Intermittent Cycles Research Articles

Cardiorespiratory plasticity in humans following two patterns of acute intermittent hypoxia.

What is the central question of this study? Do cardiorespiratory experience-dependent effects (EDEs) differ between two different stimulus durations of acute isocapnic intermittent hypoxia (IHx; 5-min vs. 90-s cycles between hypoxia and normoxia)? What is the main finding and its importance? There was long-term facilitation in ventilation and blood pressure in both IHx protocols, but there was no evidence of progressive augmentation or post-hypoxia frequency decline. Not all EDEs described in animal models translate to acute isocapnic IHx responses in humans, and cardiorespiratory responses to 5-min versus 90-s on/off IHx protocols are largely similar. Peripheral respiratory chemoreceptors monitor breath-by-breath changes in arterial CO2 and O2 , and mediate ventilatory changes to maintain homeostasis. Intermittent hypoxia (IHx) elicits hypoxic ventilatory responses, with well-described experience-dependent effects (EDEs), derived mostly from animal work involving intermittent 5-min cycles of hypoxia and normoxia. These EDEs include post-hypoxia frequency decline (PHxFD), progressive augmentation (PA) and long-term facilitation (LTF). Comparisons of these EDEs between animal models and humans using similar IHx protocols are lacking. In addition, it is unknown whether shorter bouts of hypoxia, which may be more relevant to clinical conditions, elicit EDEs of similar magnitudes in humans. Respiratory (frequency, tidal volume and minute ventilation ( ) and cardiovascular (heart rate and mean arterial pressure (MAP)) variables were measured during and following two patterns of acute isocapnic IHx in 14 healthy human participants (four female): (1) 5×5min and (2) 5×90s on/off hypoxia. Participants' end-tidal was clamped at 45Torr during hypoxia and 100Torr during normoxia. We found that (1) PHxFD and PA were not present in either IHx pattern (P>0.14), (2) LTF was present in following both 5-min (P<0.001) and 90-s isocapnic IHx trials (P<0.001), and (3) LTF was present in MAP following 5-min isocapnic IHx (P<0.001), and trended towards significance following 90-s IHx (P=0.058). We demonstrate that acute isocapnic IHx alone may not elicit all of the EDEs that have been described in animal models. Additionally, ventilatory LTF occurred regardless of the length of hypoxia-normoxia cycles.

Extreme guanotrophication by phosphorus in contradiction with the productivity of alkaline soda pan ecosystems

Waterbirds as nutrient vectors can cause high phosphorus loading in shallow inland aquatic ecosystems. The main goal of this study was to determine the causal relationships between the characteristic physico-chemical properties of intermittent (temporary) alkaline soda pan (playa) ecosystems and specific (surface and volume-related) P loading of waterbirds by in situ field investigation, estimation as well as laboratory experiments using standard methods. In addition, our aim was to estimate the contribution of groundwater and precipitation to the total phosphorus pool of soda pans in Hungary.The estimated high specific external P loading of waterbirds (mean: 185 mg P/m2/y, 3.32 mg P/L/year) can explain the majority of the hypertrophic TP pool (mean: 5.17 mg/L, 64%) in soda pans, which is mediated by large-bodied herbivorous (e.g. geese and ducks) and medium-bodied omnivorous (e.g. gulls) waterbirds, who are important external nutrient importers and major phosphorus source. The results also confirm the hypothesis that groundwater (3%) and precipitation (5%) together account for a smaller estimated (8% in this study) contribution to the hypertrophic TP pool in soda pans, while the contribution of waterbirds (64% in this study) to the TP is much higher (64–100%). In this study, the remaining part of TP (maximum 28%) pool can be explained by internal P sources.Soda pans are characterized by physical and chemical characteristics coupled with high densities of waterbirds, as biotic mediators of external P sources, which together cause the maintenance of high concentrations of P-forms. The extreme guanotrophication by high P loading of herbivorous waterbirds causing a hypertrophic state is in contradiction with the limited primary production of natural soda pans. This unique phenomenon can be explained by the multiple impact of prevailing extreme physico-chemical drivers (intermittent hydrological cycle, shallow water depth, high turbidity, salinity, alkalinity) and by the specific nutrient cycle of these alkaline soda ecosystems.

A single oral glucose load decreases arterial plasma [K+ ] during exercise and recovery.

AimWe investigated whether acute carbohydrate ingestion reduced arterial potassium concentration ([K+]) during and after intense exercise and delayed fatigue.MethodsIn a randomized, double‐blind crossover design, eight males ingested 300 ml water containing 75 g glucose (CHO) or placebo (CON); rested for 60 min, then performed high‐intensity intermittent cycling (HIIC) at 130% V˙O2peak, comprising three 45‐s exercise bouts (EB), then a fourth EB until fatigue. Radial arterial (a) and antecubital venous (v) blood was sampled at rest, before, during and after HIIC and analyzed for plasma ions and metabolites, with forearm arteriovenous differences (a‐v diff) calculated to assess inactive forearm muscle effects.ResultsGlucose ingestion elevated [glucose]a and [insulin]a above CON (p = .001), being, respectively, ~2‐ and ~5‐fold higher during CHO at 60 min after ingestion (p = .001). Plasma [K+]a rose during and declined following each exercise bout in HIIC (p = .001), falling below baseline at 5 min post‐exercise (p = .007). Both [K+]a and [K+]v were lower during CHO (p = .036, p = .001, respectively, treatment main effect). The [K+]a‐v diff across the forearm widened during exercise (p = .001), returned to baseline during recovery, and was greater in CHO than CON during EB1, EB2 (p = .001) and EB3 (p = .005). Time to fatigue did not differ between trials.ConclusionAcute oral glucose ingestion, as used in a glucose tolerance test, induced a small, systemic K+‐lowering effect before, during, and after HIIC, that was detectable in both arterial and venous plasma. This likely reflects insulin‐mediated, increased Na+,K+‐ATPase induced K+ uptake into non‐contracting muscles. However, glucose ingestion did not delay fatigue.

Revealing Ageing Mechanisms of Ni-Rich NCA in State-of-the-Art Commercial High-Energy Li-Ion Cells

Ni-rich Li[NixCoyAlz]O2 (NCA) positive electrode materials are today found in the state-of-the-art high-energy Li-ion batteries [1]. Considering the high production cost of these batteries combined with the scarcity and environmental impact of the included transition metals, large benefits would be gained by prolonging the lifetime of the Li-ion cells. Although NCAs are the key to a high energy density, they are generally believed to be the main culprit behind the failure of the cell [2]. The NCAs are subjected to adverse structural phase transformation and display increased surface reactivity towards the electrolyte upon electrochemical charging [3]. Particle cracking, surface reconstruction and associated electrolyte decomposition are well-known processes leading to both Li+ inventory loss and increased cell impedance. Yet, several aspects governing these underlying ageing mechanisms remain to be explained, particularly for Ni-rich NCAs contained in state-of-the-art commercial Li-ion cells today.Herein we present a combined structural and electrochemical study based on detailed X-ray diffraction analysis, electron microscopy, and intermittent current interruption cycling. The extent and impact of the various ageing mechanisms at each stage of battery life will be assessed and discussed [4]. Reference s : [1] Yuliya Preger et al 2020 J. Electrochem. Soc. 167 120532[2] A. Manthiram, B. Song, and W. Li, Energy Storage Mater. 6 (2017) pp. 125–139.[3] E. Flores, P. Novák, U. Aschauer, and E. J. Berg, Chem. Mater. 2020, 32, 1, 186–194[4] Mikheenkova et al. In preparation.

Numerical Investigation of the Deformable Porous Media Treated by the Intermittent Microwave

A 2D axi-symmetric theoretical model of dielectric porous media in intermittent microwave (IMW) thermal process was developed, and the electromagnetic energy, multiphase transport, phase change, large deformation, and glass transition were taken into consideration. From the simulation results, the mass was mainly carried by the liquid water, and the heat was mainly carried by liquid water and solid. The diffusion was the dominant mechanism of the mass transport during the whole process, whereas for the heat transport, the convection dominated the heat transport near the surface areas during the heating stage. The von Mises stress reached local maxima at different locations at different stages, and all were lower than the fracture stress. A material treated by a longer intermittent cycle length with the same pulse ratio (PR) tended to trigger the phenomena of overheat and fracture due to the more intense fluctuation of moisture content, temperature, deformation, and von Mises stress. The model can be extended to simulate the intermittent radio frequency (IRF) process on the basis of which one can select a suitable energy source for a specific process.

Acute effects of aerobic continuous, intermittent, and resistance exercise on glycemia in adolescents males with type 1 diabetes

Increased levels of physical activity is often associated with reduced HbA1c in individuals with diabetes. However, the effect on glycemic control differs between different programs of exercise. The aim of this study was to compare the acute effects on glycemia of resistance and two aerobic continuous and intermittent exercise bouts in adolescent males with type 1 diabetes. Eight active males with type 1 diabetes (17.5 ± 0.8 years, BMI: 20.8 ± 2.2 kg/m2 , HbA1c: 7.2 ± 0.5% [54.9 ± 5.3 mmol/mol]) performed four experimental sessions-nonexercise (control), resistance exercise (RE) and two isocaloric continuous (CE) and intermittent (IE) cycling exercise trials-in a randomized order. Each session consisted of 45 min of exercise (except for the control modality) and 60 min of passive recovery. Venous blood was drawn for assessment of plasma glucose (PG). A two-way repeated-measures ANOVA was used for statistical comparisons. A significant time-to-exercise interaction effect on PG was detected. PG significantly decreased during IE (-5.1 ± 1.6 mmol/L) and CE (-5.4 ± 1.8 mmol/L) but not during RE (-1.0 ± 1.4 mmol/L, ns). Additionally, decreases in PG after IE and CE were sustained throughout the recovery period. While intermittent and continuous aerobic exercises are associated with a lowering of glycemia in male adolescents with type 1 diabetes, glycemia remained stable without significant alterations after resistance exercise. These findings hold important implications related to clinical exercise advice and disease management in adolescents with type 1 diabetes.

Low-carbon production of iron and steel: Technology options, economic assessment, and policy

Summary Given increased urgency to transition the global economy to net-zero CO2 emission, governments and industry have increased focus on decarbonizing hard-to-abate sectors, including steel making, which contributes roughly 6% of global CO2 emission and 8% of energy-related emission (including power consumption emission). This paper reviews current global iron and steel production and assesses available decarbonization technologies, including hydrogen injection, solid biomass substitution, zero-C electricity substitution, carbon capture and storage (CCS) retrofit, and combinations of these decarbonization approaches. Blast furnace-basic oxygen furnace (BF-BOF) dominates production (71%) and is particularly stubborn to any decarbonization technology. Direct reduced iron to electric arc furnace (DRI-EAF) production is 5% and growing, it appears to have better decarbonization potential to move toward net-zero. Secondary steel production using mainly steel scrap in electric arc furnace (EAF-scrap) is 24% of global production and has both the lowest energy consumption and is technically simplest to decarbonize through electrification but is limited in market share to recycled steel capacity. Of the options assessed, blue hydrogen, carbon neutral biomass, and CCS appear to have the lowest cost and highest technical maturity. However, no single approach today can deliver deep decarbonization to the iron and steel industry and all approaches lead to substantial production cost increase. No uniform ideal solution exists, and different geographies, infrastructure, and economies will determine the local optimum solution with viability and cost. Policy measures will be required to provide financial incentives for decarbonization and to avoid unwelcome outcomes such as emissions leakage or job loss.

Interval Hypoxic Training in Rehabilitation Program for Adolescents with Overweight / Obesity and Comorbid Arterial Hypertension: Open-Label Randomized Study

Background. Searching for new strategies for the rehabilitation of adolescents with obesity and comorbid arterial hypertension (AHT) before significant pathological changes development in the cardiovascular system remains the urgent challenge.Objective. The aim of the study was to examine the effect of interval hypoxic training (IHT) on blood pressure (BP) levels in adolescents with overweight / obesity and comorbid AHT.Methods. Adolescents aged 14-17 years with body mass index SDS ≥ 1 and grade I AHT (mean level of systolic and/or diastolic BP ≥ 95th percentile for population of corresponding age, sex and height) have been randomized to the group «aerobic training» (treadmill walking) and “aerobic training + IHT” (usage of hypoxicator in intermittent operation cycles). All patients were on subcaloric diet (10% reduction in caloric intake for given age). Primary outcome measure was the difference between groups on systolic/diastolic BP levels according to 24-hour BP monitoring after completion of training program (10 classes each). The effects of IHT on body composition (bioelectrical impedance analysis), heart rate variability and psychoemotional state (Spielberger scale, assessment of health, activity and mood) were further estimated.Results. 43 patients were assigned to the index group, and 42 — to the control group. 67 patients have completed the research program. 5 patients (12%) from the IHT group and 13 patients (31%; p = 0.029) from the control group prematurely discontinued participation in the trial due to poor exercise tolerance. The groups were comparable in baseline systolic and diastolic BP. Decrease in BP occurred in both groups after 10 workouts. There were no differences in decrease value: mean difference for SBP was 2.4 mm Hg (95% CI -6.6 ... 1.8), for DBP — 0.2 mm Hg (-3.6 ... 4.0). However, the incidence of reaching the targeted SBP (&lt; 95th percentile for the corresponding age and sex) after completion of the treatment was recorded in 66% patients in the experimental group and in 42% patients in the control group (p = 0,047). Positive dynamics in several indicators of heart rate variability and psychoemotional state were mentioned in the IHT group.Conclusion. The IHT implementation in the complex of rehabilitation program for adolescents with overweight / obesity and AHT has no additional positive effect on BP levels. However, the incidence of reaching the targeted SBP (&lt; 95th percentile for the corresponding age and sex) after completion of the treatment was recorded in 66% patients in the experimental group and in 42% patients in the control group (p = 0,054).

The application of intermittent cycle extended aeration systems (ICEAS) in wastewater treatment

Many biological methods are currently used to treat wastewaters, such as e.g. aerobic, anaerobic, sequencing batch reactors, biofilters. However, these technologies are limited by low nutrient removal efficiency, high energy and large area requirements. Hereby, the intermittent cycle extended aeration system (ICEAS), or continuous flow sequencing batch reactor (SBR) can be an alternative solution. Therefore, understanding all aspects of this technology – such as reaction mechanisms, nitrogen conversion cycle, and operation conditions – are very necessary. This paper reviews the mechanism and key factors affecting the ICEAS operation conditions to treat many wastewaters. An ICEAS combines many biological processes as aerobic, anoxic, and anaerobic in one tank. ICEAS has some advantages compared with traditional activated sludge such as less space demand, low investment costs, low aeration to save operating costs, and automatic operation. An ICEAS shows its high efficiencies in removing organic compounds (90–97 % of COD removal) and nutrients (97–99 % of TN removal), limiting the accumulation of nitrite and nitrate. The continuous inflow feeding into ICEAS reduces organic loading shock and is beneficial to the growth of microorganisms community. Hope this paper will help to promote further application of ICEAS technology for wastewater treatment around the world.

Brain function during central fatigue induced by intermittent high-intensity cycling.

The central governor model putatively explains the mechanism of endurance exercise-induced central fatigue, however high-intensity exercise-induced central fatigue strategies have not been investigated yet. This study aimed to examine how central fatigue affects neural response alterations, as measured by electroencephalographic (EEG) recordings, in intermittent high-intensity cycling. Neural responses were assessed by measuring the alteration of brainwaves based on spectral energy band estimates during an intermittent, high-intensity, 60-min exercise bout on a cycle ergometer. The cycle ergometer incline was changed every 10min in an intermittent pattern (10-20-5-20-5-10°). EEG was used to analyze altering brain function. Heart rate (HR), blood lactate (BL), and rating of perceived exertion (RPE) were measured after the participants completed each change in incline. The results showed that HR, BL, and RPE increased at an incline of 20° in comparison to a 5° incline. The spectral power of EEG was significantly increased (P˂0.01) in the alpha and beta frequency ranges with a change in inclines between 5 and 20°. The spectral power of the EEG was significantly increased (P˂0.01) over the whole frequency range from rest (theta + 251%, alpha + 165%, beta + 145%). Higher, relative intensities (10 and 20°) increased brain function, regardless of fatigue occurrence. HIIT (high-intensity interval training) led to an alteration in the neural response. Further work investigating the usefulness of HIIT to improve brain function is warranted.

How universal is the vibration-velocity controlled granular convection?

Recently, a number of articles have reported that granular convection induced by continuous vibration is controlled by vibration velocity, in contrast with some previous studies. We have reported such an example for the Brazil nut effect when the vibration is given discontinuously, using a one-layer granular bed in a cell with down-facing side walls. Here, we report the effect of vibration phase and wall friction using the same experimental system, to confirm rising motion of an intruder induced by granular convection is again governed by vibration velocity. We compare two different cases of vibration phase for giving intermittent vibration cycles, and found one, in which granular packing is well established before grains start to lose contacts due to vibration, provides distinctly high reproducibility. We further control the side wall friction using a microfabrication technique, and found that significantly high reproducibility is attained in a cell with vertical side walls when a millimeter texture is introduced on the side walls. Our results indicate that the granular convection is universally controlled by vibration velocity. The present study opens a way to conduct highly reproducible experiments on granular dynamics, which is indispensable for deep physical understanding of granular flow and segregation.

Combination Chemotherapy of Advanced Non-Hodgkin Lymphoma with Bleomycin, Adriamycin, Cyclophosphamide, Vincristine, and Prednisone (BACOP)

Seventy-three patients with advanced non-Hodgkin lymphoma were treated with bleomycin, Adriamycin, cyclophosphamide, vincristine (Oncovin) and prednisone (BACOP), administered intensively during a 7-wk induction course followed by intermittent cycles every 3 wk for a total of 28 wk. The objective response in 44 evaluable nonleukemic patients with diffuse histology was 86%, with 66% achieving a complete remission (CR), varying from 80% for diffuse poorly differentiated lymphocytic (DPDL) to 56% for diffuse histiocytic (DH) lymphoma. In patients with nodular histology 89% (8/9) achieved a CR with a projected 75% of patiients in CR at 14 mo. Median follow-up from time of CR for nodular histology was 17 mo. The projected median duration of CR in diffuse histology was 14 mo. with median survival 14 mo. Patients with a partial response survived a median of 7 mo, compared to 3 mo for nonresponders. Of 29 patients with diffuse histology, 17 (59%) have remained disease free for 5-34 mo with a median follow-up of 12 mo. Survival beyond 20 mo has been projected for 42% of patients with diffuse histology (58% with DPDL and 32% with DH). The central nervous system (CNS) was involved in a total of 11/44 (25%) patients with diffuse histology, including 5 with primary CNS relapse. BACOP resulted in a higher CR rate and longer survival than a previous three-drug program (COP), especially in patients with diffuse histology.

Removal of Nutrients From Anaerobically Digested Swine Wastewater Using an Intermittent Cycle Extended Aeration System.

Swine wastewater contains high concentrations of organic compounds, nutrients (nitrogen and phosphorus), heavy metals, and residual antibiotics, amongst others, that have negative impacts on the water environment. The main aim of this work was to remove nutrients from anaerobically digested swine wastewater using an intermittent cycle extended aeration system (ICEAS). The effects of operational parameters such as cycle time, organic loading rate, C/N ratio, and aeration/mixing ratio on the pollutant removal efficiencies of ICEAS were studied and compared with the performance of a conventional sequencing batch reactor (SBR). The following optimal conditions were obtained: cycle time, 6 h; organic loading rate, 0.86 kg COD m−3 day−1; C/N ratio, 2.49–2.82; and aeration/mixing ratio, 1.57. The pH was maintained in the range of 6.0–8.0. The total organic carbon (TOC), total nitrogen (TN), ammonium (NH4+), total phosphorus (TP), and color removal efficiencies of ICEAS were higher than those of the conventional SBR, with removal efficiencies of 95.22, 88.29, 97.69, 85.81, and 97.84%, respectively, compared to 94.34, 81.16, 94.15, 77.94, and 96.95%, respectively, observed in the SBR. TOC, TN, NH4+, TP, and the color removal efficiencies of ICEAS were higher by 0.88, 7.13, 3.54, 7.87, and 0.95%, respectively, than the conventional SBR. The good results from this study show that ICEAS is a promising technology for the removal of organic contaminants and nutrients from anaerobically digested swine wastewater and that the effluent water quality meets the Vietnamese discharge standard (QCVN 62-MT:2016/BTNMT) for swine wastewater effluents.

A multi-decadal record of oceanographic changes of the past ~165 years (1850-2015 AD) from Northwest of Iceland.

Extending oceanographic data beyond the instrumental period is highly needed to better characterize and understand multi-decadal to centennial natural ocean variability. Here, a stable isotope record at unprecedented temporal resolution (1 to 2 years) from a new marine core retrieved off western North Iceland is presented. We aim to better constrain the variability of subsurface, Atlantic-derived Subpolar Mode Water (SPMW), using near surface-dwelling planktic foraminifera and Arctic Intermediate Water (AIW) mass changes using benthic foraminifera over the last ~165 years. The reconstruction overlaps in time with instrumental observations and a direct comparison reveals that the δ18O record of Neogloboquadrina pachyderma is reliably representing temperature fluctuations in the SPMWs. Trends in the N. pachyderma δ13C record match the measured phosphate concentration in the upper 200 m on the North Icelandic Shelf well. Near surface-dwelling foraminifera trace anthropogenic CO2 in the Iceland Sea by ~ 1950 ± 8, however, a reduced amplitude shift in the Marine Suess effect is identified. We argue that this is caused by a contemporary ongoing increase in marine primary productivity in the upper ocean due to enhanced Greenland’s freshwater discharge that has contributed to a nutrient-driven fertilization since the 1940s/50s (Perner et al., 2019). Multi-decadal variability is detected. We find that the 16-year periodicity evident in SPMW and AIWs based on the δ18O of N. pachyderma and M. barleeanum is a signal of SST anomalies propagated into the Nordic Seas via the Atlantic inflow branches around Iceland. Spectral analyses of the planktic foraminiferal δ13C signal indicate intermittent 30-year cycles that are likely reflecting the ocean response to atmospheric variability, presumably the East Atlantic Pattern. A long-term trend in benthic δ18O suggests that Atlantic-derived waters are expanding their core within the water column from the subsurface into deeper intermediate depths towards the present day. This is a result of increased transport by the North Icelandic Irminger Current to the North Iceland Shelf over the historical era.

Oxygen availability affects exercise capacity, but not neuromuscular fatigue characteristics of knee extensors, during exhaustive intermittent cycling.

To compare the effects of different hypoxia severities on exercise capacity, cardio-respiratory, tissue oxygenation and neuromuscular fatigue characteristics in response to exhaustive intermittent cycling. Eleven well-trained cyclists, repeated supra-maximal cycling efforts of 15s (30% of anaerobic power reserve, 609 ± 23W), interspersed with 45s of passive rest until task failure. The exercise was performed on separate days in normoxia (SL; simulated altitude/end-exercise arterial oxygen saturation = 0m/~ 96%), moderate (MH; 2200m/~ 90%) and severe (SH; 4200m/~ 79%) hypoxia in a cross-over design. Neuromuscular tests, including brief (5s) and sustained (30s) maximal isometric voluntary contractions of the knee extensors, were performed at baseline and exhaustion. Exercise capacity decreased with hypoxia severity (23 ± 9, 16 ± 6 and 9 ± 3 cycle efforts in SL, MH and SH, respectively; P < 0.001; η2 = 0.72). Both cerebral (P < 0.001; η2 = 0.86) and muscle (P < 0.01; η2 = 0.54) oxygenation decreased throughout the exercise, independent of condition (P ≥ 0.45; η2 ≥ 0.14). Compared to SL, muscle oxygenation was globally lower in MH and SH (P = 0.011; η2 = 0.36). Cardiovascular solicitation neared maximal values at exhaustion in all conditions. Peak twitch amplitude with single and paired electrical stimuli (P < 0.001; η2 ≥ 0.87), maximal torque (P < 0.001; η2 ≥ 0.48) and voluntary activation measured using transcranial magnetic stimulation (P ≤ 0.034; η2 ≥ 0.31) during brief and sustained MVCs were all reduced at exhaustion, independent of condition (P ≥ 0.196; η2 ≥ 0.15). Despite reduced exercise capacity with increasing severity of hypoxia during exhaustive intermittent cycling, neuromuscular fatigue characteristics were not different at task failure and cardiovascular solicitation neared maximum values.

A forecasting framework for predicting perceived fatigue: Using time series methods to forecast ratings of perceived exertion with features from wearable sensors

Advancements in sensing and network technologies have increased the amount of data being collected to monitor the worker conditions. In this study, we consider the use of time series methods to forecast physical fatigue using subjective ratings of perceived exertion (RPE) and gait data from wearable sensors captured during a simulated in-lab manual material handling task (Lab Study 1) and a fatiguing squatting with intermittent walking cycle (Lab Study 2). To determine whether time series models can accurately forecast individual response and for how many time periods ahead, five models were compared: naïve method, autoregression (AR), autoregressive integrated moving average (ARIMA), vector autoregression (VAR), and the vector error correction model (VECM). For forecasts of three or more time periods ahead, the VECM model that incorporates historical RPE and wearable sensor data outperformed the other models with median mean absolute error (MAE) <1.24 and median MAE <1.22 across all participants for Lab Study 1 and Lab Study 2, respectively. These results suggest that wearable sensor data can support forecasting a worker’s condition and the forecasts obtained are as good as current state-of-the-art models using multiple sensors for current time prediction.

Sodium Bicarbonate Ingestion Improves Time-to-Exhaustion Cycling Performance and Alters Estimated Energy System Contribution: A Dose-Response Investigation.

This study investigated the effects of two sodium bicarbonate (NaHCO3) doses on estimated energy system contribution and performance during an intermittent high-intensity cycling test (HICT), and time-to-exhaustion (TTE) exercise. Twelve healthy males (stature: 1.75 ± 0.08 m; body mass: 67.5 ± 6.3 kg; age: 21.0 ± 1.4 years; maximal oxygen consumption: 45.1 ± 7.0 ml.kg.min−1) attended four separate laboratory visits. Maximal aerobic power (MAP) was identified from an incremental exercise test. During the three experimental visits, participants ingested either 0.2 g.kg−1 BM NaHCO3 (SBC2), 0.3 g.kg−1 BM NaHCO3 (SBC3), or 0.07 g.kg−1 BM sodium chloride (placebo; PLA) at 60 min pre-exercise. The HICT involved 3 × 60 s cycling bouts (90, 95, 100% MAP) interspersed with 90 s recovery, followed by TTE cycling at 105% MAP. Blood lactate was measured after each cycling bout to calculate estimates for glycolytic contribution to exercise. Gastrointestinal (GI) upset was quantified at baseline, 30 and 60 min post-ingestion, and 5 min post-exercise. Cycling TTE increased for SBC2 (+20.2 s; p = 0.045) and SBC3 (+31.9 s; p = 0.004) compared to PLA. Glycolytic contribution increased, albeit non-significantly, during the TTE protocol for SBC2 (+7.77 kJ; p = 0.10) and SBC3 (+7.95 kJ; p = 0.07) compared to PLA. GI upset was exacerbated post-exercise after SBC3 for nausea compared to SBC2 and PLA (p < 0.05), whilst SBC2 was not significantly different to PLA for any symptom (p > 0.05). Both NaHCO3 doses enhanced cycling performance and glycolytic contribution, however, higher doses may maximize ergogenic benefits.

The Application of Critical Power, the Work Capacity above Critical Power (W'), and its Reconstitution: A Narrative Review of Current Evidence and Implications for Cycling Training Prescription.

The two-parameter critical power (CP) model is a robust mathematical interpretation of the power–duration relationship, with CP being the rate associated with the maximal aerobic steady state, and W′ the fixed amount of tolerable work above CP available without any recovery. The aim of this narrative review is to describe the CP concept and the methodologies used to assess it, and to summarize the research applying it to intermittent cycle training techniques. CP and W′ are traditionally assessed using a number of constant work rate cycling tests spread over several days. Alternatively, both the 3-min all-out and ramp all-out protocols provide valid measurements of CP and W′ from a single test, thereby enhancing their suitability to athletes and likely reducing errors associated with the assumptions of the CP model. As CP represents the physiological landmark that is the boundary between heavy and severe intensity domains, it presents several advantages over the de facto arbitrarily defined functional threshold power as the basis for cycle training prescription at intensities up to CP. For intensities above CP, precise prescription is not possible based solely on aerobic measures; however, the addition of the W′ parameter does facilitate the prescription of individualized training intensities and durations within the severe intensity domain. Modelling of W′ reconstitution extends this application, although more research is needed to identify the individual parameters that govern W′ reconstitution rates and their kinetics.

Effect of dopamine on the sensitivity of carotid body to hypoxia induced by acute intermittent hypoxia in rats

Objective: To investigate the sensitivity of carotid body to hypoxia and the effect of dopamine on the sensitivity of carotid body to hypoxia after acute intermittent hypoxia stimulation in rats. Methods: The isolated carotid body-sinus nerve in rat was transferred to incubator, and then the isolated sinus nerve was inhaled into the recorded glass electrode for recording electrical signals. The baseline buffer was bubbled with 95% O 2 + 5% CO 2 mixture gas, and the hypoxic stress was treated with 5% O 2 + 5% CO 2 + 90% N2 mixture gas, hypoxic stimulation was given for 30 seconds, 95% O 2 + 5% CO 2 for 90 seconds, a total of 10 cycles. No less than 5 rats in each group. Results: In this experiment, the electrical activity of sinus nerve isolated from rats was enhanced by hypoxia stimulation after acute intermittent hypoxia, but the response of sinus nerve to hypoxia was inhibited by dopamine. Before acute intermittent hypoxic stress, dopamine also inhibited the firing activity of sinus nerve, but after acute intermittent hypoxic cycle, the inhibition of dopamine on the firing activity of sinus nerve was strengthened. Conclusion: Acute intermittent hypoxia enhances the response of sinus nerve isolated from rats to hypoxia, dopamine inhibits the enhancement of carotid body sensitivity to hypoxia induced by acute intermittent hypoxic.

Low caffeine dose improves intermittent sprint performance in hot and humid environments.

While the effects of caffeine have been evaluated in relation to endurance exercise, few studies have assessed the ergogenic effects of low caffeine doses on intermittent exercise performance in hot and humid environments. Thus, we aimed to determine the effects of low-dose caffeine supplementation on intermittent exercise performance under these conditions. Eight male soccer players (age, 19.9±0.3 years; height, 173.7±6.3cm; body mass, 65.1±5.5kg; V˙O2max, 50.0±3.1mL ⋅ kg-1⋅ min-1) participated in this double-blind, randomized, cross-over study. Caffeine was orally administered at 60min before exercise (dosage, 3mg ⋅kg-1). The participants completed a 90-min intermittent sprint cycling protocol under two conditions (after receiving caffeine and placebo) at 32°C and at 70% relative humidity. A significant improvement in the total amount of work was observed in the caffeine condition compared to the placebo condition (155.0±15.8 vs 150.8±14.5kJ, respectively; p<0.05, d=0.28). In contrast, the rectal temperature measured at the end of exercise showed no significant difference between the conditions (38.9±0.4°C and 38.7±0.5°C in the caffeine and placebo conditions, respectively; p>0.05, d=0.57). Other thermal responses, such as the mean skin temperature, heart rate, or sweat volume, were not significantly different between these conditions. These results suggested that a low caffeine dose improved the intermittent sprint performance and the reasons could be explained by the fact that a low caffeine dose ingestion did not affect the thermoregulatory responses compared to the placebo condition and, thus, did not attenuate its ergogenic effect on exercise in hot and humid environments.