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Nobuyuki Inui

An experiment was conducted to examine the coupling of force variability in bimanual finger tapping sequences with asymmetrical forces. Right-handed participants were trained to produce bimanual finger tapping sequences consisted of an intertap interval of 500 ms and eight force conditions: two alternating force left high, two alternating force right high, two simultaneous force left high, and two simultaneous force right high conditions. During practice, visual force feedback was provided for both hands performing the bimanual tapping sequences. After practice, the participants produced the learned tapping sequences in the absence of feedback. Most importantly, whereas the peak force variability of the nondominant left hand was larger than that of the dominant right hand under the right high conditions, there was no left–right difference under the simultaneous left high conditions. This suggests that under the simultaneous left high conditions, both hemispheres were activated, resulting in overflow in the right hand, and bringing the two force variabilities closer together.

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E. Yu Shapkova, A.V. Terekhov and M.L. Latash

We studied the coordination of arm movements in standing persons who performed an out-of-phase arm-swinging task while stepping in place or while standing. The subjects were instructed to stop one of the arms in response to an auditory signal while trying to keep the rest of the movement pattern unchanged. A significant increase was observed in the amplitude of the arm that continued swinging under both the stepping and standing conditions. This increase was similar between the right and left arms. A dynamic model was developed including two coupled nonlinear van der Pol oscillators. We assumed that stopping an arm did not eliminate the coupling but introduced a new constraint. Within the model, superposition of two factors, a command to stop the ongoing movement of one arm and the coupling between the two oscillators, has been able to account for the observed effects. The model makes predictions for future experiments.

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Joseph O.C. Coyne, Sophia Nimphius, Robert U. Newton and G. Gregory Haff

acute rolling average (ATL) divided by the 28-day chronic rolling average (CTL), although several studies have assessed the ACWR using weekly data. 1 , 3 The use of the ACWR is contentious, with 1 criticism of the ACWR suggesting that the mathematical coupling in the calculation of the ACWR (ie

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Kunlin Wei, Gary Wertman and Dagmar Sternad

An asymmetric bimanual task was investigated in which participants performed a rhythmic movement with their dominant arm and initiated a second movement with their nondominant arm at a random phase of the continued oscillations. The objective was to examine whether different constraints existed between rhythmic and discrete movements and, more generally, whether rhythmic and discrete movements can be regarded as two different movement primitives. Participants performed rhythmic forearm rotations at 1 of 4 prescribed metronome periods. After a random interval, a trigger signaled to initiate either a discrete or rhythmic movement with the left forearm as fast as possible while continuing the oscillations. Analyses extracted the mutual influences that the two movements exerted on each other and contrasted discrete-rhythmic and rhythmic-rhythmic coupling. (a) The initiation of the rhythmic movement was constrained to occur in-phase with the ongoing rhythmic movement, while the discrete movement could be initiated at any arbitrary phase. (b) Reaction time of the initiated rhythmic movement scaled with the oscillation period, while the discrete movement's reaction time was invariant across periods. (c) Peak velocity of the initiated movement scaled with the oscillatory period in both tasks but more strongly in the discrete movement. (d) Synchronization of EMG bursts of both arm flexors was evident in both tasks but more strongly in the rhythmic-rhythmic combination. The results are interpreted as support for the hypothesis that discrete and rhythmic actions are two different control regimes, and coupling occurs at a higher level in the central nervous system.

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Mark D. Tillman, Chris J. Hass, John W. Chow and Denis Brunt

During ballistic locomotion and landing activities, the lower extremity joints must function synchronously to dissipate the impact. The coupling of subtalar motion to tibial and knee rotation has been hypothesized to depend on the dynamic requirements of the task. This study was undertaken to look for differences in the coupling of 3-D foot and knee motions during walking, jogging, and landing from a jump. Twenty recreationally active young women with normal foot alignment (as assessed by a licensed physical therapist) were videotaped with high-speed cameras (250 Hz) during walking, jogging, hopping, and jumping trials. Coupling coefficients were compared among the four activities. The ratio of eversion to tibial rotation increased from the locomotion to the landing trials, indicating that with the increased loading demands of the activity, the requirements of foot motion increased. However, this increased motion was not proportionately translated into rotation of the tibia through the subtalar joint. Furthermore, the ratio of knee flexion to knee internal rotation increased significantly from the walking to landing trials. Together these findings suggest that femoral rotation may compensate for the increase in tibial rotation as the force-dissipating demands of the task increase. The relative unbalance among the magnitude of foot, tibial, and knee rotations observed with increasing task demands may have direct implications on clinical treatments aimed at reducing knee motion via controlling motion at the foot during landing tasks.

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C. Collin Herb, Lisa Chinn, Jay Dicharry, Patrick O. McKeon, Joseph M. Hart and Jay Hertel

Chronic ankle instability (CAI) results in longstanding symptoms and subjective feelings of “giving way” following initial ankle sprain. Our purpose was to identify differences in joint coupling and variability between shank internal/external rotation and rearfoot inversion/eversion throughout the gait cycle of CAI subjects and healthy controls. Twenty-eight young adults participated (CAI, n = 15, control, n = 13). Kinematics were collected while walking and jogging on a treadmill. A vector coding method in which direction (θ) and magnitude of the angle-angle relationship and stride-to-stride variability (VCV) in shank-rearfoot coupling were calculated. In walking, the CAI group demonstrated lower θ, indicating a greater proportion of rearfoot-to-shank motion, compared with the control group in early and late swing. The CAI group had higher magnitude, indicating greater combined motion between the two segments, in early swing, but lower magnitude, indicating less combined motion, during late swing. The CAI group also had lower VCV measures, indicating less stride-to-stride variability during stance. In jogging, the CAI group had lower θ measures than the control group during stance and swing. Differences in shank-rearfoot coupling of the CAI group may be related to changes in sensorimotor control and lead to further instances of instability.

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Mehmet Uygur, Goran Prebeg and Slobodan Jaric

We compared two standard methods routinely used to assess the grip force (GF; perpendicular force that hand exerts upon the hand-held object) in the studies of coordination of GF and load force (LF; tangential force) in manipulation tasks. A variety of static tasks were tested, and GF-LF coupling (i.e., the maximum cross-correlation between the forces) was assessed. GF was calculated either as the minimum value of the two opposing GF components acting upon the hand-held object (GFmin) or as their average value (GFavg). Although both methods revealed high GF-LF correlation coefficients, most of the data revealed the higher values for GFavg than for GFmin. Therefore, we conclude that the CNS is more likely to take into account GFavg than GFmin when controlling static manipulative actions as well as that GFavg should be the variable of choice in kinetic analyses of static manipulation tasks.

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Irene McClay and Kurt Manal

This study was undertaken to investigate whether differences exist in the coupling of foot and knee motions during the support phase of running in subjects with normal rearfoot motion and those who pronate. Excursion ratios between rearfoot eversion and tibial internal rotation were compared between the two groups. Timing between peak eversion, knee flexion, and knee internal rotation was also examined, and correlations between various foot and knee angles were assessed. Timings between peak knee and rearfoot angles were not significantly different between groups, although times were more closely matched in the normal subjects. The eversion to tibial internal rotation excursion ratio was significantly lower in the pronator subjects. Correlation analyses revealed significant relationships between a number of rearfoot and knee parameters. Results suggest that increased motion of the rearfoot can lead to excessive movement at the knee. In addition, excessive pronation may disrupt the normal kinematic interaction between the rearfoot and knee.

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S. Morrison, Murray G. Tucker and Rod S. Barrett

This study examined changes in movement variability, coupling, and muscle activity across three different bilateral finger movements (e.g., postural, isometric, and isotonic). It was predicted that movements characterized by increased interlimb coupling would be associated with increased levels of muscle activity and reduced movement variability. The results demonstrated task-specific differences in interlimb relations with coupling being lowest during postural tasks and highest under isotonic conditions. However, a similar pattern was not observed for muscle activity and movement variability. Of the three tasks, postural tremor movements were more variable and had lower levels of muscle activity. Alternatively, increased muscle activity and more regular movement dynamics were seen under isometric conditions. Overall, it would appear that differences in bilateral coupling across tasks are not reflective of a single driving mechanism but rather reflect differential contribution from intrinsic neuromuscular and mechanical sources.

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Rebecca Avrin Zifchock, Kristamarie Pratt, Allison Brown and Howard Hillstrom

The purpose of this study was to compare the magnitude of knee kinematic coupling between genders and among open- and closed-chain tasks. A secondary purpose was to compare the consistency of knee kinematic coupling between genders and among open- and closed-chain tasks. Vector-coding methods were used to quantify coupling in the sagittal and transverse planes of the knee between full extension and 20 degrees of flexion as 10 males and 10 females walked, ascended and descended stairs, and performed a passive pendulum leg drop. An ANOVA showed no main effect of gender. There was a main effect of task, where coupling during the stance phase of walking was significantly greater than each of the other tasks. Intraclass correlation values suggested that males were slightly more consistent than females. A general lack of divergence between genders may be related to the tasks analyzed in this study. It is possible that more strenuous tasks may elicit larger differences.