Downhill versus two-state protein folding in a statistical mechanical model

The authors address the problem of downhill protein folding in the framework of a simple statistical mechanical model, which allows an exact solution for the equilibrium and a semianalytical treatment of the kinetics. Focusing on protein 1BBL, a candidate for downhill folding behavior, and comparing it to the WW domain of protein PIN1, a two-state folder of comparable size, the authors show that there are qualitative differences in both the equilibrium and kinetic properties of the two molecules. However, the barrierless scenario which would be expected if 1BBL were a true downhill folder is observed only at low enough temperature.Comment: 20 pages, 13 figure

Rate Determining Factors in Protein Model Structures

Previous research has shown a strong correlation of protein folding rates to the native state geometry, yet a complete explanation for this dependence is still lacking. Here we study the rate-geometry relationship with a simple statistical physics model, and focus on two classes of model geometries, representing ideal parallel and antiparallel structures. We find that the logarithm of the rate shows an almost perfect linear correlation with the "absolute contact order", but the slope depends on the particular class considered. We discuss these findings in the light of experimental results.Comment: 4 pages, 2 figure

Achilles Tendon mechanical behavior and ankle joint function at the walk-to-run transition

Walking at speeds higher than transition speed is associated with a decrease in the plantar-flexor muscle fibres' ability to produce force and, potentially, to an impaired behaviour of the muscle-tendon unit (MTU) elastic components. This study aimed to investigate the ankle joint functional indexes and the Achilles tendon mechanical behaviour (changes in AT force and power) to better elucidate the mechanical determinants of the walk-to-run transition. Kinematics, kinetic and ultrasound data of the gastrocnemius medialis (GM) were investigated during overground walking and running at speeds ranging from 5-9 km·h-1. AT and GM MTU force and power were calculated during the propulsive phase; the ankle joint function indexes (damper, strut, spring and motor) were obtained using a combination of kinetic and kinematic data. AT force was larger in running at speeds > 6.5 km/h. The contribution of AT to the total power provided by the GM MTU was significantly larger in running at speeds > 7.5 km/h. The spring and strut indexes of the ankle were significantly larger in running at speeds > 7.5 km/h. These data suggest that the walk-to-run transition could (at least partially) be explained by the need to preserve AT mechanical behaviour and the ankle spring function

The exploding-reflector concept for ground-penetrating-radar modeling

The simulation of a stacked radargram requires the calculation of a set of common-source experiments and application of the standard processing sequence. To reduce computing time, a zero-offset stacked section can be obtained with a single simulation, by using the exploding-reflector concept and the so-called non-reflecting wave equation. This non-physical modification of the wave equation implies a constant impedance model to avoid multiple reflections, which are, in principle, absent from stacked sections and constitute unwanted artifacts in migration processes. Magnetic permeability is used as a free parameter to obtain a constant impedance model and avoid multiple reflections. The reflection strength is then implicit in the source strength. Moreover, the method generates normal-incidence reflections, i.e. those having identical downgoing and upgoing wave paths.Exploding reflector experiments provide correct travel times of diffraction and reflection events, in contrast to the plane-wave method

Traditional vs non-motorized curve treadmill: differences in energetic requirements

Previous studies suggest that exercise performed on curve surface treadmill (CT) can increase energy expenditure more than exercise performed on a traditional motorized treadmill (MT). However, to date, there are no data about energy cost that confirm this hypothesis. Thus, the purpose of the study is to analyze the physiological requirements of walking and running on a CT as compared to a traditional MT. 26 subjects (11M + 15W) (24.1±3.4yy; 64.7±11.2kg; 171.1±8.6cm) performed preferred walking speed test and running ramp test to exhaustion on both treadmill in two separated sessions. The gross energy cost of walking (Cw) is greater (p<.05) in CT than in MT (3.79±0.35 j/m/kg, 2.43±0.38 j/m/kg, respectively). The gross energy cost of running (Cr) is greater (p<.05) in CT than in MT (5.05±1.67 j/m/kg, 4.09±0.70 j/m/kg, respectively). Moreover, MT allows to reach higher speeds than CT (MT:15.5±1.7 km/h, CT:13.9±1.4 km/h, p<.05) with lower peak blood lactate concentrations (MT: 8.98±2.43 mmol/L, CT: 10.75±2.76 mmol/L, p<.05). Our data confirm that i) the Cw, matched for speed, is greater in CT than MT; ii) the Cr, analyzed during incremental ramp test, is greater in CT than MT; iii) during the ramp test, for the same metabolic load, the mechanical load is lower in the CT compared to MT. The increased physical effort is due to the greater frictional characteristics and force generation requirements inherent with the use of a CT

Benefits of 8 weeks of High Intensity Training in healthy women: the Trion project

Aim High-intensity training (HIT) has recently been shown to be a suitable alternative time-saving strategy to improve athletic performance, cardiovascular fitness and muscle metabolism1. Nevertheless, women have rarely participated in studies investigating the efficacy of HIT2. Therefore, the aim of this study was to evaluate in moderately active women the effectiveness of an HIT intervention performed on a new device called Trion. Methods Before and after 8 weeks of HIT (3 time/week, 7reps x 30sec all-out interspersed with 2 min of active rest), in 35 healthy women volunteers (22.5±3.7 yy; BMI: 21.2±2.6), we measured maximal oxygen uptake (V’O2max), ventilatory threshold (VT), anaerobic performance, muscle structure, body composition, hematochemical (CHOLtot) and blood pressure profile at rest. The HIT workout was performed running on non-motorized curve treadmill and cycling on an competition bike mounted on an electromagnetic roller. Results Absolute and relative V’O2max significantly increased by 10% (p<.05); maximal power and power@VT increased by 7.2% and 6.3 % (p<.05), respectively; peak anaerobic performance significantly increased by 10% (p<.05). Large significant differences (p<.05) were identified for vastus lateralis thickness and pennation angle, +4.9% and +10.1%, respectively. Fat mass and CHOLtot decreased by 3.9% and 5.7% (p<.05), respectively. Conclusions Our results confirm the feasibility and effectiveness of HIT to improve exercise performance and health related parameters: HIT performed on Trion device was absolutely safe and well tolerated by the subjects. As confirmed in previous studies, our findings shows that exercise intensity, rather than duration, is the key factor in determining functional benefits. References 1Weston M, Effects of Low-Volume High-Intensity-Interval-Training (HIT) on Fitness in Adults: A Meta-Analysis of Controlled and Non-Controlled Trials Sports Med. 2014; 44(7): 1005–1017. 2Batacan, RB Jr. Effects of high-intensity-interval-training on cardiometabolic health: a systematic review and meta-analysis of intervention studies. Br J Sports Med. 2017 Mar;51(6):494-503

Measuring movement fluency during the sit-to-walk task

Restoring movement fluency is a key focus for physical rehabilitation; it's measurement, however, lacks objectivity. The purpose of this study was to find whether measurable movement fluency variables differed between groups of adults with different movement abilities whilst performing the sit-to-walk (STW) movement. The movement fluency variables were: (1) hesitation during movement (reduction in forward velocity of the centre of mass; CoM), (2) coordination (percentage of temporal overlap of joint rotations) and (3) smoothness (number of inflections in the CoM jerk signal)

Effects of confinement on thermal stability and folding kinetics in a simple Ising-like model

In cellular environment, confinement and macromulecular crowding play an important role on thermal stability and folding kinetics of a protein. We have resorted to a generalized version of the Wako-Saito-Munoz-Eaton model for protein folding to study the behavior of six different protein structures confined between two walls. Changing the distance 2R between the walls, we found, in accordance with previous studies, two confinement regimes: starting from large R and decreasing R, confinement first enhances the stability of the folded state as long as this is compact and until a given value of R; then a further decrease of R leads to a decrease of folding temperature and folding rate. We found that in the low confinement regime both unfolding temperatures and logarithm of folding rates scale as R-{\gamma} where {\gamma} values lie in between 1.42 and 2.35

Gastrocnemius Medialis and Vastus Lateralis in vivo muscle-tendon behaviour during running at increasing speeds.

This study combines in vivo ultrasound measurements of the Vastus Lateralis (VL) and Gastrocnemius Medialis (GM) muscles with electromyographic, kinematic and kinetic measurements during treadmill running at different speeds (10, 13 and 16 km⋅h-1 ) to better understand the role of muscle and tendon behaviour in two functionally different muscle-tendon units. In addition, the Force-Length and Force-Velocity relationships of VL and GM were experimentally assessed by combining dynamometry and EMG data with ultrasound measurements. With increasing running speed, the operating length of the fascicles in the stance phase shifted towards smaller lengths in the GM (P<0.05; moving down the ascending limb of the F-L relationship) and longer lengths in the VL (P<0.05; moving down the descending limb) at all speeds; however, both muscles contracted close to their optimal length L0 , where isometric force is maximal. Whereas the length of VL SEE did not change as a function of speed, GM SEE lengthened and shortened more at higher speeds. With increasing running speed, the contribution of elastic strain energy to the positive power generated by the MTU increased more for GM (from 0.75 to 1.56 W⋅kg-1 ) than for VL (from 0.62 to 1.02 W⋅kg-1 ). Notwithstanding these differences, these results indicate that, at increasing running speeds, both the VL and GM muscles produce high forces at low contraction velocities, and that the primary function of both muscle-tendon units is to enhance the storage and recovery of elastic strain energy

Anatomically asymmetrical runners move more asymmetrically at the same metabolic cost.

We hypothesized that, as occurring in cars, body structural asymmetries could generate asymmetry in the kinematics/dynamics of locomotion, ending up in a higher metabolic cost of transport, i.e. more 'fuel' needed to travel a given distance. Previous studies found the asymmetries in horses' body negatively correlated with galloping performance. In this investigation, we analyzed anatomical differences between the left and right lower limbs as a whole by performing 3D cross-correlation of Magnetic Resonance Images of 19 male runners, clustered as Untrained Runners, Occasional Runners and Skilled Runners. Running kinematics of their body centre of mass were obtained from the body segments coordinates measured by a 3D motion capture system at incremental running velocities on a treadmill. A recent mathematical procedure quantified the asymmetry of the body centre of mass trajectory between the left and right steps. During the same sessions, runners' metabolic consumption was measured and the cost of transport was calculated. No correlations were found between anatomical/kinematic variables and the metabolic cost of transport, regardless of the training experience. However, anatomical symmetry significant correlated to the kinematic symmetry, and the most trained subjects showed the highest level of kinematic symmetry during running. Results suggest that despite the significant effects of anatomical asymmetry on kinematics, either those changes are too small to affect economy or some plastic compensation in the locomotor system mitigates the hypothesized change in energy expenditure of running