Effect Of Small Changes Research Articles

Small changes in the transducer position cause a systematic change in cardiac output readings: implications for clinical practice.

To systematically evaluate the effect of small changes in transducer position on key hemodynamic variables including CO generated by 4th generation FloTrac software. After cardiac surgery, cardiac output, mean arterial pressure, systemic vascular resistance, and stroke volume variation were measured with 4 generation Flotrac software. The transducer position was randomly placed at the midaxillary plane, 4cm higher than the midaxillary plane or 4cm lower than the midaxillary plane. Averages of three measurements were used. Data was available from 20 patients. Cardiac output increased from 4.59L/min (± 0.92) to 4.78L/min (± 0.99) with the transducer position at the midaxillary plane to 4cm higher than the midaxillary plane, and cardiac output decreased to 4.43L/min (± 0.90) with the transducer 4cm lower than midaxillary plane (P < 0.001). On the relative scale, CO increased 4.1% (95% CI 3.1-5.0) when comparing the higher transducer level with the midaxillary plane position, and CO decreased 3.4% (95% CI 2.4-4.4) when comparing the midaxillary plane position with the lower transducer level, correspondiong to changes in CO of ≈ 1% per 1cm change in transducer position. Mean arterial pressure and systemic vascular resistance both changed significantly with transducer position (both P < 0.001), whereas no statistically or clinically significant effect was seen on stroke volume variation (P = 0.98). A four-centimeter change in vertical transducer position induced clinically significant changes in cardiac output measurements by 4th generation FloTrac software. Definitions of optimal cardiac output in goal-directed therapy algorithms require meticulous transducer adjustment and can only be used in the reference patient position.

Impact of atomic packing and electronic structure on icosahedral short-range order and glass-forming ability of Zr–Cu metallic glasses

ABSTRACT Chemical and topological short-range ordering are important for glass formation in metallic alloys. Yet, it remains little understood from the viewpoint of the electronic bonding among the constituent elements of the alloys. In this work, we study CuxZr100−x, (46 ≤ x ≤ 70) metallic glasses, where the atomic packing efficiency and the electronic structure of the full icosahedra, the key short-range order structures, have been investigated in detail. To capture a realistic picture of the electronic bonding in the icosahedra in the as-quenched metastable state, DFT study of the electronic structure of the icosahedra extracted from classical molecular dynamics simulation is carried out. Results for the CunZr13−n , (4 ≤ n ≤ 9) clusters reveal that Cu6Zr7, Cu7Zr6 and Cu8Zr5 are the most abundant, electronically stable in Cu50Zr50 , Cu58Zr42 and Cu64Zr36, respectively. These three clusters also exhibit pseudo-gap in the density of states at the Fermi level – a feature linked with glass-forming ability according to the nearly-free electron approach. The partial density of states demonstrates the effect of small changes in the stoichiometry of the clusters on the s, p and d states of Cu and Zr in Cu–Cu and Cu–Zr bonding and hence, the stability of the clusters.

Real-Time Tracking of Carbon Dioxide Concentration Using an Optical Microsphere Resonator Sensor.

Whispering gallery mode resonator sensors are nondisruptive optical sensors that can detect and monitor perturbations in a gaseous environment. Through its resonant properties of peak wavelength, amplitude, and quality factor (Q factor), changes in concentration can be quantified within seconds and monitored over days with great stability. In addition, the small footprint, low cost, and high sensitivity are ideal properties for a disposable sensor that can be utilized in extreme environments. The large Q factor of the resonant cavity enables long interaction lengths and amplifies the effect of small changes in the background refractive index, which is detectable in picometer shifts of the resonance wavelength. However, this measurement is susceptible to changes in other environmental factors such as temperature, pressure, and humidity, which manifest on the picometer wavelength scale, reinforcing the need to decouple the variables. In this work, we compare the spectral response of different diameter resonators to carbon dioxide, nitrogen, and its mixtures, observing the spectral shifting and broadening of the cavity resonance near 1550 nm. In addition, the effect of environmental temperature on spectral shifting due to the thermo-optic effect is characterized and quantified. Lastly, the gas concentrations are changed in real time to showcase the tracking and recovery capabilities of the resonator sensor.

Structural Isomers: Small Change with Big Difference in Anion Storage

HighlightsThe effect of small changes in isomers on electrochemical performance have not been focused in batteries and two isomers are reported for Zn-ion batteries here. The isomer tetrathiafulvalene (TTF) could store two monovalent anions reversibly, showing remarkable performance that outperformed most of the reported organic electrode materials for zinc-ion batteries.The isomer tetrathianaphthalene (TTN) could only reversibly store one monovalent anion and upon further oxidation, it would undergo an irreversible solid-state molecular rearrangement to TTF.

Analysis of parametric instability of cigarettes based on computational fluid dynamics methods

In actual production tests, there are large fluctuations in the ventilation rate and smoking resistance of cigarettes. In this paper, fluctuations in ventilation rate and smoking resistance are attributed to variations in the number of ventilation holes in the joint paper and the porosity of each component. The effects of small changes in porosity of each component were analyzed by using computational fluid dynamics methods. The results showed that the difference in the effective number of ventilation holes caused by the gluing process had little effect on the ventilation rate and smoking resistance of cigarettes in the practical production process. The smoking resistance is mainly affected by the structural parameters of filter tow and cut tobacco section in the length direction of cigarettes, the porosity of cigarette paper and packaging paper is positively related to the cigarette ventilation rate, the porosity of cut tobacco and the porosity of filter tow are negatively related to the cigarette ventilation rate, and the influence of shaped paper is the smallest. The results can provide technical and theoretical basis for the optimization of cigarette process parameters and the stabilization of ventilation rate.

On measuring axiom violations due to each tax instrument applied in a real-world personal income tax

In their seminal paper, Kakwani and Lambert (Eur J Polit Econ 14:369–380, 1998) state three Axioms an equitable tax system should respect. By proposing a measurement system based on re-ranking indexes of taxes, tax rates and post-tax incomes, they show how to evaluate the negative influences that Axiom violations exert on the redistributive effect of a tax. By considering each element of a real-world personal income tax, i.e. deductions and tax credits as well as statutory tax rates, in this study we take a theoretical step further by decomposing the magnitude of the three Axiom violations produced by all these tax elements. We propose two complementary strategies. The first one is a ‘stepwise’ decomposition computing the effect of each element of the tax on the redistributive effect when they are sequentially applied; the second strategy is an ‘overall and simultaneous’ decomposition always evaluating the effect of small changes in deductions, tax rates and tax credits with respect to the pre-tax income distribution, once all the three tax instruments have been simultaneously applied. These strategies can be more suitable and effective in measuring the loss of the redistributive effect produced by each tax element because of axiom violations. We also show that they can give different information on the existing inequities of the tax. We finally emphasize the goodness of our approach by applying it to a real world personal income tax.

Effect of Small Change in Reaction Conditions on the Size of Monoclinic BiVO4 Nanoparticles and their Photocatalytic Abilities

AbstractBiVO4 is an effective material and highly used in different applications. Here, we have synthesized BiVO4 using bismuth nitrate pentahydrate and ammonium metavanadate by simple reflux condensation method without addition of any surfactant. To check the effect on the structure and activity of BiVO4 different ratios of bismuth nitrate pentahydrate to ammonium metavanadate e. g. 1 : 1, 1 : 2 and 2 : 1 were used. Obtained BiVO4 nanomaterial was successfully analysed using various analytical techniques such X‐ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Field emission scanning electron microscopy (FE‐SEM) and X‐ray photoelectron spectroscopy (XPS). The nanoparticles were shown spherical morphology, high porosity and monoclinic scheelite (m) crystalline phase. It was observed that BiVO4 nanoparticles prepared using 1 : 1 ratio have very small size as compared to those prepared using other ratios. Further, the photocatalytic activity of the BiVO4 nanoparticles was assessed by photodegradation of crystal violet dye (CV) under visible light irradiation and found that the particles prepared with 1 : 1 ratio were showing high efficiency of degradation. In addition, prepared nanoparticles have shown good antibacterial properties.

Cracking susceptibility of maraging parts manufactured by laser powder bed fusion additive manufacturing: study on the powder characteristics and baseplate preheating influence

ABSTRACT Maraging steel 300 processed by laser powder bed fusion (PBF-LB/M) is widely used for manufacturing inserts and moulds with conformal cooling channels. For such applications, high fracture toughness and strength are required to withstand thermal fatigue and any defect like pores, lack of fusion and cracks should be avoided so that the durability of the mould is not reduced. Maraging steel is prone to be cracked due to thermal gradients which arise during PBF-LB/M. Moreover, it was recently observed that slight variations in composition led to the crack’s presence, which implied lower mechanical properties. In this study, two powder batches, from the same powder producer, were employed with the same processing parameters. The effect of small changes in minor elements composition of the powder batch on cracking was studied and the preheating temperature was varied to significantly reduce the crack density. The presence of cracks significantly reduced the ductility of the parts.

Computational Prodrug Design Methodology for Liposome Formulability Enhancement of Small-Molecule APIs.

Encapsulation into liposomes is a formulation strategy that can improve efficacy and reduce side effects of active pharmaceutical ingredients (APIs) that exhibit poor biodistribution or pharmacokinetics when administered alone. However, many APIs are unsuitable for liposomal formulations intended for parenteral administration due to their inherent physicochemical properties─lipid bilayer permeability and water-lipid equilibrium partitioning coefficient. Too high permeability results in premature leakage from liposomes, while too low permeability means the API is not able to pass across biological barriers. There are several options for solving this issue: (i) change of the lipid bilayer composition, (ii) addition of a permeability enhancer, or (iii) modification of the chemical structure of the API to design a prodrug. The latter approach was taken in the present work, and the effect of small changes in the molecular structure of the API on its permeation rate across a lipidic bilayer was systematically explored utilizing computer simulations. An in silico methodology for prodrug design based on the COSMOperm approach has been proposed and applied to four APIs (abiraterone, cytarabine, 5-fluorouracil, and paliperidone). It is shown that the addition of aliphatic hydrocarbon chains via ester or amide bonds can render the molecule more lipophilic and increase its permeability by approximately 1 order of magnitude for each 2 carbon atoms added, while the formation of fructose adducts can provide a more hydrophilic character to the molecule and reduce its lipid partitioning. While partitioning was found to depend only on the size and type of the added group, permeability was found to depend also on the added group location. Overall, it has been shown that both permeability and lipid partitioning coefficient can be systematically shifted into the desired liposome formulability window by appropriate group contributions to the parental drug. This can significantly increase the portfolio of APIs for which liposome or lipid nanoparticle formulations become feasible.

Does Head and Neck Posture Affect Cone-Beam Computed Tomography Assessment of the Upper Airway?

Radiographic analysis is often used as a screening tool to assess for risk of sleep-related breathing disorders. This study aimed to address 2 questions: (1) Does head posture significantly affect the minimum cross-sectional area (MCA)? and (2) Is the NBC3 (nasion-basion-C3) angle a reliable measurement to control for alteration of head position in cone-beam computed tomography (CBCT) scans? Study design: prospective cohort study. Private practices affiliated with a research institution. convenience sample of adult volunteers. CBCT scans were taken in 2 conditions: baseline (natural head position, NHP) and 1 of 5 experimental conditions (head tilted up, head tilted down, sitting vs standing, use of chin-rest, and swallow variation). For the primary aim of our study, the primary predictor variable was head posture and the main outcome variable was percentage change in MCA. For the secondary aim, the primary predictor variable was head posture and the main outcome variable was degree change in NBC3 angle. Ninety subjects were included (age 40.7±13.7years, 70% female). Mean NBC3 at baseline was 112.4±8.3°. Head tilted down significantly decreased (-41.4±18.5mm2, P=.03∗) and head tilted up significantly increased MCA (+147.4±43.3mm2, P=.0018∗). Head tilted down significantly reduced the NBC3 angle measurement (-10.5±6.8°, P=.006) and head tilted up significantly increased the NBC3 angle measurement (+14.4±5.8°, P=.0004). A quadratic regression model was fitted with moderately strong correlation (R2=0.54) showing an exponential effect of small changes in the NBC3 angle on MCA, P<.0001. The model predicts that increasing NBC3 by+5 and+10° resulted in MCA changes of+25% and+88%, whereas a decrease in NBC3 by -5 and -10° results in MCA changes of -21% and -23%, respectively. Alterations in head posture significantly affect the MCA of the upper airway on CBCT. The NBC3 angle can be used to reliably assess changes in cranio-cervical extension and validate comparisons of MCA between CBCT scans for the same patient. A standardized protocol for CBCT acquisition is proposed.

Specimen-displacement correction for powder X-ray diffraction in Debye-Scherrer geometry with a flat area detector.

The effect of small changes in the speci-men-to-detector distance on the unit-cell parameters is examined for synchrotron powder diffraction in Debye-Scherrer (transmission) geometry with a flat area detector. An analytical correction equationis proposed to fix the shift in 2θ values due to speci-men capillary displacement. This equationdoes not require the use of an internal reference material, is applied during the Rietveld refinement step, and is analogous to the speci-men-displacement correction equations for Bragg-Brentano and curved-detector Debye-Scherrer geometry experiments, but has a different functional form. The 2θ correction equationis compared with another speci-men-displacement correction based on the use of an internal reference material in which new integration and calibration parameters of area-detector images are determined. Example data sets showing the effect of a 3.3 mm speci-men displacement on the unit-cell parameters for 25°C CeO2, including both types of displacement correction, are described. These experiments were performed at powder X-ray diffraction beamlines at the National Synchrotron Light Source II at Brookhaven National Laboratory and the Advanced Photon Source at Argonne National Laboratory.

TASK inhibition by mild acidosis increases Ca2+ oscillations to mediate pH sensing in rat carotid body chemoreceptor cells.

Severe levels of acidosis (pH < 6.8) have been shown to cause a sustained rise in cytosolic Ca2+ concentration in carotid body Type 1 (glomus) cells. To understand how physiologically relevant levels of acidosis regulate Ca2+ signaling in glomus cells, we studied the effects of small changes in extracellular pH (pHo) on the kinetics of Ca2+ oscillations. A decrease in pHo from 7.4 to 7.3 (designated mild) and 7.2 (designated moderate) acidosis produced significant increases in the frequency and amplitude of Ca2+ oscillations. These effects of acidosis on Ca2+ oscillations were not blocked by NS383 and amiloride [acid-sensing ion channel (ASIC) inhibitors]. Mild and moderate levels of acidosis, however, caused a small but significant inhibition of two-pore domain acid-sensing K+ channels (TASK) (TASK-1- and TASK-3-like channels) and depolarized the cell by 6-13 mV. Acidosis-induced increase in Ca2+ oscillations was inhibited by nifedipine (1 µM; L-type Cav inhibitor) and by TTA-P2 (20 µM; T-type Cav inhibitor). Mild inhibition of TASK activity by N-[(2,4-difluorophenyl)methyl]-2'-[[[2-(4methoxyphenyl)acetyl]amino]methyl][1,1'-biphenyl]-2-carboxamide (A1899) (0.3 µM) and 1-[1-[6-[[1,1'-biphenyl]-4-ylcarbonyl)-5,6,7,8-tetrahydropyrido[4,3-d]pyrimidine-4-yl]-4-piperidinyl]-1-butanon (PK-THPP) (0.1 µM) increased Ca2+ oscillation frequency to levels similar to those observed with mild-moderate acidosis. Mild acidosis (pHo 7.3) and mild hypoxia (∼5%O2) produced similar levels of changes in the kinetics of Ca2+ oscillations. Block of tetraethylammonium (TEA)-sensitive Kv channels did not affect acid-induced increase in Ca2+ oscillations. Our study shows that mild and moderate levels of acidosis increase the frequency and amplitude of Ca2+ oscillations primarily by inhibition of TASK without involving ASICs, and suggests a major role of TASK for signal transduction in response to a physiological change in pHo.

On the Sensitivity of a Tool–Workpiece Thermocouple to Chemical Composition and Microstructure

Meeting the increasing demands on part quality and profitability of manufacturing processes despite difficult-to-machine materials is only possible with a deep understanding of the process. Herein, knowledge about the process temperature is of critical importance since it affects the material properties, such as hardness or forming behavior, as well as the chemical and physical interactions between the tool, workpiece, and lubricant. A proven thermoelectric method of temperature measurement in machining, forming, and blanking is a tool–workpiece thermocouple. Herein, instantaneous measurement of the temperature development is allowed in this setup during the manufacturing process in situ at the contact area of the tool and workpiece. The accuracy of this method is dependent on the calibration of the thermocouple, for which the Seebeck coefficients of the tool and workpiece material have to be determined. Usually, material samples from different batches are used for this purpose, although the resulting measurement errors due to slight changes in material properties are hardly known. Herein, the effects of small changes in the chemical composition and the transformation of the crystal lattice due to hardening on the Seebeck coefficient are investigated for the first time to allow precise quantification of the measurement error resulting from the calibration process.

Topological antiferromagnetic semimetal for spintronics: A case study of a layered square-net system EuZnSb2

We use the first-principles and effective Hamiltonian methods to study the electronic structure and magnetic properties of a recently synthesized layered antiferromagnetic square-net topological semimetal ${\mathrm{EuZnSb}}_{2}$ [Phys. Rev. Res. 2, 033462 (2020)]. The main message of the paper is that effects of small changes in the band structure produced by the magnetic ordering and changes in the orientation of the N\'eel vector are amplified in such transport properties as the spin Hall conductivity. We predict that the effects of the broken symmetry introduced by the ordering of the N\'eel vector, being very weak in the bulk, are pronounced in the surface electronic dispersion, suggesting that surface probes may be more suited to measure them. The coexistence of the magnetism with many other competing phases make this material interesting and possibly useful for quantum spintronics applications.

Asymmetric impacts of renewable energy consumption and economic complexity on economic growth in Saudi Arabia: evidence from the NARDL model.

This paper examines the asymmetric impacts of both renewable energy consumption and economic complexity on Saudi Arabia's economic growth in nonlinear autoregressive distributed lag (NARDL) frameworks. We firstly adopt the methodology of both standard NARDL and multiple threshold NARDL (MT-NARDL) models using quarterly data over the period 2000Q1-2015Q4. Then, we test the direction of the causal relationships between the underlying variables using both symmetric and asymmetric Granger causality tests. Our results from the standard NARDL model indicate that the long-term impact of a negative shock in renewable energy consumption on economic growth is significantly negative, while the short-term impact of either positive or negative shocks has a significant positive effect. Moreover, both positive and negative shocks in economic complexity have significant negative effects on economic growth in the long term, while economic growth is only affected by the negative change in economic complexity in the short term. Our estimates based on the best MT-NARDL model indicate that, in the long run, the effect of extremely large changes in renewable energy consumption is significantly different from the effect of small changes in renewable energy consumption on Saudi Arabia's economic growth. However, the effect of extremely large changes in economic complexity does not significantly differ from the effect of small changes in economic complexity on economic growth in the long run. Alternatively, in the short run, the effects of extremely large changes in both renewable energy consumption and economic complexity are not significantly different from the effects of small changes in those variables on economic growth. Finally, the symmetric/asymmetric causality nexus between positive/negative shocks to either renewable energy consumption or economic complexity and positive/negative shocks to economic growth is found to be neutral. The findings of this study provide deeper insights into the relationship between renewable energy consumption, economic complexity, and economic growth in Saudi Arabia and can be used for recommending different policies in the long run and short run.

The effect of changes in saddle height on coordination and its variability during pedalling cycle

ABSTRACT Modifications in saddle height affect the range of movement of the lower limb’s joints during pedalling. Although its effect on movement patterns is poorly understood. The purpose of this study was to analyse the acute effects of small changes in bicycle saddle height on pedalling coordination and its variability. Lower extremity kinematic data were collected in random order for ten well-trained cyclists while pedalling at three different saddle heights: preferred, 2% higher and 2% lower than preferred position. A dynamical systems approach was used to quantify the coordination and its variability for selected joint couplings. Modifications in saddle height produced large changes in the frequency of movement patterns, although they were not enough to alter the coordination classification. Lowering the saddle height increased the frequency of the proximal coordinative hip-ankle pattern (F = 11.77, p < .01) and knee-ankle couplings (F = 14.39, p < .01), while decreasing inphase coordination (F > 11.03, p < .01) during the propulsive phase. Pedalling coordination variability was not affected, being greatest during the movement transitions and when the ankle joint was included in the coupling. This study demonstrated that pedalling pattern coordination and coordination variability were generally stable to acute small changes in saddle height in well-trained cyclists.

Effect of Mild Acidosis on CA2+ Signaling in Rat Carotid Body Chemoreceptor Cells: Role of CAV, ASIC, and Task

Carotid body (CB) glomus cells serve as peripheral chemoreceptors that detect changes in arterial O2 pressure (pO2) and pH, and adjust the level of ventilation to help maintain a normal level of blood pO2 and pH. Severe levels of hypoxia and acidosis are well known to cause sustained rise in cytosolic Ca2+ concentration ([Ca2+]c) in CB glomus cells. We showed recently that isolated gloms cells exhibit spontaneous [Ca2+]c oscillations and that mild levels of hypoxia increase the frequency and amplitude of Ca2+oscillations to augment the secretory response. To understand how mild levels of acidosis regulate Ca2+signaling in glomus cells, we studied the effects of small changes in extracellular pH (pHo) on the kinetics of Ca2+oscillations and the roles of Cav, ASIC and TASK. A decrease in pHo from 7.4 to 7.3 (mild acidosis) and 7.2 (moderate acidosis) produced significant increases in the frequency and amplitude of Ca2+ oscillations without affecting the resting basal [Ca2+]c. These effects on Ca2+ oscillations were not blocked by 0.1 mM amiloride (an ASIC inhibitor) that blocked Na‐H exchange in glomus cells. Mild acidosis was associated with a small but significant inhibition of TASK current and cell depolarization. The increase in Ca2+oscillations produced by mild acidosis was strongly inhibited by nifedipine (1 µM; L‐type Cav inhibitor), as well as by TTA‐P2 (20 µM; T‐type Cav inhibitor). Mild acidosis (0.1 pH unit decrease) and mild hypoxia (~5% O2) produced similar levels of change in the kinetics of Ca2+oscillations and produced an additive effect on Ca2+oscillations. Our study shows that mild to moderate levels of acidosis inhibit TASK to increase Ca2+ influx via both L‐ and T‐type Cav, resulting in increased frequency and amplitude of Ca2+ oscillations. Our study also indicate that ASICs are not involved in the stimulatory effects of mild acidosis on Ca2+oscillations.

The changes to interaural acoustics imparted by placing circumaural headphones over bilateral cochlear-implant sound processors

Interaural level differences (ILDs) are the primary binaural cue used by bilateral cochlear-implant (BiCI) listeners for horizontal-plane sound localization. As such, factors affecting their fidelity are important to understand. One approach for delivering binaural stimuli to BiCI listeners is to present virtually spatialized signals via circumaural headphones placed over the listener’s sound processors. An assumption of this approach is that the binaural cues presented are relatively unaltered by the transmission process and headphone placement; yet there is a lack of evidence supporting this assumption. Therefore, this study measured the effect of small changes to headphone placement on the ILDs received by BiCI sound processors. The intent was to determine both the extent and frequency range in which ILDs are affected using recordings of sine-sweeps received by the device microphones. Results show that slight changes in headphone placement affect coupling to the sound processor microphones and outer ear, primarily influencing ILDs between 1 and 5 kHz as much as 8.6 dB at the midline. They also show that occluding the listener’s ear canals with earplugs or moldable putty significantly reduces ILD variability from inconsistent headphone placement. In summary, these data suggest ways to improve this presentation method for BiCI research studies.

The effect of small changes in rate of force development on muscle fascicle velocity and motor unit discharge behaviour

When rate of force development is increased, neural drive increases. There is presently no accepted explanation for this effect. We propose and experimentally test the theory that a small increase in rate of force development increases medial gastrocnemius fascicle shortening velocity, reducing the muscle’s force-generating capacity, leading to active motor units being recruited at lower forces and with increased discharge frequencies. Participants produced plantar flexion torques at three different rates of force development (slow: 2% MVC/s, medium: 10% MVC/s, fast: 20% MVC/s). Ultrasound imaging showed that increased rate of force development was related to higher fascicle shortening velocity (0.4 ± 0.2 mm/s, 2.0 ± 0.9 mm/s, 4.1 ± 1.9 mm/s in slow, medium, fast, respectively). In separate experiments, medial gastrocnemius motor unit recruitment thresholds and discharge frequencies were measured using fine-wire electromyography (EMG), together with surface EMG. Recruitment thresholds were lower in the fast (12.8 ± 9.2% MVC) and medium (14.5 ± 9.9% MVC) conditions compared to the slow (18.2 ± 8.9% MVC) condition. The initial discharge frequency was lower in the slow (5.8 ± 3.1 Hz) than the fast (6.7 ± 1.4 Hz), but not than the medium (6.4 ± 2.4 Hz) condition. The surface EMG was greater in the fast (mean RMS: 0.029 ± 0.017 mV) compared to the slow condition (0.019 ± 0.013 mV). We propose that the increase in muscle fascicle shortening velocity reduces the force-generating capacity of the muscle, therefore requiring greater neural drive to generate the same forces.

Acute effects of small changes in antero-posterior shoe-cleat position on physiological and biomechanical variables in road cycling

ABSTRACT The aim of this study was to investigate the effect of changes in cycling shoe-cleat position on pedalling biomechanics, physiological variables, and performance in road cycling. Twelve competitive road cyclists performed three pedalling trials with the cleat positioned at the first metatarsal head, 15-mm anterior and 15-mm posterior. Each trial included three sets of 5 min performed at 35%, 50%, and 65% of maximal aerobic power (MAP) followed by a 10-s sprint. Results showed no significant changes in physiological variables, pedalling kinetics, muscular activity of six lower limb muscles, sprint performance and perceived exertion. However, significant differences were found regarding joint kinematics: hip, knee, and ankle angles during both extension and flexion were reduced in the anterior cleat position. Therefore, this study suggests that cleat position does not affect sprint performance, physiological variables, pedalling kinetics, muscle activity, and perceived exertion regardless of the cycling intensity. However, joint kinematics, and particularly knee extension angle which could be related to the risk of overuse injuries, was affected by the shoe-cleat position.