SUMMARYVoluntary loss of an appendage, or autotomy, is a remarkable behavior that is widespread among many arthropods and lower vertebrates. Its immediate benefit, generally escape from a predator, is balanced by various costs, including impaired locomotor performance, reproductive success and long-term survival. Among vertebrates, autotomy is most widespread in lizards, in which tail loss has been documented in close to 100 species. Despite numerous studies of the potential costs of tail autotomy in lizards, none have focused on the importance of the tail in jumping. Using high-speed video we recorded jumps from six lizards (Anolis carolinensis) both before and after removing 80% of the tail to test the hypothesis that tail loss has a significant effect on jumping kinematics. Several key performance metrics, including jump distance and takeoff velocity, were not affected by experimental tail removal, averaging 21 cm and 124 cm s Supplementary material available online at

Sonomicrometry and electromyography were used to determine how surface grade influences strain and activation patterns in the biceps femoris and vastus lateralis of the rat. Muscle activity is generally present during much of stance and is most intense on an incline, intermediate on the level, and lowest on a decline, where the biceps remains inactive except at high speeds. Biceps fascicles shorten during stance, with strains ranging from 0.07-0.30 depending on individual, gait, and grade. Shortening strains vary significantly among grades (P = 0.05) and average 0.21, 0.16, and 0.14 for incline, level, and decline walking, respectively; similar trends are present during trotting and galloping. Vastus fascicles are stretched while active over the first half of stance on all grades, and then typically shorten over the second half of stance. Late-stance shortening is highest during galloping, averaging 0.14, 0.10, and 0.02 in the leading limb on incline, level, and decline surfaces, respectively. Our results suggest that modulation of strain and activation in these proximal limb muscles is important for accommodating different surface grades.

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While in vitro studies of individual fibers, fiber bundles and whole muscles have greatly expanded our knowledge of the physiological properties and contractile mechanisms of skeletal muscle over the past 40·years, our understanding of how muscles actually operate in vivo is rather lacking in comparison. Consider the seemingly straightforward question of how much a given muscle changes length during any particular animal movement; for example, a limb muscle during a locomotor stride. Although detailed limb kinematics can provide some insight into the answer, the complex architecture, biarticular nature and/or in-series compliance of many muscles often render joint angular excursions unreliable as surrogates for determining muscle strain trajectories. Hence, unless more direct length-change measurements are made, we are unlikely to know the specific actions of a particular muscle during locomotion, nor can we appreciate more interesting issues that might arise if more complex questions are asked: how do speed or gait influence the way a muscle works; do

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