Differences in Autonomic Recovery Between Physically Active and Inactive Women Following an Automated Massage Chair Intervention

Background and Rationale Massage therapy is widely utilized to promote overall health, alleviate stress, and facilitate recovery following physical exertion. A primary mechanism through which massage aids recovery is by modulating the autonomic nervous system (ANS). The ANS consists of the sympathetic nervous system (SNS), which drives the "fight-or-flight" stress response, and the parasympathetic nervous system (PNS), which governs "rest-and-digest" processes vital for tissue repair and cardiovascular recovery.In recent years, automated electric massage chairs (AEMCs) have surged in popularity as an accessible means to replicate therapist-delivered manual massage. Despite their widespread commercial use for health and wellness, research examining their physiological impacts-particularly on autonomic regulation-remains limited. Furthermore, while physically active individuals typically demonstrate greater autonomic flexibility and faster physiological recovery than inactive individuals, it is largely unknown if these baseline physical activity levels influence the body's acute response to an automated massage intervention.

Study Objective This study aims to evaluate the acute physiological effects of a single AEMC session on autonomic regulation among healthy female university students. By utilizing heart rate variability (HRV) as a non-invasive marker of sympathovagal balance, researchers will compare the physiological responses of physically active participants against those of inactive participants over a 72-hour recovery period.

Study Procedures Participants will be assigned to one of two groups based on their habitual physical activity levels: a physically active group (engaging in at least three supervised training sessions per week) and an inactive group (identified via the International Physical Activity Questionnaire as having low physical activity levels).

The study involves the following procedural sequence:

• Familiarization: Prior to the initial assessment, participants will complete a familiarization session to acclimate to the monitoring devices and the AEMC while it is both powered off and on.
• Baseline Assessment: On the experimental day, participants will be fitted with a wrist-worn heart rate monitor and a chest strap heart rate transmitter. Participants will sit in the powered-off AEMC for five minutes to capture baseline HRV data. During this time, they will be instructed to remain relaxed and minimize both body movements and communication.
• Intervention: Participants will be positioned in a reclined posture, with their upper bodies supported and legs and feet elevated to heart level. They will then undergo a 20-minute standardized "Recharge" program on the AEMC. This program delivers a continuous, moderate-intensity massage using kneading and rolling techniques focused on the back, neck, shoulders, forearms, and thighs. The intensity will be subjectively selected by the participant to a moderate level and adjusted via a Bluetooth-connected application to ensure suitable pressure.
• Post-Intervention Monitoring: Following the massage session, participants will be instructed to resume normal daily activities but must refrain from structured exercise for three days. Participants will return to the laboratory at 24, 48, and 72 hours post-session to have their HRV recorded. All follow-up HRV measurements will be recorded at the same time of day to control for circadian variations.

Data Analysis and Mechanisms Heart rate data will be synced and analyzed using specialized software to calculate frequency-domain HRV indices. The analysis will specifically look at the high-frequency (HF) component, the low-frequency (LF) component, and the LF/HF ratio. The HF component primarily reflects parasympathetic activity, whereas the LF component represents a mixture of sympathetic and parasympathetic influences. The LF/HF ratio serves as an index of autonomic balance, with lower values indicating a state of parasympathetic dominance and enhanced recovery capacity. Tracking these metrics across multiple time points will allow researchers to observe the timeline of short-term autonomic changes and determine if habitual physical activity primes individuals to derive greater physiological recovery benefits from automated massage chair therapy.

Participants in the physically active group were university athletes from various sports (athletics, football, volleyball, and badminton) with at least one year of competition experience at the university level and who engaged in supervised training sessions at least three times per week. Physically inactive were those who did not meet these criteria and were identified as having low physical activity levels based on the International Physical Activity Questionnaire (IPAQ).