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This Article Full Text Full Text (PDF) All Versions of this Article: 107/4/1113    most recent 00480.2009v1 Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Vianna, L. C. Articles by Fisher, J. P. PubMed PubMed Citation Articles by Vianna, L. C. Articles by Fisher, J. P.

Influence of central command and muscle afferent activation on anterior cerebral artery blood velocity responses to calf exercise in humans

¹School of Sport and Exercise Sciences, University of Birmingham, Edgbaston, Birmingham, United Kingdom; and ; ²Graduate Program in Physical Education, Gama Filho University, Rio de Janeiro, Brazil

Submitted 9 May 2009 ; accepted in final form 9 August 2009

The purpose of the present study was to determine the relative importance of peripheral feedback from mechanically (mechanoreflex) and metabolically (metaboreflex) sensitive muscle afferents and central signals arising from higher centers (central command) to the exercise-induced increases in regional cerebral perfusion. To accomplish this, anterior cerebral artery (ACA) mean blood velocity (V_mean) responses were assessed during sustained and rhythmic passive calf muscle stretch (mechanoreflex), volitional calf exercise (mechanoreflex, metaboreflex, and central command), and electrically stimulated calf exercise (mechanoreflex and metaboreflex but no central command) at 35% of maximum voluntary contraction (n = 16). In addition, a period of postexercise muscle ischemia (PEMI) was used to isolate the metaboreflex. Blood pressure, cardiac output, and the end-tidal partial pressure of carbon dioxide (PET_CO2) were also measured. ACA V_mean was unchanged from rest during either sustained or rhythmic calf muscle stretch (P > 0.05). However, ACA V_mean was increased from rest during both isometric (+15 ± 1%) and rhythmic (+15 ± 2%, voluntary exercise P < 0.05) but remained unchanged during stimulated exercise (P > 0.05). Isometric and rhythmic exercise-induced increases in blood pressure and cardiac output were similar during voluntary and stimulated exercise (P > 0.05 between conditions). Blood pressure remained elevated during PEMI after all exercise conditions (P < 0.05 vs. rest), whereas cardiac output and ACA V_mean were not different from rest (P > 0.05). PET_CO2 was unchanged from rest throughout. These data suggest that selective activation of skeletal muscle afferents (i.e., stretch, PEMI, or stimulated exercise) does not increase ACA V_mean and that increases in ACA V_mean during volitional contractions of an exercising calf muscle are dependent on the presence of central command.

cardiovascular response; cerebral circulation