Table 2. Characteristics of included studies.
| Study | Country | Design | Patients | Exercise | HRV measures | Other outcomes* | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| n analyzed | Age, mean (years±SD) | Men (%) | Type / group | Duration (months) | Intensity | Session | /week | Super-vision | HRV parameters* | Deep breathing | ECG (min) | ||||
| Abdelbasset 2019 | Egypt | RCT | 20 | 52.4±4.6 | 100% | HIIT | 4 | 4 intervals of 4 min at 80–90% of MHR with 2 min at 50–60% of MHR between each | 30 min | 3 | Yes | HRV lying (RR↘, SDNN ↗, RMSSD↗, LF, HF↗, LF/HF↘) | No | 5 | HbA1c, BMI, total cholesterol, HDL, LDL, triglycerides, VO2 |
| 20 | 51.5±5.1 | Control | - | ||||||||||||
| Bellavere 2018 | Italy | R Comp. Type of exercise | 19 | 57.1±1.6 | 68% | End. | 4 | Up to 60–65% of HRR | 60 min | 3 | Yes | HRV lying and standing (TP, LF↘, HF↗, LF/HF↘) | No | 10 | HbA1c, BMI, total cholesterol, HDL, LDL, triglycerides, VO2 |
| 11 | 53.4±2.0 | 82% | Resist. | Up to 3 sets of 10 repetitions at 70–80% 1-RM | Yes | ||||||||||
| Bhagyalakshmi 2007† | India | Non-RCT | 28 | 61.8±3.1 | 79% | End. | 9 | Unclear | 45 min | 7 | Yes | HRV lying (↗ difference shortest and longest RR) | Yes | 1 | HbA1c |
| 20 | 59.5±2.8 | 50% | Control | - | |||||||||||
| Cassidy 2019 | UK | RCT | 11 | 60.0±3.0 | 82% | HIIT | 3 | 5 intervals of 2 min (up to 3 min 50 s) at > 80 RPM and RPE 16–17 with 3 min recovery between each | 30–40 min | 3 | No | HRV lying (RR, SDNN, LF, HF, LF/HF) | No | 20 | HbA1c, BMI, blood pressure, VO2 |
| 11 | 59.0±3.0 | 73% | Control | - | |||||||||||
| Duennwald 2014 | Austria | R Comp. Type of exercise | 8 | 59.6±5.7 | 75% | HIIT | 1 | 5 intervals of 4 min at 90–95% of MHR with 3 min at 70% of MHR between each 70% of MHR | 42 min | 3 | Yes | HRV lying (RR, SDNN) | No | 4 | HbA1c, BMI, blood pressure, total cholesterol, HDL, VO2 |
| 7 | 59.6±6.1 | 71% | End. | 50.3 min | Yes | ||||||||||
| Faulkner 2014 | USA | Non-R T2DM vs no T2DM | 9 | 14.7±1.8 | 11% | End. (T2DM) | 4 | 60–75% of MHR | 60 min | 5 | No | HRV 24h (RMSSD, pNN50, SDNN, TP, LF, HF) | No | 1440 | HbA1c, BMI, total cholesterol, HDL, LDL, triglycerides, VO2 |
| 10 | 14.6±1.6 | 40% | End. (No T2DM) | No | |||||||||||
| Figueroa 2007 | USA | Non-R T2DM vs no T2DM | 8 | 50.0±2.8 | 0% | End. (T2DM) | 4 | 65% of VO2peak | 30–45 min | 4 | +/- | HRV lying (LF, HF, LF/HF) | Yes | 5 | HbA1c, BMI, blood pressure, VO2 |
| 12 | 48.0±6.9 | 0% | End. (No T2DM) | +/- | |||||||||||
| Goit 2014 | Nepal | Pre-post | 20 | 42.2±6.4 | 100% | End. | 6 | 60–85% of HRR | 50 min | 3 | Yes | HRV lying (SDNN, RMSSD↗, pNN50↗, LF↘, HF↗, LF/HF↘) | No | 5 | HbA1c, BMI, blood pressure, HDL, LDL, triglycerides |
| Goit 2017 | Nepal | Pre-post | 41 | 44.2±4.5 | 100% | End. | 6 | 50–70% of HRR | 50 min | 3 | Yes | HRV lying (SDNN↗, RMSSD↗, pNN50↗, LF↘, HF↗, LF/HF↗) | No | 5 | HbA1c, BMI, blood pressure, total cholesterol, HDL, LDL, triglycerides |
| Goulopoulou 2010 | USA | Non-R T2DM vs no T2DM | 26 | 50.0±5.1 | 50% | End. (T2DM) | 4 | 65% of VO2peak | 30–45 min | 4 | +/- | HRV lying (TP) | Yes | 5 | HbA1c, BMI, blood pressure, total cholesterol, HDL, LDL, triglycerides, VO2 |
| 36 | 49.0±6.0 | 39% | End. (No T2DM) | +/- | |||||||||||
| Kanaley 2009 | USA | Non-R. T2DM vs no T2DM | 22 | 50.0±1.6 | 45% | End. (T2DM) | 4 | 65% of VO2peak | 30–45 min | 4 | +/- | HRV lying (TP) | Yes | 5 | HbA1c, BMI, VO2 |
| 34 | 49.0±0.9 | 38% | End. (No T2DM) | ||||||||||||
| Kang 2016 | Korea | RCT | 8 | 56.0±7.4 | 0% | End. & Resist. | 3 | 60% of HRR + 2 sets 9 exercises 8–12 repetitions at 1-RM of 60–80% | 30 + 30 min | 3 | Yes | HRV lying (RMSSD, SDNN, LF, HF, LF/HF) | No | 5 | HbA1c, BMI, blood pressure, total cholesterol, HDL, LDL, triglycerides, VO2 |
| 8 | 57.5±4.6 | 0% | Control | - | |||||||||||
| Loimaala 2003 | Finland | RCT | 24 | 53.6±6.2 | 100% | End. & Resist. | 12 | 65–75% of VO2peak 3 sets of 10–12 repetitions at 70–80% max. voluntary contraction | 30 min | 4 | +/- | HRV lying (SDNN, pNN50, LF, HF, LF/HF) | No | 1440 | HbA1c, BMI, blood pressure, VO2 |
| 25 | 54.0±5.0 | Control | - | ||||||||||||
| Moawd 2015 | Egypt | Non-R Comp. Type of exercise | 20 | 50.5±8.6 | 100% | End. | 3 | 60–85% of HRR RPE “very to fairly light” up to “somewhat hard” | 50 min | 3 | Yes | HRV lying (RMSSD↗, SDNN↗, pNN50↗) | No | 10 | BMI, blood pressure |
| 18 | 51.3±6.1 | 100% | Resist. | 5–20 min | - | ||||||||||
| Pagkalos 2008 | Greece | Non-R Comp. CAN status | 15 | 55.8±5.6 | 27% | End. (CAN -) | 6 | 70–85% of HRR | 45–75 min | 3 | Yes | HRV lying (RMSSD↗, SDNN↗, pNN50↗, LF↘, HF↗, LF/HF↘) | No | 1440 | HbA1c, BMI, blood pressure, total cholesterol, HDL, LDL, triglycerides, VO2 |
| 17 | 56.2±5.8 | 35% | End. (CAN +) | Yes | |||||||||||
| Parpa 2009 | USA | Pre-post | 14 | 57.0±6.7 | 36% | HIIT | 3 | 6 intervals of 2 min at 80–90% of MHR with 2 min at 50–60% MHR between each | 30 min | 4 | Yes | HRV lying (SDNN↗) | No | 5 | Blood pressure |
| Sacre 2014 | Australia | Non-RCT | 22 | 59.0±10.0 | 59% | End. & Resist. | 6 | RPE “moderate-vigorous” | 75 min | 2 | +/- | HRV lying (RR↘, SDNN↗, RMSSD, TP↗, LF, HF, LF/HF) | No | 5 | HbA1c, BMI, blood pressure, total cholesterol, HDL, LDL, triglycerides |
| 25 | 60.0±9.0 | 40% | Control | ||||||||||||
| Simmonds 2012 | Australia | R Comp. frequency & duration of sessions | 8 | 68.6±2.8 | 0% | End. | 3 | At 100% of Tge | 60 min | 2 | unclear | HRV lying (RR, SDNN↗, RMSSD↗, LF, HF↗, LF/HF) | No | 10 | HbA1c, total cholesterol, HDL, LDL, triglycerides, VO2 |
| 7 | 69.3±2.5 | 0% | End. | 30 min | 4 | unclear | |||||||||
| Sridhar 2010† | India | RCT | 55 | 61.8±3.1 | 56% | End. | 12 | Unclear | 45 min | 5 | Yes | HRV lying: ↗ ratio between longest RR and shortest | Yes | 1 | HbA1c, BMI, blood pressure |
| 50 | 59.5±2.8 | 55% | Control | - | |||||||||||
| Wormgoor 2018† | New Zealand | R Comp. Type of exercise | 11 | 52.5±7.0 | 100% | End. & Resist. | 3 and 6 | Up to 26 min 55% eWLmax & 2 sets of 12 repetitions at 75% of 1-RM | 60 min | 3 | +/- | HRV lying: ratio between longest RR and shortest | Yes | 1 | HbA1c, BMI, HDL, triglycerides, VO2 |
| 11 | 52.2±7.1 | 100% | HIIT & Resist | Up to 12 (or 8) intervals of 1 min at 95% (or 120) eWLmax with 1 (or 2.25) min at 40 (or 30)% eWLmax between each & 2 sets of 12 repetitions at 75% of 1-RM | +/- | ||||||||||
| Zoppini 2007 | Italy | Pre-post | 12 | 65.7±5.6 | 42% | End. | 6 | 50–70% of HRR | 60 min | 2 | Yes | HRV lying (RR, TP, LF, HF, LF/HF) | No | 10 | HbA1c, BMI, blood pressure, HDL, LDL, triglycerides |
1-RM: one repetition maximum, DB: Deep Breathing, End.: endurance training, eWLmax: estimate maximal workload, HBP: high-blood pressure; HIIT: high intensity interval training, HRR: heart rate reserve, MHR: maximum heart rate, N: sample size, Non-RCT: non-randomized controlled trial, R Comp. Type of exercise: randomized comparative on type of exercise, RCT: randomized controlled trial, Resist.: resistance training, RPE: rating of perceived exertion, RPM: revolutions per minute, Tge: gas-exchange threshold, +/- means partially supervised, * supervised during 12 weeks, not supervised after, data at 6 months considered as “partially supervised”.
*: only significant increase (↗) or decrease (↘) are presented (differences between groups or after vs before exercise training).
†: not included in the meta-analyses.