Effect of brain activation in circulatory dynamics of upper and lower extremity muscles during maintaining neck flexion

Abstract

  The present study investigated whether brain activation while maintaining neck flexion affects changes to circulatory dynamics in the upper and lower extremity muscles. We selected 15 healthy volunteers with a mean age of 20.6 years (range, 18-22 years). All had played some kind of sports from elementary school through university. Neck flexion angles were randomly set at 0° (neck resting) or 20° (neck flexion). Muscle oxygenated hemoglobin concentration (oxy-Hb) in right upper and lower extremity muscles was measured using near-infrared spectroscopy. Oxy-Hb and electromyogram (EMG) of biceps brachii (BB), triceps brachii (TB), tibialis anterior (TA) and gastrocnemius (GS) were measured. Skin blood flow (SBF) was measured over BB and TA. Heart rate (HR), blood pressure (BP) and cardiac output (CO) were measured during neck flexion. Muscle oxy-Hb in BB, TB and TA were significantly increased during neck flexion. This indicated that blood flow within those muscles was clearly increased while maintaining neck flexion. However, oxy-Hb in GS did not change with neck flexion. Significant correlations were found in the enhancement of blood flow during neck flexion between BB and TB (r = 0.83), BB and TA (r = 0.78), and TB and TA (r = 0.57). No significant effect of posture was found for HR, BP, CO, SBF or EMG. These findings indicate that the increase in muscle blood flow in upper and lower extremity muscles was elicited by brain activation during maintenance of neck flexion.