ðiːz bɹˈɪdʒᵻz ɑːɹ sˈʌbdʒɛkt tə θˈɜːməl mˈoʊʃən wˌɪtʃ pɹɪvˈɛnts ðˌɛm fɹʌm ɐsˈuːmɪŋ ɐ fˈʊli ɛkstˈɛndᵻd kɑːnfoːɹmˈeɪʃən.
These bridges are subject to thermal motion which prevents them from assuming a fully extended conformation.