1. Previous studies have used tendon vibration to investigate kinesthetic illusions in the isometric limb and end point control in the moving limb. These previous studies have shown that vibration distorts the perceptions of static joint angle and movement and causes systematic errors in the end point of movement. In this paper we describe the effects of tendon vibration during movement while human subjects performed a proprioceptively coordinated motor task. In an earlier study we showed that the CNS coordinates this motor task-a movement sequence-with proprioceptive information related to the dynamic position and velocity of the limb. 2. When performing this movement sequence, each subject sat at a table and opened the right hand as the right elbow was passively rotated in the extension direction through a prescribed target angle. Vision of the arm was prevented, and the movement velocity was changed randomly from trial to trial, leaving proprioception as the only useful source of kinematic information with which to perform the task. 3. In randomly occurring trials, vibration was applied to the tendon of the biceps brachii, a muscle that lengthens during elbow extension. In some experiments the timing of tendon vibration was varied with respect to the onset of elbow rotation, and in other experiments the frequency of vibration was varied. In each experiment we compared the accuracy of the subject's response (i.e., the elbow angle at which the subject opened the hand) in trials with tendon vibration with the accuracy in trials without tendon vibration. 4. The effect of tendon vibration depended on the frequency of vibration. When the biceps tendon was vibrated at 20 Hz, subjects opened the hand after the elbow passed through the target angle ("overshooting"). Overshooting is consistent with an underestimate of the actual displacement or velocity of the elbow. Vibration at 30 Hz had little or no effect on the elbow angle at hand opening. Vibration at 40 Hz caused subjects to open the hand before the elbow reached the target angle ("undershooting"). Undershooting is consistent with an overestimate of the actual displacement or velocity of the elbow. The size of the error depended on the velocity of the passively imposed elbow rotation. 5. The effect of tendon vibration also depended on the timing of vibration. If 40-Hz vibration began at the onset of movement, the subject undershot the target. If 40-Hz vibration started 5 s before movement onset and continued throughout the movement, the undershoot error increased in magnitude. However, if 40-Hz vibration started 5 s before movement onset and then stopped at movement onset, the subject overshot the target. When vibration was shut off during movement, a transition occurred from an over-shooting error to an undershooting error at a time that depended on the velocity of elbow rotation. 6. In a separate experiment, subjects were instructed to match either the perceived dynamic position or the perceived velocity of rotation imposed on the right elbow by actively rotati...

1. Recent studies have shown that the CNS uses proprioceptive information to coordinate multijoint movement sequences; proprioceptive input related to the kinematics of one joint rotation in a movement sequence can be used to trigger a subsequent joint rotation. In this paper we adopt a broad definition of "proprioception," which includes all somatosensory information related to joint posture and kinematics. This paper addresses how the CNS uses proprioceptive information related to the velocity and position of joints to coordinate multijoint movement sequences. 2. Normal human subjects sat at an experimental apparatus and performed a movement sequence with the right arm without visual feedback. The apparatus passively rotated the right elbow horizontally in the extension direction with either a constant velocity trajectory or an unpredictable velocity trajectory. The subjects' task was to open briskly the right hand when the elbow passed through a prescribed target position, similar to backhand throwing in the horizontal plane. The randomization of elbow velocities and the absence of visual information was used to discourage subjects from using any information other than proprioceptive input to perform the task. 3. Our results indicate that the CNS is able to extract the necessary kinematic information from proprioceptive input to trigger the hand opening at the correct elbow position. We estimated the minimal sensory conduction and processing delay to be 150 ms, and on the basis of this estimate, we predicted the expected performance with different degrees of reduced proprioceptive information. These predictions were compared with the subjects' actual performances, revealing that the CNS was using proprioceptive input related to joint velocity in this motor task. To determine whether position information was also being used, we examined the subjects' performances with unpredictable velocity trajectories. The results from experiments with unpredictable velocity trajectories indicate that the CNS extracts proprioceptive information related to both the velocity and the angular position of the joint to trigger the hand movement in this movement sequence. 4. To determine the generality of proprioceptive triggering in movement sequences, we estimated the minimal movement duration with which proprioceptive information can be used as well as the amount of learning required to use proprioceptive input to perform the task. The temporal limits for proprioceptive processing in this movement task were established by determining the minimal movement time during which the task could be performed.(ABSTRACT TRUNCATED AT 400 WORDS)

SUMMARY1. The main purpose of this study was to examine the effects of two subtly different stimulus patterns on the force developed by fast-twitch, fatiguable motor units in a cat hindlimb muscle during control (pre-fatigue) and fatiguing contractions.2. The peak force and the force-time integral responses of nineteen high fatigue (FF) and three intermediate fatigue (FI) motor units of the tibialis posterior muscle in five deeply anaesthetized adult cats were measured at selected times during the course of a 360-s fatigue test.3. The fatigue test involved a pseudo-random alternation of two patterns of stimulation. One pattern (regular) was composed of a train of stimuli with constant interpulse intervals, set at 1-8 x the twitch contraction time of each unit (interval range, 27-51 ms), and delivered for 500 (or 400) ms. For the total (FF + FI) motorunit sample, the mean (±S.D.) stimulation frequency was 26 + 4 Hz (range, 19-37 Hz). The other stimulus pattern (optimized) consisted of three initial stimuli with short (10 ms) interpulse intervals, followed by a constant interpulse-interval train that was adjusted (interval range, 29-62 ms; frequency, 23 + 5 Hz; frequency range, 16-36 Hz) such that the total train had the same number of pulses, and the same average frequency and duration as the regular train.4. The stimulus trains were delivered at 1 s-5 for 360 s, using three-train sequences of each pattern, randomly alternating with one another. The response of the third train in each sequence was selected for the force measurements. The force profile obtained from the fatigue test was subsequently decomposed into two profiles: one attributable to regular and one to optimized stimulation.5. During the initial responses to the fatigue test, the optimized stimulus pattern produced significantly more force than the regular stimulus pattern. For FF units, the mean increase in peak force (141 %) was significantly greater than the increase in the force-time integral (59 %).6. All motor units exhibited an initial potentiation of peak force with the regular stimulation pattern, whereas peak force declined monotonically with the optimized pattern. In contrast, the force-time integral potentiated in the first 30 s for both regular and optimized stimulus patterns. L. BEVAN AND OTHERS 7. Each motor unit maintained an increased force response to optimized stimulation during the fatigue test, with the greatest relative increase occurring about 120 s into the test, well after the potentiation effect had subsided. At 360 s of stimulation, the force enhancement with optimization was still substantial (83 % for peak force and 37 % for the force-time integral), yet force was virtually non-existent in response to regular stimulation.8. These results suggest that subtle changes in the activation pattern are a potential mechanism by which the central nervous system might increase force during fatigue. Furthermore, force optimization and potentiation seem to be motorunit properties that are as fundamental as the more conventionally stu...

Although osteoporosis in men is increasingly recognized as an important health issue and bone mass appears to be a major determinant of fracture, there remain few data concerning the determinants of bone mass in men. To determine the correlates of bone density in men, we studied a large group of older subjects recruited from three rural communities in the northwestern United States. Three hundred and fifty-five men over the age of 60 years (mean 71.5 +/- 7.4 years) without known disorders of mineral metabolism were recruited by community advertising. Bone mineral density was measured at the lumbar spine, proximal femur and radius by dual-energy X-ray absorptiometry, and factors potentially related to skeletal status were assessed by direct measurements or questionnaire. In univariate analyses weight (positively) and age (negatively) were associated with bone density. After adjustment for these two factors, alcohol intake, osteoarthritis and thiazide use were associated with higher bone density, while previous fractures, gastrectomy, peptic ulcer disease, rheumatoid arthritis, glucocorticoid use, hypertension, previous hyperthyroidism, height loss since age 20 years, chronic lung disease and smoking were related to lower density. In multivariate models, only weight and a history of cancer were related to higher bone mass, and age, previous fracture, rheumatoid arthritis, gastrectomy and hypertension were associated with lower density. These data contribute to the emerging field of osteoporosis in men, and may help in the clinical identification of men at higher risk of osteopenia.

Oxidants have been shown to be involved in alcohol-induced liver injury. This study was designed to test the hypothesis that the antioxidant polyphenolic extract of green tea, comprised predominantly of epigallocatechin gallate, protects against early alcohol-induced liver injury in rats. Male Wistar rats were fed high-fat liquid diets with or without ethanol (10-14 g kg(-1) day(-1)) and green tea (300 mg kg(-1) day(-1)) continuously for 4 weeks using an intragastric enteral feeding protocol. Mean body weight gains (approximately 4 g/day) were not significantly different between treatment groups, and green tea extract did not the affect average concentration or the cycling of urine ethanol concentrations (0-550 mg dl(-1) day(-1)). After 4 weeks, serum ALT levels were increased significantly about 4-fold over control values (35+/-3 IU/l) by enteral ethanol (114+/-18); inclusion of green tea extract in the diet significantly blunted this increase (65+/-10). Enteral ethanol also caused severe fatty accumulation, mild inflammation, and necrosis in the liver. While not affecting fat accumulation or inflammation, green tea extract significantly blunted increases in necrosis caused by ethanol. Furthermore, ethanol significantly increased the accumulation of protein adducts of 4-hydroxynonenal, a product of lipid peroxidation and an index of oxidative stress; green tea extract blocked this effect almost completely. TNFalpha protein levels were increased in liver by alcohol; this phenomenon was also blunted by green tea extract. These results indicate that simple dietary antioxidants, such as those found in green tea, prevent early alcohol-induced liver injury, most likely by preventing oxidative stress.

The purpose of this study was to quantify the changes in motor-unit action potentials (MUAP) and force during a standard motor-unit fatigue test. MUAP waveforms were characterized by the measurement of amplitude, duration, area, and shape (as reflected in a coefficient of proportionality). Fatigue-resistant motor units exhibited small, but statistically significant, changes in MUAP amplitude and area during the fatigue test, whereas fatigable motor units displayed variable changes in MUAP amplitude, duration, and area. For all motor-unit types, the coefficient of proportionality did not change, and hence the change in MUAP area was proportional to the combined changes in amplitude and duration. The between- and within-train changes in MUAP were also distinct for the fatigue-resistant and fatigable motor units. Although several mechanisms could be responsible for the changes in the MUAP as the fatigue test proceeded, the dissociation of the time courses for MUAP and force indicated that these MUAP changes were not the principal reason for the decline in force under these conditions.

A "discrete" movement sequence is defined as a movement with a single goal that involves a series of overlapping joint rotations. Reaching-and-grasping and throwing are examples of discrete movement sequences. The central nervous system (CNS) can use reafferent proprioceptive information from one joint rotation in a sequence to coordinate subsequent rotations at other joints. The experiments reported in this paper demonstrate how the human CNS uses proprioceptive information to coordinate discrete movement sequences. We examined the mechanism (at an information processing level) underlying proprioceptive coordination and the generality (i.e., the boundary conditions) of these mechanisms as they apply to everyday movement sequences. Adult human subjects performed a discrete movement sequence that resembles backhand throwing: elbow extension followed by hand opening. The task was to open the hand as the elbow passed through a prescribed "target" angle. We eliminated visual information and made the arrival time at the target angle unpredictable so that the available kinematic information was provided exclusively by proprioception. The subjects were capable of performing this motor task with a high degree of precision, thereby demonstrating that the nervous system can use proprioceptive input to coordinate discrete movement sequences. Our data indicate that precise coordination is achieved by extracting kinematic information related to both the velocity of elbow rotation as well as the elbow position during movement (i.e., "dynamic position"). Dynamic position information appears to be encoded as both absolute joint angle and angular distance, although more precisely as angular distance. Although our experiments were conducted under rather restrictive laboratory conditions, this mechanism of motor coordination might also apply to everyday movement. Our results suggest that this mechanism could be employed for passive as well as active movement sequences, with and without opposing loads; it could exert its influence in discrete movement sequences as brief as 210 ms or as long as 1.5 s; and it does not involve any significant degree of learning (this proprioceptive mechanism appears to be readily available for use on the first attempt of a novel motor task).

1. The purpose of these experiments was to determine the accuracy with which human subjects could discriminate proprioceptive (nonretinotopic) targets during movement. The targets were located at either a specified angle in joint space, or a specified angular distance from an initial joint angle. 2. In these experiments the right elbows of normal human subjects were passively extended from either predictable or unpredictable starting angles. The subjects were instructed to open the right hand to indicate that the elbow was passing through a target joint angle or a target angular distance. The subjects were not given visual information about the location of the elbow, so they had to rely on proprioceptive input to perform this task. The target (criterion joint angle or angular distance) was learned by the use of proprioception during 8-15 practice trials. 3. Four experiments were conducted. In three experiments the target was located at a constant joint angle, and in the fourth experiment the target was located at a constant angular distance from the starting angle. The starting angle in all four experiments was pseudorandomly varied from trial to trial. 4. On the basis of an analysis of constant errors, subjects were more accurate at discriminating angular distance than joint angle. The slope of the relationship between the starting position and the constant errors was dictated by the task requirement. 5. In the distance discrimination experiment, when the starting angle was more flexed than the intermediate (i.e., central) position, the subjects slightly overshot the target distance. Conversely, when the starting angle was more extended than the intermediate position, the subjects slightly undershot the target distance. 6. In the joint angle discrimination experiments, the opposite results were obtained. Subjects overshot the target when the starting position of the elbow was more extended than the intermediate starting position, and they undershot the target when the starting position was more flexed than the intermediate starting position. The amplitude of these systematic errors increased when the subjects were unaware that the initial angle of their elbow was variable. 7. It is concluded that, in kinesthetic tasks of this type, the discrimination of angular distance is more accurate than the discrimination of joint angle. We hypothesize that the nervous system extracts kinematic information related to both joint angle and angular distance from proprioceptors, and that the encoding and or decoding of angular distance is more accurate than that of absolute joint angle.(ABSTRACT TRUNCATED AT 400 WORDS)