Contractions of isolated cat papillary muscle were studied using a lever system with an electromagnetic load which allowed an on-line computer to control the experiment and to process all the data. Isotonic force-velocity curves were determined in 17 cat papillary muscles; the curves were not hyperbolic. Force-velocity curves at constant time in the contraction and constant contractile element length were obtained with a systolic quick-release technique in 9 muscles. The velocity of shortening after release to low force was almost always less than the maximum recorded following release to slightly higher force. When quick-release force-velocity curves determined at different times in the contraction were compared, the maximum velocity occurred at approximately 60% of the time to peak isometric force. The fall in velocity at lower forces was more marked later in the contraction. The shape of the quick-release force-velocity curves was found to depend on muscle length. At a constant time of release, and ignoring the low force end of the curves, the quick-release force-velocity relationships were not hyperbolic at muscle lengths appreciably below optimum, but near the optimal length the curves were hyperbolic. When these quick-release force-velocity curves were corrected for the presence of an elastic element in parallel with the contractile and series elastic elements, it was found that none of the contractile element force-velocity curves was hyperbolic.

Environmental limits of animal life are invariably revised when the animals themselves are investigated in their natural habitats. Here we report results of a scientific mountaineering expedition to survey the high-altitude rodent fauna of Volcán Llullaillaco in the Puna de Atacama of northern Chile, an effort motivated by video documentation of mice (genus Phyllotis) at a record altitude of 6,205 m. Among numerous trapping records at altitudes of >5,000 m, we captured a specimen of the yellow-rumped leaf-eared mouse (Phyllotis xanthopygus rupestris) on the very summit of Llullaillaco at 6,739 m. This summit specimen represents an altitudinal world record for mammals, far surpassing all specimen-based records from the Himalayas and other mountain ranges. This discovery suggests that we may have generally underestimated the altitudinal range limits and physiological tolerances of small mammals simply because the world’s high summits remain relatively unexplored by biologists.

Swarms of insects instrumented with wireless electronic backpacks have previously been proposed for potential use in search and rescue operations. Before deploying such biobot swarms, an effective long-term neural-electric stimulus interface must be established, and the locomotion response to various stimuli quantified. To this end, we studied a variety of pulse types (mono- vs. bipolar; voltage- vs. current-controlled) and shapes (amplitude, frequency, duration) to parameters that are most effective for evoking locomotion along a desired path in the Madagascar hissing cockroach (G. portentosa) in response to antennal and cercal stimulation. We identified bipolar, 2 V, 50 Hz, 0.5 s voltage controlled pulses as being optimal for evoking forward motion and turns in the expected contraversive direction without habituation in ≈50% of test subjects, a substantial increase over ≈10% success rates previously reported. Larger amplitudes for voltage (1–4 V) and current (50–150 μA) pulses generally evoked larger forward walking (15.6–25.6 cm; 3.9–5.6 cm/s) but smaller concomitant turning responses (149 to 80.0 deg; 62.8 to 41.2 deg/s). Thus, the radius of curvature of the initial turn-then-run locomotor response (≈10–25 cm) could be controlled in a graded manner by varying the stimulus amplitude. These findings could be used to help optimize stimulus protocols for swarms of cockroach biobots navigating unknown terrain.

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