26
Effect of Foot Orthotics on Quadriceps and Gluteus Medius Electromyographic Activity During Selected Exercises Jay Hertel, PhD, ATC, Brent R. Sloss, ATC, Jennifer E. Earl, PhD, ATC ABSTRACT. Hertel J, Sloss BR, Earl JE. Effect of foot orthotics on quadriceps and gluteus medius electromyographic activity during selected exercises. Arch Phys Med Rehabil 2005;86:26-30. Objective: To compare electromyographic activity of the vastus medialis, vastus lateralis, and gluteus medius during functional activities in subjects with different foot types while wearing various off-the-shelf foot orthotics. Design: Experimental, controlled; 3 foot-type groups (pes planus, pes cavus, pes rectus) each tested in 4 orthotic conditions while performing 3 different exercises. Setting: Laboratory. Participants: Thirty healthy young adults, 10 with each foot type. Interventions: Four conditions: no orthotic, 7° medial rearfoot post, 4° lateral rearfoot post, and neutral rearfoot post. Main Outcome Measure: Surface electromyographic activity for the vastus medialis, vastus lateralis, and gluteus medius during single-leg squatting, lateral stepdown, and maximum vertical jump exercises. Results: Greater vastus medialis and gluteus medius activity was found with all 3 orthotic conditions, regardless of subject foot type, during the single-leg squat and lateral stepdown. Less vastus lateralis activity was found with the vertical jump with all orthotic conditions, again regardless of foot type. Conclusions: During slow controlled exercises such as the single-leg squat and lateral stepdown, vastus medialis and gluteus medius activity may be enhanced with an off-the-shelf orthotic, regardless of posting or foot type. These same findings do not appear to carry over to a more explosive task such as the maximal vertical jump. Key Words: Electromyography; Foot; Muscles; Orthotic devices; Pain; Rehabilitation. © 2005 by American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation OOT ORTHOTICS HAVE BEEN shown to be an effective component of conservative treatment of patellofemoral F pain syndrome (PFPS). This syndrome is characterized by 1,2
diffuse anterior knee pain and is thought to be related to abnormal movement and joint reaction forces between the
From the Kinesiology Program, University of Virginia, Charlottesville, VA (Hertel); Georgia Southern University, Statesboro, GA (Sloss); and Department of Human Movement Sciences, College of Health Sciences, University of Wisconsin, Milwaukee, WI (Earl). Presented in part to the National Athletic Trainers’ Association, June 17, 2002, Dallas, TX. No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated. Reprint requests to Jay Hertel, PhD, ATC, Kinesiology Program, University of Virginia, 210 Emmet St S, PO Box 400407, Charlottesville, VA 22904-4407, e-mail: jhertel@virginia.edu. 0003-9993/05/8601-8467$30.00/0 doi:10.1016/j.apmr.2004.03.029
Arch Phys Med Rehabil Vol 86, January 2005
patella and the femur. Abnormal patellofemoral mechanics have been hypothesized to arise from 2 primary causes: abnormal mechanics of the lower-extremity linked to hyperpronation3 and abnormal neuromuscular control of the muscles acting on the patella and the femur.4,5 Although foot orthotics have traditionally been thought to lessen symptoms of PFPS by correcting abnormal lower-extremity mechanics,6,7 little attention has been given to the effect that orthotics have on the activation patterns of lower-extremity muscles involved in the etiology of PFPS. Recent evidence suggests that orthotics may have beneficial effects on sensorimotor function through stimulation of the plantar cutaneous afferent receptors.8,9 It is possible that the clinical improvement in PFPS associated with foot orthotics may be caused, at least in part, by altered neuromuscular activity of the quadriceps and gluteus medius. Lower-extremity malalignments, such as pes planus, genu valgum, and femoral anteversion, are thought to predispose people to PFPS.10,11 Hyperpronation of the foot and the subsequent increased internal rotation of the tibia and femur during gait are thought to increase the lateral tracking of the patella on the distal femur and thus create abnormal joint reaction forces to the articular cartilage on the retropatellar surface.3 Reduction of hyperpronation and the subsequent rotations of the lower extremity with foot orthotics intervention have been used successfully in the treatment of PFPS.1,2 Patients with PFPS are typically treated clinically with medially posted orthotics in an effort to improve lower-extremity alignment; however, it is unclear whether the clinical efficacy of orthotic intervention is entirely caused by the correction of abnormal lower-extremity mechanics or whether orthotics also positively affect neuromuscular activation patterns. Although all 4 quadriceps muscles act to pull the patella superiorly when they concentrically contract, the vastus medialis and vastus lateralis muscles have antagonist roles in controlling medial and lateral patellar motion, respectively. Inhibition of the vastus medialis relative to the vastus lateralis has been consistently identified in the etiology of PFPS.4,5,12,13 Therapeutic exercise for PFPS typically targets neuromuscular retraining of the vastus medialis in an effort to correct the imbalance between the vastus medialis and vastus lateralis. Alteration of foot position and subsequent lower-extremity motion with orthotics may also alter neuromuscular activation patterns of the quadriceps.14 For example, a medially posted orthotic may decrease the amount of hyperpronation and internal rotation of the lower extremity and thus place the patella in a less laterally deviated position in relation to the femur; this position may optimize the length-tension relationship of the vastii muscles and lead to optimized neuromuscular activation. Conversely, a laterally posted orthotic may lead to increased pronation and limb rotation, leading to less than optimal contraction of the vastii. Unfortunately, there has been very little research examining what effects differently posted orthotics have on neuromuscular activity proximal to the lower leg. The gluteus medius muscle also has been suggested to have a role in the etiology of PFPS.15 This muscle is critical to providing pelvic stability during weight-bearing activities.16 Inhibition of the gluteus medius may contribute to diminished
FOOT ORTHOTICS AND ELECTROMYOGRAPHIC ACTIVITY, Hertel
pelvic control, thus allowing greater femoral internal rotation to occur. The rotation could contribute to excessive lateral tracking of the patella relative to the distal femur and to increased tibial internal rotation and foot pronation distally.15 By controlling pronation with foot orthotics one may achieve better control of rotary motions in the lower extremity; such control may enhance pelvic stability and the activation of the gluteus medius, for reasons similar to those described earlier. The effect that foot orthotics have on gluteus medius activation has not previously been investigated. Our goal was to identify the differential effects of variously posted orthotics on muscle activation patterns in subjects with different lower-extremity alignment patterns. We compared the activation levels of the vastus medialis, vastus lateralis, and gluteus medius muscles during 3 functional activities under 4 different off-the-shelf orthotic conditions in healthy people with different foot types. We hypothesized that, in addition to correcting faulty lower-extremity mechanics, foot orthotics would lead to heightened activation of muscles associated with the etiology of PFPS. We expected that increases in muscle activity of the vastus medialis, vastus lateralis, and gluteus medius because of orthotic intervention would be most pronounced in people with pes planus and would be more pronounced with medially posted orthotics compared with neutral or laterally posted orthotics. METHODS Participants Thirty healthy, recreationally active young adults (15 men, 15 women; height, 170.2⫾6.1cm; weight, 69.1⫾13.9kg; age, 21.1⫾1.6y) participated. Subject inclusion was based on architectural foot type, with 5 men and 5 women each having pes planus, pes cavus, and pes rectus. The study was approved by the university’s institutional review board, and all subjects read and signed an informed consent form before their participation. Foot Type Classification Foot type was subjectively categorized by a clinician experienced in lower-extremity biomechanic evaluation. The clinician’s assessement was made with the subject standing barefoot in full weight bearing on both feet on a hard tile floor. These methods were reported in another experimental investigation of foot type.17 Pes planus feet were identified as those having a flat medial longitudinal arch and at least 1 of the following malalignments: excessive rearfoot valgus, substantially plantar flexed first ray, and/or excessive forefoot varus. Pes cavus feet were defined as those having a high medial longitudinal arch accompanied by either excessive rearfoot varus and/or excessive forefoot valgus. Pes rectus feet were defined as those displaying characteristics of neither pes planus nor pes cavus. Materials Rigid off-the-shelf Superfeet Footbed orthoticsa were used. These orthotics consisted of a full-foot soft covering over a rigid plastic shell that extended to the level of the metatarsal heads. The shell contained 7° medial and 4° lateral rearfoot postings. By using a grinding wheel, the medial or lateral postings were removed resulting in either a medially or laterally posted orthotic. Subjects inserted the orthotics into their own pair of low-top athletic shoes. Instrumentation The Biopac MP100b was used to collect all electromyographic data. Surface electromyograms were collected by Ag-
27
AgCl disposable electrodes that had a 10-mm contact area. Signals were amplified, digitized, and collected with AcqKnowledge software, version 3.5.b The following parameters were used to collect the electromyographic data: band width, 10 to 500Hz; input impedance, 2M⍀ (differential); common mode rejection ratio, 11dB; maximum voltage, ⫾10V; sampling rate, 1000Hz; and gain, 1000. Data were then processed by using a custom program written with Matlab software.c Electrode Placement The leg tested in all subjects was the leg contralateral to their dominant throwing arm. Electromyographic activity was recorded from the vastus medialis, vastus lateralis, and gluteus medius muscles. For the vastus medialis, the electrodes were placed at a 55° angle to the long axis of the femur, parallel to the presumed direction of the muscle fibers. For the vastus lateralis, the electrodes were placed proximal to the distal tendon and over the area of greatest muscle bulk. These locations were verified to be consistently over the muscle belly during a minisquat. For the gluteus medius, the electrodes were placed half the distance between the iliac crest and the greater trochanter. Placement was verified by palpation during singleleg stance. The interelectrode distance of all electrode pairs was 2cm. A ground electrode was placed on the medial aspect of the shaft of the proximal tibia. The 4 areas were shaved with a dry razor and scrubbed with rubbing alcohol before electrode placement. Procedures Maximum voluntary isometric contractions (MVICs) of the vastus medialis, vastus lateralis, and gluteus medius were recorded during a weight-bearing isometric task by using a custom-made testing apparatus18 (fig 1). This device consisted of a platform angled at 30° and covered with a nonslip surface. Participants stood with their back against the wall and their test leg on the platform in front of them with their knee positioned in 60° of flexion. Knee joint angle was measured with a standard goniometer before each trial to ensure consistent positioning across the trials of all subjects. To account for differences in subject height and leg length, the distance of the platform from was adjustable. A heavy rubber mat was placed in front of the platform to prevent it from sliding. Shoulder straps ensured that subjects did not move their trunk, hip, or knee when performing the isometric contractions. Subjects were instructed to lift their contralateral foot and to maximally push up and back into the wall with their test leg. Practice repetitions were performed at 25%, 50%, 75%, and 100% intensities. Electromyographic data were not recorded during the practice trials. Subjects then performed 3 maximal contractions, which were recorded. Each trial was separated by a 90-second rest. Subjects performed 3 trials of each task under each of the 4 orthotic conditions. The 4 orthotics conditions were no orthotic, 7° medial rearfoot post, 4° lateral rearfoot post, and neutral rearfoot post (7° medial and 4° lateral posts). The 3 functional tasks were single-leg squat, lateral stepdown exercise, and maximum vertical jump. The order of orthotic conditions and functional tasks was assigned by using a Latin square design to prevent any order effects from contaminating the data. Subjects were given 5 minutes to adjust to each new orthotic condition before testing commenced. The single-leg squat was performed as subjects stood on their test leg and reached anteriorly with their nonstance leg as far as they could. Subjects were given standardized instructions to use ankle, knee, and hip motion of their stance leg in an Arch Phys Med Rehabil Vol 86, January 2005
28
FOOT ORTHOTICS AND ELECTROMYOGRAPHIC ACTIVITY, Hertel
the dependent variable was expressed as a percentage of maximum electromyographic activity. Statistical Analysis The dependent variables were the percentage of MVIC for the vastus medialis, vastus lateralis, and gluteus medius. The independent variables were foot-type group and orthotic condition. For each of the 3 functional tasks, a 1 between-factor (foot type), 1 within-factor (orthotic) mixed-model analysis of variance with repeated measures was calculated. Tukey post hoc tests were used to identify specific differences. The level of statistical significance was set a priori at .05 for all analyses. Additionally, intraclass correlation coefficients (ICC3,1) were calculated for 3 repeated measures for each muscle during each of the 3 tasks to assess the reliability of the dependent measures. RESULTS No significant interactions existed between foot type and orthotic condition during any of the 3 tasks for any of the tested muscles (P⬎.05). A significant main effect for orthotic condition, however, was found for all 3 tasks (figs 2, 3). For the single-leg squat, vastus medialis (F3,81⫽8.43, P⬍.001) and gluteus medius (F3,81⫽3.96, P⫽.01) activity was significantly higher than the no-orthotic condition. No single orthotic posting was more advantageous than the others in increasing vastus medialis or gluteus medius activity. No significant main effects
Fig 1. Custom-made closed-kinetic chain device used to collect the MVIC. Subjects pushed maximally into knee and hip extension into the wall with their weight-bearing limb while the straps and platform remained in place to ensure isometric contractions.
effort to reach as far as they could with their nonstance leg, lightly tap their nonstance foot on the ground, and then return themselves to the starting position. Electromyographic data were collected throughout the entire squatting task. The lateral stepdown was performed with subjects standing on a 30-cm high wooden box. Subjects stood with their nontest leg close to the edge of the box. A metronome sounding at 60 beats per minute helped subjects perform the lateral stepdown at a consistent speed. Subjects were instructed to lower their nontest leg as far down as they could while bending their test leg over 2 seconds, lightly touch their nonstance foot to the floor, and then return to the starting position over 2 seconds. Electromyographic data were collected throughout the entire stepdown task. Subjects performed the maximum vertical jump by leaping as high as they could from a bilateral stance. Subjects were instructed to flex their knees and hips and swing their arms in attempting to jump as high as possible. Subjects were also instructed to land using both legs. Electromyographic data were collected throughout the entire jumping task. Data Processing The recorded electromyographic signals for each muscle were corrected for a baseline drift and the root mean square (RMS) was calculated over a 0.5-second moving window. For each muscle, the maximum RMS values of all MVIC trials were averaged and used for normalization. For the 3 functional tasks, the maximum RMS value for each trial was calculated. The mean of the maximum RMS values for each task were then averaged and divided by the respective MVIC maximums, and Arch Phys Med Rehabil Vol 86, January 2005
Fig 2. Mean percentage of integrated electromyographic (iEMG) activity relative to MVIC for the (A) vastus medialis muscle and the (B) gluteus medius muscle during the single-leg squat and stepdown activities. Muscle activity was significantly greater (P<.05) during all 3 orthotic conditions relative to the no-orthotic condition (nⴝ30). Error bars represent 1 standard deviation (SD). *Statistically significant difference.
FOOT ORTHOTICS AND ELECTROMYOGRAPHIC ACTIVITY, Hertel
Fig 3. Mean percentage of integrated electromyographic activity relative to MVIC for the vastus lateralis muscle during the vertical jump. Muscle activity was significantly less (P<.05) during all 3 orthotic conditions relative to the no-orthotic condition (nⴝ30). Error bars represent 1 SD. *Statistically significant difference.
or interaction were found with vastus lateralis activity for the single-leg squat. With the lateral stepdown, vastus medialis activity was again significantly higher in all 3 orthotic conditions compared with the no-orthotic condition (F3,81⫽6.57, P⬍.0005). No single orthotic posting was more advantageous than the others in increasing vastus medialis activity. The same trend was seen with gluteus medius activity; however, the differences did not reach statistical significance (F3,81⫽2.34, P⫽.08). No significant differences were found with the vastus lateralis for the lateral stepdown. For the vertical jump, vastus lateralis activity was significantly less during the 3 orthotic conditions compared with the no-orthotic condition (F3,81⫽3.32, P⫽.02). No single orthotic posting was more deleterious than the others in decreasing vastus lateralis activity during the vertical jump. No significant differences were identified for the vastus medialis or gluteus medius activity for the vertical jump. The ICC analysis revealed high reliability of the maximal integrated electromyographic measures across trials for all 3 muscles during all 3 tasks. The ICC3,1 values ranged from .96 to .98 for the vastus medialis, .95 to .96 for the vastus lateralis, and .91 to .96 for the gluteus medius. DISCUSSION Foot orthotics, in conjunction with a therapeutic exercise program, have been shown to be advantageous in the treatment of patients with PFPS.1 Eng and Pierrynowski’s study1 was limited to female adolescents with more than 6° of rearfoot valgus or forefoot varus, and subjects in their treatment group were fitted with soft orthotics with appropriate medial forefoot and rearfoot posts to help limit hyperpronation. Their subjects in both the orthotic and control groups completed a supervised rehabilitation program that emphasized strengthening and flexibility exercises for the quadriceps and hamstring muscles. Both groups showed improvement in symptoms over 8 weeks; however, the group treated with the orthotics had significantly greater reduction in symptoms than the control group. The authors speculated that the benefits of using orthotics in the treatment of PFPS were derived from altering the biomechanics associated with hyperpronation at the tibiofemoral and patellofemoral joints.1
29
Semirigid orthotic intervention to correct hyperpronation positively influences patellar position during weight bearing in patients with PFPS. Klingman et al7 found that the patella immediately repositioned medially when a medial wedge orthosis was applied. Although this finding provides a biomechanic rationale for the clinical efficacy of treating PFPS with orthotic intervention, the effects that foot orthotics have on neuromuscular activation patterns should not be discounted. Foot orthotics have been associated with altered neuromuscular activation patterns during gait.14,19 In the present study, vastus medialis and gluteus medius activity increased with orthotic intervention during the slow, controlled movements associated with the single-leg squat and lateral stepdown exercises. Increased activity of the vastus medialis and gluteus medius are potentially advantageous in patients with PFPS because of the role that both these muscles have in preventing excessive lateral tracking of the patella. Further research on the effects of orthotics on neuromuscular activation patterns in PFPS patients is warranted. Our findings are in contrast to a study by Hung and Gross20 that found no significant changes in vastus medialis and vastus lateralis activity during squatting activities performed under 3 conditions: level surface, a 10° medial wedge, and 10° lateral wedge. A key difference is that our subjects performed exercises while wearing rearfoot-posted orthotics in their shoes, whereas Hung and Gross20 used wedges that extended the full length of the foot. Although we found increased vastus medialis and gluteus medius activity with orthotic intervention in the slower tasks, we did not see these same effects with the vertical jump, a more explosive task. We did, however, find diminished vastus lateralis activity in the vertical jump with orthotic intervention. These findings are consistent with those of Nawoczenski and Ludewig14 who found reductions, albeit statistically insignificant ones, in vastus lateralis activity with orthotic intervention during gait. It is possible that the vertical jump was a lessconstraining task than our 2 other tasks. This difference may have led to greater intersubject variability during the performance of the vertical jump, thus providing greater variability in electromyographic measures during this task. Our most unexpected finding was that muscle activity did not vary when differently posted orthotics were used by subjects with different foot types. We hypothesized, for example, that the pes planus group would exhibit the most profound increases in muscle activation with the medially posted orthotics. Instead, changes in muscle activation were seen across all foot types regardless of posting. Perhaps these alterations were not caused by any biomechanic effects of the orthotics, but instead by the altered afferent feedback stemming from the cutaneous receptors on the plantar aspect of the foot.21 Our subjects were given only 5 minutes to adjust to the different orthotics, and it is unknown if a longer accommodation period would alter the neuromuscular activation changes we found in the present study. Considerable individual variation in neuromuscular recruitment in response to orthotic intervention were previously reported.14,22 Finding different responses between the vastus medialis and vastus lateralis throughout the 3 tasks is difficult to explain. Possibly, vastus medialis activity was enhanced with orthotic intervention because of mechanical changes at the patellofemoral joint that led to vastus medialis facilitation. Were this the case, however, we would have expected to find differences most pronounced with medial posting. This finding would seem to lend some credence to the argument that the changes in neuromuscular activity with orthotic intervention were caused, at least in part, by enhanced plantar cutaneous Arch Phys Med Rehabil Vol 86, January 2005
30
FOOT ORTHOTICS AND ELECTROMYOGRAPHIC ACTIVITY, Hertel
afferent activity. An alternative explanation may be that all the orthotics we tested, regardless of posting, moved the bony skeleton and muscles relative to the skin-mounted electrodes in a manner that caused consistent changes in the electromyography recordings. Limitations We studied the muscle activation patterns of healthy subjects, and the generalizability of these findings to PFPS patients who exhibit altered neuromuscular activation patterns cannot be directly made. We used surface electromyographic measures, and we assumed that the signal was representative of each muscle in its entirety. We also compared measures of electromyographic amplitude rather than timing, and we cannot speculate on what effects orthotics may have on the timing of neuromuscular activation patterns. Last, our “neutral” orthotics came from the manufacturer with a 7° medial post and a 4° lateral post, so they were not truly neutral. Instead, they represent the manufacturer’s definition of a neutral rearfoot post. CONCLUSIONS Off-the-shelf orthotics, regardless of rearfoot posting, increased vastus medialis and gluteus medius muscle activity during single-leg squat and lateral stepdown exercises; however, these same increases were not seen with the vertical jump, a more explosive activity. The posting of the orthotics did not significantly influence changes in muscle activity in subjects with different architectural foot types. References 1. Eng JJ, Pierrynowski MR. Evaluation of soft foot orthotics in the treatment of patellofemoral pain syndrome. Phys Ther 1993;73: 62-70. 2. Way MC. Effects of a thermoplastic foot orthosis on patellofemoral pain syndrome in a collegiate athlete: a single subject design. J Orthop Sports Phys Ther 1999;29:331-8. 3. Tiberio D. Effect of excessive subtalar joint pronation on patellofemoral mechanics: a theoretical model. J Orthop Sports Phys Ther 1987;9:160-5. 4. Cowan SM, Bennell KL, Hodges PW, Crossley KM, McConnell J. Delayed onset of electromyographic activity of vastus medialis obliquus relative to vastus lateralis in subjects with patellofemoral pain syndrome. Arch Phys Med Rehabil 2001;82:183-9. 5. Cowan SM, Hodges PW, Bennell KL, Crossley KM. Altered vastii recruitment when people with patellofemoral pain syndrome complete a postural task. Arch Phys Med Rehabil 2002;83:989-95. 6. D’Amico JC, Rubin M. The influence of foot orthoses on the quadriceps angle. J Am Podiatr Med Assoc 1986;78:337-40. 7. Klingman RE, Liaos SM, Hardin KM. The effect of subtalar joint posting on patellar glide position in subjects with excessive rearfoot pronation. J Orthop Sports Phys Ther 1997;25:185-91.
Arch Phys Med Rehabil Vol 86, January 2005
8. Nurse MA, Nigg BM. The effect of changes in foot sensation on plantar pressure and muscle activity. Clin Biomech (Bristol, Avon) 2001;16:719-27. 9. Hertel J, Denegar CR, Buckley WE, Sharkey NA, Stokes WL. Effect of rear-foot orthotics on postural control in healthy subjects. J Sport Rehabil 2001;10:36-47. 10. James SL, Bates BT, Osternig LR. Injuries to runners. Am J Sports Med 1978;6:40-50. 11. Aglietti P, Insall JN, Cerulli G. Patellar pain and incongruence. I: Measurements of incongruence. Clin Orthop 1983;Jun(176):21724. 12. Boucher JP, King MA, Lefebvre R, Pepin A. Quadriceps femoris muscle activity in patellofemoral pain syndrome. Am J Sports Med 1992;20:527-32. 13. Cerny K. Vastus medialis oblique/vastus lateralis muscle activity ratios for selected exercises in persons with and without patellofemoral pain syndrome. Phys Ther 1995;75:672-83. 14. Nawoczenski DA, Ludewig PM. Electromyographic effects of foot orthotics on selected lower extremity muscles during running. Arch Phys Med Rehabil 1999;80:540-4. 15. Host J, Craig R, Lehman R. Patellofemoral dysfunction in tennis players: a dynamic problem. Clin Sports Med 1995;14:177-203. 16. Schmitz RJ, Riemann BL, Thompson T. Gluteus medius activity during isometric closed-chain hip rotation. J Sport Rehabil 2002; 11:179-88. 17. Hertel J, Gay MR, Denegar CR. Differences in postural control measures among healthy individuals with different foot types. J Athl Train 2002;37:129-32. 18. Hertel J, Earl JE, Tsang KK, Miller SJ. Combining isometric knee extension exercises with hip adduction or abduction does not increase quadriceps EMG activity. Br J Sports Med 2004;382: 210-3. 19. Tomaro J, Burdett RG. The effects of foot orthotics on the EMG activity of selected leg muscles during gait. J Orthop Sports Phys Ther 1993;18:532-6. 20. Hung YJ, Gross MT. Effect of foot position on electromyographic activity of the vastus medialis oblique and vastus lateralis during lower-extremity weight-bearing activities. J Orthop Sports Phys Ther 1999;29:93-102. 21. Nigg BM, Nurse MA, Stefanyshyn DJ. Shoe inserts and orthotics for sport and physical activities. Med Sci Sports Exerc 1999;31(7 Suppl):S421-8. 22. Neptune RR, Wright IC, van den Bogert AJ. The influence of orthotic devices and vastus medialis strength and timing on patellofemoral loads during running. Clin Biomech (Bristol, Avon) 2000;15:611-8. Suppliers a. Superfeet Worldwide LLC, 1419 Whitehorn St, Ferndale, WA 98248. b. Biopac Systems Inc, 42 Aero Camino, Goleta, CA 93117. c. The MathWorks Inc, 3 Apple Hill Dr, Natick, MA 01760-2098.