Electromyographic study of two-joint muscles.

To determine the nervous control of two-joint muscles and their coordination with other muscles in monoarticular and biarticular motions, action patterns of important two-joint muscles (rectus femoris and the medial hamstrings) and related one-joint muscles were observed. The EMG analysis of ten subjects led to the conclusion that the effect of contraction of two-joint muscles is never limited to one joint; whenever a two-joint muscle participates in a monoarticular motion its role shifts in close coordination with the other muscles. In biarticular concurrent motion the activity of the rectus femoris and the medial hamstrings is inhibited when they are antagonists, especially when motion of the knee is concerned.     

Optimum length of muscle contraction.

OBJECTIVE: The purpose of this study was to develop a mathematical method to determine optimum muscle length and muscle stress based on the measurable physiological and biomechanical data. DESIGN: The values of optimum muscle length and muscle stress are investigated. BACKGROUND: Understanding the characteristics of muscle function in vivo is important for assisting the design of the tendon transfer and other rehabilitation procedures. In vivo determination of the physiological and anatomical parameters of muscle contraction is difficult but not impossible. Optimum muscle length and muscle stresses are important parameters for understanding muscle function. METHODS: A Cybex dynamometer was used to measure isometric elbow flexion torque in eight different joint positions in seven subjects. Then the optimization method was used to determine optimum muscle length and muscle stress of three major elbow flexors, the biceps brachii, the brachialis, and the brachioradialis based on the model and joint torque data. RESULTS: The calculated muscle stress for each subject was on average 109 N/cm(2), while the optimum muscle length for the biceps brachii, the brachialis, and the brachioradialis was on average 14.05, 6.53, 17.24 cm, respectively. The joint angles corresponding to these optimum muscle lengths are 110 degrees, 100 degrees and 50 degrees of elbow flexion, respectively. CONCLUSIONS: Optimum muscle length and muscle stress can be properly predicted using an analytical mathematical model along with an experimentally measured joint torque. RELEVANCE: The estimate of optimum muscle length is important for muscle modeling and tendon transfer surgery by taking advantage of length-tension relationship of individual muscles.     

One session of whole body vibration increases voluntary muscle strength transiently in patients with stroke

OBJECTIVE: To determine the effect of whole body vibration on isometric and eccentric torque and electromyography (EMG) variables of knee extensors on the affected side of stroke patients. DESIGN: A randomized controlled study. SETTING: A rehabilitation centre. SUBJECTS: Sixteen patients (age 58.2+/-9.4 years) were enrolled in an inpatient rehabilitation programme 27.2+/-10.4 days after a stroke. INTERVENTIONS: Eight patients were randomly assigned to the vibration group and received 20 Hz vibration (5 mm amplitude) while standing on a vibration platform for 1 minute six times in one session. Patients in the control group also stood on the platform but did not receive vibration. MAIN MEASURES: Maximum isometric and eccentric torque, rate of torque development, root-mean-squared EMG, median frequency of vastus lateralis, and co-activation of knee flexors. RESULTS: Isometric and eccentric knee extension torque increased 36.6% and 22.2%, respectively, after vibration (P<0.05) and 8.4% and 5.3% in the control group. Vibration increased EMG amplitude 44.9% and the median frequency in the vastus lateralis by 13.1% (all P<0.05) without changes in the control group (10.6% and 3.9%). Vibration improved the ability to generate mechanical work during eccentric contraction (17.5%). Vibration reduced biceps femoris co-activation during isometric (8.4%, ns) and eccentric (22.5%, P<0.05) contraction. CONCLUSION: These results suggest that one bout of whole body vibration can transiently increase voluntary force and muscle activation of the quadriceps muscle affected by a stroke.     

Altered hamstring-quadriceps muscle balance in patients with knee osteoarthritis

BACKGROUND: To compare hamstring to quadriceps muscle coactivity during level walking, stair ascent, and stair decent between individuals with and without knee osteoarthritis. METHODS: In a cross-sectional study, subjects with grade II knee osteoarthritis (n = 26), healthy age- and gender-matched (n = 20) and healthy, young adults (n = 20) performed three activities of daily living. During the stance phase of these activities surface electromyography was measured. Two coactivity ratios were computed, the biceps femoris to vastus lateralis ratio and the ratio of the biceps femoris EMG activity relative to the EMG activity measured during contraction- and velocity-specific maximal voluntary biceps femoris contraction, i.e., biceps femoris to maximal biceps femoris activity. FINDINGS: Subjects with knee osteoarthritis had significantly higher coactivity than age-matched healthy adults and young adults and healthy adults had more coactivity than young adults regardless the type of coactivity ratio. The biceps femoris to vastus lateralis ratio yielded 25% higher coactivity value than the biceps femoris to maximal biceps femoris ratio (P < 0.0001). The EMG activity of the vastus lateralis relative to maximal vastus lateralis EMG activity was 92% in subjects with knee osteoarthritis, 57% in age-matched controls, and 47% in young adults (P < 0.0001). INTERPRETATION: Patients with knee osteoarthritis revealed increased hamstring muscle activation while executing activities of daily living. Altered muscle activation at the knee may interfere with normal load distribution in the knee and facilitate disease progression. Therapeutic interventions should focus not only on quadriceps strengthening but also on improving muscle balance at the knee.     

Electromyographic analysis of knee exercises in healthy subjects and in patients with knee pathologies

Little information exists about the intensity of contraction required from knee and hip musculature during common therapeutic exercises used for patient populations. This study, therefore, was designed to compare electromyographic data obtained from the vastus medialis, rectus femoris, gluteus medius, and biceps femoris muscles during maximally resisted straight-leg-raising (SLR) exercises with EMG data obtained from the same muscles during quadriceps femoris muscle setting (QS) exercises in healthy subjects and in patients with knee pathologies. Of the 30 participants in the study, 16 had a history of knee injury or surgery. All participants performed randomly ordered trials of the SLR and QS exercises while the EMG data were recorded from surface electrodes and normalized to values derived from maximal effort isometric contraction trials. An analysis of variance demonstrated significantly greater activity (p less than .05) of the vastus medialis, biceps femoris, and gluteus medius muscles during QS exercises than during SLR exercises. The rectus femoris muscle was significantly more active (p less than .05) during SLR exercises than during QS exercises. The study demonstrated remarkably different degrees of muscle activation between the SLR and QS exercises, indicating that the exercise selected will affect the therapeutic intention.     

Biomechanical changes at the knee after lower limb fatigue in healthy young women

Background

The purpose of this study was to identify changes in knee kinematics, kinetics and stiffness that occur during gait due to lower limb neuromuscular fatigue.

Methods

Kinematic, kinetic and electromyographic measures of gait were collected on healthy, young women (n = 20) before and after two bouts of fatigue. After baseline gait analysis, two bouts of fatiguing contractions were completed. Fatigue was induced using sets of 50 isotonic knee extensions and flexions at 50% of the peak torque during a maximum voluntary isometric contraction. Fatigue was defined as a drop in knee extension or flexion maximum voluntary isometric torques of at least 25% from baseline. Gait analyses were completed after each bout of fatigue. Dynamic knee stiffness was calculated as the change in knee flexion moment divided by the change in knee flexion angle from 3 to 15% of the gait cycle. Co-activations of the biceps femoris and rectus femoris muscles were calculated from 3 to 15% and 40 to 52% of gait. Repeated measures analyses of variance assessed differences in discrete gait measures, knee torques, and electromyography amplitudes between baseline and after each bout of fatigue.

Findings

Fatigue decreased peak isometric torque. Fatigue did not alter knee adduction moments, knee flexion angles, dynamic knee stiffness, or muscle co-activation. Fatigue reduced the peak knee extension moment.

Interpretation

While neuromuscular fatigue of the knee musculature alters the sagittal plane knee moment in healthy, young women during walking, high intensity fatigue is not consistent with known mechanical environments implicated in knee pathologies or injuries.     

How Different Knee Flexion Angles Influence the Hip Extensor in the Prone Position

[Purpose] The present study examined the effects of knee flexion angle on hip extensor muscle activity. [Subjects and Methods] Twenty healthy subjects maintained knee flexion angles of 0°, 30°, 60°, 90° and 110° in the prone position and performed maximal voluntary contraction in hip extension. Maximum torque in hip extension at the different angles was measured, and surface electromyogram activities of the gluteus maximus (GM), biceps femoris (BF) and semitendinosus (ST) were recorded and normalized by the maximum voluntary isometric contraction (MVIC). [Results] The maximum torque of the hip extensor showed significant decreases between 0°and 60°, 90° and 110° of knee flexion. The muscle activity of BF was significantly high at 0°, and GM showed a significantly higher activity than both BF and ST at 60°, 90°and 110° of knee flexion. [Conclusion] The maximum torque in hip extension and muscle activities of BF and ST were significantly high at 0° but they decreased at knee flexion angles of more than 60°. Therefore, we consider that more than 60° of knee joint flexion is required to increase GM activity, and to reduce the muscle activities of BF and ST.Key words: Gluteus maximus, Hamstring muscle, Prone hip extension     

Electrically elicited fatigue test of the quadriceps femoris muscle. Description and reliability

The purposes of this study were to develop an electrically elicited fatigue test (EEFT) that uses electrically elicited isometric muscle contractions and to examine the reliability of this test on a group of healthy individuals. Fifteen subjects were tested on two occasions, one week apart. The subjects were seated and the left leg secured to an isokinetic dynamometer with the knee positioned at 45 degrees of flexion. Maximum voluntary isometric contraction (MVIC) of the quadriceps femoris muscle was obtained and resultant knee extension torque was recorded. The quadriceps femoris muscle then was stimulated 50 times at the current level that elicited a knee extension torque level equal to 60% of that obtained during the MVIC. Percentages of decline in torque were calculated. Test-retest reliability indexes were calculated for the means of contractions 21 to 25 (r = .82, ICC = .83) and for contractions 46 to 50 (r = .92, ICC = .82). The EEFT was found to be reliable and may provide a clinically applicable means of measuring peripheral muscle fatigue.     

屈膝肌群在不同起始角度下的募集特征分析

目的:探讨在不同起始角度下,股后肌群与腓肠肌群参与屈膝动作的募集程度与动员顺序,为运动训练、运动康复的运动处方设计提供建议.方法:20例健康成年男子在坐姿屈膝训练器上,以5个起始角度做负荷为1RM(1次重复最大负荷)的80％屈膝动作3次,采集其屈膝肌群的表面肌电图.结果:①在同一起始角度下,屈膝动作中各肌群的募集比例一...     

Fatigue-induced changes in phasic muscle activation patterns during dynamic trunk extension exercise

OBJECTIVE: To investigate the influence of fatigue on phasic muscle-activation patterns during dynamic trunk extension exercise. DESIGN: Fifteen healthy volunteers performed dynamic trunk-extension exercise through a 30-degree range-of-motion (ROM) exercise to task failure at an intensity of 50% of maximum. Electromyography (EMG) signals were recorded unilaterally from the lumbar extensor, gluteus maximus, and biceps femoris muscles, and signal amplitude was analyzed in 10-degree increments during the unfatigued and fatigued states (0-10 degrees from torso horizontal to the ground was considered extension, and 11-20 and 21-30 degrees of flexion relative to this were considered midphase and flexion, respectively). RESULTS: Lumbar extensor EMG was approximately 75% of maximum EMG, with no differences being observed with respect to ROM or fatigue state. The gluteus maximus demonstrated an altered phasic activation pattern with fatigue, with an increased recruitment during the extension phase (fatigued-state extension-phase EMG: 89.1 +/- 8.3% > flexion phase EMG: 37.8% +/- 9.1%). The biceps femoris demonstrated a similar response during both the fatigued and unfatigued states (fatigued-state extension EMG: 77.8 +/- 5.4% > midphase EMG: 65.8 +/- 5.7% > flexion EMG: 46.8 +/- 4.0%; unfatigued-state extension EMG: 46.1 +/- 3.7% > flexion EMG: 27.1 +/- 2.6%). CONCLUSIONS: During this exercise, as one moves from flexion to extension, hip extensor muscle activity increases, whereas lumbar extensor activity does not. Additionally, fatigue results in an altered recruitment pattern, with the hip extensors being activated to a greater extent in the extension phase. These findings suggest that when this exercise is performed in the prone position, it can be used to stimulate the lumbar and hip extensor muscles, but the specific exercise protocol in terms of set/repetition number and ROM will influence which muscles are primarily targeted.     

运动疗法对膝关节骨关节炎患者肌发电量的影响

目的：研究肌发电量在膝关节骨关节炎患者股四头肌肌力训练中的变化情况及股四头肌的详细变化情况。方法：采用股四头肌的等长收缩运动训练方法和其他疗法进行比较,用肌电图进行股直肌、股内侧肌、股外侧肌的肌发电量测定,同时用“膝关节功能评定表”进行功能的辅助评定。结果：两种方法治疗后,股直肌、股内侧肌的肌发电量都有显著的变化,尤其以股内侧肌的变化极显著,股外侧的肌发电量无显著变化。两种方法中肌力训练较其他治疗方法在提高肌发电量方面更为有效。结论：股内侧肌在膝关节肌力锻炼中的变化最大,说明股内侧肌比股直肌和股外侧肌在稳定膝关节方面更重要。股外侧肌在训练中的变化最小,在维护膝关节的稳定性方面起的作用比股内侧肌和股直肌小;肌力训练比其他方法在增加肌发电量方面更有效,更能提高膝关节的稳定性。     

Three-dimensional geometry of the human biceps femoris long head measured in vivo using magnetic resonance imaging

Background

The human biceps femoris long head is susceptible to injury, especially when sprinting. The potential mechanical action of this muscle at a critical stage in the stride cycle was evaluated by calculating three-dimensional lines-of-action and moment arms about the hip and knee joints in vivo.

Methods

Axial magnetic resonance images of the right lower-limb (pelvis to proximal tibia) were recorded from four participants under two conditions: a reference pose, with the lower-limb in the anatomical position and the hamstrings relaxed; and a terminal swing pose, with the hip and knee joints flexed to mimic the lower-limb orientation during the terminal swing phase of sprinting and the hamstrings isometrically activated. Images were used to segment biceps femoris long head and the relevant bones. The musculotendon path and joint coordinate systems were defined from which lines-of-action and moment arms were computed.

Findings

Biceps femoris long head displayed hip extensor and adductor moment arms as well as knee flexor, abductor and external-rotator moment arms. Sagittal-plane moment arms were largest, whereas transverse-plane moment arms were smallest. Moment arms remained consistent in polarity across all participants and testing conditions, except in the transverse-plane about the hip. For the terminal swing pose compared to the reference pose, sagittal-plane moment arms for biceps femoris long head increased by 19.9% to 48.9% about the hip and 42.3% to 93.9% about the knee.

Interpretation

Biceps femoris long head has the potential to cause hip extension and adduction as well as knee flexion during the terminal swing phase of sprinting.     

Gait and electromyographic analysis of patients recovering after limb-saving surgery

OBJECTIVE: Control of gait after limb-saving surgery.Design. Case series study. BACKGROUND: At the moment little is known about adaptations in patients' gait after limb-saving surgery. METHODS: Nineteen patients who underwent limb-saving surgery at least 1 yr earlier and 10 normal subjects were studied during treadmill walking. The main outcome measures were walking speed, step parameters and angular displacement of both legs and EMG of the biceps femoris, rectus femoris and medial gastrocnemius in the affected leg. RESULTS: Preferred walking speed in the patients was lower than in the controls (0.7 versus 1.1 m/s). Furthermore, stance phase of the non-affected leg was lengthened. All patients showed reduced stance phase knee flexion in the affected leg, while during the swing phase no difference was seen. The EMG signals of the rectus femoris and biceps femoris show changes, which are related to the location of surgery. CONCLUSIONS: The results showed that the gait pattern of the patients differed compared to normal gait. The reduced stance phase knee flexion in the hip group is based on a high degree of co-contraction between quadriceps and hamstring activity, while in the knee group this is based on the quadriceps avoidance pattern. The finding that there is still side-to-side asymmetry indicates that there is no complete reorganisation following the massive loss of input and output of the leg. It is possible that some reprogramming of the locomotor process occur. RELEVANCE: Gait and electromyographic analysis are essential for the quantitative assessments of the functional outcome in this type of surgery.     

Activity of the Femoral Muscles during Toe-gripping Action

[Purpose] In the present study, we investigated femoral muscle activity during toe-gripping, and the role of the femoral muscles in toe-gripping strength. [Subjects] Fourteen healthy young women were selected. [Methods] We measured the maximum voluntary contraction of the rectus femoris and long head of the biceps femoris muscles. We then calculated the percent integrated EMG (%IEMG) during the toe-gripping action. [Results] We found that the %IEMG of the biceps femoris was significantly higher than that of the rectus femoris. Moreover, a significant positive correlation was found between the %IEMG of the rectus femoris and that of the biceps femoris. [Conclusion] These results suggest that femoral muscles co-contract during the toe-gripping action, and thus possibly contribute to knee joint stability.     

Changes in muscle activity during fast, alternating flexion-extension movements of the knee

The effects of high frequency alternating knee flexion-extension on muscle activity of the quadriceps and hamstring muscle groups has been investigated. Standard loads were used for each subject. The muscle activity in vastus medialis, vastus lateralis, rectus femoris and the lateral hamstrings were recorded by electromyography during increasing velocities. Rectus femoris and hamstrings were found to increase their activities significantly with increasing speed while vastus medialis and vastus lateralis showed no such change. The individual thigh muscles thus differ in function in relation to the velocity of movement.     

Neuromuscular and architectural alterations of the vastus lateralis muscle in elderly patients with unilateral knee osteoarthritis]

AIM: The aim of this study was to determine the mechanisms involved in muscle weakness in elderly patients with unilateral knee osteoarthritis. SUBJECTS: We investigated 7 patients with unilateral knee osteoarthritis. METHOD: We measured knee position sense and isometric maximal voluntary contraction (MVC) of the knee extensors. Electromyographic (EMG) measurement of biceps femoris (BF), rectus femoris (RF), vastus lateralis (VL) and vastus medialis (VM) involved different levels of contraction (25, 50, 75 and 100% MVC). Neuromuscular efficiency of quadriceps was also calculated (MVC/EMG). Ultrasonography was used to investigate the VL architectural parameters at the median part of the VL for different levels of contraction (25, 50, and 75% MVC). All tests were performed on the osteoarthritic and healthy knees. RESULTS: The quadriceps MVC of the affected knee was reduced by 30%. The VL thickness of the affected knee was 10% smaller than that of the unaffected knee. VL activity seen on EMG did not differ between knees, but RF, VM and BF activity was greater in the unaffected than affected knee. Neuromuscular efficiency was higher (26%) in the unaffected knee. Knee position sense was reduced by 33% in the affected knee. CONCLUSION: Quadriceps weakness associated with knee osteoarthritis seems to be related to changes in muscle rather than pennation angle and changes in fascicule length.     

Electromyographic activity of the quadriceps components during the final degrees of knee extension

An imbalance in the recruitment patterns of the quadriceps muscle has been implicated in patellofemoral knee pain; however ambiguity remains in the normal recruitment patterns of this muscle. We investigated the activity of the quadriceps muscle during the final degrees of knee extension, specifically in the medial and lateral components. Sixteen healthy subjects (age; 22.5 (± 3.4) years, body mass; 67.5 (± 12.1) kg and height; 173.9 (± 10.4) cm) participated.Torque and electromyographic (EMG) activity of the quadriceps muscle were measured during isokinetic and isometric knee extensions. Torque and EMG activity reduced in all component muscles during the final degrees of isokinetic extension, but this did not occur during isometric contractions at similar angles. Normalised activity of rectus femoris (RF) was greater than that of vastus lateralis (VL) and vastus medialis obliquus (VMO) during the final degrees of isokinetic knee extension at 30°/sec; there were no differences between any component muscles at the higher velocities. VMO:VL and vastus medialis longus (VML):VL ratios were unchanged during knee extensions, except that VML:VL ratio increased significantly during the final degrees of extension at 30°/sec. Future work should compare these results with people with anterior knee pain, and explore this further during activities of daily living.     

An electromyographic analysis of quadriceps femoris muscle setting and straight leg raising

Physical therapists routinely advise patients to perform quadriceps femoris muscle setting or straight leg raising or both following knee surgery or trauma from knee injury. Little information exists, however, about the intensity of effort required from knee and hip musculature during the exercises. This study was designed to compare the level of electromyographic activity during maximally resisted straight leg raises with the level during quadriceps femoris muscle setting exercises for the vastus medialis, rectus femoris, gluteus medius, and biceps femoris muscles. Forty healthy young adult men and women performed randomly ordered trials of each exercise in the supine position. Electromyographic activity was recorded from surface electrodes and normalized to values derived from maximal isometric trials. Statistical analysis demonstrated significantly greater (p less than .0001) vastus medialis, biceps femoris, and gluteus medius muscle activity during quadriceps femoris muscle setting. The rectus femoris muscle was significantly more active (p less than .0001) during the straight leg raise. The study demonstrated remarkably different muscle activation levels between the exercises studied and clearly indicates that selection of the exercises needs to be based on the therapeutic objectives.     

Intra-articular anesthesia and knee muscle response

BACKGROUND: Many receptors located within the intra-articular knee structures contribute to the neuromuscular responses of the knee. The purpose was to compare the automatic postural response induced by a perturbation at the foot before and after an intra-articular injection of a local anesthetic (bupivicaine), after a saline (sham) injection, and after no intra-articular injection (control) in the knee. METHODS: Muscle onset latencies and automatic response magnitudes for the vastus medialis, vastus lateralis, biceps femoris, medial hamstrings, tibialis anterior, and gastrocnemius were measured using electromyography (EMG) when anteriorly directed perturbations were applied to the feet of 30 subjects. All subjects then received a lidocaine skin injection followed by: an intra-articular bupivicaine injection (treatment group); an intra-articular saline injection (sham group); or no injection (control group), depending on their randomized group assignment. The perturbation tests were then repeated. FINDINGS: Muscle onset latencies and automatic response magnitudes did not change as a result of the intra-articular injections. Latencies were significantly greater for the vastus medialis and vastus lateralis when compared to the medial hamstrings, biceps femoris and tibialis anterior (P<0.001). Automatic response magnitudes for the tibialis anterior were significantly greater than those of the hamstrings, which were greater than those of the quadriceps (P<0.001). INTERPRETATION: There were no differences in muscle response when anteriorly directed perturbations were applied to the foot with or without an injection of local anesthetic in the knee. Intra-articular receptors were either unaffected by the anesthetic or the extra-articular receptors or receptors of the other joints were able to compensate for their loss.     

Electrically elicited co-contraction of thigh musculature after anterior cruciate ligament surgery. A description and single-case experiment

The purpose of this article is to describe a method for strengthening the quadriceps femoris muscle in a patient after anterior cruciate ligament (ACL) surgery. The method incorporates electrically elicited co-contraction of the quadriceps femoris and hamstring muscles. A single-case experimental design based on a split-middle (ABAB) technique was used to assess the effects of the systematic administration and withdrawal of electrical stimulation with respect to changes in knee isometric extension and flexion torque and circumferential measurements of the thigh in a patient six weeks after ACL reconstruction. Results show increases in extension and flexion torque and thigh circumferential measurements that are associated with both stimulation (treatment) phases in addition to a maintenance effect demonstrated during the withdrawal phase. In this patient, the technique appears to be effective in increasing muscle strength and circumferential measurements, particularly quadriceps femoris muscle torque. Implications and suggestions for future research are included.