INTRODUCTION: Experiments concerning the influence of temperature on mammalian muscles have reported that contractile properties and metabolism are sensitive to the temperature. However, in the literature, there is no information concerning consequences of reduced temperature for the motor unit (MU) contractile properties. Based on available data, we expected predominantly a slowdown in twitch time parameters of three types of MUs. AIM(S): The main goal of this study was to determine how hypothermia modifies MUs contractile properties. METHOD(S): Experiments were performed on adult Wistar anesthetized rats. MUs were activated by electrical stimulation of single axons isolated from ventral roots of spinal nerves. Two groups of animals were tested: 1) control (at physiological temperature 37±1°C) and 2) hypothermia (at 25±1°C). RESULTS: We observed that hypothermia increased delay of twitch in FF and FR but not in S MUs. Furthermore, the twitch time was considerably prolonged in FF and FR MUs in contrast to S ones. The half relaxation time (HRT) was significantly slower in all types of MUs in the hypothermia group. The twitch force was lower in FF MUs, while in FR and S MUS we observed moderate differences between hypothermia and control groups. Finally, tetanus force was also significantly lower in FF, but we have not found significant differences in FR and S MUs. The twitch‑to‑tetanus ratio was considerably higher in hypothermia, indicating a reduced possibility of force regulation by changes in motoneuronal firing. CONCLUSIONS: Hypothermia dramatically reduced motor control processes and force regulation of MUs in skeletal muscles. The results indicated that FF and FR MUs are more sensitive to the influence of low temperature than S ones.
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