Abstract
Objectives: To compare the acute effects of upper cervical manipulation (CM) and manual massage (MM) to simulated CM (Sham) and Control conditions (Control) on heart rate variability (HRV) and blood pressure (BP) responses in women with non-elevated BP. Methods: A single-blind, four-arm, parallel-group, randomized, crossover, placebo-controlled trial recruited 15 apparently healthy women with non-elevated BP who visited the lab on four occasions with 48 h intervals to ensure adequate washout between interventions. A Latin square randomization approach was employed to assign participants to one of four experimental conditions: (1) Control: Rest without intervention; (2) CM: Bilateral high-velocity, low-amplitude manipulation of the upper cervical spine (C0-C2); (3) MM: A single 120 s session of MM release applied unilaterally to the anterior and posterior thigh, posterior lower leg, and lumbar musculature; or (4) Sham: Mimicking the positioning used in CM without the application of thrust manipulation. In each experiment, HRV, systolic and diastolic BP were measured at rest (Baseline) and every 15 min for 60 min after each intervention. All procedures were performed in the morning to avoid any confounding circadian rhythm effect on HRV and BP. Results: We found significant increases within conditions for RMSSDms (Control: Post-0 (p = 0.032), Post-15 (p = 0.023); Sham: Post-15 (p = 0.014); CM: Post-15 (p = 0.027)); SDNNms (Control: Post-45 (p = 0.037); CM: Post-45 (p = 0.014) and Post-60 (p = 0.019)); PNN50% (CM: Post-0 (p = 0.044), Post-15 (p = 0.044) and Post-45 (p = 0.019)); LF Power (ms2) (CM: Post-60 (p = 0.001)), and LF/HF ratio (MM: Post-60 (p = 0.022). Conclusions: Although no statistically significant between-condition differences were detected, within-condition changes with moderate-to-large effect sizes suggest potential clinical relevance of CM and MM. These preliminary findings emphasize the importance of effect sizes and may indicate greater translational significance in populations with non-elevated cardiovascular risk.