Center of mass position does not drive energetic costs during climbing.

Climbing animals theoretically should optimize the energetic costs of vertical climbing while also maintaining stability. Many modifications to climbing behaviors have been proposed as methods of satisfying these criteria, focusing on controlling the center of mass (COM) during ascent. However, the link between COM movements and metabolic energy costs has yet to be evaluated empirically. In this study, we manipulated climbing conditions across three experimental setups to elicit changes in COM position, and measured the impact of these changes upon metabolic costs across a sample of 14 humans. Metabolic energy was assessed via open flow respirometry, while COM movements were tracked both automatically and manually. Our findings demonstrate that, despite inducing variation in COM position, the energetic costs of climbing remained consistent across all three setups. Differences in energetic costs were similarly not affected by body mass; however, velocity had a significant impact upon both cost of transport and cost of locomotion, but such a relationship disappeared when accounting for metabolic costs per stride. These findings suggest that climbing has inescapable metabolic demands driven by gaining height, and that attempts to mitigate such a cost, with perhaps the exception of increasing speed, have only minimal impacts. We also demonstrate that metabolic and mechanical energy costs are largely uncorrelated. Collectively, we argue that these data refute the idea that efficient locomotion is the primary aim during climbing. Instead, adaptations towards effective climbing should focus on stability and reducing the risk of falling, as opposed to enhancing the metabolic efficiency of locomotion.

Walking speeds are lower for short distance and turning locomotion: Experiments and modeling in low-cost prosthesis users.

Preferred walking speed is a widely-used performance measure for people with mobility issues, but is usually measured in straight line walking for fixed distances or durations, and without explicitly accounting for turning. However, daily walking involves walking for bouts of different distances and walking with turning, with prior studies showing that short bouts with at most 10 steps could be 40% of all bouts and turning steps could be 8-50% of all steps. Here, we studied walking in a straight line for short distances (4 m to 23 m) and walking in circles (1 m to 3 m turning radii) in people with transtibial amputation or transfemoral amputation using a passive ankle-foot prosthesis (Jaipur Foot). We found that the study participants' preferred walking speeds are lower for shorter straight-line walking distances and lower for circles of smaller radii, which is analogous to earlier results in subjects without amputation. Using inverse optimization, we estimated the cost of changing speeds and turning such that the observed preferred walking speeds in our experiments minimizes the total cost of walking. The inferred costs of changing speeds and turning were larger for subjects with amputation compared to subjects without amputation in a previous study, specifically, being 4x to 8x larger for the turning cost and being highest for subjects with transfemoral amputation. Such high costs inferred by inverse optimization could potentially include non-energetic costs such as due to joint or interfacial stress or stability concerns, as inverse optimization cannot distinguish such terms from true metabolic cost. These experimental findings and models capturing the experimental trends could inform prosthesis design and rehabilitation therapy to better assist changing speeds and turning tasks. Further, measuring the preferred speed for a range of distances and radii could be a more comprehensive subject-specific measure of walking performance than commonly used straight line walking metrics.

Understanding the experiences, needs, and strengths of people with incomplete spinal cord injury who can ambulate.

PURPOSE: To identify the experiences, needs, and strengths of people with incomplete spinal cord injury who can ambulate and to explore and discuss potential supports, services, and programs that would best assist them in the community. MATERIAL AND METHODS: In this qualitative descriptive study, interviews were the primary means of data collection. These were supplemented with descriptive standardized measures of function and life satisfaction. Qualitative data were analyzed thematically. RESULTS: Twenty-four participants were interviewed, their average age was 55 years and 46% were female. We identified three themes: 'I really couldn't go there', described the physical and social barriers experienced by participants, 'It'd be really nice to let the public know there are people out there like me' expressed the desire for greater social understanding of incomplete spinal cord injury, and 'I just don't quit', displayed the perseverance that participants demonstrated following their injury. CONCLUSION: Findings indicate service providers to improve the inclusion of ambulatory individuals with incomplete spinal cord injury in their programs. Suggestions include designing programs (community, healthcare, return to work, peer support), environments using the principles of universal design for people with incomplete spinal cord injury who ambulate, and increasing consideration of their perspectives.Implication for rehabilitation:People with incomplete spinal cord injury who can ambulate live with invisible impairments, which are often not acknowledged by family, friends, health professionals, and people with complete spinal cord injuryThey may feel excluded from activities (organized by spinal cord injury associations) that were originally designed for people with complete spinal cord injuryGreater awareness among health professionals, friends, family, and people with complete spinal cord injury of the needs of people with incomplete spinal cord injury who can ambulate is needed to increase their inclusion.

Metabolic cost and mechanical work of walking in a virtual reality emulator.

PURPOSE: The purpose of this study was to investigate the metabolic cost (C), mechanical work, and kinematics of walking on a multidirectional treadmill designed for locomotion in virtual reality. METHODS: Ten participants (5 females, body mass 67.2 ± 8.1 kg, height 1.71 ± 0.07 m, age 23.6 ± 1.9 years, mean ± SD) walked on a Virtuix Omni multidirectional treadmill at four imposed stride frequencies: 0.70, 0.85, 1.00, and 1.15 Hz. A portable metabolic system measured oxygen uptake, enabling calculation of C and the metabolic equivalent of task (MET). Gait kinematics and external, internal, and total mechanical work (WTOT) were calculated by an optoelectronic system. Efficiency was calculated either as WTOT/C or by summing WTOT to the work against sliding frictions. Results were compared with normal walking, running, and skipping. RESULTS: C was higher for walking on the multidirectional treadmill than for normal walking, running, and skipping, and decreased with speed (best-fit equation: C = 20.2-27.5·speed + 15.8·speed2); the average MET was 4.6 ± 1.4. Mechanical work was higher at lower speeds, but similar to that of normal walking at higher speeds, with lower pendular energy recovery and efficiency; differences in efficiency were explained by the additional work against sliding frictions. At paired speeds, participants showed a more forward-leaned trunk and higher ankle dorsiflexion, stride frequency, and duty factor than normal walking. CONCLUSION: Walking on a multidirectional treadmill requires a higher metabolic cost and different mechanical work and kinematics than normal walking. This raises questions on its use for gait rehabilitation but highlights its potential for high-intensity exercise and physical activity promotion.

Neural Endophenotype Assessment in Zebrafish Larvae Using Optomotor and ZebraBox Locomotion Assessment.

Due to the highly conserved genetics across the central nervous system, the easily probed visual system can act as an endophenotype for assessing neurological function. Here, we describe a psychophysics approach to assess visually driven swimming behavior in the high-throughput zebrafish genetic model system. We use the optomotor response test together with general locomotion behavior to assess neural processing while excluding motor defects related to muscle function.

Development of a Methodology for Low-Cost 3D Underwater Motion Capture: Application to the Biomechanics of Horse Swimming.

Hydrotherapy has been utilized in horse rehabilitation programs for over four decades. However, a comprehensive description of the swimming cycle of horses is still lacking. One of the challenges in studying this motion is 3D underwater motion capture, which holds potential not only for understanding equine locomotion but also for enhancing human swimming performance. In this study, a marker-based system that combines underwater cameras and markers drawn on horses is developed. This system enables the reconstruction of the 3D motion of the front and hind limbs of six horses throughout an entire swimming cycle, with a total of twelve recordings. The procedures for pre- and post-processing the videos are described in detail, along with an assessment of the estimated error. This study estimates the reconstruction error on a checkerboard and computes an estimated error of less than 10 mm for segments of tens of centimeters and less than 1 degree for angles of tens of degrees. This study computes the 3D joint angles of the front limbs (shoulder, elbow, carpus, and front fetlock) and hind limbs (hip, stifle, tarsus, and hind fetlock) during a complete swimming cycle for the six horses. The ranges of motion observed are as follows: shoulder: 17 ± 3°; elbow: 76 ± 11°; carpus: 99 ± 10°; front fetlock: 68 ± 12°; hip: 39 ± 3°; stifle: 68 ± 7°; tarsus: 99 ± 6°; hind fetlock: 94 ± 8°. By comparing the joint angles during a swimming cycle to those observed during classical gaits, this study reveals a greater range of motion (ROM) for most joints during swimming, except for the front and hind fetlocks. This larger ROM is usually achieved through a larger maximal flexion angle (smaller minimal angle of the joints). Finally, the versatility of the system allows us to imagine applications outside the scope of horses, including other large animals and even humans.

It is not just the work you do, but how you do it: the metabolic cost of walking uphill and downhill with varying grades.

The cost of walking and running on uneven terrain is not directly explained by external mechanical work. Although metabolic cost of transport increases linearly with gradient at uphill and downhill gradients exceeding 15%, at shallower gradients, the relationship is nonlinear, with the minimum cost occurring at ∼10% downhill grade. Given these nonlinear relationships between grade and metabolic cost, we projected a significant difference in the total metabolic cost of two walking conditions that required the same total external mechanical work be performed over the same total period of time; in one condition, time was spent walking to gradients that were fixed at +10.5% and -10.5% and in the other condition time was spent walking to gradients that varied from 0 to +21% and from -21 to 0%. We compared these two conditions experimentally, using an approach to quantify nonsteady-state oxidative energy expenditure. In line with our projection, the "variable" grade condition resulted in an 8.3 ± 2.2% higher total cumulative oxidative energy expenditure (J·kg-1) compared with the "fixed" grade condition (P < 0.001). Future work should aim to apply our approach across different gradients, speeds, and forms of locomotion; especially those that might provide insight into how humans optimize locomotion on variable grade routes.NEW & NOTEWORTHY We use a method for quantifying nonsteady-state energetics to show that regardless of whether the same total gain and loss in elevation (i.e., same total external mechanical work) is achieved over the same period of time, the total energy expenditure of different graded walking conditions can vary depending on the grades that are walked at and for how long they are walked at.

Validation of Metabolic Models for Estimation of Energy Expenditure During Isolated Concentric and Eccentric Muscle Contractions.

Musculoskeletal modeling uses metabolic models to estimate energy expenditure of human locomotion. However, accurate estimation of energy expenditure is challenging, which may be due to uncertainty about the true energy cost of eccentric and concentric muscle contractions. The purpose of this study was to validate three commonly used metabolic models, using isolated isokinetic concentric and eccentric knee extensions/flexions. Five resistance-trained adult males (25.6 ± 2.4 year, 90.6 ± 7.5 kg, 1.81 ± 0.09 m) performed 150 repetitions at four different torques in a dynamometer. Indirect calorimetry was used to measure energy expenditure during these muscle contractions. All three models underestimated the energy expenditure (compared with indirect calorimetry) for up to 55.8% and 78.5% for concentric and eccentric contractions, respectively. Further, the coefficient of determination was in general low for eccentric contractions (R2 < 0.46) indicating increases in the absolute error with increases in load. These results show that the metabolic models perform better when predicting energy expenditure of concentric contractions compared with eccentric contractions. Thus, more knowledge about the relationship between energy expenditure and eccentric work is needed to optimize the metabolic models for musculoskeletal modeling of human locomotion.

More than energy cost: multiple benefits of the long Achilles tendon in human walking and running.

Elastic strain energy that is stored and released from long, distal tendons such as the Achilles during locomotion allows for muscle power amplification as well as for reduction of the locomotor energy cost: as distal tendons perform mechanical work during recoil, plantar flexor muscle fibres can work over smaller length ranges, at slower shortening speeds, and at lower activation levels. Scant evidence exists that long distal tendons evolved in humans (or were retained from our more distant Hominoidea ancestors) primarily to allow high muscle-tendon power outputs, and indeed we remain relatively powerless compared to many other species. Instead, the majority of evidence suggests that such tendons evolved to reduce total locomotor energy cost. However, numerous additional, often unrecognised, advantages of long tendons may speculatively be of greater evolutionary advantage, including the reduced limb inertia afforded by shorter and lighter muscles (reducing proximal muscle force requirement), reduced energy dissipation during the foot-ground collisions, capacity to store and reuse the muscle work done to dampen the vibrations triggered by foot-ground collisions, reduced muscle heat production (and thus core temperature), and attenuation of work-induced muscle damage. Cumulatively, these effects should reduce both neuromotor fatigue and sense of locomotor effort, allowing humans to choose to move at faster speeds for longer. As these benefits are greater at faster locomotor speeds, they are consistent with the hypothesis that running gaits used by our ancestors may have exerted substantial evolutionary pressure on Achilles tendon length. The long Achilles tendon may therefore be a singular adaptation that provided numerous physiological, biomechanical, and psychological benefits and thus influenced behaviour across multiple tasks, both including and additional to locomotion. While energy cost may be a variable of interest in locomotor studies, future research should consider the broader range of factors influencing our movement capacity, including our decision to move over given distances at specific speeds, in order to understand more fully the effects of Achilles tendon function as well as changes in this function in response to physical activity, inactivity, disuse and disease, on movement performance.

Stop, then go! Rapid acceleration offsets the costs of intermittent locomotion when turning in Florida scrub lizards.

Intermittent locomotion is a common locomotor mode in small vertebrates. Pausing is thought to aid in locating a predator or prey, enhancing crypsis, lowering energy costs, and/or maneuvering around obstacles or toward a refuge. Many lizards flee predators by turning into potential refugia and subsequently pausing, presumably to conceal themselves. Intermittent locomotion may be associated with turning by allowing an animal time to assess its surroundings and/or decreasing the likelihood of losing its footing. In this study, we quantify locomotor performance and the use of intermittent locomotion in Florida scrub lizards (Sceloporus woodi) when navigating either a 45° or 90° turn. Lizards paused in 92.91% of all trials, and yet despite pausing, instantaneous speed was not different entering or exiting the turn. This result suggests that turning comes at minimal cost to forward speed for lizards under these conditions. Pausing during a turn, however, did slow speed in the turn. Interestingly, the speed in the turn did not differ in trials with a pause before the turn versus trials without a pause. The angle of the turn also had no effect on whether lizards paused. We found that lizards increase peak acceleration following pauses to compensate for lost speed during the pause, providing a mechanism that may minimize negative fitness effects associated with slow running speeds and allow intermittent locomotion to be such a common strategy in lizards.

Assessment of behavioural effects of three water-soluble polymers in zebrafish embryos.

The water-soluble polymers (WSPs) are widely used in many industrial applications and are present in several commonly used products due to their physical-chemical characteristics: as their name indicates, despite being synthetic polymers, they are able to solubilize in water. Because of this peculiar property, both the qualitative-quantitative evaluation in aquatic ecosystems and their potential (eco)toxicological effects have been neglected until now. The aim of this study was to evaluate the possible effects of three of the most widely used WSPs as polyacrylic acid (PAA), polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) on the swimming behaviour of zebrafish (Danio rerio) embryos after the exposure to different concentrations (0.001, 0.5, 1 mg/L). The exposure lasted from the eggs' collection up to 120 h post fertilization (hpf) also using three different light intensity (300 lx, 2200 lx, 4400 lx) to better evaluate any effects related to different gradients of light/dark transitions. In order to analyze individual behavioural changes in embryos, their swimming movements were tracked and a number of parameters for locomotion and directionality were quantified. The main results showed that all three WSPs resulted in significant (p ≤ 0.05) variations in different movement parameters, suggesting a possible toxicity scale: PVP > PEG â‰« PAA.

The estimation and evolution of hominin body mass.

Body mass is a critical variable in many hominin evolutionary studies, with implications for reconstructing relative brain size, diet, locomotion, subsistence strategy, and social organization. We review methods that have been proposed for estimating body mass from true and trace fossils, consider their applicability in different contexts, and the appropriateness of different modern reference samples. Recently developed techniques based on a wider range of modern populations hold promise for providing more accurate estimates in earlier hominins, although uncertainties remain, particularly in non-Homo taxa. When these methods are applied to almost 300 Late Miocene through Late Pleistocene specimens, the resulting body mass estimates fall within a 25-60 kg range for early non-Homo taxa, increase in early Homo to about 50-90 kg, then remain constant until the Terminal Pleistocene, when they decline.

A Serious Game for the Assessment of Visuomotor Adaptation Capabilities during Locomotion Tasks Employing an Embodied Avatar in Virtual Reality.

The study of visuomotor adaptation (VMA) capabilities has been encompassed in various experimental protocols aimed at investigating human motor control strategies and/or cognitive functions. VMA-oriented frameworks can have clinical applications, primarily in the investigation and assessment of neuromotor impairments caused by conditions such as Parkinson's disease or post-stroke, which affect the lives of tens of thousands of people worldwide. Therefore, they can enhance the understanding of the specific mechanisms of such neuromotor disorders, thus being a potential biomarker for recovery, with the aim of being integrated with conventional rehabilitative programs. Virtual Reality (VR) can be entailed in a framework targeting VMA since it allows the development of visual perturbations in a more customizable and realistic way. Moreover, as has been demonstrated in previous works, a serious game (SG) can further increase engagement thanks to the use of full-body embodied avatars. Most studies implementing VMA frameworks have focused on upper limb tasks and have utilized a cursor as visual feedback for the user. Hence, there is a paucity in the literature about VMA-oriented frameworks targeting locomotion tasks. In this article, the authors present the design, development, and testing of an SG-based framework that addresses VMA in a locomotion activity by controlling a full-body moving avatar in a custom VR environment. This workflow includes a set of metrics to quantitatively assess the participants' performance. Thirteen healthy children were recruited to evaluate the framework. Several quantitative comparisons and analyses were run to validate the different types of introduced visuomotor perturbations and to evaluate the ability of the proposed metrics to describe the difficulty caused by such perturbations. During the experimental sessions, it emerged that the system is safe, easy to use, and practical in a clinical setting. Despite the limited sample size, which represents the main limitation of the study and can be compensated for with future recruitment, the authors claim the potential of this framework as a useful instrument for quantitatively assessing either motor or cognitive impairments. The proposed feature-based approach gives several objective parameters as additional biomarkers that can integrate the conventional clinical scores. Future studies might investigate the relation between the proposed biomarkers and the clinical scores for specific disorders such as Parkinson's disease and cerebral palsy.

Human locomotion over obstacles reveals real-time prediction of energy expenditure for optimized decision-making.

Despite decades of evidence revealing a multitude of ways in which animals are adapted to minimize the energy cost of locomotion, little is known about how energy expenditure shapes adaptive gait over complex terrain. Here, we show that the principle of energy optimality in human locomotion can be generalized to complex task-level locomotor behaviours requiring advance decision-making and anticipatory control. Participants completed a forced-choice locomotor task requiring them to choose between discrete multi-step obstacle negotiation strategies to cross a 'hole' in the ground. By modelling and analysing mechanical energy cost of transport for preferred and non-preferred manoeuvres over a wide range of obstacle dimensions, we showed that strategy selection was predicted by relative energy cost integrated across the complete multi-step task. Vision-based remote sensing was sufficient to select the strategy associated with the lowest prospective energy cost in advance of obstacle encounter, demonstrating the capacity for energetic optimization of locomotor behaviour in the absence of online proprioceptive or chemosensory feedback mechanisms. We highlight the integrative hierarchic optimizations that are required to facilitate energetically efficient locomotion over complex terrain and propose a new behavioural level linking mechanics, remote sensing and cognition that can be leveraged to explore locomotor control and decision-making.

Carrying eggs uphill: are costs of reproduction stronger on steeper slopes?

Locomotor impairment during pregnancy is a well-documented cost of reproduction, but most empirical studies have not incorporated ecological complexity, such as locomotion on sloping inclines rather than horizontal surfaces. Biomechanical factors suggest that carrying a heavy burden-including shifts in the body's centre of mass-may impair locomotor ability even more when an animal is running uphill. If so, then measuring costs of reproduction on horizontal racetracks may underestimate these costs in nature for arboreal species. To evaluate this prediction, we measured the pregnancy-induced reduction in speed for jacky dragons (Amphibolurus muricatus) at inclines ranging from 0 to 45°. Both pregnancy and steeper slopes reduced lizard performance, but pregnancy did not exacerbate the locomotor decrement on steeper racetracks. An ability to maintain mobility on steep slopes during pregnancy may be a target of selection in arboreal taxa. To understand the evolutionary context of locomotion-based costs of reproduction, we also need studies on the relationship between organismal performance and ecologically relevant measures such as predation risk.

Linking muscle mechanics to the metabolic cost of human hopping.

Many models have been developed to predict metabolic energy expenditure based on biomechanical proxies of muscle function. However, current models may only perform well for select forms of locomotion, not only because the models are rarely rigorously tested across subtle and broad changes in locomotor task but also because previous research has not adequately characterised different forms of locomotion to account for the potential variability in muscle function and thus metabolic energy expenditure. To help to address the latter point, the present study imposed frequency and height constraints to hopping and quantified gross metabolic power as well as the activation requirements of medial gastrocnemius (MG), lateral gastrocnemius (GL), soleus (SOL), tibialis anterior (TA), vastus lateralis (VL), rectus femoris (RF) and biceps femoris (BF), and the work requirements of GL, SOL and VL. Gross metabolic power increased with a decrease in hop frequency and increase in hop height. There was no hop frequency or hop height effect on the mean electromyography (EMG) data of ankle musculature; however, the mean EMG of VL and RF increased with a decrease in hop frequency and that of BF increased with an increase in hop height. With a reduction in hop frequency, GL, SOL and VL fascicle shortening, fascicle shortening velocity and fascicle to MTU shortening ratio increased, whereas with an increase in hop height, only SOL fascicle shortening velocity increased. Therefore, within the constraints that we imposed, decreases in hop frequency and increases in hop height resulted in increases in metabolic power that could be explained by increases in the activation requirements of knee musculature and/or increases in the work requirements of both knee and ankle musculature.

Circulating blood eNAMPT drives the circadian rhythms in locomotor activity and energy expenditure.

Nicotinamide adenine dinucleotide (NAD+) is an essential cofactor of critical enzymes including protein deacetylase sirtuins/SIRTs and its levels in mammalian cells rely on the nicotinamide phosphoribosyltransferase (NAMPT)-mediated salvage pathway. Intracellular NAMPT (iNAMPT) is secreted and found in the blood as extracellular NAMPT (eNAMPT). In the liver, the iNAMPT-NAD+ axis oscillates in a circadian manner and regulates the cellular clockwork. Here we show that the hypothalamic NAD+ levels show a distinct circadian fluctuation with a nocturnal rise in lean mice. This rhythm is in phase with that of plasma eNAMPT levels but not with that of hypothalamic iNAMPT levels. Chemical and genetic blockade of eNAMPT profoundly inhibit the nighttime elevations in hypothalamic NAD+ levels as well as those in locomotor activity (LMA) and energy expenditure (EE). Conversely, elevation of plasma eNAMPT by NAMPT administration increases hypothalamic NAD+ levels and stimulates LMA and EE via the hypothalamic NAD+-SIRT-FOXO1-melanocortin pathway. Notably, obese animals display a markedly blunted circadian oscillation in blood eNAMPT-hypothalamic NAD+-FOXO1 axis as well as LMA and EE. Our findings indicate that the eNAMPT regulation of hypothalamic NAD+ biosynthesis underlies circadian physiology and that this system can be significantly disrupted by obesity.

Comparative Observation and Analysis of Preference Behavior Based on Three Types of Taxes and Locomotor Activity in the Goldfish, Carassius auratus.

Psychophysiological studies in vertebrates have focused on taxes as indicators of behavioral change. Actually, a considerable number of studies about anxiety-like and anti-anxiety-like behaviors involving geotaxis, scototaxis, and thigmotaxis have been conducted on fish. However, few analyses considering these behaviors based on taxes in fish have been conducted. Here, using goldfish, we measured the time spent in the bright or dark area of a horizontally long rectangular tank (HLRT), in the upper or lower area of a vertically long rectangular tank (VLRT), and in the central or edge area of a circular tank (CT), respectively, for the first 30 min and the last 30 min in a 3-h period after fish had been introduced to tanks. Dark, lower, and edge preference behaviors were observed for the first 30 min in all tanks. While dark and edge preference behaviors were maintained even for the last 30 min, the lower preference was lost. Swimming distance and the number of area crossings in each tank were also compared between the first 30 min and the last 30 min. Both decreased significantly or tended to decrease in the last 30 min in the HLRT and the CT, but no change was observed in the VLRT. These results suggest that, in goldfish, preference behavior is stable for a short time, and that environmental habituation may depend on the shape of the tank and the elapsed time.

Developmental and mitochondrial toxicity assessment of perfluoroheptanoic acid (PFHpA) in zebrafish (Danio rerio).

The potential toxicity of several perfluoroalkyl and polyfluoroalkyl substances (PFASs) to aquatic species are not well understood. Here, we assessed the sub-lethal toxicity potential of perfluoroheptanoic acid (PFHpA) to developing zebrafish. PFHpA was not acutely toxic to fish up to 50 µM and there was > 96% survival in all treatments. Exposure to 200 µM PFHpA decreased ATP-linked respiration of embryos. There was no evidence for ROS induction in 7-day-old larvae fish exposed to 0.1 µM or 1 µM PFHpA. Twenty-four transcripts related to mitochondrial complexes I through V were measured and atp06, cox4i1, and cyc1 levels were decreased in larval zebrafish in a concentration-dependent manner by PFHpA exposure. Locomotor activity was reduced in fish exposed to 0.1 µM PFHpA based on a visual motor response test. Anxiolytic-type behaviors were not affected by PFHpA. This study contributes to environmental risk assessments for perfluorinated chemicals.

Changes in Cost of Locomotion Are Higher after Endurance Cycling Than Running When Matched for Intensity and Duration.

INTRODUCTION: Cost of locomotion (C L ) has been shown to increase after endurance running and cycling bouts. The main purpose of this study was to compare, in the same participants, the effect of both modalities on C L when matched for relative intensity and duration. METHODS: Seventeen recreational athletes performed two incremental tests in running and cycling to determine the first ventilatory threshold then two 3-h bouts of exercise at 105% of threshold, with gas exchange measurements taken for 10 min at the start, middle and end of the 3 h to calculate C L . Neuromuscular fatigue during isometric knee extensor contractions and force-velocity profile on a cycle ergometer were assessed before and immediately after the 3-h trials. RESULTS: C L significantly increased at mid (+3.7%, P = 0.006) and end (+7.4%, P < 0.001) of exercise for cycling compared with start, whereas it did not change with time for running. Cardio-respiratory and metabolic variables changed similarly for cycling and running, therefore not explaining the time-course differences in C L between modalities. Changes in C L during cycling correlated significantly with loss of maximal force extrapolated from the force-velocity profile ( r = 0.637, P = 0.006) and changes in cadence ( r = 0.784, P < 0.001). CONCLUSIONS: The type of locomotion influences the effects of exercise on energy cost because 3 h of exercise at the same relative intensity caused a significant increase of cycling C L , and no changes in running C L . The changes in C L in cycling are likely due, at least in part, to fatigue in the locomotor muscles.