June 2011

Functional knee bracing and athletic performance

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Functional knee braces can’t be effective if athletes won’t wear them, and many athletes won’t wear them because they fear their athletic performance will be negatively affected. But early research suggests that athletes accommodate to knee brace wear almost immediately.

By Neetu Rishiraj, ATC, PhD, Jack E. Taunton, MSc, MD, Robert Lloyd-Smith, MD, William Regan, MD, and Navin Prasad, MSc, MD

More than 30 years after the first knee brace was introduced, emphasis is still on competition for mechanical design superiority rather than on the possible efficacy of a functional knee brace (FKB) for preventing injuries. Published literature presents data regarding the potential inability of a knee brace to provide knee joint stability;1,2 however, individuals with deficiencies in the anterior cruciate ligament (ACL) refute this information.3

Physicians continue to prescribe FKBs to individuals with a conservatively managed ACL-deficient knee joint, as well as post-ACL reconstruction.1 However, uncertainty remains regarding the potential stability offered by a FKB in reducing or preventing knee joint ligament injury in athletes, as there have been few studies conducted on the effectiveness of functional knee bracing, even in noninjured individuals, during sporting competition.4 Some experts attribute this lack of evidence to compliance issues surrounding the use of FKBs by injured and noninjured individuals, who may have concerns that the brace will hinder their athletic performance.5-7

Previous authors have proposed that ACL injury prevention should begin with a comprehensive evaluation of all mechanisms and internal and external risk factors involved in the injury,8,9 but before using this approach one must address the perception of performance hindrance in noninjured athletes who use FKBs. A change in perception is essential because new protective equipment is not always welcomed by athletes, parents, or sports officials if performance impediment is perceived, regardless of its size, shape, or potential benefits.10,11

The introduction of the mouthguard some 60 years ago10,12 is a foremost example of players’ concerns of performance hindrance. Players and others may believe mouthguards interfere with breathing and speech and adversely affect self-image, despite growing evidence supporting this piece of athletic equipment for injury prevention.13-17
Published literature has presented similar concerns about FKB

use. A study of U.S. football players revealed that prophylactic knee braces were utilized during only 50% of 55,722 knee exposures due to the association of knee brace use with impeded athletic performance.4 Research identified this poor adherence with brace use some time ago,18-20 yet athletes and others continue to connect knee brace utilization with impaired performance, specifically perceptions that performance is restricted with respect to power, speed, agility, and anaerobic and aerobic activities.18-23

To avoid the “mouthguard resistance” scenario and facilitate investigations of the efficacy of FKBs in reducing knee injury, researchers must first convince athletes and coaches how little, if at all, functional braces restrict function.

Bracing and athletic performance

Various researchers have demonstrated that wearing a knee brace requires additional energy consumption.20,24-26 According to Branch and Hunter27 weight added to the feet has a greater impact on energy consumption than weight added to the body anywhere else. Early knee braces could weigh as much as 0.9 kg (2 lbs), and placed greater demand on the cardiovascular system than modern braces, which could lead to fatigue. This was first demonstrated by Soule and Goldman,26 who showed that wearing a 6 kg (13.2 lbs) weight on each foot while walking at 93 m/min (3.47 mph [5.58 km/h]) caused a 420% increase in energy expenditure.

A 1991 study of the effects of knee bracing reported significantly slower and lower performance levels on only the first day of brace use: performance decreased by 4% in the 60-meter dash; VO2max was 6% lower; peak torque of knee flexion at 60°/s and 120°/s were 6% and 9% lower, respectively; and peak extension torque at 60°/s was 9% lower.23

After participants wore the knee brace for four weeks, the authors reported, “…the test performances were practically identical to their base value.”23 One day after the brace removal all test parameters were statistically similar to the base values. As a result, these authors concluded, “…performance in sports with test-like exercise patterns is not affected by the brace tested. Bracing does not ‘weaken the knee’ as it is believed in sports practice and…brace wearers go through a familiarization process.”23

Some years after that 1991 study it was reported that, following application of a knee brace, leg muscle microcapillary pressure at rest increased significantly while participants were supine, sitting, or standing; similarly, muscle relaxation pressure during exercise also increased significantly on brace application.18,28 Furthermore, “the tested functional knee braces increased muscle pressures at rest and muscle relaxation pressure during exercise to levels that might decrease muscle blood flow significantly.”28 As a result, these researchers suggested external pressure on the leg muscle might lead to premature muscle fatigue because of local insufficient perfusion of the working muscle.18,28

Until 2008, only four studies had investigated the effects of knee bracing on noninjured individuals. The first study tested 20 noninjured collegiate basketball players and reported no significant difference in straight-line or successive-turning running times between braced (two different knee braces were tested) and nonbraced conditions.29

A 2000 study by Greene et al30 evaluated the effects of knee braces on noninjured athletes’ speed and agility, as well as brace tendency to migrate in dynamic and game-like settings. This study tested six knee braces using the 40-yard dash (speed test) and the four-cone drill (agility test). The authors reported that performance was not hindered while using two of the six knee braces in the 40-yard sprint. During the agility drill, only one of the six braces was associated with a decrease in participants’ performance levels. Greene et al concluded that selected knee braces do not significantly reduce speed and agility. However, all braces showed a tendency to migrate, which could affect their protective function and athletic performance.

A third study in 2000 assessed 30 university athletes with no known history of knee injury.31 Knee joint laxity was quantified using a KT-1000 knee ligament arthrometer.  Investigators randomized participants into two groups, nonbraced (NBR) and braced (BR), which used “ideal-fitting” knee braces that were manufactured according to right leg, midthigh, and midcalf measurements. All participants performed five functional tests: a 10-meter dash, figure-of-eight run, slalom run, hop (horizontal) test, and running down the stairs test. The BR group demonstrated significantly inferior performances during the 10-meter dash, figure-of-eight, and the slalom tests, significantly superior performance in the horizontal hop test, and no statistically significant difference when completing the running down stairs test. Once participants had accommodated to the brace according to best performance measures, investigators noted no significant differences between the braced and nonbraced conditions for any of the tests.31

In 2004, 20 healthy, physically active, noninjured participants wore a prophylactic knee brace while performing double-leg squats to 45º and 75º knee flexion reference angles and maintaining these selected positions for 10 seconds.30 Participants were fatigued using a resisted squatting protocol, with fatigue defined as the point in time when participants failed to complete two successive squat cycles or fell four squat cycles behind the set pace.32 Culp and colleagues reported that, based on participants’ ability to reproduce the desired knee flexion angle while performing a double-leg squat, knee bracing appeared neither to enhance nor inhibit proprioception at the knee joint. The authors also reported that braced participants performed a greater number of double-leg squats and suggested that therefore the prophylactic knee brace may function to absorb external loads placed on the knee.

Our research

We have recently published several pilot study papers to alleviate concern regarding FKB use and performance hindrance during dynamic sports-specific tasks.33-36 The pilot study was a 2 x 3 factorial design with repeated measures on the testing condition (NBR or BR) and testing day (days one to three). Each participant was provided with a custom-fitted FKB. The FKB’s mean weight was 0.80 kg, with weight ranging from 0.78 kg (1.76 lbs) to 0.82 kg (1.80 lbs).

A battery of seven tests encompassing aerobic capacity, anaerobic capacity, agility, hop-and-drop jump kinetics and kinematics, lower extremity power, and speed were used to evaluate potential accommodation to FKB use. Testing for each participant lasted up to 3.5 hours per day and was conducted at the same time each day over six days. In the first three days participants performed all tests without the brace, followed by three days of testing with the brace.

Össur Canada provided its Extreme ligament functional knee braces for our study participants. Although this may be perceived as a conflict of interest or product testing, the retail cost of each brace is approximately Can $1000 (U.S. $1023); this was prohibitive for the pilot study, which was designed to investigate whether accommodation to FKBs was possible prior to commencing a large-scale study for which the required number of braces would be purchased. Investigators obtained ethical approval for the study and all participants signed an informed consent form prior to entering the study.

The dependent variables were the performance measures (i.e., vertical ground reaction force, time, distance, or predicted oxygen consumption) for the respective tests.  Statistical significance for all tests was determined at the p < 0.05 level. Investigators analyzed only the data from the five participants who completed all tests and calculated percentage differences between NBR and BR conditions.

Aerobic capacity

A significantly higher group mean oxygen consumption for the three testing days was recorded for the BR group (p = 0.036), while no significant difference was seen for the rate of perceived exertion (RPE) data (p = 0.123) (Table 1). Over the three days of testing, the oxygen consumption and RPE interaction between the two testing conditions was not significant (p = 0.517 and p = 0.802, respectively) (Table 2). However, accommodation to FKB use was noted, as the percentage performance difference between NBR and BR conditions decreased by day three of testing. (Table 3)

Anaerobic capacity

Anaerobic capacity was assessed using the repeated high intensity shuttle test (RHIST). Nonsignificant (p = 0.299) faster group mean performance time was recorded for BR participants relative to the NBR condition (Table 1). Although relatively faster performance levels were noted during the BR testing condition on days one and three compared with the NBR condition, these results were not significant (p = 0.118) (Table 2). Lower percent fatigue level was recorded during all three BR days compared with NBR days. Furthermore, a tendency for accommodation to knee brace use was noted as the percentage performance difference between the two conditions had decreased by the last day of testing (Table 3).

Jump kinetics and kinematics

During both jump tasks, lower group mean peak vertical ground reaction forces (PVGRF) were generated while using a FKB; the hop-jump data were statistically significant (p = 0.036) (Table 1). The lower PVGRF during both tasks was generated with the knee joint in greater extension and the ankle joint in greater dorsiflexion.  Furthermore, an accommodation trend was noted as PVGRF percent performance difference decreased with continued FKB use (Tables 2 and 3).

Agility, power, and speed

For the three testing days, higher group mean vertical jump height and slower group mean agility performance were recorded for BR participants, but the differences were not statistically significant. Significantly slower (p = 0.023) group mean performance was recorded for the BR participants during the 10-meter sprint (Table 1). Looking at the average of the three trials for each of the respective tests, some accommodation to FKB use was apparent (Tables 2-3).

Going forward

Since our pilot study publications, we have continued this research using a larger sample size and over a longer duration to confirm any effect on performance levels and accommodation trend while performing aerobic capacity, anaerobic capacity, agility, drop jump kinetics, lower extremity power, and speed tasks.

In a recently e-published study,43 27 healthy male athletes were provided with a custom-fitted FKB. Each subject performed acceleration, agility, leg power, and speed tests over six days; five NBR testing sessions over three days were followed by five BR testing sessions, also over three days. Initial performance levels were lower for the BR sessions compared with the NBR sessions for all tests (i.e., acceleration, agility, leg power, and speed). However, after participants had used the FKB for a minimum of 12 hours, no significant performance differences were noted between the two brace conditions for these three tests.

A second study has been accepted for publication44 and a third study is under review.45

Discussion and conclusion

It stands to reason that the introduction and use of new equipment by athletes will initially decrease performance levels. Similar to the break-in period required for new footwear, continued use of any athletic equipment leads to familiarization.

The present pilot study data illustrated that accommodation to a FKB is possible while performing dynamic aerobic and anaerobic capacity, agility, hop-and-drop jump kinetics and kinematics, lower extremity power, and speed tasks. Decrement in performance should be expected on initial application of a FKB. However, in our pilot study, after participants wore the braces for seven to 10.5 hours over three days, similar performance levels were observed for all physiologic parameters measured. This finding is important as previous research37, 38 had presented concerns that muscular fatigue would result in an increased risk of injury. It should be noted, however, that data from the present study do not reveal which factors led to the accommodation process or improved performance levels for some tasks.

The present study also suggests the absorption of the PVGRF by the dorsiflexed ankle joint or use of the FKB could keep traumatic forces from reaching the ACL after initial foot contact with the ground. The lower PVGRF could assist in dampening the effects of the electromechanical delay until activation of the neuromuscular active restraint is able to provide protection to the knee joint and the ACL.39-42

Neetu Rishiraj, ATC, PhD, is director of Human Performance and Rehabilitation at ACTIN Health & Rehabilitation, in Vancouver, Canada. Jack E. Taunton, MD, is professor of medicine and human kinetics, Robert Lloyd-Smith, MSc, MD, is clinical professor of medicine, William Regan, MD, is associate professor of orthopedic surgery, and Navin Prasad, MSc, MD, is clinical assistant professor of medicine at the University of British Columbia in Vancouver.

Disclosure: None of the authors has a financial conflict of interest with regards to this study, nor do the authors endorse one brace manufacturer over another.


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44. Rishiraj N, Taunton JE, B. N, Lloyd-Smith R, Regan W, Woollard R. Performance of healthy braced subjects during aerobic and anaerobic capacity tasks. J Athl Train in press.

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