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Cold exposure increases running [VO.sub.2 max] and cost of transport in goats. Am J Physiol Regulatory Integrative Comp Physiol 280: R42-R47, 2001.--We inadvertently subjected a group of goats to 5 mo of cold exposure (mean minimum temperature less than - 13 [degrees] C) during an experiment designed to examine the effects of training by daily running on one member of each sibling pair. During the three coldest months, the sedentary but cold-exposed goats experienced a 34% increase in maximal oxygen uptake ([VO.sub.2 max], P [is less than] 0.01) and a 29% increase in running speed at maximal (P [is less than] 0.05). When temperatures increased in the spring, both oxygen uptake and running speed decreased. We interpret these findings as evidence that cold is a sufficient stimulus to invoke the development of aerobic structures in muscle and that these structures subsequently can be utilized for the novel task of running. When the experiment was subsequently repeated without the cold exposure, running speed and [VO.sub.2 max] of trained animals increased less than in either group of cold-exposed animals. However, the cost of transport of these warm runners was lower than either group of cold-exposed animals (from 13-19%, P [is less than] 0.0001). Thus, although aerobic capacity was increased with acclimation to severe winter weather, cold-acclimated goats operated with lower efficiency during locomotion. shivering thermogenesis; nonshivering thermogenesis; muscle adaptability; cross-adaptation.

Reich, T. E., S. L. Lindstedt, P. C. LaStayo, and D. J. Pierotti. Is the spring quality of muscle plastic? Am J Physiol Regulatory Integrative Comp Physiol 278: R1661-R1666, 2000.--During locomotion, major muscle groups are often activated cyclically. This alternate stretch-shorten pattern of activity could enable muscle to function as a spring, storing and recovering elastic recoil potential energy. Because the ability to store and recover elastic recoil energy could profoundly affect the energetics of locomotion, one might expect this to be an adaptable feature of skeletal muscle. This study tests the hypothesis that chronic eccentric (Ecc) training results in a change in the spring properties of skeletal muscle. Nine female Sprague-Dawley rats underwent chronic Ecc training for 8 wk on a motorized treadmill. The spring properties of muscle were characterized by both active and passive lengthening force productions. A single 'spring constant' ([Delta]force/[Delta]length) from the passive length-tension curves was calculated for each muscle. Results from measurements on long heads of triceps brachii muscle indicate that the trained group produced significantly more passive lengthening force (P = 0.0001) as well as more active lengthening force (P = 0.0001) at all lengths of muscle stretch. In addition, the spring constants were significantly different between the Ecc (1.71 N/mm) and the control (1.31 N/mm) groups. A stiffer spring is capable of storing more energy per unit length stretched, which is of functional importance during locomotion. eccentric contraction; muscle spring; elastic energy; titin; stiffness

Eccentric ergometry: increases in locomotor muscle size and strength at low training intensities. Am J Physiol Regulatory Integrative Comp Physiol 278: R1282-R1288, 2000.--Lengthening (eccentric) muscle contractions are characterized by several unusual properties that may result in unique skeletal muscle adaptations. In particular, high forces are produced with very little energy demand. Eccentrically trained muscles gain strength, but the specific nature of fiber size and composition is poorly known. This study assesses the structural and functional changes that occur to normal locomotor muscle after chronic eccentric ergometry at training intensities, measured as oxygen uptake, that do not influence the muscle when exercised concentrically. Male subjects trained on either eccentric or concentric cycle ergometers for 8 wk at a training intensity starting at 54% and ending at 65% of their peak heart rates. The isometric leg strength increased significantly in the eccentrically trained group by 36%, as did the cross-sectional area of the muscle fiber by 52%, but the muscle ultrastructure remained unchanged. There were no changes in either fiber size, composition, or isometric strength in the concentrically trained group. The responses of muscle to eccentric training appear to be similar to resistance training. oxygen consumption; strength training