A molecular dynamics simulation for a Kuhn and Grun polymer chain segment has been developed and compared with the theory. Agreement of the computer experiments and theory, including a short-chain adaptation of the theory due to Weiner, was for practical purposes exact. The work discovered that due to the basic assumption and inextensible bonds temperature, or thermal energy, is not isotropic in a Kuhn and Grun chain segment. This anisotropy increases with the relative extension r/nl. This should not occur in a real material, which is held together by potential energy rather than by mathematical constraints. In this regard, therefore, this theory, and possibly any theory which depends on fixed-length interatomic bonds, may not be a good approximation to reality with varying chain extension. Introducing a harmonic potential function which maintains the angle between bonds close to an equilibrium value theta(0), changes the force/extension relation of a chain segment such that the end-to-end length of the segment is finite at zero force. This modification, however, did not eliminate the anisotropic temperature problem caused by inextensible bonds.