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PubMed2004

The effects of estradiol and progesterone on plantarflexor muscle fatigue in ovariectomized mice.

The aim of this study was to examine specific and interactional effects of estradiol and progesterone on the time-to-fatigue of eccentrically contracted plantarflexor muscles and on the percent of plantarflexor isometric torque remaining immediately after an eccentric contraction (EC) protocol. Ovariectomized 6- to 8-week-old C57BL/6 mice were implanted with 21-day 0.05 mg-placebo, 0.05 mg-17-beta estradiol (OE), 15 mg-progesterone (OP), or estradiol and progesterone pellets (OEP). On the 16th day of hormone treatment, the isometric torque of the left plantarflexor muscles was measured. The left plantarflexor muscles then underwent 1 set of 150 ECs followed by 2 immediate post-EC isometric torque measurements. A group of ovarian-intact female mice of a similar age underwent the same isometric torque measurements and EC protocol. Plantarflexor muscle fatigue during ECs took 30%-41% longer to occur in the OP group (n = 9) than it did in the intact (n = 8, P = 0.02), OC (n = 11, P = 0.003), and OEP (n = 9, P = 0.007) groups. Peak active isometric torque had decreased immediately after ECs at 2 time points (M1 and M2). The OP group exhibited the greatest percent of isometric torque remaining immediately after ECs (M1, P = 0.03; M2, P = 0.04). These findings suggest that progesterone reduces muscle fatigue in response to ECs and that this progesterone effect is blunted when estradiol also is present. Therefore, ovarian hormone status may need to be considered when evaluating a response to physical activities, especially those activities involving ECs.

Analysis of Variance↗
PubMed2004

In vivo and noninvasive load sharing among the vasti in patellar malalignment.

PURPOSE: It is not clear how the knee extension torque is distributed quantitatively among the lateral and medial vasti in patellofemoral pain (PFP) patients with patellar malalignment, which was investigated in vivo and noninvasively in ten PFP patients and eleven controls. We hypothesized that the vastus medialis oblique (VMO) and vastus medialis longus (VML) of PFP patients contribute less to knee extension than that in controls. METHODS: Electrical stimulation was used to activate each vastus component selectively. The relationship between the knee extension torque generated by each individual vastus component and the corresponding compound muscle action potential (M-wave) was established over different contraction levels, which was used to calibrate the corresponding voluntary EMG signal and determine torque ratios of VMO/VL (vastus lateralis), VMO/VML, VML/VL and (VMO+VML)NL during voluntary isometric knee extension. RESULTS: The VMO and VML of PFP patients contributed significantly less to knee extension than their counterparts in controls. The combination of VMO and VML generated comparable amount of extension torque as the VL in the controls, while it produced significantly lower extension torque than that of the VL in the PFP patients. In addition, the VMO/VL was lower than VMO/VML and VML/VL in both PFP and control groups. CONCLUSIONS: Compared to controls, the VMO and VML in the PFP patients contributed significantly less to the knee extension torque. The approach can be used to investigate load sharing among quadriceps muscles in vivo and noninvasively, in both healthy subjects and patients with patellofemoral disorder and patellar malalignment.

Action Potentials↗
PubMed2006

The effects of isokinetic contraction velocity on concentric and eccentric strength of the biceps brachii.

The purpose of this investigation was to determine the influence of contraction velocity on the eccentric (ECC) and concentric (CON) torque production of the biceps brachii. After performing warm-up procedures, each male subject (n = 11) completed 3 sets of 5 maximal bilateral CON and ECC isokinetic contractions of the biceps at speeds of 90, 180, and 300 degrees x s(-1) on a Biodex System 3 dynamometer. The men received a 3-minute rest between sets and the order of exercises was randomized. Peak torque (Nm) values were obtained for CON and ECC contractions at each speed. Peak torque scores (ECC vs. CON) were compared using a t-test at each speed. A repeated measures analysis of variance was used to determine differences between speeds. ECC peak torque scores were greater than CON peak torque scores at each given speed: 90 degrees x s(-1), p = 0.0001; 180 degrees x s(-1), p = 0.0001; and 300 degrees x s(-1), p = 0.0001. No differences were found between the ECC peak torque scores (p = 0.62) at any of the speeds. Differences were found among the CON scores (p = 0.004). Post hoc analysis revealed differences between 90 degrees x s(-1) (114.61 +/- 23) and 300 degrees x s(-1) (94.17 +/- 18). These data suggest that ECC contractions of the biceps brachii were somewhat resistant to a force decrement as the result of an increase in velocity, whereas CON muscular actions of the biceps brachii were unable to maintain force as velocity increased.

Adult↗
PubMed2006

Mechanomyographic and electromyographic responses during submaximal to maximal eccentric isokinetic muscle actions of the biceps brachii.

The purpose of this investigation was to determine the mechanomyography (MMG) and electromyography (EMG) amplitude and mean power frequency (MPF) vs. eccentric isokinetic torque relationships for the biceps brachii muscle. Nine adults (mean +/- SD age = 23.1 +/- 2.9 years) performed submaximal to maximal eccentric isokinetic muscle actions of the dominant forearm flexors. After determination of isokinetic peak torque (PT), the subjects randomly performed submaximal step muscle actions in 10% increments from 10 to 90% PT. Polynomial regression analyses indicated that the MMG amplitude vs. eccentric isokinetic torque relationship was best fit with a quadratic model (R(2) = 0.951), where MMG amplitude increased from 10 to 60% PT and then plateaued from 60 to 100% PT. There were linear increases in MMG MPF (r(2) = 0.751) and EMG amplitude (r(2) = 0.988) with increases in eccentric isokinetic torque, but there was no significant change in EMG MPF from 10 to 100% PT. The results suggested that for the biceps brachii, eccentric isokinetic torque was increased to approximately 60% PT through concurrent modulation of the number of active motor units and their firing rates, whereas additional torque above 60% PT was produced only by increases in firing rates. These findings contribute to current knowledge of motor-control strategies during eccentric isokinetic muscle actions and could be useful in the design of training programs.

Adult↗
PubMed1999

Influence of age on length and passive elastic stiffness characteristics of the calf muscle-tendon unit of women.

BACKGROUND AND PURPOSE: Therapeutic stretching of the calf muscle-tendon unit is used to increase its length and to ameliorate decreased dorsiflexion range of motion (ROM), but the influence of age on the passive properties of the calf muscle-tendon unit has not been studied adequately The purpose of this study was to examine the influence of age on length and passive elastic stiffness (PES) characteristics of the calf muscle-tendon unit when stretched through the full, available dorsiflexion ROM. SUBJECTS: Twenty-four younger women (aged 20-39 years), 24 middle-aged women (aged 40-59 years), and 33 older women (aged 60-84 years) participated. METHODS: An isokinetic dynamometer was used to passively stretch the right calf muscle-tendon unit from relaxed plantar flexion to the maximal angle of available dorsiflexion at 5(ús-1. The maximal passive resistive torque was measured, and passive angle-torque curves were constructed for a full ROM from an initial angle of passive resistive torque to the maximal dorsiflexion angle. The full ROM represented length extensibility. The average PES was calculated for this full stretch ROM and for the first half and the last half of this stretch ROM. The maximal passive dorsiflexion angle, maximal passive resistive torque, angular change for the full stretch ROM, and average PES for the full stretch ROM and the first half and the last half of the full stretch ROM were examined for group differences and their relationships with age. RESULTS: The maximal passive dorsiflexion angle, maximal passive resistive torque, angular change for the full stretch ROM, and average PES within the last half of the full stretch ROM were less for the older women than for the younger women. Age was negatively associated with these variables. CONCLUSION AND DISCUSSION: Decreased maximal passive dorsiflexion ROM in older women was associated with decreased maximal passive resistive torque, decreased calf muscle-tendon unit length extensibility, and decreased average PES within the last half of their available passive dorsiflexion ROM.

Adult↗
PubMedDate not supplied

Implant-abutment screw joint preload of 7 hex-top abutment systems.

This study measured the screw joint preload of the implant-abutment interface for 7 common hex-top abutment systems. Increasingly, prosthetic designs are utilizing a direct prosthetic connection to the implant, placing the implant-abutment screw joint under direct functional loads and moments. Sufficiently high screw joint preloads are required to maintain screw joint integrity and confer clinical longevity to implant prosthetic components to prevent such complications as abutment screw loosening and screw fracture. Strain-gauged abutment load cells were calibrated to measure screw joint pre-load at the implant-abutment interface. Torque delivery by electronic torque controller was varied at low- and high-speed settings. At manufacturer's recommended torques, the overall mean preload measured was 181.6 +/- 60.0 N for the Nobel Biocare Standard abutment, 291.3 +/- 41.2 N for the Nobel Biocare EsthetiCone abutment, 456.5 +/- 44.0 N for the Nobel Biocare MirusCone abutment, 369.7 +/- 32.9 N for the 3i Titanium Abutment post, 643.4 +/- 143.1 N for the Nobel Biocare CeraOne abutment, 536.3 +/- 68.6 N for the Nobel Biocare "Gold Cylinder to Fixture" abutment, and 556.9 +/- 145.6 N for the Nobel Biocare TiAdapt abutment. Analysis of variance revealed significant differences between abutment systems (P < .001) and between torque driver speed settings (P < .001). Implant-abutment screw joint preload of external-hex implants is dependent on abutment design, screw diameter, material, tightening torque, and torque controller speed.

Analysis of Variance↗
PubMedDate not supplied

Evaluation of the ITI Morse taper implant/abutment design with an internal modification.

PURPOSE: The purpose of this study was to compare internal Morse taper connections in 2 separate modes: repeated torque/reverse-torque values and compressive bending at a 30-degree off-axis angle. MATERIALS AND METHODS: Three sample groups (n = 12 in each group)--a solid-screw implant paired with a 5.5-mm solid abutment (SSI), a synOcta implant with a 5.5-mm solid abutment (SOI), and a synOcta implant with a synOcta 5.5-mm solid abutment (SOSA)--were torqued to 35 Ncm, and the reverse torque to remove the abutment was recorded. This was repeated for 3 trials. Additionally, the sample groups were loaded 30 degrees off-axis, and the ultimate compressive values were recorded. RESULTS: There was a significant difference in the initial reverse-torque values. The SOSA setup showed significantly lower torque than the SOI and SSI setups (P < .05). In addition, the compressive bending test showed that the SOSA setup was significantly different (P < .05) from the SSI and SOI setups. Radiographic survey of the test groups following compressive bending revealed no implant fractures, but bending of the implant-abutment complex occurred. DISCUSSION: The alteration within the Morse taper did not reduce the strength of the implant-abutment connection, ie, the reduction in surface area did not significantly reduce the torque properties or tensile properties. The new 2-piece synOcta 5.5-mm solid abutment was shown to have a stronger implant-abutment connection when torqued down a second time. CONCLUSIONS: In this in vitro study, alteration of the Morse taper with an internal octagon indexing did not significantly reduce the strength of the implant connection. Sufficient strength was exhibited, which would indicate this implant-abutment design for anterior as well as posterior edentulous sites.

Analysis of Variance↗
PubMed2003

Growth trends of dynamic strength in adolescent boys. A 2-year follow-up survey.

AIM: The present study aims to investigate the growth trends of dynamic torque during adolescence through a 2-year follow-up survey. METHODS: Concentric torque during elbow flexions and knee extensions at 3 constant velocities (1.05, 3.14, and 5.24 rad x sec(-1)) were determined year-by-year, i.e., 3 times (T1, T2, and T3), using an isokinetic dynamometer in 10 boys aged 12.7 to 13.5 years at the start of the study. In addition, the muscle thickness at the anterior sites of the upper arm and thigh were measured using a brightness mode ultrasound apparatus. For the two motions, torque output at 1.05 rad x sec-1 increased significantly year by year, but those at 3.14 and 5.24 rad x sec-1 did not show significant changes between T2 and T3. RESULTS: The muscle thickness showed significant differences between T1 and T3 for the anterior upper arm and between T3 and either T1 or T2 for the anterior thigh. In both motions, the ratio of torque output at 1.05 rad x sec-1 to the product of muscle thickness squared and height was significantly higher in T2 and T3 than in T1. The corresponding ratios in elbow flexions at 3.14 and 5.24 rad x sec-1 were also significantly higher in T2 compared to T1, but those in the knee extensions did not show significant effects of age. CONCLUSION: These results indicate that, for adolescent boys, 1) the age-related changes in dynamic torque at high velocity contractions differ from those at slow velocity contractions, and 2) the growth rate of dynamic torque at slow velocity contractions exceeds that of muscle size in the earlier stage of adolescence.

Adolescent↗
PubMed1998

The effects of superimposed electrical stimulation of the quadriceps muscles on performance in different motor tasks.

BACKGROUND: Some examples are presented to show how superimposed electrical stimulation of muscles during maximum voluntary effort can be used to enable subjects to achieve greater joint torque, rate of joint torque development, and the joint angular velocity as when performing only voluntarily with maximum effort. METHODS PARTICIPANTS: Ten students of physical education not involved into a regular sport training participated the study. INTERVENTIONS: The subjects performed isometric and concentric knee extensions and squat jumps, without and with superimposed electrical stimulation of the quadriceps muscles. MEASURES: A knee torque and angular displacement were observed during isometric and concentric knee extension. During the jumping, a vertical component of the ground reaction force was measured. RESULTS: Results showed that the maximal knee torque, as well as a torque rise, were higher in isometric knee extension trials with superimposed electrical stimulation. The same was observed in concentric knee extensions, where greater knee torque during superimposed electrical stimulation also resulted in higher angular velocity and a more extended knee at the end of the movement. In squat jumps, the application of the superimposed electrical stimulation resulted in poorer performance. CONCLUSIONS: It was concluded that superimposed electrical stimulation was effective in some simple motor tasks, but not in more complex tasks where a co-ordination of multiple muscles of different groups was necessary for improved performance.

Acceleration↗
PubMed1999

Superimposed single impulse and pulse train electrical stimulation: A quantitative assessment during submaximal isometric knee extension in young, healthy men.

Superimposed electrical stimulation techniques can be used to detect central activation failure (CAF), defined as incomplete central nervous system recruitment, suboptimal activation of motor units, or both. The purpose of this study was to evaluate superimposed electrical stimulation techniques to be used to detect CAF during isometric knee extension. We performed three sets of experiments and compared the torque increments from transcutaneous electrical stimulation with: (i) single impulses of different amplitudes (100 V, 150 V, and 200 V) and a pulse train of 100 Hz (100 V, 100 ms); (ii) pulse trains (100 Hz, 100 V) of different lengths (100 ms, 200 ms, and 300 ms); and (iii) pulse trains (100 Hz, 100 ms) of different amplitudes (50 V, 100 V, 150 V, and 200 V). Stimulation was evaluated at submaximal (80% of MVC) isometric knee extension in 24 healthy young men using a Biodex isokinetic dynamometer. Electrodes were placed over the rectus femoris muscle and all stimulation impulses were monophasic, rectangular waves of 0.2-ms duration. Pulse train stimulation at 100 V always elicited a torque increment, whereas single impulse stimulation, even at 200 V, only caused a torque increment in about half of the trials. For each subject, the pulse train generated a significantly larger torque increment than for any of the three single impulses. There was no significant difference in torque increment between the three pulse trains of different lengths. Pulse trains at 150 V and 200 V generated significantly larger torque increments than at 50 V and 100 V. High-frequency maximal train stimulation may thus improve the detection of CAF during isometric knee extension. Detection of CAF may be important in the clinical assessment of muscle weakness, investigating the mechanisms underlying muscle weakness, and evaluating potential therapeutic strategies.

Adult↗
PubMed1992

Strain in the anteromedial bundle of the anterior cruciate ligament under combination loading.

Strain within the anteromedial bundle (AMB) of the anterior cruciate ligament (ACL) was measured in 13 human knee specimens in order to determine the combination of external loads most likely to cause injury. Using a load application system that allowed 5 df with the flexion angle being fixed, pure loads of anterior/posterior force, medial/lateral force, varus/valgus torque, and internal/external axial torque were applied at three flexion angles: 0 degrees, 15 degrees, 30 degrees. Combined loads were applied in pairs at two flexion angles: 0 degrees and 30 degrees. Liquid mercury strain gauges were used to measure strain in the ACL. Anterior tibial force was the primary determinant of strain in the anteromedial bundle. This strain was significantly larger at 30 degrees flexion than at 0 degrees. The strain sensitivity of the AMB to medial force was approximately one-half that to pure anterior force. The effect of anterior and medial forces was additive when applied in combination. Neither pure axial torque nor pure varus/valgus torque was observed to strain significantly the AMB at any of the flexion angles investigated. However, valgus torque in combination with anterior force resulted in a significantly larger strain than pure anterior force. Internal axial torque in combination with anterior force also resulted in a larger strain than pure anterior force.

Aged↗
PubMed1992

Dynamic response of the occipito-atlanto-axial (C0-C1-C2) complex in right axial rotation.

The torque-angular deformation in right axial rotation until failure of the ligamentous occipito-atlanto-axial complex subjected to variable loading rate (dynamic) axial torque was characterized using a biaxial MTS system. A special fixture and gear box that permitted right axial rotation of the specimen until failure without imposing any additional constraints were used to obtain the data. The specimens were divided into three groups and tested until failure at three different dynamic loading rates: 50, 100, and 400 degrees/s. A previous study by the authors provided data for quasi-static (4 degrees/s) loading conditions. The torque versus rotation curves can be divided into two straight regions and two transition zones. The plots clearly indicated that at loading rates higher than 4 degrees/s, the specimens became stiffer in the region of steadily increasing resistance prior to failure. The increase in stiffness was maximum at 100 degrees/s. The stiffness decreased somewhat at 400 degrees/s in comparison with 100 degrees/s, but this decrease was not significant. The resulting torque-right axial rotation curves were also examined to estimate the magnitude of maximum resistance (torque) and the corresponding angular rotation value. The average maximum resistance torque increased from 13.6 Nm at 4 degrees/s to 27.8 Nm at 100 degrees/s. The corresponding right angular rotation data (65-78 degrees), however, did not show any significant variation with loading rate. Posttest dissection of the specimens indicated that the type of injury observed was related to the rate of axial loading imposed on a specimen during testing.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1998

Biomechanical characterization of osseointegration: an experimental in vivo investigation in the beagle dog.

This study reports the results of torsion tests, pull-out tests, and lateral loading tests on osseointegrated commercially pure titanium fixtures. The tests were performed in vivo on six beagle dogs. Three fixtures, each with a diameter of 3.7 mm, were installed bilaterally in the tibia of each animal. The mean maximal pull-out load was 1.55 kN (n = 4), the mean maximal lateral transverse load was 0.21 kN (n = 2), the mean maximal lateral axial load was 0.18 kN (n = 2), the mean breakpoint torque was 0.31 Nm (n = 3), and the mean maximal torque was 0.43 Nm (n = 3). The torsion test revealed an almost immediate plastic deformation of the interface between the implant and bone; this indicates that although the contact between the bone and the implant is close, there is no strong bond, at least not in shear. The major transfer of load from the implant to the surrounding bone tissue must therefore depend on the design of the implant. A histological evaluation with measurements of the amount of bone in contact with the fixtures was performed. By the use of the histological and mechanical data, it is possible to estimate shear stresses in bone tissue (pull-out test) and in the interface (torque test). The mean maximal shear stress in bone tissue in the pull-out tests was 100 MPa (n = 4); the mean shear stress in the interface was 4.3 MPa (n = 3) in the torsion tests at the breakpoint torque and was 6.0 MPa (n = 3) at the maximal torque. It was also possible to estimate the shear modulus of elasticity in the pull-out and torque tests. The mean shear modulus in pull-out was 119 MPa (n = 4), and the mean apparent shear modulus in torsion was 9 kPa (n = 3) for an assumed interface thickness of 100 nm and was 86 kPa (n = 3) for an assumed interface thickness of 1,000 nm.

Animals↗
PubMed2000

Loosening of sacral screw fixation under in vitro fatigue loading.

Sacral screw fixation is frequently used for fusion of the lower lumbar spine, but sacral screws appear to offer less secure fixation than lumbar pedicle screws, and failure due to loosening under fatigue loading is common. The aim of this study was to examine in vitro the stability of medial and lateral bicortical and unicortical sacral screw fixation under a physiologically relevant fatigue-loading pattern. Bone mineral density, screw insertion torque, and screw-fixation stiffness were measured prior to cyclic loading between 40 and 400 N compression at 2 Hz for 20,000 cycles. The screw-fixation stiffness was measured every 500 cycles, and the axial pullout strength of the screws was recorded following loading. All of the lateral insertions loosened under the applied loading, but some of the medial insertions remained stable. Medial insertions proved stiffer and stronger than lateral insertions, and bicortical fixations were stronger than unicortical fixations. Bone mineral density and insertion torque were correlated with screw stiffness and pullout strength, although better correlation was found for insertion torque than bone mineral density. Bone mineral density is a good preoperative indicator of sacral screw-fixation strength, and insertion torque is a good intraoperative indicator. An insertion torque greater than 1.5 Nm is suggested as an indicative value for a stable medial unicortical insertion, whereas an insertion torque greater than 2 Nm suggests a stable medial bicortical insertion. It appears that, apart from the choice of technique (screw orientation and depth), minimizing the load on the screws during the initial part of the fusion process is also critical to maintain stability of the fused section and to obtain a solid fusion mass.

Adult↗
PubMed1978

Spinal mechanisms of the functional stretch reflex.

A sudden and rapid angular displacement of the limb evokes, in human and monkey subjects, a segmented pattern of electromyographic activity in muscles which are stretched. While the first segment is acknowledged to represent a tendon jerk, it has been proposed that the second segment, occurring with a shorter latency than a reaction time, is mediated by a transcortical loop. The present experiments were conducted in cats to determine the properties of muscle responses to torque perturbations analogous to those used in the monkey, and to determine if the integrity of supraspinal pathways is required for the individual response segments to occur. Torque perturbations which flexed the forearm evoked a segmented response in the electromyogram of the cat triceps muscle. This response typically consisted of three early segments with latencies of 10, 30 and 60 msec which were similar to the M1, M2, and M3 segments described in the monkey. The M3 and occasionally M2 components were depressed when the cat followed rather than resisted the perturbation. A torque pulse of 10 msec duration was sufficient to elicit a near maximal M1 response while torque pulses in excess of 20 msec were required to evoke the M2 response. To determine if any of these components required mediation by the cerebral cortex, experiments were conducted in decerebrate and spinal cats. Similar torque perturbations produced segmented electromyographic responses in the triceps muscles which were indistinguishable in their timing from those observed in intact cats. The torque required to produce the segmented responses was comparable as well. All three segments were dependent upon the activation of receptors in the homonymous muscle and did not require cutaneous input. These observations show that receptor properties and/or spinal mechanisms involved in the stretch reflex are sufficient to produce a segmented response similar to that observed in intact animals.

Animals↗
PubMed1991

Muscle activation during maximal voluntary eccentric and concentric knee extension.

The aim of this investigation was to study the relationships among movement velocity, torque output and electromyographic (EMG) activity of the knee extensor muscles under eccentric and concentric loading. Fourteen male subjects performed maximal voluntary eccentric and concentric constant-velocity knee extensions at 45, 90, 180 and 360 degrees.s-1. Myoelectric signals were recorded, using surface electrodes, from the vastus medialis, vastus lateralis and rectus femoris muscles. For comparison, torque and full-wave rectified EMG signals were amplitude-averaged through the central half (30 degrees-70 degrees) of the range of motion. For each test velocity, eccentric torque was greater than concentric torque (range of mean differences: 20%-146%, P less than 0.05). In contrast, EMG activity for all muscles was lower under eccentric loading than velocity-matched concentric loading (7%-31%, P less than 0.05). Neither torque output nor EMG activity for the three muscles changed across eccentric test velocities (P greater than 0.05). While concentric torque increased with decreasing velocity, EMG activity for all muscles decreased with decreasing velocity (P less than 0.05). These data suggest that under certain high-tension loading conditions (especially during eccentric muscle actions), the neural drive to the agonist muscles was reduced, despite maximal voluntary effort. This may protect the musculoskeletal system from an injury that could result if the muscle was to become fully activated under these conditions.

Adult↗
PubMed1995

Effects of unilateral isometric strength training on joint angle specificity and cross-training.

The purpose of this study was to examine the effects of unilateral isometric leg extension strength training on the strength and integrated electromyogram (IEMG) of both the trained and untrained limbs at multiple joint angles. A training (TRN) group [nine women; mean (SD) age, 20(1) years] exercised for 6 weeks with isometric leg extensions at 80% of maximal isometric torque. A control (CTL) group [eight women; 21(1) years] did not exercise. The training was performed three times per week on a Cybex II isokinetic dynamometer at a joint angle where the lever arm was 0.79 rad below the horizontal plane. The subjects were tested pre- and posttraining for maximal unilateral isometric torque in both limbs at joint angles of zero, 0.26, 0.79, 1.31, and 1.57 rad below the horizontal plane. Bipolar surface electrodes were used to record the IEMG of the vastus lateralis (VL) and vastus medialis (VM) during the isometric tests. Three univariate (torque, IEMG-VL, and IEMG-VM) four-way (group x time x limb x angle) mixed factorial ANOVAs were used to analyze the data. The results indicated joint angle specificity for isometric torque in the TRN group only, with significant increases in torque at 0.79 (P = 0.0004) and 1.31 (P = 0.0039) rad. No significant increases in torque were found in the untrained limb of the TRN group or in either limb of the CTL group. Similarly, there were no significant changes in IEMG as a result of the training for the VL or VM.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed2007

Early versus late start of open kinetic chain quadriceps exercises after ACL reconstruction with patellar tendon or hamstring grafts: a prospective randomized outcome study.

The purpose of the present investigation was to evaluate physical outcome after anterior cruciate ligament (ACL) reconstruction with early versus late initiation of open kinetic chain (OKC) exercises for the quadriceps in patients operated on either patellar tendon or hamstring grafts. Sixty-eight patients, 36 males and 32 females, with either patellar tendon graft (34 patients) or hamstring graft (34 patients) were enrolled in this study. All patients were randomly allocated to either early (the 4th postoperative week) or late (the 12th postoperative week) start of OKC exercises for the quadriceps, resulting in four subgroups: patellar tendon reconstruction, early start (P4) or late start (P12) of OKC quadriceps exercises, hamstring tendon reconstruction, early start (H4) or late start (H12) of quadriceps OKC exercises. Prior to surgery and 3, 5 and 7 months later, assessments of range of motion (goniometer), anterior knee laxity (KT-1000), postural sway (KAT 2000), thigh muscle torques (Kin-Com dynamometer) and anterior knee pain (anterior knee pain score) were evaluated. No significant group differences were found in terms of range of motion 3, 5 and 7 months postoperatively. The H4 group showed a significantly higher mean difference of laxity over time of 1.0 mm (CI: 0.18-1.86) than the P4 group (P=0.04). Within the same type of surgery, the H4 against the H12, the mean difference over time was 1.2 mm (0.37-2.1) higher in the H4 group than in the H12 group (P=0.01). There were no significant group differences in terms of postural sway or anterior knee pain at the different test occasions. Significant differences in trends (changes over time) were found when comparing the four groups, for both quadriceps muscle torques (P<0.001) and hamstring muscle torques (P<0.001). All groups, except the P4 group, reached preoperative values of quadriceps muscle torques at the 7 months follow-up. In the H4 and the H12 groups, significantly lower hamstring muscle torques at the 7 months follow-up compared with preoperative values were found. In conclusion, early start of OKC quadriceps exercises after hamstring ACL reconstruction resulted in significantly increased anterior knee laxity in comparison with both late start and with early and late start after bone-patellar tendon-bone ACL reconstruction. Furthermore, the early introduction of OKC exercises for quadriceps did not influence quadriceps muscle torques neither in patients operated on patellar tendon nor hamstring tendon grafts. On the contrary, it appears as if the choice of graft affected the strength of the specific muscle more than the type of exercises performed. Our results could not determine the appropriate time for starting OKC quadriceps exercises for patients who have undergone ACL reconstruction with hamstring tendon graft. Future studies of long-term results of anterior knee laxity and functional outcome are needed.

Adult↗