Sex Differences in Heart Rate Variability Responses to Eight Weeks of Circuit Training

Physical Inactivity

Heart rate variability, Autonomic recovery, Sex differences, Circuit training, Frequency domain, Physically inactive

The main goal of this study is to find out how an 8-week circuit training exercise program affects heart health and how the body recovers in young adults who do not regularly exercise. The researchers also want to see if these responses are different between men and women. The body's nervous system controls automatic functions like heart rate. Measuring changes in heart rate patterns-known as heart rate variability (HRV)-helps show how well the body switches between "fight-or-flight" (stress/exercise mode) and "rest-and-digest" (recovery mode). While men and women naturally have different heart rate patterns at rest, less is known about whether they recover differently after a structured exercise program. The main questions this study aims to answer are: 1. Does 8 weeks of circuit training improve heart rate recovery and nervous system balance in inactive young adults? 2. Do men and women show different heart rate responses or recovery patterns after taking part in circuit training? To answer these questions, inactive university students took part in an 8-week supervised circuit training program. Participants were considered inactive if they did less than 150 minutes of moderate exercise or less than 75 minutes of vigorous exercise per week. Participants completed 20 exercise sessions (2 times per week) led by the study team: * Exercise Sessions: Each session started with a 5-minute warm-up, followed by 10 exercise stations using light weights, resistance bands, and bodyweight movements. Exercises targeted both upper and lower body muscles. * Workouts and Rest: Participants did each exercise for 30 seconds, rested for 1 minute between stations, and rested for 5 minutes between full sets. * Progression: During Weeks 1 to 4, participants did 2 sets per session. During Weeks 5 to 8, they increased to 3 sets per session. To measure heart rate recovery, participants wore a heart rate chest monitor while resting quietly lying down: 1. Before starting the 8-week program (Baseline) 2. At 10 minutes after a workout at Week 8 (Short-term recovery) 3. At 24 hours after a workout at Week 8 (Full recovery) The researchers compared the heart rate data between men and women across these time points to see how quickly their nervous systems returned to a resting state after exercise.

This study evaluates the effects of an 8-week supervised circuit training program on heart rate variability (HRV) and autonomic recovery patterns among physically inactive young adults, with a specific focus on sex-related differences. Participants undergo an 8-week exercise intervention consisting of 20 total sessions scheduled twice per week. The intervention follows a progressive volume design: * Weeks 1 to 4: Participants perform 2 complete sets per session (8 sessions total). * Weeks 5 to 8: Participants perform 3 complete sets per session (12 sessions total). Each exercise session begins with a 5-minute dynamic warm-up. The circuit consists of 10 sequential exercise stations targeting major upper-body and lower-body muscle groups using body weight, resistance bands, and dumbbells: 1. Heel raises with dumbbells 2. Lateral raises with resistance bands 3. Leg abductions with resistance bands 4. Shoulder extensions and flexions with resistance bands 5. Jump rope 6. Triceps extensions with dumbbells 7. Half squats with resistance bands 8. Standing chest fly with dumbbells 9. Leg curls with resistance bands 10. Bicep curls with dumbbells Participants perform each exercise station for 30 seconds, followed by a 1-minute rest interval between stations. A 5-minute rest period is provided between complete circuits. All sessions take place under direct supervision. Autonomic function is evaluated via continuous beat-to-beat R-R interval recordings using a validated heart rate monitor while participants rest quietly in a supine position in a climate-controlled room (21 °C). Heart rate variability is assessed across three specific time points: 1. Baseline: Pre-intervention assessment prior to beginning the 8-week training protocol. 2. Post-10 Minutes: Immediate post-exercise recovery assessment within 10 minutes following the final training session at Week 8. 3. Post-24 Hours: Delayed recovery assessment 24 hours following the final training session at Week 8. Extracted frequency-domain HRV parameters include Low Frequency (LF: 0.04-0.15 Hz), High Frequency (HF: 0.15-0.40 Hz), and the LF/HF ratio, analyzed in both absolute power values (ms2) and normalized units (n.u.). Comparisons are conducted between male and female participants across time points to analyze sex-specific autonomic adaptations and recovery trajectories following circuit training.

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