Aspirational nitrogen interventions accelerate air pollution abatement and ecosystem protection.

Although reactive nitrogen (Nr) emissions from food and energy production contribute to multi-dimensional environmental damages, integrated management of Nr is still lacking owing to unclear future mitigation potentials and benefits. Here, we find that by 2050, high-ambition compared to low-ambition N interventions reduce global ammonia and nitrogen oxide emissions by 21 and 22 TgN/a, respectively, equivalent to 40 and 52% of their 2015 levels. This would mitigate population-weighted PM2.5 by 6 g/m3 and avoid premature deaths by 817 k (16%), mitigate ozone by 4 ppbv, avoid premature deaths by 252k (34%) and crop yield losses by 122 million tons (4.3%), and decrease terrestrial ecosystem areas exceeding critical load by 420 Mha (69%). Without nitrogen interventions, most environmental damages examined will deteriorate between 2015 and 2050; Africa and Asia are the most vulnerable but also benefit the most from interventions. Nitrogen interventions support sustainable development goals related to air, health, and ecosystems.

Achieving partial nitrification by sludge treatment using sulfide: Optimal conditions determination, long-term stability evaluation and microbial mechanism exploration.

This study proposes an innovative strategy for achieving PN in synthetic domestic wastewater by side-stream sludge treatment using sulfide as the sole control factor. By conducting controllable batch experiments and response surface analysis, optimal sulfide treatment conditions were firstly determined as 90 mg/L of sulfide, 7.5 of pH, 100 rpm of rotation and 12 h of treatment time. After treatment, half of ammonia oxidizing bacteria (AOB) activity remained, but nitrite oxidizing bacteria (NOB) activity was barely detected. Nitrite accumulation rate of long-term running PN steadily reached 83.9 % with 99.1 % of ammonia removal efficiency. Sulfide treatment increased community diversity and facilitated stability of microbiota functioning with PN phenotype, which might be sustained by the positive correlation between ammonia oxidation gene (amoA) and sulfur oxidation gene (soxB). Correspondingly, the network analysis identified the keystone microbial taxa of persistent PN microbiota as Nitrosomonas, Thauera, Truepera, Defluviimonas and Sulitalea in the later stage of long-term reactor.

Improving landfill liner performance with bentonite-slag blend permeated with ammonia for a Municipal solid waste landfill.

Leachate emanating from landfills contains ammonia which may cause serious health effects on living things. An effectively designed clay barrier should not allow the contaminant to infiltrate the soil and groundwater systems. The utilization of certain industrial by-products in engineered landfill barriers, not only reduces the need for conventional liner materials but also helps in sustainable waste management. This study investigated the hydraulic conductivity, unconfined compressive strength, compaction, and adsorption characteristics of lithomargic clay blended with an optimum percentage of bentonite (10%) and granulated blast furnace slag (15%) permeated with ammonia. The results revealed that increasing the content of granulated blast furnace slag decreased the maximum dry density while increasing the optimum moisture content. In comparison to lithomargic clay, the hydraulic conductivity of the amended soil liner permeated with ammonia decreased from a value of 3 × 10-8 m/s to 5 × 10-10 m/s. The unconfined compressive strength of the amended soil specimens showed an increasing trend with curing times (i.e., 0, 14, 28, and 56 days). The batch adsorption results revealed that Freundlich and Langmuir's isotherm fits the equilibrium adsorption data and the adsorption of ammonia on clay liner follows non-linear behaviour. Overall, the experimental results implied that lithomargic clay blended with 10% bentonite and 15% granulated blast furnace slag can be used as an impermeable soil reactive barrier in engineered landfills.

Novel therapeutic targets: bifidobacterium-mediated urea cycle regulation in colorectal cancer.

BACKGROUND AND PURPOSE: Colorectal cancer (CRC) is a widespread malignancy with a complex and not entirely elucidated pathogenesis. This study aims to explore the role of Bifidobacterium in the urea cycle (UC) and its influence on the progression of CRC, a topic not extensively studied previously. EXPERIMENTAL APPROACH: Utilizing both bioinformatics and experimental methodologies, this research involved analyzing bacterial abundance in CRC patients in comparison to healthy individuals. The study particularly focused on the abundance of BA. Additionally, transcriptomic data analysis and cellular experiments were conducted to investigate the impact of Bifidobacterium on ammonia metabolism and mitochondrial function, specifically examining its regulation of the key UC gene, ALB. KEY RESULTS: The analysis revealed a significant decrease in Bifidobacterium abundance in CRC patients. Furthermore, Bifidobacterium was found to suppress ammonia metabolism and induce mitochondrial dysfunction through the regulation of the ALB gene, which is essential in the context of UC. These impacts contributed to the suppression of CRC cell proliferation, a finding corroborated by animal experimental results. CONCLUSIONS AND IMPLICATIONS: This study elucidates the molecular mechanism by which Bifidobacterium impacts CRC progression, highlighting its role in regulating key metabolic pathways. These findings provide potential targets for novel therapeutic strategies in CRC treatment, emphasizing the importance of microbiota in cancer progression.

Procedimento operacional padrão para validação de métodos analíticos para determinação do conteúdo e emissões de produtos do tabaco. Método Oficial TobLabNet da OMS - POP 02

Para estabelecer medidas equivalentes para o ensaio de produtos de tabaco em escala mundial é necessário que haja métodos consensuais de mensuração do conteúdo e das emissões específicas dos cigarros. Nenhum regime de tragada obtido por máquinas é capaz de representar plenamente o comportamento humano de fumar: os ensaios realizados em máquinas de fumar são úteis para caracterizar as emissões de cigarro para fins de design e regulação, mas a divulgação aos fumantes das medições em máquinas pode resultar em interpretações equivocadas a respeito das diferenças de exposição e risco existentes entre as marcas. Os dados de emissão de fumaça obtidos por medições em máquinas podem ser usados como elementos para a avaliação do perigo do produto, mas não são e nem se destinam a ser medidas válidas de exposição ou risco para os seres humanos. A apresentação de diferenças nas medições em máquina como diferenças de exposição ou risco constitui uso indevido dos resultados do ensaio com métodos recomendados da TobLabNet da OMS. Este documento foi preparado por membros da Rede de Laboratórios de Tabaco (TobLabNet) da Organização Mundial da Saúde (OMS) como um procedimento operacional padrão (POP) para a validação de métodos analíticos para determinação do conteúdo em corrente primária e tabaco de cigarro.

Método Oficial TobLabNet da OMS - POP 7. Procedimento operacional padrão para determinação de amônia em tabaco total de cigarros

Para estabelecer medidas equivalentes para o ensaio de produtos de tabaco em escala mundial é necessário que hajam métodos consensuais de medição do conteúdo e das emissões específicas dos cigarros. Nenhum regime de tragada obtido por máquinas é capaz de representar plenamente o comportamento humano de fumar: os ensaios realizados em máquinas de fumar são úteis para caracterizar as emissões de cigarro para fins de design e regulação, mas a divulgação aos fumantes das medições em máquinas pode resultar em interpretações equivocadas a respeito das diferenças de exposição e risco existentes entre as marcas. Os dados de emissão de fumaça obtidos por medições em máquinas podem ser usados como elementos para a avaliação do perigo do produto, mas não são e nem se destinam a ser medidas válidas de exposição ou risco para os seres humanos. A apresentação de diferenças nas medições em máquina como diferenças de exposição ou risco constitui uso indevido dos resultados do ensaio com métodos recomendados da TobLabNet da OMS. Este documento foi preparado por membros da Rede de Laboratórios de Tabaco (TobLabNet) da Organização Mundial da Saúde (OMS) como um procedimento operacional padrão (POP) de método analítico para medição de amônia em tabaco total de cigarro.

Impact of additives on syntrophic propionate and acetate enrichments under high-ammonia conditions.

High ammonia concentrations in anaerobic degradation systems cause volatile fatty acid accumulation and reduced methane yield, which often derive from restricted activity of syntrophic acid-oxidising bacteria and hydrogenotrophic methanogens. Inclusion of additives that facilitate the electron transfer or increase cell proximity of syntrophic species by flocculation can be a suitable strategy to counteract these problems, but its actual impact on syntrophic interactions has yet to be determined. In this study, microbial cultivation and molecular and microscopic analysis were performed to evaluate the impact of conductive (graphene, iron oxide) and non-conductive (zeolite) additives on the degradation rate of acetate and propionate to methane by highly enriched ammonia-tolerant syntrophic cultures derived from a biogas process. All additives had a low impact on the lag phase but resulted in a higher rate of acetate (except graphene) and propionate degradation. The syntrophic bacteria 'Candidatus Syntrophopropionicum ammoniitolerans', Syntrophaceticus schinkii and a novel hydrogenotrophic methanogen were found in higher relative abundance and higher gene copy numbers in flocculating communities than in planktonic communities in the cultures, indicating benefits to syntrophs of living in close proximity to their cooperating partner. Microscopy and element analysis showed precipitation of phosphates and biofilm formation in all batches except on the graphene batches, possibly enhancing the rate of acetate and propionate degradation. Overall, the concordance of responses observed in both acetate- and propionate-fed cultures highlight the suitability of the addition of iron oxide or zeolites to enhance acid conversion to methane in high-ammonia biogas processes. KEY POINTS: • All additives promoted acetate (except graphene) and propionate degradation. • A preference for floc formation by ammonia-tolerant syntrophs was revealed. • Microbes colonised the surfaces of iron oxide and zeolite, but not graphene.

Enhanced Room-Temperature NO2 Sensing through Deep Functional Group Hybridization in Nitrogen-Doped Monolayer Ti3C2Tx.

Nitrogen dioxide (NO2) is a significant environmental and human health hazard. Current NO2 sensors often lack sensitivity and selectivity under ambient conditions. This study investigates ammonia pyrolysis modification of monolayer Ti3C2Tx MXene to enhance NO2 detection at room temperature. Nitrogen-doped Ti3C2Tx demonstrates a substantial improvement in sensitivity, with a response of 8.87% to 50 ppm of NO2 compared to 0.65% for the original sensor, representing a 13.8-fold increase. The nitrogen-doped sensor also exhibits superior selectivity and linearity for NO2 under ambient conditions. Theoretical analysis shows that nitrogen incorporation promotes enhanced interaction between Ti3C2Tx and its surface oxygen-containing functional groups through electronic hybridization, resulting in improved adsorption energy (1.80 |eV|) and electron transfer efficiency (0.67 |e|) for NO2, thereby enhancing its gas-sensing performance. This study highlights the potential of ammonia pyrolysis-treated Ti3C2Tx MXene for advancing NO2 sensor technologies with heightened performance at room temperature.

Assessment of oxygen kinetic parameters for closely related ammonia-oxidizing bacteria.

The reaction kinetics of lithotrophic ammonia-oxidizing bacteria (AOB) are strongly dependent on dissolved oxygen (DO) as their metabolism is an aerobic process. In this study, we estimate the kinetic parameters, including the oxygen affinity constant (Km[O2]) and the maximum oxygen consumption rate (Vmax[O2]), of different AOB species, by fitting the data to the Michaelis-Menten equation using nonlinear regression analysis. An example for three different species of Nitrosomonas bacteria (N. europaea, N. eutropha, and N. mobilis) in monoculture is given, finding a Km[O2] of 0.25 ± 0.05 mg l-1, 0.47 ± 0.09 mg l-1, and 0.28 ± 0.08 mg l-1, and a Vmax[O2] of 0.07 ± 0.04 pg h-1cell-1, 0.25 ± 0.06 pg h-1cell-1, and 0.02 ± 0.001 pg h-1cell-1 for N. europaea, N. eutropha, and N. mobilis, respectively. This study shows that of the analyzed AOB, N. europaea has the highest affinity towards oxygen and N. eutropha the lowest affinity towards oxygen, indicating that the former can convert ammonia even under low DO conditions. These results improve the understanding of the ecophysiology of AOB in the environment. The accuracy of mathematically modelled ammonia oxidation can be improved, allowing the implementation of better management practices to restore the nitrogen cycle in natural and engineered water systems.

Innovative Wearable Sweat Sensor Array for Real-Time Volatile Organic Compound Detection in Noninvasive Diabetes Monitoring.

Wearable sweat sensors are reshaping healthcare monitoring, providing real-time data on hydration and electrolyte levels with user-friendly, noninvasive devices. This paper introduces a highly portable two-channel microfluidic device for simultaneous sweat sampling and the real-time detection of volatile organic compound (VOC) biomarkers. This innovative wearable microfluidic system is tailored for monitoring diabetes through the continuous and noninvasive tracking of acetone and ammonia VOCs, and it seamlessly integrates with smartphones for easy data management. The core of this system lies in the utilization of carbon polymer dots (CPDs) and carbon dots (CDs) derived from monomers such as catechol, resorcinol, o-phenylenediamine, urea, and citric acid. These dots are seamlessly integrated into hydrogels made from gelatin and poly(vinyl alcohol), resulting in an advanced solid-state fluorometric sensor coating on a cellulose paper substrate. These sensors exhibit exceptional performance, offering linear detection ranges of 0.05-0.15 ppm for acetone and 0.25-0.37 ppm for ammonia, with notably low detection limits of 0.01 and 0.08 ppm, respectively. Rigorous optimization of operational parameters, encompassing the temperature, sample volume, and assay time, has been undertaken to maximize device performance. Furthermore, these sensors demonstrate impressive selectivity, effectively discerning between biologically similar substances and other potential compounds commonly present in sweat. As this field matures, the prospect of cost-effective, continuous, personalized health monitoring through wearable VOC sensors holds significant potential for overcoming barriers to comprehensive medical care in underserved regions. This highlights the transformative capacity of wearable VOC sweat sensing in ensuring equitable access to advanced healthcare diagnostics, particularly in remote or geographically isolated areas.

Synergistic effect and microbial community structure of waste-activated sludge and kitchen waste solids residue mesophilic anaerobic co-digestion.

Anaerobic co-digestion was conducted on the solid residues after three-phase separation of kitchen waste (KWS) and waste-activated sludge (WAS), the synergistic effects and process performance were studied during co-digestion at different ratios of KWS to WAS. KWS and WAS mix ratios of 0:1, 1:4, 1:3, 1:2, 1:1, 2:1, 3:1, 4:1 and 1:0 (based on TS). The results showed that a ratio of KWS to WAS of 1:1 got a very high methane recovery with a methane yield of 310.45 ± 30.05 mL/g VSadded. The highest concentration of free ammonia among all reaction systems was only 70.23 ± 5.53 mg/L, which was not enough to produce ammonia inhibition in the anaerobic co-digestion system. However, when the KWS content exceeded 50%, methane inhibition and prolongation of the lag phase were observed due to the accumulation of volatile fatty acids (VFAs), and during the lag phase. Microbial community analysis showed that various bacterial groups involved in acid production and hydrolysis were mainly dominated by phylum Firmicutes, Chloroflexi, Proteobacteria and Bacteroidetes. Hydrogenotrophic methanogen was found to dominate all archaeal communities in the digesters. Co-digestion of KWS with WAS significantly increased the relative abundance of Methanobacterium compared with anaerobic digestion of WAS alone.

Microdiversity in marine pelagic ammonia-oxidizing archaeal populations in a Mediterranean long-read metagenome.

The knowledge of the different population-level processes operating within a species, and the genetic variability of the individual prokaryotic genomes, is key to understanding the adaptability of microbial populations. Here, we characterized the flexible genome of ammonia-oxidizing archaeal (AOA) populations using a metagenomic recruitment approach and long-read (PacBio HiFi) metagenomic sequencing. In the lower photic zone of the western Mediterranean Sea (75 m deep), the genomes Nitrosopelagicus brevis CN25 and Nitrosopumilus catalinensis SPOT1 had the highest recruitment values among available complete AOA genomes. They were used to analyse the diversity of flexible genes (variable from strain to strain) by examining the long-reads located within the flexible genomic islands (fGIs) identified by their under-recruitment. Both AOA genomes had a large fGI involved in the glycosylation of exposed structures, highly variable, and rich in glycosyltransferases. N. brevis had two fGIs related to the transport of phosphorus and ammonium respectively. N. catalinensis had fGIs involved in phosphorus transportation and metal uptake. A fGI5 previously reported as 'unassigned function' in N. brevis could be associated with defense. These findings demonstrate that the microdiversity of marine microbe populations, including AOA, can be effectively characterized using an approach that incorporates third-generation sequencing metagenomics.

Application of physicochemical techniques to the removal of ammonia nitrogen from water: a systematic review.

Ammonia nitrogen is a common pollutant in water and soil, known for its biological toxicity and complex removal process. Traditional biological methods for removing ammonia nitrogen are often inefficient, especially under varying temperature conditions. This study reviews physicochemical techniques for the treatment and recovery of ammonia nitrogen from water. Key methods analyzed include ion exchange, adsorption, membrane separation, struvite precipitation, and advanced oxidation processes (AOPs). Findings indicate that these methods not only remove ammonia nitrogen but also allow for nitrogen recovery. Ion exchange, adsorption, and membrane separation are effective in separating ammonia nitrogen, while AOPs generate reactive species for efficient degradation. Struvite precipitation offers dual benefits of removal and resource recovery. Despite their advantages, these methods face challenges such as secondary pollution and high energy consumption. This paper highlights the development principles, current challenges, and future prospects of physicochemical techniques, emphasizing the need for integrated approaches to enhance ammonia nitrogen removal efficiency.

Diverse metabolism drives comammox in continental-scale agricultural streams: Important ammonia oxidation but low N2O production.

Agriculture receives approximately 25 % of the annual global nitrogen input, 37 % of which subsequently runs off into adjacent low-order streams and surface water, where it may contribute to high nitrification and nitrous oxide (N2O). However, the mechanisms of nitrification and the pathways controlling N2O production in agricultural streams remain unknown. Here, we report that the third microbial ammonia oxidation process, complete ammonia oxidation (comammox), is widespread and contributes to important ammonia oxidation with low ammonia-N2O conversion in both basin- and continental-scale agricultural streams. The contribution of comammox to ammonia oxidation (21.5 ± 2.3 %) was between that of bacterial (68.6 ± 2.7 %) and archaeal (9.9 ± 1.8 %) ammonia oxidation. Interestingly, N2O production by comammox (18.5 ± 2.1 %) was higher than archaeal (10.5 ± 1.9 %) but significantly lower than bacterial (70.2 ± 2.6 %) ammonia oxidation. The first metagenome-assembled genome (MAG) of comammox bacteria from agricultural streams further revealed their potential extensive diverse and specific metabolism. Their wide habitats might be attributed to the diverse metabolism, i.e. harboring the functional gene of nitrate reduction to ammonia, while the lower N2O would be attributed to their lacking biological function to produce N2O. Our results highlight the importance of widespread comammox in agricultural streams, both for the fate of ammonia fertilizer and for climate change. However, it has not yet been routinely included in Earth system models and IPCC global assessments. Synopsis Widespread but overlooked comammox contributes to important ammonia oxidation but low N2O production, which were proved by the first comammox MAG found in agricultural streams.

Ammonia recovery via direct contact membrane distillation: Modeling and performance optimization.

Ammonia recovery from wastewater has positive environmental benefits, avoiding eutrophication and reducing production energy consumption, which is one of the most effective ways to manage nutrients in wastewater. Specifically, ammonia recovery by membrane distillation has been gradually adopted due to its excellent separation properties for volatile substances. However, the global optimization of direct contact membrane distillation (DCMD) operating parameters to maximize ammonia recovery efficiency (ARE) has not been attempted. In this work, three key operating factors affecting ammonia recovery, i.e., feed ammonia concentration, feed pH, and DCMD running time, were identified from eight factors, by a two-level Plackett-Burman Design (PBD). Subsequently, Box-Behnken design (BBD) under the response surface methodology (RSM) was used to model and optimize the significant operating parameters affecting the recovery of ammonia though DCMD identified by PBD and statistically verified by analysis of variance (ANOVA). Results showed that the model had a high coefficient of determination value (R2 = 0.99), and the interaction between NH4Cl concentration and feed pH had a significant effect on ARE. The optimal operating parameters of DCMD as follows: NH4Cl concentration of 0.46 g/L, feed pH of 10.6, DCMD running time of 11.3 h, and the maximum value of ARE was 98.46%. Under the optimized conditions, ARE reached up to 98.72%, which matched the predicted value and verified the validity and reliability of the model for the optimization of ammonia recovery by DCMD process.

Coordination of elemental sulfur and organic carbon source stimulates simultaneous nitrification and denitrification toward low C/N ratio wastewater.

The feasibility of inducing simultaneous nitrification and denitrification (SND) by S0 for low carbon to nitrogen (C/N) ratio wastewater remediation was investigated. Compared with S0 and/or organics absent systems (-3.4 %∼5.0 %), the higher nitrogen removal performance (18.2 %∼59.8 %) was achieved with C/N ratios and S0 dosages increasing when S0 and organics added simultaneously. The synergistic effect of S0 and organics stimulated extracellular polymeric substances secretion and weakened intermolecular binding force of S0, facilitating S0 bio-utilization and reducing the external organics requirement. It also promoted microbial metabolism (0.16 âˆ¼ 0.24 µg O2/(g VSS·h)) and ammonia assimilation (5.9 %∼20.5 %), thereby enhancing the capture of organics and providing more electron donors for SND. Furthermore, aerobic denitrifiers (15.91 %∼27.45 %) and aerobic denitrifying (napA and nirS) and ammonia assimilating genes were accumulated by this synergistic effect. This study revealed the mechanism of SND induced by coordination of S0 and organics and provided an innovative strategy for triggering efficient and stable SND.

[Start-up and Recovery Performance of ANAMMOX Reactors Under Long-term Starvation].

The application of ANAMMOX technology is constrained by sluggish growth and difficulty in enriching ANAMMOX bacteria. Long-term starvation of functioning bacteria due to limited substrate supply makes the steady operation of ANAMMOX reactors more difficult. Re-examining the start-up and recovery performance of the ANAMMOX reactor and identifying its resistance mechanism are important from the standpoint of long-term starvation. By inoculating nitrifying and denitrifying sludge under various operating circumstances, the ANAMMOX reactors were successfully started. Under various start-up procedures, the tolerance mechanism and recovery performance were examined. The outcomes demonstrated that the denitrifying sludge-inoculated reactor operated steadily with a high substrate concentration and low flow rate. After 85 days of operation, the removal efficiencies of NH4+-N, NO2--N, and total nitrogen reached 98.7%, 99.3%, and 89.3%, respectively. After 144 days of starvation and 30 days of recovery, the better nitrogen removal performance was achieved at a low substrate concentration and high flow rate, and the removal efficiencies were 99.8% （NH4+-N）, 99.8% （NO2--N）, and 93.6% （total nitrogen）. During the starvation, extracellular polymeric substances wrapped the ANAMMOX bacteria and kept them intact to resist long-term starvation stress. The expression of nirS, hzsA, and hdh genes ensured the synthesis of nitrite/nitric oxide oxidoreductase, hydrazine synthase, and hydrazine dehydrogenase to maintain ANAMMOX activity. There was no significant difference in the relative abundance of ANAMMOX bacteria before and after starvation recovery. Candidatus Kuenenia had better anti-hunger ability, and the relative abundance increased by more than 86% after 30 days of recovery, confirming its tolerance to long-term starvation.

Ambipolar Heterojunction Sensors: Another Way to Detect Polluting Gases.

Gas sensors based on ambipolar materials offer significant advantages in reducing the size of the analytical system and enhancing its efficiency. Here, bilayer heterojunction devices are constructed using different octafluorinated phthalocyanine complexes, with Zn and Co as metal centers, combined with a lutetium bisphthalocyanine complex (LuPc2). Stable p-type behavior is observed for the ZnF8Pc/LuPc2 device under both electron-donating (NH3) and -oxidizing (NO2 and O3) gaseous species, while the CoF8Pc/LuPc2 device exhibits n-type behavior under reducing gases and p-type behavior under oxidizing gases. The nature of majority of the charge carriers of Co-based devices varies depending on the nature of target gases, displaying an ambipolar behavior. Both heterojunction devices demonstrate stable and observable response toward all three toxic gases in the sub-ppm range. Remarkably, the Co-based device is highly sensitive toward ammonia with a limit of detection (LOD) of 200 ppb, whereas the Zn-based device demonstrates exceptional sensitivity toward oxidizing gases, with excellent LOD values of 4.9 and 0.75 ppb toward NO2 and O3, respectively, which makes it one of the most effective organic heterojunction sensors reported so far for oxidizing gases.

Workload and spirometry associated with untethered swimming in horses.

BACKGROUND: Swimming has been used empirically for rehabilitation and conditioning of horses. However, due to challenges imposed by recording physiological parameters in water, the intensity of free swimming effort is unknown. OBJECTIVES: Measure the physiological workload associated with untethered swimming in horses. Five fit Arabian endurance horses were assessed while swimming in a 100 m-long indoor pool. Horses were equipped with a modified ergospirometry facemask to measure oxygen consumption (V̇O2) and ventilatory parameters (inspired/expired volumes, VI, VE; peak inspiratory/expiratory flows, PkVI, PkVE; respiratory frequency, Rf; minute ventilation, VE; inspiratory/expiratory durations and ratios, tI, tE, tI/ttot, tE/ttot); and an underwater electrocardiogram that recorded heart rate (HR). Postexercise venous blood lactate and ammonia concentrations were measured. Data are reported as median (interquartile ranges). RESULTS: Horses showed bradypnea (12 breaths/min (10-16)) for the first 30 s of swimming. V̇O2 during swimming was 43.2 ml/(kg.min) (36.0-56.6). Ventilatory parameters were: VI = 16.7 L (15.3-21.8), VE = 14.7 L (12.4-18.9), PkVI = 47.8 L/s (45.8-56.5), PkVE = 55.8 L/s (38.3-72.5), Rf = 31.4 breaths/min (20.0-33.8), VE = 522.9 L/min (414.7-580.0), tI = 0.5 s (0.5-0.6), tE = 1.2 s (1.1-1.6), tI/ttot = 0.3 (0.2-0.4), tE/ttot = 0.7 (0.6-0.8). Expiratory flow tracings showed marked oscillations that coincided with a vibrating expiratory sound. HR was 178.0 bpm (148.5-182.0), lactate = 1.5 mmol/L (1.0-1.9) and ammonia = 41.0 µmol/L (36.5-43.5). CONCLUSIONS: Free (untethered) swimming represents a submaximal, primarily aerobic exercise in horses. The breathing pattern during swimming is unique, with a relatively longer apneic period at the beginning of the exercise and an inspiratory time less than half that of expiration.

Effect of rest duration between sets on fatigue and recovery after short intense plyometric exercise.

Plyometric training is characterized by high-intensity exercise which is performed in short term efforts divided into sets. The purpose of the present study was twofold: first, to investigate the effects of three distinct plyometric exercise protocols, each with varying work-to-rest ratios, on muscle fatigue and recovery using an incline-plane training machine; and second, to assess the relationship between changes in lower limb muscle strength and power and the biochemical response to the three exercise variants employed. Forty-five adult males were randomly divided into 3 groups (n = 15) performing an exercise of 60 rebounds on an incline-plane training machine. The G0 group performed continuous exercise, while the G45 and G90 groups completed 4 sets of 15 repetitions, each set lasting 45 s with 45 s rest in G45 (work-to-rest ratio of 1:1) and 90 s rest in G90 (1:2 ratio). Changes in muscle torques of knee extensors and flexors, as well as blood lactate (LA) and ammonia levels, were assessed before and every 5 min for 30 min after completing the workout. The results showed significantly higher (p < 0.001) average power across all jumps generated during intermittent compared to continuous exercise. The greatest decrease in knee extensor strength immediately post-exercise was recorded in group G0 and the least in G90. The post-exercise time course of LA changes followed a similar pattern in all groups, while the longer the interval between sets, the faster LA returned to baseline. Intermittent exercise had a more favourable effect on muscle energy metabolism and recovery than continuous exercise, and the work-to-rest ratio of 1:2 in plyometric exercises was sufficient rest time to allow the continuation of exercise in subsequent sets at similar intensity.