Purpose The aim of this non-randomized parallel group study was to examine the 12 week effects of a very low-carbohydrate high-fat diet (VLCHF) on maximal cardiorespiratory capacity, high-intensity interval training (HIIT) performance, and cardiac autonomic regulation. Methods Twenty-four recreationally trained participants allocated to either a VLCHF ( N = 12) or a habitual diet (HD; N = 12) group completed 12 weeks of a diet and exercise (VLCHF) or an exercise only intervention (HD). Maximal graded exercise tests (GXT) were performed at baseline, after 4, 8, and 12 weeks. A supervised HIIT session and the 30-15 Intermittent Fitness Test (30-15 IFT ) were conducted once a week. Results Total time to exhaustion (TTE) in both GXT and 30-15 IFT largely increased in both VLCHF ( p = 0.005, BF 10 = 11.30 and p = 0.001, BF 10 ≥ 100, respectively) and HD ( p = 0.018, BF 10 = 3.87 and p = 0.001, BF 10 ≥ 100, respectively) groups after 12 weeks. Absolute maximal oxygen uptake ( O 2max ) was not changed in both groups but relative O 2max increased in VLCHF in concert with reductions in body mass (66.7 ± 10.2–63.1 ± 8.5 kg). Cardiac autonomic regulation did not reveal any between-group differences after 12 weeks. VLCHF diet induced an increase in β-hydroxybutyrate, which tended to normalize during the intervention period. Conclusion The 12 week VLCHF diet did not impair high-intensity continuous or intermittent exercise lasting up to 25 min, nor did it impair maximal cardiorespiratory performance or autonomic nervous system (ANS) activity.

The aim of this study was to investigate changes of 51 ± 0.63, 0.84 ± 0.34 and 1.80 ± 0.60 for the 15s/15s, 30s/30s and 60s/60s protocol, respectively) and myoglobin (1.11 ± 0.29, 0.45 ± 0.48 and 1.09 ± 0.22 for the 15s/15s, 30s/30s and 60s/60s protocol, respectively). There were no substantial between-trial differences in other biochemical variables. In conclusion, the 15s/15s and 60s/60s protocols might be preferred to the 30s/30s protocols in order to maximize the training stimulus.

At present, analysis of heart rate variability (HRV) is becoming widely used as a clinical or research tool. Supported reliability studies for HRV measurement are, however, still limited. The main purpose was to perform an assessment of the absolute and relative reliability of HRV parameters from short-term recordings by means of orthoclinostatic stimulation and to investigate, whether there is a difference in repeating the retest immediately or after several days. The study group consisted of 99 participants (mean age 22 ± 1.24 years). Standard HRV indexes were computed: PT (total spectral power), PHF (high frequency spectral power), PLF (low frequency spectral power) and LF/HF. Absolute reliability was assessed by the standard error of measurement and 95% limits of agreement; relative reliability was assessed by the intraclass correlation coefficient. There was also an estimate of the sample size needed to detect the mean difference ≥ 30% of the between-subject standard deviation. In conclusion, a large random variation (within individuals) of HRV parameters was revealed, regardless of whether the retest was repeated immediately or with an interruption. For most HRV parameters (particularly in the immediately repeated test-retest), however, random variation represents a limited portion of the between-subject variability.

Purpose: This randomized controlled parallel-group study examined the effects of a very low-carbohydrate high-fat (VLCHF) diet and high-intensity interval training (HIIT) program over 12 weeks on visceral adipose tissue (VAT) and cardiorespiratory fitness (CRF) level in overfat individuals.Methods: Ninety-one participants were randomly allocated to the HIIT (N = 22), VLCHF (N = 25), VLCHF+HIIT (N = 25), or control (N = 19) groups for 12 weeks. Body composition and CRF were analyzed before the experimental period and after 4, 8, and 12 weeks. Dual-energy X-ray absorptiometry (DXA) and graded exercise test (GXT) to volitional exhaustion were used for the body composition and CRF assessments, respectively.Results: There were significant between-group differences in the VAT mass and body composition outcome changes. VAT mass decreased after 12 weeks only in the VLCHF and VLCHF+HIIT groups (p < 0.001, median [95% CI]: VLCHF: −142.0 [−187.0; −109.5] g; VLCHF+HIIT: −104.0 [−135.0; −71.0] g). Similarly, changes in body mass, total body fat, trunk fat mass, waist and hip circumferences were distinctly decreased in the VLCHF and VLCHF+HIIT groups, when compared to HIIT and Control groups. Total lean mass significantly decreased in the VLCHF and VLCHF+HIIT groups (−2.1 [−3.0; −1.6] kg and −2.5 [−3.6; −1.8] kg, respectively) after 12 weeks. While the HIIT program significantly increased total time to exhaustion in the GXT, peak oxygen uptake was unchanged.Conclusions: A VLCHF diet, either in isolation or in combination with HIIT, was shown to induce a significant reduction in VAT mass and body composition variables. HIIT alone did not cause such effects on body composition, but improved exercise capacity. Our findings indicate that the VLCHF diet and exercise training provoked different and isolated effects on body composition and CRF.Clinical Trial Registration: https://clinicaltrials.gov/ct2/show/NCT03934476, identifier: NCT03934476.

PurposeThe aim of this study was to investigate the influence of the cardiorespiratory fitness level on the response to high-intensity interval training (HIIT) with an individually adjusted running speed of the same relative intensity. The evaluation focused on acute cardiorespiratory response, postexercise cardiac autonomic modulation (heart rate variability (HRV)) and biochemical markers of inflammation, oxidative stress, and muscle damage.MethodsThirty participants were divided into 3 subgroups: well trained, moderately trained, and untrained. All the participants performed 30 min HIIT composed of 6 × 2 min interval exercise with work-to-relief ratio = 1 and work intensity 100% of individual velocity at maximal oxygen consumption (VO2​max ). Acute cardiorespiratory variables, postexercise HRV, lactate, interleukin-6 (IL-6), total antioxidant capacity (TAC), creatine kinase, and myoglobin up to 4 h after HIIT were monitored.ResultsThe differences in relatively expressed cardiorespiratory variables (heart rate, VO2) during HIIT were at most moderate, with the most pronounced between-group differences in absolute VO2 values. The disruption of the postexercise HRV was the most pronounced in untrained individuals, and this difference persisted 1 h after HIIT. The highest postexercise IL-6 and TAC concentrations and the lowest changes in creatine kinase and myoglobin were revealed in well-trained individuals.ConclusionThe higher fitness level was associated with the less pronounced postexercise cardiac autonomic changes and their faster restoration, even when there were similar acute cardiorespiratory responses. These findings were simultaneously accompanied by the higher postexercise IL-6 and TAC concentrations and less significant changes in muscle damage biochemical markers in well-trained individuals.

The cardiorespiratory, cardiac autonomic (via heart rate variability (HRV)) and plasma volume responses to varying sequences of high-intensity interval training (HIT) of consistent external work were investigated. Twelve moderately trained males underwent three HIT bouts and one control session. The HIT trials consisted of warm-up, followed by 12 min of 15 s, 30 s or 60 s work:relief HIT sequences at an exercise intensity of 100% of the individual velocity at [Formula: see text]O2max (v[Formula: see text]O2max), interspersed by relief intervals at 60% [Formula: see text]O2max (work/relief ratio = 1). HRV was evaluated via the square root of the mean sum of the squared differences between R-R intervals (rMSSD) before, 1 h, 3 h and 24 h after the exercise. Plasma volume was assessed before, immediately after, and 3 h and 24 h after. There were no substantial between-trial differences in acute cardiorespiratory responses. The rMSSD values remained decreased 1 h after the exercise cessation in all exercise groups. The rMSSD subsequently increased between 1 h and 3 h after exercise, with the most pronounced change in the 15/15 group. There were no relationships between HRV and plasma volume. All HIT protocols resulted in similar cardiorespiratory responses with slightly varying post-exercise HRV responses, with the 30/30 protocol eliciting the least disruption to post-exercise HRV. These post-exercise HRV findings suggest that the 30/30 sequence may be the preferable HIT prescription when the between-training period is limited.

The main purpose of the present study is to investigate the relationship between anaerobic power achieved in repeated anaerobic exercise and aerobic power. The study group consisted of 40 soccer players (age 17.3 ± 1.36 years). All participants performed 3 tests: a running-based anaerobic sprint test (RAST), a graded treadmill test (GXT), and a multistage fitness test (20mPST). A statistically significant correlation was found among peak power in the GXT and the maximum (r = 0.365, p=0.02), minimum (r=0.334, p=0.035) and average (r=0.401, p=0.01) power in the RAST. No relationships were found between VO2max obtained from both aerobic tests and any performance indices in the RAST. A statistically significant correlation was found between the VO2max obtained from the spiroergometry examination (GXT) and the calculated VO2max of 20mPST (r=0.382, p=0.015). In conclusion, the level of VO2max does not influence the performance indices in the RAST in elite junior soccer players. It is possible that the modification of anaerobic test protocol or a more heterogeneous study group would influence the results. The estimation of the VO2max in the 20mPST is too inaccurate and should not replace the laboratory spiroergometry examination.

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