Mobility, motion, and exercise

Abstract

Sir Isaac Newton's 1686 "Philosophiae Naturalis Principia Mathematica"1 has repeatedly, and notably by biomedical scientists, been cited as the most influential single piece of scientific writing ever produced2: Movement, the laws pertaining to which are laid down in this work, is a fundamental characteristic of life, and as such, essential for various biological functions. Thus, life scientists across disciplines study processes that involve changes in location, from a molecular level to that of groups of complex organisms. Most complex organisms move from one place to another—in search for nutrition, new habitats, mates or to escape predators. Importantly, humans can convey complex information through speech, while animals must often also move their bodies to communicate. This is highly relevant for animal models with respect to translational physiology and has inspired numerous creative solutions by bioscientists to enable the study of, for example, the brain during movement.3 Translational biomedical research—still so, and across disciplines—relies on animal models.4, 5 When cognitive processes are studied, free movement is, despite the additional challenge of controlling or monitoring sensory input in a mobile subject, a prerequisite, as, for example, crucial behavioral patterns can only be observed and studied during free movement.3 Nevertheless, telemetry-based studies in freely moving animals are extremely valuable for many more areas of application in physiology, for example in cardiovascular research,6 studies of vegetative function and cardiovascular reflex responses7 or renal function.8 This is exemplified in recent studies: Wu et al. show the relevance of VIP+ miRNAs in sensory processing, olfactory neural activity, and "successful" olfactory function in rodents.9 Toledo et al10 did not primarily observe behavioral changes; however, the modulating effects of RVLM-C1 neurons on cardiorespiratory function at rest had never before studied in conscious, adult animals able to move freely, which adds great relevance to their results. As Pilowsky remarks, one crucial advantage of this study in awake animals, with reflexes intact, is the possibility to study changes in the sleep–wake cycle and normal breathing patterns, while, however, the effects of reflexes on the phenomena observed confounds the results and need to be taken into account critically.11 Baseline heart rate recordings at rest in freely moving animals12 are of particular value from a translational perspective, as they more closely resemble the natural situation. At the cellular level, movement occurs during cell division, intracellular transport, and the functioning of immune cells. Movement is also integral to growth, such as phototropism and gravitropism, whereby plants grow toward light and/or against gravity to optimize their conditions for photosynthesis and stability. Both growing and mature organisms respond to environmental stimuli: Tropisms in plants and taxis in microorganisms are examples of how movement helps adapt to environmental conditions. Organisms do not only move for homeostasis and survival, but also for reproductive processes: Sperms move toward the egg for fertilization in many animals, and pollen movement via wind, water, or pollinators is crucial for plant reproduction. Movement can thus be seen as a defining characteristic of living organisms that supports essential functions such as feeding, growth, reproduction, and adaptation to the environment. When we study movement, there is a multitude of technical terms being used. Most of them share the Latin root "movēre," which highlights their common origin related to the concept of moving or being in motion. These different terms warrant a closer look to avoid unwanted ambiguity, especially since database search engines, which rely on automatically generated thesauri for efficiency and speed, unfortunately automatically and often incorrectly synonymize these terms. Momentum is a fundame