Performance of Healthy Braced Participants During Aerobic and Anaerobic Capacity Tasks
Context:
Knee braces were introduced in sports approximately 30 years ago. However, the effects of a functional knee brace (FKB) on aerobic and anaerobic performance after fatigue are unknown.
Objective:
To investigate whether FKB use in noninjured participants hindered performance during aerobic (Léger beep test) and anaerobic (repeated high-intensity shuttle test [RHIST]) tasks.
Design:
Crossover study.
Setting:
Laboratory.
Patients or Other Participants:
Twenty-seven healthy male provincial and national basketball and field hockey athletes (age = 19.4 ± 3.0 years, range, 17–26 years; height = 182.6 ± 6.8 cm, range, 168–196 cm; mass = 80.0 ± 9.1 kg, range, 66–108 kg).
Intervention(s):
Each participant was provided a custom-fitted FKB and performed 5 nonbraced (NBR) testing sessions over 3 days, followed by 5 braced (BR) testing sessions over 3 days, for a total of 17.5 hours of testing per condition. During each testing session, participants performed 1 trial of the Léger beep test and 1 trial of the RHIST in each condition.
Main Outcome Measure(s):
Predicted maximal oxygen consumption (V˙o2max) and time performance measures were recorded for each NBR and BR trial.
Results:
Initial performance levels were lower for BR than NBR for both the Léger beep test (BR = 44.3 mL/kg/min, NBR = 47.3 mL/kg/min; F1,26 = 8.726; P = .007) and the RHIST (BR = 16.5 seconds, NBR = 16.2 seconds; F1,26 = 13.98, P = .001). However, with continued FKB use, the aerobic performance measure remained higher for only the first 2 BR testing sessions (NBR = 46.9 mL/kg/min, BR = 42.4 mL/kg/min; F3.0,79.8 = 4.95, P = .003). For the anaerobic test, no performance difference was noted between the testing conditions (NBR = 16.2 seconds, BR = 16.4 seconds; P = .7), whereas fatigue levels were lower during BR testing sessions (NBR = 33%, BR = 31%). After 14.0 hours of FKB use, performance levels were almost equal between the testing conditions (NBR = 47.6 mL/kg/min, BR = 46.1 mL/kg/min).
Conclusions:
We found an initial decrement in performance when the FKB was used during an aerobic or anaerobic task. However, after 14.0 hours of FKB use, accommodation to the FKB was possible.
Knee injuries are particularly common in collision sports, such as ice hockey and North American football.1–3 In the United States, the estimated total cost for operative treatment and rehabilitation of anterior cruciate ligament (ACL) injuries has reached $2.0 billion per annum.45 This amount does not include the cost of initial evaluation and treatment of injured people who receive nonoperative care and does not include the potential expenses related to future medical treatment.67 Researchers have provided evidence about the long-term risk of developing osteoarthritis associated with an ACL knee injury in soccer for both sexes 12 to 14 years after injury.89
Investigators have addressed numerous risk factors associated with ACL injury.510–23 Although prevention programs have shown some promise, no conclusive evidence has been presented, and widespread disagreement about the effectiveness of these programs remains.24–27
Present knowledge about the effect of functional knee braces (FKBs) has resulted from studies performed on ACL-deficient knees in cadaver and surrogate models28–36 and in humans.3738 These studies showed that FKBs reduce pathologic anterior-posterior laxity associated with the ACL-deficient knee.39–41 According to a 2004 American Academy of Orthopaedic Surgeons42 position statement, “studies designed to test whether functional knee braces protect against the knee ‘giving way’ have demonstrated some beneficial effect of the brace.” Despite the apparent preventive role, players and many authors have perceived knee braces as being cumbersome and hindering athletes' performance,642 especially for highly skilled playing positions.4344 The American Academy of Orthopaedic Surgeons42 concurred with these concerns: “On the negative side, braces might slow an athlete's straight-ahead speed and cause early fatigue to its wearer.” However, several researchers224345–48 have provided limited evidence that FKB use by noninjured athletes might not hinder performance. Nevertheless, researchers have not investigated how FKB use in noninjured athletes restricts performance levels or, if there is hindrance, whether wearers need a period of familiarization or learning. We refer to this relearning process as the adaptation or accommodation phase.
Therefore, the primary purpose of our study was to ascertain whether performance of noninjured participants was hindered while they wore FKBs during aerobic and anaerobic capacity running tests. The secondary purpose was to ascertain whether continued FKB use allowed accommodation to the FKB, thus potentially minimizing concerns about performance hindrance during these tasks.
METHODS
Study Design
Our goal was to ascertain whether accommodation to the FKB was possible. The repeated-measures design allowed potential participants (control and experimental groups) to be matched for performance ability and physiologic performance levels (energy systems) for all tests conducted during all testing sessions (Table 1). If 1 or more participants had inferior or superior performance or functional ability or had greater or lesser developed energy systems, then the results might have been biased. If participants were prescreened for functional or physiologic performance levels (ie, muscle biopsies), then the results might have been prejudiced. In addition, because the FKBs were purchased to eliminate product testing bias, the repeated-measures design allowed cost efficiency; a counterbalanced, randomized study design would have required twice the number of participants and FKBs to ensure adequate study power.
Our independent variables were testing sessions, FKB use, and the accommodation to using an FKB over the testing period. The dependent variable was performance measure: predicted maximal oxygen consumption (V˙o2max) for the aerobic capacity test and time for the anaerobic test.
Participants
A total of 375 noninjured potential participants were contacted through their national or provincial sport, university, or high school athletic directors to volunteer for the study. Participants were excluded if they had sustained a knee ligament or meniscus injury 6 months before testing (n = 51) or had any other lower extremity injury that might hinder performance (n = 114), had reconstructive ligament surgery to either lower extremity (n = 18), or had any identified potential medical conditions or risk factors likely to be exacerbated by exercise (n = 25). All information was verified in consultation with the respective team physician. Of those contacted, 140 were unavailable or did not respond.
Twenty-seven male athletes (age = 19.4 ± 3.0 years, range, 17–26 years; height = 182.6 ± 6.8 cm, range, 168–196 cm; mass = 80.0 ± 9.1 kg, range, 66–108 kg) started and completed the study. All participants provided written informed consent, and the study was approved by the University of Otago Human Ethics Committee and the University of British Columbia Clinical Research Ethics Board.
Casting for Custom Functional Knee Brace
Each participant was custom fitted with an FKB (mass = 0.76 ± 0.10 kg, range, 0.65–0.95 kg; Extreme; Össur, Richmond, BC) on his dominant leg. The participant's dominant leg was defined as the stance or push-off leg during a running jump. Only the dominant leg was braced because Matava et al49 suggested that no correlation exists between dominant or nondominant limb and injury rate.
All participants had their dominant legs casted using Tech-form I casting tape (Össur) while seated with their knees in approximately 10° of flexion. A protective elastic compression sock was applied to the participant's leg for easier removal of the solidified cast. Casting tape was applied approximately 15 cm proximal and distal from the superior and inferior aspects of the patella, respectively, and was allowed to set for 5 to 7 minutes to ensure that the cast solidified. Two layers of casting tape were applied to preserve the integrity of the solidified cast after removal from the participant's limb. When the cast had solidified, a cut was made on its medial side, allowing for optimal cast integrity on the lateral side for accurate brace hinge placement. The cast was numbered and forwarded to the brace manufacturer.
Testing Procedures
Before the first day of testing, floor markers were placed using temporary colored floor tape (model 2070; 3M Canada, London, ON). Participants were divided randomly into 4 groups of 6 or 7 individuals, and the groups were scheduled to start testing at 2-hour intervals. Each group rotated through 6 testing stations during each testing session, and data were collected at each station over the 6 days (11 sessions) of testing (Table 1). To allow for and then evaluate potential accommodation to FKB use, each participant performed 2 testing sessions (total duration = 6.0 to 7.0 h) on days 1 and 2 and 1 session on day 3 for the NBR condition (sessions 1–5) and performed 2 testing sessions on days 4 and 5 and 1 session on day 6 for the BR condition (sessions 7–11). Testing session 6 on day 3 was a rest session for all participants. To ensure that all testing sessions were completed at the same time each day, 5 different gymnasiums with wood playing surfaces were used. In this study, we concentrated on the results from the repeated high-intensity shuttle test (RHIST; fourth testing station) and the Léger beep/multistage test (beep test; last testing station); the results from the remaining tests will be presented in subsequent studies.
Brace Use and Accommodation
After completing the 5 NBR testing sessions (days 1–3) and before the first BR testing session (day 4, session 7), participants were provided their FKBs and brace application guidelines. These guidelines included anatomic landmarks for brace positioning and included tension requirements and application sequence for the brace straps. Participants were given 3 brace application trials with feedback on bracing procedure after each trial. After these 3 trials, participants wore the braces for a 20-minute warmup period and then proceeded to the first test. No additional time was permitted for brace use and accommodation. Participants were instructed not to remove the brace for the entire warmup and testing duration but were allowed to readjust the strap for tension and brace repositioning as needed. After each morning's BR testing session (sessions 7, 9, and 11), participants removed their braces during the 30-minute rest period and reapplied the braces for the afternoon testing session (sessions 8 and 10) according to the morning brace application protocol. Participants then followed the morning 20-minute warmup protocol. At the end of the afternoon sessions, all braces were collected, cleaned, and left to air dry overnight.
Data Collection
Anaerobic Capacity. The RHIST was designed to measure anaerobic capacity and endurance or the ability to recover from high-intensity work bouts.50 It has been validated as an accurate measure of anaerobic capacity and has been used to evaluate anaerobic endurance in high-caliber athletes.51 Data were collected using an electronic timing light system with an accuracy of 0.01 second (Brower ID XS Training System; Brower Timing Systems, Draper, UT) at the end of each 70-m run. The RHIST was the fourth test performed through all testing sessions.
The RHIST consisted of running 6 sprints for a total of 70 m. Participants sprinted to a marker and then back to the start line before sprinting to the next marker. Markers were placed at distances of 5 m, 10 m, and 20 m. A 60-second rest period was provided between sprints. The electronic lights used to collect data at the end of each 70-m run were set at a height of 75 cm. All floor markings remained in place for the entire testing duration, were remeasured before each testing day, and were re-marked when necessary.
Aerobic Capacity. The beep test has been found to be an accurate estimate of aerobic capacity (predicted V˙o2max).5253 In addition, the testing activity is similar to that of many team sports with respect to the stop, start, and change-of-direction movement patterns. In our study, it was the last test performed during each testing session. Predicted V˙o2max was calculated with the following regression equation: y = 5.857x – 19.458, where x is the maximal level attained.53
During the beep test, participants ran continuously between 2 lines that were 20 m apart in time to recorded beeps. The time between recorded beeps decreased each minute (level), and participants exercised at increasing intensities until volitional fatigue occurred. The athletes' scores were the levels and numbers of shuttles reached before they were unable to keep up with the recorded beeps. These data were used to calculate the predicted maximal oxygen consumption. All floor markings remained in place for the entire testing duration, were remeasured before each testing day, and were re-marked when necessary.
Statistical Analysis
A power analysis on the pilot study data (5 participants: 3 women, 2 men) demonstrated that a minimum of 20 participants would be needed for both tests and that the power of the study would be increased in both tests if only 1 sex was tested (Table 2). The statistical power was set to 0.80, and the α level was set at .05.
This study was a 2 × 5 factorial design with repeated-measures analysis of variance (ANOVA) completed on the testing conditions (NBR, BR) and testing sessions (NBR, 1–5; BR, 7–11). The 2 × 5 study design allowed potential participants to be their own controls and, therefore, they were matched for performance ability and physiologic performance levels (energy systems) for the 6 tests conducted during all testing sessions. All 27 participants were familiar with the beep test and the RHIST because their coaches used these tests for team pre-season and in-season physiologic evaluations. The study design and previous familiarization with the tests reduced the performance effect and allowed evaluation for an accommodation effect over the testing sessions. In addition, the test order (NBR followed by BR) allowed continual accommodation to FKB use because an interruption in FKB use could have hindered accommodation progression.
The main outcome measures were predicted V˙o2max (beep test) and time in seconds (RHIST). Participants performed 1890 sprints/trials (beep test, 1 trial × 10 sessions × 27 participants; RHIST, 6 sprints/trials × 10 sessions × 27 participants) over 10 testing sessions in 2 conditions (NBR, BR) while we collected predicted V˙o2max and performance times. When we found a difference, we conducted a post hoc Tukey test to ascertain where changes might have occurred over the respective condition and test sessions. For the RHIST, percentage of fatigue ([slowest time – fastest time]/fastest time × 100) was determined.54 The α level for all tests was .05. Percentage difference analysis was conducted between NBR and BR conditions. Data were analyzed using SPSS (version 13.0 for Windows; SPSS Inc, Chicago, IL).
RESULTS
Group Mean Performance Levels Between Conditions
The group mean performance level is an average of all test sessions within each group (NBR, NR) of the respective outcome measure. The group mean performance measures of BR participants were lower than the mean NBR performance levels for the beep test (F1,26 = 8.726, P = .007) and the RHIST (F1,26 = 13.98, P = .001), respectively (Table 3). However, the fatigue levels during the RHIST were lower during the BR than the NBR conditions (Table 3).
Mean Performance Levels Over Days (Accommodation) Between Conditions
Beep Test. Fatigue levels were consistent during the 5 NBR testing sessions (SD ± 2.3 mL/kg). Conversely, a steady improvement was noted during BR testing conditions, and by testing sessions 10 and 11 (approximately 14.0 hours of brace use), a 1.5-kg/mL/min predicted V˙o2max difference remained between the NBR and BR conditions (Figure 1). In considering the mean SD of ±1.4 kg/mL over the 5 BR testing sessions, the performance measures between the NBR and BR testing conditions were comparable during testing sessions 4 and 10 and sessions 5 and 11, respectively. This similar performance measure during the 2 testing conditions was illustrated further by the post hoc Tukey test results (Table 4); after the first 2 testing sessions, no differences were noted between the NBR and BR testing conditions.
Citation: Journal of Athletic Training 46, 4; 10.4085/1062-6050-46.4.395
Repeated High-Intensity Shuttle Test. Running speed during NBR conditions was constant over the 5 testing sessions, with the best performance time recorded in session 3. During BR testing conditions, performance levels showed an initial decrease (session 8) followed by improved performance measures (sessions 9 and 10); by testing session 10, a 0.20-second difference remained between the testing conditions (Figure 2). A post hoc analysis was not conducted because the mean performance measures over the 5 testing sessions between the conditions were not different (F4,104 = 0.556, P = .7).
Citation: Journal of Athletic Training 46, 4; 10.4085/1062-6050-46.4.395
Performance Percentage Difference. Performance improvement tendency was further illustrated in the performance measure percentage differences between NBR and BR conditions over the 5 NBR (sessions 1–5) and 5 BR (sessions 7–11) testing sessions. For the beep test, BR performance measures improved 11.1% between testing sessions 7 and 10 (Table 4). Although BR performance measures improved by session 10 in the RHIST, performance levels were 1.3% lower than for the NBR group in session 4 (Table 4).
DISCUSSION
In our study, oxygen consumption during the beep test for the NBR participants was lower than published standards for similar-caliber Australian52 and for Canadian athletes.55 The lower results (10.6 mL/kg/min, range, 10.7–11.1 mL/kg/min) in our study probably can be attributed to the training periodization cycle because all athletes were completing their “active rest” periods and starting their competitive training cycles. The “average normative” results recorded in our study should not be a factor; as Highgenboten et al56 stated, “individuals of average and above-average fitness levels will respond similarly to the effect of brace wear.” For the anaerobic capacity test, data obtained for NBR participants were also similar to available standards.57
We found a 12% higher fatigue level in the first 7.0 hours of FKB use during the beep test. However, with 14.0 hours of brace use, brace accommodation seemed to occur as fatigue levels declined, so that only a 0.9% difference remained between the NBR and BR testing conditions. A post hoc analysis of the aerobic capacity test further illustrated that familiarization with FKBs did take place during this test, as the elevated metabolic cost was noted only during the initial 7.0 hours (sessions 1 and 2) of brace use.
These results are similar to the findings of Highgenboten et al,56 who tested asymptomatic BR participants and reported a 3% to 8% increase in oxygen consumption. Although High-genboten et al56 provided a 3-week “adjustment period with the braces” and then completed treadmill testing over a 2-week period, no specific data about the duration of accommodation to the knee brace were provided. Veldhuizen et al58 reported a 6% lower V˙o2max on day 1 of testing for NBR participants than for BR participants. After 28 days of brace use, they reported, “the performance results were practically identical to their base value.”58 However, as with the Highgenboten et al56 study, specific knee brace accommodation data were not provided.
Performance in the anaerobic capacity test (RHIST) also was hindered substantially while participants were wearing an FKB over the first 11.0 hours. However, after they used a brace for 12.0 to 14.0 hours (session 4), no difference in performance levels between noninjured BR and NBR participants was found. This lack of difference in performance levels is of interest because the RHIST involves challenging the anaerobic metabolic system and involves the turning and pivoting skills observed in most team sports. Our data could not be compared with previous research because we were the first to test healthy BR participants completing a high-intensity anaerobic capacity task. The percentage of fatigue levels of the BR participants were lower than those of the NBR participants.
These findings are important for many team sports in which the energy produced by the aerobic and anaerobic metabolic systems can be overtaxed.5259 Furthermore, fatigue has been shown to negatively influence dynamic muscle control of the lower extremities and potentially contribute to ACL injury.6061 Fatigue and the initial use of the FKB could have been factors during the first 2 BR testing sessions (sessions 7 and 8) because performance levels decreased while participants performed both tests. However, if fatigue had contributed to the lower performance measures during testing sessions 7 and 8, then oxygen consumption levels (beep test) and performance times and fatigue levels (RHIST) should have decreased further (increased fatigue) during BR testing sessions 9 and 10. In fact, the opposite results were recorded for both tests. Furthermore, because no differences were found between the 2 testing conditions after 14.0 hours of brace use, our results suggested that fatigue and hindered performance should not be concerns during the beep test or RHIST capacity activity while participants use an FKB.
The lack of difference in performance results recorded between the 2 testing conditions after accommodation could be attributed to the proprioceptive effect of wearing a knee brace. Several authors suggested that participants with ACL-deficient or ACL-reconstructed knee joints lack a certain amount of prop-rioceptive input to the central nervous system.62 Researchers62–64 also have illustrated that alterations in proprioceptive feedback (in participants with ACL-deficient and ACL-reconstructed knees) as a result of bracing might be partly responsible for performance improvement. Given this central nervous system relearning philosophy, if we apply this concept to a noninjured (“normal” proprioceptive) knee joint, perhaps the noninjured BR participants experienced altered proprioceptive feedback and therefore were able to perform with greater perceived knee joint stability and confidence with continued brace use. This notion is supported by the data reported by Herrington et al.63 They reported that the application of a knee sleeve on noninjured participants increased active tracking accuracy by 28% (P = .004), the angle reproduction test showed a 23% increase in accuracy (P = .03), and the accuracy of the perceived angle test improved by 27% (P = .04).63
Our study design could have included rest periods between testing sessions within each condition; however, because our goal was to measure possible accommodation to FKB use, successive testing sessions were needed. Furthermore, the chosen study design allowed an assessment of muscular fatigue during FKB use because researchers661 have suggested that fatigue is a negative factor in dynamic muscle control that can lead to a knee ligament injury. Concern also might be raised about a learning effect due to the study design. However, both tests in this study have been used consistently by researchers and physiologists to evaluate athletes' training progression.525457 Therefore, all athletes participating in our study should have been familiar with the testing procedures, which should have minimized a learning effect. Although ideally desired, a counterbalanced study design for brace condition (NBR, BR), in which a comparison of the ordering effect was needed would have necessitated additional participants (and increased cost to purchase the braces) to maintain the desired power levels because each testing group would have included half the number of participants. Furthermore, because one objective of the study was to evaluate accommodation to FKB use, potential learning progression was an essential aspect of the study.
This information might assist physicians and athletic trainers and therapists in discussing potential concerns of athletes regarding FKB use, specifically increased fatigue levels, importance of an adaptation or accommodation phase, and the duration of the phase that is needed before performance levels are not hindered.
In future studies of measures to prevent knee ligament injury, researchers should investigate the potential role of the FKB during practice and games, especially in collision and contact sports. Authors need to conduct competition-related studies because research performed in laboratory settings might exclude important components of actual game play that contribute directly to the chosen movement response and resultant risk.2326 Furthermore, a game-based setting assessment involving sports in which participants are at high risk for ACL injury might provide strategies for more reliable neuromuscular injury screening and prevention compared with a laboratory setting.
Our study might be limited by the performance ability of each athlete. Although each athlete was screened to be competitive and to be of provincial or national caliber, athletes differ in their individual intensity and motivation levels. The competitive nature of these participants also might cause peer competition, leading to increased motivation and possibly enhanced performance. Because the FKBs were purchased, finances limited the study design (counterbalanced, randomized control study) and limited the duration of the adaptation or accommodation phase. A longer-duration use of braces might lead to greater accommodation, which might further improve performance measures. Time and financial constraints also did not allow for in-depth evaluation of brace migration concerns. In addition, no clinical laboratory test can replicate game conditions.
CONCLUSIONS
Despite extensive research, the risk of injury to a knee ligament during a sporting activity continues to be of concern. Our data illustrated that performance levels in aerobic and anaerobic tasks were hindered when the FKB initially was used. However, after 14.0 hours of brace use, no differences in performance or fatigue levels were recorded between noninjured NBR and BR participants. Therefore, all FKB users should complete an adaptation or accommodation phase before engaging in full sport participation.
Léger beep test (aerobic capacity – predicted maximal oxygen consumption). Accommodation over days for nonbraced sessions 1 through 5 versus braced sessions 7 through 11.
a Indicates difference between conditions (P < .05).
Repeated high-intensity shuttle test (anaerobic capacity). Accommodation over days for nonbraced sessions 1 through 5 versus braced sessions 7 through 11.
Contributor Notes