Search Results (41)

Quantifying oxidative, glycolytic, and phosphagen energy system contributions during exercise is challenging due to their simultaneous activation and reliance on indirect estimation. This narrative review critically examines the methodological foundations, assumptions, and practical implications of current approaches used to estimate energy system contributions during continuous and intermittent exercise, with the aim of clarifying how these methods shape the interpretation of bioenergetic responses. Oxidative contribution, primarily estimated through oxygen uptake (VO₂) integration, typically exceeds (~75–88%) in continuous efforts longer than 6 min and can reach values above ~87% when exercise duration allows full development of VO₂ kinetics, particularly in trained young adult cohorts. In contrast, supramaximal efforts shorter than 30–90 s involve markedly lower oxidative contribution, commonly below ~50% and as low as ~8–19%. Glycolytic contribution is inferred from net blood lactate concentration accumulation and increases with exercise intensity, ranging from ~3–5% in longer severe-intensity efforts to values up to ~60% during brief maximal tasks lasting 15–30 s. Phosphagen contribution is estimated using the fast component of post-exercise VO₂ recovery or theoretical phosphocreatine breakdown models, and can reach ~39–48% in maximal efforts lasting 10–15 s, while declining to values below ~10% in prolonged exercise. Each method is shaped by exercise duration, intensity, structural format, and physiological assumptions, contributing to methodological heterogeneity and limiting direct comparability between studies. Advances in portable gas analyzers, near-infrared spectroscopy, and biosensing technologies have improved temporal resolution and ecological validity. To enhance the accuracy and practical application of energy system profiling, standardized and integrative frameworks are urgently required. Full article

Exercise-induced desaturation is an uncommon but clinically significant manifestation of patent foramen ovale, which is present in approximately one-quarter of the general population. Although patent foramen ovale is usually asymptomatic, exertion may provoke transient right-to-left shunting when dynamic changes in venous return and intrathoracic pressure favour intermittent right-to-left transit across the interatrial septum. This narrative review synthesises current evidence on exertion-provoked shunting and its contribution to otherwise unexplained dyspnoea and hypoxaemia. To illustrate these concepts, we present an illustrative case with marked exercise-induced desaturation in the absence of pulmonary disease. The evaluation combined contrast transthoracic and transoesophageal echocardiography with cardiopulmonary exercise testing, and the shunt magnitude was quantified invasively using catheter-based thermodilution at rest and during Valsalva provocation. Six months after percutaneous closure, repeat cardiopulmonary exercise testing showed complete resolution of exercise-induced desaturation without a statistically significant change in exercise tolerance (work performed). Notably, normalisation of oxygen saturation during exercise may occur without a measurable increase in maximal exercise capacity. Overall, patent foramen ovale-mediated right-to-left shunting is an under-recognised yet potentially reversible cause of exertional hypoxaemia; diagnosis typically requires deliberate physiological provocation and integrated imaging, and closure can be considered in carefully selected individuals. Full article

Anxiety is a common psychological challenge among athletes, particularly in response to intense training sessions. This randomized crossover study investigated the immediate effects of a single session of focused attention meditation on anxiety, autonomic responses, and performance during high-intensity intermittent training (HIIT) in twenty-six university-level speed skaters. Participants completed three pre-exercise interventions (focused attention meditation, controlled breathing, and random thinking) on separate occasions in a randomized order. Following each intervention, participants performed a leg cycling-based HIIT protocol consisting of 20 s of maximal effort work followed by 10 s of passive rest, repeated for 8 sets using a cycling ergometer. State anxiety was assessed using the State–Trait Anxiety Inventory, and mood disturbance was evaluated using the Profile of Mood States. Autonomic and physiological responses were assessed via heart rate variability (coefficient of variation), oxygen uptake, and power output, measured before and after the intervention and the HIIT bout. Focused attention meditation significantly reduced state anxiety compared with random thinking (ΔSTAI: −5.0 [6.0] vs. −1.0 [4.3]; p < 0.05, effect size = 0.527), whereas controlled breathing primarily influenced heart rate variability (CV: 0.10 [0.11] vs. 0.07 [0.03]; p = 0.041, effect size = 0.736). No significant differences were observed among conditions in mean power output or fatigue index during HIIT. These findings suggest that single-session focused attention meditation may serve as a practical pre-exercise strategy for an immediate reduction in state anxiety, without compromising subsequent high-intensity exercise performance. Full article

Background: Carbon dioxide (CO₂) is traditionally regarded as a metabolic by-product; however, growing evidence indicates that it plays an active regulatory role across multiple physiological systems. Acute hypercapnia elicits respiratory, cardiovascular, metabolic, immune, and neurocognitive responses, some of which may transiently influence exercise performance. This narrative review summarizes current evidence on CO₂ inhalation in healthy individuals and critically evaluates whether controlled hypercapnia may serve as a targeted stimulus in sport and exercise contexts. Methods: A narrative review of peer-reviewed English-language articles indexed in PubMed and Web of Science was conducted. A narrative approach was chosen due to the marked heterogeneity of study designs, hypercapnia-induction methods (e.g., CO₂ inhalation, voluntary hypoventilation, increased respiratory dead space), participant characteristics, and outcome measures, which precluded systematic synthesis. The review focused on studies involving healthy or physically active individuals and examined acute or short-term hypercapnic exposure. No strict publication date limits were applied. Studies conducted exclusively in clinical populations were excluded. Results: Short-term, controlled hypercapnia reliably increases ventilation, sympathetic activation, cerebral and muscular blood flow, and metabolic stress. Certain hypercapnia-based interventions—such as voluntary hypoventilation or added respiratory dead space—may enhance buffering capacity, reduce lactate accumulation and improve maximal oxygen uptake (VO₂max) during submaximal efforts and repeated-sprint performance during high-intensity, short-duration exercise. However, CO₂ inhalation frequently induces dyspnea, anxiety, and cognitive disruption, and higher concentrations pose clear safety risks. Current evidence does not support long-term improvements in VO₂max or long-duration endurance performance following hypercapnia-based interventions. Conclusions: Controlled, intermittent hypercapnia may provide a targeted metabolic and ventilatory stimulus that enhances tolerance to high-intensity exercise, yet its application remains experimental and context-dependent. The risks associated with CO₂ inhalation in healthy individuals currently outweigh its potential benefits, and safe, effective training protocols have not been fully established. Further research is needed to clarify the mechanisms, long-term adaptations, and practical utility of hypercapnia-based training strategies. Full article

Objectives: We examined how opposing running slopes can modulate interval training effects on aerobic performance and reduction–oxidation (REDOX) determinants. Methods: Fourteen physically active volunteers, assigned to either the Uphill group (UG) or the Downhill group (DG), completed 16 workouts of ten 30-s runs, at either +10% or −10% grade, with a work-to-rest ratio of 1:2 at 90% of their Maximum Aerobic Speed (MAS) over 8 weeks. Maximal oxygen uptake (VO_2max), MAS, Running Economy (RE), time to exhaustion at MAS (Tmax), respiratory exchange ratio (RER), and blood lactate at rest, 5th, and 10th runs were evaluated pre-, mid-, and post-training. Also, REDOX markers [Total Antioxidant Capacity (TAC), Protein Carbonyls (PCs) were assessed in blood samples taken at rest and 3 min post-exercise of the first and last workouts. Results: VO_2max was unchanged in both groups; in the DG, MAS increased (from 14.2 ± 1.7 to 15.0 ± 1.5 km/h, d = 0.43), and post-training RER significantly increased (from 1.06 ± 0.07 to 1.12 ± 0.03). In the last training session, blood lactate levels increased in the UG (from 9.30 ± 2.69 mmοl/L to 13.34 ± 4.64 mmοl/L) but remained low and unchanged in DG (<2 mmοl/L). Post-training, resting TAC decreased in both groups, and the exercise-induced rise in PC levels was attenuated. Conclusions: Despite the brief intervention, VO₂max levels were maintained in both groups, with divergent changes in metabolic, REDOX, and performance indicators; uphill HIIT may serve for enhancing lactate tolerance, while downhill intermittent running may improve running economy. Full article

Intake of anthocyanin-rich blackcurrant extract showed muscle fibre-type specific force responses during fatigue development from combined use of voluntary maximal isometric contractions and electrically evoked twitch contractions of the m. quadriceps femoris. In the present exploratory study, we examined the fibre-type specific effects by blackcurrant extract on high-intensity intermittent treadmill running performance to exhaustion. Active males (n = 16, age: 23 ± 3 years, height: 179 ± 5 cm, body mass: 79 ± 3 kg, $\dot{V}$O_2max: 55.3 ± 5.0 mL·kg⁻¹·min⁻¹) completed a fatiguing protocol with 16 voluntary maximal isometric contractions to predict muscle fibre typology. The high-intensity intermittent running protocol was completed twice following a 7-day intake of blackcurrant extract (210 mg anthocyanins per day) and twice following a placebo (PL) in a randomized, double blind, crossover design. Heart rate and lactate were recorded at exhaustion. Data were averaged for each condition. There were no significant correlations between the percentage force decline by the repeated isometric contractions (mean ± SD: 29.3 ± 12.4%) and total and high-intensity running distance. Participants were categorized into a predominant muscle fibre type I (slow-twitch, n = 3 with the lowest isometric force decline: 12 ± 9%) and type II typology (fast-twitch, n = 3 with the highest isometric force decline: 46 ± 10%). Only the individuals with a predominant type I fibre typology improved the total running and high-intensity running distance by 17 ± 12% and 15 ± 11%. At exhaustion, there were no differences between individuals with a type I or II fibre typology for heart rate and lactate. These exploratory results suggest that the ergogenic potential of anthocyanin-rich blackcurrant extract on high-intensity intermittent exercise may depend on muscle fibre type, though larger and more robust studies are needed to confirm this observation. Future work will establish whether our exploratory results contributed to our understanding of the underpinning of inter-individual responses to the intake of anthocyanin-rich nutritional ergogenic aids. Full article

Objectives: This study assessed the influence of oral and topical sodium bicarbonate (SB) on recovery and soccer-specific performance after exercise-induced muscle damage (EIMD). Methods: In a randomized, double-blind, placebo-controlled, parallel group design, 24 soccer players were allocated to oral SB, topical SB (PR Lotion, Momentous), or placebo (PLA) (n = 8 per condition) and attended six laboratory sessions: (i) familiarization, (ii) baseline measures, and (iii) four experimental trials on consecutive days. Muscle damage was induced on day 1 using 40 × 15 m sprints, after which either 0.3 g·kg⁻¹ body mass (BM) SB (SB-ORAL), 0.9036 g·kg⁻¹ BM PR Lotion (SB-LOTION), or an equivalent PLA was given. Recovery outcomes were measured post-EIMD, 1 d, 2 d, and 3 d post (day 1–4). Soccer-specific performance was repeated 3 d post, with supplements administered again 2 h pre-exercise. Recovery measures included muscle soreness, vertical jump height, and maximal voluntary isometric contraction. Illinois agility test (IAT), 8 × 25 m repeated sprints, and Yo-Yo Intermittent Recovery Test Level 2 (Yo-Yo IR2) were assessed as soccer-specific performance. Results: Neither SB-ORAL nor SB-LOTION accelerated indices of recovery but decline in soccer-specific performance from baseline to 3 d post was attenuated for SB-ORAL, with significant effects for IAT (p = 0.032, g = 1.69) and Yo-Yo IR2 (p = 0.026, g = 1.61) compared with PLA. Conclusions: SB did not accelerate recovery following EIMD but prescribing oral SB before subsequent exercise might rescue key performance indicators. These findings offer implications for practitioners working with soccer players during periods where full recovery is not achieved. Full article

Brazilian jiu-jitsu (BJJ) is a combat sport that requires intermittent high-intensity actions, strong technical skills, strength, and aerobic capacity. Yet, there is limited evidence of validated sport-specific field protocols. This study aimed to determine the validity, reliability, and sensitivity of the BJJ Cardiorespiratory Fitness Test (BJJ-CRFT). Twenty-three trained practitioners (20 men and 3 women; age 34.4 ± 7.6 years) performed a cardiopulmonary exercise test on a treadmill and completed the BJJ-CRFT on two occasions, one week apart. Construct validity was examined using receiver operating characteristic (ROC) analysis, while concurrent validity was tested against maximal oxygen uptake (VO₂max) and maximal aerobic speed (MAS). Intra-session reliability was determined through the intraclass correlation coefficient (ICC) and the coefficient of variation (CV%). Main results showed a good discriminative ability (ROC: 0.82; 95% CI: 0.64–0.99, p = 0.001). Total repetitions in the BJJ-CRFT showed a large positive correlation with VO₂max (r = 0.66; 95% CI: 0.35–0.85, p = 0.0006) and a very large positive correlation with MAS (r = 0.72; 95% CI: 0.44–0.87, p = 0.0001). Key performance metrics, including guard passes and test duration, demonstrated excellent relative reliability (ICC = 0.99) and good absolute reliability (CV% = 4.4% and 3.6%), being sensitive to small changes. These results confirm that the BJJ-CRFT is a valid, reliable, and sensitive field test for monitoring aerobic adaptations and guiding training prescription in BJJ. Full article

Background: Chronic chlorella intake combined with high-intensity intermittent training (HIIT) has been shown to accelerate aerobic and anaerobic capacities in rodents. This study aimed to clarify the effects of combining chlorella intake with short-term HIIT on exercise performance in humans, and to investigate the impact of chlorella intake on cardiac adaptation. Materials and Methods: In Study 1, twelve healthy young men completed a 3-week exhaustive HIIT, comprising 6–7 bouts of 20 s of cycling on a leg ergometer at an intensity of 170% maximal oxygen uptake ($\dot{\mathrm{V}}$O_2max), with a 10 s rest between each bout, 3 days/week. They were orally administered either placebo or chlorella during the 3 weeks in a double-blinded, randomized crossover trial (RCT). In Study 2, six healthy young men were orally administered either placebo or chlorella during 4 weeks in a double-blinded, placebo-controlled RCT. We measured $\dot{\mathrm{V}}$O_2max and cardiac function (stroke volume [SV], heart rate [HR], and cardiac output [CO]) during maximal exercise. In Study 3, chlorella-induced changes in molecular markers of maladaptation of the heart were measured in healthy rats. Results: [Study 1] After each HIIT, $\dot{\mathrm{V}}$O_2max significantly increased in the placebo and chlorella groups (p < 0.05). Changes in $\dot{\mathrm{V}}$O_2max were significantly higher in the chlorella group than in the placebo group (p < 0.05). [Study 2] Changes in SV and CO during maximal exercise were significantly higher in the chlorella group than in the placebo group (p < 0.05 each), but HR_max did not change. [Study 3] Chronic chlorella intake did not change the molecular markers of pathological cardiac hypertrophy. Conclusions: Chronic chlorella intake, which improves aerobic capacity by enhancing cardiac function without causing cardiac maladaptation, combined with short-term HIIT, further enhanced aerobic capacity. Thus, the chlorella-induced increase in cardiac function may further enhance aerobic capacity through HIIT. Full article

Cortisol is an important marker of hypothalamic-pituitary-adrenal function and follows robust circadian and diurnal rhythms. However, biomarker sampling protocols can be labor-intensive and cost-prohibitive. Objectives: Explore analytical approaches that can handle differing biological sampling frequencies to maximize these data in more detailed and time-dependent analyses. Methods: Healthy adult males [N = 8; 26.1 (±3.1) years; 176.4 (±8.6) cm; 73.1 (±12.0) kg)] completed two 24 h admissions: one at rest and one including a high-intensity exercise session on the cycle ergometer. Serum and salivary cortisol were sampled every 60 and 120 min, respectively. Six alternative sampling profiles were defined by downsampling from the observed data and creating two intermittent sampling profiles. A polynomial (1–6 degrees) validation process was performed, and interpolation was conducted to match the observed data. Model fit and performance were assessed using the coefficient of determination (R²) and the root mean square error (RMSE), as well as an examination of the equivalence, via two one-sided t-tests (TOST), of 24 h cortisol output between the observed and interpolated data. Results: Mean serum cortisol output was higher than salivary cortisol (p < 0.001), and no effect was observed for condition (p = 0.61). Second- and third-degree polynomial regressions were determined to be the optimal models for fitting salivary. TOST tests determined that serum data and estimated 24 h output from these models (with interpolation) provided statistically similar estimates to the observed data (p < 0.05). Conclusions: Second- and third-degree polynomial fits of salivary and serum cortisol provide a reasonable means for interpolation without introducing bias into estimates of 24 h output. This allows researchers to sample biomarkers at biologically relevant frequencies and subsequently match necessary sampling frequencies during the data processing stage of various machine learning workflows. Full article

Background: This investigation aimed to examine sex-based differences in deoxy[heme] (HHb), tissue saturation (StO₂), and force-deoxygenation ratio (FD) of the forearm flexor muscles during a maximal-effort intermittent fatiguing handgrip protocol. Methods: Thirty-three healthy males (n = 15) and females (n = 18) completed a fatiguing handgrip protocol consisting of 60 4 s contractions separated by a 1 s rest. Near-infrared spectroscopy was used to measure muscle oxygenation before, during, and after the protocol. Results: Sex differences in HHb (p = 0.033) and StO₂ (p = 0.021) were observed with significantly greater values for females (HHb: 110.204 ± 12.626% of baseline; StO₂: 72.091 ± 5.812%) in comparison to males (HHb: 101.153 ± 12.847% of baseline; StO₂: 66.978 ± 7.799%). Females (0.199 ± 0.081 AU) also demonstrated significantly (p = 0.001) lower FD in comparison to males (0.216 ± 0.094 AU). However, males (b = −0.023 ± 0.008 AU) demonstrated a significantly (p < 0.001) greater rate of decline in FD in comparison to females (b = −0.017 ± 0.006 AU). Conclusions: Prior to, during, and after a maximal-effort intermittent fatiguing handgrip fatiguing protocol, males demonstrate significantly lower StO₂ than females and a faster rate of decline in FD. Moreover, females demonstrate greater HHb values than males when assessed relative to a resting baseline. Full article

High-intensity interval exercise (HIIE) is a type of structured physical training characterized by repeated bouts of high-intensity exercise interspersed with recovery periods. Although HIIE was found to improve physical performance in a relatively short period of time, there is emerging evidence suggesting that acute HIIE may induce oxidative stress. The purpose, therefore, of the present study was to examine the effect of intermittency and/or acceleration during HIIE on oxidative stress in male participants. Nine healthy males [(age: 21.0 ± 3.0 years; height: 180.0 ± 4.0 cm; body mass: 79.4 ± 7.9 kg; maximal oxygen uptake ($\dot{V}$O_2max) 52.0 ± 6.0 mL·kg⁻¹·min⁻¹)] were recruited to perform six distinct exercise protocols of various intermittency (high, medium, and low) and acceleration (high, medium, and low) while a control session was also included. Blood samples were obtained to determine oxidative stress indices (lipid hydroperoxides, superoxide dismutase, and total glutathione) at rest, 1 h, 2 h, and 24 h following exercise on a non-motorized treadmill. The intra-individual variability of participants was observed in lipid hydroperoxides at baseline, ranging from 1.80 to 20.69 μmol·L⁻¹. No significant differences among the six different exercise protocols in any of the oxidative stress indices evaluated were observed (p > 0.05). These results suggest that the influence of various intermittency levels and acceleration patterns upon exercise-induced oxidative stress is negligible. Full article

This study aimed to compare the effects of an 8-week short-term training program, comprising repeated sprints or running-based high-intensity intermittent training (HIIT), on the aerobic fitness and repeated sprint ability (RSA) performance of sub-elite basketball referees. Twenty male referees participated in supervised training sessions twice a week. They were randomly assigned to either the RSA-based group (RSAG) or the running-based HIIT group (HIITG). The RSAG conducted 3–4 sets of 8 × 20-m all-out sprints, while the HIITG performed 2–3 sets of 6 × 20-s runs at 90% of their maximal velocity achieved in the 30–15 intermittent fitness test (30–15_IFT). Referees underwent a graded exercise test on a treadmill, the 30–15_IFT, and an RSA test before and after the training program. Both groups showed significant improvement (~3%) in the fastest (22.6 ± 1.4 vs. 23.4 ± 1.7 and 22.0 ±1.9 vs. 22.4 ± 1.7 km·h⁻¹ in RSAG and HIITG, respectively) and mean (21.5 ± 1.2 vs. 22.4 ± 1.4 and 21.3 ± 1.8 vs. 21.7 ± 1.6 km·h⁻¹ in RSAG and HIITG, respectively) sprint velocity of the RSA test (p < 0.05). Moreover, positive changes (p < 0.05) were observed in the 30–15_IFT maximal velocity (18.6 ± 1.1 vs. 19.3 ± 1.0 and 19.4 ± 0.9 vs. 20.5 ± 0.9 km·h⁻¹ in RSAG and HIITG, respectively). In conclusion, an 8-week training intervention using either RSA or running-based HIIT led to similar improvements in referees’ RSA performance and specific aerobic fitness measures. These findings could assist in devising tailored training programs for basketball referees. Full article

The kinetic responses of leukocyte subsets to exercise and their recovery may serve as indicators of immunological resilience. These time-dependent responses were investigated in healthy young men using a bicycle ergometer test. Fifteen recreationally active male cyclists (20–35 years, VO_2max 56.9 ± 3.9 mL kg⁻¹ min⁻¹) performed four exercise protocols with a 1 h duration in a cross-over design: at 70% of the maximal workload (Wmax) in a hydrated and a mildly dehydrated state, at 50% of the Wmax, and intermittently at 85/55% of the Wmax in blocks of 2 min. The numbers of lymphocytes, monocytes, neutrophils, eosinophils, basophils, thrombocytes, and NK cells (CD16 and CD56) were measured at different time points up to 24 h post-exercise. The total leukocyte counts and those of most subsets increased from the start of the exercise, peaking after 30–60 min of exercising. The neutrophil numbers, however, peaked 3 h post-exercise. The CD16^brightCD56^dim NK cells showed a 1.5-fold increase compared to the CD16^brightCD56^bright NK cells. Other than for MCP-1, no significant differences were found in the serum cytokine levels. Our results show that exercise intensity is reflected in different time-dependent changes in leukocyte subsets, which supports the concept that the exchange of immune cells between peripheral blood and tissues contributes to enhanced immune surveillance during strenuous exercise. Full article

This study aims to investigate the effects of self-paced high-intensity interval training (Sp-HIIT) vs. self-paced moderate-intensity continuous training (Sp-MICT) on aerobic fitness levels, psychophysiological responses, and antioxidant status to assess the relationship between aerobic fitness levels and antioxidant markers. Physically active young adults were randomised into Sp-HIIT and Sp-MICT groups. The intervention consisted of three weekly sessions during an eight-week period. Sp-HIIT consisted of performing two sets of 12–24 × 30 s high-intensity runs ≥ 85% HR_max followed by 30 s rest periods, while Sp-MICT consisted of performing 24–48 min of continuous running at 60–75% HR_max. Pre- and post-intervention testing included a maximal oxygen uptake (VO_2max) assessment during a 30-15 intermittent fitness test (30-15 IFT), as well as resting blood samples, which were analysed for oxidative stress markers (malondialdehyde (MDA)) and activity of intracellular antioxidant enzymes (catalase (CAT), superoxide dismutase (SOD) and reduced (GSH) and oxidized glutathione (GSSG)). The Sp-HIIT group showed a greater improvement in velocity of 30-15 IFT, VO_2max, and MDA responses. Furthermore, the Sp-HIIT group demonstrated higher psychophysiological responses than the Sp-MICT group, except for anger responses. In conclusion, these results suggest that Sp-HIIT has a higher level of beneficial exercise-induced effects in physiological responses with greater perceived exertion in physically active young adults. Full article