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Cycling stands as one of the most widely embraced leisure activities and serves purposes such as exercise, rehabilitation, and commuting. This study aimed to assess the feasibility of assisting three unimpaired participants (age: 34.0 ± 7.9 years, height: 1.86 ± 0.02 m, weight: 75.7 ± 12.7 kg) using the GuroX hip exoskeleton, originally designed for walking assistance, during cycling against a resistance of 1 W/kg. The performance evaluation employed a sweep protocol that manipulated the timing of the exoskeleton's peak extension and flexion torque in addition to human-in-the-loop optimization to enhance these timings based on metabolic cost. Our findings indicate that with a peak assistance torque of approximately 10.3 Nm for extension and flexion, the GuroX substantially reduced the net metabolic cost of cycling by 31.4 ± 8.1% and 26.4 ± 14.1% compared to transparent and without exoskeleton conditions, respectively. This demonstrates the significant potential of a hip exoskeleton developed for walking assistance to profoundly benefit cycling. Additionally, customizing the assistance strategy proves beneficial in maximizing assistance. While we attribute the average motor power to be a major contributor to the reduced cycling effort, participant feedback suggests that user comfort and synchronization between the user and exoskeleton may have played integral roles. Further research should validate our initial findings by employing a larger participant pool in real-world conditions. Incorporating a more diverse set of parameters for the human-in-the-loop optimization could enhance individualized assistance strategies. [ABSTRACT FROM AUTHOR]

Musculoskeletal modeling is a cost-effective way to design and test wearable robots, ensuring maximum efficiency for individuals. This article explores the simulation of exoskeletons to support the lower limbs and reduce the metabolic cost of walking. The exoskeleton consists of a flexible joint as an actuator made up of four elastomers that store the negative power of the knee joint during the walking cycle as energy, and release it to assist the wearer in the next phase of walking. The Computed Muscle Control (CMC) algorithm in OpenSim is used to find joint torque, total metabolic savings, and the resulting changes in muscle activity. Subsequently, the behavior of implementing the passive exoskeleton is evaluated and the results are compared to a semi-active robot on lower body limbs. The study concluded that while the passive robot exerts extra force on the hamstring muscles in the first half of the swing phase and increases the torque applied to the knee joint. It decreases the activity of the quadriceps muscles in the second half. To compensate for this problem exoskeletons are commonly equipped with a motor. However, this article's findings suggest that utilizing the motorized robot, while decreasing the torque in the targeted joint, actually boosts the performance of surrounding muscles and consumes more metabolic energy than in a passive state. [ABSTRACT FROM AUTHOR]

Understanding metabolic cost through biomechanical data, including ground reaction forces (GRFs) and joint moments, is vital for health, sports, and rehabilitation. The long stabilization time (2–5 min) of indirect calorimetry poses challenges in prolonged tests. This study investigated using artificial neural networks (ANNs) to predict metabolic costs from the GRF and joint moment time series. Data from 20 participants collected over 270 walking trials, including the GRF and joint moments, formed a detailed dataset. Two ANN models were crafted, netGRF for the GRF and netMoment for joint moments, and both underwent training, validation, and testing to validate their predictive accuracy for metabolic cost. NetGRF (six hidden layers, two input delays) showed significant correlations: 0.963 (training), 0.927 (validation), 0.883 (testing), p < 0.001. NetMoment (three hidden layers, one input delay) had correlations of 0.920 (training), 0.956 (validation), 0.874 (testing), p < 0.001. The models' low mean squared errors reflect their precision. Using Partial Dependence Plots, we demonstrated how gait cycle phases affect metabolic cost predictions, pinpointing key phases. Our findings show that the GRF and joint moments data can accurately predict metabolic costs via ANN models, with netGRF being notably consistent. This emphasizes ANNs' role in biomechanics as a crucial method for estimating metabolic costs, impacting sports science, rehabilitation, assistive technology development, and fostering personalized advancements. [ABSTRACT FROM AUTHOR]

Unsteady locomotion (e. g., sprints and shuttle runs) requires additional metabolic (and mechanical) energy compared to running at constant speed. In addition, sprints or shuttle runs with relevant speed changes (e. g., with large accelerations and/or decelerations) are typically short in duration and, thus, anaerobic energy sources must be taken into account when computing energy expenditure. In sprint running there is an additional problem due to the objective difficulty in separating the acceleration phase from a (necessary and subsequent) deceleration phase. In this review the studies that report data of energy expenditure during sprints and shuttles (estimated or actually calculated) will be summarized and compared. Furthermore, the (mechanical) determinants of metabolic energy expenditure will be discussed, with a focus on the analogies with and differences from the energetics/mechanics of constant-speed linear running. [ABSTRACT FROM AUTHOR]

Background: Foot and ankle unloading is essential in various clinical contexts, including ulcers, tendon ruptures, and fractures. Choosing the right assistive device is crucial for functionality and recovery. Yet, research on the impact of devices beyond crutches, particularly ankle-foot orthoses (AFOs) designed to unload the ankle and foot, is limited. This study investigates the effects of three types of devices—forearm crutches, knee crutch, and AFO—on biomechanical, metabolic, and subjective parameters during walking with unilateral ankle-foot unloading. Methods: Twenty healthy participants walked at a self-selected speed in four conditions: unassisted able-bodied gait, and using three unloading devices, namely forearm crutches, iWalk knee crutch, and ZeroG AFO. Comprehensive measurements, including motion capture, force plates, and metabolic system, were used to assess various spatiotemporal, kinematic, kinetic, and metabolic parameters. Additionally, participants provided subjective feedback through questionnaires. The conditions were compared using a within-subject crossover study design with repeated measures ANOVA. Results: Significant differences were found between the three devices and able-bodied gait. Among the devices, ZeroG exhibited significantly faster walking speed and lower metabolic cost. For the weight-bearing leg, ZeroG exhibited the shortest stance phase, lowest braking forces, and hip and knee angles most similar to normal gait. However, ankle plantarflexion after push-off using ZeroG was most different from normal gait. IWalk and crutches caused significantly larger center-of-mass mediolateral and vertical fluctuations, respectively. Participants rated the ZeroG as the most stable, but more participants complained it caused excessive pressure and pain. Crutches were rated with the highest perceived exertion and lowest comfort, whereas no significant differences between ZeroG and iWalk were found for these parameters. Conclusions: Significant differences among the devices were identified across all measurements, aligning with previous studies for crutches and iWalk. ZeroG demonstrated favorable performance in most aspects, highlighting the potential of AFOs in enhancing gait rehabilitation when unloading is necessary. However, poor comfort and atypical sound-side ankle kinematics were evident with ZeroG. These findings can assist clinicians in making educated decisions about prescribing ankle-foot unloading devices and guide the design of improved devices that overcome the limitations of existing solutions. [ABSTRACT FROM AUTHOR]

Why do we move slower as we grow older? The reward circuits of the brain, which tend to invigorate movements, decline with aging, raising the possibility that reduced vigor is due to the diminishing value that our brain assigns to movements. However, as we grow older, it also becomes more effortful to make movements. Is age-related slowing principally a consequence of increased effort costs from the muscles, or reduced valuation of reward by the brain? Here, we first quantified the cost of reaching via metabolic energy expenditure in human participants (male and female), and found that older adults consumed more energy than the young at a given speed. Thus, movements are objectively more costly for older adults. Next, we observed that when reward increased, older adults, like the young, responded by initiating their movements earlier. Yet, unlike the young, they were unwilling to increase their movement speed. Was their reluctance to reach quicker for rewards due to the increased effort costs, or because they ascribed less value to the movement? Motivated by a mathematical model, we next made the young experience a component of aging by making their movements more effortful. Now the young responded to reward by reacting faster but chose not to increase their movement speed. This suggests that slower movements in older adults are partly driven by an adaptive response to an elevated effort landscape. Moving slower may be a rational economic response the brain is making to mitigate the elevated effort costs that accompany aging. [ABSTRACT FROM AUTHOR]

This study focused on designing and evaluating a bilateral semi-rigid hip exoskeleton. The exoskeleton assisted the hip joint, capitalizing on its proximity to the body's center of mass. Unlike its rigid counterparts, the semi-rigid design permitted greater freedom of movement. A temporal force-tracking controller allowed us to prescribe torque profiles during walking. We ensured high accuracy by tuning control parameters and series elasticity. The evaluation involved experiments with ten participants across ten force profile conditions with different end-timings and peak magnitudes. Our findings revealed a trend of greater reductions in metabolic cost with assistance provided at later timings in stride and at greater magnitudes. Compared to walking with the exoskeleton powered off, the largest reduction in metabolic cost was 9.1%. This was achieved when providing assistance using an end-timing at 44.6% of the stride cycle and a peak magnitude of 0.11 Nm kg−1. None of the tested conditions reduced the metabolic cost compared to walking without the exoskeleton, highlighting the necessity for further enhancements, such as a lighter and more form-fitting design. The optimal end-timing aligns with findings from other soft hip exosuit devices, indicating a comparable interaction with this prototype to that observed in entirely soft exosuit prototypes. [ABSTRACT FROM AUTHOR]

Plants store chemical defenses that act as toxins against herbivores, such as toxic isothiocyanates (ITCs) in Brassica plants, hydrolyzed from glucosinolate (GLS) precursors. The fitness of herbivorous larvae can be strongly affected by these toxins, causing immature death. We modeled this phenomenon using a set of ordinary differential equations and established a direct relationship between feeding, toxin exposure, and the net energy of a larva, where the fitness of an organism is proportional to its net energy according to optimal foraging theory. Optimal foraging theory is widely used in ecology to model the feeding and searching behavior of organisms. Although feeding provides energy gain, plant toxins and foraging cause energy loss for the larvae. Our equations explain that toxin exposure and foraging can sharply reduce larval net energy to zero at an instar. Since herbivory needs energy, the only choice left for a larva is to stop feeding at that time point. If that is significantly earlier than the end of the last instar stage, the larva dies without food. Thus, we show that plant toxins can cause immature death in larvae from the perspective of optimal foraging theory. [ABSTRACT FROM AUTHOR]

Background: The maximal running speed (VMAX) determined on a graded treadmill test is well-recognized as a running performance predictor. However, few studies have assessed the variables that predict VMAX in recreationally active runners. Methods: We used a mathematical procedure combining Fick's law and metabolic cost analysis to verify the relation between (1) VMAX versus anthropometric and physiological determinants of running performance and, (2) theoretical metabolic cost versus running biomechanical parameters. Linear multiple regression and bivariate correlation were applied. We aimed to verify the biomechanical, physiological, and anthropometrical determinants of VMAX in recreationally active runners. Fifteen recreationally active runners participated in this observational study. A Conconi and a stead-steady running test were applied using a heart rate monitor and a simple video camera to register the physiological and mechanical variables, respectively. Results: Statistical analysis revealed that the speed at the second ventilatory threshold, theoretical metabolic cost, and fat-mass percentage confidently estimated the individual running performance as follows: VMAX = 58.632 + (-0.183* fat percentage) + (-0.507* heart rate percentage at second ventilatory threshold) + (7.959* theoretical metabolic cost) (R² = 0.62, p = 0.011, RMSE = 1.50 km.h-1). Likewise, the theoretical metabolic cost was significantly explained (R² = 0.91, p = 0.004, RMSE = 0.013 a.u.) by the running spatiotemporal and elastic-related parameters (contact and aerial times, stride length and frequency, and vertical oscillation) as follows: theoretical metabolic cost = 10.421 + (4.282* contact time) + (-3.795* aerial time) + (-2.422* stride length) + (-1.711* stride frequency) + (0.107 - vertical oscillation). Conclusion: Critical determinants of elastic mechanism, such as maximal vertical force and vertical and leg stiffness were unrelated to the metabolic economy. VMAX, a valuable marker of running performance, and its physiological and biomechanical determinants can be effectively evaluated using a heart rate monitor, treadmill, and a digital camera, which can be used in the design of training programs to recreationally active runners. [ABSTRACT FROM AUTHOR]

Background: The impact of a single-session Pilates exercise on cardiorespiratory fitness and metabolic parameters is still uncertain. Aims: The aim of this study was to examine the cardiorespiratory changes during a single-session Pilates exercise and compare cardiorespiratory fitness-related parameters with walking at different speeds on a treadmill, at low (3.2 kph) and moderate intensities (4.8 kph). Methods: Cardiorespiratory responses were measured with a cardiopulmonary exercise test device in 31 healthy young adults at rest, during a single Pilates session, walking at 3.2 kph and walking at 4.8 kph. The study design employed a cross-over design. Participants were randomly assigned to two experimental groups: a Pilates training session following treadmill walking or treadmill walking following a Pilates training session. Results: Mean MET, oxygen and energy consumption during Pilates were similar to walking at 3.2 kph (p > 0.05), but significantly lower than walking at 4.8 kph (p < 0.05). The mean heart rate during Pilates was higher than walking at 3.2 kph (p < 0.05), but similar to walking at 4.8 kph (p > 0.05). Significantly higher carbohydrate metabolism was used during Pilates compared to walking (p < 0.05). Conclusion: The cardiopulmonary responses to a single Pilates session are similar to walking at a speed of 3.2 kph but lower than walking at 4.8 kph. These results indicate that while Pilates may not generate sufficient cardiopulmonary changes to enhance cardiorespiratory fitness as a moderate-intensity exercise in healthy young adults, it may still offer other benefits such as improvements in flexibility, core strength, and posture. [ABSTRACT FROM AUTHOR]

The term metabolic cost (MС) is often used for assessment of energy consumption in the biosynthesis of various substances under different growth conditions or by different cell types. The MC of the metabolite is calculated according to a specified algorithm in universal ~P units, multiples of ATP molecules hydrolyzed to ADP and inorganic phosphate. Our analysis of the published data showed that the interpretation of the MC concept and the algorithms for its calculation, proposed by different authors, differ significantly. Since the MС is often considered in connection with system-level tasks, such as the metabolic flux analysis and the natural selection mechanisms, it seems appropriate to characterize this concept in detail. In this work, the term MС was clearly defined and used to calculate the energy consumption for the synthesis of 13 metabolic precursors of Escherichia coli biomass based on the modern model of the central metabolism of this bacterium. It was found that the MC, expressed in units of stored or hydrolyzed ATP molecules (~P), depends on the characteristics of the metabolism of an individual organism, its culturing conditions, and the P/O ratio, which characterizes the number of ATP molecules formed during the transfer of one electron pair to one oxygen atom in oxidative phosphorylation. [ABSTRACT FROM AUTHOR]

This study was designed to examine the metabolic power (MP) responses of football and futsal players to different small sided games (SSG). Twelve football and 12 futsal players participated in this study voluntarily. Maximal oxygen consumption(VO2max) and coach scoring (CS) were used for SSG player matching. Football and futsal players participated in two bouts of 2vs2, 3vs3 and 4vs4-SSG in random order. Kinematic and MP variables during SSG were measured by using GPS. To determine the effects of branch and SSG on each dependent variable of total distance (TD), relative TD (TDRel), MPaverage, relative TD in four different MP levels, and negative and positive acceleration numbers, a main effects 2-way analysis of variance with Bonferroni post hoc was used. MPaverage was significantly higher in futsal players compared to football players (p = 0.000). TD (p = 0.000) and TDRel(p = 0.013) of futsal players was significantly higher compared to football players. Total deceleration and acceleration numbers during SSG were significantly higher for futsal players than football players (p = 0.026). MP requirements were independent of the game format (p > 0.05), except for 2vs2-SSG (p < 0.05), when the playing area per player was kept constant. The results of this study showed that external load indicators during SSG were higher in futsal players compared to football players. [ABSTRACT FROM AUTHOR]

Key points Breathing mild bouts of low oxygen air (i.e. acute intermittent hypoxia, AIH) has been shown to improve locomotor function in humans after a spinal cord injury. How AIH‐induced gains in motor performance are achieved remains unclear. We examined the hypothesis that AIH augments motor learning and motor retention during a locomotor adaptation task. We further hypothesized that gains in motor learning and retention will be associated with reductions in net metabolic power, consistent with the acquisition of energetically favourable mechanics. Thirty healthy individuals were randomly allocated into either a control group or an AIH group. We utilized a split‐belt treadmill to characterize adaptations to an unexpected belt speed perturbation of equal magnitude during an initial exposure and a second exposure. Adaptation was characterized by changes in spatiotemporal step asymmetry, anterior–posterior force asymmetry, and net metabolic power. While both groups adapted by reducing spatial asymmetry, only the AIH group achieved significant reductions in double support time asymmetry and propulsive force asymmetry during both the initial and the second exposures to the belt speed perturbation. Net metabolic power was also significantly lower in the AIH group, with significant reductions from the initial perturbation exposure to the second. These results provide the first evidence that AIH mediates improvements in both motor learning and retention. Further, our results suggest that reductions in net metabolic power continue to be optimized upon subsequent learning and are driven by more energetically favourable temporal coordination strategies. Our observation that AIH facilitates motor learning and retention can be leveraged to design rehabilitation interventions that promote functional recovery. Brief exposures to low oxygen air, known as acute intermittent hypoxia (AIH), improves locomotor function in humans after a spinal cord injury, but it remains unclear how gains in motor performance are achieved. In this study, we tested the hypothesis that AIH induces enhancements in motor learning and retention by quantifying changes in interlimb coordination, anterior–posterior force symmetry and metabolic cost during a locomotor adaptation task. We show the first evidence that AIH improves both motor learning and savings of newly learned temporal interlimb coordination strategies and force asymmetry compared to untreated individuals. We further demonstrate that AIH elicits greater reductions in metabolic cost during motor learning that continues to be optimized upon subsequent learning. Our findings suggest that AIH‐induced gains in locomotor performance are facilitated by enhancements in motor learning and retention of more energetically favourable coordination strategies. [ABSTRACT FROM AUTHOR]

In Principles of Neural Design (2015, MIT Press), inspired by Charles Darwin, Sterling and Laughlin undertook the unfashionable task of distilling principles from facts in the technique-driven, data-saturated domain of neuroscience. Their starting point for deriving the organizing principles of brains are two brainless single-celled organisms, Escherichia coli and Paramecium, and the 302-neuron brain of the nematode Caenorhabditis elegans. The book is an exemplar in how to connect the dots between simpler and (much) more complex organisms in a particular area. Here, they have generously agreed to republish an abridged version of Chapter 2 (Why an Animal Needs a Brain), in which many of their principles are first described. [ABSTRACT FROM AUTHOR]

Background: Efficient gait assistance by augmentative exoskeletons depends on reliable control strategies. While numerous control methods and their effects on the metabolic cost of walking have been explored in the literature, the use of different exoskeletons and dissimilar protocols limit direct comparisons. In this article, we present and compare two controllers for hip exoskeletons with different synchronization paradigms.Methods: The implicit-synchronization-based approach, termed the Simple Reflex Controller (SRC), determines the assistance as a function of the relative loading of the feet, resulting in an emerging torque profile continuously assisting extension during stance and flexion during swing. On the other hand, the Hip-Phase-based Torque profile controller (HPT) uses explicit synchronization and estimates the gait cycle percentage based on the hip angle, applying a predefined torque profile consisting of two shorter bursts of assistance during stance and swing. We tested the controllers with 23 naïve healthy participants walking on a treadmill at 4 km ⋅ h−1, without any substantial familiarization.Results: Both controllers significantly reduced the metabolic rate compared to walking with the exoskeleton in passive mode, by 18.0% (SRC, p < 0.001) and 11.6% (HPT, p < 0.001). However, only the SRC led to a significant reduction compared to walking without the exoskeleton (8.8%, p = 0.004). The SRC also provided more mechanical power and led to bigger changes in the hip joint kinematics and walking cadence. Our analysis of mechanical powers based on a whole-body analysis suggested a reduce in ankle push-off under this controller. There was a strong correlation (Pearson’s r = 0.778, p < 0.001) between the metabolic savings achieved by each participant with the two controllers.Conclusion: The extended assistance duration provided by the implicitly synchronized SRC enabled greater metabolic reductions compared to the more targeted assistance of the explicitly synchronized HPT. Despite the different assistance profiles and metabolic outcomes, the correlation between the metabolic reductions with the two controllers suggests a difference in individual responsiveness to assistance, prompting more investigations to explore the person-specific factors affecting assistance receptivity.

Background The maximal running speed (VMAX) determined on a graded treadmill test is well-recognized as a running performance predictor. However, few studies have assessed the variables that predict VMAX in recreationally active runners. Methods We used a mathematical procedure combining Fick’s law and metabolic cost analysis to verify the relation between (1) VMAX versus anthropometric and physiological determinants of running performance and, (2) theoretical metabolic cost versus running biomechanical parameters. Linear multiple regression and bivariate correlation were applied. We aimed to verify the biomechanical, physiological, and anthropometrical determinants of VMAX in recreationally active runners. Fifteen recreationally active runners participated in this observational study. A Conconi and a stead-steady running test were applied using a heart rate monitor and a simple video camera to register the physiological and mechanical variables, respectively. Results Statistical analysis revealed that the speed at the second ventilatory threshold, theoretical metabolic cost, and fat-mass percentage confidently estimated the individual running performance as follows: VMAX = 58.632 + (−0.183 * fat percentage) + (−0.507 * heart rate percentage at second ventilatory threshold) + (7.959 * theoretical metabolic cost) (R2 = 0.62, p = 0.011, RMSE = 1.50 km.h−1). Likewise, the theoretical metabolic cost was significantly explained (R2 = 0.91, p = 0.004, RMSE = 0.013 a.u.) by the running spatiotemporal and elastic-related parameters (contact and aerial times, stride length and frequency, and vertical oscillation) as follows: theoretical metabolic cost = 10.421 + (4.282 * contact time) + (−3.795 * aerial time) + (−2.422 * stride length) + (−1.711 * stride frequency) + (0.107 * vertical oscillation). Conclusion Critical determinants of elastic mechanism, such as maximal vertical force and vertical and leg stiffness were unrelated to the metabolic economy. VMAX, a valuable marker of running performance, and its physiological and biomechanical determinants can be effectively evaluated using a heart rate monitor, treadmill, and a digital camera, which can be used in the design of training programs to recreationally active runners.

Olive ridley sea turtles, Lepidochelys olivacea, exhibit a polymorphic reproductive behavior, nesting solitarily or in mass aggregations termed "arribadas", where thousands of individuals nest synchronously. Arribada nesting provides fitness benefits including mate finding during nearshore aggregations and predator satiation at the time of hatching, but it is unknown if such benefits come with a physiological cost. We used plasma metabolite profiling, stable isotope analysis, biochemical and endocrine assays to test whether metabolic parameters differ between nesting modes, and if arribada nesting is associated with increased levels of oxidative damage compared to solitary nesting. Arribada nesters were bigger and had higher circulating thyroid hormone levels than solitary nesters. Similarly, pathways related to phospholipid and amino acid metabolism, catabolic processes, and antioxidant defense were enriched in individuals nesting in arribada. Stable isotope signatures in skin samples showed differences in feeding zones with arribada nesters likely feeding on benthic and potentially more productive grounds. Arribada nesters had increased levels of plasma lipid peroxidation and protein oxidation products compared to solitary nesters. These results suggest that metabolic profiles differ between nesting modes and that oxidative stress is a trade-off for the fitness benefits associated with arribada nesting.

The mussel Mytilus edulis, a host to various trematode species, experiences performance decrements due to these infections. Yet, the impact magnitude and potential interactions with environmental stressors remain largely unexplored. This study scrutinizes the effect of Renicola roscovita infections on mussel filtration and respiration. We first assessed performance in both uninfected and lab-infected mussels at a mild temperature (16 °C), following an acute heat ramp to 30.5 °C and subsequent cooling. The experiment revealed neither a significant direct impact of the infection on the mussels' performance, nor any significant interplay between the infection and temperature variations. To account for possible infection effects obscured by low sample sizes or mussel size disparities, we conducted a reassessment at 16 °C using both small and large mussels. Infection notably hampered filtration in large mussels, with a marginal impact on smaller ones. A positive correlation was found between infection intensity and mussel filtration capacity, though the infection had no discernible impact on respiration. Our consistent finding of an 11-12 % infection effect size across all experiments indicates a slight reduction in mussel filtration due to trematode infections. While the exacerbating effect of transient heat stress on the infection's impact on filtration was not statistically significant, future investigations should explore potential interactions with prolonged heat stress. Our findings underscore the nuanced ways in which parasitic infections can influence marine bivalve physiology, emphasizing the need for more comprehensive studies that incorporate environmental stressors, such as heat stress, to fully elucidate the impact of parasitism on marine ecosystem health and resilience.

Understanding metabolic cost through biomechanical data, including ground reaction forces (GRFs) and joint moments, is vital for health, sports, and rehabilitation. The long stabilization time (2–5 min) of indirect calorimetry poses challenges in prolonged tests. This study investigated using artificial neural networks (ANNs) to predict metabolic costs from the GRF and joint moment time series. Data from 20 participants collected over 270 walking trials, including the GRF and joint moments, formed a detailed dataset. Two ANN models were crafted, netGRF for the GRF and netMoment for joint moments, and both underwent training, validation, and testing to validate their predictive accuracy for metabolic cost. NetGRF (six hidden layers, two input delays) showed significant correlations: 0.963 (training), 0.927 (validation), 0.883 (testing), p < 0.001. NetMoment (three hidden layers, one input delay) had correlations of 0.920 (training), 0.956 (validation), 0.874 (testing), p < 0.001. The models’ low mean squared errors reflect their precision. Using Partial Dependence Plots, we demonstrated how gait cycle phases affect metabolic cost predictions, pinpointing key phases. Our findings show that the GRF and joint moments data can accurately predict metabolic costs via ANN models, with netGRF being notably consistent. This emphasizes ANNs’ role in biomechanics as a crucial method for estimating metabolic costs, impacting sports science, rehabilitation, assistive technology development, and fostering personalized advancements.

In today's world, in order to increase the movement abilities of amputees, different types of passive prostheses are used according to the level of the person's disability. Although these types of prostheses increase a person's mobility; however, they still have a limited ability to help the amputee walk normally on uneven terrain, as there is no net stimulus input power for the target joint. These limitations have led to the growth of the use of active prostheses in recent years, which has led to a variety of prosthetic designs. The purpose of this research is, first of all, to provide a suitable design and control of active transtibial prosthesis close to the performance of lost limb of a healthy person, and second and more importantly, to develop a 7-link inverse dynamic model of human gait and use it to analyze of an amputee gait with the designed prosthesis. Winter's reference data are used in the entire process of design and simulation of prosthesis performance. Also, it is assumed that the amputation occurred in only one leg of the person. Based on the obtained results, when an amputee with 57 kg weight and 1.55 cm height wears an active prosthesis designed with 0.5 kg extra weight, the amount of metabolic cost of amputee in the swing phase increases by about 20%. By using this obtained model, it will be possible to optimize different prosthesis designs for people with different weight and height conditions. [ABSTRACT FROM AUTHOR]

The mussel Mytilus edulis , a host to various trematode species, experiences performance decrements due to these infections. Yet, the impact magnitude and potential interactions with environmental stressors remain largely unexplored. This study scrutinizes the effect of Renicola roscovita infections on mussel filtration and respiration. We first assessed performance in both uninfected and lab-infected mussels at a mild temperature (16 °C), following an acute heat ramp to 30.5 °C and subsequent cooling. The experiment revealed neither a significant direct impact of the infection on the mussels' performance, nor any significant interplay between the infection and temperature variations. To account for possible infection effects obscured by low sample sizes or mussel size disparities, we conducted a reassessment at 16 °C using both small and large mussels. Infection notably hampered filtration in large mussels, with a marginal impact on smaller ones. A positive correlation was found between infection intensity and mussel filtration capacity, though the infection had no discernible impact on respiration. Our consistent finding of an 11-12 % infection effect size across all experiments indicates a slight reduction in mussel filtration due to trematode infections. While the exacerbating effect of transient heat stress on the infection's impact on filtration was not statistically significant, future investigations should explore potential interactions with prolonged heat stress. Our findings underscore the nuanced ways in which parasitic infections can influence marine bivalve physiology, emphasizing the need for more comprehensive studies that incorporate environmental stressors, such as heat stress, to fully elucidate the impact of parasitism on marine ecosystem health and resilience. [Display omitted] [ABSTRACT FROM AUTHOR]

Purpose: To study the consequences of a fatiguing ultratrail run of 6 hours on self-optimizing capability during uphill and downhill (DR) running. Methods: The authors collected temporal stride kinematics and metabolic data in 8 (experimental group) male runners before and after the ultratrail run and in 6 (control group) male ultramarathon runners who did not run but stayed awake and performed normal, daily physical activities avoiding strenuous exercises over the 6-hour period. For each subject, preferred and optimal stride frequencies were measured, where stride frequency was systematically varied above and below the preferred one (±4% and ±8%) while running 3 conditions on level, 5% uphill, or 5% DR in a randomized order. Results: Preferred and optimal stride frequencies across grade, group, and time showed no significant differences (P ≥.184). Metabolic cost and the energetically optimum metabolic cost showed a grade × group × time interaction (P ≥.011), with an ∼11% increase in the 2 variables only during the DR bouts (P ≥.037). Conclusions: Despite maintaining similar dynamics of stride frequency adjustments during the DR bout, the experimental group was not able to optimize its gait. This suggests that the DR section of ultratrail runs can introduce a perturbing factor in the runners' optimization process, highlighting the need for incorporating DR bouts in the training programs of ultratrail runners to minimize the deleterious effects of DR on the energetically optimal gait. [ABSTRACT FROM AUTHOR]

Personalizing wearable robots by incorporating user physiological feedback can improve energy efficiency and comfort. However, many current personalization methods are specific to a particular device and often require reprogramming, making them less accessible. In this study, we present an open-source, device-independent personalization framework that allows for human-in-the-loop optimization. This modular framework includes cost functions and optimization algorithms that use a physiological response to optimize wearable robot parameters. We tested this framework in three case studies involving diverse subjects and wearable robots. The first case study focused on personalizing an ankle-foot prosthesis using indirect calorimetry feedback. This resulted in a 5.3% and 18.1% reduction in metabolic cost for walking for two individuals with transtibial amputation, compared to the weight-based assistance. The second case study personalized a robotic ankle exoskeleton for three different walking speeds using indirect calorimetry feedback for two subjects. The metabolic cost was reduced by 1%, 2%, and 5.8% for one subject and by 20.8%, 1.9%, and 19% for the other subject, compared to a generic assistance condition for increasing speeds. The third case study personalized gait parameters, specifically step frequency, using an electrocardiogram (ECG)-based cost function along with an optimization algorithm variant, resulting in a 43% reduction in optimization time for one non-disabled subject. These case studies suggest that our personalization framework can effectively personalize wearable robot parameters and potentially enhance assistance benefits.

In this study, we improve the existing model for force distribution over the muscles by considering reflex excitation as a nonvoluntary mechanism of our neuromuscular system. The improved model can explain the large difference between biological torque and experimentally optimized assistive torque profiles. Accordingly, we hypothesize that the “nonvoluntary nature of reflexive excitation highly restricts biological torque compensation”. The proposed model can also potentially characterize co-activation behavior in antagonistic muscles. Using our improved model, we introduce a well-posed framework to optimize the exoskeleton torque profile by metabolic rate minimization. Methods: To support our hypothesis and the proposed method, we utilize two experimental datasets for exoskeleton torque optimization; passive and active ankle exoskeletons. First, we use the passive exoskeleton dataset to identify the parameters of our model; i.e., reflex gains. Then, to validate the proposed model, the identified parameters are used to optimize the exoskeleton torque profile for the second experimental study. Limitations: It is assumed that joint kinematic and reflex gains are fixed with and without exoskeleton. Results: 74% of biological torque at the ankle joint cannot be experimentally compensated and the existing models can only explain that 17% of the biological torque is uncompensable. Our improved model can explain that 58% of biological torque is uncompensable (but still 16% remains unexplained). This achievement provides support for our hypothesis and shows undeniable contribution of reflex excitation for exoskeleton torque profile optimization.

This study focused on designing and evaluating a bilateral semi-rigid hip exoskeleton. The exoskeleton assisted the hip joint, capitalizing on its proximity to the body’s center of mass. Unlike its rigid counterparts, the semi-rigid design permitted greater freedom of movement. A temporal force-tracking controller allowed us to prescribe torque profiles during walking. We ensured high accuracy by tuning control parameters and series elasticity. The evaluation involved experiments with ten participants across ten force profile conditions with different end-timings and peak magnitudes. Our findings revealed a trend of greater reductions in metabolic cost with assistance provided at later timings in stride and at greater magnitudes. Compared to walking with the exoskeleton powered off, the largest reduction in metabolic cost was 9.1%. This was achieved when providing assistance using an end-timing at 44.6% of the stride cycle and a peak magnitude of 0.11 Nm kg−1. None of the tested conditions reduced the metabolic cost compared to walking without the exoskeleton, highlighting the necessity for further enhancements, such as a lighter and more form-fitting design. The optimal end-timing aligns with findings from other soft hip exosuit devices, indicating a comparable interaction with this prototype to that observed in entirely soft exosuit prototypes.

Plants store chemical defenses that act as toxins against herbivores, such as toxic isothiocyanates (ITCs) in Brassica plants, hydrolyzed from glucosinolate (GLS) precursors. The fitness of herbivorous larvae can be strongly affected by these toxins, causing immature death. We modeled this phenomenon using a set of ordinary differential equations and established a direct relationship between feeding, toxin exposure, and the net energy of a larva, where the fitness of an organism is proportional to its net energy according to optimal foraging theory. Optimal foraging theory is widely used in ecology to model the feeding and searching behavior of organisms. Although feeding provides energy gain, plant toxins and foraging cause energy loss for the larvae. Our equations explain that toxin exposure and foraging can sharply reduce larval net energy to zero at an instar. Since herbivory needs energy, the only choice left for a larva is to stop feeding at that time point. If that is significantly earlier than the end of the last instar stage, the larva dies without food. Thus, we show that plant toxins can cause immature death in larvae from the perspective of optimal foraging theory.

Using load-suspended backpacks to reduce vertical peak dynamic load exerted on humans can reduce metabolic costs. However, is it possible to further reduce metabolic cost by modulating dynamic load phase shift? If so, is anti-phase better than the others? In this study, we investigated the biomechanics, energetics and trunk response under phase shifts. Nine subjects wearing an active backpack with 19.4 kg loads walked on a treadmill at 5 km h−1 with four phase shift trials (T1–T4) and a load-locked trial (LK). Our results show that anti-phase trial (T3) assists ankle more and reduces the moment and gastrocnemius medialis activity, while T4 assists knee more and reduces the moment and rectus femoris activity. Due to the load injecting more mechanical energy into human in T3 and T4, the positive centre-of-mass work is significantly reduced. However, the gross metabolic rate is lowest in T4 and 4.43% lower than in T2, which may be because the activations of erector spinae and gluteus maximus are reduced in T4. In addition, T3 increases trunk extensor effort, which may weaken the metabolic advantage. This study provides guidance for improving assistance strategies and human–load interfaces and deepens the understanding of the energetics and biomechanics of human loaded walking.

Purpose: In the last decades, the energy cost assessment provided new insight on shuttle or constant running as training modalities. No study, though, quantified the benefit of constant/shuttle running in soccer-players and runners. Therefore, the aim of this study was to clarify if marathon runners and soccer players present specific energy cost values related to their training experience performing constant and shuttle running. Methods: To this aim, eight runners (age 34 ± 7.30y; training experience 5.70 ± 0.84y) and eight soccer-players (age 18.38 ± 0.52y; training experience 5.75 ± 1.84y) were assessed randomly for 6' on shuttle-running or constant-running with 3 days of recovery in-between. For each condition, the blood lactate (BL) and the energy cost of constant (Cr) and shuttle running (CSh) was determined. To assess differences for metabolic demand in terms of Cr, CSh and BL over the two running conditions on the two groups a MANOVA was used. Results: VO2max were 67.9 ± 4.5 and 56.8 ± 4.3 ml·min-1 kg-1 (p = 0.0002) for marathon runners and soccer players, respectively. On constant running, the runners had a lower Cr compared to soccer players (3.86 ± 0.16 J kg-1m-1 vs. 4.19 ± 0.26 J kg-1m-1; F = 9.759, respectively; p = 0.007). On shuttle running, runners had a higher CSh compared to soccer players (8.66 ± 0.60 J kg-1m-1 vs. 7.86 ± 0.51 J kg-1m-1; F = 8.282, respectively; with p = 0.012). BL on constant running was lower in runners compared to soccer players (1.06 ± 0.07 mmol L-1 vs. 1.56 ± 0.42 mmol L-1, respectively; with p = 0.005). Conversely, BL on shuttle running was higher in runners compared to soccer players 7.99 ± 1.49 mmol L-1 vs. 6.04 ± 1.69 mmol L-1, respectively; with p = 0.028). Conclusion: The energy cost optimization on constant or shuttle running is strictly related to the sport practiced. [ABSTRACT FROM AUTHOR]

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A hybrid training system (HTS) combining antagonist muscle electrical stimulation and voluntary muscle contraction has been developed using eccentric antagonist muscle contractions with electrical stimulation as resistance to voluntary muscle contractions. We devised an exercise method using HTS combined with a cycle ergometer (HCE). The purpose of this study was to compare the muscle strength, muscle volume, aerobic functions and lactate metabolism of HCE and a volitional cycle ergometer (VCE). A total of 14 male participants performed exercise on a bicycle ergometer for 30 min per session, 3 times per week for 6 weeks. We divided 14 participants into an HCE group (7 participants) and a VCE group (7 participants). The workload was set at 40% of each participant's peak oxygen uptake ( V. O2peak). Electrodes were placed over each motor point on the quadriceps and hamstrings. The V. O2peak and anaerobic threshold significantly increased before and after training when using HCE rather than VCE. The HCE group had significantly increased extension and flexion muscle strength at 180 degrees/s in post-training measurements over pre-training measurements. Knee flexion muscle strength at 180 degrees/s tended to increase in the HCE group compared to the VCE group. The quadricep muscle cross-sectional area was significantly increased in the HCE group compared to the VCE group. Additionally, the HCE group had significantly decreased maximal lactate, measured every 5 min during exercise at the end of study, between pre and post-training. Thus, HCE may be a more effective training method for muscle strength, muscle mass and aerobic functions at 40% of each participant's V. O2peak than conventional cycling exercise. HCE could be applied not only as aerobic exercise but also as resistance training. [ABSTRACT FROM AUTHOR]

The acute phase response (APR), coordinated by a complex network of components of the immune and neuroendocrine systems, plays a key role in early immune defense. This response can be elicited by a wide variety of pathogens at different intensities (frequencies and doses), hence experimental immune challenges with antigen gradients makes it possible to evaluate sickness progression with a better representation of what occurs in natural systems. However, how infection intensity could shape the APR magnitude in wild species is still poorly understood. Here, the immune response was activated in the subterranean rodent Ctenomys talarum with a gradient of lipopolysaccharide (LPS) doses (0.5, 1, 1.5, and 2 mg/kg of body mass). Changes in body temperature, body mass, and energetic costs were evaluated over time. We also assessed cortisol levels, white blood cells counts and neutrophil: lymphocyte ratios, before and after injection. Results indicated that during the APR, C. talarum shows a hyperthermic response, which is maintained for 6 h, with slight differences among antigen doses in the pattern of thermal response and body mass change. A maximum increase in body temperature of 0.83°C to 1.63°C was observed during the first hour, associated with a metabolic cost that ranged from 1.25 to 1.41 ml O2/gh. Although no clear effects of treatment were detected on leukocyte abundance, we found increments in neutrophil: lymphocyte ratios and gradual increases in cortisol levels corresponding to the intensity of simulated infection, which may indicate redistribution of immune cells and enhancement of immune function. An evident sickness syndrome was observed even at the lowest LPS dose that was characterized by an increase in body temperature, energy expenditure, and N: L ratio, as well as a dose‐dependent increase in cortisol levels. Although in nature, other constraints and challenges could affect the magnitude and costs of immune responses, C. talarum mounts an effective APR with a low increase in their daily energy expenditure, regardless of LPS dose. Research Highlights: Acute‐phase immune response in Ctenomys talarum involves fever and increases in metabolic rate, N:L ratio and cortisol levels. Fever entails a considerable energy cost. The higher the antigen dose, the greater the increase in cortisol levels. [ABSTRACT FROM AUTHOR]

This paper presents a set of test methods for evaluating the performance of active knee-assisted exoskeleton. A motor-driven assist model is established to calculate the theoretical assist efficiency of exoskeleton knee joints. Six healthy examinees are selected to measure comprehensive metabolic indexes of the human body and lower limb muscle activity under the condition of wearing and not wearing exoskeleton. The results of the comprehensive metabolic cost test of the human body showthat, compared with the experiment without wearing the exoskeleton, examinees wearing the exoskeleton see an increase of oxygen consumption of the human body by 3.21% on average, an increase of exhalation of carbon dioxide by 1.27% on average, and an increase of net metabolic power per unit mass by 2.80% on average. The results of the lower limb muscle activity test show that, compared with the experiment without exoskeleton, wearing exoskeleton can effectively reduce the muscle activity of rectus femoris, vastus lateralis and vastus medialis. A controlled weight-bearing test is designed, and the results prove that the weight of the exoskeleton itself cannot be ignored, which increases the comprehensive metabolic cost of the examinees. The exoskeleton can effectively reduce the activity of the wearer’s lower limb muscles, which is basically in line with the theoretical assisting efficiency of exoskeleton knee joints, and the overall power-assisting efficiency is not obvious due to the weight of the wearer. [ABSTRACT FROM AUTHOR]

Assessment of metabolic cost as a metric for human performance has expanded across various fields within the scientific, clinical, and engineering communities. As an alternative to measuring metabolic cost experimentally, musculoskeletal models incorporating metabolic cost models have been developed. However, to utilize these models for practical applications, the accuracy of their metabolic cost predictions requires improvement. Previous studies have reported the benefits of using personalized musculoskeletal models for various applications, yet no study has evaluated how model personalization affects metabolic cost estimation. This study investigated the effect of musculoskeletal model personalization on estimates of metabolic cost of transport (CoT) during post-stroke walking using three commonly used metabolic cost models. We analyzed walking data previously collected from two male stroke survivors with right-sided hemiparesis. The three metabolic cost models were implemented within three musculoskeletal modeling approaches involving different levels of personalization. The first approach used a scaled generic OpenSim model and found muscle activations via static optimization (SOGen). The second approach used a personalized electromyographic (EMG)-driven musculoskeletal model with personalized functional axes but found muscle activations via static optimization (SOCal). The third approach used the same personalized EMG-driven model but calculated muscle activations directly from EMG data (EMGCal). For each approach, the muscle activation estimates were used to calculate each subject's CoT at different gait speeds using three metabolic cost models (Umberger et al., 2003; Bhargava et al., 2004; Umberger, 2010). The calculated CoT values were compared with published CoT data as a function of walking speed, step length asymmetry, stance time asymmetry, double support time asymmetry, and severity of motor impairment (i.e., Fugl-Meyer score). Overall, only SOCal and EMGCal with the Bhargava metabolic cost model were able to reproduce accurately published experimental trends between CoT and various clinical measures of walking asymmetry post-stroke. Tuning of the parameters in the different metabolic cost models could potentially resolve the observed CoT magnitude differences between model predictions and experimental measurements. Realistic CoT predictions may allow researchers to predict human performance, surgical outcomes, and rehabilitation outcomes reliably using computational simulations.

Purpose: Unilateral skipping is an asymmetrical gait only exceptionally used by humans, due to high energetic demands. In skipping, the cost of transport decreases as speed increases, and the spring–mass model coexists with the vaulting pendular one. However, the mechanisms of energy transfers and recovery between the vaulting and the bouncing steps are still unclear in this gait. The objective of this work is to study how spatiotemporal and spring–mass asymmetries impact on metabolic cost, lowering it despite speed augmentation. Methods: Kinematics and metabolic rates of healthy subjects were measured during running and skipping on a treadmill at controlled speeds. Results: Metabolic power in skipping and running increased with similar slope but different intercepts. This fact determined the different behaviour of the cost of transport: constant in running, decreasing in skipping. In skipping the step time asymmetry remained constant, while the step length asymmetry decreased with speed, almost disappearing at 2.5 m/s−1. Leg stiffness in trailing limb increased with higher slope than in leading limb and running; however, the relative leg stiffness asymmetry remained constant. Conclusions: Slow skipping presents short bouncing steps, even shorter than the vaulting, impacting the stride mechanics and the metabolic cost. Faster speeds were achieved by taking longer bouncing steps and a stiffer trailing limb, allowing to improve the effectiveness of the spring–mass mechanism. The step asymmetries' trends with respect to speed in skipping open the possibility to use this gait as an experimental paradigm to study mechanisms of metabolic cost reduction in locomotion. [ABSTRACT FROM AUTHOR]

The aim of this study was to assess the metabolic cost (Cr) with marathon shoes (Adidas Adizero 3 [AA]) vs. track spikes (Nike Zoom Matumbo 3 [NZM]) on track. For this, five experienced runners were randomly assessed (NZM/AA) on a running track at 73% and 85% of best performance speed on 1500-m race. At first, speed (4.39 ± 0.53 m·s−1), Crs with AA and NZM resulted 3.63 ± 0.29 and 3.64 ± 0.43 J·kg−1·m−1 (+0.3% with NZM, effect size [ES] small and p = 0.951), respectively. Besides, at second speed (5.20 ± 0.18 m·s−1), Crs were 4.09 ± 0.28 and 4.07 ± 0.22 J·kg−1·m−1 (−0.5% with NZM, ES small and p = 0.919) with AA and NZM, respectively. It resulted in an increased Cr (+12.2%) between s1 and s2 with both shoe conditions (ES large and p = 0.009 and 0.011 with AA and NZM, respectively). There is a pattern yet to be confirmed for track spikes to become more beneficial at higher speeds (when duty factor becomes lower and therefore grip on track is crucial). [ABSTRACT FROM AUTHOR]

In human walking, power for propulsion is generated primarily via ankle and hip muscles. The addition of a 'passive' hip spring to simple bipedal models appears more efficient than using only push-off impulse, at least, when hip spring associated energetic costs are not considered. Hip flexion and retraction torques, however, are not 'free', as they are produced by muscles demanding metabolic energy. Studies evaluating the inclusion of hip actuation costs, especially during the swing phase, and the hip actuation's energetic benefits are few and far between. It is also unknown whether these possible benefits/effects may depend on speed. We simulated a planar flat-feet model walking stably over a range of speeds. We asked whether the addition of independent hip flexion and retraction remains energetically beneficial when considering work-based metabolic cost of transport (MCOT) with different efficiencies of doing positive and negative work. We found asymmetric hip actuation can reduce the estimated MCOT relative to ankle actuation by up to 6%, but only at medium speeds. The corresponding optimal strategy is zero hip flexion and some hip retraction actuation. The reason for this reduced MCOT is that the decrease in collision loss is larger than the associated increase in hip negative work. This leads to a reduction in total positive mechanical work, which results in an overall lower MCOT. Our study shows how ankle actuation, hip flexion, and retraction actuation can be coordinated to reduce MCOT. [ABSTRACT FROM AUTHOR]

In this study, we improve the existing model for force distribution over the muscles by considering reflex excitation as a nonvoluntary mechanism of our neuromuscular system. The improved model can explain the large difference between biological torque and experimentally optimized assistive torque profiles. Accordingly, we hypothesize that the “nonvoluntary nature of reflexive excitation highly restricts biological torque compensation”. The proposed model can also potentially characterize co-activation behavior in antagonistic muscles. Using our improved model, we introduce a well-posed framework to optimize the exoskeleton torque profile by metabolic rate minimization. Methods: To support our hypothesis and the proposed method, we utilize two experimental datasets for exoskeleton torque optimization; passive and active ankle exoskeletons. First, we use the passive exoskeleton dataset to identify the parameters of our model; i.e., reflex gains. Then, to validate the proposed model, the identified parameters are used to optimize the exoskeleton torque profile for the second experimental study. Limitations: It is assumed that joint kinematic and reflex gains are fixed with and without exoskeleton. Results: 74% of biological torque at the ankle joint cannot be experimentally compensated and the existing models can only explain that 17% of the biological torque is uncompensable. Our improved model can explain that 58% of biological torque is uncompensable (but still 16% remains unexplained). This achievement provides support for our hypothesis and shows undeniable contribution of reflex excitation for exoskeleton torque profile optimization. [ABSTRACT FROM AUTHOR]

Purpose: In the last decades, the energy cost assessment provided new insight on shuttle or constant running as training modalities. No study, though, quantified the benefit of constant/shuttle running in soccer-players and runners. Therefore, the aim of this study was to clarify if marathon runners and soccer players present specific energy cost values related to their training experience performing constant and shuttle running.Methods: To this aim, eight runners (age 34 ± 7.30y; training experience 5.70 ± 0.84y) and eight soccer-players (age 18.38 ± 0.52y; training experience 5.75 ± 1.84y) were assessed randomly for 6’ on shuttle-running or constant-running with 3 days of recovery in-between. For each condition, the blood lactate (BL) and the energy cost of constant (Cr) and shuttle running (CSh) was determined. To assess differences for metabolic demand in terms of Cr, CSh and BL over the two running conditions on the two groups a MANOVA was used.Results:V·O2max were 67.9 ± 4.5 and 56.8 ± 4.3 ml·min−1 kg−1 (p = 0.0002) for marathon runners and soccer players, respectively. On constant running, the runners had a lower Cr compared to soccer players (3.86 ± 0.16 J kg−1m−1 vs. 4.19 ± 0.26 J kg−1 m−1; F = 9.759, respectively; p = 0.007). On shuttle running, runners had a higher CSh compared to soccer players (8.66 ± 0.60 J kg−1 m−1 vs. 7.86 ± 0.51 J kg−1 m−1; F = 8.282, respectively; with p = 0.012). BL on constant running was lower in runners compared to soccer players (1.06 ± 0.07 mmol L−1 vs. 1.56 ± 0.42 mmol L−1, respectively; with p = 0.005). Conversely, BL on shuttle running was higher in runners compared to soccer players 7.99 ± 1.49 mmol L−1 vs. 6.04 ± 1.69 mmol L−1, respectively; with p = 0.028).Conclusion: The energy cost optimization on constant or shuttle running is strictly related to the sport practiced.

Introduction: Recent studies found that wearable exoskeletons can reduce physical effort and fatigue during squatting. In particular, subject-specific assistance helped to significantly reduce physical effort, shown by reduced metabolic cost, using human-in-the-loop optimization of the exoskeleton parameters. However, measuring metabolic cost using respiratory data has limitations, such as long estimation times, presence of noise, and user discomfort. A recent study suggests that foot contact forces can address those challenges and be used as an alternative metric to the metabolic cost to personalize wearable robot assistance during walking.Methods: In this study, we propose that foot center of pressure (CoP) features can be used to estimate the metabolic cost of squatting using a machine learning method. Five subjects’ foot pressure and metabolic cost data were collected as they performed squats with an ankle exoskeleton at different assistance conditions in our prior study. In this study, we extracted statistical features from the CoP squat trajectories and fed them as input to a random forest model, with the metabolic cost as the output.Results: The model predicted the metabolic cost with a mean error of 0.55 W/kg on unseen test data, with a high correlation (r = 0.89, p < 0.01) between the true and predicted cost. The features of the CoP trajectory in the medial-lateral direction of the foot (xCoP), which relate to ankle eversion-inversion, were found to be important and highly correlated with metabolic cost.Conclusion: Our findings indicate that increased ankle eversion (outward roll of the ankle), which reflects a suboptimal squatting strategy, results in higher metabolic cost. Higher ankle eversion has been linked with the etiology of chronic lower limb injuries. Hence, a CoP-based cost function in human-in-the-loop optimization could offer several advantages, such as reduced estimation time, injury risk mitigation, and better user comfort.

Abstract Background Reducing the energy cost of running with exoskeletons could improve enjoyment, reduce fatigue, and encourage participation among novice and ageing runners. Previously, tethered ankle exoskeleton emulators with offboard motors were used to greatly reduce the energy cost of running with powered ankle plantarflexion assistance. Through a process known as “human-in-the-loop optimization”, the timing and magnitude of assistance torque was optimized to maximally reduce metabolic cost. However, to achieve the maximum net benefit in energy cost outside of the laboratory environment, it is also necessary to consider the tradeoff between the magnitude of device assistance and the metabolic penalty of carrying a heavier, more powerful exoskeleton. Methods In this study, tethered ankle exoskeleton emulators were used to characterize the effect of peak assistance torque on metabolic cost during running. Three recreational runners participated in human-in-the-loop optimization at four fixed peak assistance torque levels to obtain their energetically optimal assistance timing parameters at each level. Results We found that the relationship between metabolic rate and peak assistance torque was nearly linear but with diminishing returns at higher torque magnitudes, which is well-approximated by an asymptotic exponential function. At the highest assistance torque magnitude of 0.8 Nm/kg, participants’ net metabolic rate was 24.8 ± 2.3% (p = 4e–6) lower than running in the unpowered devices. Optimized timing of peak assistance torque was as late as allowed during stance (80% of stance) and optimized timing of torque removal was at toe-off (100% of stance); similar assistance timing was preferred across participants and torque magnitudes. Conclusions These results allow exoskeleton designers to predict the energy cost savings for candidate devices with different assistance torque capabilities, thus informing the design of portable ankle exoskeletons that maximize net metabolic benefit.

Humans make a number of choices when they walk, such as how fast and for how long. The preferred steady walking speed seems chosen to minimize energy expenditure per distance traveled. But the speed of actual walking bouts is not only steady, but rather a time-varying trajectory, which can also be modulated by task urgency or an individual’s movement vigor. Here we show that speed trajectories and durations of human walking bouts are explained better by an objective to minimize Energy and Time, meaning the total work or energy to reach destination, plus a cost proportional to bout duration. Applied to a computational model of walking dynamics, this objective predicts dynamic speed vs. time trajectories with inverted U shapes. Model and human experiment (N=10) show that shorter bouts are unsteady and dominated by the time and effort of accelerating, and longer ones are steadier and faster and dominated by steady-state time and effort. Individual-dependent vigor may be characterized by the energy one is willing to spend to save a unit of time, which explains why some may walk faster than others, but everyone may have similar-shaped trajectories due to similar walking dynamics. Tradeoffs between energy and time costs can predict transient, steady, and vigor-related aspects of walking.

Objectives. This study evaluated the effects of wearing the Laevo v2.56 exoskeleton (Laevo, The Netherlands) on physiological parameters related to working load and metabolic cost (MC) during a lifting task, explored the variability in exoskeleton performance among users and determined whether perceived discomfort negatively correlates with a reduction in MC. Methods. Twenty participants completed a 4-min repetitive lifting task with/without the exoskeleton. Respiratory gases, heart rate, blood lactate and ratings of perceived exertion and experienced discomfort were collected, and MC was calculated. Results. Wearing the exoskeleton significantly reduced MC and oxygen uptake during the lifting task by 4.8 and 3.8%, respectively. Workload reduction occurred in 65% of the participants. Conclusion. The Laevo v2.56 exoskeleton reduced MC and workload in a repetitive lifting task in a subject-dependent manner. Future studies should focus on identifying factors that could cause performance variability such as user–robot interaction forces. [ABSTRACT FROM AUTHOR]

For exoskeletons to be successful in real-world settings, they will need to be effective across a variety of terrains, including on inclines. While some single-joint exoskeletons have assisted incline walking, recent successes in level-ground assistance suggest that greater improvements may be possible by optimizing assistance of the whole leg. To understand how exoskeleton assistance should change with incline, we used human-in-the-loop optimization to find whole-leg exoskeleton assistance torques that minimized metabolic cost on a range of grades. We optimized assistance for three non-disabled, expert participants on 5 degree, 10 degree, and 15 degree inclines using a hip-knee-ankle exoskeleton emulator. For all assisted conditions, the cost of transport was reduced by at least 50% relative to walking in the device with no assistance, which is a large improvement to walking comparable to the benefits of whole-leg assistance on level-ground (N = 3). Optimized extension torque magnitudes and exoskeleton power increased with incline. Hip extension, knee extension and ankle plantarflexion often grew as large as allowed by comfort-based limits. Applied powers on steep inclines were double the powers applied during level-ground walking, indicating that greater exoskeleton power may be optimal in scenarios where biological powers and costs are higher. Future exoskeleton devices could deliver large improvements in walking performance across a range of inclines if they have sufficient torque and power capabilities.

Management of heat stress and metabolic cost is vital for preventing any work-related disorders. In this paper, we integrated rest time formulations for heat strain and metabolic cost to develop a new lot sizing model for preventing heat exposure and work-related musculoskeletal disorders. The effects of heat strain and rest allowance on the total cost of the production supply process were investigated. The problem studied in this paper was the handling of the raw materials placed in boxes by manual material handling in order to supply the material requirement of a production line placed in a production area. For the realisation of the material handling transactions between the raw material warehouse and the production line, Electric Pallet Jack (EPJ) was used. The study covers the investigation of picking, storing, and carrying motions for the manual handling of these materials. The result of the analysis has shown that 8.5% savings were achieved by using the heat strain and rest time in comparison to the total cost of this part of the production line supply process with the ISO 7243 maximum metabolic work limit. Consequentially, the analysis results showed that the developed method demonstrated the viability of lot sizing model optimisation with multiple objectives and complex constraints with regards to the metabolic cost and heat strain.

For exoskeletons to be successful in real-world settings, they will need to be effective across a variety of terrains, including on inclines. While some single-joint exoskeletons have assisted incline walking, recent successes in level-ground assistance suggest that greater improvements may be possible by optimizing assistance of the whole leg. To understand how exoskeleton assistance should change with incline, we used human-in-the-loop optimization to find whole-leg exoskeleton assistance torques that minimized metabolic cost on a range of grades. We optimized assistance for three non-disabled, expert participants on 5 degree, 10 degree, and 15 degree inclines using a hip-knee-ankle exoskeleton emulator. For all assisted conditions, the cost of transport was reduced by at least 50% relative to walking in the device with no assistance, which is a large improvement to walking comparable to the benefits of whole-leg assistance on level-ground (N = 3). Optimized extension torque magnitudes and exoskeleton power increased with incline. Hip extension, knee extension and ankle plantarflexion often grew as large as allowed by comfort-based limits. Applied powers on steep inclines were double the powers applied during level-ground walking, indicating that greater exoskeleton power may be optimal in scenarios where biological powers and costs are higher. Future exoskeleton devices could deliver large improvements in walking performance across a range of inclines if they have sufficient torque and power capabilities. [ABSTRACT FROM AUTHOR]

Pest resistance of trees should be taken into account in future forest strategy planning and predicting risks of defoliation. The gypsy moth (GM) (Lymantria dispar L.) is a serious forest pest with outbreaking population dynamics. To estimate defoliation risk of the most widely distributed tree species in Balkan Peninsula and Europe (Turkey oak Quercus cerris L., European beech Fagus sylvatica L. and hornbeam Carpinus betulus L.), we carried out laboratory feeding trials and investigated their acceptability and suitability for GM development. We determined morphological and chemical attributes of these hosts as well as larval host preference, growth and nutritional indices. Preference, growth, and efficiency of food conversion into biomass were ranked in the order: Turkey oak ˃ European beech ˃ hornbeam. Hornbeam was the most avoided and showed the lowest conversion efficiency although, comparing to optimal oak host, its leaves were less tough, contained more water and exhibited similar values of nitrogen (index of protein content) and C/N ratio (index of investment into carbon based plant defense). We suggest that hornbeam and beech leaf chemical profiles should be further studied to reveal specific compounds that impose high metabolic cost to GM larvae. Moreover, additional research are needed to understand how intermediate hosts in natural populations affect GM outbreaks. [ABSTRACT FROM AUTHOR]