Limited information is available regarding cerebral vascular responses to dynamic exercise in older adults. We examined the influence of age on exercise-induced changes in the critical closing pressure (CCP) of the cerebral vasculature. Twelve young and twelve older subjects performed two bouts of steady-state cycling at low and moderate intensities (30 and 50% heart rate reserve). Mean arterial pressure (MAP), middle cerebral artery blood velocity (MCA V) and partial pressure of end-tidal carbon dioxide (P-ET,P- (CO2)) were measured. The CCP was estimated by linear extrapolation of pairs of systolic and diastolic blood pressure and MCA V waveforms. Exercise-induced increases in MAP were greater in older subjects (P <0.01), while mean MCA V (MCA V-mean) responses to exercise were similar between groups (P = 0.59). The CCP was elevated from rest during low-and moderate-intensity exercise in both groups (moderate exercise: young, +13 +/- 2 mmHg and older, +22 +/- 2 mmHg; P <0.01), with the older subjects exhibiting greater increases in CCP during both exercise intensities (moderate exercise: young, +43 +/- 9% rest versus older, +153 +/- 45% rest; P = 0.04). In contrast, cerebral vascular conductance index (MCA V-mean/MAP; CVCi) was only decreased during moderate exercise in older subjects (P <0.01) and CVCi was not altered from rest in young subjects during low-or moderate-intensity cycling. No age-group differences were observed in P-ET,P- CO2 at rest or during two intensities of exercise (P = 0.40). These data demonstrate that older subjects exhibit larger exercise-induced increases in CCP and decreases in CVCi. Thus, ageing is associated with greater increases in cerebral vascular tone during low-and moderate-intensity dynamic exercise.