Combined study of segmental movements and motion of the centre of mass during adaptation on a split-belt treadmill

BACKGROUND AND AIM: Walking on a split-belt treadmill (each of the two belts running at different speed) has been proposed as an experimental paradigm to investigate the flexibility of the neural control of gait and as a form of therapeutic exercise for hemi-paretic patients[1]. However the scarcity of dynamic investigations both for segmental aspects and for the entire body system, represented by the Centre of Mass (CoM), challenges the validity of the available findings on split-gait. Thus, the aim of the present study is to describe the dynamic adaptation of healthy subjects in terms of segmental and CoM motion, using Gait Analysis on Force Treadmill [2]. The study intends to clarify the effect of "split-gait", underlining its differences with pathologic claudication. METHODS: Ten healthy adults walked on a split-belt treadmill mounted on force sensors, with belts running either at the same speed ('Tied Condition', TC) or at different speeds ('Split Condition', SC, 0.4 vs 0.8 m/s). For the study of segmental motion, the surface Electromyography (sEMG), sagittal power and work provided by ankle, the main engine of body propulsion, were simultaneously recorded. For the study of the CoM motion, the Total Energy (Etot) and the percentage of Recovery (%R), the index of efficiency of the pendulum-like mechanism, were simultaneously analyzed. Various tied/split walking sequences were requested. The study was approved by the Local Ethic Committee. RESULTS: In the SC, the segmental motion analysis revealed a marked asymmetry between the two sides. The work provided by the ankle was 4.8 times higher (in the 0.4 vs 0.8 m/s conditions, respectively) compared with the slower side, and 1.2 times higher compared with the same speed in the TC (0.6 m/s) [3]. Paradoxically, the analysis of the CoM revealed an increased efficiency of the pendulum mechanism, with a higher %R in SC with respect to the TC at the same speed. CONCLUSIONS: Split gait entails its own pattern of locomotion, very different from pathologic claudication. The faster leg mimics the paretic limb temporally, but the unimpaired limb from the spatial and dynamic point of view[3]. This must be considered when a therapeutic application is designed. REFERENCES:1. Helm et al. Phys Med Rehabil Clin N Am. 2015;26(4):703-13. 2. Tesio et al. Am J Phys Med Rehabil. 2008;87(7):515-26. 3. Tesio et al. Int J Rehabil Res. 2018;41(4):304-315

Walking on a split-belt treadmill induces a higher power output and a shorter step length from the faster leg in healthy subjects, with opposite (after)-effect lasting less than 5 minutes after exercise

Walking on a split-belt treadmill has been claimed as a possible treatment of pathologic step asymmetries: in particular, the step lengthening on the affected side [1]. Placing the paretic limb on the slower belt would increase this asymmetry, reverting to long-lasting symmetry after exposure (after-effect). These studies neglected the underlying dynamics. Recently, it has been demonstrated that this paradigm entails an opposite spatial and dynamic asymmetry in healthy subjects. The stance on the faster belt is shortened, thus mimicking the paretic step temporally. On the contrary, the step is shorter and more muscle power is produced [2]. This challenges the rationale of the previous researches. The present study aims at extending these findings by investigating the after-effect both on spatiotemporal step parameters and power output from the plantar flexors on either belt. METHODS Ten healthy adults (21-34 years, 1.61-1.91 m tall, 5 women) participated in the study. After a brief familiarization, participants walked on a force-sensorized split-belt treadmill with one belt running at 0.4 m s-1 and the other belt running at 1.2 m s-1 (split condition) for 15 minutes and then, with no interruption, with the belts running at the same velocity (0.4 m s-1, tied condition) for other 5 minutes. The dominant lower limb was assigned to the faster belt. Kinematic data were recorded through an optoelectronic system as per the Davis anthropometric model. Joint sagittal power was computed by multiplying the moment generated by the ground reaction forces at the joints, times the rotation speed. All signals were simultaneously recorded [2]. The study was approved by the Local Ethics Committee. RESULTS Consistently with previous studies [3], during the split condition, the step length on the slower belt was longer, reaching gradually about 130% of the opposite step length. Ankle peak power attained about 15% of that observed on the opposite side. During the following tied condition, the step length on the formerly slower belt initially shortened by about 65% (after-effect), compared to the opposite step, and returned to values similar to that of the opposite side within 5 minutes. During this transition phase, ankle peak power gradually increased by up to 50% compared to baseline. On the formerly faster belt, step length did not change, while ankle peak power suddenly dropped to the contralateral level (Figure 1). Figure 1 Stride by stride plots (moving average, time-window 30 strides) of step length (upper panel) and ankle power (lower panel) from one representative subject (woman, 21 years, 1.65 m tall, body mass 60 kg) walking on a split-belt treadmill with the dominant lower limb on the faster belt (red) and the nondominant lower limb on the slower belt (blue). Strides from 1 to 867 refer to the split condition, and stride from 868 to 1025 refer to the following tied condition. DISCUSSION The increase in plantar flexor power on the faster belt, despite the shorter stance period and length, may reflect the priority need to counteract the backward drag from the faster belt, with respect to the slower one. This adaptation does not seem to lead to substantial learning, given that an after-effect, both on step length and ankle peak power, is only seen during the 5 minutes following split walking. In pathologic claudication, placing the affected lower limb on the faster belt might represent an effective form of \u201cforced-use\u201d [4], as far as enhanced power is requested. Long term effects remain questionable

Erosion waves: transverse instabilities and fingering

Two laboratory scale experiments of dry and under-water avalanches of non-cohesive granular materials are investigated. We trigger solitary waves and study the conditions under which the front is transversally stable. We show the existence of a linear instability followed by a coarsening dynamics and finally the onset of a fingering pattern. Due to the different operating conditions, both experiments strongly differ by the spatial and time scales involved. Nevertheless, the quantitative agreement between the stability diagram, the wavelengths selected and the avalanche morphology reveals a common scenario for an erosion/deposition process.Comment: 4 pages, 6 figures, submitted to PR

The path curvature of the body centre of mass during walking as an index of balance control in patients with Multiple Sclerosis

BACKGROUND AND AIM: The path curvature of the centre of mass (CM), mechanically representative of the whole body system, may provide hints to detection of fall risk during walking. Here, an example is taken from results of an ongoing controlled study. It shows the comparison between the CM path in a healthy subject and in a fully autonomous patient with Multiple Sclerosis (MS). METHODS: A representative healthy subject (woman, 26 years, 1.55 m tall) and a MS patient (woman, 34 years, 1.65 m tall, with very mild left hemiparesis) are presented. Subjects walked on a force-sensorized treadmill (1) at 0.6 m/s. Data were averaged across 6 subsequent strides. The 3D displacements of the CM were computed via double integration of the ground reaction forces (Cavagna's Method). The path curvature of the CM during one stride was computed according to the Frenet-Serret formula (2). The instantaneous efficiency of the kinetic-potential, pendulum-like energy transfer of the CM was also computed (percent recovery, R: 100%=complete recovery, i.e. fully passive CM translation) (3). RESULTS: The left and right panels refer to the control and the MS subject, respectively. In the upper set of panels the human sketches on top of the figure help identifying the stride phases (% cycle) and give a frontal and a sagittal perspectives. The first and second rows of curves from the top give the instantaneous R and the path curvature of the CM during one stride. Each step begins with the single stance of the front leg (R=right; L=left). The horizontal bars under the curves mark the double and the single stance phases (continuous and dashed lines, respectively; grey tract=left step). The lower set of panels (closed curves) gives the planar projections of the CM path during the same stride. The space-time correspondence between the 2 sets of curves is facilitated by the shared A-D labeling of peak curvatures and the shared graphic conventions (dashed line=single stance; gray tract=left step). In both steps the curvature is peaking when R suddenly drops from 100 to 0, demonstrating that the passive pendulum-like mechanism of translation is briskly substituted by a short lasting, fully muscle-driven, propulsion. The highest peaks (A and C) are coincident with the lateral redirection during single stance. Of note, the patient's CM path is characterized by a 10-fold higher C peak (single stance, paretic-to-unaffected side redirection). This may be interpreted as a feature of "escape" limp, barely perceivable by clinical observation, when seen from the perspective of the body CM on the horizontal plane (bottom curves). CONCLUSIONS: Increased curvature peaks may reveal the attempt to shorten the stance on the affected side yet, placing at risk the lateral stability of the body. REFERENCES:[1] Tesio L, Rota V, Am J Phys Med Rehabil 2008;87:515-526 [2] Tesio L et al, J Biomech 2011;44:732-740 [3] Cavagna GA, J Appl Physiol 1975;39:174-179

First Toxicological Analysis of the Pufferfish Sphoeroides pachygaster Collected in Italian Waters (Strait of Sicily): Role of Citizens Science in Monitoring Toxic Marine Species

Pufferfish (Tetraodontidae) inhabiting the Mediterranean Sea may represent an emerging public health risk due to the possible accumulation of marine neurotoxins such as tetrodotoxin (TTXs) and saxitoxin (STXs) in their tissues. In this study, the presence of pufferfish species in the Strait of Sicily (Lampedusa Island, Italy) was investigated using a citizen science (CS) approach, involving local fishermen. Samples (liver, intestine, gonads, muscle, skin) from 20 specimens were sent to the National Reference Laboratory on Marine Biotoxins for TTXs detection using a validated HILIC-MS/MS method on fish tissue. The presence of STXs was also screened in part of the specimens. Overall, 56 specimens identified as Sphoeroides pachygaster (Müller &Troschel, 1848) were collected. Data on their total length, body weight, fishing method and catch area (with relative depth temperature and salinity) were analyzed and compared with the S. pachygaster records reported in literature which were updated to 2022. All the analysed tissues were found to be negative for both TTXs and STXs. CS played an essential role in monitoring potentially toxic marine species in this investigation. Outcomes from this study, which is the first investigating S. pachygaster toxicity in Italian waters, may provide useful data for the proper assessment of this emerging risk

Breaking of the Bancroft rule for multiple emulsions stabilized by a single stimulable polymer

International audienceWe investigated emulsions of water and toluene stabilized by (co)polymers consisting of styrene (S) and 2-(dimethylamino)ethyl methacrylate (DMAEMA) monomer units with different compositions and structures such as a PDMAEMA homopolymer, a P(S-co-DMAEMA) random copolymer and various PS-b-PDMAEMA and PS-b-(S-co-DMAEMA) block copolymers. The model system is used to study the fundamental conditions under which the different kinds of polymer-stabilized emulsions (direct oil in water, inverse water in oil and multiple emulsions) are stabilized or destabilized by pH change (at constant temperature). Polymer properties like chain conformation at the toluene-water interface as probed by SANS and neutron reflectivity at the liquid-liquid interface, the oil-water partitioning of the polymer chains (Bancroft's rule of thumb) as determined by UV spectroscopy and interfacial tensions measured by the rising and spinning drop techniques are determined. Overall, results evidence that the curvature sign, as defined by positive and negative values as the chain segments occupy preferentially the water and toluene sides of the interface respectively, reliably predicts the emulsion kind. In contrast, the Bancroft rule failed at foreseeing the emulsion type. In the region of near zero curvature the crossover from direct to inverse emulsions occurs through the formation of either unstable coexisting direct and inverse emulsions (i) or multiple emulsions (ii). The high compact adsorption of the chains at the interface as shown by low interfacial tension values does not allow to discriminate between both cases. However, the toluene-water partitioning of the polymeric emulsifier is still a key factor driving the formation of (i) or (ii) emulsions. Interestingly, the stabilization of the multiple emulsions can be tuned to a large extent as the toluene-water polymer partitioning can be adjusted using quite a large number of physico-chemical parameters linked to polymer architecture like diblock length ratio or polymer total molar mass, for example. Moreover, we show that monitoring the oil-water partitioning aspect of the emulsion system can also be used to lower the interfacial tension at low pH to values slightly higher than 0.01 mN m-1, irrespective of the curvature sign

Measuring voluntary activation of the quadriceps femoris during isokinetic concentric contractions

BACKGROUND: It is known that Voluntary Activation (VA) of muscles may be lower during isokinetic concentric (CON) contractions than during isometric (ISOM) contractions, and that it may be further decreased in various motor impairments. OBJECTIVE: The aim of this study was to validate the Interpolated Twitch Technique (ITT) for quantifying VA of the Quadriceps femoris during CON contractions (knee extension at 60 and 120_/s, CON60 and CON120, respectively). METHODS: Pairs of electrical stimuli were delivered to the Quadriceps femoris of twenty-two healthy subjects at 50_ of knee flexion. Participants were instructed to exert five different levels of effort in decreasing order between 100% and 20% maximal voluntary efforts in ISOM and CON contractions. RESULTS: Through a linear regression model, a significant relationship between measures of VA and moment was observed for all the three contraction conditions: slopes (95% confidence intervals) = 1.04 (0.98\u20131.11), 0.96 (0.89\u20131.02) and 0.84 (0.78\u20130.91); intercepts = - 5.22 (\u2013 8.61\u2013 \u20131.83), 4.16 (0.71\u20137.62) and 14.58 (10.76\u201318.39), for ISOM, CON60 and CON120 contractions, respectively. This supported the validity of the method. CONCLUSIONS: It is concluded that ITT can be a valid method for measuring VA during CON contractions, potentially useful both in sports and rehabilitation studies

Crouch gait can be an effective form of forced-use/no constraint exercise for the paretic lower limb in stroke

In hemiplegic gait the paretic lower limb provides less muscle power and shows a briefer stance compared with the unaffected limb. Yet, a longer stance and a higher power can be obtained from the paretic lower limb if gait speed is increased. This supports the existence of a 'learned non-use' phenomenon, similar to that underlying some asymmetric impairments of the motion of the eyes and of the upper limbs. Crouch gait (CG) (bent-hip bent-knee, about 30 degrees minimum knee flexion) might be an effective form of 'forced-use' treatment of the paretic lower limb. It is not known whether it also stimulates a more symmetric muscle power output. Gait analysis on a force treadmill was carried out in 12 healthy adults and seven hemiplegic patients (1-127 months after stroke, median: 1.6). Speed was imposed at 0.3 m/s. Step length and single and double stance times, sagittal joint rotations, peak positive power, and work in extension of the hip, knee, and ankle (plantar flexion), and surface electromyography (sEMG) area from extensor muscles during the generation of power were measured on either side during both erect and crouch walking. Significance was set at P less than 0.05; corrections for multiplicity were applied. Patients, compared with healthy controls, adopted in both gait modalities and on both sides a shorter step length (61-84%) as well as a shorter stance (76-90%) and swing (63-83%) time. As a rule, they also provided a higher muscular work (median: 137%, range: 77-250%) paralleled by a greater sEMG area (median: 174%, range: 75-185%). In erect gait, the generation of peak extensor power across hip, knee, and ankle joints was in general lower (83-90%) from the paretic limb and higher (98-165%) from the unaffected limb compared with control values. In CG, peak power generation across the three lower limb joints was invariably higher in hemiparetic patients: 107-177% from the paretic limb and 114-231% from the unaffected limb. When gait shifted from erect to crouch, only for hemiplegic patients, at the hip, the paretic/unaffected ratio increased significantly. For peak power, work, sEMG area, and joint rotation, the paretic/unaffected ratio increased from 55 to 85%, 56 to 72%, 68 to 91%, and 67 to 93%, respectively. CG appears to be an effective form of forced-use exercise eliciting more power and work from the paretic lower limb muscles sustained by a greater neural drive. It also seems effective in forcing a more symmetric power and work from the hip extensor muscles, but neither from the knee nor the ankle

Limping on split-belt treadmills implies opposite kinematic and dynamic lower limb asymmetries

Walking on a split-belt treadmill (each of the two belts running at a different speed) has been proposed as an experimental paradigm to investigate the flexibility of the neural control of gait and as a form of therapeutic exercise. However, the scarcity of dynamic investigations challenges the validity of the available findings. The aim of the present study was to investigate the dynamic asymmetries of lower limbs of healthy adults during adaptation to gait on a split-belt treadmill. Ten healthy adults walked on a split-belt treadmill mounted on force sensors, with belts running either at the same speed ('tied' condition) or at different speeds ('split' condition, 0.4 vs. 0.8 or 0.8 vs. 1.2\u2009m/s). The sagittal power and work provided by ankle, knee and hip joints, joint rotations, muscle lengthening, and surface electromyography were recorded simultaneously. Various tied/split walking sequences were requested. In the split condition a marked asymmetry between the parameters recorded from each of the two lower limbs, in particular from the ankle joint, was recorded. The work provided by the ankle (the main engine of body propulsion) was 4.8 and 2.2 times higher (in the 0.4 vs. 0.8, and 0.8 vs. 1.2\u2009m/s conditions, respectively) compared with the slower side, and 1.2 and 1.1 times higher compared with the same speed in the tied condition. Compared with overground gait in hemiplegia, split gait entails an opposite spatial and dynamic asymmetry. The faster leg mimics the paretic limb temporally, but the unimpaired limb from the spatial and dynamic point of view. These differences challenge the proposed protocols of split gait as forms of therapeutic exercise

Changes in dream features across the first and second waves of the Covid-19 pandemic

Research during the Covid-19 pandemic has highlighted its significant impact on dreaming. Here we address changes in dream features both during the first wave, when the Italian government imposed a total lockdown, and the second wave (autumn 2020), when a partial lockdown was effected. In April 2020 (total lockdown), 1,622 participants (Mage\ua0=\ua034.1\ua0\ub1\ua013.6 years; 1171F) completed an online survey including the Pittsburgh Sleep Quality Index and a set of questions on dream features and their possible changes relative to the month preceding the lockdown (pre-total lockdown). In November 2020 (partial lockdown), 214 participants (Mage\ua0=\ua036.78\ua0\ub1\ua014.2\ua0years; 159F) from the previous sample completed the same survey. Approximately half of the subjects reported increased or decreased dream frequency (30.5% and 21.8%), length (27.1% and 15.8%) and vividness (31.5% and 17.1%) during total lockdown as well as during partial lockdown (frequency: 30.3% and 13.5%; length: 23.3% and 12.6%; vividness: 31.6% and 24.1%). Dream affect became significantly more negative in total lockdown relative to pre-total lockdown and in partial lockdown relative to pre-partial lockdown (both p\ua0<.001). Both in total lockdown and partial lockdown, increased negative dream emotionality significantly predicted changes in dream frequency, length and vividness, and was significantly predicted, in turn, by worsened sleep quality. Our data confirm that dream features are significantly affected by major life changes such as those imposed by a pandemic. The fact that between lockdowns negative dream affect returned almost to baseline level suggests that dream emotionality is closely related to lifestyle and wake-time emotional changes. Also, our findings point to a modulating role of sleep quality on dream emotionality