Seasonal variations in the contractile behaviour of gastrocnemius muscles of Uromastix hardwickii.

Seasonal variations in the isometric activity of the isolated gastrocnemius muscle of Uromastix hardwickii was studied from winter to summer in Karachi, Pakistan. A constant 20 degrees C temperature was maintained during experimentation to avoid influence of this factor on seasonal changes. The twitch and tetanic tensions recorded at resting lengths showed a significant rise from winter to summer (p less than 0.0005) with a greater effect on tetanic tensions. The rate of rise of tensions also showed a significant elevation (p less than 0.0005) from winter to summer, while the duration of active state decreased by 66% during spring and summer. The results are discussed in terms of speed of summation of active state, cross bridge interaction, and characteristic expression of gastrocnemius muscle morphology on its mechanical behaviour from winter to summer.