Marches frequently change keys once, modulating to the subdominant key, and occasionally returning to the original tonic key. If it begins in a minor key, it modulates to the relative major. Marches frequently have counter-melodies introduced during the repeat of a main melody. Marches frequently have a penultimate "dogfight" strain in which two groups of instruments (high/low, woodwind/brass, etc.) alternate in a statement/response format. In most traditional American marches, there are three strains. The third strain is referred to as the "trio".