Central Command Related Changes in Anterior Cerebral Artery Blood Velocity and Prefrontal Oxygenation at the Onset of Moderate Voluntary Hand-Grip Exercise.

Recently, it has been identified that volitionally initiated finger tapping, which is a "very light motor effort" physical activity, elicits greater increases in mean anterior cerebral artery blood velocity (ACAmean), ACA vascular conductance index (ACAvci) and prefrontal oxygenation (Oxy-Hb) responses compared to a cued start. These findings suggest that differences in ACAmean and prefrontal Oxy-Hb responses between the exercise initiation modes may be related to central command. However, it remains unknown if similar responses are observed at the onset of voluntary exercise of a "moderate motor effort". Therefore, the purpose of this study was to determine ACAmean, ACAvci and prefrontal Oxy-Hb responses during dynamic hand grip exercise at 40% of maximal voluntary contraction (MVC) during two exercise initiation modes (voluntary or cued start). ACAmean, ACAvci, and prefrontal Oxy-Hb were measured in seven participants (4 females and 3 males; aged 26 ± 3 years) at baseline (-30 sec to -20 sec prior to initiation of exercise), pre-exercise (-20 sec to 0 sec) and the onset of exercise (0 sec to 15 sec) of each exercise initiation condition. Participants perceived exertion Borg Scale rating for the 40%-MVC was 11.5 (median). A two-way repeated measures ANOVA was conducted for the variables of interests. A significant factor interactions was identified for ACAmean ((F(2,12) = 5.02, p=0.03)) and Oxy-Hb ((F(2,12) = 5.86, p= 0.02)). Post hoc test revealed that a voluntary start to hand grip exercise increased ACAmean by 2.6±1.0 cm/s (p=0.002) v.s. 0.7± 2.0 cm/s for a cued start (p=0.3) and increased Oxy-Hb by 11.6±10.7 µM (p=0.02) v.s. 2.9±9.5 µM for a cued start (p=0.7) at the onset of exercise when compared to baseline. Furthermore, there was tendency in ACAvci to also increase with voluntary start by 3.9%±6.0 (p=0.06) vs. cued start 0.43% ± 6.0 p=0.57 from baseline to the initial onset of exercise. These primary findings suggest that moderate dynamic hand grip exercise elicits similar anterior cerebral blood flow and prefrontal oxygenation responses previously observed and thus, showing similar metabolic demands as finger-tapping.