Change In Direction Of Force Research Articles

Spatial Instability during Precision Grip-Lift in Children with Poor Manual Dexterity.

Although children with developmental coordination disorder (DCD) show impaired precision grip control due to a sensory-motor integration deficit, their spatial instability (such as changes in force direction and object roll during a precision grip task) is unclear. Herein, we investigated the spatial instability in the precision grip force control of children with poor manual dexterity. We divided 66 school-aged children who performed a precision gripping and lifting of heavy- or lightweight objects into those with low manual dexterity (n = 11) and those with high manual dexterity (n = 55) as revealed by the Movement Assessment Battery for Children (2nd edition). The group and weight effects were then determined. The results revealed that the total trajectory lengths of the center of pressure (COP) were longer in the lightweight object data of the children in the low-manual-dexterity group and were related to the children’s grip force. The low-manual-dexterity group also showed a shifted COP position from the center of the object in the medial–lateral direction and in the object roll regardless of the object’s weight; these were closely related in both weights’ tests. These results demonstrated that children with poor manual dexterity show spatial instability and different adaptations to the weight of objects during a precision grip task. Further studies are needed to determine whether these findings would be replicated in children with a diagnosis of DCD.

Reorganized Force Control in Elbow Pain Patients During Isometric Wrist Extension.

Reorganized force control may be an important adaptation following painful traumas. In this study, force control adaptations were assessed in elbow pain patients. Increasing the contraction demand may overcome pain interference on the motor control and as such act as an internal control. It was hypothesized that elbow pain patients compared with controls would present greater change in the direction of force when increasing the demand of the motor task. Elbow pain patients (n=19) and asymptomatic participants (n=21) performed isometric wrist extensions at 5% to 70% of maximum voluntary contraction. Pressure pain thresholds were recorded at the lateral epicondyle and tibialis anterior muscle. Contraction force was recorded using a 3-directional force transducer. Participants performed contractions according to visual feedback of the task-related force intensity (main direction of wrist extension) and another set of contractions with feedback of the 3 force directions. Going from the simple to the detailed force feedback will increase the demand of the motor task. Force steadiness in all 3 dimensions and force directions were extracted. Compared with controls, elbow pain patients presented lower pressure pain thresholds at both sites (P<0.05). Force steadiness was not significantly different between groups or feedback methods. The change in force direction when providing simple visual feedback in contrast with feedback of all force components at all contraction levels was greater for patients compared with controls (P<0.05). The larger change in force direction in pain patients implies redistribution of loads across the arm as an associated effect of pain.

Reduced Maximal Force during Acute Anterior Knee Pain Is Associated with Deficits in Voluntary Muscle Activation.

Although maximal voluntary contraction (MVC) force is reduced during pain, studies using interpolated twitch show no consistent reduction of voluntary muscle drive. The present study aimed to test if the reduction in MVC force during acute experimental pain could be explained by increased activation of antagonist muscles, weak voluntary activation at baseline, or changes in force direction. Twenty-two healthy volunteers performed maximal voluntary isometric knee extensions before, during, and after the effects of hypertonic (pain) and isotonic (control) saline injections into the infrapatellar fat pad. The MVC force, voluntary activation, electromyographic (EMG) activity of agonist, antagonist, and auxiliary (hip) muscles, and pain cognition and anxiety scores were recorded. MVC force was 9.3% lower during pain than baseline (p < 0.001), but there was no systematic change in voluntary activation. Reduced MVC force during pain was variable between participants (SD: 14%), and was correlated with reduced voluntary activation (r = 0.90), baseline voluntary activation (r = − 0.62), and reduced EMG amplitude of agonist and antagonist muscles (all r > 0.52), but not with changes in force direction, pain or anxiety scores. Hence, reduced MVC force during acute pain was mainly explained by deficits in maximal voluntary drive.

Localized Pressure Pain Sensitivity is Associated With Lower Activation of the Semispinalis Cervicis Muscle in Patients With Chronic Neck Pain

To investigate the relation between localized pressure pain sensitivity and the amplitude and specificity of semispinalis cervicis muscle activity in patients with chronic neck pain. Pressure pain detection thresholds (PPDTs) were measured over the C2-C3 and C5-C6 cervical zygapophyseal joints in 10 women with chronic neck pain and 9 healthy age-matched and sex-matched controls. Intramuscular electromyography (EMG) was acquired from the semispinalis cervicis at the levels of C2 and C5 during isometric circular contractions in the horizontal plane at 15 and 30 N, with continuous change in force direction in the range 0 to 360 degrees. The average rectified value and directional specificity of semispinalis cervicis muscle activity were computed and regression analyses were performed between measures of EMG and PPDT. Patients showed significantly lower PPDT compared with controls (P<0.01). Patients also displayed lower EMG amplitude of the semispinalis cervicis at both spinal levels during the circular contractions (average across spinal levels, mean±SD: 129.01±58.99 and 126.83±58.78 µV for the 15- and 30-N contractions, respectively) compared with controls (158.69±66.27 and 187.64±87.82 µV; P<0.05). Furthermore, the directional specificity of semispinalis cervicis muscle was lower for the patients during the circular contractions (P<0.05). The PPDT (C2 and C5 pooled) was positively correlated to both, directional specificity (R=0.22, P<0.05) and amplitude (R=0.15, P<0.05) of the EMG. In contrast to asymptomatic individuals, the semispinalis cervicis muscle displays reduced and less-defined EMG activity during a multidirectional isometric contraction in patients with chronic neck pain. The altered behavior of the semispinalis cervicis is weakly associated to pressure pain sensitivity.

Effectiveness of an 8‐week exercise programme on pain and specificity of neck muscle activity in patients with chronic neck pain: A randomized controlled study

Although exercise can be effective for relief of neck pain, little is known about the effect of exercise on the neural control of neck muscles. A randomized controlled trial was conducted on 46 women with chronic neck pain to investigate the immediate effectiveness of an 8-week exercise programme on pain and directional specificity of neck muscle activity. At baseline, the patients completed questionnaires including the neck disability index (NDI) and performed a circular contraction of their head in the horizontal plane at 15 N force, with continuous change in force direction in the range 0-360°. Electromyography (EMG) was recorded from the sternocleidomastoid (SCM) and splenius capitis (SCap) muscles. Tuning curves of the EMG amplitude were computed, which depicts muscle activity over a range of force directions. The mean point of the tuning curves defined a directional vector, which determined the specificity of muscle activity. Patients were randomly assigned either to a training or control group. A significant between-group difference in the change in NDI was observed. A reduction in NDI was observed following training (pre: 18.2 ± 7.4; post: 14.1 ± 6.5; p < 0.01) but not for the control group (pre: 17.5 ± 6.3; post: 16.6 ± 7.4). The training group showed higher specificity of muscle activity post-intervention (pre: 18.6 ± 9.8%, post: 24.7 ± 14.3%; p < 0.05), whereas no change occurred for the control group (pre: 19.4 ± 11.9%, post: 18.2 ± 10.1%). An exercise programme that aims to enhance motor control of the cervical spine improves the specificity of neck muscle activity and reduces pain and disability in patients with neck pain.

Chronic trauma-induced neck pain impairs the neural control of the deep semispinalis cervicis muscle

ObjectiveThe deep cervical extensors show structural changes in patients with neck pain however their activation has never been investigated in patients. This study is the first to present neurophysiological data from the deep semispinalis cervicis muscle in patients. MethodsTen women with chronic neck pain and 10 healthy controls participated. Activity of the semispinalis cervicis was measured as subjects performed isometric contractions at 15 and 30N force with continuous change in force direction in the range 0–360°. Tuning curves of the EMG amplitude (average rectified value, ARV) were computed and the mean point of the ARV curves defined a directional vector, which determined the directional specificity of the muscle activity. ResultsPatients displayed reduced directional specificity of the semispinalis cervicis (P<0.05). Furthermore, the EMG amplitude during the circular contraction was lower for the patients (86.3±38.0 and 104.4±47.0μV for 15 and 30N, respectively) compared to controls (226.4±128.5 and 315.8±205.5μV; P<0.05). ConclusionsThe activity of the semispinalis cervicis muscle is reduced and less defined in patients with neck pain confirming a disturbance in the neural control of this muscle. SignificanceThis finding suggests that exercises that target the deep semispinalis cervicis muscle may be relevant to include in the management of patients with neck pain.

Effect of pain on the modulation in discharge rate of sternocleidomastoid motor units with force direction

To compare the behavior of sternocleidomastoid motor units of patients with chronic neck pain and healthy controls. Nine women (age, 40.4+/-3.5 yr) with chronic neck pain and nine age- and gender-matched healthy controls participated. Surface and intramuscular EMG were recorded from the sternocleidomastoid muscle bilaterally as subjects performed isometric contractions of 10-s duration in the horizontal plane at a force of 15 N in eight directions (0-360 degrees ; 45 degrees intervals) and isometric contractions at 15 and 30 N force with continuous change in force direction in the range 0-360 degrees . Motor unit behavior was monitored during the 10-s contractions and the subsequent resting periods. The mean motor unit discharge rate depended on the direction of force in the control subjects (P<0.05) but not in the patients. Moreover, in three of the nine patients, but in none of the controls, single motor unit activity continued for 8.1+/-6.1s upon completion of the contraction. The surface EMG amplitude during the circular contraction at 15N was greater for the patients (43.5+/-54.2 microV) compared to controls (16.9+/-14.9 microV; P<0.05). The modulation in discharge rate of individual motor units with force direction is reduced in the sternocleidomastoid muscle in patients with neck pain, with some patients showing prolonged motor unit activity when they were instructed to rest. These observations suggest that chronic neck pain affects the change in neural drive to muscles with force direction.

2P1-F02 ポテンシャル法における連続斥力ベクトル生成アルゴリズムの提案

We developed a guidance robot "NWR001" that can control intuitively. An obstacle avoidance feature based on the potential field approach was added this time. The potential field approach was used for generating a path that avoids obstacles. However, that method has some issues, those are concave shape obstacles and contiguous obstacles. This paper proposed a new method that generates a continuous change of force direction by dividing a potential field in to a positive and a negative axes and combine both maximum values. Our method can apply to the point cloud data such as scanning laser or range image sensor.

Cutting force signal pattern recognition using hybrid neural network in end milling

Under certain cutting conditions in end milling, the signs of cutting forces change from positive to negative during a revolution of the tool. The change of force direction causes the cutting dynamics to be unstable which results in chatter vibration. Therefore, cutting force signal monitoring and classification are needed to determine the optimal cutting conditions and to improve the efficiency of cut. Artificial neural networks are powerful tools for solving highly complex and nonlinear problems. It can be divided into supervised and unsupervised learning machines based on the availability of a teacher. Hybrid neural network was introduced with both of functions of multilayer perceptron (MLP) trained with the back-propagation algorithm for monitoring and detecting abnormal state, and self organizing feature map (SOFM) for treating huge datum such as image processing and pattern recognition, for predicting and classifying cutting force signal patterns simultaneously. The validity of the results is verified with cutting experiments and simulation tests.

Counterrolling of the eyes and its dependence on the magnitude of gravitational or inertial force acting laterally on the body

Counterrolling of the eyes was measured in five healthy persons when inclined on a tilt-chair and when exposed to a change in direction of force on a human centrifuge. For equivalent changes in direction of force incident to the subject, the magnitude of the force was greater on the centrifuge. When the amount of roll was plotted as a function of the incident angle of force, divergent curves were obtained for tilt-chair and centrifuge data. When the amount of roll was plotted as a function of magnitude of laterally-acting force as the independent variable, a single curve resulted indicating a straight line relation within the range of 1 g. These findings not only constitute definitive proof that the counterrolling reflex can be released by gravitational (and inertial) force but also are consistent with the current theory of the functioning of the otolith organs. Submitted on January 20, 1959

The “aperiodic” ballistocardiogram as a function of age

1. 1. A modification of the Wittern “aperiodic” ballistocardiograph, capable of quantitative registration of force in 2 degrees of freedom is described in detail. 2. 2. The records of seventy-three normal subjects ranging in age from 2 1 2 to 87 years comprise the material for this report. 2.1. A. The wave form of the “aperiodic” ballistocardiogram varies with age and force direction, though the shape of the record for any single individual is a unique and highly reproducible characteristic. 2.2. B. Progressive shift of the frontal plane vector toward the transverse axis of the body begins at approximately age 40. Bidirectional recordings are therefore essential in the age group of primary clinical interest. 2.3. C. Respiratory variation cannot be explained on the basis of change in force direction. Though reversed respiratory variation is highly significant in subjects under 40, it may be entirely normal beyond age 50. 3. 3. The most important fact elucidated by this study is that reaction force remains constant throughout adult life. The hemodynanic alterations responsible for constant force output despite progressive decrease in stroke volume and contractility are discussed. 4. 4. Though the “aperiodic” ballistocardiogram has proved to be a valuable clinical and investigative technique, the complexity of instrumentation and interpretation precludes its use as a “service” diagnostic procedure in its present state of development.