PubMed Health⌕ Search

Biomedical subjects

R W Christina

Publications and source records attributed to R W Christina.

8 recordsLinked to original sources
PubMed1990

Time needed to change the isometric force production of a response.

This study investigated the time needed to change a motor program that specified the elbow flexor muscles to gradually increase the isometric force production from 15% to 75% of one's maximum voluntary contraction (MVC). A double-stimulation paradigm was used with the restriction that subjects (N = 12) be at 15% of their MVC before the presentation of the first stimulus. Subjects reacted to the first stimulus (randomly presented) by gradually increasing their isometric force from 15% to 75% of their MVC and then reacted to the second stimulus by altering the force production in one of four ways: (a) increasing the force to the 75% level rapidly instead of gradually, (b) discontinuing the increase and maintaining the level of force attained, (c) discontinuing all force production, or (d) reversing the direction of force so that it is produced by the elbow extensors. The data revealed that more time was needed to increase the force rapidly than to perform any of the other three conditions.

Adult↗
PubMed1989

Psychomotor decline can be described by discontinuities in response trajectories: comments on Vrtunski and Patterson (1985).

Five methodological and experimental design concerns are identified in Vrtunski and Patterson's (1985) article. The discussed concerns involved: (a) the use of misleading premotor segment terminology, (b) the uncertain status of the repeated measures sphericity assumptions, (c) mean calculations across unequal trials of the four levels of stimulus conditions, (d) improper selection of a main effect for post hoc analysis and discussion of these results when a significant interaction was present, and (e) conflicting text and table values. These concerns have prompted us to question their psychomotor decline conclusions. And unless Vrtunski and Patterson can convince us that these concerns are unjustified, we have no choice but to doubt seriously the validity of their conclusions.

Animals↗