Optimal stride frequencies in running at different speeds

During running at a constant speed, the optimal stride frequency (SF) can be derived from the u-shaped relationship between SF and heart rate (HR). Changing SF towards the optimum of this relationship is beneficial for energy expenditure and may positively change biomechanics of running. In the current study, the effects of speed on the optimal SF and the nature of the u-shaped relation were empirically tested using Generalized Estimating Equations. To this end, HR was recorded from twelve healthy (4 males, 8 females) inexperienced runners, who completed runs at three speeds. The three speeds were 90%, 100% and 110% of self-selected speed. A self-selected SF (SFself) was determined for each of the speeds prior to the speed series. The speed series started with a free-chosen SF condition, followed by five imposed SF conditions (SFself, 70, 80, 90, 100 strides·min-1) assigned in random order. The conditions lasted 3 minutes with 2.5 minutes of walking in between. SFself increased significantly (p<0.05) with speed with averages of 77, 79, 80 strides·min-1 at 2.4, 2.6, 2.9 m·s-1, respectively). As expected, the relation between SF and HR could be described by a parabolic curve for all speeds. Speed did not significantly affect the curvature, nor did it affect optimal SF. We conclude that over the speed range tested, inexperienced runners may not need to adapt their SF to running speed. However, since SFself were lower than the SFopt of 83 strides·min-1, the runners could reduce HR by increasing their SFself

Решение уравнений движения вязкой несжимаемой жидкости для установления характеристик качеия колеса по рельсу при наличии промежуточной среды

Стальные колеса обладают сравнительно стабильными фрикционными свойствами и широко ис-пользуются на рельсовом транспорте и в подъемно-транспортной технике. Кинематические и динамиче-ские свойства фрикционной пары колесо-рельс определяются их геометрическими параметрами, внеш-ними нагрузками и наличием промежуточной среды. Рельсовый путь в шахтах покрыт значительным за-грязняющим мелкодисперсным слоем, представляющим собой смесь породы, частиц износа тормозных колодок и колес в почвенных водах. При торможении локомотива жидкая или многодисперсная среда, находящаяся на рельсах, значительно влияет на коэффициент сцепления колеса с рельсом и силу сопротивления качению

Sub-movement organisation, pen pressure and muscle activity are modulated to precision demands in 2D tracking

The authors investigated how tracking performance, submovement organization, pen pressure and muscle activity in forearm and shoulder muscles were affected by target size in a 2D tracking task performed with a pen on a digitizer tablet. Twenty-six subjects took part in an experiment, in which either a small dot or a large dot was tracked, while it moved quasirandomly across a computer screen at a constant velocity of 2cm/s. The manipulation of precision level was successful, because mean distance to target and the standard deviation of this distance were significantly smaller with the small target than with the large target. With a small target, subjects trailed more behind the center of target and used submovements with larger amplitudes and of shorter duration, resulting in higher tracking accuracy. This change in submovement organization was accompanied by higher pen pressure, while at the same time muscle activity in the forearm extensors and flexors was increased, indicating higher endpoint stability. In conclusion, increased precision demands were accommodated by both a different organization of submovements and higher endpoint stability in a 2D tracking task performed with a pen on a digitizer tablet. © 2012 Copyright Taylor and Francis Group, LLC

Synchronization in OFDM systems sensitivity to the choice of pulse shape

Problème traité : dans cette publication, nous nous intéressons au problème de la synchronisation dans les systèmes à porteuses multiples : estimation du début du symbole et de l'écart de fréquence. Nous utilisons la redondance introduite par le temps de garde ainsi qu'une fonction de mise en forme des symboles. Originalité de la contribution : Les performances d'un système utilisant uniquement la corrélation introduite par le temps de garde ont été évaluées dans un article précédent dans le cas d'un canal gaussien. Dans cette contribution, nous introduisons une fonction de mise en forme sur les symboles OFDM et nous évaluons les performances du système ainsi obtenu. Résultat nouveaux : Nous avons déterminé les performances du système proposé pour différentes fonctions de mise en forme

Analyse des PI3K-Signalwegs bei der Entstehung des duktalen Pankreaskarzinoms

Job rotation is often advocated to reduce workload, but its efficacy has seldom been investigated. The aim of this study is to compare the work demands, workload, and recovery among truck driving, refuse collecting, and rotating between these two jobs, between days and during the day. Three teams of 3 employees each participated in this study. Work demands were assessed by systematic observation of tasks and activities. Workload was quantified by means of heart rate, oxygen uptake, subjective ratings, and urinary excretion rates of catecholamines. Recovery was quantified by excretion rates of catecholamines after work. Job rotation between driving and collecting is an effective measure to reduce physical workload as compared with collecting only and to decrease mental workload as compared with driving only. However, job rotation resulted. in increased physical workload as compared with driving only. Job rotation did not increase mental workload as compared with collecting only. No effects were seen on recovery. No differences were found between rotating between days and during the day. Actual or potential applications of this research include the recommendation that before job rotation is introduced, its efficacy be determined in terms of well-chosen workload measures because a reduction in work demands does not directly imply a reduction in workload. Therefore, job rotation might be less effective than expecte

Cumulative Low Back Load at Work as a Risk Factor of Low Back Pain: A Prospective Cohort Study

Purpose Much research has been performed on physical exposures during work (e.g. lifting, trunk flexion or body vibrations) as risk factors for low back pain (LBP), however results are inconsistent. Information on the effect of doses (e.g. spinal force or low back moments) on LBP may be more reliable but is lacking yet. The aim of the present study was to investigate the prospective relationship of cumulative low back loads (CLBL) with LBP and to compare the association of this mechanical load measure to exposure measures used previously. Methods The current study was part of the Study on Musculoskeletal disorders, Absenteeism and Health (SMASH) study in which 1,745 workers completed questionnaires. Physical load at the workplace was assessed by video-observations and force measurements. These measures were used to calculate CLBL. Furthermore, a 3-year follow-up was conducted to assess the occurrence of LBP. Logistic regressions were performed to assess associations of CLBL and physical risk factors established earlier (i.e. lifting and working in a flexed posture) with LBP. Furthermore, CLBL and the risk factors combined were assessed as predictors in logistic regression analyses to assess the association with LBP. Results Results showed that CLBL is a significant risk factor for LBP (OR: 2.06 (1.32-3.20)). Furthermore, CLBL had a more consistent association with LBP than two of the three risk factors reported earlier. Conclusions From these results it can be concluded that CLBL is a risk factor for the occurrence of LBP, having a more consistent association with LBP compared to most risk factors reported earlier. © 2012 The Author(s)

D6.2 - Prototype description and field trial results

Deliverable D6.2 del projecte FARAMIRPostprint (published version