Abstract
Aim: MicroRNA-222 (miR-222) and miR-29c have been identified as important modulators of cardiac growth and may protect against pathological cardiac remodeling. miR-222 and -29c may thus serve as functional biomarkers for exercise-induced cardiac adaptations. This investigation compared the effect of two workload-matched high-intensity interval training (HIIT) protocols with different recovery periods on miR-222 and -29c levels.Methods: Sixty-three moderately trained females and males (22.0 ± 1.7 years) fulfilled the eligibility criteria and were randomized into two HIIT groups using sex and exercise capacity. During a controlled 4-week intervention (two sessions/week) a 4 × 30 HIIT group performed 4 × 30 s runs (all-out, 30 s active recovery) and a 8 × 15 HIIT group performed 8 × 15 s runs (all-out, 15 s active recovery). miR-222 and -29c as well as transforming growth factor-beta1 (TGF-beta1) mRNA levels were determined during high-intensity running as well as aerobic exercise using capillary blood from earlobes. Performance parameters were assessed using an incremental continuous running test (ICRT) protocol with blood lactate diagnostic and heart rate (HR) monitoring to determine HR recovery and power output at individual anaerobic threshold (IAT).Results: At baseline, acute exercise miR-222 and -29c levels were increased only in the 4 × 30 HIIT group (both p < 0.01, pre- vs. post-exercise). After the intervention, acute exercise miR-222 levels were still increased in the 4 × 30 HIIT group (p < 0.01, pre- vs. post-exercise) while in the 8 × 15 HIIT group again no acute effect was observed. However, both HIIT interventions resulted in elevated resting miR-222 and -29c levels (all p < 0.001, pre- vs. post-intervention). Neither of the two miRNAs were elevated at any ICRT speed level at baseline nor follow-up. While HR recovery was improved by >24% in both HIIT groups (both p ≤ 0.0002) speed at IAT was improved by 3.6% only in the 4 × 30 HIIT group (p < 0.0132). Correlation analysis suggested an association between both miRNAs and TGF-beta1 mRNA (all p ≤ 0.006, r ≥ 0.74) as well as change in speed at IAT and change in miR-222 levels (p = 0.024, r = 0.46).Conclusions: HIIT can induce increased circulating levels of cardiac growth-associated miR-222 and -29c. miR-222 and miR-29c could be useful markers to monitor HIIT response in general and to identify optimal work/rest combinations.
Highlights
High-intensity interval training (HIIT) has become a wellestablished training component of athletes to improve aerobic endurance and maximal exercise capacity (Sloth et al, 2013; Weston et al, 2014; Milanovicet al., 2015)
In terms of cardiac adaptations, recent investigations suggested that metabolic and functional changes in the heart are already detectable after 2 weeks of HIIT (Eskelinen et al, 2016; Heiskanen et al, 2016)
Our main findings are (1) speed at individual anaerobic threshold (IAT) was increased by a 4 × 30 but not a 8 × 15 HIIT protocol, (2) miR222 and -29c levels were elevated by a single session of 4 × 30 but not 8 × 15 HIIT at baseline, (3) miR-222 levels were still elevated by 4 × 30 HIIT at follow-up while again no effect was seen in the 8 × 15 HIIT group, (4) resting miR-222 and -29c levels were increased after the intervention in both HIIT groups and (5) miR-222 and -29c levels were not increased during incremental continuous runs
Summary
High-intensity interval training (HIIT) has become a wellestablished training component of athletes to improve aerobic endurance and maximal exercise capacity (Sloth et al, 2013; Weston et al, 2014; Milanovicet al., 2015). In terms of cardiac adaptations, recent investigations suggested that metabolic and functional changes in the heart are already detectable after 2 weeks of HIIT (six exercise sessions, 4 – 6 × 30 s of all-out cycling) (Eskelinen et al, 2016; Heiskanen et al, 2016). Stöggl and Björklund (2017) analyzed the cardiovascular response in terms of acute HR recovery to a 9-week HIIT intervention in endurance athletes (27 exercise sessions, 4 × 4 min at > 90% HRmax running or cycling) and found that HR recovery was improved by 11.2%. A 12-week HIIT (4 × 4 min at > 90% HRmax, 3 times/week, uphill walking) performed by patients with stable post-infarction heart failure induced reverse remodeling of the left ventricle (Wisløff et al, 2007)
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