In a relatively inactive state and not exposed to wind, a bear does not expend extra energy even in cold weather.
Literal
Relatively active-not state [at-で], wind [to-に] exposed-not [if-ば], bear [topic-は] cold weather [in-において] extra energy [object-を] consume [nominalizer-こと] [topic-は] not-exist.
A dense scientific sentence. 比較的 means 'relatively.' 活動していない状態 means 'a state of not being active.' ~にさらされていなければ is a conditional passive: 'if not exposed to.' The overall structure presents a conditional scientific observation about bear energy conservation.