Biomedical subjects

William P Berg

Publications and source records attributed to William P Berg.

5 recordsLinked to original sources

PubMed2006

Fatigue-induced adaptive changes of anticipatory postural adjustments.

To examine the fatigue-induced adaptive changes (e.g., timing) of anticipatory postural adjustments (APAs), APAs of 30 research participants were recorded before (baseline) and after (post-test) conditions of either rest (control group, n=15) or fatigue (fatigue group, n=15). Muscle fatigue was generated using a dead-lift exercise performed to exhaustion. Self-initiated postural perturbations were induced using a rapid unilateral arm-raising maneuver (focal movement), and APAs were obtained using electromyography (EMG) recorded bilaterally in the lumbar and thoracic paraspinal muscles as well as the hamstring muscles. Postural stability during the focal movement was assessed using a force plate. Results showed that fatigue had no effect on postural stability during the focal movement, and yet caused earlier APA onsets in three of the six muscles evaluated. In spite of early APA activation, the APA EMG integrals of two of the three postural control muscles which exhibited fatigue-induced early APA onsets (T9 and L4 contralateral paraspinals) did not differ between baseline and post-test measures. The findings suggest that early APA onset may enhance postural stability by permitting a longer duration APA which can counteract fatigue-induced decreases in the force-producing capability of muscles that contribute to postural stability.

Adaptation, Physiological↗

PubMed2006

The effect of the direction of gaze on the kinematics of the squat exercise.

The purpose of this study was to determine whether the direction of gaze influences the kinematics of the squat exercise. Ten men experienced in the squat exercise performed a total of 30 repetitions of the squat in the form of 2 sets of 5 repetitions under 3 different conditions. Conditions varied with respect to the direction of the subjects' gaze as they performed the exercise. Condition D entailed gazing downward at the intersection of the facing wall and the floor throughout the exercise. Condition S required subjects to gaze straight ahead at their own reflection (eyes) in the mirror on the wall directly in front of them. Condition U involved gazing upward at the intersection of the facing wall and the ceiling throughout the exercise. Dependent variables included the linear displacement of the bar and hip, linear velocity of the bar, and the angular displacement/position and velocity of the head, trunk, hip, and knee. The mean data were subjected to a repeated measures analysis of variance, and, where appropriate, pairwise comparisons using Tukey's Studentized Range Test. The results revealed overall similarity in movement kinematics when performing the squat exercise using the 3 different gaze directions. In particular, the upward and straight gaze conditions were not differentiated by the analysis. Conversely, the downward gaze was shown to increase the extent of hip flexion (F[2, 9] = 4.82, p < .05), especially relative to the upward gaze, and possibly trunk flexion as well (F[2, 9] = 3.02, p = .07). In terms of the practical application, because excessive hip and trunk flexion in the squat are contraindicated, cautioning athletes against allowing the head or direction of gaze to drop below a neutral position appears to be warranted.

Adult↗

PubMed2005

Information for step length adjustment in running.

The purpose of this study was to directly test the hypothesis that the tau parameter, as introduced by Lee et al. [Lee, D. N., Lishman, J. R., & Thomson, J. A. (1982). Regulation of gait in long jumping. Journal of Experimental Psychology: Human Perception and Performance, 8, 448-459] and Warren et al. [Warren, W. H., Young, D. S., & Lee, D. N. (1986). Visual control of step length during running over irregular terrain. Journal of Experimental Psychology: Human Perception and Performance, 12, 259-266], is the primary information used to regulate step length in running toward a ground target. Visual information available to research participants performing a facsimile of a long jump approach run was manipulated, and the effects on task performance and running gait were observed. Task performance and running gait were unaffected or minimally affected by (a) a perturbation of the normal optical expansion of the target, (b) elimination of global optical flow - including the focus of expansion, and (c) elimination or severe degradation of visual information about distance from the target as well as running velocity. The findings are inconsistent with notions that time-to-arrival with a ground target while running is predominantly specified optically by (a) local tau, (b) global tau, or (c) a distance/velocity computational strategy. A multisensory tau hypothesis regarding informational support for step length adjustment in running is offered.

Adaptation, Physiological↗

PubMed2003

Effect of cellular telephone conversations and other potential interference on reaction time in a braking response.

This experiment studied the effect of phone conversations and other potential interference on reaction time (RT) in a braking response. Using a laboratory station which simulated the foot activity in driving, 22 research participants were requested to release the accelerator pedal and depress the brake pedal as quickly as possible following the activation of a red brake lamp. Mean reaction time was determined for five conditions: (a) control, (b) listening to a radio, (c) conversing with a passenger, (d) conversing using a hand-held phone, and (e) conversing using a hands-free phone. Results indicated that conversation, whether conducted in-person or via a cellular phone caused RT to slow, whereas listening to music on the radio did not.

Adolescent↗

PubMedDate not supplied

Differential mastication kinematics of the rabbit in response to food and water: implications for conditioned movement.

Analysis of naturalistic chewing patterns may provide insight into mapping the neural substrates of jaw movement control systems, including their adaptive modification during the classically conditioned jaw movement (CJM) paradigm. Here, New Zealand White rabbits were administered food and water stimuli orally to evaluate the influence of stimulus consistency on masticatory pattern. Chewing patterns were recorded via video camera and movements were analyzed by computerized image analysis. The mandibular kinematics, specifically the extent of dorsal/ventral, medial/lateral, and rostral/caudal movement, were significantly larger in food-evoked than water-evoked chewing. Water-evoked chewing frequency, however, was significantly higher than that of food-evoked movements. In light of known cortical mastication modulatory centers, our findings implicate different neural substrates for the responses to food and water stimuli in the rabbit. A detailed delineation of jaw movement patterns and circuitry is essential to characterize the neural substrates of CJM.

Animals↗