Cerebrovascular adaptations to habitual resistance exercise with aging.

Resistance training (RT) is associated with improved metabolism, bone density, muscular strength, and lower risk of osteoporosis, sarcopenia, and cardiovascular disease. Although RT imparts many physiological benefits, cerebrovascular adaptations to chronic RT are not well defined. Participation in RT is associated with greater resting peripheral arterial diameters, improved endothelial function, and general cardiovascular health, whereas simultaneously linked to reductions in central arterial compliance. Rapid blood pressure fluctuations during resistance exercise, combined with reduced arterial compliance, could lead to cerebral microvasculature damage and subsequent cerebral hypoperfusion. Reductions in cerebral blood flow (CBF) accompany normal aging, where chronic reductions in CBF are associated with changes in brain structure and function, and increased risk of neurodegeneration. It remains unclear whether reductions in arterial compliance with RT relate to subclinical cerebrovascular pathology, or if such adaptations require interpretation in the context of RT specifically. The purpose of this narrative review is to synthesize literature pertaining to cerebrovascular adaptations to RT at different stages of the life span. This review also aims to identify gaps in the current understanding of the long-term impacts of RT on cerebral hemodynamics and provide a mechanistic rationale for these adaptations as they relate to aging, cerebral vasculature, and overall brain health.

Effects of single and bilateral limb immersion on systemic and cerebral hemodynamic responses to the cold pressor test.

The cold pressor test (CPT) involves cold water immersion of either the upper or lower limb(s) and elicits autonomic and hemodynamic increases via stimulation of pain and cutaneous thermoreceptors. It is unclear whether the choice of limb(s) in CPT studies differentially affects systemic and cerebral hemodynamic responses. Herein, we assessed systemic and cerebral hemodynamic and ventilatory responses to different CPT protocols of the hand (CPTH), foot (CPTF), or bilateral feet (CPTBF). We hypothesized CPTBF would elicit greatest physiological responses due to increased exposure area to the cold stimulus. Methods. Twenty-eight (14M;14F) healthy young adults [23.4 (SD: 2.4) years] participated in three 3-minute CPT protocols during a single visit. Mean arterial pressure (MAP), heart rate (HR), middle cerebral artery blood velocity (MCAv) and cerebrovascular conductance index, and end-tidal carbon dioxide (PETCO2), and pain perception were recorded throughout CPT protocols. Results. There was a time-CPT protocol interaction on systolic (p=0.02) and diastolic blood pressure (p<0.01), MAP (p<0.01), HR (p<0.001), presented as mean(SD). MCAv and cerebrovascular conductance index did not change with CPTs. Peak delta HR from baseline occurred in CPTBF (Δ13.6(15.5)BPM) compared to CPTH (Δ4.85(12.6)BPM; p=0.01) and CPTF (Δ4.04(13.3)BPM; p=0.02). Delta MAP was greater in CPTH (Δ12.3(7.95)mmHg) and CPTBF (Δ12.9(9.24)mmHg) compared to CPTF (Δ8.42(7.12)mmHg; p<0.01). Perceived pain was higher in CPTBF compared to single limb protocols (p≤0.01). Conclusion. Our findings suggest choice of limb(s) in CPT protocols affects systemic hemodynamic responses and should be considered when designing CPT studies.

No influence of steady-state postural changes on cerebrovascular compliance in humans.

The aim of this study was to determine the effect of posture changes on vascular compliance in intracranial (brain) versus extracranial vascular beds (forearm). Eighteen young adults (nine females) performed a supine-to-seated-to-standing protocol involving 5 min of rest in each position. Continuous blood pressure, middle cerebral artery (MCA) blood velocity, and brachial artery blood velocity were recorded at each posture. Three to five consecutive steady-state cardiac cycles at each posture were analyzed by a four-element lumped parameter modified Windkessel model to calculate vascular compliance. Mean arterial pressure (MAP) increased from supine to seated (76(9) vs. 81(12) mmHg; P = 0.006) and from supine to standing (76(9) vs. 82(13) mmHg; P = 0.034). Mean blood flow was greater in the MCA relative to the forearm (forearm: 40(5) mL·min-1, MCA: 224(17) mL·min-1; main effect P < 0.001). Conversely, vascular resistance (forearm: 3.25(0.50) mmHg-1·mL·min-1, brain: 0.36(0.04) mmHg-1·mL·min-1; main effect P < 0.001) and compliance (forearm: 0.010(0.001) mL·min-1·mmHg-1, brain: 0.005(0.001) mL·min-1·mmHg-1; main effect P = 0.001) were greater in the forearm compared to the brain. Significant main effects of posture were observed with decreasing values in upright positions for mean blood flow (P = 0.001) in both vascular beds, but not for resistance (P = 0.163) or compliance (P = 0.385). There were no significant interaction effects between vascular bed and posture for mean flow (P = 0.057), resistance (P = 0.258), or compliance (P = 0.329). This study provides evidence that under steady-state conditions, posture does not affect cerebrovascular compliance.

Targeting skeletal muscle health with exercise in people with type 1 diabetes: A protocol for HOMET1D, a prospective observational trial with matched controls.

INTRODUCTION: Individuals with type 1 diabetes (T1D) experience a complex set of alterations to skeletal muscle metabolic, neuromuscular, and vascular health; collectively referred to as diabetic myopathy. While the full scope of diabetic myopathy is still being elucidated, evidence suggests that even when individuals with T1D are physically active, indices of myopathy still exist. As such, there is a question if adherence to current physical activity guidelines elicits improvements in skeletal muscle health indices similarly between individuals with and without T1D. The objectives of this trial are to: 1) compare baseline differences in skeletal muscle health between adults with and without T1D, 2) examine the association between participation in a home-based exercise program, detraining, and retraining, with changes in skeletal muscle health, and 3) examine the roles of age and sex on these associations. METHODS AND ANALYSIS: This will be a prospective interventional trial. Younger (18-30 years) and older (45-65 years) males and females with T1D and matched individuals without T1D will engage in a four-phase, 18-week study sequentially consisting of a one-week lead-in period, 12-week exercise training program, one-week detraining period, and four-week retraining period. The exercise program will consist of aerobic and resistance exercise based on current guidelines set by Diabetes Canada. Metabolic, neuromuscular, and vascular outcome measures will be assessed four times: at baseline, post-exercise program, post-detraining, and post-retraining. Differences in baseline metrics between those with and without T1D will be examined with independent sample t-tests, and with two-way analyses of variance for age- and sex-stratified analyses. Changes across the duration of the study will be examined using mixed-model analyses. DISSEMINATION: Findings from this research will be shared locally and internationally with research participants, clinicians, diabetes educators, and patient advocacy organizations via in-person presentations, social media, and scientific fora. TRIAL REGISTRATION NUMBER: NCT05740514.