Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…2002); (2) spike-frequency adaptation is elicited by phase 1 high-frequency spiking and acts to reduce spike rate during following depolarization
(Krans and Chapple 2005); (3) the dynamics of muscle shortening may change with motoneuron frequency and over time when activated (Chapple 1989b;…
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