This strategy for parameterizing helix-coil transitions was originally developed for alpha helices, whose hydrogen bonds occur between residues i and i+4 ; however, it is straightforward to extend the model to 3 10 helices and pi helices, with i+3 and i+5 hydrogen bonding patterns respectively. The complete alpha/3 10 /pi transfer matrix includes weights for transitions between helix types as well as between helix and coil states. However, because 3 10 helices are much more common in the tertiary structures of proteins than pi helices, extension of the Lifson–Roig model to accommodate 3 10 helices - resulting in a 9x9 transfer matrix when capping is included - has found a greater range of application. Analogous extensions of the Zimm–Bragg model have been put forth but have not accommodated mixed helical conformations.