropractic health care within the 6 months before participating in the study;
- Current presence of back, knee, shoulder or wrist pain;
- History of stroke, heart attack or angina;
- A handicap (subjectively reported) greater than or equal to 10.
Of the 12 subjects (11 men and one woman) tested on the first day, nine were able to return for subsequent data collection 2 months later. One was unable to return because of an out-of-state golf tournament, one because of an acute fracture and the last because of a job conflict.
All subjects were required to sign a consent form before data collection. Subjects were informed that the study would be examining the biomechanics of golf performance. This study was approved by the Human Subjects Committee on the campus of NWCC.
Subjects were tested using the Cybex FASTEX (Functional Assessment System for Testing and Exercise) (Ronkonkoma, Long Island, New York) which offers a variety of testing options, such as proprioception, balance and center of gravity. Force platforms measure oscillations applied by the subject (i.e. subtle shifts in weight-bearing) through piezoelectric film sensors located within the platforms.
The platform sensors are connected to a computer with a software program that translates this information into quantitative data. Of the many objective testing parameters available with this instrumentation, we chose stabilization index and stabilization time as the primary outcomes for this study. The double-leg static balance protocol (DLSB) was chosen because it reflects the balance parameters associated with the typical golf stance. Protocols with and without visual acuity, as well as single-leg static balance (SLSB) and single-leg forward hop (SLFH) protocols, were included, because of the assumption that it would be necessary to challenge human performance skills beyond those required for golf to test the relative effects of orthotic intervention.
All subjects were screened with a health questionnaire to decrease the likelihood that the physiological demands of the tests exceeded the subject’s musculoskeletal or cardiovascular capabilities. A standard written communication template was devised by the head technician to be used with all subjects to insure consistency.
The objective measurement of both the DLSB and SLSB reflected stabilization index, or mean oscillations per unit time.
Each subject was instructed to stand in the center of one platform with the feet shoulder-width apart and knees slightly flexed. They were to focus on a marker on the wall in front of them, approximately 5 feet from the floor. Subjects were instructed to remain as stable as possible for the duration of the 30-second test. The test administrator verbally commanded the subject to “begin.” A computer-generated tone indicated when the test was complete. A minimum of two tests were conducted. The coefficient of variation was used to determine whether a third test was required. The DLSB maneuver was performed with and without visual input (i.e. eyes open and eyes closed).
This protocol was conducted in a similar manner to DLSB, except right and left limbs were tested separately. The dominant limb was always tested first (all subjects in this study were right-side dominant). To test the right leg, subjects were instructed to stand in the center of one platform on the right leg only, with the supporting knee slightly flexed and the other positioned with the knee flexed and the thigh perpendicular to the floor (i.e. vertical). Instructions for knee flexion were approximately the same for all subjects. Test instructions, duration, options and number of tests remained the same as described previously. This SLSB maneuver was repeated with each leg serving as the supporting limb and was used with and without visual input (i.e. eyes open and eyes closed).
Linear reaction/stabilization hop, forward movement (also SLFH)
This maneuver objectively measured stabilization time. The objective was to complete the hop set in minimum time. The test set consisted of three single-leg hops in a straight line across a designated group of platforms. The subject hopped to the next platform in response to an audio cue, and attempted to reach a preset threshold of minimal stability as quickly as possible. Once this threshold was detected by the computer, subsequent cues to advance were given. Upon completion of the test set, the data was displayed and stored. Retests were performed if, according to the data, the subject failed to reach the minimal stability threshold. This SLFH protocol was repeated with the left leg serving as the supporting limb.
Nine Holes of Simulated Golf
Our rationale for requiring subjects to participate in nine holes of simulated golf was to reproduce a fatigue factor that one would typically experience on the golf course. In addition, there were times when subjects were required to wait for those ahead of them, which reflected real course situations.
Average distances and level of challenge for various courses in the Minneapolis-St. Paul area were assessed and an on-campus simulated golf course was established to reflect these average values. Each subject was required to carry their own bag and wear turf-type golf shoes or golf shoes with the spikes removed. The quantity and type of clubs and the quantity of balls (six) that subjects were allowed to carry in their bags was consistent among all subjects. The only variation allowed was the composition of specific clubs (shaft material, etc.) and the size of the bag. This was done so that subjects would be allowed to carry the bag and clubs they were already accustomed to using.
Each hole was assigned a specific par and total distance value in yards from white and red tees (Table 1). This provided different distances for males vs. female subjects, and may have influenced club selection. Male subjects used the white tees and the female subject used the red tees. Subjects were given a distance for each shot (consistent with each subject based on gender), they were allowed to choose the club they would typically use for the specific scenario provided and they were limited to the same number of strokes (i.e. same relative work load) for each hole.
Supervisors were assigned to individual subjects or groups of subjects (maximum of four subjects per group) and assumed responsibility for subject compliance throughout the entire nine holes of simulated golf. The supervisors also completed a comprehensive checklist, with data entered on every hole, to ensure compliance. Please refer to Figure 1 for a portion of the flow chart and checklist.
The orthotics used in this study were manufactured by Foot Levelers, Inc. (Roanoke, Va.), and consisted of two specific styles, a full-length design for use in recreational shoes and a three-quarter length design for use in dress and/or oxford style shoes. The men received a pair of full length FirmFlex Plus and a pair of Sir Energy Plus. The woman received a pair of full length FirmFlex Plus and a pair of Ms. Energy Plus. These orthotics were manufactured from multiple layers of functional materials, including Zorbacel inserted into the heel for shock attenuation.
Weight-Bearing Casting Procedure
The weight-bearing casting procedure was completed on the first day of data collection by a chiropractic physician and certified orthotic technician. The casting procedure followed the manufacturer’s protocol.
Timeframe and Wear Protocol
Subjects were cast for their custom-made, flexible orthotics on November 30, 1995. They returned to NWCC to receive the orthotics two weeks later with verbal and written instructions per manufacturer guidelines. After wearing the orthotics daily for 6 weeks, subjects were retested while wearing them on Jan. 25, 1996 (two months after initial data collection) (Figure 2).
Compliance and Subjective Feedback
All subjects were contacted by telephone between the first and last day of data collection to promote wear compliance. On the second day of data collection, each subject completed an Orthotic Fit and Initial Response Questionnaire to provide feedback regarding their experience with the orthotics.
The data were analyzed using a paired t test, controlling for individual characteristics and modeling the effect of treatment, before and after nine holes of simulated golf and before and after orthotic intervention. The paired t statistic assessed each subject’s change from pre to post-test and indicates whether the overall average change for all subject is greater than zero. The t statistic used is the quotient of the mean change over all subjects, divided by the standard error of that mean difference. The t value, if large enough, indicates that the average change for the subjects is significantly greater than zero, the value that would normally have been expected by chance. In addition, a mathematical correction was made, (Bonferroni T Procedure; also known as Dun's multiple comparison procedure) for the number of statistical tests conducted in this research study.49 This strategy was introduced to decrease the likelihood that a result would seem to be statistically significant when in fact, it may have been due only to chance. Because the number of statistical group comparisons was 32, the usual significance criterion for a single test, p < .05, was divided by 32. As a result, the new threshold for reaching statistical significance became a more conservative p < .002. Statistical analysis was performed by establishing a preliminary data set with Alpha 4, and then conducting mean and group calculations with the SPSS statistical software (SPSS, Chicago. IL).
Table 2 summarizes the mean values and standard deviations obtained for all objective evaluations performed in this study. Although not universally consistent, reading the mean values horizontally from left to right demonstrates a relative and progressive decrease in both quantified proprioception (measured as number of oscillations per unit time) and stabilization time (time required to reach pre-established threshold, in seconds). These trends reflect the presence of several patterns.
First, the effect of fatigue associated with nine hoIes of golf seemed to be minimal regardless of orthotic usage. In some instances, proprioception actually improved after the completion of nine holes of golf, with or without the use of orthotics. However, the differences in balance and proprioception before and after nine holes of golf were less when orthotics were worn than when orthotics were not worn. When comparing data between the right and left single-leg static stance protocol (eyes open) balance was better when subjects were tested on the left/nondominant side.
When measured after completing nine holes of golf, without the use of orthotics, balance ability on the dominant side improved, whereas that on the nondominant side worsened. Balance ability improved after nine holes of simulated golf, when comparing these same values for the same measurement, after orthotics had been used for 6 weeks. The difference in balance ability between the right and left sides was also less. The observation was also present when measuring proprioception without the assistance of visual input (eyes closed). The data reveals that proprioception on the nondominant side is better than on the dominant side (significant even with the use of Bonferroni's correction), before using orthotic intervention. After the use of orthotics for 6 weeks, however, there is no apparent difference between the right and left sides.
One of the most important project questions was to address changes identified in golfers tested without the use of orthotics compared with the effects measured after having worn the custom-made, flexible orthotics for 6 weeks. The data showed that proprioception was significantly enhanced (p < .001) when golfers were tested before completing nine holes of simulated golf and after having worn their custom-made, flexible orthotics on a daily basis for 6 weeks. This difference was measured when subjects assumed a double-leg stance and were tested with their eyes closed (i.e., proprioception was tested instead of balance ability). Although the double-leg stance did not seem to be influenced by fatigue, the use of single-leg protocols did suggest significant difference. Data shows a reduction in balance ability when orthotics were not worn. The differences observed before and after golf are less with when orthotics were worn compared with when orthotics were not worn. Data illustrates an increase in proprioceptive ability after completing nine holes of simulated golf, when orthotics were used.
The data suggests that proprioception worsens without the assistance of visual input. The effects of fatigue associated with nine holes of golf and the use of orthotics for 6 weeks did not seem to influence this pattern (Table 2). SLFH maneuvers were used to accentuate the possible presence of balance deficits within experienced golfers. Although not statistically significant, mean values suggest that orthotic intervention reduces the mean stabilization time for the right and left side. This pattern did not seem to be influenced by fatigue associated with nine holes of golf. When testing subjects assuming a posture most parallel to the classic golf stance (double-leg. eyes open). Mean stabilization index was better after orthotics had been worn for the 6 week period. This pattern was consistent with or without the fatigue associated with nine holes of simulated golf.
The data outlined in Table 2 suggests that proprioceptive ability improves after orthotic intervention. However, this trend was inconsistent, demonstrated by the observation that some subjects had improved proprioceptive ability after the completion of nine holes of simulated golf. This inconsistency may have been caused in part by the possible presence of a learning curve independent of intervention and should be accounted for in subsequent studies. The observation that the difference in balance ability between the right and left sides decreased after the use of orthotics for 6 weeks suggests that the use of orthotics assisted in promoting symmetrical balance ability and enhancing proprioceptive symmetry. Orthotics are made to address structural deficiencies such as excessive pronation and arch integrity, in an attempt to minimize differences in structural alignment, and this may be contributory to the changes observed.
Analysis of data from each of the subjects revealed the presence of a very high standard deviation for only one subject. Upon reviewing the survey results after completion of the study, one subject reported that he did not care for the orthotics, whereas all others had very positive experiences. This may correlate with the high standard deviation and the particular subject's excessive variation in oscillations. If the data from this subject were eliminated during the process of statistical analysis, most differences within subjects with orthotics vs. subjects with no orthotics would have been statistically significant. Though extreme data variations from large studies are often eliminated, it was considered appropriate for this study to include all data sets to account for individual variations. Another reason why this unusual data set may be important reflects the possible need to address unique, individual differences, especially one's candidacy for orthotic intervention. The increase in proprioception that was observed after completing nine holes of simulated golf when orthotics were used suggests that the effects of fatigue were reduced with orthotic intervention.
This difference was obtained without the use of visual input and therefore does not reflect a demand consistent with the recreational or elite-level golfer. It was assumed, however, that because individuals are used to relying on visual input, subjects would have to be challenged with higher physical demands to detect measurable differences (i.e., single leg protocols). It was also assumed that even though balance ability may be reasonably good, minimal deficiencies might result in long term performance changes or compensations and, possibly, musculoskeletal symptoms. This may explain the "insidious" onset of back pain commonly observed in golfers.50 As mentioned earlier, some data sets suggest the presence of a learning curve associated with repeat testing.
The reason for this specific observation is not clear, because changes in some parameters were statistically significant. The patterns or (trends observed in this study may be the result of the combined effects of both learning and intervention). The statistical trends observed in this study suggest that it is likely that orthotics play a role in influencing proprioceptive abilities in the population evaluated. However, in addition to orthotic intervention, other variables could be responsible for some of the observed changes. For example, as mentioned above, a learning curve could improve the likelihood for better balance ability. Furthermore, the instrumentation was not tested independently for intra- and interexaminer reliability, so measurement artifact could have played a role in data generation. One assumption made in this study was that the data generation capabilities for the Cybex Fastex would be consistent, even though construct validity had not been previously established. A power calculation was not conducted because of the relatively small sample size. but conservative measures were introduced, as described in the Statistical Analysis section, to arrive at appropriate p threshold values.
The data trends associated with the use of these specific, custom-made, flexible orthotics suggest a positive influence on balance, proprioception and proprioceptive symmetry in a small population of experienced golfers. This influence seemed to be most strongly correlated with measured changes in proprioception, compared with general balance ability. However, the effect of fatigue on proprioception was less consistent. Improvement of proprioceptive fonction may potentially enhance performance ability and influence injury potential.51
We thank Drs. Jeff Gullickson and Andrew Klein for coordinating the logistics associated with nine holes of simulated golf; the Cybex corporation for the PASTEX instrumentation used in this study: and Scott Morrow and Kevin Hardesty for serving as measurement technicians. Thanks to Dr. William M. Austin for serving as the orthotic fit specialist and to Foot Levelers, Inc. for supplying casting materials and laboratory technician assistance fur this study. Thanks also to Dr. David Gabrielson, to Northwestern College of Chiropractic for supporting the working environment necessary to complete this study, and to Jim Hulbert. Ph.D., for serving as biostatisocian. Thanks to MaryAnna Hanson for providing computer software support for, the development of tables and graphs. Thanks to Drs. Terry Yochum, Tom Bergmann, Timothy Mick and Becky Mjoen for serving as editorial review consultants. Special thanks to the students at NWCC for their volunteer efforts in supporting this project, and to Ron Way and Dr. Golf.
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