ABSTRACT Ageing is associated with a higher net cost of transport of running (COTnet), reduced stiffness of the Achilles tendon and a decrease in plantar flexor force. As it reduces distal propulsion capacity, the latter has been suggested as the cause of a redistribution of joint work during running, a potential cause of the increase in COTnet. Eighteen young athletes and 18 master athletes were recruited. In the first session, maximal isometric plantar flexion moment and Achilles tendon stiffness were measured; in the second, participants ran two 6 min treadmill trials at 2.5 and 3.0 m s−1, where ground reaction forces, kinematics and gas exchange were recorded to compute COTnet, joint work and Achilles tendon strain energy. Master athletes exhibited a higher COTnet than young athletes at 2.5 m s−1 (estimated marginal mean±s.e. 4.02±0.11 and 3.81±0.11 J kg−1 m−1, respectively), and this difference was greater at 3.0 m s−1 (4.29±0.12 and 3.81±0.11 J kg−1 m−1, respectively). Master athletes exhibited lower maximal isometric plantar flexor moment and, during running, lower ankle work and higher hip work. However, hip, knee and ankle work were not associated with COTnet, and Achilles tendon strain energy did not differ between groups. These findings show that the higher COTnet in master athletes coincides with a distal-to-proximal redistribution of joint work and lower Achilles tendon force, while a tendency toward lower tendon stiffness may have helped preserve tendon strain energy despite reduced loading. Whether these age-related adaptations contribute to the higher COTnet remains to be established.
ABSTRACT With sophisticated behaviors, a flexible body and unique motor control, octopuses are compelling models for both biological and bio-inspired robotics. Their lack of a rigid skeleton allows them to undergo extreme deformations, letting them navigate tight apertures and narrow geometries, offering a biological solution to one of the most persistent challenges in robotics. However, how the animal organizes its arms and body to interact and adapt to environmental constraints remains unclear. Here, we examined octopus behavior when squeezing through small apertures to identify the underlying transition strategies. We characterized a consistent ‘3-step’ or ‘4-step’ strategy with progression: probing, shifting 3–5 arms and squeezing. Strategy selection is governed by aperture size, and in smaller openings, non-shifted arms and mantle are squeezed separately, adding an additional step. These findings provide insights into mechanisms of octopus squeezing behavior and offer a robust biological blueprint for the design of next-generation bio-inspired soft robots.
Embryonic development in ectotherms is strongly shaped by temperature, yet the multivariate nature of metabolism complicates attempts to link local thermal environments to developmental physiology and energetic costs. In this study, we examined embryonic heart rate, metabolic rate (V˙CO2), and developmental time in two populations of the prairie lizard, Sceloporus consobrinus, from a cool, northern versus a warm, southern environment. Eggs from each population were incubated at 25 and 31°C to test for countergradient variation in developmental physiology and assess how populations differentially use these physiological pathways in relation to developmental cost and time. To that end we evaluated predictions of developmental cost theory, which posits that the energetic cost of development is a product of metabolism and developmental time, with natural selection acting on each to minimize developmental costs, although both phenotypes respond to temperature differently. Developmental time decreased with increasing temperature in both populations, but embryos from the cool environment developed faster overall, consistent with countergradient variation. Across populations and temperatures, heart rate and metabolic rate were dissociated: at the warmer incubation temperature, cool-population embryos exhibited higher heart rates but lower metabolic rates relative to the warm population, achieving faster development at lower estimated energetic cost, whereas reliance on increased metabolic rate in the warm population produced slower development and higher costs. These results show that populations can evolve distinct combinations of physiological traits to meet similar developmental challenges and underscore the complex nature of metabolism as a multivariate trait when predicting ectotherm responses to thermal variation.
