Your cardiopulminary system is lacks the capacity of a normal human, or you have mostly "white meat" low endurance muscle rather than "red meat" high endurance muscle. This comes in two levels:
Level 1: You loose FP from physical exertion at twice the normal rate. This does not affect mental or supernatural FP loss. This is appropriate for cats, monitor lizards, and animals that can put out bursts of activity but not sustain it for very long. -3 points
Level 2: As above, but you recover FP at half the normal rate. This is appropriate for most reptiles and other cold blooded creatures. -10 points.
Reduced endurance can be taken with Fit, Very Fit, Unfit, or Very Unfit; the effects stack. A very fit crocodile (with Reduced Endurance 2 as part of its racial template) would lose and recover fatigue at the same rate as someone with neither trait, while a very unfit crocodile would lose fatigue at four times the normal rate and recover at one quarter the normal rate.