Responses of finger flexor and extensor muscles to transcranial magnetic stimulation during isometric force production tasks.

INTRODUCTION: In this study we investigated neural mechanisms of finger force control. METHODS: Ten right-handed subjects performed isometric finger flexion and extension force productions at 10-60% of maximum voluntary contraction (MVC) using 4 fingers of the dominant hand. Transcranial magnetic stimulation (TMS) was applied over the contralateral hand motor area. We measured fluctuation of the background force and TMS responses from finger flexor and extensor muscles. RESULTS: Force fluctuation was greater during finger extension than during finger flexion. Motor evoked potentials (MEPs) increased with force levels in the flexor digitorum superficialis (FDS) during finger flexion and in the extensor digitorum communis (EDC) during finger extension. TMS-induced forces increased up to 40% MVC and then decreased during finger flexion, whereas they decreased continuously through the tested force levels during finger extension. CONCLUSIONS: These results suggest that FDS and EDC are controlled by different neural mechanisms, most likely attributable to their different functional roles in daily activities.

Asymmetrical gait in adolescents with idiopathic scoliosis.

PURPOSE: This study investigated side-to-side gait asymmetry in subjects with adolescent idiopathic scoliosis. METHODS: There were 20 adolescents with idiopathic scoliosis and 20 age-matched control subjects, who participated in the study. To minimize confounding effects, we recruited patients with similar spinal curvature for the scoliosis group, and all participants are right hand dominant. The participants were instructed to ambulate on a 10 m walkway while barefoot. There were two force plates in the middle of the walkway. The ground reaction force (GRF) and angular displacements of six segments (foot, shank, thigh, pelvis, trunk, and head) were measured during one gait cycle based on the right and left lower extremities. To remove the positional information in the kinematic data, the derivative of angular displacement in each segment was calculated. To evaluate the side-to-side gait symmetry, we calculated the cross-correlation of each bilateral gait parameter. RESULTS: In the kinematics, the scoliosis group demonstrated asymmetrical gait in the frontal and transverse planes compared to the control group. In the GRF data, the scoliosis group demonstrated asymmetrical gait in the medial-lateral (M/L) direction compared to the control group. CONCLUSIONS: These results indicated that the scoliosis group produced an asymmetrical rotation pattern of the segments bilaterally in the frontal and transverse planes, resulting in asymmetrical GRF patterns in the M/L direction. This asymmetrical gait may be produced by changes in global postural control during gait and not simply by changes in control of only one or two specific segments.

Phase-dependent respiratory-motor interactions in reaction time tasks during rhythmic voluntary breathing.

The study investigated squeezing reaction time (RT) in response to a visual cue during rhythmic voluntary breathing at 0.6 Hz paced by a metronome, breath holding, or at rest in 13 healthy subjects. Rhythmic voluntary breathing slowed down RT, only in the expiratory phase with accompanied changes in the length of respiratory phases, while breath-holding reduced RT. The prolonged RT during voluntary expiratory phases and the absence of changes in RT during voluntary inspiratory phases are most likely related to disproportionally increased cognitive demands during the expiratory phase of voluntary breathing. The absence of changes in RT during voluntary inspiration is likely to be compensated by respiratory-motor facilitation mechanisms in this phase. Shortened RT during breath holding is possibly associated with increased attention.

Coordination of trunk and pelvis in young and elderly individuals during axial trunk rotation.

It has been well known that complex tasks such as walking and arm reaching can be achieved by the coordination of the trunk and pelvis. However, understanding of the effect of aging on the coordination of the trunk and pelvis during axial trunk rotation is still lacking. The present study examined relative phase of the trunk and pelvis during axial trunk rotation, and compared it between young and older groups. 22 healthy young (age: 23.9±4.6, gender: 11 male and 11 female) and 22 healthy elderly (age: 68.4±4.9, gender: 11 male and 11 female) individuals participated in the experiment and performed axial trunk rotation. Relative phase between the trunk and pelvis was calculated based on the angular displacements of the two segments. The results demonstrated age-related changes in coordination pattern of the trunk and pelvis during axial trunk rotation.

Factors affecting shoulder-pelvic integration during axial trunk rotation in subjects with recurrent low back pain.

INTRODUCTION: Shoulder-pelvic integration could play a central role in the control of dynamic posture and movement. However, kinematic coordination during axial trunk rotation has not been carefully investigated in subjects with recurrent low back pain (LBP). The purpose of this study was to compare the maximum rotational angles of the shoulders and pelvis in the transverse plane between subjects with and without recurrent LBP. MATERIALS AND METHODS: A total of 38 age-matched subjects (19 control subjects: 69.00 ± 5.75 years old and 19 subjects with LBP: 68.79 ± 5.40 years old) participated in the study. The axial trunk rotation test was conducted in the upright position with bilateral hips and knees fully extended and both feet shoulder width apart. RESULTS: The results of this study indicated that there was a difference in pelvic girdle rotation between groups (100.79 ± 26.46 in the control group, 82.12 ± 23.16 in the LBP group; t = 2.31, p = 0.02); however, there was no difference for the shoulder girdle (177.63 ± 36.98 in the control group, 156.42 ± 30.09 in the LBP group; t = 1.91, p = 0.06). There were interactions with age (F = 9.27, p = 0.004) and BMI (F = 7.50, p = 0.01) with the rotational angles of the shoulder and pelvis. CONCLUSION: These results indicated a different pattern of trunk rotation movement with the age and BMI serving as important factors to consider for recurrent LBP. The results of our study also indicated a different pattern of shoulder and pelvic coordination with age and gender. Clinicians need to consider the consequences of limited shoulder-pelvic rotational angles, especially limited rotational angle on the pelvis during trunk axial rotation. Further studies are required to determine the causes of the underlying problems for clinical decision-making and altered shoulder-pelvic rotation in subjects with recurrent LBP.

Three-dimensional kinematic lumbar spine motion analyses of trunk motion during axial rotation activities.

STUDY DESIGN: An experimental design was conducted to investigate kinematic changes in 3-dimensional trunk motions between subjects with and without chronic low back pain (LBP) while demonstrating axial rotation. OBJECTIVES: The purpose of this study was to compare 3-dimensional kinematic data for the upper and lower thorax and the lumbar spine from the axis of the core spine during axial rotation activities in the standing position while considering anthropometric factors in subjects with and without LBP. SUMMARY OF BACKGROUND DATA: Rotation of the trunk is associated with a large number of LBP cases and surrounding spinal tissue injuries. METHODS: Fifteen subjects with chronic LBP (5 men, 10 women) and 15 subjects without LBP (9 men, 6 women) participated in this study. The outcome measures included kinematic data of actual trunk rotation angles for the upper and lower thorax and the lumbar regions relative to the core spine (spinal root) in sagittal, coronal, and transverse axes. RESULTS: The spinal range of motion was significantly different for each spinal region (F=240.25, P=0.001) and axis (F=213.91, P=0.001). There was a significant interaction between the spinal region and the group (F=4.34, P=0.04). There was also a 3-way interaction with the spinal region, the axis, and the group (F=11.04, P=0.001). These results indicated that spinal region and axes are important to consider because the upper thorax demonstrated a significantly greater rotational displacement in subjects with chronic LBP. Among the anthropometric factors, age (F=6.24, P=0.02) interacted with the spinal region and the axis. CONCLUSIONS: Decreased spinal range of motion in older subjects might result in a stiffened spine in addition to possible poor proprioception from back injuries to passive structures in subjects with chronic LBP.

No graded responses of finger muscles to TMS during motor imagery of isometric finger forces.

Previous studies of motor imagery have shown that the same neural correlates for actual movement are selectively activated during motor imagery of the same movement. However, little is known about motor imagery of isometric force. The aim of the present study was to investigate the neural correlates involved in motor imagery of isometric finger forces. Ten subjects were instructed to produce a finger flexion or extension force ranging from 10% to 60% of maximal isometric force and to mentally reproduce the force after an eight-second delay period. Transcranial magnetic stimulation (TMS) was applied over the hand motor area during imagining the force. We measured the amplitude of motor evoked potentials (MEPs) from the flexor digitorum superfialis (FDS) and the extensor digitorum communis (EDC) muscles and TMS-induced forces from the proximal phalanxes. The results showed that, as compared to the rest condition, the MEP amplitude was greater in the FDS during imagining flexion forces, whereas it was greater in the EDC during imagining extension forces. MEP amplitudes were similar for motor imagery of graded flexion or extension forces. Also, TMS produced flexion forces during imagining flexion forces, whereas it produced extension forces during imagining extension forces. There was no change in the amplitude of TMS-induced forces across graded motor imagery task. These results support the notion that the same neural correlates for actual movement could be selectively activated during motor imagery of the same movement, but demonstrated that the magnitude of isometric force could not be mentally simulated.

Finger force perception during ipsilateral and contralateral force matching tasks.

The aims of the present study were to compare matching performance between ipsilateral and contralateral finger force matching tasks and to examine the effect of handedness on finger force perception. Eleven subjects were instructed to produce reference forces by an instructed finger (index-I or little-L finger) and to reproduce the same amount force by the same or a different finger within the hand (i.e., ipsilateral matching task), or by a finger of the other hand (i.e., contralateral matching task). The results of the ipsilateral and contralateral tasks in the present study commonly showed that (1) the reference and matching forces were matched closely when the two forces were produced by the same or homologous finger(s) such as I/I task; (2) the weaker little finger underestimated the magnitude of reference force of the index finger (I/L task), even with the higher level of effort (relative force), but the two forces were matched when considering total finger forces; (3) the stronger index finger closely matched the reference force of the little finger with the lower level of relative force (i.e., L/I task); (4) when considering the constant errors, I/L tasks showed an underestimation and L/I tasks showed an overestimation compared to I/I tasks. There was no handedness effect during ipsilateral tasks. During the contralateral task, the dominant hand overestimated the force of the non-dominant hand, while the non-dominant hand attempted to match the absolute force of the dominant hand. The overall results support the notion that the absolute, rather than relative, finger force is perceived and reproduced during ipsilateral and contralateral finger force matching tasks, indicating the uniqueness of finger force perception.

The effect of intervening forces on finger force perception.

The purpose of the present study was to investigate the effect of intervening forces on the estimation of finger forces. To do this, we introduced intervening forces during a delayed force matching task. The basic idea in the present study was that when a reference force (or to-be-remembered force) is followed by another force, this second force (i.e., intervening force) will interfere with the estimation of the reference force. Subjects performed a modified delayed force matching task using the index finger of their dominant hand. This study consisted of eight experimental conditions which combined two reference forces (i.e., 10 and 30% MVCs) with four intervening forces (i.e., No, Half, Same and Double the reference force). The main finding of the present study was that the matching performance was systematically affected by intervening forces. The results showed that the reference force was underestimated in the condition where the intervening force was half the reference force, and overestimated in the condition where the intervening force was double the reference force. When the reference and intervening forces were the same, no intervening force effect was found. The effect of intervening force was explained by a distortion of force memory.

Perception of finger forces within the hand after index finger fatiguing exercise.

The effect of fatigue on finger force perception within a hand during ipsilateral finger force matching was examined. Thirteen subjects were instructed to match a reference force of an instructed finger using the same or different finger within the hand before and after index finger fatigue. Absolute reference force targets for the index or little finger were identical during pre- and post-fatigue sessions. Fatigue was induced by a 60-s sustained maximal voluntary contraction (MVC) of the index finger. Index finger MVC decreased approximately 29%, while there was a non-significant (about 5%) decrease in the little finger MVC. The results showed that: (1) the absolute reference and matching forces of the instructed fingers were not significantly changed after fatigue, while the total forces (sum of instructed and uninstructed finger forces) were increased after fatigue. (2) The relative forces (with respect to corresponding pre- and post-fatigue MVCs) of the index finger increased significantly in both reference and matching tasks, while the relative forces of the little finger remained unchanged after fatigue. (3) Matching errors remained unchanged after fatigue when the fatigued index finger produced the reference force, while the errors increased significantly when the fatigued index finger produced the matching force. (4) Enslaving (difference between total and instructed finger forces) increased significantly after fatigue, especially during force production by the fatigued index finger and when the little finger produced matching forces at higher force levels. (5) Enslaving significantly increased matching errors particularly after fatigue. Taken together, our results suggest that absolute finger forces within the hand are perceived within the CNS during ipsilateral finger force matching. Perception of absolute forces of the fatigued index finger is not altered after fatigue. The ability of the fatigued index finger to reproduce little finger forces is impaired to a certain degree, however. The impairment is likely to be attributable to altered afferent/efferent relationships of the fatigued index finger.