scholarly journals Effect of Descent Velocity upon Muscle Activation and Performance in Two-Legged Free Weight Back Squats

Sports ◽  
2019 ◽  
Vol 7 (1) ◽  
pp. 15 ◽  
Author(s):  
Roland Van den Tillaar
Keyword(s):  
Muscle Activation ◽  
Peak Velocity ◽  
Maximal Velocity ◽  
Negative Effect ◽  
Slow Condition ◽  
Minimal Velocity ◽  
And Performance ◽  
Stored Elastic Energy ◽  
Ascent Phase ◽  
Second Peak

Background: The aim of this study was to investigate the effect of descent velocity during two-legged full back squats upon muscle activation and squat ascent performance. Methods: Eleven healthy resistance-training males (age: 24 ± 6 years, body mass: 89.5 ± 21.5 kg, height: 1.84 ± 0.10 m) performed 4-repetition maximum (4-RM) two-legged full squats with slow, normal, and fast descent phases. Kinematics and muscle activity of ten muscles divided into five regions were measured. Results: The main findings were that maximal and minimal velocity were lower and maximal velocity occurred later in the slow condition, while there was no difference in second peak velocity or ascent displacement when compared with the normal and fast conditions. Furthermore, no differences in muscle activation were found as an effect of the descent velocity. Conclusion: It was concluded that the slow descent velocity had a negative effect upon the ascent phase, because of the lower peak velocity and peak force increasing the chance of failure. The lower velocities were not caused by lower pre-activation of the muscles but were probably a result of potentiation and/or utilization of stored elastic energy and/or the stretch reflex.

scholarly journals The acute and post-activation potentiation effects of the SPEEDMAKER™ on step-by step kinematics, muscle activation and performance in 30-m sprints

2019 ◽  
Vol 24 ◽  
pp. 74-88
Author(s):  
Hågen Fjørkenstad Dybdal ◽  
Roland Van Den Tillaar
Keyword(s):  
Muscle Activity ◽  
Muscle Activation ◽  
Soccer Player ◽  
Gluteus Maximus ◽  
Soccer Players ◽  
Repeated Measure ◽  
Maximal Velocity ◽  
Postactivation Potentiation ◽  
Acute Effects ◽  
And Performance

The purpose of this study was to examine the acute effects of using the SpeedMaker™ on step-by-step kinematics and muscle activity in 30-m sprints and if it is possible to elicit a post-activation potentiation stimulus with the SpeedMaker™ upon subsequent 30-m sprint performance. Thirteen male soccer players (age: 22.8±1.8 yr, body mass: 75.1±11.9 kg, height: 1.80±0.08 m) participated in a repeated measure and cross-over design consisting of two conditions: three normal 30-m sprints (control) and two normal 30-m sprints divided by one 30-m sprint with the SpeedMaker™ (intervention). Kinematics were measured for each step together with the peak muscle activity of the hamstrings, quadriceps and gluteus during each stride of each 30-m sprint. The main findings were that sprinting with the SpeedMaker™ increased sprint times by 1.7% compared to normal 30-m sprints. However, no occurrence of a postactivation potentiation (PAP) response was found when performing a 30-m sprint with the SpeedMaker™ prior to a normal 30-m sprint in male soccer players. Furthermore, no detectable differences in step-by-step analysis on kinematics and muscle activity were found between the sprints with and without the SpeedMaker™. Only hamstrings and gluteus activity increased per stride over 30-m. It was concluded that the SpeedMaker™ did influence sprint times, but only in a small way that kinematics and muscle activity did not change detectable. Furthermore, that the SpeedMaker™ did not elicit a PAP effect. In addition, increased hamstring and gluteus maximus activation during the 30-m sprints suggests that these muscles are very important for acceleration, and that it is likely that acute hamstring strains occur when a soccer player is close to maximal velocity, as hamstring activation is maximal at that point.

scholarly journals Relationship of Limb Lengths and Body Composition to Lifting in Weightlifting

2021 ◽  
Vol 18 (2) ◽  
pp. 756
Author(s):  
Dafnis Vidal Pérez ◽  
José Miguel Martínez-Sanz ◽  
Alberto Ferriz-Valero ◽  
Violeta Gómez-Vicente ◽  
Eva Ausó
Keyword(s):  
Body Composition ◽  
Skill Acquisition ◽  
Performance Indicator ◽  
Relative Length ◽  
Maximal Velocity ◽  
Anthropometric Measures ◽  
Positive Correlation ◽  
Level I ◽  
And Performance ◽  
Relationship Of

Weightlifting is a discipline where technique and anthropometric characteristics are essential to achieve the best results in competitions. This study aims to analyse the relationships between body composition, limb length and barbell kinematics in the performance of weightlifters. It consists of an observational and descriptive study of 19 athletes (12 men [28.50 ± 6.37 years old; 84.58 ± 14.11 kg; 176.18 ± 6.85 cm] and 7 women [27.71 ± 6.34 years old; 64.41 ± 7.63 kg; 166.94 ± 4.11 cm]) who met the inclusion criteria. A level I anthropometrist took anthropometric measures according to the methodology of the International Society for the Advancement of Kinanthropometry (ISAK), and the measurement of the barbell velocity was made with the software Kinovea. In terms of body composition, both genders are within the percentage range of fat mass recommended for this sport. In female weightlifters, there is a positive correlation between foot length, maximal velocity in the Snatch (ρ = 0.775, p = 0.041), and performance indicator in the Snatch and the Clean & Jerk (ρ = 0.964, p < 0.001; ρ = 0.883, p = 0.008, respectively). In male weightlifters, a positive correlation between tibial length and average velocity of the barbell in the Snatch is observed (ρ = 0.848, p < 0.001). Muscle mass percentage correlates positively with performance indicator in both techniques (ρ = 0.634, p = 0.027; ρ = 0.720, p = 0.008). Also, the relative length of the upper limb is negatively correlated with the performance indicator (ρ = −0.602, p = 0.038). Anthropometry and body composition may facilitate skill acquisition among this sport population, contributing to increase the limited body of scientific knowledge related to weightlifting.

scholarly journals Visual search behavior and performance in luggage screening: effects of time pressure, automation aid, and target expectancy

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Tobias Rieger ◽  
Lydia Heilmann ◽  
Dietrich Manzey
Keyword(s):  
Visual Search ◽  
Target Location ◽  
Time Pressure ◽  
Response Times ◽  
Search Behavior ◽  
High Time ◽  
Luggage Screening ◽  
Negative Effect ◽  
And Performance ◽  
Automated Support

AbstractVisual inspection of luggage using X-ray technology at airports is a time-sensitive task that is often supported by automated systems to increase performance and reduce workload. The present study evaluated how time pressure and automation support influence visual search behavior and performance in a simulated luggage screening task. Moreover, we also investigated how target expectancy (i.e., targets appearing in a target-often location or not) influenced performance and visual search behavior. We used a paradigm where participants used the mouse to uncover a portion of the screen which allowed us to track how much of the stimulus participants uncovered prior to their decision. Participants were randomly assigned to either a high (5-s time per trial) or a low (10-s time per trial) time-pressure condition. In half of the trials, participants were supported by an automated diagnostic aid (85% reliability) in deciding whether a threat item was present. Moreover, within each half, in target-present trials, targets appeared in a predictable location (i.e., 70% of targets appeared in the same quadrant of the image) to investigate effects of target expectancy. The results revealed better detection performance with low time pressure and faster response times with high time pressure. There was an overall negative effect of automation support because the automation was only moderately reliable. Participants also uncovered a smaller amount of the stimulus under high time pressure in target-absent trials. Target expectancy of target location improved accuracy, speed, and the amount of uncovered space needed for the search.Significance Statement Luggage screening is a safety–critical real-world visual search task which often has to be done under time pressure. The present research found that time pressure compromises performance and increases the risk to miss critical items even with automation support. Moreover, even highly reliable automated support may not improve performance if it does not exceed the manual capabilities of the human screener. Lastly, the present research also showed that heuristic search strategies (e.g., areas where targets appear more often) seem to guide attention also in luggage screening.

scholarly journals Impact of Electronic Monitoring on Employees: A Meta-Analysis

2021 ◽  
Author(s):  
Rudolf Siegel ◽  
Cornelius J. König ◽  
Veronika Lazar
Keyword(s):  
Job Satisfaction ◽  
Electronic Monitoring ◽  
Negative Impact ◽  
Meta Analysis ◽  
Well Being ◽  
Negative Effect ◽  
And Performance ◽  
Relationship Of ◽  
Positive Effect ◽  
Small Positive Effect

Electronic monitoring is more and more widespread and affects many employees around the globe. The current meta analysis collected data of 59 independent samples (with 223 effect sizes) to estimate the effect of electronic monitoring on job satisfaction, stress, and performance. A random-effects model indicated a small negative effect of monitoring on job satisfaction, r=-.09, and a small positive effect on stress, r=.12. There was no relationship with performance, r=-.01. Even if the effects of monitoring on job satisfaction and stress are small, taking the large number of employees who are monitored for several hours a day into account, these effects may have a severe and negative impact on employees’ well-being. Performance maintenance is the main justification for the use of electronic monitoring, but the non-existing relationship of monitoring with performance questions the validity of this justification.

scholarly journals The Impact of Covid-19 on Physical Education: Mobility-Restrictive Measures on the Remote Learning Setup

2021 ◽  
Vol 11 (10) ◽  
pp. 474-489
Author(s):  
Rowena Nery Monte ◽  
Aivi Reyes Buan
Keyword(s):  
Physical Education ◽  
The Philippines ◽  
New Normal ◽  
First Semester ◽  
Negative Effect ◽  
And Performance ◽  
Restrictive Measures ◽  
The University ◽  
The Impact ◽  
Remote Learning

The remote learning setup engendered numerous disadvantages to both learner and educator. Mental health, accessibility affected by one’s socioeconomic classification, availability of technological apparatuses, and lack of social integration are some of the reported disadvantages caused by remote learning. The effects are far more notable in subjects that demand physical activities given that several prerequisites must be accessible to the learner for him/her to successfully participate. To specifically assess the impact of this new normal in physical education, a specific course offering in University of the Philippines Los Baños (UPLB), Human Kinetics 12: Walking for Fitness, is examined through a quantitative study involving students who were enrolled. Surveys and other statistical tools are utilized to yield accurate data about the impact of mobility-restrictive measures to the perception and performance of the students. The findings of this study revealed what they feel about the quarantines and lockdowns have a negative effect to their perception and performance in HK12: Walking for Fitness. Besides the fact that the policies are meant to restrict mobility and that HK12: Walking for Fitness requires mobility, it must also be considered that the First Semester, A.Y. 2020-2021 is the first semester of the university to observe remote learning. Even though the study did not capture such behavior, it must be noted that the drastic shift to online classes made it difficult to students to cope with the new normal in education.

Pectoral fin locomotion in the striped surfperch. II. Scaling swimming kinematics and performance at a gait transition

1996 ◽  
Vol 199 (10) ◽  
pp. 2243-2252 ◽  
Author(s):  
E Drucker ◽  
J Jensen
Keyword(s):  
Body Size ◽  
Swimming Speed ◽  
Beat Frequency ◽  
Small Fish ◽  
Maximal Velocity ◽  
Pectoral Fin ◽  
Gait Transition ◽  
Transition Speed ◽  
Aspect Ratios ◽  
And Performance

In this study, we report the first allometric equations relating gait parameters and swimming speed to body size for fish employing pectoral fin locomotion. Comparisons of locomotor kinematics and performance among striped surfperch (Teleostei: Embiotocidae) are made at the pectoral&shy;caudal gait transition speed (Up-c). Up-c is considered to elicit physiologically equivalent levels of exercise in animals varying over 100-fold in body mass (Mb) by virtue of dynamically similar pectoral fin movements (constant duty factor, length-specific stride length and fin-beat amplitude) and size-independent propulsive efficiency. At Up-c, pectoral fin-beat frequency scales in proportion to Mb-0.12&plusmn;0.03, a size-dependence consistent with that observed for stride frequency in fishes swimming by axial undulatory propulsion and in many running tetrapods. It is proposed that the similarity in the scaling of frequency in these vertebrate groups reflects an underlying similarity in the allometry of the maximal velocity of muscle shortening. Absolute Up-c (m s-1) generally increases with body size, but the fastest speeds are not exhibited by the largest animals. A pattern of declining performance in fish 23 cm in standard length and longer may be related to their disproportionately small fin areas and aspect ratios. The pronounced negative allometry of Up-c expressed as standard body lengths per second indicates that a given length-specific speed does not induce comparable levels of activity in large and small fish. Thus, normalization of swimming speed to body length may not be a sufficient correction for kinematic comparisons across size.

The Effects of Taping on Muscle Activity and Throwing Velocity in Fatigued Baseball Players

2021 ◽  
Vol 3 (1) ◽  
pp. 18-29
Author(s):  
Kara-Lyn R. Harrison ◽  
Paolo Sanzo ◽  
Carlos Zerpa ◽  
Taryn Klarner
Keyword(s):  
Pilot Study ◽  
Muscle Activity ◽  
Muscle Activation ◽  
Performance Enhancement ◽  
Maximum Velocity ◽  
Baseball Players ◽  
Kinesio Tape ◽  
Significant Difference ◽  
Post Test ◽  
And Performance

Due to the repetitive high forces and torques placed on an individual during a baseball pitch, shoulder pain is present in 46-57% of pitchers. Therapeutic taping has been proposed to have beneficial qualities in injury prevention, rehabilitation, and performance enhancement via muscular facilitation. Therefore, the purpose of this pilot study was to investigate the effect of taping on the velocity of an overhead baseball throw and muscle activation patterning of the supraspinatus, infraspinatus, and pectoralis major muscles in baseball players after muscle fatigue was induced. Participants were asked to complete three pre-test maximum velocity overhead throws, a fatiguing protocol, followed by three post-test maximum velocity pitches. There was no statistically significant difference in throwing velocity or muscle activity with the application of the different taping conditions in the three phases of an overhead baseball throw. These finding suggest Kinesio Tape® does not change muscle activation or velocity of overhead baseball throws when compared to a no tape condition.

Abstract 14534: In vitro Assessment of Transvalvular Peak Velocity Measurement for Various Orifice Shapes: Comparison Between 4D Flow MRI vs. Doppler Echocardiography

Circulation ◽  
2020 ◽  
Vol 142 (Suppl_3) ◽  
Author(s):  
Jeesoo Lee ◽  
Nadia El hangouche ◽  
Liliana Ma ◽  
Michael Scott ◽  
Michael Markl ◽  
...  
Keyword(s):  
Temporal Resolution ◽  
Continuous Wave ◽  
Peak Velocity ◽  
Left Ventricular ◽  
Patient Specific ◽  
Maximal Velocity ◽  
4D Flow Mri ◽  
4D Flow ◽  
Flow Phantom ◽  
Flow Mri

Introduction: 4D flow MRI can assess transvalvular velocity, but validation against continuous wave (CW) Doppler echo is limited in high-velocity regurgitation and stenosis situations. We sought to compare 4D flow MRI and echo peak velocity using a pulsatile echo-MRI flow phantom. Materials and Methods: An MRI-compatible flow phantom with restrictive orifice situated was driven by a left ventricular assist device at 50 bpm (figure 1A). Three orifice shapes were tested: circular, elliptical and 3D-printed patient-specific mitral regurgitant orifice model of prolapse with areas of 0.5, 0.41 and 0.35 cm 2 , respectively. CW Doppler was acquired with peak velocity extracted from the profile. Retrospectively-gated 4D flow MRI was performed (spatial resolution = 2 mm isotropic, temporal resolution = 36 ms, encoding velocity = 400 cm/s). Maximal velocity magnitude was extracted volumetrically (figure 1B). An echo-mimicking profile was also obtained with a “virtual” ultrasound beam in the 4D flow data to simulate CW Doppler (figure 1C). Bland-Altman analysis was used to assess the agreement of temporal peak velocities. Results: 4D flow MRI demonstrated a centrally directed jet for the circular and elliptical orifices and an oblique jet for the prolapse orifice (figure 1B). Peak velocities were in excellent agreement between 4D flow MRI vs. echo for the circular (peak: 5.13 vs. 5.08 m/s, bias = 0.06 ± 0.66 m/s, figure 1D) and the elliptical orifice (peak: 4.95 vs. 4.79 m/s, bias = 0.07 ± 0.87 m/s, figure 1E). The prolapse orifice velocity was underestimated somewhat by MRI by ~10% (peak: 4.41 vs. 4.90 m/s, bias=0.26±1.18, figure 1F). Conclusion: 4D flow MRI can quantify high velocities like echo for simple geometries while underestimating for more complex geometry, likely due to partial volume effects. Further investigation is warranted to systematically investigate the effects of 4D flow MRI spatial and temporal resolution as well as the jet angle on velocity quantification accuracy.

scholarly journals Business Strategy, Accounting Conservatism and Performance

2020 ◽  
Vol 9 (2) ◽  
pp. 23
Author(s):  
Han Li
Keyword(s):  
Corporate Governance ◽  
Financial Performance ◽  
Internal Control ◽  
Business Strategy ◽  
Joint Effect ◽  
Accounting Conservatism ◽  
Governance Mechanism ◽  
Negative Effect ◽  
Corporate Governance Mechanism ◽  
And Performance

This research consists with prior business strategy typology and accounting conservatism theories. It investigates the joint effect of business strategy and accounting conservatism on the firm’s financial performance. The paper finds that accounting conservatism as a prudent accounting reporting principle plays an important corporate governance mechanism. The conservatism can mitigate the negative effect of the aggressive business strategy. The joint effect between business strategy and accounting conservatism is positively related with financial performance. The result is robustness when the different measurements of the strategy and the conservatism are applied. When the firm has weak internal control quality, the joint effect on financial performance also exists significantly.

Insurance regulations, risk and performance in Ghana

2019 ◽  
Vol 28 (1) ◽  
pp. 74-96
Author(s):  
Baah Aye Kusi ◽  
Abdul Latif Alhassan ◽  
Daniel Ofori-Sasu ◽  
Rockson Sai
Keyword(s):  
Random Effect ◽  
Least Square ◽  
Insurance Market ◽  
Content Type ◽  
Ordinary Least Square ◽  
Negative Effect ◽  
And Performance ◽  
First Time

Purpose This study aims to examine the hypothesis that the effect of insurer risks on profitability is conditional on regulation, using two main regulatory directives in the Ghanaian insurance market as a case study. Design/methodology/approach This study used the robust ordinary least square and random effect techniques in a panel data of 30 insurers from 2009 to 2015 to test the research hypothesis. Findings The results suggest that regulations on no credit premium and required capital have insignificant effects on profitability of insurers. On the contrary, this study documents evidence that both policies mitigate the effect of underwriting risk on profitability and suggests that regulations significantly mitigate the negative effect of underwriting risk to improve profitability. Practical implications The finding suggests that policymakers and regulators must continue to initiate, design and model regulations such that they help tame risk to improve the performance of insurers in Ghana. Originality/value This study provides first-time evidence on the role of regulations in controlling risks in a developing insurance market.

Sign in / Sign up

Export Citation Format

Share Document