Fig. 6. Comparisons, in two horses trotting, of the patterns of vastus fascicle strain over the whole stride period at 3.0 m s^-1 in two different years. Implants were placed in approximately the same area of the vastus muscle in each animal. Each strain pattern represents the mean of ten consecutive strides. The variance ratio is a quantitative measure of the similarity of two waveforms. It can range from a value of zero (identical) to 1.0 (no similarity). These two horses represent the range of constancy (variance ratios in two different years) obtained in this study: (A) variance ratio=0.203 and (B) variance ratio=0.028. Constancy is the term used to describe the similarity between two different experiments and reliability the similarity between successive strides from the same experiment. Constancy and reliability are reported in Tables 5 and 6 for three horses and four speeds. These two horses exhibit the two different patterns of vastus strain shown in Fig. 2. Focusing on the stance phase (up to 40% of stride) it can be seen that the two patterns are reasonably similar in the two different years.