Biomedical subjects

M W Rogers

Publications and source records attributed to M W Rogers.

29 records · Page 2Linked to original sources

PubMed1992

Influence of task dynamics on the organization of interlimb responses accompanying standing human leg flexion movements.

The organization of electromyographic (EMG) and kinetic (ground reaction forces) responses in postural (single stance limb) and primary task (flexing limb) components was examined in standing human subjects during single leg flexion movements over a range of speeds. Interlimb responses occurred coincidently prior to unloading and were scaled as a function of movement speed, suggesting a centrally organized, synchronous mode of coordination which reflected the mechanical constraints related to stance support function.

Adult↗

PubMed1992

Age-related changes in postural responses preceding rapid self-paced and reaction time arm movements.

The electromyographic responses in postural (thigh and trunk) and primary agonist (shoulder) muscles were examined in standing young and older adults prior to rapid self-paced (SP) and simple reaction time (RT) arm flexion movements. In contrast to younger subjects, older adults demonstrated significantly lower frequencies of trials for self-paced movements in which thigh muscle responses preceded the activation of the shoulder muscle. Furthermore, younger adults showed more frequent early lower limb postural responses for SP versus RT movements, whereas older subjects retained comparable frequencies between task conditions. Overall, a significantly shorter intermuscular timing interval between leg and arm muscle onsets was also found for the older group.

Adult↗

PubMed1992

Reliability of ground reaction force measurements during dynamic transitions from bipedal to single-limb stance in healthy adults.

The consistency of ground reaction force (GRF) variables underlying dynamic transitions from bipedal to single-limb stance during a single-leg flexion movement was examined in 18 healthy adult subjects aged 21 to 47 years (mean = 31.1, SD = 8.6). Force platforms were used to measure the GRFs during fast and natural speeds of movement. Separate intraclass correlation coefficients (ICCs) were calculated for three temporal variables (ie, onset of the propulsive and braking phases of the lateral horizontal GRF component and time to unload the flexing limb) and for two magnitude variables (ie, propulsive impulse [PROP] and braking impulse [BRAK]). The ICCs for both PROP and BRAK were > or = .73 for fast movements and > or = .88 at the natural speed. The ICCs for the temporal variables were > or = .66 at fast speeds and > or = .37 at the natural speed. We concluded that measurements of PROP and BRAK are reliable across a range of speeds during transitions in stance support and that these variables may be tightly regulated by the movement control system. Temporal variables, particularly at the natural speed, exhibited lower reliability estimates, suggesting that measurements of these events have greater variability. Reliability of measurements of GRF variables provides useful information for the clinician regarding underlying control processes governing dynamic transitions in stance support.

Adult↗

PubMed1991

Speed variation and resultant joint torques during sit-to-stand.

The purpose of this study was to test the hypothesis that a progressively faster speed of ascent requires significantly greater peak resultant joint torque (RJT) at major load-bearing joints of the lower limb during the sit-to-stand (STS) transfer. Eight healthy adults performed the STS at slow, natural, and fast speeds. A motion analysis system and two force platforms were employed to record kinetic data, and equations of motion were applied to compute the RJT for the ankle, knee, and hip. The results of the study supported the hypothesis that when the speed of ascent increased progressively, the peak hip flexion, knee extension, and ankle dorsiflexion RJTs increased disproportionately. However, the peak hip extension and ankle plantar flexion RJTs remained relatively constant across the range of the speeds. Implications for clinical practice pertaining to the timing and magnitude of RJT, as well as for interventions that emphasize the adaptive characteristics of movements, are suggested.

Adult↗

PubMed1991

Segmental contributions to total body momentum in sit-to-stand.

In a previous investigation, we reported that the maximum linear momentum of the body center of mass (CM) during a sit-to-stand task showed a relative invariance in the horizontal vs the vertical direction of motion as the speed of ascent increased from natural to fast. The present study investigated the segmental origin of this directionally specific difference by examining the linear momentum of the shank, thigh, and head-arm-trunk segments for ten healthy young adults at slow, natural, and fast self-selected speeds. Findings indicated that the head-arm-trunk was the major contributor to the horizontal maximum linear momentum of the CM and accounted for the relative invariance in its magnitude. In contrast, the thigh was the major contributor to the vertical maximum linear momentum of the CM and was responsible for the progressive increase in its magnitude across the range of speeds. Moreover, the compatibility between the motions of the head-arm-trunk and of the shank in their general profile and peak magnitudes further suggested that a simplifying strategy may have been employed to reduce the overall number of degrees of freedom associated with the sit-to-stand movement.

Adult↗

PubMed1990

Dynamic transitions in stance support accompanying leg flexion movements in man.

The control processes underlying dynamic transitions in stance support during single leg flexion movements were investigated in human subjects as a function of the intended speed of movement, by examining the vertical and lateral horizontal components of the ground reaction forces, the frontal plane trajectory of the body center of mass (CM) recorded via motion analysis, and the electromyographic (EMG) recordings of selected lower limb muscles. For the slowest movements, the measured vertical force beneath the flexing and single stance limbs closely matched the vertical force-time history predicted by a quasi-static mechanical model, whereas, the more rapid natural and fast speeds showed progressively larger discrepancies between measured and predicted forces. The initial resultant horizontal force component was exerted in the flexing to stance limb direction but was proportionately greater (4:1) beneath the flexing versus the stance limb during fast and natural speeds, and became equivalent for slow movements. Speed related EMG differences included an early phasic recruitment of the lateral hip muscle of the flexing limb which always preceded the ground reaction force changes for fast and natural but not slow movements, and a considerably earlier onset of the stance leg knee extensor relative to the flexing limb knee flexor for slow versus fast and natural speeds. Overall, the findings suggested two different speed related strategies for linking the postural and intentional movement components, where the choice of the strategy selected appeared to reflect the mechanical requirements needed to overcome the inertial force of the body mass during transitions from bipedal to single limb stance support.

Adult↗

PubMed1990

Control of body mass transfer as a function of speed of ascent in sit-to-stand.

The purpose of this study was to test the hypothesis that a progressive variation in the speed of ascent would result in differences in the horizontal and vertical motions of the body center of mass (CM) and in the governing impulse-momentum relationship. A motion analysis system and two force platforms were used to examine the STS task among 10 healthy adults at each of three self-selected speeds. As the speed of ascent became faster, a progressively earlier time to the maximum vertical linear momentum and an increase in its magnitude occurred. In contrast, a relatively constant time to the maximum linear momentum, which was also the time when the propulsive impulse became the braking impulse, was found in the horizontal direction, and the propulsive impulse showed a disproportionately (1:3) smaller increase from slow to fast speeds than its vertical counterpart. The relative invariance in the horizontal motion suggested that different neuromuscular control strategies may have been employed in the horizontal and vertical directions to accomplish the different tasks of balance control in one direction and changing the gravitational potential energy in the other direction.

Adult↗

PubMed1988

Motor planning is impaired in Parkinson's disease.

Reaction times (RTs) were assessed in parkinsonian and normal subjects under simple ballistic (bRT), simple tracking (tRT), and choice tracking (CRT) ankle plantarflexion RT paradigms. While RTs were prolonged in both groups for tracking versus bRT movements, between-group differences were not detectable for the simple RT (either ballistic or tracking) tasks. In contrast, parkinsonians demonstrated significantly greater CRT and CRT-bRT delays than normals, suggesting that parkinsonian akinesia may involve a disturbance in central processing related to motor planning.

Aged↗

PubMed1987

Postural adjustments preceding rapid arm movements in parkinsonian subjects.

The electromyographic (EMG) responses in postural (thigh and trunk) and agonist (shoulder) muscles were examined in standing parkinsonian subjects and healthy controls prior to visual reaction time and self-paced rapid arm flexion movements. Recruitment of postural muscles typically preceded arm displacement in normals, but was less frequent, of shorter duration, and characterized by multiple EMG bursts which extended to the agonist in parkinsonians. Moreover, parallel delays in EMG recruitment times relative to the visual signal for both postural and agonist muscles were observed in akinetic patients. These abnormalities suggest that the basal ganglia may serve a preparatory motor function, by linking synergistic muscles through a common selection process.

Aged↗

PubMed1987

Effects of arm acceleration and behavioral conditions on the organization of postural adjustments during arm flexion.

Nine standing subjects performed unilateral arm flexion movements over an eight-fold range of speeds, under two behavioral conditions. In the visually-guided condition, a visual target informed subjects about the correct movement speed. Seven subjects also made movements of different speeds during a self-paced condition, without a visual target. Angular displacement and acceleration of the arm, and EMG activity from the hamstrings (HM), erector spinae (ES) and the anterior deltoid (AD) muscles were measured. The following results were observed. Mean rectified amplitudes of EMG activity in HM and ES were typically correlated with the average arm acceleration and presumably the disturbance to posture and/or balance. HM and ES amplitudes were correlated for only six subjects. Functions relating the ratios of HM/ES EMG amplitudes to acceleration varied between subjects. HM onset latencies were highly variable for slow movements and usually lagged movement. For movements above a threshold-like point in acceleration, HM latencies were correlated with arm acceleration and recruited before movement. ES latencies were constant for fast movements, and negatively correlated with acceleration for slower movements. The recruitment order of HM and AD was influenced by the behavioral condition but not by arm acceleration for fast movements. HM and AD were recruited coincidentally for visually-guided movements, while for self-paced movements, HM was recruited before AD. We conclude that for the arm flexion task: HM and ES are not tightly coupled; both behavioral and mechanical conditions affect the recruitment of postural muscles; and postural and focal components of the movement are probably organized by parallel processes.

Acceleration↗

PubMed1982

Factors contributing to the regulation and clinical assessment of muscular strength.

This paper reviews the physiological, anatomical, and biomechanical factors that contribute to the regulation of muscular strength and the factors to be considered in the clinical assessment of strength. In light of the procedural and mechanical aspects discussed, a comparison of various strength testing methods is made in order to assist the therapist in selecting the appropriate testing procedure to meet his objectives.

Biomechanical Phenomena↗