Biomedical subjects

Rahul Marwaha

Publications and source records attributed to Rahul Marwaha.

4 recordsLinked to original sources

PubMed2006

Load and grip force coordination in static bimanual manipulation tasks in multiple sclerosis.

The aim of the study was to reveal specific aspects of impaired hand function in mildly affected multiple sclerosis (MS) patients. Static manipulation tasks were tested in 13 mildly impaired (EDSS 1.5-4) MS patients and 13 age and gender matched controls. The tasks were based either on presumably visually (i.e., feedback) controlled tracing of depicted patterns of load force (LF; produced by symmetric bimanual tension and/or compression applied against an externally fixed device) or on predominantly feed-forward controlled amplitudes of sinusoidal patterns of LF. The task variables (based on accuracy of exerting the required LF pattern) suggested poor performance of MS subjects in feedback, but not in the feed-forward controlled tasks. The patients also revealed higher GF/LF ratio in all tasks. However, the coordination of GF and LF appeared to be comparable in the two groups. These results continue to support the chosen experimental paradigm and suggest that in mildly affected MS patients, sensorimotor deficits and overgripping precede the decoupling of grip and load forces observed in more severely affected patients.

Adult↗

PubMed2005

Interlimb and within limb force coordination in static bimanual manipulation task.

The aim of the study was to compare the coordination of hand grip (G) and load force (a force that tends to cause slippage of a grasped object; L) in static bimanual manipulation tasks with the same data obtained from the similar dynamic tasks. Based on the previous findings obtained from dynamic tasks, it was hypothesized that an increase in the rate of L change would be predominantly associated with a decrease in the coordination of the within limb forces (coordination of G and L of each hand as assessed through the correlation coefficients), while a decrease in coordination of interlimb forces (between two G and two L) will be less pronounced. Regarding the pattern of modulation of G, the same increase in L frequency was also expected to be associated with a decrease in G gain and an increase in G offset (as assessed by slope and intercept of the regression lines obtained from G to L diagrams, respectively), as well as with an increase in average G/L ratio. Subjects exerted oscillatory isometric L profiles by simultaneous pulling out two handles of an externally fixed device under an exceptionally wide range of L frequencies (0.67-3.33 Hz). The results demonstrated relatively high correlation coefficients between both the interlimb and within limb forces that were only moderately affected under sub-maximal L frequencies. Furthermore, the hypothesized changes in G gain and offset appeared only under the highest L frequency, while the G/L ratio remained unaffected. We conclude that, when compared with the dynamic tasks based on the unconstrained movements of hand-held objects that produce similar pattern of L change, the static manipulation tasks demonstrate a consistent and highly coordinated pattern of bilateral G and L under a wide range of frequencies. However, the neural mechanisms that play a role in the revealed differences need further elucidation.

Adult↗

PubMed2005

Coordination of hand grip and load forces in uni- and bidirectional static force production tasks.

The purpose of the study was to explore the differences in coordination of grip (G) and load forces (L) in a unidirectional and bidirectional bimanual static force production task. Subjects (N=10) exerted oscillatory isometric L profiles against an externally fixed hand-held device, modulated either in pure tension (unidirectional) or in alternating tension and compression (bidirectional) at a rate of either 1.33 or 2.67 Hz. The unidirectional task revealed a high level of coordination of both the ipsilateral (i.e., G and L of each hand) and contralateral pairs of forces (two Gs and two Ls) as assessed by correlation and stability of force ratios. The bidirectional task demonstrated a low level of inconsistently modulated Gs with respect to the change of L, which resulted in a deteriorated coordination, particularly between the ipsilateral forces. The overall effect of task on the force coordination was higher than the effect of frequency suggesting that the higher frequency of G modulation required in the bidirectional task is not likely to be the main cause of the observed phenomenon. We interpret these differences by a relative simplicity of the control mechanisms of the unidirectional task based on a single synergy of G and L muscles that allows simultaneous coordination of both the ipsilateral and contralateral forces. Due to the switching between two distinctive synergies involving G muscles, the bidirectional task could possess a higher control complexity causing a decoupled coordination of the ipsilateral forces, while retaining the coordination of contralateral forces at a relatively high level.

Adult↗

PubMed2005

Evaluation of a method for bimanual testing coordination of hand grip and load forces under isometric conditions.

The purpose of the study was to evaluate a method for testing bimanual prehension based on a novel experimental device. The device consists of two handles allowing for simultaneous measurement of bimanual hand grip forces (GF) and different patterns of load forces (LF) exerted during compression and tension along the longitudinal axis. In order to assess the reliability of the obtained measures, eight healthy subjects were tested over three consecutive test, while three moderately impaired neurological patients were tested once. In healthy subjects, high coordination was observed between GFs and LFs, as well as between two GFs and two LFs. The results also suggest a satisfactory task performance in regards to exerting the instructed LF profile, as well as a sufficient, but not excessive GF. The reliability of most of the assessed variables proved to be either moderate or high. When compared to healthy subjects, the data obtained from neurological patients mainly revealed irregular patterns of LFs, excessive GFs, as well as a relatively weak relationship between GFs and LFs. It was concluded that the evaluated methodological approach can be applied not only to explore uni- and bi-manual coordination of arm and hand grip forces in various prehensile activities, but also to serve as a basis for future development of specific clinical tests for neurological patients and other populations that demonstrate impaired hand function.

Adult↗