Kinematic performance and muscle activation patterns during post-freeze locomotion in the Wood Frog (Rana sylvatica)

Wood Frogs (Rana sylvatica LeConte, 1825 = Lithobates sylvaticus (LeConte, 1825)) exhibit one of the most extreme freeze tolerance responses found in vertebrates. While extensive work is continuing to resolve the physiological mechanisms involved, few have studied the effects of freezing on locomotor performance. The ability to mount an appropriate locomotor response is vital, as locomotion can affect both survivorship and reproductive success. To investigate how the biomechanical processes during locomotion are altered following freezing, stroke cycle timings and kinematic performance were measured prior to and immediately following a freeze–thaw cycle. Additionally, the effects of cooling rate (0.3 versus 0.8 °C/h) were also assessed. While jumping and swimming performance were both reduced post-freeze, the effects were more pronounced during swimming, with observed reductions in velocity and distance travelled. Interestingly, these changes occurred largely independent of cooling rate. Altered stroke cycle timings and highly variable muscle activation/deactivation patterns suggest an impairment in muscle function as frogs continued to recover from the effects of freezing. This was supported by the physiology of frogs post-freeze, specifically, the persistence of elevated glucose levels in muscles important during locomotion. Collectively, these findings suggest that reductions in locomotor performance observed immediately following a freeze–thaw cycle are driven by alterations in muscle function.This work was supported by a NSERC Discovery Grant and a Canadian Foundation for Innovation Grant to EMS, and an ERASMUS MUNDUS – NOVA DOMUS CHEMEDPHO Action 2 Grant to JHSS. We also acknowledge the University of Barcelona and the University of Ottawa for their collaboration in the ERASMUS MUNDUS framework financed by the European Commission.Peer reviewe