How a Reduction of Standard Working Hours Affects Employment Dynamics

On December 1, 1996, a new law was implemented in Portugal to gradually reduce the stan- dard working week from 44 to 40 hours. We study how this mandatory reduction affected employment through job creation and job destruction. We find evidence that the working hours reduction had a positive effect on employment through a fall in job destruction.Workweek reduction;policy reform;employment dynamics

How Working Time Reduction Affects Employment and Earnings

December 1, 1996 Portugal introduced a new law on working hours which gradually reduced the standard workweek from 44 hours to 40 hours. We study how this mandatory working hours reduction affected employment and earnings of workers involved. We find for workers who were affected by the new law that working hours decreased, while hourly wages increased, keeping monthly earnings approximately constant. We also find that the working hours reduction did not lead to an increased job loss of workers directly affected. Finally, we find that workers who themselves were not directly affected were influenced by the working hours reduction indirectly. If they worked in a firm with many workers working more than 40 hours before the change in law was introduced.Workweek reduction;policy reform;employment dynamics;earnings

Charge and CP symmetry breaking in two Higgs doublet models

We show that, for the most generic model with two Higgs doublets possessing a minimum that preserves the $U(1)_{em}$ symmetry, charge breaking (CB) cannot occur. If CB does not occur, the potential could have two different minima, and there is in principle no general argument to show which one is the deepest. The depth of the potential at a stationary point that breaks CB or CP, relative to the $U(1)_{em}$ preserving minimum, is proportional to the squared mass of the charged or pseudoscalar Higgs, respectively

EMG AND CINEMATIC PATTERNS ON ELBOW EXTENSION DURING A THROWING TASK PERFORMED AT DIFFERENT SPEEDS

The myoelectric activity of agonist and antagonist muscles in fast human movements is characterized by a phasic pattern, normally composed by three bursts and known as the friphasicpatfern. The most important events of this pattern are the initial agonist activation (AGI) responsible for the initial limb acceleration, and the antagonist activation (AMI), coincident with the electrical silence of the agonist muscle. On last 15 years, a lot of experimental research was done to understand how the Central Nervous System programs ballistic movements performed at different speeds. The most part of these studies were done with single-joint movements, performed an laboratorial environments, which became more attractive as a paradigm for testing hypotheses but didn't allow direct applications to more complex and "natural" movements. Purposes of this study were (1) to characterize the activation pattern of agonist and antagonist muscles of elbow extension on a dart throw to a target, (2) to analyze the effects of movement velocity on EMG and cinematic parameters and (3) to compare the above mentioned variables on trained and untrained subjects. Experiments were performed on four skilled dart throwers and nine untrained subjects. The task was a dart throw to a concentric target at a distance of 3 m and 1,70 m of centre height. Each subject performed 30 trials on each of three different conditions. Subjects were instructed before each condition: (P) "try to reach the target centre", (C) "try to reach the target centre as fast as possible" and (V) '3ust try to be as fast as possible". Two electrogoniometers on shoulder and elbow joints were used to measure position and velocity movement parameters on each joint. Surface EMGs were recorded from triceps (vastus medialis) and biceps brachii with active bipolar electrodes. The EMG signals were filtered, fullwave rectified and smoothed. The angle, velocity and EMG signals were time normalized using the shortest movement time as a reference and averaged in blocks of 20 trials representatives of each condition. Then, the EMG bursts (AGI and ANT) were isolated for parameters determination. A laser system developed on our Faculty allowed the dart speed determination. The elbow extension on initial condition (P) were accomplished by a tri- or biphasic EMG pattern with a clear tendency for a reciprocal activation: the maximum peak of ANT was always coincident with the silent period between the two agonist bursts AG 1 was a short duration burst (90- 135 ms) which began before movement onset and ceased before the moment of elbow peak velocity. The antagonist pattern contained a phasic burst (ANT) which began before the end of AGl and presented its maximum peak near the end of the acceleration phase. This burst was normally preceded by a tonic activation which started near movement imitation. The results show that either the modulation on amplitude and timing of AGI can be seen together or separate when we compare different throwing conditions. The subjects adjusted the time and the size af the burst to the nature of the task with a possible individual predominance of one of these mechanisms. Nevertheless, the increase of the initial EMG slope, measured by the integrated EMG of the first 30 rns of AGI [iEMG30), revealed to be the most related variable with the elbow movement speed. This finding agrees with a "dual-strategy" model (Gottlieb et al., 1989a,b, 1990). The antagonist EMG presented identical timing structure between different throwing conditions, but revealed a general tendency to an increase on its intensity when subjects throw quickly. The similar behaviour of agonist and antagonist activation intensities suggests a common mechanism of magnitude control. The untrained subjects show longer acceleration phases and longer duration of EMG events (duration of AGl, time to agonist and antagonist EMG peak, time of antagonist onset) than the skilled throwers. Those trained subjects presented reduced variability on temporal structure among throwing conditions

DROP JUMP TRAINING STIMULUS INDUCES DIFFERENT QUALITATIVE ADAPTATIONS ON THE ELECTROMYOGRAPHIC (EMG) PATTERN OF THE LEG EXTENSOR MUSCLES

INTRODUCTION Jumping technique can dramatically affect drop jump performance (Warren et al., 1995), which suggests that the quality of the training stimulus may also influence the neuromuscular control of drop jump exercises. The present study was designed to investigate the changes in performance characteristics and in neuronal activation patterns, induced by different drop jump training stimulus. Thirteen healthy males were involved in an 8 weeks training program, followed by a detraining period o 4 weeks and a new training period of 4 additional weeks. The subjects exercised 3 to 4 times per week. They performed reactive.DJ from their best drop height. All the training sessions were supervised. During the sessions of the first 4 weeks the subjects were informed on the flight time of each jump and a reactive jump with maximal effort with a short contact time were continuously demanded by the supervisor. On the training sessions from week 4 to week 8 the supervisor only informed the subjects about the flight time of the jump. Finally, on the last 4 weeks the subjects were informed both on the flight and contact time of each jump. The testing procedures took place before and after each 4 weeks. The subjects performed reactive drop jump (DJ) exercises from the heights of 25, 40, 55 and 70 cm. The vertical ground reaction forces and the surface electromyograms (EMG) of the triceps surae muscles (GAS and SOL) were recorded. The EMGs were full-wave rectified and integrated (iEMG) over different functional phases (Schmidtbleicher et al., 1988): Preactivation phase (PRE) (100ms before ground contact); Reflex Induced Activation phase (i.e. the activation phase from 40 ms to 120 ms after impact); Late EMG Response phase (LER) (activity from 120 ms until the end of contact). RESULTS Table 1 summarises the results observed on the jump heightlcontact time ratio (JHCT) during the training process. Table 1- Mean and standard deviation of the jump height contacV contact time ratio (JHICT), for drop jump exercises from 25 cm (DJ25), 40 cm (DJ40), 55 cm (DJ55) and 70 cm (DJ70), during the training The increase on the jump height/contact time ratio (JHCT) corresponds to the training periods where the subjects were continuously instructed to jump reactively and received feedback information on the jump height and contact time of each individual drop jump. A decrease on the jump height/contact time ratio (JHCT) occurred when the feedback was only the jump height of the drop jumps. The EMG results showed a qualitative shifting in the EMG-patterns toward an accented RIA-phase activation, when the JHCT ratio increased. Additionally the changes in contact time were correlated negatively (r=-0.70 ; -0.85, pc0.001) with the iEMG of the RIA-phase for GAS and SOL muscles. CONCLUSION These results revealed that feedback on the jumping performance, produced clear differences on the biomechanics of the jump. Qualitative adaptations on the EMG pattern induced by a strength training program with drop jump exercises, are only observed if the jumping technique allows for a good jump height/contact time ratio. These parameter should be used to monitor the quality of reactive strength training stimulus

CINEMATIC ANALYSIS OF THE ANKLE AND SUBTALAR JOINTS RELATED TO MYOELECTMC ACTIVATION PATTERNS IN JUMPING EXERCISES UNDER INCREASE STRETCHING LOADS

The study of the Rear foot mobility around the subtalar joint during running and jumping exercises, has been done since 1978. In epidemiological studies the amount of eversion (pronation) is often related to injuries on the mediolateral muscles an also to Tibialis and Achilles tendons injuries. Same experiments have been made to study the rearfoot mobility considering the action of muscles located around the subtalar and ankle joints. Stacoff et al. (1988) used one mechanical model that included mediolateral muscles, the maximal force of each muscles was considered to be function of is cross sectional area. Studies that integrate both, the cinematic analysis of the rearfoot mobility around the subtalar joint and the determination of EMG activation patterns of the muscles acting on the subtalar joints are uncommon. The purpose of this work is to study the EMG patterns of same of the leg muscles involved in ankle and subtalar movements, during action against the ground, in jumping exercises under increase stretching load, looking for possible relations with the cinematic analysis of subtalar movement during ground contact phase. Five adult elite sprinters performed drop jumps under three load conditions 40cm, 50cm and 70cm. On condition five trials were recorded allowing the use of average techniques. The signals from Force Plate, Knee and Ankle electrogoniometers, and surface EMG, were A/D converted at IOOOHz (Biopac-MP100). The EMGs of Gastrocnemius (GN), Soleus (SOL), Tibialis A. (TA) and Peronis L. (PL) were filtered, fullwave rectified and smoothed. The subjects foot and leg were filmed from behind at 50 framesls. The EMG patterns of extensor muscles under SSC conditions have three functional phases, Preactivation (before touchdown (TD), Reflexive Potenciation 30-100 ms after TD and Voluntary Activation, iEMGs of this phases were calculated. PL SOL and GN act almost simultaneously during ground contact, the a higher preactivation on the GN, could be explained by the higher rate of FastT. fibbers, greater crossectional area and is superficial position. The high level of preactivation on TA appears to be related with anticipation of the forced eversion occurring after touchdown, notice that TA works as extension antagonist. This amount of activation of TA on Touchdown could explain same of the stress related TA tendon injuries

Consumer Social Media Engagement with Video Ad in the Context of the COVID-19 Pandemic

The main objective of this article is to analyze the narrative of an advertising video in the context of the COVID-19 pandemic through a utilitarian (informativeness) and hedonic (playfulness) perspective and evaluate its consequences on brand engagement. In this article, we propose a quantitative approach based on structural equation models. The questionnaire was disseminated in April 2020, and 235 valid responses were obtained and analyzed using the software AMOS v26. The results confirmed the adjustment of the data to the conceptual model established and that empathy with the content in advertising videos has a mediating effect on playfulness and informativeness effects in brand engagement in social networks during COVID-19 pandemic. Our study analyses the narrative of an advertising video in the context of the COVID-19 pandemic through a utilitarian (informativeness) and hedonic (playfulness) perspective and evaluates its consequences on brand engagement. Despite the existence of several studies on advertising, its relationship with brand engagement is still poorly studied in the literature, especially in the pandemic period. This work demonstrates the importance of empathy with video as important factor in digital brand engagement, even in times of crisis.info:eu-repo/semantics/publishedVersio