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The aim of this study was to determine the acute effects of high‐intensity interval training (HIIT) exercise and endurance exercise (EE) on pulmonary function, sympathetic/parasympathetic balance, and cardiorespiratory coupling (CRC) in healthy participants. Using a crossover repeated‐measurements design, four females and four males were exposed to EE (20 min at 80% maximal heart rate [HR]), HIIT (1 min of exercise at 90% maximal HR per 1 min of rest, 10 times), or control condition (resting). Pulmonary function, HR, CRC, and heart rate variability (HRV) were assessed before and after the interventions. Results revealed no significant effects of EE or HIIT on pulmonary function. The EE, but not HIIT, significantly increased CRC. In contrast, HRV was markedly changed by HIIT, not by EE. Indeed, both the low‐frequency (LFHRV) and high‐frequency (HFHRV) components of HRV were increased and decreased, respectively, after HIIT. The increase in LFHRV was greater after HIIT than after EE. Therefore, a single bout of HIIT or EE has no effects on pulmonary function. Moreover, CRC and cardiac autonomic regulation are targeted differently by the two exercise modalities.

It has been suggested that time at a high fraction (%) of maximal oxygen uptake (VO2max) plays a decisive role for adaptations to interval training. Yet, no study has, to date, measured the % of VO2max during all interval sessions throughout a prolonged training intervention and subsequently related it to the magnitude of training adaptations. Thus, the present study aimed to investigate the relationship between % of VO2max achieved during an interval training intervention and changes in endurance performance and its physiological determinants in well‐trained cyclists. Twenty‐two cyclists (VO2max 67.1 (6.4) mL·min−1 ·kg−1; males, n = 19; females, n = 3) underwent a 9‐week interval training intervention, consisting 21 sessions of 5 × 8‐min intervals conducted at their 40‐min highest sustainable mean power output (PO). Oxygen uptake was measured during all interval sessions, and the relationship between % of VO2max during work intervals and training adaptations were investigated using linear regression. A performance index was calculated from several performance measures. With higher % of VO2max during work intervals, greater improvements were observed for maximal PO during the VO2max test (R2adjusted = 0.44, p = 0.009), PO at 4 mmol·L−1 [blood lactate] (R2adjusted = 0.25, p = 0.035), the performance index (R2adjusted = 0.36, p = 0.013), and VO2max (R2adjusted = 0.54, p = 0.029). Other measures, such as % of maximal heart rate, were related to fewer outcome variables and exhibited poorer session‐to‐session repeatability compared to % of VO2max. In conclusion, improvements in endurance measures were positively related to the % of VO2max achieved during interval training. Percentage of VO2max was the measure that best reflected the magnitude of training adaptations. Highlights In the present study, we measured well‐trained cyclists' oxygen uptake during 21 power output‐matched interval sessions throughout a 9‐week training intervention and related it to the magnitude of training adaptations. For the first time, we demonstrate that gains in endurance measures following an interval training intervention are positively related to the fraction of maximal oxygen uptake (V̇O2max) and time spent ≥90% of V̇O2max during interval sessions. Fraction of V̇O2max during sessions demonstrated better session‐to‐session repeatability and displayed stronger associations with improvements in indicators of endurance performance compared to the percentage of maximal heart rate.

ABSTRACT The purpose of this study was to compare the effects of a 1‐week block of moderate‐intensity interval training (MIT) and high‐intensity interval training (HIT) in well‐trained cyclists. Cyclists (♀ = 1; ♂ = 21; maximal oxygen uptake (V̇O2max) = 69.5 (6.0) mL·min−1·kg−1) performed both a MIT block involving 6 sessions over 7 days (5–7 × 10–14‐min work intervals, rate of perceived exertion (RPE): 14.5 (0.3)) and a HIT block involving 5 sessions over 6 days (5 × 8.75‐min with multiple short intervals, RPE: 17.1 (0.4)). Post‐testing was performed after 6 days of active recovery, and blocks were separated by 2 months. Testing included 15‐min maximal cycling power (PO15min), 10 s maximal sprint power (PO10sec), and power output at a blood lactate concentration of 4 mmol·L−1 (PO4mmol). Both the MIT and HIT block improved PO15min (4.9 (8.7)% and 2.8 (5.3)%, respectively), with no difference between blocks (p = 0.44). MIT displayed greater improvement than HIT in PO4mmol (4.5 (4.5)% vs. 2.1 (2.7)%, respectively, p = 0.03, moderate effect size (ES)), while HIT had a moderate ES compared to MIT for improvement in PO10sec (1.5 (3.7)% vs. −1.5 (7.3)%, respectively), that was not significant (p = 0.08). No differences were observed between blocks in changes in V̇O2max (p = 0.43) or measures of gross efficiency (p range = 0.43–0.79). However, MIT induced a larger increase in % of V̇O2max at PO4mmol compared to HIT (1.2 (3.4)%‐points vs. −0.9 (2.5)%‐points, respectively, p = 0.02, moderate ES). In conclusion, both a MIT block (lower work interval intensity but longer work duration) and a HIT block (higher work interval intensity but shorter work duration) can improve endurance performance determinants and PO15min with some work intensity‐specific adaptations. Highlights This study investigated the effects of a short moderate‐intensity interval training (MIT) block (lower exercise intensity but longer work intervals) compared to a short high‐intensity interval training (HIT) block (higher exercise intensity but shorter work intervals) within well‐trained cyclists. Both a 1‐week MIT block and a 1‐week HIT block followed by a 6‐day active recovery period effectively improve endurance performance determinants and 15‐min maximal power output

High-intensity functional training (HIFT) has become more popular, and the number of practitioners has increased; however, it remains unclear whether perturbations in the immune parameters occur, even after one single bout. Our aim was to examine acute leucocyte, muscle damage, and stress marker responses following a single 'Cindy' workout session, and compare the results between novice and experienced participants. Twenty-three HIFT practitioners (age 31.0 ± 1.0 years) completed the 'Cindy' workout. They were categorized as novice (3-8 months of experience; n = 10) and experienced (≥18 months; n = 13). White blood cell (WBC) count, plasma creatine kinase (CK) activity, blood cortisol level, and lactate concentration were measured. Blood analysis was performed before (pre-ex), immediately after (post-ex), 30 min after (post-30 min), and 24 h after (post-24 h) a single 'Cindy' workout session. WBC count was higher post-ex (6.8 to 11.8x103/μL) and returned to baseline values within post-30 min (p<0.01). Neutrophil (3.3 to 4.5x103/μL) and lymphocyte levels (2.8 to 5.9x103/μL) were higher post-ex and returned to baseline values after post-24 h, yet lymphocytopoenia (2.2x103/μL) was observed at post-30 min (p<0.01). CK increased post-ex (174.9 to 226.7 U.L-1) and remained elevated post-24 h. Cortisol (14.7 to 17.0 μg/dL) and lactate (1.9 to 13.5 mmol.l-1) responses increased post-ex, but only the lactate level was reduced at post-30 min (p<0.01). The experienced participants had higher WBC, lymphocyte, and cortisol concentrations post-ex than the novice ones (p<0.01). A single HIFT session elicited significant acute perturbations in WBC count, stress markers, and muscle tissue, which is like other similar regimens. Importantly, the experienced participants showed greater lymphocyte and cortisol responses than the novice ones.

Background Aging is associated with a progressive decline in skeletal muscle mass and strength as well as an increase in adiposity. These changes may have devastating impact on the quality of life of older adults. Mitochondrial dysfunctions have been implicated in aging‐related and obesity‐related deterioration of muscle function. Impairments in mitochondrial quality control processes (biogenesis, fusion, fission, and mitophagy) may underlie this accumulation of mitochondrial dysfunction. High‐intensity interval training (HIIT) was shown to improve muscle and mitochondrial function in healthy young and old adults and to improve body composition in obese older adults. Recent studies also positioned citrulline (CIT) supplementation as a promising intervention to counter obesity‐related and aging‐related muscle dysfunction. In the present study, our objectives were to assess whether HIIT, alone or with CIT, improves muscle function, functional capacities, adipose tissue gene expression, and mitochondrial quality control processes in obese older adults. Methods Eighty‐one‐old and obese participants underwent a 12 week HIIT with or without CIT on an elliptical trainer [HIIT‐CIT: 20 men/25 women, 67.2 ± 5.0 years; HIIT‐placebo (PLA): 18 men/18 women, 68.1 ± 4.1 years]. Handgrip and quadriceps strength, lower limb muscle power, body composition, waist circumference, and functional capacities were assessed pre and post intervention. Vastus lateralis muscle biopsies were performed in a subset of participants to quantify markers of mitochondrial content (TOM20 and OXPHOS subunits), biogenesis (TFAM), fusion (MFN1&2, OPA1), fission (DRP1), and mitophagy (Parkin). Subcutaneous abdominal adipose tissue biopsies were also performed to assess the expression of genes involved in lipid metabolism. Results HIIT‐PLA and HIIT‐CIT displayed improvements in functional capacities (P < 0.05), total (mean ± SD: HIIT‐PLA: +1.27 ± 3.19%, HIIT‐CIT: +1.05 ± 2.91%, P < 0.05) and leg lean mass (HIIT‐PLA: +1.62 ± 3.85%, HIIT‐CIT: +1.28 ± 4.82%, P < 0.05), waist circumference (HIIT‐PLA: −2.2 ± 2.9 cm, HIIT‐CIT: −2.6 ± 2.5 cm, P < 0.05), and muscle power (HIIT‐PLA: +15.81 ± 18.02%, HIIT‐CIT: +14.62 ± 20.02%, P < 0.05). Only HIIT‐CIT decreased fat mass (−1.04 ± 2.42%, P < 0.05) and increased handgrip and quadriceps strength (+4.28 ± 9.36% and +10.32 ± 14.38%, respectively, P < 0.05). Both groups increased markers of muscle mitochondrial content, mitochondrial fusion, and mitophagy (P < 0.05). Only HIIT‐CIT decreased the expression of the lipid droplet‐associated protein CIDEA (P < 0.001). Conclusions High‐intensity interval training is effective in improving functional capacities, lean mass, muscle power, and waist circumference in obese older adults. HIIT also increases markers of mitochondrial biogenesis, mitochondrial fusion, and mitophagy. Importantly, adding CIT to HIIT results in a greater increase in muscle strength and a significant decrease in fat mass. The present study therefore positions HIIT combined with CIT as an effective intervention to improve the health status of obese older adults.

Time-restricted eating (TRE) and high-intensity interval training (HIIT) improve cardiometabolic health in individuals with overweight/obesity, with high adherence rates in supervised settings. Long-term maintenance of TRE and HIIT in real-world settings is unknown. In our previous TREHIIT trial, 131 women (body mass index (BMI) ≥ 27 kg/m 2 ) were randomized to 7 weeks of TRE (eating window 10-h/day), HIIT (3 sessions/week), a combination (TREHIIT), or no intervention (CON). We investigated self-reported continuation of TRE and/or HIIT after 2 years. Fifty-nine participants (39.0 years (standard deviation (SD) 6.1), BMI 30.7 kg/m 2 (SD 4.2)) attended the follow-up. Of those who completed the 7-week TRE or HIIT intervention, 46% maintained TRE and 45% continued HIIT for 2 years. There were no statistically significant (at p  < .01) between-group differences in cardiometabolic outcomes, but non-significant lower body mass in HIIT (-4.2 kg, 95% confidence interval (CI), -7.7 to -0.7, p  = .019) and visceral fat in TREHIIT (-18 cm 2 , CI, -33 to -4, p  = .015) versus CON. After 2 years, HIIT and TREHIIT had ~ 4 kg lower fat mass and ~ 20 cm² lower visceral fat (both p  < .001) compared with baseline. A short-term TRE and HIIT intervention may promote long-term lifestyle changes and health benefits. Future studies should collect objective adherence data to understand long-term maintenance of TRE and HIIT.

PurposeTo compare the effects of high-intensity interval training (HIIT) and moderate-intensity training (CONT), matched for total work, on cardiorespiratory coordination and aerobic fitness.MethodsThis is a two-arm parallel group single-blind randomised study. Twenty adults were assigned to 6 weeks of HIIT or volume-matched CONT. Participants completed a progressive maximal cycling test before and after the training period. Principal component (PC) analysis was performed on the series of cardiorespiratory variables to evaluate dimensionality of cardiorespiratory coordination, before and after lactate turnpoint. PC1 eigenvalues were compared.ResultsBoth HIIT and CONT improved aerobic fitness (main effects of time, p < 0.001, \\[ \\eta_{\\text{p}}^{2} \\] ≥ 0.580), with no differences between groups. CONT decreased the number of PCs from two to one at intensities both below and above the lactate turnpoint; PC1 eigenvalues increased after CONT both below (Z = 2.08; p = 0.04; d = 0.94) and above the lactate turnpoint (Z = 2.10; p = 0.04; d = 1.37). HIIT decreased the number of PCs from two to one after the lactate turnpoint only; PC1 eigenvalues increased after HIIT above the lactate turnpoint (Z = 2.31; p = 0.02; d = 0.42).ConclusionsAlthough CONT and HIIT improved aerobic fitness to a similar extent, there were different patterns of change for cardiorespiratory coordination. These changes appear training-intensity specific and could be sensitive to investigate the individual response to endurance training.

Background This study assessed the feasibility and acceptability of two common types of exercise training—high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT)—in adults with Crohn’s disease (CD). Methods In this mixed-methods pilot trial, participants with quiescent or mildly-active CD were randomly assigned 1:1:1 to HIIT, MICT or usual care control, and followed up for 6 months. The HIIT and MICT groups were offered three exercise sessions per week for the first 12 weeks. Feasibility outcomes included rates of recruitment, retention, outcome completion, and exercise attendance. Data were collected on cardiorespiratory fitness (e.g., peak oxygen uptake), disease activity, fatigue, quality of life, adverse events, and intervention acceptability (via interviews). Results Over 17 months, 53 patients were assessed for eligibility and 36 (68%) were randomised (47% male; mean age 36.9 [SD 11.2] years); 13 to HIIT, 12 to MICT, and 11 to control. The exercise session attendance rate was 62% for HIIT (288/465) and 75% for MICT (320/429), with 62% of HIIT participants (8/13) and 67% of MICT participants (8/12) completing at least 24 of 36 sessions. One participant was lost to follow-up. Outcome completion rates ranged from 89 to 97%. The mean increase in peak oxygen uptake, relative to control, was greater following HIIT than MICT (2.4 vs. 0.7 mL/kg/min). There were three non-serious exercise-related adverse events, and two exercise participants experienced disease relapse during follow-up. Conclusions The findings support the feasibility and acceptability of the exercise programmes and trial procedures. A definitive trial is warranted. Physical exercise remains a potentially useful adjunct therapy in CD. [ID: ISRCTN13021107].

To investigate the release of lipolytic hormones during various high-intensity interval training (HIIT) and moderate-intensity continuous training (MICT), and their effects on fat loss. 39 young women categorized as obese (with a body fat percentage (BFP) ≥30%) were randomly allocated to one of the following groups: all-out sprint interval training (SIT, n =10); supramaximal HIIT (HIIT120, 120%V̇O2peak, n = 10); HIIT (HIIT90, 90%V̇O2peak, n = 10), or MICT, (60%V̇O2peak, n = 9) for a twelve-week observation period consisting of 3 to 4 exercise sessions per week. Serum epinephrine (EPI) and growth hormone (GH) were measured during the 1st, 20th, and 44th training sessions. Body weight (BW), body mass index (BMI), whole-body fat mass (FM) and BFP were assessed pre- and post-intervention. Following the 1st and 20th sessions, significant increases in EPI (p < 0.05) were observed post-exercise in HIIT120 and HIIT90, but not in SIT and MICT. In the 44th session, the increased EPI was found in SIT, HIIT120, and HIIT90, but not in MICT (p < 0.05). For the GH, a significant increase was observed post-exercise in all groups in the three sessions. The increased EPI and GH returned to baselines 3 hours post-exercise. After the 12-week intervention, significant reductions in FM and BFP were found in all groups, while reductions in BW and BMI were only found in the SIT and HIIT groups. Greater reductions in FM and BFP, in comparison to MICT, were observed in the SIT and HIIT groups (p < 0.05). 12-week SIT, HIIT120, and HIIT90, in comparison to MICT, were more efficacious in fat reduction in obese women, partly benefiting from the greater release of lipolytic hormones during training sessions.

PurposeThe aim of this study was to compare the combined effects of resistance and sprint training, with very short efforts (5 s), on aerobic and anaerobic performances, and cardiometabolic health-related parameters in young healthy adults.MethodsThirty young physically active individuals were randomly allocated into four groups: resistance training (RTG), sprint interval training (SITG), concurrent training (CTG), and control (CONG). Participants trained 3 days/week for 2 weeks in the high-intensity interventions that consisted of 6–12 “all out” efforts of 5 s separated by 24 s of recovery, totalizing ~ 13 min per session, with 48–72 h of recovery between sessions. Body composition, vertical jump, lower body strength, aerobic and anaerobic performances, heart rate variability (HRV), and redox status were evaluated before and after training. Total work (TW), rating of perceived exertion (CR-10 RPE) and mean HR (HRmean) were monitored during sessions. Incidental physical activity (PA), dietary intake and perceived stress were also controlled.ResultsMaximum oxygen consumption (VO2max) significantly increased in SITG and CTG (P < 0.05). Lower body strength improved in RTG and CTG (P < 0.05), while countermovement jump (CMJ) was improved in RTG (P = 0.04) only. Redox status improved after all interventions (P < 0.05). No differences were found in TW, PA, dietary intake, and psychological stress between groups (P > 0.05).ConclusionsRT and SIT protocols with very short “all out” efforts, either performed in isolation, or combined, demonstrated improvement in several physical fitness- and health-related parameters. However, CT was the most efficient exercise intervention with improvement observed in the majority of the parameters.