Changes in head and neck position affect elbow joint position sense

Cervical proprioception in Parkinson's disease and its correlation with manual dexterity function

OBJECTIVE

Cervical proprioception plays a crucial role in posture and movement control. This study aimed to determine the relationships of cervical proprioception, cervical muscle strength and endurance with manual dexterity and hand strength in individuals with idiopathic Parkinson's disease (PD).

METHODS

Twenty individuals with PD (mean age: 63.9 years) and 20 healthy individuals as a control group (mean age: 61.9 years) were recruited. Cervical joint position error (JPE), static endurance of neck muscles, activation of deep cervical flexor muscles (Craniocervical Flexion Test, CCFT), manual dexterity (Purdue Pegboard Test, PPT), cognitive and motor tasks of the PPT, finger tapping test (FTT), pinch strength, and grip strength were assessed.

RESULTS

Cervical JPE was significantly higher in individuals with PD than in controls (p < 0.05). The strength and endurance of the cervical muscles were significantly decreased in individuals with PD (p < 0.05). Cervical JPE measurements were negatively correlated with PPT, cognitive and motor tasks of the PPT in individuals with PD (all p < 0.05). The endurance of cervical flexor muscles was negatively correlated with PPT and cognitive PPT scores in the PD group (p < 0.05). In addition, a significant positive correlation was found between cervical flexor endurance and hand strength in the PD group (p < 0.05).

CONCLUSION

Cervical proprioception and the strength and endurance of cervical muscles decrease in individuals with PD compared to healthy individuals. Impairment of cervical proprioception appears to be associated with poorer upper extremity performance. Detailed evaluation of the cervical region in PD may help determine the factors affecting upper extremity function.

Immediate Effects of Mulligan Mobilization on Elbow Proprioception in Healthy Individuals: A Randomized Placebo-Controlled Single-Blind Study

OBJECTIVE

The aim of this study was to investigate the immediate effects of Mulligan's mobilization with movement (MWM) on elbow proprioception.

METHODS

The study included 26 participants in the intervention group and 30 participants in the control group. The intervention group received MWM, while the control group received a sham application. Proprioception was assessed with joint position sense error at baseline, immediately after mobilization, and 30 minutes after mobilization with 70° and 110° of elbow flexion. The hypothesis of interest was the group × time interaction.

RESULTS

At 110° of elbow flexion, group × time interaction was significant (F[2, 108] = 11.48, P = .001). In the paired comparisons, there was a statistically significant difference in favor of the control group in the first measurement (P = .003). No difference was detected in other time points (P = 1.00). At 70° of elbow flexion, there was no significant difference between the time point × group interaction (F[2, 108] = 1.37, P = .10). Therefore, no pairwise comparison was made.

CONCLUSION

In this study of healthy participants, no immediate difference was found between MWM and sham application on elbow proprioception.

Neck Muscle Vibration Alters Upper Limb Proprioception as Demonstrated by Changes in Accuracy and Precision during an Elbow Repositioning Task

Upper limb control depends on accurate internal models of limb position relative to the head and neck, accurate sensory inputs, and accurate cortical processing. Transient alterations in neck afferent feedback induced by muscle vibration may impact upper limb proprioception. This research aimed to determine the effects of neck muscle vibration on upper limb proprioception using a novel elbow repositioning task (ERT). 26 right-handed participants aged 22.21 ± 2.64 performed the ERT consisting of three target angles between 80−90° (T1), 90−100° (T2) and 100−110° (T3). Controls (CONT) (n = 13, 6F) received 10 min of rest and the vibration group (VIB) (n = 13, 6F) received 10 min of 60 Hz vibration over the right sternocleidomastoid and left cervical extensor muscles. Task performance was reassessed following experimental manipulation. Significant time by group interactions occurred for T1: (F1,24 = 25.330, p < 0.001, ηp2 = 0.513) where CONT improved by 26.08% and VIB worsened by 134.27%, T2: (F1,24 = 16.157, p < 0.001, ηp2 = 0.402) where CONT improved by 20.39% and VIB worsened by 109.54%, and T3: (F1,24 = 21.923, p < 0.001, ηp2 = 0.447) where CONT improved by 37.11% and VIB worsened by 54.39%. Improvements in repositioning accuracy indicates improved proprioceptive ability with practice in controls. Decreased accuracy following vibration suggests that vibration altered proprioceptive inputs used to construct body schema, leading to inaccurate joint position sense and the observed changes in elbow repositioning accuracy.

Influence of Neck Pain, Cervical Extensor Muscle Fatigue, and Manual Therapy on Wrist Proprioception

OBJECTIVE

The purpose of this study was to examine the effects of submaximal isometric neck muscle fatigue and manual therapy on wrist joint position sense (JPS) within healthy individuals and individuals with subclinical neck pain (SCNP).

METHODS

Twelve healthy participants and 12 participants with SCNP were recruited. Each group completed 2 sessions, with 48 hours between sessions. On day 1, both groups performed 2 wrist JPS tests using a robotic device. The tests were separated by a submaximal isometric fatigue protocol for the cervical extensor muscles (CEM). On day 2, both groups performed a wrist JPS test, followed by a cervical treatment consisting of manual therapy (SCNP) or neck rest (20 minutes, control group) and another wrist JPS test. Joint position sense was measured as the participant's ability to recreate a previously presented wrist angle. Each wrist JPS test included 12 targets, 6 into wrist flexion and 6 into wrist extension. Kinematic data from the robot established absolute, variability, and constant error.

RESULTS

Absolute error significantly decreased (P = .01) from baseline to post-fatigue in the SCNP group (baseline = 4.48 ± 1.58°; post-fatigue = 3.90 ± 1.45°) and increased in the control group (baseline = 3.12 ± 0.98°; post-fatigue = 3.81 ± 0.90°). The single session of manual cervical treatment significantly decreased absolute error in participants with SCNP (P = .004).

CONCLUSION

This study demonstrated that neck pain or fatigue can lead to altered afferent input to the central nervous system and can affect wrist JPS. Our findings demonstrate that acute wrist proprioception may be improved in individuals with SCNP by a single cervical manual therapy session.

Effect of Neck Muscle Fatigue on Hand Muscle Motor Performance and Early Somatosensory Evoked Potentials

Even on pain free days, recurrent neck pain alters sensorimotor integration (SMI) measured via somatosensory evoked potentials (SEPs). Neck muscle fatigue decreases upper limb proprioception, and thus may interfere with upper limb motor task acquisition and SMI. This study aimed to determine the effect of cervical extensor muscle (CEM) fatigue on upper limb motor acquisition and retention; and SMI, measured via early SEPs. Twenty-four healthy right-handed individuals were randomly assigned to control or CEM fatigue. Baseline SEPs were elicited via median nerve stimulation at the wrist. Participants then lay prone on a padded table. The fatigue group supported a 2 kg weight until they could no longer maintain the position. The control group rested their neck in neutral for 5 min. Participants completed pre- and post-motor skill acquisition while seated, SEPs were again collected. Task retention was measured 24 h later. Accuracy improved post acquisition and at retention for both groups (p < 0.001), with controls outperforming the fatigue group (p < 0.05). The fatigue group had significantly greater increases in the N24 (p = 0.017) and N30 (p = 0.007) SEP peaks. CEM fatigue impaired upper limb motor learning outcomes in conjunction with differential changes in SEP peak amplitudes related to SMI.

Does My Neck Make Me Clumsy? A Systematic Review of Clinical and Neurophysiological Studies in Humans

Introduction: Clumsiness has been described as a symptom associated with neck pain and injury. However, the actuality of this symptom in clinical practice is unclear. The aim of this investigation was to collect definitions and frequency of reports of clumsiness in clinical studies of neck pain/injury, identify objective measures of clumsiness and investigate the association between the neck and objective measures of clumsiness.

Methods: Six electronic databases were systematically searched, records identified and assessed including a risk of bias. Heterogeneity in designs of studies prevented pooling of data, so qualitative analysis was undertaken.

Results: Eighteen studies were retrieved and assessed; the overall quality of evidence was moderate to high. Eight were prospective cross-sectional studies comparing upper limb sensorimotor task performance and ten were case series involving a healthy cohort only. Clumsiness was defined as a deficit in coordination or impairment of upper limb kinesthesia. All but one of 18 studies found a deterioration in performing upper limb kinesthetic tasks including a healthy cohort where participants were exposed to a natural neck intervention that required the neck to function toward extreme limits.

Conclusion: Alterations in neck sensory input occurring as a result of requiring the neck to operate near the end of its functional range in healthy people and in patients with neck pain/injury are associated with reductions in acuity of upper limb kinesthetic sense and deterioration in sensorimotor performance. Understanding the association between the neck and decreased accuracy of upper limb kinesthetic tasks provide pathways for treatment and rehabilitation strategies in managing clumsiness.

The effect of neck muscle fatigue on shoulder humeral rotation joint position sense

INTRODUCTION

Cervical extensor muscle (CEM) fatigue causes decrements in upper limb proprioceptive accuracy during constrained single-joint tasks. This study used a novel humeral rotation joint position sense (JPS) measurement device to compare JPS accuracy in participants who received acute CEM fatigue vs. non-fatigued controls.

METHODS

Participants had vision occluded and were passively guided into postures of internal humeral rotation from a baseline posture before and after a CEM fatigue or control protocol. Mixed model repeated measures ANOVAs were used to verify fatigue and compared absolute, constant, and variable JPS error between groups.

RESULTS

CEM fatigue was verified via pre-post reduction in CEM strength, and myoelectric indicators of fatigue. However, between-group comparisons of absolute, constant, and variable JPS error were not statistically significant, despite having large effect sizes.

DISCUSSION

Contrary to prevailing literature, unconstrained humeral rotation JPS did not appear to be affected by CEM fatigue in this study. However, between-group differences in JPS error were dwarfed by inter-trial variability, which likely arose due to the unconstrained nature of this task, conflating chances for a Type II error. Future research should perform a kinematic analysis of task constraints to highlight potential compensatory mechanisms obscuring significant findings in this otherwise robust effect.

Neck muscle fatigue impacts plasticity and sensorimotor integration in cerebellum and motor cortex in response to novel motor skill acquisition

The cerebellum undergoes neuroplastic changes in response to motor learning. Healthy human individuals demonstrate reduced cerebellar inhibition (CBI) following motor learning. Alterations in neck sensory input due to muscular fatigue are known to impact upper limb sensorimotor processing, suggesting that neck fatigue may also impact cerebellum to motor cortex (M1) pathways in response to motor learning. Therefore, this study aimed to determine whether cervical extensor muscle (CEM) fatigue alters CBI in response to motor learning. We examined 16 participants (8 CEM fatigue and 8 CEM control). A double cone transcranial magnetic stimulation (TMS) coil stimulated the ipsilateral cerebellar cortex 5 ms before application of contralateral test stimuli of the M1 to the right first dorsal interosseous muscle. Cerebellar-M1 activity curves were established pre- and post-motor skill acquisition (consisting of tracing sinusoidal-pattern waves with the index finger) and following either the CEM fatigue or control intervention. The control group showed greater cerebellar disinhibition than the fatigue group following motor skill acquisition (P < 0.006), while the fatigue group showed similar levels of CBI pre- and post-motor skill acquisition. Both groups improved in accuracy following acquisition (P = 0.012) and retention (P = 0.007), but the control group improved significantly more (17% at acquisition and 22% at retention) versus lower (6% and 9%) improvements for the fatigue group. Lessened cerebellar disinhibition in the CEM fatigue versus control group, coupled with diminished motor learning, suggests that CEM fatigue affects the cerebellar-M1 interaction, influencing the cerebellum's ability to adjust motor output to acquire and learn a novel motor task.NEW & NOTEWORTHY Normally motor learning decreases cerebellar inhibition (CBI) to facilitate learning of a novel skill. In this study, neck fatigue before motor skill acquisition led to less of a decrease in CBI and significantly less improvement in performance accuracy relative to a control group. This study demonstrated that neck fatigue impacts the cerebellar-motor cortex interaction to distal hand muscles, a highly relevant finding due to the altered neck postures and fatigue accompanying increased technology use.

Effect of Force Level and Gender on Pinch Force Perception in Healthy Adults

This study investigated the effects of both force level and gender on pinch force reproduction errors in normal participants during an ipsilateral force reproduction task. In total, 20 healthy participants were asked to generate a range of levels of reference forces ranging from 5% to 60% maximal voluntary isometric contraction (MVIC) in increments of 5% MVIC using the tip pinch and to reproduce these forces using the same hand. The results showed that the males more accurately and consistently reproduced the forces than did the females, and the most accurate estimation occurred at approximately 20% to 35% MVIC. This finding can help us better understand the reasons for the higher rate of musculoskeletal disorders in females than in males and to develop tools and preventive strategies to decrease the rate of hand injuries in both genders.

Test-retest reliability of tip, key, and palmar pinch force sense in healthy adults

Background

No previous studies have investigated the test–retest reliability of tip, key, and palmar pinch force sense in healthy adults. The present study explores the test-retest reliability of tip, key, and palmar pinch force sense for different force levels in healthy adults during an ipsilateral force reproduction task.

Methods

Fifty-six healthy subjects were instructed to produce varying levels of reference forces (10, 30, and 50% maximal voluntary isometric contraction (MVIC)) using three types of pinches (tip pinch, palmar pinch, and key pinch) and to reproduce these forces using the same hand. The subjects were tested twice by the same experienced testers, 1 week apart.

Results

Based on the high values of the intraclass correlation coefficient (ICC), the tip pinch (0.783–0.895) and palmar pinch (0.752–0.903) force sense tests demonstrated good reliability for all the variables. The ICCs for the key pinch (0.712–0.881) indicated fair to good relative test-retest reliability.

Conclusion

1) This study demonstrates that high test-retest reliability of tip, key, and palmar pinch force sense in healthy adults can be achieved using standardized positioning and the proposed approach. 2) According to the reliability measurements, 30 and 50% maximal voluntary isometric contraction (MVIC) are the most reliable pinch force sense levels.

Audiohaptic Feedback Enhances Motor Performance in a Low-Fidelity Simulated Drilling Task

When used in educational settings, simulations utilizing virtual reality (VR) technologies can reduce training costs while providing a safe and effective learning environment. Tasks can be easily modified to maximize learning objectives of different levels of trainees (e.g., novice, intermediate, expert), and can be repeated for the development of psychomotor skills. VR offers a multisensory experience, providing visual, auditory, and haptic sensations with varying levels of fidelity. While simulating visual and auditory stimuli is relatively easy and cost-effective, similar representations of haptic sensation still require further development. Evidence suggests that mixing high- and low-fidelity realistic sensations (e.g., audition and haptic) can improve the overall perception of realism, however, whether this also leads to improved performance has not been examined. The current study examined whether audiohaptic stimuli presented in a virtual drilling task can lead to improved motor performance and subjective realism, compared to auditory stimuli alone. Right-handed participants (n = 16) completed 100 drilling trials of each stimulus type. Performance measures indicated that participants overshot the target during auditory trials, and undershot the target during audiohaptic trials. Undershooting is thought to be indicative of improved performance, optimizing both time and energy requirements.

The kinematics of 1-on-1 rugby tackling: a study using 3-dimensional motion analysis

BACKGROUND

Although past studies using video analysis indicated that the arm tackle and head-in-front shoulder tackle are possible risks for shoulder dislocation, the underlying mechanisms of tackling-related shoulder dislocation have not been sufficiently investigated. This study aimed to analyze the kinematic aspects of these tackling motions in 1-on-1 tackles in an experimental setting using a 3-dimensional motion-capture system.

METHODS

A total of 65 one-on-one tackles were recorded using a marker-based, automatic, digitizing motion-capture system. A documented tackle was classified into 1 of 3 types, which was decided based on the first point of contact on the ball carrier and the head position at the time of impact: shoulder tackle (reference tackle), arm tackle, and head-in-front tackle. The orientations of the head, trunk, and shoulder at impact were calculated and statistically compared with each other.

RESULTS

The distribution of tackles recorded in this study was as follows: 38 shoulder, 23 arm, and 4 head-in-front tackles. In comparison with the shoulder tackle as a reference, shoulder abduction on the side of impact was higher in both the arm and head-in-front tackles, while shoulder external rotation was lower in the head-in-front tackles. In the latter type of tackle, significant decreases in neck extension and ipsilateral neck rotation were also indicated.

CONCLUSION

The kinematics in both the arm tackle and the head-in-front tackle is significantly different from that in the shoulder tackle and may represent a distinct risk factor for shoulder dislocation.

Kinematics of Rugby Tackling: A Pilot Study With 3-dimensional Motion Analysis

BACKGROUND

Although improper tackling technique in rugby can affect the outcome of the tackle and lead to head, neck, and shoulder injuries, the effects of the height of the tackle or the side of the leading leg at the time of impact have not been investigated. Hypothesis/Purpose: The purpose was to characterize the trunk orientation at impact during various tackles. It was hypothesized that 3-dimensional motion analysis would be able to capture the critical kinematic differences in the 4 types of tackles studied.

STUDY DESIGN

Controlled laboratory study.

METHODS

A total of 66 tackles on a tackle bag were recorded among 13 elite rugby players. Four types of tackles were evaluated: the normal shoulder tackle, in which the tackler's dominant shoulder made impact while the leading foot was on the same side as that shoulder; the low tackle, in which the tackler targeted the lower portion of the tackle bag; the opposite-leg tackle, in which the tackler's leading leg was on the opposite side as the shoulder making impact; and the low and opposite-leg tackle, which was a combination of the previous 2 types of tackles. The orientation of the trunk at impact was calculated, and 2-way repeated-measures analyses of variance were used to compare the characteristics of these tackles.

RESULTS

Trunk inclination at impact was lower in the low tackle than in the normal tackle ( P < .01), regardless of the side of the leading leg. Trunk bending to the side of the impacted shoulder was lower in the opposite-leg tackle ( P < .01), and these findings were more significant in the normal-height tackles ( P < .01). Trunk rotation to the side of the impacted shoulder was lower in the opposite-leg tackles ( P < .01) and more significant in the lower-height tackles ( P = .03).

CONCLUSION

The 3-dimensional motion capture system was effective in investigating the kinematics of rugby tackling. The kinematics in the low and opposite-leg tackles were significantly different from those in the normal shoulder tackle, which may affect tackle performance and the possible risk of contact injury.

CLINICAL RELEVANCE

When a rugby coach provides tackling instructions to players, it is advantageous to have information about the kinematics of different types of tackles.

Subclinical recurrent neck pain and its treatment impacts motor training-induced plasticity of the cerebellum and motor cortex

The cerebellum processes pain inputs and is important for motor learning. Yet, how the cerebellum interacts with the motor cortex in individuals with recurrent pain is not clear. Functional connectivity between the cerebellum and motor cortex can be measured by a twin coil transcranial magnetic stimulation technique in which stimulation is applied to the cerebellum prior to stimulation over the motor cortex, which inhibits motor evoked potentials (MEPs) produced by motor cortex stimulation alone, called cerebellar inhibition (CBI). Healthy individuals without pain have been shown to demonstrate reduced CBI following motor acquisition. We hypothesized that CBI would not reduce to the same extent in those with mild-recurrent neck pain following the same motor acquisition task. We further hypothesized that a common treatment for neck pain (spinal manipulation) would restore reduced CBI following motor acquisition. Motor acquisition involved typing an eight-letter sequence of the letters Z,P,D,F with the right index finger. Twenty-seven neck pain participants received spinal manipulation (14 participants, 18–27 years) or sham control (13 participants, 19–24 years). Twelve healthy controls (20–27 years) also participated. Participants had CBI measured; they completed manipulation or sham control followed by motor acquisition; and then had CBI re-measured. Following motor acquisition, neck pain sham controls remained inhibited (58 ± 33% of test MEP) vs. healthy controls who disinhibited (98 ± 49% of test MEP, P<0.001), while the spinal manipulation group facilitated (146 ± 95% of test MEP, P<0.001). Greater inhibition in neck pain sham vs. healthy control groups suggests that neck pain may change cerebellar-motor cortex interaction. The change to facilitation suggests that spinal manipulation may reverse inhibitory effects of neck pain.

Relationship between Joint Position Sense, Force Sense, and Muscle Strength and the Impact of Gymnastic Training on Proprioception

The aims of this study were (1) to assess the relationship between joint position (JPS) and force sense (FS) and muscle strength (MS) and (2) to evaluate the impact of long-term gymnastic training on particular proprioception aspects and their correlations. 17 elite adult gymnasts and 24 untrained, matched controls performed an active reproduction (AR) and passive reproduction (PR) task and a force reproduction (FR) task at the elbow joint. Intergroup differences and the relationship between JPS, FS, and MS were evaluated. While there was no difference in AR or PR between groups, absolute error in the control group was higher during the PR task (7.15 ± 2.72°) than during the AR task (3.1 ± 1.93°). Mean relative error in the control group was 61% higher in the elbow extensors than in the elbow flexors during 50% FR, while the gymnast group had similar results in both reciprocal muscles. There was no linear correlation between JPS and FS in either group; however, FR was negatively correlated with antagonist MS. In conclusion, this study found no evidence for a relationship between the accuracy of FS and JPS at the elbow joint. Long-term gymnastic training improves the JPS and FS of the elbow extensors.

Effect of head and limb orientation on trunk muscle activation during abdominal hollowing in chronic low back pain

Background

Individuals with chronic low back pain (CLBP) have altered activations patterns of the anterior trunk musculature when performing the abdominal hollowing manœuvre (attempt to pull umbilicus inward and upward towards the spine). There is a subgroup of individuals with CLBP who have high neurocognitive and sensory motor deficits with associated primitive reflexes (PR). The objective of the study was to determine if orienting the head and extremities to positions, which mimic PR patterns would alter anterior trunk musculature activation during the hollowing manoeuvre.

Methods

This study compared surface electromyography (EMG) of bilateral rectus abdominis (RA), external oblique (EO), and internal obliques (IO) of 11 individuals with CLBP and evident PR to 9 healthy controls during the hollowing manoeuvre in seven positions of the upper quarter.

Results

Using magnitude based inferences it was likely (>75%) that controls had a higher ratio of left IO:RA activation with supine (cervical neutral), asymmetrical tonic neck reflex (ATNR) left and right, right cervical rotation and cervical extension positions. A higher ratio of right IO:RA was detected in the cervical neutral and ATNR left position for the control group. The CLBP group were more likely to show higher activation of the left RA in the cervical neutral, ATNR left and right, right cervical rotation and cervical flexion positions as well as in the cervical neutral and cervical flexion position for the right RA.

Conclusions

Individuals with CLBP and PR manifested altered activation patterns during the hollowing maneuver compared to healthy controls and that altering cervical and upper extremity position can diminish the group differences. Altered cervical and limb positions can change the activation levels of the IO and EO in both groups.

Subclinical neck pain and the effects of cervical manipulation on elbow joint position sense

OBJECTIVE

The objectives of this study were to investigate whether elbow joint position sense (JPS) accuracy differs between participants with a history of subclinical neck pain (SCNP) and those with no neck complaints and to determine whether adjusting dysfunctional cervical segments in the SCNP group improves their JPS accuracy.

METHOD

Twenty-five SCNP participants and 18 control participants took part in this pre-post experimental study. Elbow JPS was measured using an electrogoniometer (MLTS700, ADInstruments, New Zealand). Participants reproduced a previously presented angle of the elbow joint with their neck in 4 positions: neutral, flexion, rotation, and combined flexion/rotation. The experimental intervention was high-velocity, low-amplitude cervical adjustments, and the control intervention was a 5-minute rest period. Group JPS data were compared, and it was assessed pre and post interventions using 3 parameters: absolute, constant, and variable errors.

RESULTS

At baseline, the control group was significantly better at reproducing the elbow target angle. The SCNP group's absolute error significantly improved after the cervical adjustments when the participants' heads were in the neutral and left-rotation positions. They displayed a significant overall decrease in variable error after the cervical adjustments. The control group participants' JPS accuracy was worse after the control intervention, with a significant overall effect in absolute and variable errors. No other significant effects were detected.

CONCLUSION

These results suggest that asymptomatic people with a history of SCNP have reduced elbow JPS accuracy compared to those with no history of any neck complaints. Furthermore, the results suggest that adjusting dysfunctional cervical segments in people with SCNP can improve their upper limb JPS accuracy.

Influence of head orientation on visually and memory-guided arm movements

In the absence of visual supervision, tilting the head sideways gives rise to deviations in spatially defined arm movements. The purpose of this study was to determine whether these deviations are restricted to situations with impoverished visual information. Two experiments were conducted in which participants were positioned supine and reproduced with their unseen index finger a 2 dimensional figure either under visual supervision or from memory (eyes closed). In the former condition, the figure remained visible (using a mirror). In the latter condition, the figure was first observed and then reproduced from memory. Participants' head was either aligned with the trunk or tilted 30° towards the left or right shoulder. In experiment 1, participants observed first the figure with the head straight and then reproduced it with the head either aligned or tilted sideways. In Experiment 2, participants observed the figure with the head in the position in which the figure was later reproduced. Results of Experiment 1 and 2 showed deviations of the motor reproduction in the direction opposite to the head in both the memory and visually-guided conditions. However, the deviations decreased significantly under visual supervision when the head was tilted left. In Experiment 1, the perceptual visual bias induced by head tilt was evaluated. Participants were required to align the figure parallel to their median trunk axis. Results revealed that the figure was perceived as parallel with the trunk when it was actually tilted in the direction of the head. Perceptual and motor responses did not correlate. Therefore, as long as visual feedback of the arm is prevented, an internal bias, likely originating from head/trunk representation, alters hand-motor production irrespectively of whether visual feedback of the figure is available or not.

Differences in movement mechanics, electromyographic, and motor cortex activity between accurate and nonaccurate stepping

What are the differences in mechanics, muscle, and motor cortex activity between accurate and nonaccurate movements? We addressed this question in relation to walking. We assessed full-body mechanics (229 variables), activity of 8 limb muscles, and activity of 63 neurons from the motor cortex forelimb representation during well-trained locomotion with different demands on the accuracy of paw placement in cats: during locomotion on a continuous surface and along horizontal ladders with crosspieces of different widths. We found that with increasing accuracy demands, cats assumed a more bent-forward posture (by lowering the center of mass, rotating the neck and head down, and by increasing flexion of the distal joints) and stepped on the support surface with less spatial variability. On the ladder, the wrist flexion moment was lower throughout stance, whereas ankle and knee extension moments were higher and hip moment was lower during early stance compared with unconstrained locomotion. The horizontal velocity time histories of paws were symmetric and smooth and did not differ among the tasks. Most of the other mechanical variables also did not depend on accuracy demands. Selected distal muscles slightly enhanced their activity with increasing accuracy demands. However, in a majority of motor cortex cells, discharge rate means, peaks, and depths of stride-related frequency modulation changed dramatically during accurate stepping as compared with simple walking. In addition, in 30% of neurons periods of stride-related elevation in firing became shorter and in 20-25% of neurons activity or depth of frequency modulation increased, albeit not linearly, with increasing accuracy demands. Considering the relatively small changes in locomotor mechanics and substantial changes in motor cortex activity with increasing accuracy demands, we conclude that during practiced accurate stepping the activity of motor cortex reflects other processes, likely those that involve integration of visual information with ongoing locomotion.

Poorer elbow proprioception in patients with lateral epicondylitis than in healthy controls: a cross-sectional study

Two groups of women, 15 patients with lateral epicondylitis and 21 healthy controls, were studied to compare proprioception in the elbows and knees between the groups. Outcome measures were absolute error and variable error for joint position sense and for threshold to detection of a passive movement. Both absolute error and variable error of threshold to detection of a passive movement were greater in the lateral epicondylitis-diagnosed elbows than in the controls' elbows (lateral epicondylitis, 1.8 degrees vs controls 1.1 degrees, P = .026; lateral epicondylitis, 0.8 degrees vs controls 0.3 degrees, P = .015), and there was a tendency toward a greater absolute error of joint position sense compared with the control elbows (lateral epicondylitis, 8.2 degrees vs controls, 5.6 degrees; P = .078). Absolute error of joint position sense was greater in the elbows than in the knees of the lateral epicondylitis patients, but no group differences were found for knees. Proprioception seems, therefore, to be poorer in elbows with lateral epicondylitis elbows than in the controls' elbows. This needs to be taken into consideration in the management of lateral epicondylitis.

The influence of body position on leg kinematics and muscle recruitment during cycling

The effects of upper body orientation on neuromuscular control of the leg during cycling are not well understood. Our aim was to investigate the effects of upper body orientation on control of movement of distal leg segments during cycling. We compared three-dimensional leg and foot kinematics and muscle recruitment patterns between upright and aerodynamic riding positions. Comparisons were made between 10 elite cyclists, 10 elite triathletes and 10 novice cyclists. We found that upper body orientation did not influence kinematics of the leg and foot or primary muscle activity (i.e., the main bursts of muscle activity). The aerodynamic riding position was, however, associated with less modulation of muscle activity (i.e., less relaxation of the muscle during secondary muscle activity) and greater coactivity in elite triathletes and novice cyclists. Our results suggest that orientation of the upper body influences neuromuscular control of the leg during cycling in elite triathletes and novice cyclists. The change in muscle recruitment (i.e., the change in how the goal movement was achieved) implies that the ability of the central nervous system to execute the cycling movement in the most skilled manner was adversely influenced by upper body orientation in elite triathletes and novice cyclists. Less modulation of muscle activity and greater coactivation in elite triathletes when cycling in the aerodynamic position, and the similarity of changes shown in elite triathletes and novice cyclists, may be interpreted as further evidence of less skilled control of movement in elite triathletes when compared to cyclists matched for cycling training history.

Failed jump landing trials: deficits in neuromuscular control

The purpose of this investigation was to compare neuromuscular control variables during successful and failed jump landings in multiple directions (sagittal, diagonal, and lateral). All data were collected during a single leg hop stabilization maneuver, which required subjects to stand 70 cm from the center of a force plate, jump off both legs, touch a designated marker placed at a height equivalent to 50% of their maximum vertical jump, and land on a single leg for all directions. Twenty-six subjects [10 males (22+/-3.9 years of age, 70.9+/-7.6 kg, and 176.8+/-0.5 cm) and 16 females (20.6+/-0.5 years of age, 65.6+/-9.1 kg, and 166.4+/-5.9 cm)] volunteered to participate in this investigation. Muscle activation times, average preparatory, and reactive electromyographic (EMG) amplitudes were calculated for the vastus medialis, semi-membranosis, lateral gastrocnemius, and tibialis anterior. EMG data revealed that successful jump landing trials had earlier activation times and higher preparatory and reactive EMG amplitudes. There was no difference for EMG activation times or amplitudes among directions. The results indicate neuromuscular control differences between successful and failed trials because of earlier muscle onset and greater amplitude. The results also suggest that in a healthy population, the direction of the jump protocol will not affect lower extremity EMG characteristics.

Changes in Head and Neck Position Have a Greater Effect on Elbow Joint Position Sense in People With Whiplash-associated Disorders

BACKGROUND

It has been shown that perception of elbow joint position is affected by changes in head and neck position. Further, people with whiplash-associated disorders (WAD) present with deficits in upper limb coordination and movement.

OBJECTIVES

This study is aimed to determine whether the effect of changes in head position on elbow joint position error (JPE) is more pronounced in people with WAD, and to determine whether this is related to the participant's pain and anxiety levels.

METHODS

Nine people with chronic and disabling WAD and 11 healthy people participated in this experiment. The ability to reproduce a position at the elbow joint was assessed after changes in the position of the head and neck to 30 degrees , and with the head in the midline. Pain was monitored in WAD participants.

RESULTS

Absolute elbow JPE with the head in neutral was not different between WAD and control participants (P=0.5). Changes in the head and neck position increased absolute elbow JPE in the WAD group (P<0.05), but did not affect elbow JPE in the control group (P=0.4). There was a connection between pain during testing and the effect of changes in head position on elbow JPE (P<0.05).

DISCUSSION

Elbow JPE is affected by movement of the head and neck, with smaller angles of neck rotation in people with WAD than in healthy individuals. This observation may explain deficits in upper limb coordination in people with WAD, which may be due to the presence of pain or reduced range of motion in this population.

Do you know where your arm is if you think your head has moved?

Reproduction of a previously presented elbow position is affected by changes in head position. As movement of the head is associated with local biomechanical changes, the aim of the present study was to determine if illusory changes in head position could induce similar effects on the reproduction of elbow position. Galvanic vestibular stimulation (GVS) was applied to healthy subjects in supine lying. The stimulus was applied during the presentation of an elbow position, which the subject then reproduced without stimulation. In the first study, 13 subjects received 1.5 mA stimuli, which caused postural sway in standing, confirming that the firing of vestibular afferents was affected, but no illusory changes in head position were reported. In the second study, 13 subjects received 2.0-3.0 mA GVS. Six out of 13 subjects reported consistent illusory changes in head position, away from the side of the anode. In these subjects, anode right stimulation induced illusory left lateral flexion and elbow joint position error towards extension (p=0.03), while anode left tended to have the opposite effect (p=0.16). The GVS had no effect on error in subjects who did not experience illusory head movement with either 1.5 mA stimulus (p=0.8) or 2.0-3.0 mA stimulus (p=0.7). This study demonstrates that the accuracy of elbow repositioning is affected by illusory changes in head position. These results support the hypothesis that the perceived position of proximal body segments is used in the planning and performance of accurate upper limb movements.