Sub-MHz bursts of nanosecond pulses excite neurons at paradoxically low electric field thresholds without membrane damage

Neuromodulation applications of nanosecond electric pulses (nsEP) are hindered by their low potency to elicit action potentials in neurons. Excitation by a single nsEP requires a strong electric field which injures neurons by electroporation. We bypassed the high electric field requirement by replacing single nsEP stimuli with high-frequency brief nsEP bursts. In hippocampal neurons, excitation thresholds progressively decreased at nsEP frequencies above 20–200 kHz, with up to 20–30-fold reduction at sub-MHz and MHz rates. For a fixed burst duration, thresholds were determined by the duty cycle, irrespective of the specific nsEP duration, rate, or number of pulses per burst. For 100-μs bursts of 100-, 400-, or 800-ns pulses, the threshold decreased as a power function when the duty cycle exceeded 3–5 %. nsEP bursts were compared with single “long” pulses whose duration and amplitude matched the duration and the time-average amplitude of the burst. Such pulses deliver the same electric charge as bursts, within the same time interval. High-frequency nsEP bursts excited neurons at the time-average electric field 2–3 times below the threshold for a single long pulse. For example, the excitation threshold of 139 ± 14 V/cm for a single 100-μs pulse decreased to 57 ± 8 V/cm for a 100-μs burst of 100-ns, 0.25-MHz pulses (p < 0.001). Applying nsEP in bursts reduced or prevented the loss of excitability in multiple stimulation attempts. Stimulation by high-frequency nsEP bursts is a powerful novel approach to excite neurons at paradoxically low electric charge while also avoiding the electroporative membrane damage.     

Exercise with TENS does not augment gains in balance and strength for dancers

Electrical stimulation modulates sensory feedback and improves motor performance, at least for individuals with compromised sensorimotor function. The purpose of this study was to determine the effectiveness of a 4-wk intervention with transcutaneous electrical nerve stimulation (TENS) at improving strength and balance in dancers. Nineteen dancers completed a timed, single-leg balance test, the Y-balance test, and contractions with the hip flexor and knee extensor muscles to assess maximal strength and force steadiness. They completed 4-wks of moderate-intensity bodyweight exercises (3x/wk) and were pseudo-randomized to either a Treatment or Sham group in a single-blind design. The Treatment group received constant TENS over the hamstring muscles during the exercises, whereas the Sham group was exposed to a brief TENS current. The data were pooled due to few significant between-group differences from before to after the intervention. Most outcome measures significantly improved: hip extensor muscles were stronger (P ≤ 0.01), time stood on a single-leg with eyes closed increased (P = 0.02), and the distance reached during the Y-balance test increased (P ≤ 0.001). The improvement in scores on the Y-balance test exceeded the minimal clinically significant change. Twelve sessions of moderate-intensity bodyweight exercises improved muscle strength and balance in experienced dancers. The addition of TENS, however, did not augment the gains in function.     

Achilles tendon loading during walking: application of a novel optic fiber technique

An optic fiber (? 0.5 mm) was utilized for the study of Achilles tendon forces (ATF) in eight volunteers who walked over a 10 m force platform at three speeds (1.1 ± 0.1 m × s⁻¹, 1.5 ± 0.1 m × s⁻¹ and 1.8 ± 0.2 m × s⁻¹). The presented ATF-time curves showed great intersubject variation in magnitudes of the sudden release of force after initial contact and in the peak ATF's (1430 ± 500 N). This intersubject variation in the peak force decreased only by 4% when cross-sectional area of the tendon was considered. Measured ground reaction forces and plantar pressures confirmed that the subjects walked quite normally during recordings. The peak ATF was found to be rather insensitive to speed in contrast to the rate of ATF development which increased 32% ( p < 0.5) from slow to fast walking speed. It is concluded that the optic fiber technique can be applied to study loading of the musculo-tendinous complex during normal locomotion such as walking. Accepted: 13 October 1997     

3D gait assessment in young and elderly subjects using foot-worn inertial sensors

This study describes the validation of a new wearable system for assessment of 3D spatial parameters of gait. The new method is based on the detection of temporal parameters, coupled to optimized fusion and de-drifted integration of inertial signals. Composed of two wirelesses inertial modules attached on feet, the system provides stride length, stride velocity, foot clearance, and turning angle parameters at each gait cycle, based on the computation of 3D foot kinematics. Accuracy and precision of the proposed system were compared to an optical motion capture system as reference. Its repeatability across measurements (test-retest reliability) was also evaluated. Measurements were performed in 10 young (mean age 26.1±2.8 years) and 10 elderly volunteers (mean age 71.6±4.6 years) who were asked to perform U-shaped and 8-shaped walking trials, and then a 6-min walking test (6 MWT). A total of 974 gait cycles were used to compare gait parameters with the reference system. Mean accuracy±precision was 1.5±6.8 cm for stride length, 1.4±5.6 cm/s for stride velocity, 1.9±2.0 cm for foot clearance, and 1.6±6.1° for turning angle. Difference in gait performance was observed between young and elderly volunteers during the 6 MWT particularly in foot clearance. The proposed method allows to analyze various aspects of gait, including turns, gait initiation and termination, or inter-cycle variability. The system is lightweight, easy to wear and use, and suitable for clinical application requiring objective evaluation of gait outside of the lab environment.     

Effect of stride frequency on thermoregulatory responses during endurance running in distance runners

Changing stride frequency may influence oxygen uptake and heart rate during running as a function of running economy and central command. This study investigated the influence of stride frequency manipulation on thermoregulatory responses during endurance running. Seven healthy endurance runners ran on a treadmill at a velocity of 15 km/h for 60 min in a controlled environmental chamber (ambient temperature 27 °C and relative humidity 50%), and stride frequency was manipulated. Stride frequency was intermittently manipulated by increasing and decreasing frequency by 10% from the pre-determined preferred frequency. These periods of increase or decrease were separated by free frequency running in the order of free stride frequency, stride frequency manipulation (increase or decrease), free stride frequency, and stride frequency manipulation (increase or decrease) for 15 min each. The increased and decreased stride frequencies were 110% and 91% of the free running frequency, respectively (196±6, 162±5, and 178±5 steps/min, respectively, P<0.01). Compared to the control, stride frequency manipulation did not affect rectal temperature, heart rate, or the rate of perceived exhaustion during running. Whole-body sweat loss increased significantly when stride frequency was manipulated (1.48±0.11 and 1.57±0.11 kg for control and manipulated stride frequencies, respectively, P<0.05), but stride frequency had a small effect on sweat loss overall (Cohen's d=0.31). A higher mean skin temperature was also observed under mixed frequency conditions compared to that in the control (P<0.05). While the precise mechanisms underlying these changes remain unknown (e.g. running economy or central command), our results suggest that manipulation of stride frequency does not have a large effect on sweat loss or other physiological variables, but does increase mean skin temperature during endurance running.     

Three-dimensional data-tracking dynamic optimization simulations of human locomotion generated by direct collocation

The aim of this study was to perform full-body three-dimensional (3D) dynamic optimization simulations of human locomotion by driving a neuromusculoskeletal model toward in vivo measurements of body-segmental kinematics and ground reaction forces. Gait data were recorded from 5 healthy participants who walked at their preferred speeds and ran at 2 m/s. Participant-specific data-tracking dynamic optimization solutions were generated for one stride cycle using direct collocation in tandem with an OpenSim-MATLAB interface. The body was represented as a 12-segment, 21-degree-of-freedom skeleton actuated by 66 muscle-tendon units. Foot-ground interaction was simulated using six contact spheres under each foot. The dynamic optimization problem was to find the set of muscle excitations needed to reproduce 3D measurements of body-segmental motions and ground reaction forces while minimizing the time integral of muscle activations squared. Direct collocation took on average 2.7 ± 1.0 h and 2.2 ± 1.6 h of CPU time, respectively, to solve the optimization problems for walking and running. Model-computed kinematics and foot-ground forces were in good agreement with corresponding experimental data while the calculated muscle excitation patterns were consistent with measured EMG activity. The results demonstrate the feasibility of implementing direct collocation on a detailed neuromusculoskeletal model with foot-ground contact to accurately and efficiently generate 3D data-tracking dynamic optimization simulations of human locomotion. The proposed method offers a viable tool for creating feasible initial guesses needed to perform predictive simulations of movement using dynamic optimization theory. The source code for implementing the model and computational algorithm may be downloaded at http://simtk.org/home/datatracking.     

Diurnal variation in gait characteristics and transition speed

The aim of this study was to investigate the effect of time-of-day on Preferred Transition Speed (PTS) and spatiotemporal organization of walking and running movements. Twelve active male subjects participated in the study (age: 27.2?±?4.9 years; height: 177.9?±?5.4?cm; body mass: 75.9?±?5.86?kg). First, PTS was determined at 08:00?h and 18:00?h. The mean of the two PTS recorded at the two times-of-day tested was used as a reference (PTS_m). Then, subjects were asked to walk and run on a treadmill at three imposed speeds (PTS_m, PTS_m?+?0.3?m.s^?1, and PTS_m???0.3?m.s^?1) at 08:00?h and 18:00?h. Mean stride length, temporal stride, spatial stride variability, and temporal stride variability were used for gait analysis. The PTS observed at 08:00?h (2.10?±?0.17?m.s^?1) tends to be lower (p?=?0.077) than that recorded at 18:00?h (2.14?±?0.19?m.s^?1). Stride lengths recorded while walking (p?=?0.038) and running (p?=?0.041) were shorter at 08:00?h than 18:00?h. No time-of-day effect was observed for stride frequency during walking and running trials. When walking, spatial stride variability (p?=?0.020) and temporal stride variability (p?=?0.028) were lower at 08:00?h than at 18:00?h. When running, no diurnal variation of spatial stride variability or temporal stride variability was detected.     

Effects of Aging on Arm Swing during Gait: The Role of Gait Speed and Dual Tasking

Healthy walking is characterized by pronounced arm swing and axial rotation. Aging effects on gait speed, stride length and stride time variability have been previously reported, however, less is known about aging effects on arm swing and axial rotation and their relationship to age-associated gait changes during usual walking and during more challenging conditions like dual tasking. Sixty healthy adults between the ages of 30–77 were included in this study designed to address this gap. Lightweight body fixed sensors were placed on each wrist and lower back. Participants walked under 3 walking conditions each of 1 minute: 1) comfortable speed, 2) walking while serially subtracting 3’s (Dual Task), 3) walking at fast speed. Aging effects on arm swing amplitude, range, symmetry, jerk and axial rotation amplitude and jerk were compared between decades of age (30–40; 41–50; 51–60; 61–77 years). As expected, older adults walked slower (p = 0.03) and with increased stride variability (p = 0.02). Arm swing amplitude decreased with age under all conditions (p = 0.04). In the oldest group, arm swing decreased during dual task and increased during the fast walking condition (p<0.0001). Similarly, arm swing asymmetry increased during the dual task in the older groups (p<0.004), but not in the younger groups (p = 0.67). Significant differences between groups and within conditions were observed in arm swing jerk (p<0.02), axial rotation amplitude (p<0.02) and axial jerk (p<0.001). Gait speed, arm swing amplitude of the dominant arm, arm swing asymmetry and axial rotation jerk were all independent predictors of age in a multivariate model. These findings suggest that the effects of gait speed and dual tasking on arm swing and axial rotation during walking are altered among healthy older adults. Follow-up work is needed to examine if these effects contribute to reduced stability in aging.     

Walking kinematics and kinetics following eccentric exercise-induced muscle damage

The goal of this investigation was to investigate how walking patterns are affected following muscle-damaging exercise by quantifying both lower limb kinematics and kinetics. Fifteen young women conducted a maximal isokinetic eccentric exercise (EE) muscle damage protocol (5 × 15) of the knee extensors and flexors of both legs at 60°/s. Three-dimensional motion data and ground reaction forces (GRFs) were collected 24 h pre-EE while the participants walked at their preferred self-selected walking speed (SWS). Participants were asked to perform two gait conditions 48 h post-EE. The first condition (COND1) was to walk at their own speed and the second condition (COND2) to maintain the SWS (±5%) they had 24 h pre-EE. Walking speed during COND1 was significantly lower compared to pre-exercise values. When walking speed was controlled during COND2, significant effects of muscle damage were noticed, among other variables, for stride frequency, loading rate, lateral and vertical GRFs, as well as for specific knee kinematics and kinetics. These findings provide new insights into how walking patterns are adapted to compensate for the impaired function of the knee musculature following muscle damage. The importance to distinguish the findings caused by muscle damage from those exhibited in response to changes in stride frequency is highlighted.     

Sound production in the whitemouth croaker and relationship between fish size and disturbance call characteristics

The whitemouth croaker produces two different sounds using extrinsic sonic muscles: (1) male advertisement calls during the spawning season and (2) disturbance calls, produced by both sexes. The advertisement call, related to courtship, was recorded in the field and from two marked spawning males of 28 and 30.5 cm L_T in the laboratory. It consists of individual pulses with average durations of 19.7 ms and 17.8 ms for the two males respectively, interpulse intervals of 496 ms and 718 ms, and dominant frequencies of 280 Hz and 316 Hz. Pulses are emitted in bouts of one to three min duration. Disturbance calls consist of a burst of pulses produced at short intervals, and the pulse duration, interpulse interval and dominant frequency of the pulses average 19.8 ms, 17.1 ms, and 363 Hz, respectively. Dominant frequency and interpulse interval decrease and pulse duration increases with fish size. Sound characteristics change markedly in young of the year individuals (lower than 25 cm L_T) after which they appear to stabilize. Higher dominant frequency in the advertisement than in the disturbance call and the relationship of dominant frequency to pulse duration suggest that dominant frequency is determined as a forced response to muscle contraction parameters rather than by the natural frequency of the swimbladder.     

Effects of medially posted insoles on foot and lower limb mechanics across walking and running in overpronating men

Anti-pronation orthoses, like medially posted insoles (MPI), have traditionally been used to treat various of lower limb problems. Yet, we know surprisingly little about their effects on overall foot motion and lower limb mechanics across walking and running, which represent highly different loading conditions. To address this issue, multi-segment foot and lower limb mechanics was examined among 11 overpronating men with normal (NORM) and MPI insoles during walking (self-selected speed 1.70 ± 0.19 m/s vs 1.72 ± 0.20 m/s, respectively) and running (4.04 ± 0.17 m/s vs 4.10 ± 0.13 m/s, respectively). The kinematic results showed that MPI reduced the peak forefoot eversion movement in respect to both hindfoot and tibia across walking and running when compared to NORM (p < 0.05–0.01). No differences were found in hindfoot eversion between conditions. The kinetic results showed no insole effects in walking, but during running MPI shifted center of pressure medially under the foot (p < 0.01) leading to an increase in frontal plane moments at the hip (p < 0.05) and knee (p < 0.05) joints and a reduction at the ankle joint (p < 0.05). These findings indicate that MPI primarily controlled the forefoot motion across walking and running. While kinetic response to MPI was more pronounced in running than walking, kinematic effects were essentially similar across both modes. This suggests that despite higher loads placed upon lower limb during running, there is no need to have a stiffer insoles to achieve similar reduction in the forefoot motion than in walking.     

Lower limb joint work and joint work contribution during downhill and uphill walking at different inclinations

Work performance and individual joint contribution to total work are important information for creating training protocols, but were not assessed so far for sloped walking. Therefore, the purpose of this study was to analyze lower limb joint work and joint contribution of the hip, knee and ankle to total lower limb work during sloped walking in a healthy population. Eighteen male participants (27.0 ± 4.7 yrs, 1.80 ± 0.05 m, 74.5 ± 8.2 kg) walked on an instrumented ramp at inclination angles of 0°, ±6°, ±12° and ±18° at 1.1 m/s. Kinematic and kinetic data were captured using a motion-capture system (Vicon) and two force plates (AMTI). Joint power curves, joint work (positive, negative, absolute) and each joint’s contribution to total lower limb work were analyzed throughout the stance phase using an ANOVA with repeated measures. With increasing inclination positive joint work increased for the ankle and hip joint and in total during uphill walking. Negative joint work increased for each joint and in total work during downhill walking. Absolute work was increased during both uphill (all joints) and downhill (ankle & knee) walking. Knee joint contribution to total negative and absolute work increased during downhill walking while hip and ankle contributions decreased. This study identified, that, when switching from level to a 6° and from 6° to a 12° inclination the gain of individual joint work is more pronounced compared to switching from 12° to an 18° inclination. The results might be used for training recommendations and specific training intervention with respect to sloped walking.     

Control of lateral weight transfer is associated with walking speed in individuals post-stroke

Restoring functional gait speed is an important goal for rehabilitation post-stroke. During walking, transferring of one’s body weight between the limbs and maintaining balance stability are necessary for independent functional gait. Although it is documented that individuals post-stroke commonly have difficulties with performing weight transfer onto their paretic limbs, it remains to be determined if these deficits contributed to slower walking speeds. The primary purpose of this study was to compare the weight transfer characteristics between slow and fast post-stroke ambulators. Participants (N = 36) with chronic post-stroke hemiparesis walked at their comfortable and maximal walking speeds on a treadmill. Participants were stratified into 2 groups based on their comfortable walking speeds (≥0.8 m/s or <0.8 m/s). Minimum body center of mass (COM) to center of pressure (COP) distance, weight transfer timing, step width, lateral foot placement relative to the COM, hip moment, peak vertical and anterior ground reaction forces, and changes in walking speed were analyzed. Results showed that slow walkers walked with a delayed and deficient weight transfer to the paretic limb, lower hip abductor moment, and more lateral paretic limb foot placement relative to the COM compared to fast walkers. In addition, propulsive force and walking speed capacity was related to lateral weight transfer ability. These findings demonstrated that deficits in lateral weight transfer and stability could potentially be one of the limiting factors underlying comfortable walking speeds and a determinant of chronic stroke survivors’ ability to increase walking speed.     

An effective balancing response to lateral perturbations at pelvis level during slow walking requires control in all three planes of motion

In this study we investigated balancing responses to lateral perturbations during slow walking (0.85 m/s). A group of seven healthy individuals walked on an instrumented treadmill while being perturbed at the level of waist at left heel strike in outward and inward lateral directions. Centre of mass (COM) and centre of pressure (COP), rotation of pelvis around vertical axis, step lengths, step widths and step times were assessed. The results have shown that beside control of COP in lateral direction, facilitated by adequate step widths, control of COP in sagittal direction, slowing down movement of COM was present after commencement of lateral perturbations. Sagittal component of COM was significantly retarded as compared to unperturbed walking for both inward (4.32 ± 1.29 cm) and outward (9.75 ± 2.17 cm) perturbations. This was necessary since after an inward perturbation first step length (0.29 ± 0.04 m compared to 0.52 ± 0.02 m in unperturbed walking) and step time (0.45 ± 0.05 s compared to 0.61 ± 0.04 s in unperturbed walking) were shortened while after an outward perturbation first two step lengths (0.36 ± 0.05 m and 0.32 ± 0.11 m compared to 0.52 ± 0.03 m in unperturbed walking) were shortened that needed to be accommodated by the described modulation of COP in sagittal plane. In addition pronounced pelvis rotation assisted in bringing swing leg to new location. The results of this study show that counteracting lateral perturbations at slow walking requires adequate response in all three planes of motion.     

The effect of uphill stride manipulation on race walking gait

Stride length analysis represents an easy method for assessing race walking kinematics. However, the stride parameters emerging from such an analysis have never been used to design a training protocol aimed at increasing stride length. With this aim, we investigated the effects of stride frequency manipulation during three weeks of uphill (2%) training on stride length at iso-efficiency speed. Twelve male race walkers were randomly allocated to one of two training groups: stride frequency manipulation (RWM, n=6) and free stride frequency (RWF, n=6). Results. Kinematic parameters measured before and after the 3-week training in RWM showed increased stride length (4.54%; p<0.0001) and contact time (4.58%; p<0.001); inversely, a decreased stride frequency (4.44%; p<0.0001) and internal work (7.09%; p<0.05) were found. In RWF the effect of the training showed a decrease in stride length (1.18%; p<0.0001) and contact time (<1%; p<0.0001) with respect to baseline conditions and an increased stride frequency and internal work of 1.19% (p<0.0001). These results suggest that using slopes (2%) as RWM could help coaches to provide some training methods that would improve an athlete''s performance, through increasing stride length without altering his or her race walking technique or metabolic demands.     

EMG synchrony to assess impaired corticomotor control of locomotion after stroke

Adapting one’s gait pattern requires a contribution from cortical motor commands. Evidence suggests that frequency-based analysis of electromyography (EMG) can be used to detect this cortical contribution. Specifically, increased EMG synchrony between synergistic muscles in the Piper frequency band has been linked to heightened corticomotor contribution to EMG. Stroke-related damage to cerebral motor pathways would be expected to diminish EMG Piper synchrony. The objective of this study is therefore to test the hypothesis that EMG Piper synchrony is diminished in the paretic leg relative to nonparetic and control legs, particularly during a long-step task of walking adaptability. Twenty adults with post-stroke hemiparesis and seventeen healthy controls participated in this study. EMG Piper synchrony increased more for the control legs compare to the paretic legs when taking a non-paretic long step (5.02 ± 3.22% versus 0.86 ± 2.62%), p < 0.01) and when taking a paretic long step (2.04 ± 1.98% versus 0.70 ± 2.34%, p < 0.05). A similar but non-significant trend was evident when comparing non-paretic and paretic legs. No statistically significant differences in EMG Piper synchrony were found between legs for typical walking. EMG Piper synchrony was positively associated with walking speed and step length within the stroke group. These findings support the assertion that EMG Piper synchrony indicates corticomotor contribution to walking.     

Dynamic alteration of plasma levels of betatrophin in younger female onset obesity post acute moderate-intensity exercise training

Obesity is a global metabolic disease anchored by a lack of physical activity lipid disturbances. Hitherto, betatrophin is a potential liver-derived hormone that regulates lipid metabolism. A total of 26 selected onset obese individuals (BMI range ± 28–31) were enrolled in this study and given moderate-intensity exercise. Importantly, our data show that acute moderate-intensity interval exercise (MIIE) and acute moderate-intensity continue to exercise (MICE) for 40 min significantly decrease the plasma level of full-length betatrophin respectively (174.18 ± 48.19 ng/mL; 182.31 ± 52.69 ng/mL), compared to the placebo (283.97 ± 32.23 ng/mL) post 10 min and 6 h exercise treatment (p ≤ 0.05). The plasma level of betatrophin was significantly and negatively correlated with BMI (r = ? 0.412, p = 0.037), fasting blood glucose (r = ? 0.390, p = 0.049), and positively correlated with VO_2max (r = 0.456, p = 0.019). In addition, the linear and ordinal logistic regression analysis shows that betatrophin, is a potential predictor for BMI [estimate value = 0.995, p = 0.037 and OR (95 % CI) = 0.992 (0.0984–1.00), p = 0,048]. In summary, our data demonstrate that the circulating levels of betatrophin were decreased after acute moderate-intensity exercise training.     

Treated livestock wastewater influence on soil quality and possibilities of crop irrigation

This work aims to investigate how livestock wastewater irrigation affects the quality and agricultural potential of soil. The experiments took place in 2019 on a research station with an area of 10 ha (Moscow region, Russian Federation), divided into two even sites of 5 ha (control, experimental). Eleven germination experiments were carried out to determine the influence of livestock wastewater irrigation on radish seeds (1 – control; 10 – irrigation with liquid and solid phases of wastewater samples mixed with pure water). The experimental and control plots appeared to differ in terms of the bulk density of soil. Changes occurred in all horizons (p ≤ 0.05) but a soil layer with a depth of 0.2–0.4 m. Soil horizons in the experiment plots all exhibited lower porosity (p ≤ 0.05) except for the topsoil, and the water capacity was higher in the topsoil (p ≤ 0.05) and near-surface layer (p ≤ 0.05). The experiment showed higher concentrations of hummus (p ≤ 0.01) and phosphorus (p ≤ 0.01). As for nitrogen, significant changes only occurred in the topsoil (p ≤ 0.01). In the germination experiments, more than 90% of radish seeds germinated. Besides, their root length was higher compared to the control (p ≤ 0.05). The results of the study suggest that livestock wastewater can benefit crop cultivation after preliminary treatment. Finally, the experiments revealed a reduced soil salt accumulation.