CARL L. HIGHGENBOTEN,* MD, ALLEN JACKSON, EdD, NEIL MESKE,* MS, AND JIMMY SMITH, MS. reported that selected knee braces cause decreases in speed

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1 The effects of knee brace wear on perceptual and metabolic variables during horizontal treadmill running CARL L. HIGHGENBOTEN,* MD, ALLEN JACKSON, EdD, NEIL MESKE,* MS, AND JIMMY SMITH, MS From the * Orthopaedic Consultants, Dallas, Texas, and the University of North Texas, Denton, Texas ABSTRACT Past research has indicated that runners who wear a Lenox Hill Derotation Brace during treadmill running at 6 mph have an approximate 5% increase in oxygen consumption compared to those who run without the brace. The present study expanded those findings by determining the metabolic and perceptual effects of wearing four commercially available braces while treadmill running at speeds of 6, 7, and 8 mph. The four braces used in this study were the Generation II Poli- Axial Knee Cage, the Orthotech Performer, the CTi Brace, and the Lenox Hill Derotation Brace. Results indicated that the braces caused increases (P < 0.008) in oxygen consumption, heart rate, and ventilation in the 3% to 8% range compared to running without the brace. Peripheral ratings of perceived exertion were also elevated (P < 0.001) between 9% and 13%. However, no significant differences were found between the braces. Analysis of covariance indicated the weight of the brace accounted for the increased oxygen consumption during the treadmill runs. We concluded that the braces examined in this study will cause a consistent increase in metabolic cost, which is related to the weight of the braces. Commercially available knee braces are often prescribed to provide stability to knee joints that have sustained ACL injury. Research with these braces has primarily involved determining the biomechanical changes that occur as the result of wearing the braces.6, Several researchers have t Address correspondence and reprint requests to: Carl L Highgenboten, MD, Orthopaedic Consultants, Building C, Suite 106, 7777 Forest Lane, Dallas, TX reported that selected knee braces cause decreases in speed and muscular strength.5, Zetterlund et al.1o investigated the physiologic responses to horizontal treadmill running while wearing a Lenox Hill Derotation Brace. They reported increased oxygen consumption and heart rate while running with the brace as compared to running without a brace. They found no differences in stride length between the running conditions and indicated that the weight of the brace was a principal contributor to the difference in physiologic response. The purpose of the present investigation was to expand the findings of the Zetterlund et al. study. We examined the effects of four commercially available knee braces on oxygen consumption and related physiologic variables of subjects during treadmill running. These effects were determined across three horizontal running speeds of 6, 7, and 8 mph. METHODS Subjects Fourteen male subjects formed the sample of the study. Their ages ranged from 18 to 35 years and their average weight and height were 64.7 kg and cm, respectively. They were all involved in either jogging programs or competitive distance running and were asymptomatic regarding any ankle, knee, leg, or hip injury or abnormality. All subjects were given an explanation of the study and signed an informed consent. Braces and fit The four commercial braces selected for use in this study were the Generation II Poli-Axial Knee Cage (Generation II Orthotics Inc, Orange, CA), the Orthotech Performer (Orthopedic Technology, Inc, San Leandro, CA), the CTi

2 640 Brace (Innovation Sports, Irvine, CA), and the Lenox Hill Derotation Brace (Lenox Hill Brace Inc., Long Island City, NY). Each brace has its specific design characteristics, but the purpose of their use is basically identical-to provide stability to the knee joint while allowing functional mobility. This is accomplished by preventing excessive lateral movement and limiting hyperextension and rotation. All subjects were custom-fitted for each brace according to procedures established by the brace s vendor. All braces were purchased from the vendors. Each subject was given his braces on an individual basis. During this session, appropriate fit was confirmed and instruction in correct wearing procedures were provided. All subjects went through a 3 week adjustment period with the braces. During this time they did a progressive walking to jogging program to develop familiarity with wearing the braces and to demonstrate any problems in proper fit. Submaximal treadmill run tests The subjects performed six submaximal treadmill runs on a motor driven treadmill. Each run was completed on a different day and all runs were completed within a 2 week time period. Each subject ran for 5 minutes at 6 mph, 5 minutes at 7 mph, and 5 minutes at 8 mph. The first run for all subjects was a familiarization trial, so that the subjects could become adjusted to treadmill running, the specific running program, and the metabolic measurement process. The remaining five trials required the subjects to run either without a brace or with each one of the different braces. These experimental trials were accomplished in a randomized order to prevent order effects in the data. Dependent variable measurement A Sensormedics Metabolic Measurement Cart, Model 4400 (Sensormedics, Anaheim, CA) was used to measure oxygen consumption in liters per minute (L02) and in milliliters per kilogram per minute (M02), and ventilation in liters per minute (Ve). Heart rate (HR) was recorded in beats per minute using a three-lead electrocardiogram from Quinton Instruments (Seattle, WA). Average values were recorded for 3, 4, and 5 minutes at each speed of 6, 7, and 8 mph for the metabolic variables. Ratings of perceived exertion (RPE) using Borg s scale were taken at the of the end of the 5 minutes at each running speed and ratings were elicited for overall, central, and peripheral exertion. Prior to the exercise trials, the subjects were given a description and explanation of the scale and its use during the run. During the running test, the subject indicated his RPE response by acknowledging the correct score when pointed to by a test administrator. Data analysis Data were analyzed using the following procedures: 1. A one-factor repeated measures analysis of variance (ANOVA) was used to determine if significant differences existed for L02 across Minutes 3, 4, and 5 of each stage of running speed for all run trials.9 A separate ANOVA was conducted for each experimental condition. This analysis was performed to verify that an aerobic steady-state during each stage of running speed was achieved. The level of significance for the study was established at P < A 5 (brace condition) by 3 (treadmill speed) repeated measures ANOVA was used to determined if significant main and interaction effects existed. A repeated measures analysis of covariance (ANCOVA) was used to examine the effects that brace weight had on metabolic demands. 3. If significant effects were discovered in the brace by speed ANOVA, a series of post hoc symbolic constrasts were used to examine the nature of the main effects. RESULTS A one-factor repeated measures ANOVA was conducted to determine if any significant differences existed for L02 across Minutes 3, 4, and 5 for each running speed and for all-brace and no-brace trials. No significant differences (P > 0.01) were found, and visual inspection of the means indicated steady-state was achieved for all speeds and conditions. Therefore, for all further statistical comparisons, data from the 4th minute of each running speed were used. Tables 1 through 4 present the means and standard deviations for the metabolic data measured during the 4th minute of each running speed and provide the test statistics for the two-factor repeated measures ANOVAs. The two-factor repeated measures ANOVA was conducted for the four metabolic variables L02, M02, Ve, and HR. Significant brace effects (P < 0.008) were found for all four metabolic variables. As expected, the changes in running speed produced significant effects (P < ) for these variables. Finally, a brace by speed interaction was found significant (P < 0.007) for L02. A post hoc analysis was conducted to examine the brace effects. Since four degrees of freedom were available for this factor, four statistical constrasts within the repeated measures ANOVA were analyzed. The only comparison that was TABLE 1 Average oxygen consumption in liters per minutea a Test statistics for brace by treadmill speed ANOVA: Brace F(4, 52) = 4.77, P < Speed F(2, 26) = , P < Brace by speed F(8, 104) = 2.82, P < b GII, Generation II Poli-Axial Knee Cage. c LHB, Lenox Hill Derotation Brace. d CTi, CTi Brace. e OTI, Orthotech Performer.

3 641 TABLE 2 Average oxygen consumption in milliliters per kilogram per minute Brace F(4, 52) = 4.82, P < Speed F(2, 26) = , P < Brace by speed F(8, 104) = 2.62, P > TABLE 3 Average heart rate in beats per minute Brace F(4, 52) = 3.83, P < Speed F(2, 26) = , P < Brace by speed F(8, 104) = 0.67, P > b For explanation of brace abbreviations, refer to footnotes at TABLE 4 Average ventilation in liters per minutea The brace by speed interaction for L02 was characterized by an increasing difference (P < 0.007) between the nobrace trials and the trials of brace wear. Figure 1 shows this interaction. To examine the effects of the weight of the braces on metabolic cost during the runs, a further statistical analysis was conducted. Each individual brace was weighed and the weight was recorded in grams. A covariate was computed, which was the body weight of the individual for the no-brace trial and the body weight plus the weight for the appropriate brace for each brace run. The braces varied in weight because of design (between brace type variability) and size (within brace type variability). A five (brace condition) by three (treadmill speed) ANCOVA with repeated measures and the adjusted weight variable as the covariate was conducted. The dependent variable in this analysis was LO2. There was no significant brace effect or brace by speed interaction while the speed effect was still significant (P < ). The overall, central, and peripheral ratings of perceived exertion were also analyzed with the two-factor repeated measures ANOVA. Findings indicated significant (P < ) speed effects for all three ratings. Post hoc polynomial trend analysis indicated a significant (P < 0.001) linear component while the quadratic was not significant. A significant brace effect (P < ) was present for the peripheral RPE. The statistical constrast between the no-brace run and a combination of the brace runs was significant (P < 0.001). No constrasts between the braces revealed significant differences. The means and standard deviations of the ratings of perceived exertion are provided in Table 5. DISCUSSION Zetterlund et al.l examined the metabolic cost of horizontal treadmill running at 161 m/min or 6 mph under the conditions of no brace wear and wear of a Lenox Hill Derotation Brace. The present study s primary purpose was to expand upon their findings by examining other available knee braces, increased running speeds, and perceptual responses Brace F(4, 52) = 5.62, P < Speed F(2, 26) = , P < Brace by speed F(8, 104) = 1.59, P > significant (P < 0.006) was a contrast between the no brace trials and a combination of all of the braces for the four variables. No statistically significant differences were found between any of the braces for the four variables. A polynomial trend analysis of the speed effect indicated that the linear component was significant (P < 0.001), while the quadratic was not significant for all four metabolic variables. Figure 1. Demonstration of interaction between brace trial and treadmill running speed.

4 642 TABLE 5 Average RPE-Borg s 20 Point Scalea a Test statistics for brace by treadmill speed ANOVA: Central RPE Brace F(4, 52) = 2.19, P > Speed F(2, 26) = 70.16, P < Brace by speed F(8, 104) = 1.01, P > Peripheral RPE Brace F(4, 52) = 6.91, P < Speed F(2, 26) = 93.49, P < Brace by speed F(8, 104) = 1.21, P > Overall RPE Brace F(4, 52) = 6.91, P > Speed F(2,2 6) = 94.84, P < Brace by speed F(8, 104) = 1.97, P > through the use of RPE. The previous report indicated a 5.49% increase in L02 while running with the Lenox Hill Derotation Brace compared to the no-brace trial during the 6th minute of the run.l In the current study, no differences in L02 were found between the brace runs, but the significant brace wear by running speed interaction indicated increasing differences from 3.33% (6 mph) to 5.41% (7 mph) to 6.23% (8 mph). The brace runs produced higher L02, which is in agreement with the past study. This finding is also in agreement with other research that has shown an increase in oxygen consumption when an external weight is added to a working subject.4, The HR increase of 4% because of brace wear in this study was in close agreement with the findings of Zetterlund et al.lo In the Zetterlund et al. study, the authors examined the possibility that the Lenox Hill Derotation Brace caused a stride length change, which would in turn increase L02. However, their results indicated no significant differences and numerically very similar stride lengths between the brace and no-brace trials. They concluded that the weight of the brace was the principal cause of the increased metabolic expense. The ANCOVA used in our study provides evidence that the brace weight is the dominating factor in the metabolic increase while running with the braces. This appears to be true both for individuals who have worn a brace for long periods of time, as in the Zetterlund et al. study, o and for those who have recently adjusted to the braces as was the case for the present study. The RPE results indicate the brace wear trials were providing a specific psychologic cue, as the peripheral RPE followed the metabolic results of the study while the central and overall responses did not. This is interesting since the weight of the braces did cause significantly elevated L02, M02, HR, and Ve, which are central responses. Evidently, the subject s awareness of the brace effected the accuracy of the perceptual response to the exercise. However, this effect was minimal since the RPE response to changes in speed of running were consistent with the increased workload. Based upon equations presented by the American College of Sports Medicine, predicted M02 for these three increasing speeds would be 35.7, 40.95, and ml/kg/min. The subjects of this study had actual M02, which averaged about 5 ml/kg/min less than predicted values. This is an indication of the subject s above-average fitness levels. In comparison to the subjects of Zetterlund et al.,l the present subjects had a decreased M02 of 4.2 ml/kg/min at 6 mph running speed. However, the metabolic cost of brace wear was very similar for both groups, which indicates that individuals of average and above-average fitness levels will respond similarly to the effect of brace wear. Future research should analyze the effects of commercial brace wear on performance in power and speed events. The potential dependent variables in these types of studies should be energy cost of speed or power events, and performance (speed, strength, power) changes. The work of Cook et a1.3 and Tegner et al.~ serve as models for this kind of research. CONCLUSIONS 1. Wearing knee braces produced an elevated metabolic cost of 3% to 6% during steady-state exercise in these asymptomatic subjects. This finding was consistent with past research on subjects who wear braces to provide stability due to ACL injury and repair.lo 2. Wearing knee braces causes a specific peripheral response to ratings of perceived exertion. ACKNOWLEDGMENT The authors thank Humana Hospital-Medical City, Dallas, Texas, for their financial assistance. REFERENCES 1. American College of Sports Medicine: Guidelines for exercise testing and prescription. Philadelphia, Lea & Febiger, 1986, pp 168

5 Borg G: Psychophysical basis of perceived exertion. Med Sci Sports Exerc 14: , Cook FF, Tibone JE, Redfem FC: A dynamic analysis of a functional knee brace for anterior cruciate ligament insufficiency. Am J Sports Med 17: , Graves J, Pollock M, Montain S, et al: The effect of hand-held weights on the physiological responses to walking exercise. Med Sci Sports Exerc 19: , Houston M, Goemans P: Leg muscle performance of athletes with and without knee support braces. Arch Phys Med Rehabil 63 : , Knutzen K, Bates B, Hamill J: Electrogoniometry of post surgical knee bracing in running. Am J Phys Med 62: , Soule R, Goldman R: Energy cost of loads carried on the head, hands, or feet. J Appl Physiol 27: , Tegner Y, Pettersson G, Lysholm J, et al: The effect of derotation braces on knee motion. Acta Orthop Scand 59: , Winer B: Statistical principals in experimental design. New York, McGraw Hill Inc., 1971, pp Zetterlund A, Serfass R, Hunter R: The effect of wearing the complete Lenox Hill Derotation Brace on energy expenditure during horizontal treadmill running at 161 meters per minute. Am J Sports Med 14: 73-76, 1986