The effect of external load on torque production by knee extensors

The kinematics of the knee joint are load-dependent; the length of the lever arm of the extensor mechanism and the pathway of the instant center of rotation vary with external load. This study was conducted to determine if the maximum extensor torque-generating capacity of the knee joint is dependent on the distance from the knee joint at which the external force resisting extension is located. Maximum isometric extensor torques were measured at 90 and 30 degrees of knee flexion while the distance from the knee joint to the resisting force was varied. Our results demonstrated that the subjects generated larger maximum extensor torques, at both 90 and 30 degrees of knee flexion, when the external resisting force was positioned farther distal to the knee joint. This increase was as large as 50 per cent with the knee at 30 degrees of flexion.     

Effects of upper and lower limb preference on torque production in the knee flexors and extensors

The purpose of this study was to examine the phenomena of foot preference and its relationship to hand preference and torque production in the knee flexors and extensors. Fifty-four college aged students participated in the study. Each subject's hand and foot preference was determined. Torque production in the knee flexors and extensors was evaluated isokinetically at three speeds. Chi-square analysis revealed a very weak relationship between foot preference and hand preference. Paired t-tests demonstrated no significant differences in torque production when the preferred leg was tested against the nonpreferred leg or when the left leg was compared to the right. The authors conclude that there was a tendency for the subjects to prefer their right leg. However, one cannot predict foot preference from hand preference. Implications for future research and practice were presented. J Orthop Sports Phys Ther 1989;11(5):202-207.     

Relationship between lean body mass and isokinetic peak torque of knee extensors and flexors in severely burned children

Objective

Severe burns cause hypermetabolic responses and prolonged hospitalization, resulting in loss of body mass and muscle strength. This study aimed to determine whether long-term gains in lean body mass (LBM) after structured exercise programs are functionally meaningful and related to greater muscle strength in severely burned children.

Reliability of reciprocal isokinetic testing of the knee extensors and flexors

This study was conducted to assess the reliability of torque measurements across different trials and different test sessions. Each trial consisted of three maximal, reciprocal contractions of the knee extensors and flexors at test velocities of 60 and 180 degrees /sec. Three trials were conducted on each of three test sessions, with each session separated by 48 hours. Results indicate that reliability of reciprocal isokinetic testing of the knee can be improved by 1) testing in more than one occasion, 2) testing more than three trials during a single session if testing during more than one session is impossible, and 3) allowing the subject to become familiar with the isokinetic test procedure and to warm up adequately. Data obtained in this study indicated performance variability was predominantly associated with between subject differences and secondarily related to within subject changes over trials and days. Dynamometer calibration remained stable across all test sessions, indicating that the method was reliable for recording torque output during all testing procedures. J Orthop Sports Phys Ther 1991;14(3):121-127.     

Determining the isometric point of the knee

Posteromedial and posterolateral reconstructions of the knee are frequently required in the management of knee dislocations. This study compares the accuracy of radiographic reference points to established anatomical landmarks in reproducing the isometric points of the posteromedial corner and posterolateral corner (PLC) of the knee. Posteromedial and posterolateral surgical approaches were made in 20 cadaveric knees. The posteromedial and posterolateral isometric points of each femur were determined using the anatomic landmarks and radiographic reference points in a randomized order. An Isometer was used to measure the displacement, to the nearest millimeter; knees were passed into flexion. A two-tailed t-test was used to analyze the data and statistical significance was set to p < 0.05. For the isometric point of the PLC, the radiographic method resulted in a mean displacement of 1.63 mm as the knee was passed from extension into flexion, while the anatomic method had a mean displacement of 4.84 mm (p < 0.00018). The mean displacement on the posteromedial side using the radiographic method was 2.10 mm as the knee was passed from extension into flexion, while the anatomic method resulted in 3.21 mm of displacement (p = 0.074).     

A comparison of intramedullary and extramedullary alignment systems for tibial component placement in total knee arthroplasty

Fifty-two primary total knee arthroplasties (TKAs) using an intramedullary tibial jigging system to obtain ideal tibial alignment (90 degrees +/- 2 degrees) were compared with 62 TKAs using an extramedullary tibial jigging system. The Insall-Burstein total knee system was used in all cases, and all femoral components were positioned with extramedullary jigs. Postoperative evaluation consisted of a standing, hip-to-ankle anteroposterior roentgenogram and measurement of the following angles: (1) femorotibial, (2) tibial component, (3) femoral component, and (4) mechanical axis. Ideal tibial component alignment using the intramedullary system was statistically superior to alignment achieved with the extramedullary system. All other angle comparisons showed no statistical significance.     

Effect of tension and placement of a prosthetic anterior cruciate ligament on the anteroposterior laxity of the knee.

We wished to determine the optimal tension required to restore normal joint laxity to anterior cruciate ligament (ACL)-deficient knees using a braided polyethylene ACL prosthesis (PACL). In 10 cadaveric specimens, we measured the anteroposterior (AP) laxity of the intact knee at 10 degrees, 30 degrees, 60 degrees, and 90 degrees of flexion. The ACL was then removed and replaced with the PACL using tunnel-tunnel (T-T) and "over-the-top" (OTT) placement techniques. In both positions, the PACL was initially tensioned to 0, 9, 18, and 27 N with the knee flexed to 30 degrees. AP joint laxity was then measured at each flexion angle. With an increase in initial tension, there was a corresponding decrease in AP laxity. At 30 degrees and 90 degrees of flexion, AP laxity was not significantly different from normal using T-T placement and an initial tension of 0 N. At 90 degrees of flexion, AP laxity was not significantly different from normal using OTT placement at 0 or 9 N of initial tension. For both positions, all other tension levels and flexion angles constrained AP laxity. No laxity differences were detected between the OTT and T-T positions at any flexion angle. The variability in AP laxity of the T-T position was significantly greater than OTT. With a 150-N anterior shear force applied to the proximal tibia, the maximum tensions developed in the PACL were not significantly different between the two positions except at 90 degrees. The results suggest that implantation of the PACL is best performed using OTT positioning with an initial tension of 0 N applied at 30 degrees of knee flexion.     

The ultrasonographic assessment of the knee extensors in patients with anterior knee pain syndrome]

Sonographic assessment of the extensors of the knee in patients with anterior knee pain syndrome and in control group is presented. Both groups were similar in respect of age and sex. The assessment was done according to Heckmatt. Resting transverse sizes of rectus, intermedius, vastus lateralis and vastus medialis were related to their sizes during isotonic contracture under load. Statistical analysis has been done with Mann-Whitney test. Statistically significant weakening of rectus femoris, intermedius (p < 0.00001) and vastus medialis (p < 0.01) have been found in anterior knee patients. These might explain patellar malalignement in this group.     

Isokinetic strength and endurance of the knee extensors and flexors in trans-tibial amputees

Significant levels of muscular fatigue alter the co-ordination patterns and the ability to accomplish proper daily functions, especially in patients with initial low levels of strength. The purpose of this study was to evaluate the strength and endurance of the quadriceps and hamstring muscles in trans-tibial amputees. Concentric strength and endurance of the thigh muscles were measured bilaterally by an isokinetic dynamometer. The measured variables were torque and angle. For the endurance test, a fatigue index was calculated. Peak torque for extension and flexion was significantly higher in the sound limb (p<0.01). The fatigue index for extension was not significantly different in the sound limb from the amputated limb. The fatigue index for flexion is significantly higher in the sound limb (p<0.01). The finding may imply that from a metabolic point of view, the muscles of the amputated limb function properly. It is of great importance to reduce the bilateral deficit and the degree of atrophy as soon as possible in order to improve the level of performance. By choosing a correct strength and endurance training programme, one may expect to get a significant and good reaction from the muscles of the amputated limb as is expected from training the muscles of a sound limb.     

Electrical muscle stimulation and isometric exercise effects on selected quadriceps parameters*

The purpose of the study was to compare the effects of 1) monopolar (MI) and bipolar (BI) electrical muscle stimulation (EMS) concurrent with isometric exercise, and 2) EMS (MI and BI) concurrent with isometric exercise to isometric exercise (I) alone on girth, dynamic strength, muscular power, and muscular endurance of the right quadriceps muscle. All three experimental groups completed a 6-week program of training on the right lower limb which was isometrically restrained at -30 degrees knee extension. Additionally, the MI and BI groups received low frequency (65 Hz) EMS. A control group (C) was involved in pre- and post-testing sessions only. Results indicated that 1) EMS concurrent with isometric exercise was more effective in improving quadriceps strength over a group that did no training, but was no more effective than isometric exercise alone; 2) the two EMS techniques yielded similar results for healthy innervated muscle; 3) dynamic strength was minimally increased by EMS; 4) power was positively increased more by the monopolar technique; and 5) endurance was positively increased more by the bipolar technique. It was concluded that while the two techniques of EMS concurrent with isometric exercise have the potential to positively increase selected physiological parameters in healthy innervated muscle, the greatest benefits will be noted for the weaker muscle. J Orthop Sports Phys Ther 1986;8(4):203-209.     

The surgical treatment of postburn cicatricial contractures of the knee joint extensors

In the recent 3 years operations were carried out in 8 patients with postburn extension contractures of the knee joints, which accounted for 12.9% of all cicatricial contractures of this joint. The anatomical essence of the contracture was ascertained. A method of surgical treatment was developed, which consisted in restoration of the cutaneoadipose layer in the region of the knee with a cutaneofascial graft taken from the contralateral leg and subsequent excision of the scars on the thigh, by freeing of the muscles extending the joint, and restoration of the skin surface with a split nonperforated autodermal graft. The operation restores knee joint movement and removes trophic ulcers of pathological postburn scars.     

Muscular activity and torque of the foot dorsiflexor muscles during decremental isometric test: A cross-sectional study

PurposeTo analyse the torque variation level that could be explained by the muscle activation (EMG) amplitude of the three major foot dorsiflexor muscles (tibialis anterior (TA), extensor digitorum longus (EDL), extensor hallucis longus (EHL)) during isometric foot dorsiflexion at different intensities.MethodsIn a cross-sectional study, forty-one subjects performed foot dorsiflexion at 100%, 75%, 50% and 25% of maximal voluntary contractions (MVC) with the hip and knee flexed 90° and the ankle in neutral position (90° between leg and foot). Three foot dorsiflexions were performed for each intensity. Outcome variables were: maximum (100% MVC) and relative torque (75%, 50%, 25% MVC), maximum and relative EMG amplitude. A linear regression analysis was calculated for each intensity of the isometric foot dorsiflexion.ResultsThe degree of torque variation (dependent variable) from the independent variables explain (EMG amplitude of the three major foot dorsiflexor muscles) the increases when the foot dorsiflexion intensity is increased, with values of R² that range from 0.194 (during 25% MVC) to 0.753 (during 100% MVC). The reliability of the outcome variables was excellent.ConclusionThe EMG amplitude of the three main foot dorsiflexors exhibited more variance in the dependent variable (torque) when foot dorsiflexion intensity increases.     

Negative inotropic effects of ATP on the isometric contractions of isolated rat heart muscle

The effects of ATP on the isometric contractions of isolated rat left ventricular papillary muscle were studied. Exogenously administered ATP had an immediate onset, an abrupt response, progressive recovery and produced dose-related depression in the peak developed tension, maximum rate of tension development and relaxation, which were statistically significant. There were no significant changes in the resting tension, time to peak tension and relaxation time, except for a significantly prolonged relaxation time at the highest concentration of ATP. In the studies of interactions of ATP and either epinephrine or Ca⁺⁺, we observed that ATP seemed to interfere with the inotropic effect of epinephrine, while Ca⁺⁺ antagonized the negative inotropic action of ATP. We conclude that the site of negative inotropic action of ATP is most likely on the cell membrane, where ATP interferes with Ca⁺⁺ flux, and that ATP interferes with the positive inotropic action of epinephrine.(Sohn YZ, Fukunaga AF, Katz RL: Negative inotropic effects of ATP on the isometric contractions of isolated rat heart muscle. J Anesth 2: 193–197, 1988)     

Effects of different acceleration deceleration rates on isokinetic performance of the knee extensors

The Kinetic Communicator provides three acceleration/deceleration rates (low, medium, and high) to control the limb and, thus, prevent impact forces and torque overshoot found with free acceleration. The purpose of this study was to examine the effect of three acceleration/deceleration rates on isokinetic performance of the knee extensors on the Kinetic Communicator. Thirty-one healthy females with no history of knee pathology performed three concentric/eccentric contractions of the knee extensors at each acceleration/deceleration rate at a velocity of 90 degrees /sec. A one-way repeated measures analysis of variance (ANOVA) and Scheffé post hoc tests were used to compare between each acceleration/deceleration rate: 1) the average velocity, peak torque, and average torque of the whole curve; and 2) the average velocity, average torque, and range of motion of the acceleration and deceleration phases. The acceleration/deceleration rate significantly affected the average velocity of the whole curve, acceleration phase, and deceleration phase. Although acceleration/deceleration rate had some effect on average torque in the acceleration and deceleration phases, peak torque and average torque of the whole curve were not significantly affected. Thus, in this study, the choice of acceleration/deceleration rate at 90 degrees /sec did not appear to have a clinically significant effect on average torque and peak torque for the whole curve. J Orthop Sports Phys Ther 1991;14(4):161-168.     

Electrical nerve localization: effects of cutaneous electrode placement and duration of the stimulus on motor response

BACKGROUND: Recommendations regarding the technical aspects of nerve stimulator-assisted nerve localization are conflicting. The objectives of this study were to determine whether the placement of the cutaneous electrode affects nerve stimulation and to determine the duration and intensity of an electrical stimulus that allows nerve stimulation with minimal discomfort. METHODS: Ten healthy volunteers underwent an interscalene and a femoral nerve block. After obtaining a clearly visible motor response of the biceps (interscalene) and quadriceps (femoral) muscles at the minimal current (0.1 ms, 2 Hz), the position of the cutaneous electrode was varied. Next, the duration of the stimulating current was set at 0.05, 0.1, 0.3, 0.5, or 1.0 ms, in random order. Intensity of the motor response and discomfort on stimulation were recorded. RESULTS: The minimal current at which a visible motor response was obtained was 0.32 +/- 0.1 mA (0.23-0.38 mA) for the inter-scalene block and 0.29 +/- 0.1 mA (0.15-0.4 mA) for the femoral block. Changing the position of the return electrodes did not result in any change in the grade of the motor response or in the current required to maintain it. Currents of longer duration caused discomfort and more forceful contraction at a lower current intensity as compared with currents of shorter duration (P < 0.01). When the current was adjusted to maintain the same visible motor response, there was no significant discomfort among studied current durations. CONCLUSION: Site of placement of the cutaneous electrode is not important when constant current nerve stimulators are used during nerve localization in regional anesthesia. There is an inverse relation between the current required to obtain a visible motor response and current duration. Selecting a current duration between 0.05 and 1.0 ms to specifically stimulate sensory or motor components of a mixed nerve does not seem to be important in clinical practice.     

Effects of varying electrode site placements on the torque output of an electrically stimulated involuntary quadriceps femoris muscle contraction

The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of the Army or the Department of Defense. At the time this study was performed, LTs Ferguson, Blackley, Knight, and Sutlive were students in the US. Army-Baylor University Graduate Program in Physical Therapy. This research was performed in partial fulfillment of their requirements for the Master of Physical Therapy Degrees.The purpose of this study was to evaluate the effects of varying electrode placement on the torque output of an electrically stimulated involuntary quadriceps femoris muscle contraction. Twenty-two volunteer subjects (18 men, 4 women) with a mean age of 21.7 years received electrical stimulation according to a randomized treatment order which included: Femoral nerve and 1) vastus medialis (VM), 2) rectus femoris (RF), 3) vastus lateralis (VL), 4) opposite quadriceps (OQ), and 5) the ipsilateral vastus medialis and vastus lateralis (VM/VL). The subject's knee was placed in 60 degrees of flexion, and the isokinetic dynamometer set at 0 degrees /sec. The peak torque produced by the involuntary quadriceps contraction was measured as a percentage of maximum voluntary isometric contraction (MVIC). An analysis of variance with repeated measures was used to examine the data. The results indicated the mean percentages of MVIC produced by stimulating the VM, VL, and RF sites were significantly greater (p 相似文献   

A comparison of plantar flexion torque with and without the triceps surae.

Torque generated about the ankle joints during maximum isometric contraction of the plantar flexor muscles was measured on a subject 4 months after unilateral excision of the entire triceps surae. Resulting torque output on the operated limb was 327 kg-cm, or 38 per cent of the 871 kg-cm total for the sound limb.     

Differential effects of etomidate and midazolam on vascular adenosine triphosphate-sensitive potassium channels: isometric tension and patch clamp studies

BACKGROUND: The aim of this study was to investigate the effects of two imidazoline-derived intravenous anesthetics, etomidate and midazolam, on vascular adenosine triphosphate-sensitive potassium (KATP) channel activity. METHODS: In isolated rat aorta, isometric tension was recorded to examine the anesthetic effects on vasodilator response to levcromakalim, a selective KATP channel opener. Using the patch clamp method, the anesthetic effects were also examined on the currents through (1) native vascular KATP channels, (2) recombinant KATP channels with different combinations of various types of inwardly rectifying potassium channel (Kir6.0 family: Kir6.1, 6.2) and sulfonylurea receptor (SUR1, 2A, 2B) subunits, (3) SUR-deficient channels derived from a truncated isoform of Kir6.2 subunit (Kir6.2DeltaC36 channels), and (4) mutant Kir6.2DeltaC36 channels with reduced sensitivity to adenosine triphosphate (Kir6.2DeltaC36-K185Q channels). RESULTS: Etomidate (> or = 10 m), but not midazolam (up to 10 m), inhibited the levcromakalim-induced vasodilation, which was sensitive to glibenclamide (IC50: 7.21 x 10 m; maximum inhibitory concentration: 1.22 x 10 m). Etomidate (> or = 3 x 10 m), but not midazolam (up to 10 m), inhibited the native KATP channel activity in both cell-attached and inside-out configurations with IC50 values of 1.68 x 10 m and 1.52 x 10 m, respectively. Etomidate (10 m) also inhibited the activity of various types of recombinant SUR/Kir6.0KATP channels, Kir6.2DeltaC36 channels, and Kir6.2DeltaC36-K185Q channels with equivalent potency. CONCLUSIONS: Clinical concentrations of etomidate, but not midazolam, inhibit the KATP channel activity in vascular smooth muscle cells. The inhibition is presumably through its effects on the Kir6.0 subunit, but not on the SUR subunit, with the binding site different from adenosine triphosphate at the amino acid level.