Background/Aim: The kinetics of the middle cerebral artery blood velocity (MCAv) response to hypercapnia provide insight into cerebrovascular responsiveness and function. Characterising these responses following acute exercise may provide insight beyond conventional steady-state measures of cerebrovascular reactivity. Suspension exercise combines bodyweight movements and instability in a functional resistance modality, presenting a unique haemodynamic challenge. However, the effects of suspension exercise on MCAv kinetics during hypercapnia remain unknown. Therefore, this study aimed to determine the acute effects of suspension exercise on MCAv kinetics during a hypercapnic challenge.

Methods: 9 healthy young adults, 5 male (mean age= 23.4 ± 3 years, V̇O_₂max 41.2 ± 9.3 ml/kg/min, BMI 22.9 ± 3.5kg/m²) were recruited to complete two time-matched visits: a 30-min suspension training session consisting of five different exercises performed in a circuit format, and a 30-min control condition (seated rest). Hypercapnia was induced using a Douglas bag filled with a 6% CO₂ gas mixture (21% O₂, balance N₂) for 4 min at baseline, 10 min, and 60 min post-intervention. Transcranial Doppler ultrasound measured MCAv bilaterally. MCAv Kinetic responses to hypercapnia were analysed using a monoexponential model with a time delay to determine baseline MCAv, the time constant (τ), time delay (TD), mean response time (MRT), and both the absolute and relative response amplitudes. These results were analysed using a two-way analysis of variance. 

Results: Baseline MCAv and the time delay (TD) of the MCAv response were unchanged across time and condition (all P>0.069). Although τ differed between conditions (P=0.013), no time or interaction effects were observed (P≥0.411). The amplitude of the absolute and the relative MCAv responses both had a significant main time × condition interaction effect (both P<0.001). Absolute and relative MCAv response amplitudes increased 10 minutes following suspension exercise (P≤0.007), were significantly greater than the control condition (absolute: 31.4 ± 5.9 vs 15.2 ± 5.1; relative: 48.1 ± 8.5 vs 24.0 ± 7.6; both P<0.001), and returned to baseline by 60 minutes (P≤0.001)

Conclusion: Suspension exercise transiently enhances the magnitude of the MCAv response to hypercapnia without altering its temporal dynamics, indicating a short-lived improvement in cerebrovascular reactivity. The time-based parameters of the MCAv response (τ, TD, MRT) were maintained, indicating that suspension training affected only the size of the response, not the speed. Given the small sample size of this study, these preliminary findings should be confirmed in future with larger, adequately powered studies.