Upper Cervical Manipulation and Manual Massage Does Not Modulate Sympatho-Vagal Balance or Blood Pressure in Women: A Randomized, Placebo-Controlled Clinical Trial

Objectives: To compare the acute effects of upper cervical manipulation (CM) or manual massage (MM) to simulated CM (Sham) and Control conditions (Control) on heart rate variability (HRV) and blood pressure (BP) responses in asymptomatic individuals. Methods: A double-blind, four-arm, parallel-group, randomized, crossover, place-bo-controlled trial recruited 15 healthy women with normal BP who visited the lab on four occasions with 48-hour 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-second session of MM release applied unilaterally to the anterior and posterior thigh, posterior lower leg, and lumbar musculature; or (4) Sham: mimicking the posi-tioning 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 minutes for 60 minutes 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, with a large effect size magnitude, for the HRV indices: RMSSDms (Control: Post-0 (Δ=23.34; p=0.032), Post-15 (Δ=21.47; p=0.023); Sham: Post-15 (Δ=29.22; p=0.014); CM: Post-15 (Δ=24.05; p=0.027)); SDNNms (Control: Post-45 (Δ=26.01; p=0.037); CM: Post-45 (Δ=46.02; p=0.014) and Post-60 (Δ=31.82; p=0.019)); PNN50% (CM: Post-0 (Δ=32; p=0.044), Post-15 (Δ=23; p=0.044) and Post-45 (Δ=26; p=0.019)); LF Power (ms2) (CM: Post-60 (Δ=1482.92; p=0.001)), and LF/HF ratio (MM: Post-60 (Δ=0.11; p=0.022). Conclusion: The effect size findings suggest that both SM and MM may promote autonomic modulation in normotensive women by maintaining a balanced sympa-thovagal response. However, these outcomes were not consistently accompanied by statistically significant differences. Therefore, caution will be warranted when inter-preting and applying these results, as they reveal an emerging gap in the literature that warrants further investigation.