Single administration of a psychedelic [(R)-DOI] influences coping strategies to an escapable social stress.

Psychedelic compounds have potentially rapid, long-lasting anxiolytic, antidepressive and anti-inflammatory effects. We investigated whether the psychedelic compound (R)-2,5-dimethoxy-4-iodoamphetamine [(R)-DOI], a selective 5-HT2A receptor partial agonist, decreases stress-related behavior in male mice exposed to repeated social aggression. Additionally, we explored the likelihood that these behavioral changes are related to anti-inflammatory properties of [(R)-DOI]. Animals were subjected to the Stress Alternatives Model (SAM), an escapable social stress paradigm in which animals develop reactive coping strategies - remaining in the SAM arena (Stay) with a social aggressor, or dynamically initiated stress coping strategies that involve utilizing the escape holes (Escape) to avoid aggression. Mice expressing these behavioral phenotypes display behaviors like those in other social aggression models that separate animals into stress-vulnerable (as for Stay) or stress-resilient (as for Escape) groups, which have been shown to have distinct inflammatory responses to social stress. These results show that Stay animals have heightened cytokine gene expression, and both Stay and Escape mice exhibit plasma and neural concentrations of the inflammatory cytokine tumor necrosis factor-α (TNFα) compared to unstressed control mice. Additionally, these results suggest that a single administration of (R)-DOI to Stay animals in low doses, can increase stress coping strategies such as increasing attention to the escape route, promoting escape behavior, and reducing freezing during socially aggressive interaction in the SAM. Lower single doses of (R)-DOI, in addition to shifting behavior to suggest anxiolytic effects, also concomitantly reduce plasma and limbic brain levels of the inflammatory cytokine TNFα.

Improving injury surveillance data quality: a study based on hospitals contributing to the Victorian Emergency Minimum Dataset.

OBJECTIVE: In this paper, we describe the design and baseline data of a study aimed at improving injury surveillance data quality of hospitals contributing to the Victorian Emergency Minimum Dataset (VEMD). METHODS: The sequential study phases include a baseline analysis of data quality, direct engagement and communication with each of the emergency department (ED) hospital sites, collection of survey and interview data and ongoing monitoring. RESULTS: In 2019/20, there were 371,683 injury-related ED presentations recorded in the VEMD. Percentage unspecified, the indicator of (poor) data quality, was lowest for 'body region' (2.7%) and 'injury type' (7.4%), and highest for 'activity when injured' (29.4%). In the latter, contributing hospitals ranged from 3.0-99.9% unspecified. The 'description of event' variable had a mean word count of 10; 16/38 hospitals had a narrative word count of <5. CONCLUSIONS: Baseline hospital injury surveillance data vary vastly in data quality, leaving much room for improvement and justifying intervention as described. IMPLICATIONS FOR PUBLIC HEALTH: Hospital engagement and feedback described in this study is expected to have a marked effect on data quality from 2021 onwards. This will ensure that Victorian injury surveillance data can fulfil their purpose to accurately inform injury prevention policy and practice.

Muscle damage produced by isometric contractions in human elbow flexors.

Isometric exercise is often prescribed during rehabilitation from injury to maintain muscle condition and prevent disuse atrophy. However, such exercise can lead to muscle soreness and damage. Here we investigate which parameters of isometric contractions are responsible for the damage. Bouts of 30 repetitions of maximum voluntary contractions of elbow flexors in 38 subjects were carried out and peak force, soreness, and tenderness were measured before the exercise, immediately afterwards, at 2 h, and at 24 h postexercise. When one arm was held near the optimum angle for force generation (90°), the force it produced was greater by 28% than by the other arm held at a longer length (155°). However, despite the smaller contraction forces of the muscle held at the longer length, after the exercise it exhibited a greater fall in force that persisted out to 24 h (20% fall) and more delayed soreness than the muscle exercised at 90° (7% fall at 24 h). The result indicates a length dependence of the damage process for isometric contractions at maximum effort. In four additional experiments, evidence was provided that the damage occurred during the plateau of the contraction and not the rising or relaxation phases. The damage had a prompt onset and was cumulative, continuing for the duration of the contraction. We interpret our findings in terms of the nonuniform lengthening of sarcomeres during the plateau of the contractions and conclude that muscle damage from isometric exercise is minimized if carried out at lengths below the optimum, using half-maximum or smaller contractions. NEW & NOTEWORTHY Isometric exercise, where muscle contracts while the limb is held fixed, is often possible for individuals rehabilitating from injury and can help maintain muscle condition. Such exercise has been reported to cause some muscle damage and soreness. We confirm this and show that to minimize damage, exercising muscles should be held at shorter than the optimum length for force and carried out at half-maximum effort or less.

Position sense at the human elbow joint measured by arm matching or pointing.

Position sense at the human elbow joint has traditionally been measured in blindfolded subjects using a forearm matching task. Here we compare position errors in a matching task with errors generated when the subject uses a pointer to indicate the position of a hidden arm. Evidence from muscle vibration during forearm matching supports a role for muscle spindles in position sense. We have recently shown using vibration, as well as muscle conditioning, which takes advantage of muscle's thixotropic property, that position errors generated in a forearm pointing task were not consistent with a role by muscle spindles. In the present study we have used a form of muscle conditioning, where elbow muscles are co-contracted at the test angle, to further explore differences in position sense measured by matching and pointing. For fourteen subjects, in a matching task where the reference arm had elbow flexor and extensor muscles contracted at the test angle and the indicator arm had its flexors conditioned at 90°, matching errors lay in the direction of flexion by 6.2°. After the same conditioning of the reference arm and extension conditioning of the indicator at 0°, matching errors lay in the direction of extension (5.7°). These errors were consistent with predictions based on a role by muscle spindles in determining forearm matching outcomes. In the pointing task subjects moved a pointer to align it with the perceived position of the hidden arm. After conditioning of the reference arm as before, pointing errors all lay in a more extended direction than the actual position of the arm by 2.9°-7.3°, a distribution not consistent with a role by muscle spindles. We propose that in pointing muscle spindles do not play the major role in signalling limb position that they do in matching, but that other sources of sensory input should be given consideration, including afferents from skin and joint.

The contribution of motor commands to position sense differs between elbow and wrist.

Recent studies have suggested that centrally generated motor commands contribute to the perception of position and movement at the wrist, but not at the elbow. Because the wrist and elbow experiments used different methods, this study was designed to resolve the discrepancy. Two methods were used to test both the elbow and wrist (20 subjects each). For the wrist, subjects sat with their right arm strapped to a device that restricted movement to the wrist. Before each test, voluntary contraction of wrist flexor or extensor muscles controlled for muscle spindle thixotropy. After relaxation, the wrist was moved to a test angle. Position was indicated either with a pointer, or by matching with the contralateral wrist, under two conditions: when the reference wrist was relaxed or when its muscles were contracted isometrically (30% maximum). The elbow experiment used the same design to measure position sense in the passive elbow and with elbow muscles contracting (30% maximum). At the wrist when using a pointer, muscle contraction altered significantly the perceived wrist angle in the direction of contraction by 7 deg [3 deg, 12 deg] (mean [95% confidence interval]) with a flexor contraction and 8 deg [4 deg, 12 deg] with an extensor contraction. Similarly, in the wrist matching task, there was a change of 13 deg [9 deg, 16 deg] with a flexor contraction and 4 deg [1 deg, 8 deg] with an extensor contraction. In contrast, contraction of elbow flexors or extensors did not alter significantly the perceived position of the elbow, compared with rest. The contribution of central commands to position sense differs between the elbow and the wrist.

The senses of force and heaviness at the human elbow joint.

The present-day view of the neural basis for the senses of muscle force and heaviness is that they are generated centrally, within the brain, from copies of motor commands. A corollary of the motor discharge generates a sense of effort which underlies these sensations. In recent experiments on force and heaviness sensations using thumb flexor muscles, a rather different explanation has been invoked: Subjects were proposed to rely predominantly on inputs of a peripheral origin, in particular, the signals of muscle spindles. The present experiments have been carried out at the elbow joint to determine whether these new ideas apply more widely. The effects of fatigue of elbow flexor muscles have been studied in force and heaviness matching tasks using three exercise regimes, a sustained maximum voluntary contraction (MVC), a maintained contraction of 35 % MVC, and a maintained contraction of 35 % MVC combined with muscle vibration at 80 Hz. In force-matching experiments, subjects were required to contract both arms and while the reference arm generated the target force under visual control, it was matched by the indicator arm without visual feedback. During the 100 % MVC exercise, force in the exercising reference arm fell rapidly to almost a half of its original value over 90 s while force in the indicator did not fall, leading to a significant overestimation of the reference force. During the 35 % MVC exercise, subjects also overestimated the reference force and this persisted at 5 and 10 min after the exercise. When 35 % MVC was combined with vibration, the amount by which the indicator arm overestimated the reference force was significantly reduced. In heaviness matching experiments, subjects could move their arms through a small range. The reference arm was loaded with a weight, and weights were added or removed from the indicator until heaviness felt the same in the two arms. There was a small, but significant fall in the matching weight used after 100 % MVC exercise, that is, the weight held by the fatigued arm felt lighter. The 35 % exercise did not alter heaviness sensation while 35 % MVC exercise with vibration led to a significant reduction in perceived heaviness. To conclude, while the results of these experiments on elbow flexors are not as clear cut as for thumb flexors, the central effort hypothesis falls short, in a number of respects in explaining the data which are able to be interpreted in terms of a peripheral afferent contribution to the senses of force and heaviness.

The fall in force after exercise disturbs position sense at the human forearm.

We reported previously that concentric or eccentric exercise can lead to errors in human limb position sense. Our data led us to conclude that the errors, post-exercise, were not due to an altered responsiveness of the proprioceptive afferents, and we proposed that they resulted from central changes in the processing of the afferent input. However, it remained uncertain what was responsible for triggering those changes, the volume of afferent traffic during the exercise or the developing fatigue. The afferent traffic hypothesis was tested by subjects carrying out a series of 250 lightly loaded concentric contractions of elbow flexors that produced little fatigue (6 %). This did not lead to significant position errors. In a second experiment, a series of fatiguing isometric contractions, which kept movements of the muscle to a minimum, led to a 24 % fall in force and significant position errors (3°, direction of extension). In the third experiment, at 24 h after eccentric exercise, when the short-term effects of fatigue and accumulated metabolites were gone, but force was still 28 % below control values, this was accompanied by significant position errors in the direction of extension, 3.2° in the relaxed arm and 3.3° in the self-supported arm. It is concluded that it is the fall in force accompanying exercise which is responsible for disturbing limb position sense. It is suggested that the exercise effects are generated in the brain, perhaps as a result of an alteration of the body map, triggered by the fall in force.

The effect of fatigue from exercise on human limb position sense.

We have previously shown, in a two-limb position-matching task in human subjects, that exercise of elbow flexors of one arm led the forearm to be perceived as more extended, while exercise of knee extensors of one leg led the lower leg to be perceived as more flexed. These findings led us to propose that exercise disturbs position sense because subjects perceive their exercised muscles as longer than they actually are. In order to obtain further support for this hypothesis, in the first experiment reported here, elbow extensors were exercised, with the prediction that the exercised arm would be perceived as more flexed after exercise. The experiment was carried out under three load conditions, with the exercised arm resting on a support, with it supporting its own weight and with it supporting a load of 10% of its voluntary contraction strength. For each condition, the forearm was perceived as more extended, not more flexed, after exercise. This result was confirmed in a second experiment on elbow flexors. Again, under all three conditions the exercised arm was perceived as more extended. To explore the distribution of the phenomenon, in a third experiment finger flexor muscles were exercised. This had no significant effect on position sense at the elbow. In a fourth experiment, position sense at the knee was measured after knee flexors of one leg were exercised and, as for knee extensors, it led subjects to perceive their exercised leg to be more flexed at the knee than it actually was. Putting all the observations together, it is concluded that while the influences responsible for the effects of exercise may have a peripheral origin, their effect on position sense occurs centrally, perhaps at the level of the sensorimotor cortex.

Changes in passive tension after stretch of unexercised and eccentrically exercised human plantarflexor muscles.

The study measured the effect of stretch on passive mechanical properties in unexercised and eccentrically exercised plantarflexor muscles, to obtain insight into how stretch might serve athletes as a warm-up strategy. Passive torque, voluntary contraction strength and muscle soreness were measured before and after a large amplitude stretch given before and after a period of eccentric exercise and at 0, 1, 2 and 24 h later. Stretch of the unexercised muscle led to a 20% fall in passive torque which recovered within an hour. About 40% of the fall could be recovered immediately with a voluntary contraction. After eccentric exercise there was a rise in passive torque by 20% at 2 h post-exercise. This rise was postulated to result from an injury contracture in muscle fibres damaged by the exercise. It was accompanied by a fall in maximum voluntary torque and the development of muscle soreness at 24 h. Stretch of the exercised muscle led to a fall in passive torque and rise in pain threshold. It is proposed that in response to a stretch there is a fall in passive tension in the muscle due to stable cross-bridges in sarcomeres which could be recovered with a voluntary contraction and an additional component attributable to the elastic filament, titin. The size of the fall was not significantly different between exercised and unexercised muscle. These observations provide a physiological basis for the effects of passive stretches on skeletal muscle and help to explain why they are used as a popular warm-up strategy.

Evidence from proprioception of fusimotor coactivation during voluntary contractions in humans.

In experiments on position sense at the elbow joint in the horizontal plane, blindfolded subjects were required to match the position of one forearm (reference) by placement of their other arm (indicator). Position errors were measured after conditioning elbow muscles of the reference arm with an isometric contraction while the arm was held either flexed or extended. The difference in errors after the two forms of conditioning was large when the conditioned muscles remained relaxed during the matching process and it became less when elbow muscles were required to lift a load during the match (10 and 25% of maximal voluntary contraction, respectively). Errors from muscle conditioning were attributed to signals arising in muscle spindles and were hypothesized to result from the thixotropic property of passive intrafusal fibres. Active muscle does not exhibit thixotropy. It is proposed that during a voluntary contraction the errors after conditioning are less, because the spindles become coactivated through the fusimotor system. The distribution of errors is therefore seen to be a reflection of fusimotor recruitment thresholds. For elbow flexors most, but not all, fusimotor fibres appear to be recruited by 10% of a maximal contraction.

The effect of quadriceps muscle fatigue on position matching at the knee.

This is a report of the effects of exercise on position matching at the knee. Young adult subjects were required to step down a set of stairs (792 steps), representing eccentric-biased exercise of the quadriceps muscle, or step up them, concentric-biased exercise. Immediately after eccentric exercise subjects showed a mean force drop of 28% (+/- 6%, s.e.m.) of the control value in their exercised quadriceps muscle, which was accompanied by 4.8 deg (+/- 0.8 deg) of error between reference and matching legs in a position matching task at the knee. Similarly concentric exercise was followed by a force drop of 15% (+/- 3%) and matching errors of 3.7 deg (+/- 0.4 deg). These effects were significant. The direction of the errors suggested that subjects perceived their exercised muscles to be longer that they actually were. This finding was not consistent with the hypothesis that the increase in effort required to support the leg after fatigue from exercise was responsible for the errors. It is hypothesized that position sense in an unsupported leg arises, in part, from operation of an internal forward model. When the motor command is increased to compensate for the effects of fatigue, the comparison between predicted and actual feedback from quadriceps leads to the impression that the muscle is longer than it actually is. The exercise effects on proprioception may have implications for sports injuries and for evaluation of the factors leading to falls in the elderly.

Eccentric exercise increases EMG amplitude and force fluctuations during submaximal contractions of elbow flexor muscles.

The purpose of this study was to determine the effect of eccentric exercise on the ability to exert steady submaximal forces with muscles that cross the elbow joint. Eight subjects performed two tasks requiring isometric contraction of the right elbow flexors: a maximum voluntary contraction (MVC) and a constant-force task at four submaximal target forces (5, 20, 35, 50% MVC) while electromyography (EMG) was recorded from elbow flexor and extensor muscles. These tasks were performed before, after, and 24 h after a period of eccentric (fatigue and muscle damage) or concentric exercise (fatigue only). MVC force declined after eccentric exercise (45% decline) and remained depressed 24 h later (24%), whereas the reduced force after concentric exercise (22%) fully recovered the following day. EMG amplitude during the submaximal contractions increased in all elbow flexor muscles after eccentric exercise, with the greatest change in the biceps brachii at low forces (3-4 times larger at 5 and 20% MVC) and in the brachialis muscle at moderate forces (2 times larger at 35 and 50% MVC). Eccentric exercise resulted in a twofold increase in coactivation of the triceps brachii muscle during all submaximal contractions. Force fluctuations were larger after eccentric exercise, particularly at low forces (3-4 times larger at 5% MVC, 2 times larger at 50% MVC), with a twofold increase in physiological tremor at 8-12 Hz. These data indicate that eccentric exercise results in impaired motor control and altered neural drive to elbow flexor muscles, particularly at low forces, suggesting altered motor unit activation after eccentric exercise.

Effects of muscle conditioning on position sense at the human forearm during loading or fatigue of elbow flexors and the role of the sense of effort.

In a forearm position-matching task in the horizontal plane, when one (reference) arm is conditioned by contraction and length changes, subjects make systematic errors in the placement of their other, indicator arm. Here we describe experiments that demonstrate the importance not just of conditioning the reference arm, but of the indicator arm as well. Total errors from muscle conditioning represented up to a quarter of the angular range available to subjects. The sizes of the observed effects have led us to repeat other, previously reported experiments. In a matching task in the vertical plane, when muscles of both arms were conditioned identically, if the subject supported their arms themselves, or when the arms were loaded by the addition of weights, the loading did not introduce new position errors. To test the effect of exercise, subjects' elbow flexors were exercised eccentrically or concentrically by asking them to lower or raise a set of weights using forearm muscles. The exercise produced 25-30% decreases in maximum voluntary contraction strength of elbow flexors and this led to significant position-matching errors. The directions and magnitudes of the errors were similar after the two forms of exercise and indicated that subjects perceived their exercised muscles to be longer than they actually were. To conclude, the new data from loading the arm are not consistent with the idea that the sense of effort accompanying support of a load, provides positional information in any simple way. Our current working hypothesis is that when muscles are active, position-sense involves operation of a forward internal model. Loading the arm produces predictable changes in motor output and afferent feedback whereas changes after exercise are unpredictable. This difference leads to exercise-dependent errors.

Investigation of transabdominal real-time ultrasound to visualise the muscles of the pelvic floor.

Clinical measurement of pelvic floor muscle activity commonly involves techniques that are both physically and psychologically invasive. This study investigated transabdominal application of ultrasound to measure pelvic floor muscle action. The specific aims were to establish the face validity of ultrasound measures of displacement of the posterior bladder wall as a reflection of pelvic floor muscle contraction, and the reliability of measurement between raters and between testing occasions. Non-pregnant adult female subjects aged 24 to 57 years were tested in lying with a 3.5 MHz 35 mm curved array ultrasound transducer over the lower abdomen. Posterior bladder wall displacement was observed in both sagittal and transverse planes. Digital vaginal palpation and transabdominal ultrasound were undertaken simultaneously during pelvic floor muscle contractions to confirm that pelvic floor contractions were performed correctly and to grade pelvic floor muscle strength. Displacement (mm) was measured using electronic calipers on the ultrasound monitor screen. In all subjects, a correct pelvic floor muscle contraction was confirmed on digital palpation, and consistent anterior and cephalic movement was observed on screen. Digital strength grading did not correlate with ultrasound measures in either transverse or sagittal planes (r = 0.21 and -0.13). Average intra-class correlation coefficients for within session inter-rater reliability ranged between 0.86 and 0.88 (95% CI 0.68 to 0.97), and for inter session intra-rater reliability between 0.81 and 0.89 (95% CI 0.51 to 0.96). Transabdominal application of diagnostic ultrasound is a personally non-invasive method for imaging and assessing pelvic floor muscle activity and is both valid and reliable.

Abdominal muscle recruitment during a range of voluntary exercises.

Various exercises are used to retrain the abdominal muscles in the management of low back pain and other musculoskeletal disorders. However, few studies have directly investigated the activity of all the abdominal muscles or the recruitment of regions of the abdominal muscles during these manoeuvres. This study examined the activity of different regions of transversus abdominis (TrA), obliquus internus (OI) and externus abdominis (OE), and rectus abdominis (RA), and movement of the lumbar spine, pelvis and abdomen during inward movement of the lower abdominal wall, abdominal bracing, pelvic tilting, and inward movement of the lower and upper abdominal wall. Inward movement of the lower abdominal wall in supine produced greater activity of TrA compared to OI, OE and RA. During posterior pelvic tilting, middle OI was most active and with abdominal bracing, OE was predominantly recruited. Regions of TrA were recruited differentially and an inverse relationship between lumbopelvic motion and TrA electromyography (EMG) was found. This study indicates that inward movement of the lower abdominal wall in supine produces the most independent activity of TrA relative to the other abdominal muscles, recruitment varies between regions of TrA, and observation of abdominal and lumbopelvic motion may assist in evaluation of exercise performance.

Recovery of lower limb function following 6 weeks of non-weight bearing.

Skeletal muscle weakness and atrophy occur following an extended period of decreased use, including space flight and limb unloading. It is also likely that affected muscles will be susceptible to a re-loading injury when they begin return to earth or weight bearing. However, there is a paucity of literature evaluating the response of human unloaded muscle to exercise and return to activity. The purpose of this pilot study was to evaluate the soreness, function and strength response of muscle to re-loading in seven patients who were non-weight bearing for 6 weeks, compared to five healthy subjects. Function improved significantly over time for the patients but was still less than the healthy subjects over 12 weeks of physiotherapy. Concentric quadriceps muscle strength increased significantly over time for the patients. There was considerable variability in the patients' reports of muscle soreness but there were no significant changes over time or between groups.

Damage to skeletal muscle from eccentric exercise.

Evidence is provided for a mechanical event as the first step in the process leading to muscle damage after a series of eccentric contractions. Aspects discussed include the decline in active tension, increase in passive tension, shift in length-tension relation, soreness, swelling, and disturbed proprioception.