Services on Demand
Print version ISSN 1517-8692
On-line version ISSN 1806-9940
Rev Bras Med Esporte vol.12 no.2 Niterói Mar./Apr. 2006
La efectividad de los ejercicios en cadena cinética abierta y la cadena cinética cerrada en el tratamiento del síndrome femoropatelar de dolor
Guilherme Lotierso FehrI; Alberto Cliquet JuniorII; Ênio Walker Azevedo CachoIII; João Batista de MirandaIV
in Surgery Department of Orthopedics and Traumatology FMC/Unicamp, Laboratory
of Biomechanics and Rehabilitation of the Locomotive Device HC-FMC/Unicamp,
Campinas State University Unicamp Campinas, SP
IIMaster Professor of the Department of Orthopedics and Traumatology FMC/Unicamp, Head of the Laboratory of Biomechanics and Rehabilitation of the Locomotive Device HC-FMC/Unicamp, Campinas State University Unicamp Campinas, SP
IIIMastership in Surgery FCM Unicamp, Laboratory of Biomechanics and Rehabilitation of the Locomotive Device HC - FMC/Unicamp
IVProfessor Doctor of the Department of Orthopedics and Traumatology FCM/Unicamp, Coordinator of the Knee Surgery Group HC-FMC/Unicamp, Campinas State University Unicamp Campinas, SP
The aim of this study was to analyze the therapeutic effects of the open kinetic chain (OKC) and closed kinetic chain (CKC) exercises to treat the patellofemoral syndrome (PFSD). For this, 24 volunteers, bearers of the PFSD were randomly divided in two groups: group I (n = 12) performed the OKC exercises; group II (n = 12) performed the CKC exercises. Both groups were submitted to eight consecutive weeks of treatment consisting of three weekly sessions performed in alternate days. To analyze the activation pattern of the vastus medialis oblique (VMO) and the vastus lateralis (VL) muscles, the electromyographic signals (EMG) were collected using bipolar surface electrodes quantified by the root mean square (RMS) normalized by the maximal voluntary isometric contraction of the quadriceps. The pain intensity and the functionality of the volunteers were assessed using scales. The analysis of the amounts of the VMO/VL ratio in both groups I and II showed no significant differences as to the pre- and post-treatment times in the concentric (p > 0.05) and eccentric (p > 0.05) phases of the OKC and CKC exercises. Despite of this, the VMO muscle presented a lower activation rate compared to the VL in the eccentric phase of the CKC exercise. It was found significant increases in the functionality (p < 0.05), and a reduction in the pain intensity (p < 0.05) between the pre- and post-treatment times in both groups, but group II showed higher amounts compared to group I in both variables. The results found in this study suggest that according to the conditions of the trial, the OKC and CKC exercises provoke no changes in the patterns of the EMG activation in the VMO and VL muscles. However, they promoted an improvement in the functionality and a reduction in the pain intensity after the eight week intervention, and the CKC exercises presented better performances than OKC exercises.
Keywords: Knees. Electromyography. Exercise. Functional recovery.
El objetivo de este estudio era analizar los efectos terapéuticos de los ejercicios en la cadena cinética abierta (CCA) y la cadena cinética cerrada (CCC) en el tratamiento del síndrome del dolor femoropatelar (SDFP). Para esto se ofrecieron 24 portadores de SDFP que fueron divididos aleatoriamente en dos grupos: Se agruparon en: los ejercicios I en CCA (el n = 12); y los ejercicios II en CCC (el n = 12). Los grupos se sometieron a ocho semanas consecutivas de tratamiento que consistió en tres sesiones semanales logradas en los días alternados. Para los análisis de los modelos de activación de los músculos medio oblicuo (VMO) y vasto lateral (VL) las señales electromiográficas (EMG) adquiridas con los electrodos bipolares de superficie, cuantificaron por la raíz cuadrada del promedio (la raíz el cuadrado RMS) y se normalizó por el máximo de la reducción isométrico voluntario del cuádriceps. A través de balanzas se evaluó la intensidad del dolor y la funcionalidad de los voluntarios. El análisis de los valores de la razón VMO/VL en los grupos I y II demostramos que no había diferencias significantes entre la veces de tiempos pre y post-tratamiento en las fases concéntricas (el p > 0,05) y excéntricas (el p > 0,05) de los ejercicios en CCA y CCC. A pesar de eso, el músculo VMO presentó un punto de activación más pequeño respecto a VL en la fase excéntrica del ejercicio en CCF. En ellos se encontraron aumentos significantes en la funcionalidad (p < 0,05) y en la reducción de la intensidad del dolor (p < 0,05) entre veces de tiempo y post-tratamiento en ambos grupos, sin embargo, el de grupo II se mostraron superiores al grupo I en estas dos variables. Los resultados de este estudio sugieren que, de acuerdo con las condiciones experimentales usadas, los ejercicios en CCA y CCC no provocaron los cambios en los modelos de activación EMG de los músculos VMO y VL, sin embargo, ellos promovieron mejora de la funcionalidad y reducción de la intensidad del dolor después de ocho semanas de intervención, y los ejercicios en CCC eran superiores al de en CCA.
Palabras-clave: Rodilla. Eletromiografia. Ejercicio. Recuperación funcional.
The patellofemoral pain syndrome (PFSD) is a quite often affection seen in the orthopedic practice attacking mainly athletes and young adults. Although its etiology remains unknown, the force unbalance between the vastus medialis oblique (VMO) and the vastus lateralis (VL) muscles, which are the main dynamic stabilizers of the patella is considered the main factor that causes the symptoms' onset. Such unbalance causes changing in the patellar kinematics, contributing to increase the strength of the patellofemoral's reaction and compression(1).
The electromyographic (EMG) activation patterns of these muscles have been widely investigated(2,3). Some authors point out the decrease in the EMG activity of the VMO compared to the VL in individuals bearers of the PFSD, and they are searching for exercises to promote its selective activation(1,4).
Aiming the balance and function recovery of the extensor muscles of the knees and to re-establish the joint stability, the OKC and CKC exercises have been employed in rehabilitation programs to treat patellofemoral disturbances.
During the accomplishment of the OKC exercises, the femoral quadriceps muscle actuates isolately, thus favoring the increase in the forces of the patellofemoral compression(5). The CKC exercises generate muscular co-contraction, propitiating higher stability of the joint, besides of reproducing commonly performed functional movements in the day-to-day activities(6).
Despite of the increasing preference by CKC exercises and the discontinuance of OKC exercises to treat individuals with PFSD, there is scarcity of scientific reports showing which method is most effective when employed in the form of muscular training.
The aim of this study was to analyze the therapeutic effect of the OKC and CKC exercises on the pain intensity and the patellofemoral pain in individual bearers of the PFSD. For this, the EMG activation patterns of the VMO and VL muscles, the pain intensity, and the functionality of the participants were assessed.
This study was composed by 24 volunteers (17 women and 7 men) bearers of PFSD. The inclusion criteria adopted were: pain in the knees for more than two months, pain intensity higher than three and lower than eight in the visual analog scale (VAS), and pain or discomfort reported at least when performing two of the following situations: ascending and descending steps, kneeling, running, squatting, and remaining seated for prolonged times. It was excluded from the study those individuals who presented signals of any other condition in the knees joint.
The study was conducted according to the Resolution 196/96 of the National Health and Medical Sciences Council of the Campinas State University (Unicamp). All volunteers signed a free and clarified consent term approved by the committee.
The volunteers were randomly distributed in two groups: group I (n = 12), and group II (n = 12), as shown on table 1.
The treatment protocol consisted of three weekly physiotherapy sessions performed along eight weeks in alternate days. Table 2 presents the exercises that were part of the program for both groups I and II. To perform the isometric OKC and CKC exercises, it was performed four series of 10 repetitions, and each repetition was sustained for eight seconds followed by one minute resting period. As to the isotonic CKC exercises (45º leg press) and the OKC exercises (flexor-extensor bench), it was initially analyzed the maximal repetition (MR) of the femoral quadriceps (FQ) for each participant, and next, three series of ten repetitions were performed: the first at 20%, the second at 40%, and the third at 60% of the MR.
The OKC exercises were performed with a knees' ROM comprised between a 90 and 50º flexion (0º considered as the whole extension of the knees). To the CKC exercises, the ROM of the knees was from 0 to 50 grades flexion (0º considered as the whole extension of the knees). These criteria were adopted following the works performed by Steimkamp et al.(7) and Escamilla et al.(8), who suggested these angles as the most safe to perform the OKC and CKC exercises.
Aiming the isolate assessment of the muscular training effects, all volunteers were instructed to perform no activity involving flexibility exercises along the training period(9).
Pain and functionality
Aiming to measure the pain intensity upon the rest and while performing functional activities, the VAS and the Kujala scale were respectively applied(10,11).
The electrical activity of the VMO and VL muscles was attained by means of an eight-channel Myosystem electromyography (Noraxon, Scottsdale, Arizona) that presents a 114 dB rejection ratio in the common mode, an entry impedance between 20 MW and 1 GW, and bandwidth between 16 and 500 Hz. The electromyographic signals were collected at a 1,000 Hz frequency using the MyoResearch version 2.10 data acquisition software (Noraxon, Scottsdale, Arizona). These signals were stored on a PC for later visualization and analysis. To collect the electrical activity of the muscles, bipolar surface electrodes constituted by Ag/AgCl (Duo-Trode, Myotronics, Inc.) were used with two centimeters distance between the detection sites. The electrodes of the VMO and VL muscles were fixed over the muscular abdomen, and they were oriented at 55 and 15º related to the longitudinal axle of the femur, respectively(12,13). A reference electrode (ground) was fixed on the tibia's tuberosity. In order to reproduce the same position of the electrodes in the electromyographic assessment performed after the training program, it was measured the distance and the angles between them and the center of the patella. Thus, the amounts initially attained for each volunteer were reported and repeated in the final assessment.
To control the angle variation of the knee while performing the exercises, it was used a NorAngle double-axle electrogoniometer (Noraxon, Scottsdale, Arizona) connected to the conditioner module of the electromyographic signals. To fasten it, it was used two plastic poles which were positioned on the lateral spots of the thigh (upper pole), and on the lateral portion of the leg (lower pole) of each volunteer(14). The joint positioning and the EMG activity were simultaneously recorded with the same sampling frequency (1,000 Hz).
The velocity to perform the exercises was controlled by means of a metronome adjusted to accomplish thirty touches per minute. Before starting the data collection, all volunteers were familiarized with the trial as to the correct performance of the exercises.
To the group submitted to the CKC protocol, the collections were performed during the semi-squatting exercise in its eccentric phase (down) and in the concentric phase (up). From the stand up position, the volunteers performed five repetitions of the squatting and rising movements, and it was granted one minute rest between each repetition. Each repetition lasted four seconds.
To the group submitted to the OKC protocol, the data collections were performed on a flexor-extensor bench. The volunteers remained seated having their lumbar and thoracic spine supported, hips and knees at a 90º flexion. Next, they performed five repetitions of the extension movement (concentric phase), and flexion of the knees (eccentric phase), and it was granted also one minute rest between each of them. The load used during the exercise was of 40% of the MR, and each repetition lasted four seconds.
Normalization of the EMG signals
Several studies suggest the normalization of the EMG signal by the maximal voluntary isometric contraction (MVIC)(15). For this, it is demanded an exercise that promotes the MVIC of the assessed muscles, and then, the mean value is attained by the root mean-square (RMS) of that exercise, which will represent the maximal electrical activity these muscles are able to generate(16). Thus, the means of the amounts in RMS of the other exercises are quantified as a percentage of that amount.
In this study, the MVIC of the knee extensor positioned at a 90º flexion was used to normalize the data, and having the tibia at a neutral positioning. The MVIC collections were performed on a flexor-extensor bench, and each contraction lasted four seconds.
To perform intergroup comparisons as to the amounts attained in the Kujala and VAS scales in the pre- and post-treatment times, as well as to verify the homogeneity of the groups, the Mann-Whitney test was used. As to the intergroup analysis of the VMO/VL ratio, the Kujala scale and the VAS between the pre-and post-treatment, the Wilcoxon test was used for related sampling. The significance level adopted for the statistical tests was 5%.
It is verified on table 3 the values of the means and the standard deviations of the normalized EMG activity of the VMO and VL muscles related to the group I during the concentric and eccentric phases of the flexor-extensor exercise of the knees (OKC).
There was no statistically significant differences in the VMO/VL ratio between the pre- and post-treatment times in the concentric (p = 0.79) and eccentric (p = 0.85) phases of the exercise.
As to the group II, table 4 shows the means and the standard deviations of the normalized EMG activity of the VMO and VL muscles, as well as the VMO/VL ratio in the concentric and eccentric phases of the semi-squatting exercise (CKC). These data show that there were no significant differences in the amounts of the VMO/VL ratio in the concentric (p = 0.56) and eccentric (p = 0.26) phases of the exercise after the treatment.
Tables 3 and 4 show that the amounts of the VMO/VL ratio were lower than 1, indicating a decrease in the VMO activation compared to the VL. Such decrease was observed both in the concentric and in the eccentric phases in both assessed exercises, and it was detected a higher discrepancy between the amounts of the activation percentage of those muscles in the eccentric phase of the CKC exercise.
In figure 1 it is verified the results related to the pain intensity measured by the VAS before and after the treatment.
The intergroup analysis has shown that before the beginning of the program, there was no statistically significant difference between the means of groups I and II as to the pain's VAS (p = 0.82). However, upon the completion of the program, group II attained an accentuated improvement compared to the group I (p = 0.02). The intergroup comparison disclosed that both groups presented a statistically significant improvement after the eight week treatment (p = 0.0005 for group I; p = 0.0005 for group II).
Figure 2 illustrates the results attained through the functional Kujala scale. As to the intergroup comparison, it was observed no statistically significant different in the beginning of the treatment between them (p = 0.68). But when performing the same comparison at the end of the treatment, it was evidenced better results for the group II (p = 0.03). As to the intergroup analysis, both presented significant gains in the functionality after the treatment (p = 0.0005 for group I; p = 0.0005 for group II).
The results found in this study disclosed that after an eight week treatment, the groups attained a significant reduction in the pain intensity and an improvement to perform functional activities. The group II has shown higher results than group I in both assessed variables. These findings are in accordance to the ones found by Witvirouw et al.(17), who, after submitting 60 individuals to a five week treatment using OKC and CKC exercises, observed an increase in the torque peak of the FQ and ischiotibialis muscles, pain reduction and functional gain in both assessed groups.
In another study, Witvirouw et al.(18) reported excellent results related to the pain and functionality after treating individuals reporting patellofemoral pain, but they did not evidence any effect of such treatment on the reflexive response time of the VMO and VL muscles. Likewise, Stiene et al.(19) concluded that after an eight week treatment, the CKC exercises were more effective than the OKC exercises in the functional recovery of individual bearers of patellofemoral disorder.
Bennett & Stauber(20) initially assessed 41 individuals with PFSD, and they identified a reduction in the extensor torque of the knees during the eccentric phase of the OKC exercise. Thus, they applied a treatment program using only OKC exercises performed on the isokinetic dynamometer, and they evidenced that in about four weeks, the individuals had a reduction in the pain, re-establishing the extensor torque of the knees, and they returned to the sportive activities.
The above exposed statement suggests that both the OKC and the CKC exercises can be employed to treat the PFSD. Nevertheless, before prescribing the activities to strengthen the FQ, it is necessary to understand the biomechanical principles of the patellofemoral joint in order to make an exercise scheduling that combines effectiveness and safety. In the present study, the knee's ROM was limited during the accomplishment of the exercises that integrated the treatment program, opposed to the previously mentioned studies. According to Steimkamp et al.(7), while performing OKC exercises it must be avoided the last extension grades of the knees, since such angles have a lower joint contact, but the compressive strengths are distributed over a small area, thus increasing the patellofemoral stress.
As to the CKC exercises, the authors suggest to avoid higher than 45º angles of the knee flexion, since despite the higher joint stability with the increment of the flexion, there is also an increase in the compressive strengths and a higher patellofemoral stress. Similar results were described by Doucette & Child(21), who suggest performing OKC exercises with higher than 30º angles for the knee flexion, while CKC exercises must be performed in angles closed to its whole extension.
The results related to the EMG activity has shown that after the treatment, there was no significant differences in the VMO/VL ratio in the eccentric and concentric phases of the OKC and CKC exercises. However, the comparison of these findings with prior studies was difficult, as it was not found any work in the literature assessing the isolate effects of the muscular training in OKC and CKC on the EMG activation patterns of the stabilizer muscles of the patella in PFSD bearers. Nonetheless, even being not influenced by the treatment, the EMG activation patterns of the VMO and VL muscles has shown to be distinct in the concentric and eccentric phases in the assessed exercises. The RMS amounts related to the VMO/VL ratio in the pre- and post-treatment times disclosed an accentuated reduction in the VMO activation in the eccentric phase of the CKC exercise. These findings confirm what was found by Shenny et al.(22), who reported a decrease in the VMO activation related to the VL in individuals with patellofemoral pain while descending steps (eccentric contraction). Souza & Gross(23) reported similar findings after assessing the VMO/VL ratio during isometric, concentric isotonic, and eccentric isotonic contraction of the FQ, showing a reduction in the EMG activity of the VMO compared to the VL in symptomatic individuals.
Owings & Grabiner(1) identified a higher EMG activity of the VL compared to the VMO in the eccentric phase of the leg extension OKC exercise, suggesting a deficit in the motor controlling of the patellar stabilizers in PFSD bearers.
On the other hand, Powers et al.(24) identified activation patterns similar to the VMO and VL muscles in individuals with patellofemoral pain, and they did not observe any commitment of the VMO activation while performing CKC activities. Similar results were described by Cerny(25), who did not observe significant differences in the VMO/VL ratio in individuals PFSD bearers performing CKC exercises. One possible explanation for the differences in the results of these studies is related to the diversity of methods used to the acquisition and processing the electromyographic signals(26). Furthermore, the inherent variability of the individuals with PFSD remains as a challenge to determine the specific activation patters of the stabilizer patella muscles among such population.
Even when it does not cause any alteration in the muscular activation patterns, the interventional schedule adopted in this study has shown to be effective to treat the PFSD. Such fact can be attributed to the strengthening of the FQ as a whole, once the extensor muscles of the knees absorb part of the strength imposed to the joint while performing activities that cause an overload to it. Thus, it is believed that the recovery of the quadricipital function is able to re-establish the biomechanical properties of the patellofemoral and femorotibial functions, to increase the extensor torque of the knees and to improve the clinical and functional pictures in individual bearers of PFSD(17,20).
Powers et al.(27) identified that together with a reduction in the torque generated by the FQ, there was a commitment of the locomotive function in symptomatic individuals, pointing out the importance of the quadricipital strengthening in the PFSD treatment. In recent reviews, Wilk & Reinold(28) and Crossley et al.(29) showed evidences pointing that the FQ strengthening exercises are an indispensable part of rehabilitation programs involving patellofemoral disorders. But despite these reports, the mechanism by which the FQ strengthening promotes an increase in the functionality and reduction of the symptoms in individuals bearers of patellofemoral pain is not quite clarified.
Before the scarcity of studies assessing the effects of the muscular training to treat the PFSD, it is necessary to conduct further studies involving a higher amount of individuals in the sampling, longer intervention periods and using different exercises to help in the collection of information that propitiate to perform and apply a more effective rehabilitation program that favor the improvement of the quality of life in individuals bearers of such affection.
In the experimental conditions used in this study, the OKC and CKC exercises promoted a reduction in the pain intensity and improvement of the functionality in PFSD bearers. The CKC exercises have shown to be more effective compared to the CKC exercises.
As to the EMG activation patterns, the exercises were not able to change the amounts of the VMO/VL ratio. Nevertheless, the VMO muscle presented an accentuated reduction in the activation related to the VL in the eccentric phase of the CKC exercise.
All the authors declared there is not any potential conflict of interests regarding this article.
1. Owings TM, Grabiner M. Motor control of the vastus medialis oblique and vastus lateralis is disrupted during eccentric contractions in subjects with patellofemoral pain. Am J Sports Med 2002;30:483-7. [ Links ]
2. Brody LT, Thein JM. Nonoperative treatment for patellofemoral pain. J Orthop Sports Phys Ther 1998;28:336-44. [ Links ]
3. Karst GM, Jewett PD. Electromyographic analysis of exercises proposed for differential activation of medial and lateral quadriceps femoris muscle components. Phys Ther 1993;73:286-95. [ Links ]
4. Hanten WP, Schulthies SS. Exercise effect on electromyographic activity of the vastus medialis oblique and vastus lateralis muscles. Phys Ther 1990;70:561-5. [ Links ]
5. Lam PL, Gabriel YF. Activation of the quadriceps muscle during semisquatting with different hip and knee positions in patients with anterior knee pain. Am J Phys Med Rahabil 2001;80:804-8. [ Links ]
6. Wilk KE, Escamilla RF, Fleisig GS, Barrentine SW, Andrews JR, Boyd ML. A comparison of tibiofemoral joint forces and electromyographic activity during open and closed kinetic chain exercises. Am J Sports Med 1996;24:518-27. [ Links ]
7. Steinkamp LA, Dillingham MF, Markel MD, Hill JA, Kaufman KR. Biomechanical considerations in patellofemoral joint rehabilitation. Am J Sports Med 1993;21: 438-44. [ Links ]
8. Escamilla RF, Fleisig GS, Zheng N, Barrentine SW, Wilk K, Anderws JR. Biomechanics of the knee during closed kinetic chain and open kinetic chain exercises. Med Sci Sports Exerc 1998;30:556-69. [ Links ]
9. Cyrino ES, Oliveira AR, Leite JC, Porto DB, Dias RMR, Segantin AQ, et al. Comportamento da flexibilidade após 10 semanas de treinamento com pesos. Rev Bras Med Esporte 2004;10:233-7. [ Links ]
10. Bennell K, Bartram S, Crossley K. Outcome measures in patellofemoral pain syndrome: test retest reliability and inter-relationships. Phys Ther Sport 2000; 1:32-4. [ Links ]
11. Kujala UM, Jaakola LH, Koshinen SK, Taimela S, Hurme M, Nelimarkka O. Scoring of patellofemoral disorders. Arthroscopy 1993;9:159-63. [ Links ]
12. De Luca CJ. The use of surface electromyography in biomechanics. J Appl Biomech 1997;13:135-63. [ Links ]
13. Lieb FJ, Perry J. Quadriceps function: an anatomical and mechanical study using amputated limbs. J Bone Joint Surg [Am] 1968;50:1535-48. [ Links ]
14. Araujo RC, Amadio AC. Análise biomecânica da ativação das porções superficiais do m. quadríceps femoral durante contrações excêntrica e concêntrica. Rev Bras Fisiot 1996;1:13-20. [ Links ]
15. Turker KS. Electromyography: some methodological problems and issues. Phys Ther 1993;73:698-710. [ Links ]
16. Basmajian JV, De Luca CJ. Muscle alive: their function revealed by electromyography. 5th ed. Baltimore: Willians & Wilkins, 1985. [ Links ]
17. Witvrouw E, Lysens R, Bellemans J, Peers K Vanderstraeten G. Open versus closed kinetic chain exercises for patellofemoral pain: a prospective, randomized study. Am J Sports Med 2000;28:687-94. [ Links ]
18. Witvrouw E, Cambier D, Danneels L, Bellemans J, Werner S, Almqvist F, et al. The effect of exercise regimens on reflex response time of the vasti muscles in patients with anterior knee pain: a prospective randomized intervention study. Scand J Med Sci Sports 2003;13:251-8. [ Links ]
19. Stiene HA, Brosky T, Reinking MF, Nyland J, Mason MB. A comparison of closed kinetic chain and isokinetic joint isolation exercise in patients with patellofemoral dysfunction. J Orthop Sports Phys Ther 1996;24:136-41. [ Links ]
20. Bennett JG, Stauber WT. Evaluation and treatment of anterior knee pain using eccentric exercise. Med Sci Sports Exerc 1986;18:526-30. [ Links ]
21. Doucette AS, Child D. The effect of open and closed chain exercise and knee joint position on patellar tracking in lateral patellar compression syndrome. J Orthop Sports Phys Ther 1996;23:104-10. [ Links ]
22. Sheehy P, Burdett RG, Irrgang JJ, VanSwearingen J. An electromyographic study of vastus medialis oblique and vastus lateralis activity while ascending and descending steps. J Orthop Sports Phys Ther 1998;27:423-9. [ Links ]
23. Souza DR, Gross MT. Comparison of vastus medialis obliquus: vastus lateralis muscle integrated electromyographic ratios between healthy subjects and patients with patellofemoral pain. Phys Ther 1991;71:310-6. [ Links ]
24. Powers CM, Landel R, Perry J. Timing and intensity of vastus muscle activity during functional activities in subjects with and without patellofemoral pain. Phys Ther 1996;76:946-55. [ Links ]
25. 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. [ Links ]
26. Merletti R, Rainold A, Farina D. Surface electromyography for noninvasive characterization of muscle. Exerc Sport Sci Rev 2001;29:20-5. [ Links ]
27. Powers CM, Perry J, Hsu A, Hislop HJ. Are patellofemoral pain and quadriceps femoris muscle torque associated with locomotor function? Phys Ther 1997; 77:1063-78. [ Links ]
28. Wilk KE, Reinold MM. Principles of patellofemoral rehabilitation. Sports Med Arthrosc 2001;9:325-36. [ Links ]
29. Crossley K, Bennell K, Green S, McConnell J. A systematic review of physical interventions for patellofemoral pain syndrome. Clin J Sport Med 2001;11:103-10. [ Links ]
Guilherme Lotierso Fehr
Rua João de Bortoli, 354, Jardim Flórida
14026-330 Ribeirão Preto, SP
Phone: (16) 3911-1345
Received in 10/5/05.
Final version received in 30/10/05.
Approved in 3/11/05.