Integrating biomechanics, energetics and ecology perspectives in locomotion

The 17 papers published in this thematic issue reflect our desire to improve the integration, thinking and scientific approaches of those working in the disciplines of comparative biomechanics, locomotory energetics and movement ecology. These are historically disparate disciplines which are converging on topics of mutual interest, often supported by complementary innovations in measurement technology and computational modelling. Compared with field studies, laboratory studies commonly involve the scientist selecting the activity of the subject or animal and measuring what happens using a variety of different techniques. This approach can attempt to recreate natural movement or examine how an animal responds to controlled changes in conditions. In animal studies, such an approach may reflect differences in speed or incline, whilst human participants can be given a much wider range of activities with, hopefully, greater experimental protocol compliance (at least in adults!). Nevertheless, a significant challenge to laboratory studies of animals is the ability to examine normal locomotor behaviour or to quantify performance limits (e.g. maximum speed or jump distance). In field studies, wild animals perform their natural behaviour, the instrumentation is more limited and the measurements are more indirect. However, the movement tasks far exceed what practicality or ethics committees would permit in the lab – from cheetahs hunting prey (Wilson et al., 2013, 2018) to life and death feats of endurance, such as bar-headed geese migrating over the Himalayas (Hawkes, 2025).

Unsurprisingly, these three disciplines have developed with scientists drawn from different backgrounds, research interests and, hence, perspectives on science, as well as the scale of biological interest. This variation is understandable given the differences in character, experience and skill set between those who live and operate effectively in the field and those who have trained to work in a laboratory setting. The adoption of novel technologies and the comparison and integration of results provides the opportunity to integrate and cross-fertilize these fields in new and transformative ways, motivating the proponents from each camp into the environment inhabited by the other. Therefore, the overarching goal of this Special Issue is to create a common thread across fields, identify novel insights, stimulate new approaches and guide future research directions in these vibrant fields – fields in which Journal of Experimental Biology has played a leading role in promoting.

Several themes emerge from the papers in this Special Issue, some of which are ones that might well be anticipated, whereas others emerge from reading through the Reviews and Commentaries published here. One anticipated theme, emphasized by several of the papers (Altshuler et al., 2025; Gemmell et al., 2025; Higham and Russell, 2025; Liao, 2025; Shepard, 2025), is the new scientific insights that can emerge from combining concepts and results from laboratory and field-based studies, i.e. ‘to bring the lab into the field and the field into the lab’. Another is the fundamental importance of innovative new technology [remote sensing devices – GPS, Global Navigation Satellite System (GNSS), inertial measurement units, etc.; see Glossary] that will facilitate bridging scientific investigations carried out in the laboratory and the field (Curtin et al., 2018; Gemmell et al., 2025; Goldbogen and Cade, 2025; Hawkes, 2025; Hetem et al., 2025; Shamoun-Baranes and Camphuysen, 2025; Wilson et al., 2013, 2018). Innovations in technology will stimulate new approaches and improve measures of animal performance in the field and in the lab. Finally, if one truly understands the locomotor biomechanics of an animal, one can strive to build a robot, using a biorobotics (see Glossary) approach, that recreates it.

Much of the innovation in all branches of the field of animal locomotion science has come from within the subject field itself, with technically astute biologists adopting and modifying gear to meet their needs. Considerable ingenuity, and exploitation of the items available from online vendors or at local hardware store has led to many exciting measurements. Over the years, such approaches have become easier with lower cost and higher performance low power electronics, the expansion of capable low-cost microcontrollers that are easier to program, and the burgeoning level of expertise in working with such equipment by generalist rather than specialist engineers. This is a trend that is increasing with the ‘Internet of Things’ drive for pervasive real-time sensing and will continue and broaden as more school and university graduates become software coding literate, hardware modules become widely available at low price and fabrication becomes more streamlined. An inspiring example is the design and fabrication of the AudioMoth (see Glossary) sound recorder family (Hill et al., 2018).

One recognized challenge in regard to technological innovation is how those innovators are funded and rewarded. Much of the innovation described here is underpinned by developments in the smart phone and fitness worlds, with either sensors providing raw data to process and interpret or commercial units that, particularly in the sporting world, will provide summary statistics often with limited access to the raw data. The former requires significant technical expertise whilst the latter may challenge the validation of the measurements used in analysis. Even with systems developed ‘in house’, a tension exists between innovation funding with the goal of commercial exploitation and a final polished product (one hopes) versus the more rapid (but less refined) ability to develop open-source software and hardware. The first requires a market, spin out funding and a thirst for business; the second a community with the expertise, commitment and largess to develop and share the technology and results for mutual benefit. This can be a particular problem when third-party licenses for hardware modules or software components limit what can be shared. Expanding efforts for the effective development of shared open-source software and hardware design will help to address this challenge.

A third anticipated theme expressed by several papers on this Special Issue topic is the need to marry theory with experimentation to develop interpretive models, inform statistical power analysis to underpin the design of field studies, guide future experimental approaches and identify novel hypotheses relevant to animal movement in relation to their ecology, which can be tested by new and original observations. One benefit of working in the field of locomotion biomechanics is that one's data analysis and interpretation are often bounded by Newtonian physics; meaning that a model can limit, for instance, the otherwise unbounded integration errors that can accumulate with inertial sensor data. Rigorous tests of a priori functional hypotheses are important, but studies should also seek to include tests of alternative hypotheses that emerge from acquired data (Altshuler et al., 2025), rather than simply adding data to commonly accepted phenomena [for instance, the rise and fall of Lévy walks (see Glossary) as models of animal foraging patterns; Pyke, 2015].

In order to more effectively communicate ideas, findings and stimulate integration between the fields of biology, engineering and ecology, it will be critical to develop a common terminology for communicating across the fields. In this context, well-defined key words linked to papers can facilitate the ability of scientists from different fields to accurately extract their intended meaning and communicate their ideas and results to scientists working in more distant fields (see the Glossary, including a list of Key Words associated with papers in this Special Issue).

In the context of integrating field and laboratory studies, a critical theme that emerges from several papers in this issue is the need to select organisms for study that best enable this integration owing to size, location or other factors (Altshuler et al., 2025; Gemmell et al., 2025; Higham and Russell, 2025; Liao, 2025). Small animals are tractable for potentially lower budget study in laboratory-built environments, and for invertebrates, such studies are more amenable in terms of meeting ethics guidelines. However, in the context of locomotor efficiency and decisions about route choice, speed and timing when moving in natural environments, animals that move long distances in complex environments must also be studied (Curtin et al., 2018; Goldbogen and Cade, 2025; Hawkes, 2025; Hedenström, 2025; Hetem et al., 2025; Shamoun-Baranes and Camphuysen, 2025; Shepard, 2025). If these animals are large, they can carry considerable instrumentation payloads (Goldbogen and Cade, 2025; Wilson et al., 2013, 2018). But many bird (and invertebrate) migrants are small and can only carry a few grams (or less) of electronics. This has driven hardware and signal processing innovation, for instance through the use of geolocators (see Glossary) (Alerstam and Bäckman, 2018; McKinnon et al., 2013) that localize by day length and time of sunrise rather than using satellite-based localization (e.g. GPS) or the use of acoustic telemetry and pop-up tags (see Glossary) for field measurements of aquatic animals (Goldbogen and Cade, 2025; Hellström et al., 2022).

Another emerging theme is the potential conservation benefits that derive from studying a particular species or group of species in their habitat. This provides the opportunity to raise public and political awareness for the need to conserve the species' habitat, as well as the species itself. Conservation benefits can be reinforced by developing ‘citizen-science’ approaches to field ecology studies of animal movement in relation to biomechanics and energetics, as well as making a case to funding agencies for the broader conservation impact of field-based studies. Studies of keystone species (Goldbogen and Cade, 2025: whales; Wilson et al., 2013, 2018: cheetah, gazelle, lion and zebra; Pontzer, 2025: primates) are likely to gain even greater public and conservation interest. More broadly, field-based studies of animal movement ecology, energetics and biomechanics have particular relevance for how habitats may shift geographically and respond to climate change. Further, these data become valuable to those who wish to understand the spread and evolution of the pathogens that cause global disease outbreaks (Hawkes, 2025).

An unexpected, though fundamental, theme that emerged from several of the papers is the relevance of U-shaped relationships with some midrange optimum. A mechanistic examination would suggest that many U-shaped relationships should exist and that animals will operate at the optimum minimum cost (the bottom of the U). In terms of animal movement, these connect to power output or energy use versus speed relationships that underlie swimming and flying over long distances (Di Santo and Goerig, 2025; Hedenström, 2025). However, collecting sufficient high-quality data to characterize both the location of the minimum and its depth (the additional cost of operating away from that optimal minimum) is challenging, with extreme outlying values (that may have limited physiological relevance) exaggerating the depth and narrowness of the statistical curve fit. In some situations, data are claimed to fit a U-shaped relationship when the actual experimental data are too sparse and noisy to support that fit, and a linear fit would be equally justified. U-shaped relationships also reflect other trade-offs relevant to the nature of the scientific process, such as those between technology and natural history, theory and experimentation, or movement ecology and trait-based physiology and biomechanics (Beltran et al., 2025). Just as a migrating bird, fish or whale may need to trade off speed versus energy use to minimize its cost of transport (see Glossary) and maximize its range, there is a similar need to balance trade-offs of differing scientific approaches to the study of animal biomechanics, energetics and movement in an ecological context.

With respect to the energetics of animal movement, there is considerable need for identifying the optima that drive the speed choices that different species select in the context of how speed affects their cost of transport. Most generally, animals may be expected to favour minimizing their total energy cost across a range of activities. However, steady speed choices used by terrestrial animals are generally not well known for most species other than horses (Hoyt and Taylor, 1981), humans (Margaria, 1976) and at least one fish species (Cathcart et al., 2017). Additionally, as McAllister et al. (2025) note, minimizing energy use itself may well shape locomotor behaviour during unsteady locomotor tasks, even at short timescales. Furthermore, the energetics of animals moving at different speeds and gaits in the field are often only indirectly known or poorly assessed for swimming and flying animals (Di Santo and Goerig, 2025; Hedenström, 2025; but see Liao, 2025). This is particularly relevant for migratory species such as birds that must fly long distances to reach breeding and feeding grounds suitable for reproduction and survival (Hedenström, 2025; Shamoun-Baranes and Camphuysen, 2025), and which may need to avoid adverse weather conditions, arrive at a set time of day or the year, as well as for aquatic animals that must also deal with ocean warming, as well as acidification. Critical shifts in ecological timing owing to climate change will impact both the time required to fly a given distance as well as the energy required to migrate relative to energy reserves needed for successful breeding. In these long bouts of exercise, the rate of heat accumulation and dissipation, as well as water generation and loss, are also critical to how the animal interacts with its environment (Hetem et al., 2025).

Another emerging theme is that both biotic and abiotic factors interact with an animal's physiology to influence its movement behaviour. And, in turn, the energetic state of the animal will influence its decision-making and physiological behavioural response under natural field conditions that are likely to differ from those measured in the lab (Hetem et al., 2025; Shepard, 2025; Wilson et al., 2013), for example, in field versus laboratory thermoregulatory studies of cheetah hunting (Hetem et al., 2013; Taylor and Rowntree, 1973). Environmental variables, such as temperature or food availability and quality, interact with underlying physiological and biomechanical traits of the animal to influence an animal's movement decisions and movement paths (e.g. switch from low-quality foraging to green foraging patches or the need to seek shade or water; Hetem et al., 2025). This is particularly the case in stressful environments. Similarly, turbulence within natural aerial environments, as well as wind, can lead to substantial increases in flight costs (Shepard, 2025) or for fishes that must swim against flowing water (Liao, 2025). Anthropogenic activity such as wind farms that promote turbulence, both on land and offshore, are known to influence bird migratory routes and bird flight trajectories owing to avoidance of turbulent conditions. Because of its much greater density compared with air, water turbulence and flow strongly impact the movements and behaviour of aquatic animals, which can harness energy from flow for movement as well as benefit from sensing and foraging on concentrated food patches (Goldbogen and Cade, 2025; Liao, 2025). Further, the complex flow patterns of natural aquatic environments substantially alter the swimming behaviour of fishes, with a much broader diversity of swimming behaviours observed that are not found in the lab (Liao, 2025). Given that movement behaviour and route choice depend on decisions made from sensory cues that animals receive, neural recordings from wireless or tethered systems while animals behave (Cohen et al., 2023; Liao, 2025; Yartsev and Ulanovsky, 2013) represent a key opportunity for advancing these fields.

Studies of human locomotion not only show that humans favour walking and running speeds that minimize their cost of transport, but also that humans exhibit the ability to sense energy use and can adjust movement behaviours to optimize their energy use over short timescales (McAllister et al., 2025). This has led to an emerging field of ‘behavioural energetics’ in which energetic cost is not just an outcome of movement, but also plays a key role in shaping it, enabling humans to alter their gaits to minimize energy use across a broad array of locomotor tasks and in complex environments. Building on McAllister et al.’s (2025) findings, it seems likely to us that adopting a ‘behavioural energetics’ approach to evaluating the energetics of animal movement in the field will offer important new insights into their ecology. Biomechanical studies of human locomotion also provide the opportunity to link individual variation in locomotor energetics to underlying muscle–tendon function based on subject-specific musculoskeletal modelling (see Glossary) (Lichtwark et al., 2025), which has important clinical and sports biomechanics relevance. Historically, humans have also developed tools and strategies to improve locomotor performance as well as safety (Formenti et al., 2025). This has ranged from implements developed for skiing, skating and climbing to negotiate snow, ice and mountainous terrain, to armour for protection in battle. Modern athletics attests to the continued innovation of devices that enhance human competitive performance and para-athletics allows study of the direct substitution of prosthetics for elements of the musculoskeletal system. Bioengineered device innovation based on improved technology and software control also leads to the development of more robust and enhanced performance of assistive and biorobotics devices (see Glossary) (Badri-Spröwitz et al., 2022; Collins et al., 2015). Because human movement biomechanics and energetics share parallels with animal movement, studies of each can inform broader understanding and inspire innovative design of assistive devices and biorobots. One advantage of human movement studies is that the participant can communicate with the experimental team, which other animals cannot, offering the experimentalist additional insight into the cognitive and physiological effects imposed by the experimental regimen. Although a combination of human and non-human animal studies provides many opportunities to undertake complementary investigations using the strengths of working with humans compared with other animals, few labs commonly study both. Adding a robotics or prosthetics strand to a project enables an exciting additional level of hypothesis testing with real physical systems.

A final theme that emerges from several papers (Beltran et al., 2025; Hedenström, 2025; Pontzer, 2025; Shamoun-Baranes and Camphuysen, 2025) is the need to examine movement ecology, and its underlying biomechanical and energetic features, over longer-term seasonal and annual cycles, as well as life-history timescales. For example, over short timescales, locomotion may comprise a large fraction of an animal's daily energy expenditure, but over long timescales and over the human lifespan, the link between locomotor activity and daily energy expenditure may be more tenuous (Pontzer, 2025). And over evolutionary timeframes there is little discernible effect of human locomotor ecology on daily energy expenditure. More generally, environmental constraints on movement vary across seasons. Thus, to understand how energetics and biomechanics interact with an animal's movement ecology, it is necessary to do so over longer timescales and across different seasons. For migratory animals, the energy cost of migration is often considered to be high, but over the annual cycle, other demands on energy exist that may exceed those of migration, and animals can adopt diverse strategies to manage their energy costs (Shamoun-Baranes and Camphuysen, 2025). Additionally, the evolution of exceptional physiological traits of migrating birds, which enable them to fly at high altitude, also means that migratory birds can serve as disease vectors over long distances, which may interact with their ability to respond to climate-driven shifts in predators and prey (Hawkes, 2025).

Nearly all the papers published here explore the integration of biomechanics and energetics with the locomotor ecology of vertebrate animals. We acknowledge our own bias as vertebrate biologists to have left out those who seek to carry out integrative research in these fields on invertebrate animals. Only one invited paper examines how the fluid biomechanics and energetics of gelatinous (jellyfish) and other marine invertebrates interact with their movement ecology in the open oceans, which comprise 70% of the Earth's surface (Gemmell et al., 2025). Little is known about how these processes play out over timescales longer than minutes or hours. Longer-term migration patterns of this substantial zooplankton group are largely unknown. Nevertheless, as is readily apparent from the papers in this Special Issue, miniaturization and improved technology are opening the door to being able to conduct field studies of this group of aquatic invertebrates in the challenging nature of their oceanic environment, offering the potential to track movement patterns over longer timescales and across life-history stages (e.g. aquatic invertebrate larvae and larval fish). We are convinced that the rapid pace for improving and developing novel innovative technology and analytical software tools is certain to spur the advance of invertebrate studies, as they have for the vertebrate species reviewed here. These improvements, which benefit from human technology development for real-time biomechanical and energetic sensing, open the door for future studies of diverse groups of animals operating in the field or the laboratory. We are excited to see where the integration of these fields and the technology that drives them forward will be in 10 to 20 years' time. We hope that the papers in this issue stimulate novel insights and improved integration and communication among scientists working across the boundaries of biology, engineering and ecology.