Contorted 'phantom' limbs often form when sensory inputs are removed, but the neural mechanisms underlying their formation are poorly understood. We tracked the evolution of an experimental phantom hand during ischaemic anaesthesia of the arm. In the first study subjects showed the perceived posture of their hand and fingers using a model hand. Surprisingly, if the wrist and fingers were held straight before and during anaesthesia, the final phantom hand was bent at the wrist and fingers, but if the wrist and fingers were flexed before and during anaesthesia, the final phantom was extended at wrist and fingers. Hence, no 'default' posture existed for the phantom hand. The final perceived posture may depend on the initial and evolving sensory input during the block rather than the final sensory input (which should not differ for the two postures). In the second study subjects selected templates to indicate the perceived size of their hand. Perceived hand size increased by 34 ± 4%(mean ± 95% CI) during the block. Sensory changes were monitored. In all subjects, impairment of large-fibre cutaneous sensation began distally with von Frey thresholds increasing before cold detection thresholds (Aδ fibres) increased. Some C fibres subserving heat pain still conducted at the end of cuff inflation. These data suggest that changes in both perceived hand size and perceived position of the finger joints develop early when large-fibre cutaneous sensation is beginning to degrade. Hence it is unlikely that block of small-fibre afferents is critical for phantom formation in an ischaemic block.

The goal of this study was to evaluate the influence of wrist tendon vibration on a multijoint elbow/shoulder tracking task. We hypothesized that tendon vibration applied at the wrist musculature would improve upper arm tracking performance in chronic stroke survivors through increased, Ia-afferent feedback to the central nervous system (CNS). To test this hypothesis, 10 chronic stroke and 5 neurologically intact subjects grasped the handle of a planar robot as they tracked a target through a horizontal figure-8 pattern. A total of 36 trials were completed by each subject. During the middle trials, 70-Hz tendon vibration was applied at the wrist flexor tendons. Position, velocity, and electromyography data were evaluated to compare the quality of arm movements before, during, and after trials with concurrent vibration. Despite tracking a target that moved at a constant velocity, hand trajectories appeared to be segmented, displaying alternating intervals of acceleration and deceleration. Segments were identifiable in tangential velocity data as single-peaked, bell-shaped speed pulses. When tendon vibration was applied at the wrist musculature, stroke subjects experienced improved tracking performance in that hand path lengths and peak speed variability decreased, whereas movement smoothness increased. These performance improvements were accompanied by decreases in the muscle activity during movement. Possible mechanisms behind improved movement control in response to tendon vibration may include improved sensorimotor integration or improved cortical modulation of spinal reflex activity.

Muscle vibration excites muscle spindles and creates illusory movement of a body part in a blindfolded individual. It is followed by an aftereffect, an illusion of return movement when vibration stops. The aftereffect reflects adaptation in the proprioceptive system. This adaptation is susceptible to attentional manipulations (Seizova-Cajic and Azzi in Exp Brain Res 203(1):213-219, 2010), but it is not known whether it is open to cross-modal influences unaided by those manipulations. We attempted to answer this question by allowing vision of the vibrated, stationary arm. We asked our participants (n = 20) to retain focus on the feeling of movement. They reported any illusory movement during 60-s biceps vibration (at 90 Hz), as well as following its offset, when vision of the arm was removed. During vibration, the proprioceptive movement illusion persisted, although the stationary arm was visible, but its duration and strength were much reduced in comparison with the no-vision condition. The movement aftereffect, experienced in total darkness following vibration offset, was also substantially weaker. The results show that proprioceptive adaptation is strongly modulated by vision. We propose that two processes contribute: perceptual (cross-modal binding with conflicting vision reduces the proprioceptive movement signal) and attentional (view of a stationary arm distracts from the proprioceptive movement signal). Our finding that during vibration, participants felt movement in the arm they could see, which was stationary, shows that cross-modal binding partially failed. This happened because the two percepts were too discrepant. However, only one-the visual-appeared real, and we argue that such an outcome is consistent with general principles of intersensory integration.

Visual processing of basic perceptual attributes depends on attention. This has been well documented since the surprising initial report on attentional modulation of the visual motion aftereffect (Chaudhuri 1990). Here, we investigate proprioception and show for the first time that attention modulates adaptation to perceived limb movement. We used biceps vibration to induce illusory forearm extension in 10 participants and measured the aftereffect-perceived movement in the opposite direction. The aftereffect was largest when participants focused on the illusory extension during the adaptation period. To divert attention away from the illusory extension, a rapid serial visual presentation task was performed during the adaptation. The aftereffect was much smaller in this condition, indicating interference between the visual task and proprioceptive adaptation. In tests of an analogous interaction between audition and vision, earlier research found no effect. We suggest that conscious proprioception requires more attention than conscious processing of visual or auditory input.

We report an aftereffect in perception of the extent (or degree or range) of joint movement, showing for the first time that a prolonged exposure to a passive back-and-forth movement of a certain extent results in a change in judgment of the extent of a subsequently presented movement. The adapting stimulus, movement about the wrist, had an extent of either 30 degrees or 75 degrees , while the test stimulus was a 50 degrees movement. Following a 4-min adaptation period, the estimated magnitudes of the test stimuli were 61 degrees and 36 degrees in the 30 degrees and 75 degrees condition, respectively (t test(6)= 9.6; p < 0.001). The observed effect is an instance of repulsion or contrast commonly described in perception literature, with perceived value of the test stimulus pushed away from the adapting stimulus.

While viewing an unambiguously rotating circular array of bars for an extended period, most perceive the array to occasionally move in the direction opposite to its true motion. We find that this alternation in perception has similar dynamics to rivalry, including little correlation among the durations of successive percepts. We also describe analogous reversals in touch and in proprioception. In the proprioceptive case, biceps vibration induces illusory forearm extension. Occasionally, although the same stimulation continues, reversals occur-flexion is perceived rather than extension. Temporal sampling is often invoked to explain the visual reversals but it cannot explain these proprioceptive reversals. Instead, after initial adaptation to the stimulus, rivalry between signals indicating the opposing directions could potentially explain reversals in all three modalities.

We report an aftereffect in perception of the extent (or degree or range) of joint movement, showing for the first time that a prolonged exposure to a passive back-and-forth movement of a certain extent results in a change in judgment of the extent of a subsequently presented movement. The adapting stimulus, movement about the wrist, had an extent of either 30 degrees or 75 degrees , while the test stimulus was a 50 degrees movement. Following a 4-min adaptation period, the estimated magnitudes of the test stimuli were 61 degrees and 36 degrees in the 30 degrees and 75 degrees condition, respectively (t test(6)= 9.6; p < 0.001). The observed effect is an instance of repulsion or contrast commonly described in perception literature, with perceived value of the test stimulus pushed away from the adapting stimulus.

Joint position sense is believed to be mediated by muscle afferent signals. Because a "phantom" hand produced by a sensory and motor nerve block appears to move in the direction of voluntary effort, signals of "motor command" or "effort" can influence perceived joint position. To determine whether this occurs when sensory signals are available, three studies assessed position sense when motor command and afferent signals were available, but joint movement was prevented. First, the hand was positioned to stop movement at the proximal joint of the middle finger, and movement at the distal joint was impossible because the muscles had been "disengaged". Voluntary efforts produced illusory position changes in the direction of the effort (12.6 +/- 2.0 degrees distal joint; 12.3 +/- 2.3 degrees proximal joint for efforts at 30% maximum; means +/- SD). Second, when subjects attempted to move the index finger under isometric conditions, the index finger appeared to move 7.4 +/- 1.2 degrees in the direction of efforts. These illusions graded with the level of effort (10 or 30% maximum) and far exceeded any real joint movement. Finally, because changes in muscle afferent feedback might have accompanied the voluntary efforts, all forearm and hand muscles were completely paralyzed by locally infused rocuronium. During paralysis, passive wrist position was signaled accurately, but, during attempted efforts (30% maximum), perceived wrist position changed by 9.7 +/- 4.9 degrees . Before paralysis, isometric efforts changed it by 6.7 +/- 3.6 degrees . Thus all studies concur: when joint movement is prevented, signals of motor command contribute to joint position sense.

During sustained maximal voluntary contractions (MVCs), most fatigue occurs within the muscle, but some occurs because voluntary activation of the muscle declines (central fatigue), and some of this reflects suboptimal output from the motor cortex (supraspinal fatigue). This study examines whether supraspinal fatigue occurs during a sustained submaximal contraction of 5% MVC. Eight subjects sustained an isometric elbow flexion of 5% MVC for 70 min. Brief MVCs were performed every 3 min, with stimulation of the motor point, motor cortex, and brachial plexus. Perceived effort and pain, elbow flexion torque, and surface EMGs from biceps and brachioradialis were recorded. During the sustained 5% contraction, perceived effort increased from 0.5 to 3.9 (out of 10), and elbow flexor EMG increased steadily by approximately 60-80%. Torque during brief MVCs fell to 72% of control values, while both the resting twitch and EMG declined progressively. Thus the sustained weak contraction caused fatigue, some of which was due to peripheral mechanisms. Voluntary activation measured by motor point and motor cortex stimulation methods fell to 90% and 80%, respectively. Thus some of the fatigue was central. Calculations based on the fall in voluntary activation measured with cortical stimulation indicate that about two-thirds of the fatigue was due to supraspinal mechanisms. Therefore, sustained performance of a very low-force contraction produces a progressive inability to drive the motor cortex optimally during brief MVCs. The effect of central fatigue on performance of the weak contraction is less clear, but it may contribute to the increase in perceived effort.

The role of group III and IV muscle afferents in controlling the output from human muscles is poorly understood. We investigated the effects of these afferents from homonymous or antagonist muscles on motoneuron pools innervating extensor and flexor muscles of the elbow. In study 1, subjects (n = 8) performed brief maximal voluntary contractions (MVCs) of elbow extensors before and after a 2 min MVC of the extensors. During MVCs, electromyographic responses from triceps were evoked by stimulation of the corticospinal tracts [cervicomedullary motor evoked potentials (CMEPs)]. The same subjects repeated the protocol, but input from fatigue-sensitive afferents was prolonged after the fatiguing contraction by maintained muscle ischemia. In study 2, CMEPs were evoked in triceps during brief extensor MVCs before and after a 2 min sustained flexor MVC (n = 7) or in biceps during brief flexor MVCs before and after a sustained extensor MVC (n = 7). Again, ischemia was maintained after the sustained contractions. During sustained MVCs of the extensors, CMEPs in triceps decreased by approximately 35%. Without muscle ischemia, CMEPs recovered within 15 s, but with maintained ischemia, they remained depressed (by approximately 28%; p < 0.001). CMEPs in triceps were also depressed (by approximately 20%; p < 0.001) after fatiguing flexor contractions, whereas CMEPs in biceps were facilitated (by approximately 25%; p < 0.001) after fatiguing extensor contractions. During fatigue, inputs from group III and IV muscle afferents from homonymous or antagonist muscles depress extensor motoneurons but facilitate flexor motoneurons. The more pronounced inhibitory influence of these afferents on extensors suggests that these muscles may require greater cortical drive to generate force during fatigue.

The role of afferent inflow and efferent outflow (or command) signals in judgements of limb position has been debated for over a century. One way to assess this is to check for changes during complete paralysis, with the current view being that perceived movements or position changes do not usually accompany attempts to contract paralysed muscles. To re-examine this, we asked 6 naïve subjects to carry out a simple position matching task at the wrist. In the absence of vision, subjects accurately perceived the position to which their right wrist had been moved by the experimenter by matching it with their left hand. There was no significant change in perception when position was matched during sustained flexion or extension efforts. Then we paralysed and anaesthetised the right arm with ischaemia in order to produce a 'phantom' hand. The perceived position of the wrist changed by more than 20 degrees when subjects attempted to flex or extend their hand when it was paralysed and anaesthetised. Further studies showed that this illusion was not dependent on the way in which the paralysis was produced and that the size of the position illusion increased when the level of effort during paralysis increased. These results establish for the first time a definitive a role for 'outflow' signals in position sense.

Short periods of training in motor tasks can increase motor cortical excitability. This study investigated whether changes also occur at a subcortical level. Subjects trained in ballistic finger abduction or visuomotor tracking. The right index finger rotated around the metacarpophalangeal (MCP) joint in a splint. Surface EMG was recorded from the first dorsal interosseous. Transcranial magnetic stimulation over the back of the head (double-cone coil) elicited cervicomedullary motor evoked potentials (CMEPs) by stimulation of corticospinal axons. Responses were recorded from the relaxed muscle before, between, and after two sets of training. In study 1 (n = 7), training comprised two sets of 150 maximal finger abductions. Feedback of acceleration was provided. With training, acceleration increased significantly. CMEPs increased to 248 ± 152%(± SD) of baseline immediately after training (P = 0.007) but returned to control level (155 ± 141%) 10 min later. In study 2 (n = 7), subjects matched MCP joint angle to a target path on a computer screen. After ∼30 min of training, tracking improved as shown by increased correlation between joint angle and the target pathway, reduced time lag, and reduced EMG(rms). However, CMEPs remained unchanged. These results show that transmission through the corticospinal pathway at a spinal level increased after repeated ballistic movements but not after training in a visuomotor task. Thus, changes at a spinal level may contribute to improved performance in some motor tasks.

OBJECTIVE The cortical silent period refers to a period of near silence in the electromyogram (EMG) after transcranial magnetic stimulation (TMS) of the motor cortex during contraction. However, low-level EMG of unknown origin is often present. We hypothesised that it arises through spinal reflexes. Sudden lengthening of the muscle as force drops during the silent period could excite muscle spindles and facilitate motoneurones. METHODS Subjects (n=8) performed maximal isometric, shortening and lengthening contractions of the elbow flexors during which TMS (90-100% output) was delivered over the motor cortex. The rate of flexion during shortening contractions reduced muscle lengthening caused by muscle relaxation. Surface EMG was recorded from biceps brachii and brachioradialis, and the low-level EMG during silent periods produced by TMS was measured. RESULTS Low-level EMG activity was reduced on average by 68% in biceps and 63% in brachioradialis in the shortening contraction compared to all other contraction conditions (p<0.001). Levels of pre-stimulus EMG were similar between conditions. CONCLUSIONS Muscle lengthening contributes to low-level EMG activity in the silent period, through spinal reflex facilitation by muscle spindle afferents. SIGNIFICANCE The silent period depth is not only dependent on cortical output but also reflex effects evoked by muscle lengthening.

Increases in lung volume inhibit the inspiratory output from the medulla, but the effect of lung inflation on the voluntary control of breathing in humans is not known. We tested corticospinal excitability using transcranial magnetic stimulation (TMS) to evoke a response in the scalene muscles. TMS was delivered at rest at three different lung volumes between functional residual capacity (FRC) and total lung capacity (TLC) during incremental inspiratory and incremental expiratory manoeuvres. Motor evoked potentials (MEPs) in scalenes were ∼50% larger at a high lung volume (FRC+∼90% inspiratory capacity [IC]) compared to lower lung volumes (FRC and FRC+∼40% IC) in both inspiratory and expiratory manoeuvres (p<0.001). The change in MEP size was not due to differences in pre-stimulus EMG amplitude (p=0.29). The results suggest a differential effect of lung inflation on the automatic and voluntary control of breathing in humans.

Muscle pain has widespread effects on motor performance, but the effect of pain on voluntary activation, which is the level of neural drive to contracting muscle, is not known. To determine whether induced muscle pain reduces voluntary activation during maximal voluntary contractions, voluntary activation of elbow flexors was assessed with both motor-point stimulation and transcranial magnetic stimulation over the motor cortex. In addition, we performed a psychophysical experiment to investigate the effect of induced muscle pain across a wide range of submaximal efforts (5-75% maximum). In all studies, elbow flexion torque was recorded before, during, and after experimental muscle pain by injection of 1 ml of 5% hypertonic saline into biceps. Injection of hypertonic saline evoked deep pain in the muscle (pain rating ∼5 on a scale from 0 to 10). Experimental muscle pain caused a small (∼5%) but significant reduction of maximal voluntary torque in the motor-point and motor cortical studies (P < 0.001 and P = 0.045, respectively; n = 7). By contrast, experimental muscle pain had no significant effect on voluntary activation when assessed with motor-point and motor cortical stimulation although voluntary activation tested with motor-point stimulation was reduced by ∼2% in contractions after pain had resolved (P = 0.003). Furthermore, induced muscle pain had no significant effect on torque output during submaximal efforts (P > 0.05; n = 6), which suggests that muscle pain did not alter the relationship between the sense of effort and production of voluntary torque. Hence, the present study suggests that transient experimental muscle pain in biceps brachii has a limited effect on central motor pathways.

Motoneurone excitability is rapidly and profoundly reduced during a sustained maximal voluntary contraction (MVC) when tested in the transient silent period which follows transcranial magnetic stimulation (TMS) of the motor cortex. One possible cause of this reduction in excitability is a fatigue-induced withdrawal of excitatory input to motoneurones from muscle spindle afferents. We aimed to test if muscle spindle input produced by tendon vibration would ameliorate suppression of the cervicomedullary motor-evoked potential (CMEP) in the silent period during a sustained MVC. Seven subjects performed a 2 min MVC of the elbow flexors. Stimulation of the corticospinal tract at the level of the mastoids was preceded 100 ms earlier by TMS. These stimulus pairs were delivered every 10 s during the 2 min MVC. Stimulus pairs at 30, 50, 70, 90 and 110 s were delivered while vibration (-80 Hz) was applied to the distal tendon of biceps. On a separate day, the protocol was repeated with both stimuli delivered to the motor cortex. The CMEP in the silent period decreased rapidly with fatigue (to -9% of control) and was not affected by tendon vibration (P = 0.766). The motor-evoked potential in the silent period also declined rapidly (to -5% of control) and was similarly unaffected by tendon vibration (P = 0.075). These data suggest motoneurone disfacilitation due to a fatigue-related decrease of muscle spindle discharge does not contribute significantly to the profound suppression of motoneurone excitability during the silent period. Therefore, a change to intrinsic motoneurone properties caused by repetitive discharge is most probably responsible.

OBJECTIVES (A) Describe a new method of investigation of the possible muscular effects of the commonly practiced Mills manipulation for lateral elbow pain (epicondylalgia),(B) ascertain if myoelectric activity is influenced during the pre-manipulative stretch for Mills manipulation,(C) establish whether muscle responses are influenced by ipsilateral lateral flexion of the cervical spine which reduces mechanical tension in the peripheral nerves of the upper limb. SAMPLE Eight asymptomatic subjects were tested bilaterally (N=16). METHODS Myoelectric measurements - EMG signals were recorded with a 16 channel pocket EMG patient unit and processed off-line. Measurement of joint positions-three CCD adjustable cameras sensitive to 10mm reflective passive markers applied at specific locations on the subjects' bodies were used to reconstruct and verify accuracy of body movements and were correlated with EMG recordings. RESULTS Compared with the standard (anatomical) position of the cervical spine in which Mills manipulation is typically performed, cervical spine ipsilateral lateral flexion produced significantly reduced activity in muscles that restrain the manipulation movement (elbow extension), namely biceps brachii (P=0.018) and brachioradialis (P=0.000). The affected muscles may therefore produce protective effects during the manipulation. CONCLUSIONS Changes in myoelectric activity were in a pattern that suggests that muscle and neural mechanisms may be an integral part of the Mills manipulation. Cervical spine ipsilateral lateral flexion may be used to reduce mechanical stresses in the peripheral nerves and extraneous muscle activity, making Mills' manipulation potentially safer and more specific.

Muscle vibration excites muscle spindles and creates illusory movement of a body part in a blindfolded individual. It is followed by an aftereffect, an illusion of return movement when vibration stops. The aftereffect reflects adaptation in the proprioceptive system. This adaptation is susceptible to attentional manipulations (Seizova-Cajic and Azzi in Exp Brain Res 203(1):213-219, 2010), but it is not known whether it is open to cross-modal influences unaided by those manipulations. We attempted to answer this question by allowing vision of the vibrated, stationary arm. We asked our participants (n = 20) to retain focus on the feeling of movement. They reported any illusory movement during 60-s biceps vibration (at 90 Hz), as well as following its offset, when vision of the arm was removed. During vibration, the proprioceptive movement illusion persisted, although the stationary arm was visible, but its duration and strength were much reduced in comparison with the no-vision condition. The movement aftereffect, experienced in total darkness following vibration offset, was also substantially weaker. The results show that proprioceptive adaptation is strongly modulated by vision. We propose that two processes contribute: perceptual (cross-modal binding with conflicting vision reduces the proprioceptive movement signal) and attentional (view of a stationary arm distracts from the proprioceptive movement signal). Our finding that during vibration, participants felt movement in the arm they could see, which was stationary, shows that cross-modal binding partially failed. This happened because the two percepts were too discrepant. However, only one-the visual-appeared real, and we argue that such an outcome is consistent with general principles of intersensory integration.

Here we investigated how the tactile modality is used along with muscle proprioception in hand movement perception, whether these two sensory inputs are centrally integrated and whether they work complementarily or concurrently. The illusory right hand rotations induced in eleven volunteers by a textured disk scrolling under their hand in two directions at three velocities and/or by mechanical vibration applied to their wrist muscles at three frequencies were compared. The kinesthetic illusions were copied by the subjects on-line with their left hand. Results: 1) in all the subjects, tactile stimulation alone induced an illusory hand rotation in the opposite direction to that of the disk, and the velocity of the illusion increased non-linearly with the disk velocity: the highest gain (the illusion velocity to disk velocity ratio) occurred at the slowest disk rotation; 2) adding a consistent proprioceptive stimulus increased the perceptual effects, whereas adding a conflicting proprioceptive stimulus of increasing frequency gradually decreased the tactile illusions and reversed their initial direction; 3) under both consistent and conflicting conditions, only strong proprioceptive stimulation significantly affected the gain of the resulting illusions, whereas the largest gain always occurred at low tactile stimulation levels when the illusory movements were in the same direction as the tactile-induced illusion. Tactile information may equal or even override muscle proprioceptive information in the perception of relatively small, slow hand movements. These two somatosensory inputs may be integrated complementarily, depending on their respective relevance to the task of accurately perceiving one's own hand movements.

Experiments were carried out on blindfolded human subjects to study the contribution of proprioceptive inputs from both arms in a forearm position matching task. Blindfolded matching accuracy was compared with accuracy when the subject could see their indicator (matching) arm, when they used a dummy arm for matching, and when they looked at a mirror image of the matching arm. The position of the mirror had been arranged so that the image of the indicator arm coincided with the position of the reference arm. None of these conditions significantly altered the matching errors. When reference elbow flexors were vibrated at 70-80 Hz, the illusion of extension of the vibrated arm reported by blindfolded subjects was significantly reduced by vision of the mirror image of the indicator arm or when using the dummy arm. It was concluded that visual information about the position of the indicator arm, or the apparent position of the reference arm, could reduce the size of the kinaesthetic illusion from vibration, but not abolish it. In a second experiment, subjects indicated, by tracking with their vibrated arm, the illusion of forearm extension evoked by elbow flexor vibration. It was found that the perceived speed of extension could be reduced by moving the indicator into extension and increased by moving it into flexion. These experiments demonstrate the importance for the matching process of the input provided by the indicator arm. Such a conclusion may help to explain some apparent discrepancies between observations made on position sense using one-arm and two-arm tasks. More broadly, this paper provides support for the idea that aspects of proprioceptive inputs from both arms are processed conjointly, as part of a strategy for use of the two hands as a single instrument in certain skilled tasks.

Visual processing of basic perceptual attributes depends on attention. This has been well documented since the surprising initial report on attentional modulation of the visual motion aftereffect (Chaudhuri 1990). Here, we investigate proprioception and show for the first time that attention modulates adaptation to perceived limb movement. We used biceps vibration to induce illusory forearm extension in 10 participants and measured the aftereffect-perceived movement in the opposite direction. The aftereffect was largest when participants focused on the illusory extension during the adaptation period. To divert attention away from the illusory extension, a rapid serial visual presentation task was performed during the adaptation. The aftereffect was much smaller in this condition, indicating interference between the visual task and proprioceptive adaptation. In tests of an analogous interaction between audition and vision, earlier research found no effect. We suggest that conscious proprioception requires more attention than conscious processing of visual or auditory input.

This study was conducted to investigate whether the low-frequency (5-Hz) oscillatory vibration-like stimulus, purported to be delivered by exercising with Flexi-bar, acutely affects muscle activation and maximal voluntary contraction (MVC) force. Nine healthy men participated in 2 trials, separated by at least 1 week, during which 4 x 30-second sets of exercise were performed with either the Flexi bar or a Sham bar. Maximal voluntary contraction force for elbow flexion, elbow extension, and knee extension were measured before and after the exercise. Root-mean-square amplitude and median frequency of electromyography (EMG) signal were calculated for the first and last 10 seconds of each exercise set and during the MVCs from biceps brachii (BB), triceps brachii (TB), rectus femoris (RF), and vastus lateralis (VL) for each trial. Electromyography amplitude was significantly higher for all studied muscles during Flexi-bar than Sham-bar exercise (32-203%, p < 0.05). Median frequency of EMG power spectrum was significantly lower in arm (TB:-40 +/- 13%, p < 0.0001; BB:-32 +/- 25%, p = 0.015) but not in leg (RF:-12 +/- 18%; VL:+6 +/- 32%; p > 0.05) muscles during Flexi-bar compared with Sham-bar exercise. Knee extension MVC force significantly decreased after Flexi-bar exercise (-3 +/- 7%, p = 0.048) in parallel with reduced RF EMG amplitude (-8 +/- 5%, p = 0.04), but there were no acute residual effects on elbow flexion/extension MVC or arm and VL EMG muscle activity. Using Flexi bar during exercise provoked acute alterations in arm- and leg-muscle EMG parameters and maximum force-generating capacity, indicating greater fatigue development than when exercising with the Sham bar. The results of this study indicate that Flexi bar may therefore be used to impose a stronger training stimulus on the muscle during submaximal exercise.

It has been observed anecdotally that while performing the multijoint lat pull-down exercise, novice strength trainers often rely on the elbow flexors to complete the movement rather than fully utilizing the relevant back muscles such as the latissimus dorsi (LD) and teres major (TM). The primary aim of the study was to determine whether specific technique instruction could result in a voluntary increase in LD and TM electromyographic (EMG) activity with a concurrent decrease in the activity of the biceps brachii (BB) during the front wide-grip lat pull-down exercise. Eight women with little or no background in strength training were asked to perform lat pull-down exercise with only basic instruction, performing 2 sets of 3 repetitions at 30% max. After a brief rest, subjects then performed the same 2 sets of 3 repetitions following verbal technique instruction on how to emphasize the latissimus while de-emphasizing the biceps. EMG activity of the LD, TM, and BB were recorded, converted to root mean square, and normalized to the maximum isometric EMG (NrmsEMG). A significant increase was seen in Nrms EMG in the LD (p = 0.005) from the average of preinstruction NrmsEMG to the average of postinstruction NrmsEMG. No significant differences were observed between pre- and postinstruction muscle activity in the BB or TM. The results show that untrained individuals can voluntarily increase the activity of a specified muscle group during the performance of a multijoint resistance exercise, but the increase probably does not represent "isolation" of the muscle group through voluntary reduction of activity in complementary agonist muscles.

Adaptation is essential in maintaining stability during balance-challenging situations. We studied, in standing subjects with eyes open and closed, adaptive responses of the anteroposterior head, shoulder, hip and knee movements; gastrocnemius and tibialis anterior EMG activity and anteroposterior body posture when proprioceptive information from the neck or calf muscles underwent vibratory perturbations. After 30s of quiet stance, vibratory stimuli were applied repeatedly for 200s, and adaption to stimulation was analyzed in four successive 50s periods. Repeated neck and calf vibration significantly increased linear body movement variance at all recorded sites (p<0.001, except neck stimulation with eyes closed, EC-neck), increased tibialis anterior (p<0.001, except EC-neck) and gastrocnemious muscle activity (p<0.001). Most body movement variances and tibialis anterior EMG activity decreased significantly over time (most p-values<0.01 or lower) and overall, the body leaning forward increased from 5.5 degrees to 6.5 degrees (p<0.01). The characteristics of the responses were influenced by vision and site of vibration, e.g., neck vibration affected body posture more rapidly than calf vibration. Our findings support the notion that proprioceptive perturbations have different effects in terms of nature, degree and adaptive response depending on site of vibratory proprioceptive stimulation, a factor that needs consideration in clinical investigations and design of rehabilitation programs.

In this study, we investigated a motor strategy for increasing the amplitude of movement in rapid extensions at the elbow joint. This study focused on the changes in a triphasic electromyographic (EMG) pattern, i.e., the first agonist burst (AG1), the second agonist burst (AG2) and the antagonist burst (ANT), for increasing the amplitude of movement required after the initiation of movement. Subjects performed 40 degrees (Basic task) and 80 degrees of extension (Wide task). These tasks were performed under two conditions; performing a predetermined task (SF condition) and performing a task in response to a visual stimulus immediately after movement commencement (ST condition). Kinematic parameters and EMG activity from the agonist (triceps brachii) and the antagonist (biceps brachii) muscles were recorded. As a result, the onset latency of AG1 and AG2 and the duration of AG1 were longer under the ST condition than the SF condition. No difference was observed between the SF and ST condition with respect to ANT activity. It is concluded that the motor strategy for increasing the amplitude of movement after the initiation of movement was to control the movement velocity and the timing to stop movement by the coactivation duration of AG1 and ANT and to stop the desired position accurately by AG2 activity.

PURPOSE The aim of this study was to evaluate activation and coactivation of biceps and triceps muscles during isometric exercise performed with and without superimposing a vibration stimulation. METHODS Twelve healthy volunteers (age = 22.7 +/- 2.6 yr) participated in this study. The subjects performed five trials of isometric elbow flexion and five trials of elbow extension with increasing levels of force in two conditions: vibration (V) and normal loading (C). V stimulation was characterized by a frequency of 28 Hz. Surface EMG activity of biceps and triceps muscles was simultaneously measured by bipolar surface electromyography and assessed by the estimation of the root mean square (RMS) of the electrical recordings over a fixed 5-s interval. Frequency analysis was adopted to estimate the RMS related to muscle activation and to exclude the harmonics generated by movement artifacts due to V. RESULTS The analysis of the recordings revealed a significant EMG RMS increase when V was applied. On average, the EMG RMS of biceps and triceps during elbow flexion was, respectively, 26.1%(P < 0.05) and 18.2%(P = 0.15) higher than C. During elbow extension, the EMG RMS of biceps and triceps was 77.2% and 45.2%(P < 0.05) higher than C, respectively. The coactivation was assessed as the ratio between the activation of antagonist and agonist muscles during arm flexion and extension tasks. The results revealed an increase of coactivation during V exercise, especially for lighter loads. CONCLUSION This study shows that V exercise at 28 Hz produces an increase of the activation and the coactivation of biceps and triceps. This exercise modality seems therefore suitable for various applications.