Biomedical subjects

Jeffrey M Schiffman

Publications and source records attributed to Jeffrey M Schiffman.

3 recordsLinked to original sources

PubMed2006

Discrete bandwidth visual feedback increases structure of output as compared to continuous visual feedback in isometric force control tasks.

BACKGROUND: Performance variability measures provide a partial picture of force control ability. Nonlinear analyses can reveal important information related to the randomness and complexity of the data, providing a more complete picture of the physiological process. METHODS: We investigated the effects of visual feedback on the structure and performance of the force output from isometric force control tasks. Twelve young volunteers completed isometric force control tasks using two types of visual feedback: discrete bandwidth (+/-4% maximal voluntary contraction) and continuous line matching. We determined force signal variability (standard deviation), self-similarity (fractal dimension), and complexity (approximate entropy). Analyses of variance (feedback x muscle group x force level) were conducted and P values less than 0.05 were considered significant. FINDINGS: The force signal in discrete bandwidth feedback, compared to continuous line matching, had significantly a higher standard deviation (P=.000): 2.18 Nm (SD 1.98) vs. 0.99 Nm (SD 0.91); lower fractal dimension (P=.000): 1.07 (SD 0.04) vs. 1.16 (SD 0.04); and lower approximate entropy (P=.000): 0.12 (SD 0.07) vs. 0.26 (SD 0.09). INTERPRETATION: The greater self-similarity (lower fractal dimension) and greater regularity (lower approximate entropy) of the discrete bandwidth, compared to the continuous line matching, may indicate a process that required more kinesthetic (intrinsic) feedback to modulate force. Clinicians may choose to employ visual feedback paradigms that target the use of intrinsic feedback during rehabilitation. Discrete bandwidth feedback may be useful for delineating impairments in motor skill and measuring outcomes of intervention programs.

Adult↗

PubMed2005

Effects of carried weight on random motion and traditional measures of postural sway.

The purpose of the study was to investigate the effects of load weight carried by soldiers upon postural sway. Fourteen US Army enlisted men participated. Postural sway and muscle activity were measured while participants stood on a force plate. The load weight conditions, comprised of Army clothing and load-carriage equipment were 6, 16, and 40 kg. With an increase in load weight, stabilogram-diffusion analysis revealed that random movement of postural sway decreased. Also, with an increase in load weight, center of pressure excursions increased linearly but muscle activity changed minimally. In short, increasing load weight challenged the load carriers' stability, reduced the randomness of postural sway and required the load carriers to exert greater control of the load in order to maintain balance.

Adolescent↗

PubMed2004

Effects of step length on stepping responses used to arrest a forward fall.

This study investigated effects of step length on the stepping response used to arrest an impending forward fall. Twelve healthy young (mean age 22, S.D. 3.3 years) males participated by recovering balance with a single step following a forward lean-and-release. Participants were instructed to step to one of three floor targets representing small, natural, and large step lengths. The effect of step length was examined on the primary outcome variables: pushoff time, liftoff and landing time, swing duration, balance recovery time, landing impulse, and center of mass (COM) characteristics. Pushoff and liftoff times were not affected by step length, although swing phase duration, landing and recovery times and the anterior-posterior (AP) impulse at landing increased with increasing step length. The results support the idea of an invariant step preparation phase. Given that our participants naturally chose not to utilize a step as short as they were capable of employing, healthy young individuals do not minimize recovery time nor strength requirements when selecting their step length.

Accidental Falls↗