Table 1.
Summary of included studies
| Study | Sample | Study design | Measures | Results of DFA‐alpha1 |
|---|---|---|---|---|
| Tulppo et al. (2001) | 20 male volunteers (29 ± 5yr) | 30min prolonged walking exercise (low intensity: 4km/h) | Polar R‐R recorder + continuous‐surface TEC−7100 electrocardiogram; last 500 beats during prolonged exercise; measures: HR, LF, HF, TP, ApEn, DFA‐alpha1 (window width: 4 ≤ n ≤ 11 beats), BP | Prolonged low intensity exercise versus baseline: ↑ |
| Hautala et al. (2003) | 9 male volunteers (37 ± 11yr) | Incremental cycling exercise test until voluntary exhaustion (start: 50W for 5min, increment: 25W/3min); 20min prolonged walking/running exercise (low intensity: 4km/h; mid intensity: 12km/h) | Polar real‐time microprocessor QRS detector system; 3min intervals during incremental test, 15min during prolonged exercise; measures: HR, SDNN, LF, HF, DFA‐alpha1 (window width: 4 ≤ n ≤ 11 beats) | Biphasic course with increasing exercise intensity in the incremental test: ↑↓; Prolonged low intensity exercise: ↑; Prolonged mid intensity exercise: ↓ |
| Casties et al. (2006) | 7 endurance trained male cyclists (22.9 ± 2.5yr) | Incremental cycling exercise test (3 stages: 8min at 40% VO2MAX from an incremental test, 8min at 70%, 8min at 90%), 50min recovery (sitting) | Ela medicals electrocardiogram; 5min intervals during exercise, 10min during recovery; measures: meanRR, SDNN, RMSSD, LF, HF, LLE, DFA‐alpha1 (window width: 4 ≤ n ≤ 16 beats) | Biphasic course with increasing exercise intensity: ↑↓; Recovery: ↑ |
| Platisa and Gal (2008) | 10 male volunteers (22.8 ± 2.4yr) | Incremental running exercise test until voluntary exhaustion (start: 9km/h and incline of 2%, increment: 2%/3min), 15min recovery (supine) | Viasys electrocardiogram; last stage of running, 3rd min of recovery; measures: meanRR, SDNN, DFA‐alpha1 (window width: n < 11 beats), DFA‐alpha2 (window width: n ≥ 11 beats) | Last stage versus baseline: ↓; Recovery: ↑ |
| Platisa et al. (2008) | 9 trained male basketball players (18.0 ± 0.7yr), 11 untrained male volunteers (22.8 ± 0.7yr) | Incremental running exercise test until voluntary exhaustion (start: 9km/h and incline of 2%, increment: 2%/3min), 15min recovery (supine) | Viasys electrocardiogram; last stage of running, 5th min of recovery; measures: HR, LF, HF, DFA‐alpha1 (window width: 4 ≤ n ≤ 16 beats), SampEn, BF, VO2, RER | Last stage versus baseline ‐ in both groups: ↓ (Pooled data: biphasic course with increasing exercise intensity in the incremental test: ↑↓); Recovery: ↑ |
| Karavirta et al. (2009) | 93 male volunteers (55.6 ± 7.4yr) | Incremental cycling exercise test until voluntary exhaustion (start: 50W, increment: 20W/2min, cadence: 60rpm) | Polar s810i; 2min intervals; measures: HR, LF, HF, DFA‐alpha1 (window width: 4 ≤ n ≤ 11 beats), VO2 | Biphasic course with increasing exercise intensity: ↑↓ |
| Blasco‐Lafarga et al. (2017) | 13 endurance trained male cyclists (15.43 ± 0.51yr) | Incremental cycling exercise test until voluntary exhaustion (start: 10min of warm‐up pedaling: ≈ 50% VO2MAX (< 120W, interspersed with 3 submaximal self‐selected accelerations of 10 to 20s), increment: 30W/4min, every stage followed by 30s for blood lactate collection (allowed to slow down), cadence: self‐selected) | Polar RS800; 3min intervals; measures: HR, meanRR, RMSSD, SD1, DFA‐alpha1 (window width: 4 ≤ n ≤ 16 beats), VO2, RER, BL, SaO2, RPE | Increasing exercise intensity: ↓ |
| Gronwald et al. (2018) | 16 endurance trained male cyclists (25.9 ± 3.8yr) | 60min prolonged cycling exercise at 90% IANS from an incremental test; varied cadences [rpm] every 10 min (90(1), 120(1), 60(1), 120(2), 60(2), 90(2)), 10min recovery (100W) | Polar s810i; 2min intervals; measures: HR, meanRR, SDNN, DFA‐alpha1 (window width: 4 ≤ n ≤ 16 beats), BL, RPE | 90(1) versus 120(1): ↓; 60(1) versus 120(2): ↓; 90(1) versus 90(2): ↓; Recovery: ↑ |
| Gronwald et al. (2019) | 16 endurance trained male cyclists (25.9 ± 3.8yr) | Incremental cycling exercise test until voluntary exhaustion (start: 100W, increment: 20W/3min, cadence: 80−90rpm) | Polar s810i; 2min intervals; measures: HR, meanRR, SDNN, RMSSD, DFA‐alpha1 (window width: 4 ≤ n ≤ 16 beats), VO2, RER, BL, RPE | Biphasic course with increasing exercise intensity: ↑↓ |
| Gronwald et al. (2019a) | 9 endurance trained male cyclists (26.4 ± 4.1yr) | Prolonged cycling exercise at IANS from an incremental test until voluntary exhaustion (10%–100%) | Polar s810i; 2min intervals; measures: HR, meanRR, SDNN, DFA‐alpha1 (window width: 4 ≤ n ≤ 16 beats), SpO2, BL, RPE | 10% versus 100%: ↓; Recovery: ↑ |
| Gronwald et al. (2019b) | 16 endurance trained male cyclists (25.9 ± 3.8yr) | Interval cycling session (3(IB)x5 intervals with 60s at PMAX from an incremental test; 60s recovery between intervals and 10min (AR) after each IB at 100W, cadence: 80−90rpm) | Polar s810i; 1min intervals; measures: HR, meanRR, RMSSD, DFA‐alpha1 (window width: 4 ≤ n ≤ 16 beats), BL, RPE | IB versus AR: ↑; AR versus IB: ↓; no change during the course of AR |
Abbreviations: ApEn, Approximate entropy; AR, Active recovery; BF, Breathing frequency; BL, Blood lactate concentration; BP, Blood pressure; DFA‐alpha1, Short‐term scaling exponent of detrended fluctuation analysis; DFA‐alpha2, Long‐term scaling exponent of detrended fluctuation analysis; HF, High‐frequency band; HR, Heart rate; IANS, Individual anaerobic threshold; IB, Interval block; LF, Low‐frequency band; LLE, Largest Lyapunov Exponent; meanRR, Average of normal R‐R intervals; RER, Respiratory exchange ratio; RMSSD, root mean square of successive differences; RPE, rate of perceived exertion; SampEn, Sample entropy; SDNN, Standard deviation of all normal RR‐intervals; SD1, Transversal axis from the Poincare plot; SpO2, Oxygen saturation of the blood; TP, Total power; VO2, oxygen uptake. ↑: Increase of DFA‐alpha1, ↓: Decrease of DFA‐alpha1.