Postural stability assessment in expert versus amateur basketball players during optic flow stimulation

We evaluated the role of visual stimulation on postural muscles and the changes in the center of pressure (CoP) during standing posture in expert and amateur basketball players. Participants were instructed to look at a fixation point presented on a screen during foveal, peripheral, and full field optic flow stimuli. Postural mechanisms and motor strategies were assessed by simultaneous recordings of stabilometric, oculomotor, and electromyographic data during visual stimulation. We found significant differences between experts and amateurs in the orientation of visual attention. Experts oriented attention to the right of their visual field, while amateurs to the bottom-right. The displacement in the CoP mediolateral direction showed that experts had a greater postural sway of the right leg, while amateurs on the left leg. The entropy-based data analysis of the CoP mediolateral direction exhibited a greater value in amateurs than in experts. The root-mean-square and the coactivation index analysis showed that experts activated mainly the right leg while amateurs the left leg. In conclusion, playing sports for years seems to have induced some strong differences in the standing posture between the right and left sides. Even during non-ecological visual stimulation, athletes maintain postural adaptations to counteract the body oscillation.

Validation of the 4AT, a new instrument for rapid delirium screening: a study in 234 hospitalised older people

OBJECTIVE

to evaluate the performance of the 4 'A's Test (4AT) in screening for delirium in older patients. The 4AT is a new test for rapid screening of delirium in routine clinical practice.

DESIGN

: prospective study of consecutively admitted elderly patients with independent 4AT and reference standard assessments.

SETTING

: an acute geriatrics ward and a department of rehabilitation.

PARTICIPANTS

two hundred and thirty-six patients (aged ≥70 years) consecutively admitted over a period of 4 months.

MEASUREMENTS

in each centre, the 4AT was administered by a geriatrician to eligible patients within 24 h of admission. Reference standard delirium diagnosis (DSM-IV-TR criteria) was obtained within 30 min by a different geriatrician who was blind to the 4AT score. The presence of dementia was assessed using the Alzheimer's Questionnaire and the informant section of the Clinical Dementia Rating scale. The main outcome measure was the accuracy of the 4AT in diagnosing delirium.

RESULTS

patients were 83.9 ± 6.1 years old, and the majority were women (64%). Delirium was detected in 12.3% (n = 29), dementia in 31.2% (n = 74) and a combination of both in 7.2% (n = 17). The 4AT had a sensitivity of 89.7% and specificity 84.1% for delirium. The areas under the receiver operating characteristic curves for delirium diagnosis were 0.93 in the whole population, 0.92 in patients without dementia and 0.89 in patients with dementia.

CONCLUSIONS

the 4AT is a sensitive and specific method of screening for delirium in hospitalised older people. Its brevity and simplicity support its use in routine clinical practice.

Effects of posture-related changes in motor cortical output on central oscillatory activity of pathological origin in humans

Changes in shoulder position influence motor cortical outflow to Abductor Digiti Minimi (ADM) muscle in healthy humans. We examined whether these changes may affect finger tremor of central origin. Subjects had their shoulder positioned in two different configurations: 30 degrees horizontal adduction (ANT) and 30 degrees horizontal abduction (POST) with respect to neutral position at 0 degrees in the horizontal plane. In healthy subjects, patients with Parkinsonian tremor (PT) and essential tremor (ET), transcranial magnetic stimulation (TMS) of the motor cortex was performed under resting and active conditions in ANT and POST. PT, ET and physiological tremor (PhT) were studied by accelerometric recordings from the little finger and by EMG activity from ADM and Extensor Carpi Radialis (ECR) in ANT and POST. In healthy and ET subjects, ADM motor evoked responses (MEPs) to TMS were smaller under resting, but larger under active conditions in POST. In PT patients, MEPs showed no difference at rest in ANT but were lower during ADM activation in POST. PT decreased, whereas ET increased in POST. These changes were paralleled by a decrease in PT EMG power and an increase in ET EMG power in POST. In PhT, there was no difference in tremor amplitude between ANT and POST. PT decrease and ET increase in POST parallel the changes in motor cortical outflow to ADM induced by modification of shoulder position under active conditions. This may be evidence for altered premotor-motor interaction at cortical level in PT, and for a role of the motor cortex in generating ET.

Dynamic changes in cortical and spinal activities with different representations of isometric motor actions and efforts

BACKGROUND

Positioning the shoulder joint from 30 degrees adduction (anterior [ANT]) to 30 degrees abduction (posterior [POST]) in the horizontal plane modifies the corticospinal output to hand and forearm muscles in humans.

OBJECTIVE

We investigated the mechanisms by which the central nervous system (CNS) maintains force output under conditions of increased effort and reduced corticospinal activity.

METHODS

Ten healthy subjects were studied with the shoulder joint fully supported and passively kept either in ANT or POST. Changes in motor-evoked potentials (MEPs) to transcranial magnetic stimulation (TMS), intracortical inhibition (ICI), intracortical facilitation (ICF), H-reflex and F-waves were studied at force levels corresponding to 10% maximum voluntary contraction (MVC) of abductor digiti minimi (ADM) in ANT for both shoulder positions. In addition, premovement changes in ADM MEP size were assessed in a choice reaction time paradigm in the two shoulder positions.

RESULTS

ADM MEPs were larger in POST than in ANT either during or before ADM voluntary contraction, pointing to increased corticospinal excitability in both conditions. ICI and ICF were increased and decreased, respectively, indicating a general disfacilitation on primary motor cortical (M1) output to ADM in POST. F-waves and H-reflexes were increased and decreased, respectively, indicating postsynaptic facilitation and increased presynaptic inhibition at spinal cord level in POST.

CONCLUSIONS

A larger cortical output is produced in POST to maintain the same force levels as in ANT. A contributory role of premotor regions is hypothesized.

Relation between isometric muscle force and surface EMG in intrinsic hand muscles as function of the arm geometry

Evidence exists that shoulder joint geometry influences recruitment efficiency and force-generating capacity of hand muscles [Ginanneschi, F., Del Santo, F., Dominici, F., Gelli, F., Mazzocchio, R., Rossi, A., 2005. Changes in corticomotor excitability of hand muscles in relation to static shoulder positions. Exp. Brain Res. 161 (3), 374-382; Dominici, F., Popa, T., Ginanneschi, F., Mazzocchio, R., Rossi, A., 2005. Cortico-motoneural output to intrinsic hand muscles is differentially influenced by static changes in shoulder positions. Exp. Brain Res. 164 (4), 500-504]. The present study was designed to examine the impact of changing shoulder joint position on the relation between surface EMG amplitude and isometric force production of the abductor digiti minimi muscle (ADM). EMG-force relation of ADM was examined in two shoulder positions: 30 degrees adduction (ANT) and 30 degrees abduction (POST) on the horizontal plane, i.e. under higher and lower force-generating capacity, respectively. The relation was studied over the full range isometric force (10-100% of maximum force in 10% increments, 3 s duration) by analysing root mean square (RMS), median frequency (Mf) of the power spectrum and non-linear recurrence quantification analysis (percentage of determinism: %DET) of the surface EMG signals. We found that in POST, the slope of the RMS-force relation was significantly higher than in ANT, while its general shape (strictly linear) was preserved. Averaged Mf of the EMG power spectrum was significantly higher in POST that in ANT, while no difference in %DET was observed between the two shoulder positions. The higher slope of the EMG-force relation in POST than in ANT is interpreted in terms of increased gain of the excitatory drive-firing rate relation. It is concluded that discharge from sensory receptors signalling shoulder position may act to regulate the gain of the excitatory drive-firing rate relation of motoneurones in order to compensate for reduced recruitment efficiency.

Corticospinal drive during painful voluntary contractions at constant force output

In the voluntary contractions, output force can be maintained constant although the inhibitory influences exerted by pain on muscle activity. We investigated changes in the spontaneous and evoked activity of the abductor digiti minimi muscle (ADM) and the biceps brachii muscle (BIC) in healthy volunteers during constant force noxious contraction, resulting from chemically activated nociceptive afferents. EMG-force relationship, motor-evoked response (MEP) to transcranial magnetic stimulation and determinism (DET) of surface EMG signals during constant force contraction was analyzed before, during and after chemically induced tonic activation of their nociceptive afferents. Under constant force contraction, amplitude of surface EMG signal decreased in BIC and increased in ADM during pain with respect to control condition. In both muscles, the size of motor-evoked potential (MEP) induced by transcranial magnetic stimulation (TMS) of the primary motor cortex was significantly higher during pain than in control. Level of determinism extracted from surface EMG signal by non-linear method was similarly and significantly increased in both muscles during pain stimulation. Finally, nociceptive stimulation caused a decline in steadiness of the force exerted by ADM and BIC. These results are interpreted in terms of increased corticospinal synchronizing inputs. The possibility that it may play a role in governing force production to counteract pain inhibitory influences on motor system is considered.