Elbow Rotation Research Articles

Kinesthetic control of a multijoint movement sequence

1. The individual joint rotations of a movement sequence might be controlled either by a central motor plan or by motion-dependent (i.e., kinesthetic) sensory input. Most previous research has focused on how the nervous system uses central motor plans to control movement sequences. This study examined how the nervous system uses kinesthetic input to control a multijoint movement sequence. 2. Human subjects were trained to extend the elbow horizontally at 22 degrees/s and to open the hand as the elbow passed through a 2 degrees-wide target zone. Different distances to the target zone were used to examine a wide range of movement times of the elbow to target zone (i.e., 150-1,500 ms). 3. A hydraulic apparatus simulated a spring resistance to the elbow extension. In some trials, the spring constant was unexpectedly increased or decreased just before the subject initiated the elbow extension, causing the elbow to slow down or speed up. Because these changes in spring constant were randomly imposed and because no visual feedback was available, subjects had to use kinesthetic input to control this motor task. 4. The experimental subjects employed two different strategies for the use of kinesthetic input to control this motor task. In the first strategy, the subjects used kinesthetic input related to the elbow rotation to detect and correct velocity errors caused by the changes in spring constant. The onset of error correction varied between 92 and 196 ms after the appearance of velocity errors. The proportion of the error corrected by the time the elbow reached the target zone varied between 31 and 78%, depending on the movement time to the target zone. However, because this correction for velocity errors was neither instantaneous nor complete, the changes in spring constant caused leads and lags in the time that the elbow reached the target zone. 5. In the second strategy, subjects used kinesthetic input related to the elbow rotation to advance or delay the onset of the hand movement, thereby compensating for leads and lags in the arrival of the elbow at the target zone. These adjustments in the triggering time of the hand movement allowed subjects to open the hand while the elbow was in the target zone. This kinesthetic triggering mechanism was effective for elbow rotations reaching the target zone within 150-1,500 ms. 6. These results suggest that, to fully understand how multijoint movement sequences are controlled by the nervous system, sensory mechanisms must be considered in addition to central mechanisms.

Acquisition of co-ordination between posture and movement in a bimanual task.

The acquisition of co-ordination between posture and movement was investigated in human subjects performing a load lifting task. Sitting subjects held their left (postural) forearm in a horizontal position while supporting a 1 kg load via an electromagnet. Perturbation of the postural forearm position consisted of the load release triggered either by the experimenter (control) or by the subject voluntarily moving the other arm. In the latter case, the movement involved the elbow joint (load lifting (A), isometric force change at the wrist level (B), elbow rotation (C) and pressing a button with the wrist (D] or the fingers (grip isometric force change). We recorded the maximal amplitude and maximal velocity of the rotation of the postural forearm, the EMG of the forearm flexors on both sides and the force exerted either by the load on the postural arm or by the isometric contraction of the moving arm. The maximal forearm angular velocity after unloading was known to be related to the level of muscle contraction before unloading. 1. In the control situation, repetition of the imposed unloading test resulted in a progressive reduction in the maximal forearm rotation without any decrease in the maximal velocity. The amplitude and duration of the unloading reflex were found to increase in parallel. These results suggest that an adaptive mechanism took place which increased the gain of the unloading reflex loop and reduced the mechanical effect of the perturbation. This mechanism was found to come into play not only in the control situation but also in other paradigms where the perturbation was expected by the subjects. 2. A decrease in both maximal amplitude and velocity of forearm rotation together with a weak "anticipatory" deactivation of the forearm postural flexors was observed when the unloading was caused by an elbow movement (situations A, B, C) which indicates that a feedforward postural control took place. An interlimb coordination was built up and stabilized after 40-60 trials. Pressing a button with the wrist (weak force and displacement) was a less effective means of inducing an anticipatory control of the flexors of the postural forearm, which indicates that the intensity of the central control plays a role in the building up of the coordination. 3. A distal grip action exerting either weak (100 g) or a high (1 kg) force was able to reduce the maximal amplitude of the forearm rotation, but not the maximal velocity, which indicates that an improved reflex action takes place, but not a feedforward anticipatory postural control.(ABSTRACT TRUNCATED AT 400 WORDS)

Performance of a bimanual load-lifting task by parkinsonian patients.

Normal subjects and Parkinsonian patients performed a bimanual load lifting task. In this task, one "postural" forearm, held in a horizontal position while supporting a 1 kg weight, was unloaded either by the experimenter's hand (imposed unloading) or by the subject's other hand in response to a tone burst (voluntary unloading). The variables recorded were reaction time (RT: time interval between the tone and beginning of unloading) and movement time (MT: duration of the change in force measured by a force platform on the "postural" forearm). Elbow angle changes were also measured with a potentiometer. The EMG activity from brachioradialis of the "postural" arm and that from the biceps of the "active" arm were recorded. The Parkinsonian patients showed an increase in both RT and MT and an impairment of the co-ordination between movement and posture which was reflected in an increase in amplitude of the elbow rotation after voluntary unloading. Moreover, the decrease in EMG activity in the brachioradialis of the postural arm during unloading was less in Parkinsonian patients than in the normal group. This disorder of postural command was often accompanied by a lack of anticipatory EMG changes. Comparison between treated and non-treated patients showed that dopamine agonists brought about recovery of both RT and MT but did not improve postural co-ordination. The co-ordination was less impaired when the voluntary unloading was performed by the preferred hand. Several hypotheses are discussed concerning the mechanism underlying this impaired co-ordination.

Postural forearm changes induced by predictable in time or voluntary triggered unloading in man.

Human subjects sitting in a chair were asked to maintain their right forearm in a horizontal position in half supination. The forearm was loaded with a constant weight of one kilogram. Vertical force at the wrist level, angular position of the elbow and EMG activity of biceps, brachio-radialis and triceps muscles were recorded. Unloading was tested under four different conditions, the first two having been used in a previous study (Hugon et al. 1982): Voluntary unloading by the subject's other hand. An "anticipatory" deactivation of the load bearing forearm flexors is observed preventing the elbow rotation of that arm. Unpredictable passive unloading. This results in an upward forearm rotation which provokes the classical "unloading reflex". Two new conditions were tested in the present paradigm: Imposed unloading predictable in time (tone signal preceding unloading by a fixed interval). Unloading being actively triggered when the subject presses a key. Under the two latter conditions, no anticipatory deactivation of the flexor supporting muscles preceding the onset of unloading as in situation A was observed. During the first 120 ms after the onset of unloading, the forearm rotation was the same as in situation B (unpredictable passive unloading). Thereafter, the rotation was smaller in some subjects, apparently due to an ameliorated reflex action. It is concluded that temporal information concerning the precise time of the unloading or the triggering of the load release by a voluntary movement (key press) was not by itself able to induce the anticipatory deactivation of the forearm flexors that was seen with a coordinated voluntary release of the load by the contralateral arm.

Programming of Initiation and Execution of Ballistic Arm Movements in the Monkey

Publisher Summary This chapter discusses the programming of initiation and execution of ballistic arm movements in the monkey. The experiments are performed on adult monkeys ( Macaca mulatta ), trained to perform ballistic flexion (F) or extension (X) movements of the forearm in response to a sensory cue. Juice reward is delivered when movements in the required direction and of sufficient amplitude (15–30o), are initiated within 500 msec. There is no starting or ending reference points or preparatory signals. Elbow rotation and associated electromyographic (EMG) activity are recorded together with neuronal activity in either the primary motor cortex, primary sensory cortex or in the parietal association areas (5 and 7). In two animals, electro-oculograms (EOG) and neck muscle EMGs are also recorded. In the first series of experiments, only an auditory conditioned stimulus is used. Following a period of data collection in the intact animal, the moving arm is surgically deafferented by dorsal rhyzotomy from C2 to T5. In one of these animals, a stimulating electrode is chronically implanted in the ventroposterolateral (VPL) nucleus of the thalamus contralateral to the moving arm.