scholarly journals Interaction between environmental temperature and hypoxia on central and peripheral fatigue during high-intensity dynamic knee extension

2016 ◽  
Vol 120 (6) ◽  
pp. 567-579 ◽  
Author(s):  
Alex Lloyd ◽  
Margherita Raccuglia ◽  
Simon Hodder ◽  
George Havenith
Keyword(s):  
High Intensity ◽  
Muscle Activation ◽  
Knee Extension ◽  
Climatic Conditions ◽  
Peripheral Fatigue ◽  
Time To Exhaustion ◽  
Combined Exposure ◽  
Fatigue Development ◽  
C 50 ◽  
The Impact

This study investigated causative factors behind the expression of different interaction types during exposure to multistressor environments. Neuromuscular fatigue rates and time to exhaustion (TTE) were investigated in active men ( n = 9) exposed to three climates [5°C, 50% relative humidity (rh); 23°C, 50% rh; and 42°C, 70% rh] at two inspired oxygen fractions (0.209 and 0.125 FiO2; equivalent attitude = 4,100 m). After a 40-min rest in the three climatic conditions, participants performed constant-workload (high intensity) knee extension exercise until exhaustion, with brief assessments of neuromuscular function every 110 s. Independent exposure to cold, heat, and hypoxia significantly ( P < 0.01) reduced TTE from thermoneutral normoxia (reductions of 190, 405, and 505 s from 915 s, respectively). The TTE decrease was consistent with a faster rate of peripheral fatigue development ( P < 0.01) compared with thermoneutral normoxia (increase of 1.6, 3.1, and 4.9%/min from 4.1%/min, respectively). Combined exposure to hypoxic-cold resulted in an even greater TTE reduction (−589 s), likely due to an increase in the rate of peripheral fatigue development (increased by 7.6%/min), but this was without significant interaction between stressors ( P > 0.198). In contrast, combined exposure to hypoxic heat reduced TTE by 609 s, showing a significant antagonistic interaction ( P = 0.003) similarly supported by an increased rate of peripheral fatigue development (which increased by 8.3%/min). A small decline (<0.4%/min) in voluntary muscle activation was observed only in thermoneutral normoxia. In conclusion, interaction type is influenced by the impact magnitude of the effect of the individual stressors' effect on exercise capacity, whereby the greater the effect of stressors, the greater the probability that one stressor will be abolished by the other. This indicates that humans respond to severe and simultaneous physiological strains on the basis of a worst-strain-takes-precedence principle.

Electrically-induced quadriceps fatigue in the contralateral leg impairs ipsilateral knee extensors performance

2021 ◽  
Author(s):  
Fabio Giuseppe Laginestra ◽  
Markus Amann ◽  
Emine Kirmizi ◽  
Gaia Giuriato ◽  
Chiara Barbi ◽  
...  
Keyword(s):  
Muscle Activation ◽  
Central Fatigue ◽  
Endurance Performance ◽  
Voluntary Exercise ◽  
Peripheral Fatigue ◽  
Knee Extensors ◽  
Motor Drive ◽  
Time To Exhaustion ◽  
Crossover Effect ◽  
The Impact

Muscle fatigue induced by voluntary exercise, which requires central motor drive, causes central fatigue that impairs endurance performance of a different, non-fatigued muscle. This study investigated the impact of quadriceps fatigue induced by electrically-induced (no central motor drive) contractions on single-leg knee-extension (KE) performance of the subsequently exercising ipsilateral quadriceps. On two separate occasions, eight males completed constant-load (85% of maximal power-output) KE exercise to exhaustion. In a counterbalanced manner, subjects performed the KE exercise with no pre-existing quadriceps fatigue in the contralateral leg on one day (No-PreF), while on the other day, the same KE exercise was repeated following electrically-induced quadriceps fatigue in the contralateral leg (PreF). Quadriceps fatigue was assessed by evaluating pre- to post-exercise changes in potentiated twitch force (ΔQtw,pot; peripheral-fatigue), and voluntary muscle activation (ΔVA; central-fatigue). As reflected by the 57±11% reduction in electrically-evoked pulse force, the electrically-induced fatigue protocol caused significant knee-extensors fatigue. KE endurance time to exhaustion was shorter during PreF compared to No-PreF (4.6±1.2 vs 7.7±2.4 min; p<0.01). While ΔQtw,pot was significantly larger in No-PreF compared to PreF (-60% vs -52%, p<0.05), ΔVA was greater in PreF (-14% vs -10%, p<0.05). Taken together, electrically-induced quadriceps fatigue in the contralateral leg limits KE endurance performance and the development of peripheral fatigue in the ipsilateral leg. These findings support the hypothesis that the crossover-effect of central fatigue is mainly mediated by group III/IV muscle afferent feedback and suggest that impairments associated with central motor drive may only play a minor role in this phenomenon.

Influence of endurance training on muscle [PCr] kinetics during high-intensity exercise

2007 ◽  
Vol 293 (1) ◽  
pp. R392-R401 ◽  
Author(s):  
Andrew M. Jones ◽  
Daryl P. Wilkerson ◽  
Nicolas J. Berger ◽  
Jonathan Fulford
Keyword(s):  
Endurance Training ◽  
High Intensity ◽  
Slow Component ◽  
Knee Extension ◽  
High Intensity Exercise ◽  
Whole Body ◽  
Time To Exhaustion ◽  
Exercise Tests ◽  
Before And After ◽  
Knee Extension Exercise

We hypothesized that a period of endurance training would result in a speeding of muscle phosphocreatine concentration ([PCr]) kinetics over the fundamental phase of the response and a reduction in the amplitude of the [PCr] slow component during high-intensity exercise. Six male subjects (age 26 ± 5 yr) completed 5 wk of single-legged knee-extension exercise training with the alternate leg serving as a control. Before and after the intervention period, the subjects completed incremental and high-intensity step exercise tests of 6-min duration with both legs separately inside the bore of a whole-body magnetic resonance spectrometer. The time-to-exhaustion during incremental exercise was not changed in the control leg [preintervention group (PRE): 19.4 ± 2.3 min vs. postintervention group (POST): 19.4 ± 1.9 min] but was significantly increased in the trained leg (PRE: 19.6 ± 1.6 min vs. POST: 22.0 ± 2.2 min; P < 0.05). During step exercise, there were no significant changes in the control leg, but end-exercise pH and [PCr] were higher after vs. before training. The time constant for the [PCr] kinetics over the fundamental exponential region of the response was not significantly altered in either the control leg (PRE: 40 ± 13 s vs. POST: 43 ± 10 s) or the trained leg (PRE: 38 ± 8 s vs. POST: 40 ± 12 s). However, the amplitude of the [PCr] slow component was significantly reduced in the trained leg (PRE: 15 ± 7 vs. POST: 7 ± 7% change in [PCr]; P < 0.05) with there being no change in the control leg (PRE: 13 ± 8 vs. POST: 12 ± 10% change in [PCr]). The attenuation of the [PCr] slow component might be mechanistically linked with enhanced exercise tolerance following endurance training.

scholarly journals Muscle Coactivation Before and After the Impact Phase of Running Following Isokinetic Fatigue

2011 ◽  
Vol 46 (1) ◽  
pp. 11-19 ◽  
Author(s):  
Eleftherios Kellis ◽  
Andreas Zafeiridis ◽  
Ioannis G. Amiridis
Keyword(s):  
Muscle Activation ◽  
Biceps Femoris ◽  
Knee Extension ◽  
Knee Extensors ◽  
Training Experience ◽  
Cross Sectional ◽  
Muscle Activation Patterns ◽  
Strength Capacity ◽  
Before And After ◽  
The Impact

Abstract Context: The effects of fatigue on impact loading during running are unclear, with some authors reporting increased impact forces and others reporting decreased forces. Objective: To examine the effects of isokinetic fatigue on muscle cocontraction ratios about the knee and ankle during running. Design: Cross-sectional study. Setting: Neuromechanics laboratory. Patients or Other Participants: Female middle-distance runners (age  =  21.3 ± 1.93 years) with at least 5 years of training experience. Intervention(s): Participants ran on the treadmill at 3.61 m/s before and immediately after the fatigue protocol, which consisted of consecutive, concentric knee extension-flexion at 120°/s until they could no longer produce 30% of the maximum knee-extension moment achieved in the familiarization session for 3 consecutive repetitions. Main Outcome Measure(s): Electromyographic (EMG) amplitude of the vastus medialis (VM), biceps femoris (BF), gastrocnemius (GAS), and tibialis anterior (TA) was recorded using surface electrodes. Agonist∶antagonist EMG ratios for the knee (VM∶BF) and ankle (GAS∶TA) were calculated for the preactivation (PR), initial loading response (LR1), and late loading response (LR2) phases of running. Hip-, knee-, and ankle-joint angular displacements at initial foot contact were obtained from 3-dimensional kinematic tracings. Results: Fatigue did not alter the VM∶BF EMG ratio during the PR phase (P &gt; .05), but it increased the ratio during the LR1 phase (P &lt; .05). The GAS∶TA EMG ratio increased during the LR1 phase after fatigue (P &lt; .05) but remained unchanged during the PR and LR2 phrases (P &gt; .05). Conclusions: The increased agonist EMG activation, coupled with reduced antagonist EMG activation after impact, indicates that the acute decrease in muscle strength capacity of the knee extensors and flexors results in altered muscle-activation patterns about the knee and ankle before and after foot impact.

scholarly journals High-Intensity Interval Training in Middle-Distance NCAA Division I 800/1500m Collegiate Athletes

2020 ◽  
Vol 8 (3) ◽  
pp. 28
Author(s):  
Ffion G. Price ◽  
JohnEric W. Smith ◽  
Alana J. Turner ◽  
Ben M. Krings ◽  
Hunter S. Waldman ◽  
...  
Keyword(s):  
High Intensity ◽  
Muscle Activation ◽  
Collegiate Athletes ◽  
Time Trial ◽  
Interval Training ◽  
Performance Tests ◽  
High Intensity Interval Training ◽  
Distance Runners ◽  
High Intensity Interval ◽  
The Impact

Background: High-intensity interval training (HIIT) has grown in popularity, with studies demonstrating improvements in aerobic and anaerobic performances within Sedentary and Recreationally active adults. Little research has been comprised on collegiate, middle-distance runners (800m/1500m). Objective: This research study aimed to investigate the impact of four-weeks HIIT cycling training on collegiate 800/1500m runners performance, and determine whether HIIT can be used as an alternative training method for student athletes. Methods: Twelve middle-distance runners were recruited, with six athletes completing the intervention. Athletes completed pre-testing, which included a 1500m time trial, a GXT, stride length and frequency measurements, and MVIC, using Biopac electromyography (EMG). After pre-testing, athletes completed four weeks of HIIT twice per week. The HIIT consisted of four 20-second bouts with 4 minutes recovery. Following the completion of the training intervention, post-testing was performed for all measures. A paired t-test was used to determine differences between pre- and post-performance tests. An ANOVA was used to determine changes in heart rate and RPE during the GXT. Results: Significant changes were demonstrated between the pre- and post-muscle activation tests of the quadriceps (p=0.05). Significant changes were seen with both HR (p<0.05) and RPE (p<0.05) throughout the GXT. No other significant differences were demonstrated between pre- and post-performance tests, concluding four-weeks HIIT does not alter 800/1500m performance. Conclusion: From the results of this study, HIIT could be used as an alternate method for training for 800/1500m runners. Further reasearch should be conducted toto further understand the impacts of HIIT on middle distance athletes.

Blood flow restriction impairs the inflammatory adaptations of strength training in overweight men: a clinical randomized trial

2020 ◽  
Vol 45 (6) ◽  
pp. 659-666 ◽  
Author(s):  
Igor Martins da Silva ◽  
Maeli Andressa Santos ◽  
Simone Lunelli Galvão ◽  
Gilson P. Dorneles ◽  
Fabio Santos Lira ◽  
...  
Keyword(s):  
Blood Flow ◽  
Strength Training ◽  
High Intensity ◽  
Knee Extension ◽  
Blood Flow Restriction ◽  
Monocyte Subsets ◽  
Necrosis Factor Alpha ◽  
Flow Restriction ◽  
Tnf Α ◽  
The Impact

The aim of this study was to evaluate the impact of high-intensity strength training (ST) or low-intensity strength training with blood flow restriction (ST-BFR) on monocyte subsets, the expression of C-C chemokine receptor 5 (CCR5), and CD16 on monocytes, and tumor necrosis factor alpha (TNF-α) production of overweight men. Thirty overweight men were randomly assigned to conventional ST or ST-BFR. Both groups performed exercises of knee extension and biceps curl with equal volume (3 sessions/week) over 8 weeks, and the peripheral frequency of monocytes (CD14+CD16−, classical monocytes; CD14+CD16+, intermediate monocytes; CD14−CD16+, nonclassical monocytes), the mean fluorescence intensity (MFI) of CCR5 and CD16 on CD14+ monocytes; and the production of TNF-α by lipopolysaccharide (LPS)-stimulated cells were quantified. Eight weeks of ST increased the frequency of CD14+CD16− monocytes (p = 0.04) and reduced the percentage of CD14−CD16+ (p = 0.02) and the production of TNF-α by LPS-stimulated cells (p = 0.03). The MFI of CD16 on CD14+ monocytes decreased after the ST intervention (p = 0.02). No difference in monocyte subsets, CCR5 or CD16 expression, and TNF-α production were identified after ST-BFR intervention (p > 0.05). The adoption of ST promotes anti-inflammatory effects on monocyte subsets of overweight men, but this effect was lost when BFR was adopted. Novelty High-intensity strength training reduces the production of TNF-α and the peripheral frequency of CD16+ monocytes in overweight men. Blood flow restriction method blunts the strength training adaptations on monocyte subsets and pro-inflammatory TNF-α production in overweight men.

Impact of roof shading on building energy performance in warm & humid climatic places of India

2020 ◽  
pp. 50-64
Author(s):  
Kuladeep Kumar Sadevi ◽  
Avlokita Agrawal
Keyword(s):  
Energy Consumption ◽  
Energy Conservation ◽  
Energy Performance ◽  
General Assumption ◽  
Climatic Conditions ◽  
Building Envelope ◽  
Passive Cooling ◽  
Base Case ◽  
U Value ◽  
The Impact

With the rise in awareness of energy efficient buildings and adoption of mandatory energy conservation codes across the globe, significant change is being observed in the way the buildings are designed. With the launch of Energy Conservation Building Code (ECBC) in India, climate responsive designs and passive cooling techniques are being explored increasingly in building designs. Of all the building envelope components, roof surface has been identified as the most significant with respect to the heat gain due to the incident solar radiation on buildings, especially in tropical climatic conditions. Since ECBC specifies stringent U-Values for roof assembly, use of insulating materials is becoming popular. Along with insulation, the shading of the roof is also observed to be an important strategy for improving thermal performance of the building, especially in Warm and humid climatic conditions. This study intends to assess the impact of roof shading on building’s energy performance in comparison to that of exposed roof with insulation. A typical office building with specific geometry and schedules has been identified as base case model for this study. This building is simulated using energy modelling software ‘Design Builder’ with base case parameters as prescribed in ECBC. Further, the same building has been simulated parametrically adjusting the amount of roof insulation and roof shading simultaneously. The overall energy consumption and the envelope performance of the top floor are extracted for analysis. The results indicate that the roof shading is an effective passive cooling strategy for both naturally ventilated and air conditioned buildings in Warm and humid climates of India. It is also observed that a fully shaded roof outperforms the insulated roof as per ECBC prescription. Provision of shading over roof reduces the annual energy consumption of building in case of both insulated and uninsulated roofs. However, the impact is higher for uninsulated roofs (U-Value of 3.933 W/m2K), being 4.18% as compared to 0.59% for insulated roofs (U-Value of 0.33 W/m2K).While the general assumption is that roof insulation helps in reducing the energy consumption in tropical buildings, it is observed to be the other way when insulation is provided with roof shading. It is due to restricted heat loss during night.

A Predictive Model of the Impact of the Skidding System on Forest Soil in Severe Climatic Conditions

2020 ◽  
pp. 131-144
Author(s):  
S.E. Rudov ◽  
◽  
V.Ya. Shapiro ◽  
O.I. Grigoreva ◽  
I.V. Grigorev ◽  
...  
Keyword(s):  
Forest Soil ◽  
Warm Season ◽  
Climatic Conditions ◽  
Soil Freezing ◽  
Class Iii ◽  
Freezing And Thawing ◽  
Metal Structures ◽  
Rapid Adjustment ◽  
Soil Freezing And Thawing ◽  
The Impact

In the Russian Federation logging operations are traditionally carried out in winter. This is due to the predominance of areas with swamped and water-logged (class III and IV) soils in the forest fund, where work of forestry equipment is difficult, and sometimes impossible in the warm season. The work of logging companies in the forests of the cryolithozone, characterized by a sharply continental climate, with severe frosts in winter, is hampered by the fact that forest machines are not recommended to operate at temperatures below –40 °C due to the high probability of breaking of metal structures and hydraulic system. At the same time, in the warm season, most of the cutting areas on cryosolic soils become difficult to pass for heavy forest machines. It turns out that the convenient period for logging in the forests of the cryolithozone is quite small. This results in the need of work in the so-called off-season period, when the air temperature becomes positive, and the thawing processes of the soil top layer begin. The same applies to the logging companies not operating in the conditions of cryosolic soils, for instance, in the Leningrad, Novgorod, Pskov, Vologda regions, etc. The observed climate warming has led to a significant reduction in the sustained period of winter logging. Frequent temperature transitions around 0 °C in winter, autumn and spring necessitate to work during the off-season too, while cutting areas thaw. In bad seasonal and climatic conditions, which primarily include off-season periods in general and permafrost in particular, it is very difficult to take into account in mathematical models features of soil freezing and thawing and their effect on the destruction nature. The article shows that the development of long-term predictive models of indicators of cyclic interaction between the skidding system and forest soil in adverse climatic conditions of off-season logging operations in order to improve their reliability requires rapid adjustment of the calculated parameters based on the actual experimental data at a given step of the cycles.

scholarly journals Conventional and Organic Honeys as a Source of Water- and Ethanol Soluble Molecules with Nutritional and Antioxidant Characteristics

Molecules ◽  
2021 ◽  
Vol 26 (12) ◽  
pp. 3746
Author(s):  
Magdalena Polak-Śliwińska ◽  
Małgorzata Tańska
Keyword(s):  
Antioxidant Activity ◽  
Immune System ◽  
Vitamin C ◽  
Geographical Area ◽  
Production Method ◽  
Climatic Conditions ◽  
Organic Production ◽  
Organoleptic Characteristics ◽  
Nutritional Characteristics ◽  
The Impact

The benefits of natural honeybee products (e.g., honey, royal jelly, beeswax, propolis, beevenom and pollen) to the immune system are remarkable, and many of them are involved in the induction of antibody production, maturation of immune cells and stimulation of the immune system. The type of plants in the geographical area, climatic conditions and production method have a significantly influence on the nutritional quality of honey. However, this variability can influence consumer liking by the sensory attributes of the product. The aim of this work was to compare the most popular honeys from Poland in terms of nutritional value, organoleptic properties and antioxidant activity. In the study, five varieties of honey (honeydew, forest, buckwheat, linden and dandelion) from conventional and organic production methods were tested. The nutritional characteristics of honey samples included acidity, content of water, sugars, vitamin C, HMF and phenolics (total and flavonoids), while honey color, taste, aroma and consistency were investigated in the organoleptic characteristics. The antioxidant activity was determined in water- and ethanol-soluble honey extracts using DPPH and ORAC tests. The results showed that organoleptic and nutritional characteristics of popular Polish honeys differ significantly in relation to plant source and production method. The significant effect of honey variety on the content of HMF, saccharose and phenolics, as well as acidity and antioxidant capacity were noted. The impact of variety and variety × production method interaction was significant in the case of the content of vitamin C, glucose and fructose. A visible difference of buckwheat and forest honeys from other samples was observed. The highest content of total phenolics with antioxidant activity based on the SET mechanism was found in buckwheat honeys, while forest honeys were richer in flavonoids.

scholarly journals Effects of Climatic Conditions, Season and Environmental Factors on CO2 Concentrations in Naturally Ventilated Primary Schools in Chile

2021 ◽  
Vol 13 (8) ◽  
pp. 4139
Author(s):  
Muriel Diaz ◽  
Mario Cools ◽  
Maureen Trebilcock ◽  
Beatriz Piderit-Moreno ◽  
Shady Attia
Keyword(s):  
Air Quality ◽  
Indoor Air Quality ◽  
Indoor Air ◽  
Primary Schools ◽  
Co2 Concentration ◽  
Building Design ◽  
Climatic Conditions ◽  
Indoor Environmental Quality ◽  
Co2 Concentrations ◽  
The Impact

Between the ages of 6 and 18, children spend between 30 and 42 h a week at school, mostly indoors, where indoor environmental quality is usually deficient and does not favor learning. The difficulty of delivering indoor air quality (IAQ) in learning facilities is related to high occupancy rates and low interaction levels with windows. In non-industrialized countries, as in the cases presented, most classrooms have no mechanical ventilation, due to energy poverty and lack of normative requirements. This fact heavily impacts the indoor air quality and students’ learning outcomes. The aim of the paper is to identify the factors that determine acceptable CO2 concentrations. Therefore, it studies air quality in free-running and naturally ventilated primary schools in Chile, aiming to identify the impact of contextual, occupant, and building design factors, using CO2 concentration as a proxy for IAQ. The monitoring of CO2, temperature, and humidity revealed that indoor air CO2 concentration is above 1400 ppm most of the time, with peaks of 5000 ppm during the day, especially in winter. The statistical analysis indicates that CO2 is dependent on climate, seasonality, and indoor temperature, while it is independent of outside temperature in heated classrooms. The odds of having acceptable concentrations of CO2 are bigger when indoor temperatures are high, and there is a need to ventilate for cooling.

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