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PubMed1993

Torque/velocity properties of human knee muscles: peak and angle-specific estimates.

Angle-specific (AS) torque/velocity data have been used to avoid angle related variation in peak torque capacity. However, series elastic structures cause the contractile velocity of active force-producing tissue to differ from external joint velocity except at peak torque. Alternatively, angle related variation may be removed by normalizing peak torque to the isometric maximum at that angular position. The AS, peak (P), and normalized peak (NP) methods were compared in isovelocity knee flexion and extension at velocities between 50 and 250 degrees s-1 for 8 male subjects. The P and NP methods gave more similar torque/velocity relations than the AS method. Further, very little variation in peak torque was attributed to differences in joint angle. Both the P and AS methods illustrate that relative quadriceps/hamstrings torque capability (flexor/extensor ratio) increases slightly with velocity. It is proposed that antagonist muscle torque capabilities should be compared at different angular positions to assess muscular imbalance.

Adult↗
PubMed1994

Voluntary and evoked muscle contractile characteristics in active men and women.

Eight men and 8 women were tested for voluntary and isometric evoked contractions of the dorsiflexors. Maximal voluntary contractions were conducted isometrically (30 degrees plantarflexion) and isokinetically. Men produced greater peak torques at all but the highest isokinetic velocity. They exceeded women in measures of absolute voluntary isometric (33.8%), tetanic (46.3%), and twitch (37.9%) peak torque. Men demonstrated a higher tetanus/MVC ratio (17.8%). This ratio disparity would indicate that gender differences in peak torque in this study were more dependent upon muscle mechanisms. Although men exceeded women in measures of absolute voluntary maximum rate of torque development (MRTD) (38.7%), tetanic MRTD (39.1%), twitch MRTD (27.9%), voluntary maximum rate of torque relaxation (MRTR) (46.9%), and tetanic MRTR (41.9%), there were no significant gender differences in percentage rates of torque development or relaxation with voluntary or evoked contractions. Therefore the central and peripheral mechanisms controlling MRTD and MRTR may be similar between the sexes.

Adult↗
PubMed1993

Bilateral deficit is larger for step than for ramp isometric contractions.

The force produced by a muscle group during a maximum effort bilateral task has been reported to be less than that produced during a maximum effort unilateral task. It was hypothesized that if decreased activation of primarily fast motor units is responsible for this bilateral deficit, 1) the bilateral deficit would be larger in step than in ramp isometric contractions and 2) the rate of torque generation in step contractions would be slower in bilateral than in unilateral tasks. Twelve healthy male subjects performed unilateral and bilateral isometric knee joint extension tasks in which maximum torque was generated under ramp and step conditions. The maximum torques produced in the bilateral tasks were 17.0 and 24.6% less than those produced in the unilateral tasks during the ramp and step conditions, respectively (both P < 0.001). The bilateral torque deficit for the step condition was significantly greater than that for the ramp condition (P = 0.012). The rate of torque generation in the step condition was 19.7% slower in the bilateral than in the unilateral task (P = 0.010). Thus the results from these torque measurements support the notion that decreased activation of primarily fast motor units may be responsible for the bilateral deficit.

Adult↗
PubMed1994

Influence of muscle length and force on endurance and pressor responses to isometric exercise.

Experiments were performed to determine whether endurance time, mean arterial pressure, or heart rate was related to either muscle length or external torque production in humans during isometric knee extension. Eight men and nine women performed isometric knee extension to the endurance limit at each of three muscle lengths, determined by knee angles of 40 degrees (0.698 rad, shortest), 60 degrees (1.047 rad, intermediate), and 90 degrees (1.571 rad, longest), and at intensities of 30 and 50% maximal voluntary contraction (MVC). Knee extension forms an ascending-descending length-torque curve, and lengths were chosen to result in different external torques. MVC was greatest at a knee angle of 60 degrees (P < 0.05 vs. 40 degrees, 90 degrees), with no significant difference between 90 degrees and 40 degrees. Endurance time was inversely related to muscle length, independent of torque production, at 30% MVC [40 degrees, 395 +/- 139 (SE); 60 degrees, 237 +/- 60; 90 degrees, 165 +/- 51 s; P < 0.05 vs. each other] and 50% MVC (40 degrees, 176 +/- 64; 60 degrees, 137 +/- 40; 90 degrees, 85 +/- 23 s; P < 0.05 vs. each other). Evidence is presented that endurance is a function of internal muscle force and not resultant external torque. The experimental design allowed the relationship of external torque and cardiovascular responses to be examined independent of exercise intensity. Muscle mass was also controlled in that the same muscle group was involved in all contractions. There were no differences in mean arterial pressure, heart rate, or rating of perceived exertion at any percentage of endurance time under any condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1998

Neuromuscular fatigue after maximal stretch-shortening cycle exercise.

To examine some possible sites of fatigue during short-lasting maximally intensive stretch-shortening cycle exercise, drop jumps on an inclined sledge apparatus were analyzed. Twelve healthy volunteers performed jumps until they were unable to maintain jumping height > 90% of their maximum. After the workout, the increases in the blood lactate concentration and serum creatine kinase activation were statistically significant (P < 0.001 and P < 0.05, respectively) but rather small in physiological terms. The major changes after the workout were as follows: the single twitch was characterized by smaller peak torque (P < 0.05) and shorter time to peak (P < 0.05) and half-relaxation time (P < 0.01). The double-twitch torque remained at the same level (P > 0.05), but with a steeper maximal slope of torque rise (P < 0.05); during 20- and 100-Hz stimulation the torque declined (both P < 0.01) and the maximal voluntary torque changed nonsignificantly but with a smaller maximal slope of torque rise (P < 0.01) and a higher activation level (P < 0.05), accompanied by an increased electromyogram amplitude. These findings indicate that the muscle response after the short-lasting consecutive maximum jumps on the sledge apparatus may involve two distinct mechanisms acting in opposite directions: 1) The contractile mechanism seems to be potentiated through a shorter Ca2+ transient and faster cross-bridge cycling, as implied by twitch changes. 2) High-frequency action potential propagation shows an impairment, which is suggested as the possible dominant reason for fatigue in exercise of this type.

Action Potentials↗
PubMed2002

Handedness: dominant arm advantages in control of limb dynamics.

Recent findings from our laboratory suggest that a major factor distinguishing dominant from nondominant arm performance is the ability by which the effects of intersegmental dynamics are controlled by the CNS. These studies indicated that the dominant arm reliably used more torque-efficient patterns for movements made with similar speeds and accuracy than nondominant arm movements. Whereas, nondominant hand-path curvatures systematically varied with the amplitude of the interaction torques transferred between the segments of the moving limb, dominant hand-path curvatures did not. However, our previous studies did not distinguish whether dominant arm coordination advantages emerged from more effective control of dynamic factors or were simply a secondary effect of planning different kinematics. The purpose of this study was to further investigate interlimb differences in coordination through analysis of inverse dynamics and electromyography recorded during the performance of reaching movements. By controlling the amplitude of intersegmental dynamics in the current study, we were able to assess whether systematic differences in torque-efficiency exist, even when differences in hand-path shape were minimal. Subject's arms were supported in the horizontal plane by a frictionless air-jet system and were constrained to movements about the shoulder and elbow joints. Two targets were designed, such that the interaction torques elicited at the elbow were either large or small. Our results showed that the former produced large differences in hand-path curvature, whereas the latter did not. Additionally, the movements with small differences in hand-path kinematics showed substantial differences in torque patterns and corresponding EMG profiles which implied a more torque-efficient strategy for the dominant arm. In view of these findings we propose that distinct neural control mechanisms are employed for dominant and nondominant arm movements.

Adult↗
PubMed1985

Activity of neurons in putamen during active and passive movements of wrist.

Recent studies have shown that many neurons in the basal ganglia have patterns of activity that are closely related to various parameters of active movements of the arm. The topographical distribution of these cells suggests that they are influenced by afferents from primary motor and sensory areas of the cerebral cortex. Although there is abundant evidence that information from peripheral receptors is relayed to the basal ganglia, relatively little information is available on whether neurons related to active movement are influenced by peripheral inputs. The present study was undertaken to provide information on this problem by comparing responses of putamen neurons to active and passive movements of the wrist. Two monkeys were trained to place their hand in a manipulandum and actively extend and flex their wrist against opposing torque loads. Additionally, they were trained to accept 1) passive step displacements of the wrist by the experimenter, which were comparable in amplitude, duration, and velocity to active movements, and 2) brief rapid displacements generated by a pulse of torque applied to the manipulandum by a motor. An extensive electromyographic (EMG) study was made prior to unit recording to characterize patterns of muscle activity during active and passive movements. A sample of 82 neurons was isolated in the putamen on the basis of a phasic burst of spikes associated with active movement of the wrist. Most (80%) of these cells showed directionally specific responses. The onset latency of unit firing in 91% of the cells lagged behind the onset of EMG activity in forearm agonist muscles. Phasic unit discharge during active movement increased with increasing opposing torque loads in 59% of the sample. The rate-torque curves for most of these cells were curvilinear (plateau occurred at heavy torque loads), although some cells showed a linear relationship. A comparison of these neuronal activity patterns with EMG activity-torque curves suggests that most of the cells were related to activity in forearm muscles and not to activity in proximal or axial muscles. The functional significance of these findings is interpreted in light of recent physiological and anatomic studies of the basal ganglia. A substantial proportion (44%) of the units that were related to active wrist movements showed an excitatory response during passive step displacements of the wrist in the absence of phasic EMG activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Trained slow tracking. II. Bidirectional discharge patterns of cerebellar nuclear, motor cortex, and spindle afferent neurons.

Single-unit discharge was recorded in the dentate and interposed cerebellar nuclei, motor cortex, and C7 and C8 dorsal root ganglia during trained, slow hold-ramp-hold tracking, rapid alternating movement, torque-pulse perturbation, and action tremor of the monkey's wrist. Fifty-seven dentate and 45 interposed neurons were found in two monkeys that discharged in relation to slow tracking movement. Nearly all neurons had a distinct bidirectional pattern of discharge consisting of an abrupt increase (or decrease) in firing frequency at or before the onset of movement that was variably maintained throughout the ramp and was independent of movement direction. None of the neurons showed a clear relationship to direction, position, velocity, or load during the performance of this task. Nevertheless, many of these neurons discharged in relation to rapid alternation and (for interpositus) torque pulses in patterns that were directionally reciprocal. Some interpositus neurons showed a modulation related to tremor superimposed on the bidirectional discharge related to slow ramps. Twenty-nine neurons in motor cortex of one monkey discharged during slow hold-ramp-hold tracking in two patterns. Class I neurons (14 of 29) showed gradually changing, directionally reciprocal modulations of firing frequency for movements in opposite directions. These neurons were often related to torque load and/or to wrist position but not to velocity. The discharge pattern was similar to the pattern of activity of forearm muscles. Class II neurons (15 of 29) showed an abrupt change in firing frequency that was bidirectional. They were often related to torque load and/or to velocity but not to position. Motor cortex neurons discharged in relation to rapid alternating movements, torque pulses, and tremor in similar patterns that did not distinguish the two classes. Five units in dorsal root ganglia were identified as muscle spindle afferents. During ramps, their pattern of discharge was bidirectional and resembled the bidirectional discharge patterns of neurons in motor cortex (class II) and cerebellum. For some cells the bidirectional pattern varied slightly in relation to the direction and velocity of movement and the amount of torque load, but it was not related to the large changes in wrist position (muscle length). Modulation in relation to tremor was superimposed on the bidirectional pattern related to ramps. The comparison of spindle afferent discharge with the concurrent electromyogram (EMG) of the parent muscle suggested that spindles were driven by gamma-fusimotor activity dissociated from that of homonymous alpha-skeletomotor neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Organizing principles for single-joint movements. I. A speed-insensitive strategy.

1. Normal human subjects made discrete elbow flexions and extensions in the horizontal plane from a stationary initial position to visually defined targets at different distances with a constant inertial load or made flexions to a visually defined target with different inertial loads. We measured joint angle, acceleration, and electromyograms (EMGs) from two agonist and two antagonist muscles. 2. Subjects were instructed to move their limbs accurately but quickly to the targets. Movements of greater distances or lesser loads were performed at higher velocities. 3. Peak inertial torque, acceleration and velocity, movement time, and integrated, rectified EMG were all highly correlated with the task variables, distance and inertial load. We show that peak inertial torque can be used as a linking variable that is almost sufficient to explain all correlations between the tasks, the EMG, and movement kinematics. 4. The rate at which subjects initially developed torque to accelerate their movements was invariant over changes in the value of either task variable. The rising phase of the agonist EMG was also independent of the distance or load moved. 5. Two components were distinguished in the antagonist EMG. The first had a relatively constant latency and amplitude. It terminated on the onset of the second and larger component at a latency that was delayed as both distance and load increased. 6. The integrated, rectified antagonist EMG was proportional to inertial load and peak decelerating torque for changes in inertial load. When target distance varied, proportionality between peak decelerating torque and antagonist EMG could be found if correction was made for the effects of muscle length on the torque-EMG relationship. 7. We propose organizing principles for the control of single-joint human movements in which tasks are performed by one of two strategies. These are called speed-insensitive and speed-sensitive strategies. 8. A model is described in which movements made under a speed-insensitive strategy are executed by controlling the duration and the relative timing of amplitude invariant patterns of activation to the spinal motoneuron pools.

Elbow Joint↗
PubMed1996

Coordinating movement at two joints: a principle of linear covariance.

1. Six subjects performed fast, "single-joint" flexions at either the elbow or shoulder over three angular distances in a sagittal plane. Movement endpoints were located to require flexion of only a single, "focal" joint, without any external, mechanical constraint on the other, "nonfocal" joint. Three subjects performed another series of movements between two targets while moving along different paths and in which both joints were flexed. 2. We compared the torque patterns that were produced at the two joints. For single-joint movements, they were both biphasic pulses that accelerated and then decelerated the limb. 3. The torque at the nonfocal joint of a single joint movement was very close to linearly proportional to that at the focal joint throughout the movement. Elbow and shoulder torques differed by a linear scaling constant and went through extrema and zero crossings almost simultaneously. 4. In contrast, during movements in which subjects were explicitly instructed to use a hand path they would not naturally, use the linear interjoint torque scaling rule did not apply. This demonstrated that when we wish to move along a path between two targets that is not produced by linear torque covariation, we are able to modify that rule at will. 5. We speculate that linear, dynamic covariation of the torque patterns across two joints may be an important principle for reducing the number of degrees of freedom that the nervous system must independently control in performing unconstrained limb movements over naturally chosen paths.

Analysis of Variance↗
PubMed1996

On the voluntary movement of compliant (inertial-viscoelastic) loads by parcellated control mechanisms.

1. Experiments were performed to characterize the trajectories, net muscle torques, and electromyogram (EMG) patterns when subjects performed voluntary elbow flexions against different compliant loads. Subjects made movements in a single-joint manipulandum with different loads generated by a torque motor. Some series of movements were performed under entirely known and predictable load conditions. Other series were performed with the same known loads, interspersed, just before movement onset with occasional, unpredictable changes in the magnitude of the load. 2. To move a larger load, subjects increase the impulse (torque-time integral) by prolonging the duration of the accelerating torque while keeping its rate of rise constant. Subjects modulate torque most for inertial loads, less for viscous loads, and least for elastic loads, and modulation is greater under predictable than unpredictable load conditions. 3. Even when the loads are predictable, subjects move large inertial and viscous, but not elastic, loads more slowly than small. Unpredictable changes in load have a larger effect on movement kinematics than do known changes of the same magnitude. 4. Subjects prolong the duration and increase the area of the agonist EMG burst but do not change its rate of rise to move larger, predictable loads. Subjects change the area of the antagonist burst according to the torque requirements of the load, increasing it only for increases in inertial loads. These effects are usually greater for predictable than unpredictable loads but in either case, are highly variable across subjects. 5. Predictable loads that slow the movements delay the onset of the antagonist burst. When changes in load are unpredictable, only inertial changes affect antagonist latency. 6. The initial change in muscle force when there is an unexpected change in the external load is due to the viscous properties of muscle tissue. Electromyographic evidence of reflex changes in muscle activation follow this intrinsic mechanical response by 50-70 ms. Elastic neuromuscular properties may also be important but only late in the movement as the final position is approached. 7. We propose that the central command for a voluntary movement should be described by three elements. The first element (alpha) specifies the muscle activation pattern expected to generate dynamic forces adequate and appropriate to produce a satisfactory trajectory. This feed-forward control program uses simple rules, based on an internal model of task dynamics constructed from prior experience. The second element (lambda) is a kinematic plan or reference trajectory utilizing the negative feedback of reflex action to partially compensate for errors in alpha or for unexpected perturbations during the movement. It defines the locus of a moving, instantaneous equilibrium position of the limb, a "template" for the intended trajectory. As movements become slower and require smaller dynamic (velocity and acceleration dependent) forces, lambda will become the dominant control signal. It is also used for correction and updating of the internal model used to generate alpha. The third element (gamma) modulates volitional set, the degree and manner in which multiple reflex mechanisms can contribute to the muscle activation patterns if the actual trajectory deviates from the planned one. Reflex mechanisms work in parallel with intrinsic muscle compliance to provide partial adaptation of neuromuscular system dynamics to external load dynamics. These controlled compliant mechanisms maintain the stability of the motor system, without which both posture and movement would not be possible.

Elbow↗
PubMed1998

Muscle activation patterns during two types of voluntary single-joint movement.

We examined the systematic variations in the EMG patterns during two types of single joint elbow movements. These patterns may be interpreted as exhibiting rules by which the CNS controls movement parameters. Normal human subjects performed two series of fast elbow flexion movements of 20-100 degrees in a horizontal plane manipulandum. The first series consisted of pointing movements (PMs) from an initial position to a target; the second series consisted of reversal movements (RMs) to the same targets with an immediate return to the starting position. Both series showed kinematic and electromyographic (EMG) patterns that followed our previously described speed-insensitive strategy for controlling movement distance. Kinematic patterns of PMs and RMs were identical to about the time of peak PM deceleration. Agonist EMG bursts were also initially the same, but RM bursts ended abruptly in a silent period, whereas PM bursts declined more gradually. Antagonist EMG bursts of RMs were later than those of PMs but were not larger, contrary to our prior expectation and despite the larger net extension torque during RMs. The increase in net RM extension-directed torque that takes the limb back to its initial position appears to be a consequence of reduced flexor muscle torque rather than increased extensor muscle torque. We propose that rules for movement control may be similar for different kinds of movements as long as they are functionally sufficient for the task. However, even in a single-joint movement paradigm, physics alone, that is, the knowledge of net muscle torque and limb kinematics, is not adequate to fully predict those rules or the muscle activation patterns they produce. These must be discovered by experiment. The simplest expression of such rules may not be in terms of torque or kinematic variables but rather explicitly in terms of muscle activation patterns.

Elbow Joint↗
PubMed2001

Reflex and intrinsic changes induced by fatigue of human elbow extensor muscles.

Fatigue-induced changes in intrinsic and reflex properties of human elbow extensor muscles and the underlying mechanisms for fatigue compensation were investigated. The elbow joint was perturbed using small-amplitude and pseudorandom movement patterns while subjects maintained steady levels of mean joint extension torque. Intrinsic and reflex properties were identified simultaneously using a nonlinear delay differential equation model. Intrinsic joint properties were characterized by measures of joint stiffness, viscous damping, and limb inertia and reflex properties characterized by measures of dynamic and static reflex gains. Fatigue was induced using 15 min of intermittent voluntary isometric (submaximal) exercise, and a rest period of 10 min was taken to allow the fatigued muscles to recover from acute fatigue effects. Identical experimental and data analysis procedures were used before and after fatigue. Our findings were that after fatigue, joint stiffness was significantly reduced at higher torque levels, presumably reflecting the reduced force-generating capacity of fatigued muscles. Conversely, joint viscosity was increased after fatigue potentially because of the reduced crossbridge detachment rate and prolonged relaxation associated with intracellular acidosis accompanying fatigue. Static stretch reflex gain decreased significantly at higher torque levels after fatigue, indicating that the isometric fatiguing exercise might be associated with a preferential change in properties of spindle chain fibers and bag(2) fibers. For matched pre- and postfatigue torque levels, dynamic reflexes contributed relatively more torque after fatigue, displaying higher dynamic reflex gains and larger dynamic electromyographic responses elicited by the controlled small-amplitude position perturbations. These changes appear to counteract the fatigue-induced reductions in joint stiffness and static reflex gain. The compensatory responses could be partly due to the effects of increasing the number of active motoneurons innervating the fatiguing muscles. This shift in operating point gave rise to significant compensation for the loss of contractile force. The compensation could also be due to fusimotor adjustment, which could make the dynamic reflex gain much less sensitive to fatigue than intrinsic stiffness. In short, the reduced contribution from intrinsic stiffness to joint torque was compensated by increased contribution from dynamic stretch reflexes after fatigue.

Adult↗
PubMed1985

Cybex evaluation of the relationship between anterior and posterior compartment lower leg muscles.

Twenty adult males were tested with the Cybex II isokinetic dynamometer, comparing in each leg the torque produced by the anterior and posterior muscle compartments. Significant torque is produced by the gastroc soleus muscle group, even when the knee is bent 90 degrees. There is a significant increase in anterior compartment dorsiflexion torque produced with the knee in extension as compared to flexion. There is no difference in right or left handedness in comparing the results of torque generation in the lower extremity. On the average, dorsiflexion torque is approximately one-third of plantarflexion torque at slow speeds and half that of plantarflexion at fast speeds.

Adult↗
PubMed2006

Numerical simulation of in vivo intraosseous torsional failure of a hollow-screw oral implant.

BACKGROUND: Owing to the complexity and magnitude of functional forces transferred to the bone-implant interface, the mechanical strength of the interface is of great importance. The purpose of this study was to determine the intraosseous torsional shear strength of an osseointegrated oral implant using 3-D finite element (FE) stress analysis implemented by in vivo failure torque data of an implant. METHODS: A Ø 3.5 mm x 12 mm ITI hollow screw dental implant in a patient was subjected to torque failure test using a custom-made strain-gauged manual torque wrench connected to a data acquisition system. The 3-D FE model of the implant and peri-implant circumstances was constructed. The in vivo strain data was converted to torque units (N x cm) to involve in loading definition of FE analysis. Upon processing of the FE analysis, the shear stress of peri-implant bone was evaluated to assume torsional shear stress strength of the bone-implant interface. RESULTS: The in vivo torque failure test yielded 5952 microstrains at custom-made manual torque wrench level and conversion of the strain data resulted in 750 N.cm. FE revealed that highest shear stress value in the trabecular bone, 121 MPa, was located at the first intimate contact with implant. Trabecular bone in contact with external surface of hollow implant body participated shear stress distribution, but not the bone resting inside of the hollow. CONCLUSION: The torsional strength of hollow-screw implants is basically provided by the marginal bone and the hollow part has negligible effect on interfacial shear strength.

Bone Screws↗
PubMed1989

Biodynamics of the wrist in rheumatoid arthritis--the enigma of stiffness.

The wrist has been moved rhythmically in the horizontal plane by sinusoidal torques provided by a printed motor. Measurements have been made on normal subjects and subjects with rheumatoid arthritis. Both groups exhibited a resonance, the oscillations being greatest when the applied torque was of certain frequency. In both groups the resonant frequency fell to approximately the same constant value when the torque was raised. While the main relationships were similar a somewhat lower torque resulted in the lowering of resonant frequency in the patients. The relationship between applied torque and peak velocity at resonance was also studied. For a given torque the motion was greater in the patients. No objective signs of increased viscous or elastic stiffness were demonstrable at the wrist in patients with rheumatoid arthritis.

Arthritis, Rheumatoid↗
PubMed2007

Neuromuscular fatigue profile in endurance-trained and power-trained athletes.

PURPOSE: This study examined the effects of training background on the relationship between the neuromuscular fatigue profile and maximal voluntary torque production in isometric, concentric, and eccentric contraction modes. METHODS: Before and after three sets of 31 isokinetic concentric knee extensions at 60 degrees .s(-1), voluntary and electrically induced contractions were recorded in 14 endurance-trained (ENDU) men (seven cyclists: age 25 +/- 2 yr, mass 70 +/- 8 kg, height 175 +/- 5 cm; and seven triathletes: age 27 +/- 4 yr, mass 71 +/- 5 kg, height 179 +/- 6 cm) and seven explosive power-trained men (EXPLO: age 24 +/- 1 yr, mass 73 +/- 5 kg, height 179 +/- 4 cm). Maximal knee-extension torque, activation level (twitch interpolation technique), electromyographic activity of agonist and antagonist muscles, and twitch contractile properties were assessed. RESULTS: At preexercise, the maximal voluntary isometric and concentric torques of EXPLO were greater than those of ENDU (P < 0.05). After the fatiguing exercise, significant isometric (18%; P < 0.01) and concentric (25%; P < 0.05) torque decreases in EXPLO were associated with, respectively, twitch torque (Pt) and maximal rate of twitch development (+dPt/dt) reductions (P < 0.01) and with an increase in the antagonist coactivation level (P < 0.01). No modification was observed for ENDU. Interestingly, the coactivation level was also increased (P < 0.01) in eccentric contraction for EXPLO, although the maximal eccentric torque decrease (P < 0.01) could not be specifically attributed to any group. CONCLUSION: The fatiguing exercise induced central and peripheral adaptations, but the mechanisms differed regarding the contraction mode. At pre- and postfatiguing exercise, it seems that the neuromuscular profile depends on the subject's training background and the contraction modes used to assess fatigue.

Adaptation, Physiological↗
PubMed2001

Improvement of the bone-pin interface strength in osteoporotic bone with use of hydroxyapatite-coated tapered external-fixation pins. A prospective, randomized clinical study of wrist fractures.

BACKGROUND: Achieving adequate fixation strength in osteoporotic bone is a challenge. In this study, we examined the use of hydroxyapatite-coated tapered external-fixation pins for the fixation of wrist fractures in patients with osteoporosis. METHODS: Twenty female patients with osteoporosis and a fracture of the wrist were divided into two paired groups and randomized to receive either standard tapered pins or hydroxyapatite-coated tapered pins. Two pins were inserted in the distal part of the radius, two pins were inserted in the second metacarpal, and an external fixation device was mounted. All fixation devices were removed six weeks after surgery. RESULTS: The mean pin-insertion torque (and standard deviation) was 461 +/- 254 Nmm in the group managed with standard pins and 332 +/- 176 Nmm in the group managed with hydroxyapatite-coated pins (p = 0.01). The mean pin-extraction torque was 191 +/- 155 Nmm in the group managed with standard pins and 600 +/- 214 Nmm in the group managed with hydroxyapatite-coated pins (p < 0.0001, power 95%). The mean extraction torque was lower than the corresponding insertion torque at each pin position in the group managed with standard pins (p < 0.05), whereas the mean extraction torque was higher than the corresponding insertion torque at each pin position in the group managed with hydroxyapatite-coated pins (p = 0.001). Two patients managed with standard pins and no patient managed with hydroxyapatite-coated pins had a pin-track infection. Pain during pin removal did not differ between the two groups. CONCLUSIONS: The present study showed that hydroxyapatite-coated tapered external-fixation pins provided improved fixation in the treatment of wrist fractures in patients with osteoporosis.

Aged↗