Table 2. Characteristics of included studies.

Study	Study design	Participants	Methods	Results
1. Oliveira et al : Journal of Obesity. 2020	An Observational study (clipping from RCT)	Sample Size: 64 patients with obesity. Participants: Obesity grade II (BMI ≥35 kg/m 2). Either gender and age of between 18 and 65 years.	Anthropometric measurement: BMI, WC Physical activity: Accelerometer ACTi Graph model wGT3X, and 24 h recall (R24H) HRV measurement equipment, procedure, and reported domain Equipment: V800 Polar, Finland. Kubios HRV Analysis software, version 2.2 Procedure: Room temperature was maintained at 22-24 oC and relative humidity of 50-60%. On the day of measurement and 24 hours before, participants were advised not to drink alcohol, perform moderate or intense PA and avoid copious meals. Reported domain: Frequency domain measures of HRV- LF, HF, and LF/HF ratio	Negative association b/w: moderate to vigorous PA and the sympathetic component of HRV (p = 0.043). Negative association b/w Sedentary time with HF and LF/HF. Positive association observed b/w Sedentary time with LF. Waist circumference was negatively associated with HF (β = −0.685, p = 0.010).
2. De Liao et al : PLOS ONE. 2017	Cross-sectional study	Sample size: 441 (231 males and 210 females). Participants: Older adults with obesity of either gender aged 50-80 years. BF% of the participants: >27% for men and >38% for women	Anthropometric measurement: (BMI, Body fat (BF)%). Physical activity: GCPS score HRV measurement equipment, procedure, and reported domain Equipment: ANS watch monitor (Taiwan Scientific Co., Taipei, Taiwan) Procedure: Participants were given rest for 10 min in a supine position. HRV analysis: Pulse cycle intervals instead. Reported domain: Time and frequency domain variables- SDNN, rMSSD, and HF	Moderate association was observed between - The GCPS with SDNN and HF in older men. similar findings were found in older women.
3. Pope et al : Medicine & science in sports & exercise. 2020	Cohort study	Sample size: 1668 participants. men and women, age of 18-30 years. The majority of the participants were with higher weight and obesity - n=1157 Underweight - n=20 Normal weight - n=491	Anthropometric measurement: BMI Physical activity: ActiGraph 7164 (ActiGraph Corp.; Pensacola, FL) HRV measurement equipment, procedure, and reported domain Equipment: GE MC1200 (General Electric Inc., Boston, MA) Procedure: Resting ECG recording data at 500 Hz, with three 10-s ECG strips. Reported domain: Time-domain measure of HRV- SDNN and rMSSD	VPA was associated with SDNN and rMSSD and LPA was associated with rMSSD only.
4. Tonello et al : Frontiers in physiology. 2016	Correlation study	Sample Size: 21 Young, healthy non-menopausal women with higher weight free from pathological conditions. Mean age = 34.5 ± 6.40 years. Mean BMI = 26.3 ± 4.1 kg/m 2. Mean WC = 79.7 ± 9.7.CM Mean BF% = 37.0 ± 4.7. Full-time service worker. Not involved in any structured exercise program	Anthropometric measurement: BMI, WC, body fat% Physical activity: Measured using accelerometer (GT1M, ActiGraph USA) HRV measurement equipment, procedure, and reported domain Equipment: HR monitor- RS800CX, Polar Electro Oy, Finland Procedure: Sampling rate- 1000Hz Software used for filter- (Polar ProTrainer ® version 5.0, POLAR Electro Oy, Kuopio, Finland). Software used for HRV analysis- Kubios HRV v2.0, Kuopio University, Finland. Orthostatic and ambulatory HRV recording was performed Reported domain: Time-domain measures- SDNN and RMSSD, Frequency domain measures-LF and HF	In adult women with higher weight, incidental or non-exercise-based PA was associated with increased autonomic reactivation. Correlations were observed between: VPA and RMSSD (r = -0.449, p = 0.041), VPA and HF (r = -0.520, p = 0.016), VPA and SD1 (r = -0.463, p = 0.035), VPA +VVPA and RMSSD (r = -0.453, p = 0.039), VPA +VVPA and HF (r = -0.526, p = 0.014), VPA +VVPA and SD1 (r = -0.473, p = 0.030).
5. Kaikkonen KM et al : Journal of Physical Activity and Health. 2014	Cross-sectional study	Sample Size: 107 adults with obesity (87 females and 20 males) Obese adults with a mean age of 44.5 years and median BMI of 35.7	Anthropometric measurement: BMI and WC Physical activity: Modified Paffenbarger questionnaire. Self-rated physical fitness assessment: Standardized 5-scale question with categories “very poor,” “fairly poor,” “satisfactory,” “fairly good,” and “very good.” HRV measurement equipment, procedure, and reported domain Equipment: Polar R-R recorder (Polar Electro Oy, Kempele, Finland) Procedure: Software used for analysis - Heart Signal Co, Kempele, Finland. The recording was carried out for 24 hours and HRV was computed from the entire recording. RR intervals were visually inspected to remove ectopic beats. Reported domain: Time-domain (SDNN), Frequency domain- LnHF, LnLF, LnVLF, LnULF, LF/HF ratio.	Lifetime physical activity explained 40% of the variance in SDNN in multivariate linear regression analyses. SDNN increased by 15.4 (P =.009) and 24 % of the variance in LnULF (P =.050) increased with each 1 group increase in the activity index.
6. Rennie et al : American Journal of Epidemiology. 2003	Cohort study (Data presented from the fifth phase of data collection)	Whitehall II study of civil servants age between 45–68 years. Sample Size: 3,328 participants (994 women). Participant BMI included above and below 25. Waist-hip ratio: 0.793-0.941	Anthropometric measurement: BMI and WHR Physical activity: Physical activity questionnaire derived from Minnesota leisure-time activity questionnaire HRV measurement equipment, procedure, and reported domain Equipment: 12-lead electrocardiogram (Mingorec; Siemens, Munich, Germany) Procedure: Participants were made to rest supine for at least 5 minutes in a quiet room. Five minutes of beat-to-beat heart rate data were sampled at a frequency of 500 Hz. Software used for digital recording of R wave - (Kardiosis; Tepa, Inc., Ankara, Turkey) RR intervals were visually inspected to remove ectopic beats. Reported domain: Time-domain (SDNN), Frequency domain (LF and HF)	There was a clear dose-response relationship between vigorous activity and higher SDNN, low-frequency power, high-frequency power (p 0.05, p 0.01, and p 0.01, respectively) in men.
7. Kiviniemi AM et al : Medicine & science in sports & exercise. 2017	Prospective Northern Finland Birth Cohort 1966 (NFBC1966) study	At the age of 46 years, 1383 men and 1761 women without cardiorespiratory diseases and diabetes underwent assessments of HRV. Nonsmoker: n (%) Men - 589 (43), women - 905 (51) * Ex-smoker: n (%) Men - 410 (30), women - 423 (24) Current smoker: n (%) Men - 384 (28), Women - 433 (25) .*P < 0.001 compared with men.	Anthropometric measurement: BMI, Body fat, %, and Waist-hip ratio Physical activity: PA was objectively measured with a wrist-worn Polar Active device (Polar Electro Oy, Kempele, Finland) HRV measurement equipment, procedure, and reported domain Equipment: HR monitor (RS800CX; Polar Electro Oy) was used to record R-R intervals (RRi). Standard lead II ECG (Cardiolife; Nihon Kohden, Tokyo, Japan), breathing frequency (MLT415/D, Nasal Temperature Probe; AD Instruments, Bella Vista, New South Wales, Australia), and blood pressure (BP) by finger photoplethysmography (Nexfin; BMEYE Medical Systems, Amsterdam, the Netherlands) were recorded with a sampling frequency of1000 Hz (Power Lab 8/35; AD Instruments). Procedure: The first 150 s of 3-min recording was used for analysis. Spontaneous breathing was allowed during the HRV recording. Artifacts and ectopic beats were removed and replaced by the local average (Hearts 1.2; University of Oulu, Oulu, Finland). Sequences with ≥10 consecutive beats of noise or ectopic beats were deleted before final analysis. The RRi series with ≥80% accepted data were considered for analysis. Reported domain: Time-domain RMSSD (ms)	• MVPA was independently associated with cardiac autonomic function in both men and women. • Body fat was independently associated with cardiac autonomic function in both men and women. • A negative association was found between MVPA and rMSSD when including CRF, MVPA, and Fat% in the same regression model. • Body Fat% was not significantly related to rMSSD.
8. Föhr T et al: BMC public health. 2016	Cross-sectional study	Finnish employees: (6863 men and 9412 women; Age - 18–65 years old; BMI: [18.5–40.0 kg/m 2; mean = 26.0 ± 4.1 kg/m 2].	Anthropometric measurement: BMI Physical activity: HRV-based assessment of PA. The amount and intensity of PA were determined using ambulatory beat-to-beat R-R interval data. HRV measurement equipment, procedure, and reported domain Equipment: Firstbeat Bodyguard device (Firstbeat Technologies Ltd., Jyväskylä, Finland). Procedure: Ambulatory ECG: continuous beat-to-beat R-R interval (ECG) recordings during their everyday life. R-R interval data were analyzed using Firstbeat Analysis Server software (Firstbeat Technologies Ltd, Jyväskylä, Finland. A 5-minute window was used to measure RMSSD. If a subject's measurement duration included two or more workdays, an average was used for analysis. Reported domain: RMSSD and the LF/HF ratio	For both men and women, the high PA group had the highest rMSSD (during waking hours and during sleep) and recovery index, and the lowest stress percentage and stress index. Both moderate and vigorous PA is found to be associated with higher HRV
9. Buchheit M, et al . Medicine, and science in sports and exercise. 2005	Observational study	43 non-smoking, middle-aged adults without obesity. 23 women 20 men Age: 61.2 ±4.3 years old BMI: 25.6 ± 0.3 kg/m 2	Anthropometric measurement: BMI Physical activity: MBQOA Questionnaire. The total score reflects overall PAEE. Physical activity parameters were assessed by triaxial accelerometers (RT3, Stayhealthy, Monrovia, CA) HRV measurement equipment, procedure, and reported domain Equipment: ECG was continuously monitored using a Holter with a sampling frequency of 256 Hz (Ela Medical, Paris, France). Breathing frequency was monitored using Crystal Trace Piezo Respiration Sensor (Astro-Med EEG System, Grass Instruments, West Warwick, RI). Procedure: Recording Time: Between 10:00 a.m. and 12:00 p.m. Recording environment: air-conditioned room with ambient temperature maintained at 21°C. Following 30 mins of rest, subjects were asked to remain quietly supine for 10 mins without speaking or making any movements. HRV analyses were considered from the last 5 min of the 10-min controlled breathing period. Reported domain: mean of R–R intervals (mR–R), SDNN, RMSSD, LF, HF, and LF/HF ratio.	Habitual moderate PAEE is associated with higher vagal indexes of the heart in older adults.
10. May et al . Journal of physiological anthropology. 2017	Short report	115 students Age: 23.1 ± 5.4 years old BMI: 25.4 ± 0.5 kg/m 2	Anthropometric measurement: BMI Physical activity: IPAQ HRV measurement equipment, procedure, and reported domain Equipment: Electrocardiographic recordings were collected using a BIOPAC MP-36 system (BIOPAC Systems Inc., Galeta, Ca). Software: BIOPAC Student Lab Pro software (BIOPAC Systems, Inc.) and values were natural log-transformed. Procedure: Recording Time: 0800-1030 hours Recording environment: Temperature-controlled room. Participants were seated and were instructed to breathe normally with their eyes closed. Following 5 mins of quiet rest, 5-min recordings were collected with a sample rate of 1000 samples/s. Reported domain: rMSSD, LF and HF	In regression analyses, hours of vigorous physical activity significantly predicted greater time domain and frequency domain indices of HRV.
11. Soares-Miranda et al. Circulation. 2014	Prospective study (The Cardiovascular Health Study (CHS) design)	5,201 ambulatories, non-institutionalized men and women ≥ 65 years of age were randomly selected and enrolled from Medicare eligibility lists in 4 US communities in 1989–990. BMI: 27 ± 5 kg/m 2	Anthropometric measurement: BMI Physical activity: modified Minnesota Leisure-Time Activities questionnaire. HRV measurement equipment, procedure, and reported domain Equipment: Long-term (e.g., 24-hour Holter) measures. Two-channel 24-hour Holter recordings (Del Mar Medical Systems, Irvine, California). HRV analysis was done in HRV Laboratory (GE Marquette Mars 8000 Holter analyzer, Milwaukee, Wisconsin). Procedure: Recording at baseline in 1989–90 and again in 1994–95. For cross-sectional analyses at baseline in 1989–90, 1,219 participants had 24-hour recordings for time-domain HRV and 1,150 for frequency-domain and nonlinear HRV. Reported domain: SDNN, rMSSD, SDNN Index, LF, HF, ULF, VLF, LF/HF ratio, SD12, Poincare Ratio, and DFA1	Following multivariable adjustment, the leisure-time activity was cross-sectionally related to specific indices including higher SDNN (p trend=0.001) and higher ULF (p trend<0.0001).
12. Kluttig et al . BMC cardiovascular disorders. 2010	Part of Prospective, population-based CARLA study (Cohort study)	A cross-sectional data of 1671 participants. Men (n = 967), Women (n = 812) Age range - 45-83 years old BMI: Male: 28.5 ± 4.1 kg/m 2 Female: 28.5 ± 5.4 kg/m 2	Anthropometric measurement: BMI, WHR Physical activity: Baecke questionnaire HRV measurement equipment, procedure, and reported domain Equipment: Modular ECG Analysis System (MEANS) Procedure: The 20-min ECG was recorded after a resting period (in the supine position) of ≥20 min. Throughout the ECG, subjects were asked to breathe at 15 breaths/min (0.25 Hz) Time and frequency domain parameters of HRV for 5-min segments of the ECG according was used for the HRV analysis. Reported domain: SDNN, LF, HF, and LF/HF ratio	There was no consistent or statistically significant association of physical activity with HRV in either gender was observed.