Effect of a single exercise bout on fasting cerebral blood flow and brain insulin sensitivity in middle‐aged to older adults

Reductions in brain insulin sensitivity and cerebral blood flow (CBF) have emerged as potential factors contributing to Alzheimer's disease and related dementia. However, no work has tested whether a single bout of exercise can raise brain insulin sensitivity in at-risk adults. The aim of the study was to test whether a single bout of exercise raises brain insulin sensitivity in middle-aged to older adults with cardiometabolic risk. In a counterbalanced pilot study design, 15 cognitively unimpaired (Montreal Cognitive Assessment, 28.2 ± 1.3 a.u.) adults [56.7 ± 2.1 years old; maximal oxygen consumption ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_2}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> ), 23.9 ± 0.9 mL/kg/min] with excess body weight (body mass index, 31.8 ± 1.3 kg/m²) and impaired glucose tolerance (haemoglobin A1c, 5.8% ± 0.30%) were randomized to a rest (time-matched control) or acute treadmill exercise bout (70% <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_2}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> for 60 min) in the evening. The next morning, participants arrived fasted to determine brain insulin sensitivity. Plasma glucose and insulin, in addition to CBF, were assessed by pseudo-continuous arterial spin labelling before and after intranasal insulin (40 IU). Cognition (NIH toolbox), aerobic fitness ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:semantics> <mml:msub><mml:mover><mml:mi>V</mml:mi> <mml:mo>̇</mml:mo></mml:mover> <mml:mrow><mml:msub><mml:mi>O</mml:mi> <mml:mn>2</mml:mn></mml:msub> <mml:mi>max</mml:mi></mml:mrow> </mml:msub> <mml:annotation>${\dot V_{{{\mathrm{O}}_2}{\mathrm{max}}}}$</mml:annotation></mml:semantics> </mml:math> ) and body composition (dual-energy X-ray absorptiometry) were also analysed. There was no difference in plasma glucose or insulin following intranasal with or without exercise. Although cognition was also not improved, exercise increased CBF in the hippocampus, putamen and pallidum (condition effect, P < 0.05). Exercise-induced increases in fasting hippocampus, caudate, pallidum and putamen CBF were correlated with a lowering of CBF responses to insulin. In middle-aged to older adults with cardiometabolic risk, a single bout of exercise increased fasting CBF, and this related to decreased CBF insulin responses in regions related to memory and motor control.