In human coordination studies information from the environment may not only pace rhythmic behavior, but also contribute to the observed dynamics, e.g. a phenomenon known as anchoring in the literature. For the paradigmatic case of bimanual coordination we study these contributions mathematically and develop a model of the interaction between the limb's intrinsic dynamics and environmental signals from a metronome in terms of oscillator equations. We discuss additive versus multiplicative metronome impact and show the latter to be more appropriate. Our model describes single limb-metronome interaction, as well as multilimb-metronome interaction. We establish a parametric stabilization term which preserves the characteristics of bimanual coordination and additionally explains the varying stability of movement under different metronome conditions, the frequency dependence of the amplitudes of finger movements, anchoring phenomena and geometries of phase space trajectories. Predictions of our model are tested against experimental observations.,