Latshang, Tsogyal Daniela, Daniela Juliana Mueller, Christian Maurizio Lo Cascio, Anne-Christin Stöwhas, Katrin Stadelmann, Noemi Tesler, Peter Achermann, Reto Huber, Malcolm Kohler, and Konrad Ernst Bloch. Actigraphy of wrist and ankle for measuring sleep duration in altitude travelers. High Alt Med Biol. 17:194-202, 2016-Aims: Actigraphy might be convenient to assess sleep disturbances in altitude field studies. Therefore, we evaluated whether actigraphy accurately measures sleep duration in healthy subjects traveling to altitude. METHODS Fifty-one healthy men, aged mean ± standard deviation (SD) 27 ± 9 years, were studied during one night at Zurich (490 m), two nights at Davos Wolfgang (1630 m), and two nights at Jakobshorn (2590 m), in randomized order. Sleep duration measured by actigraphy, using a one-axis device at the wrist (n = 51), a three-axis device at the other wrist, and a three-axis device at the ankle (n = 22), was compared with corresponding total sleep time (TST) measured by polysomnography. RESULTS During 255 polysomnographic overnight studies, 449 paired actigraphic recordings were obtained. The median polysomnographic-derived TST ranged from 397 to 408 minutes. Actigraphic mean TST from wrists with one-axis and three-axis devices, and from ankle agreed well with polysomnographic values with a bias of +1, -7, +6 minutes, respectively. Corresponding limits of agreement (±2 SD of bias) were ±51, ±60, and ±59 minutes. Limits of agreement of mean TST over five nights by actigraphy and polysomnography were similar to the coefficient of repeatability (2 SD of mean) of polysomnographic TST, that is, ±31, ±38, and ±36 minutes versus ±34 minutes. CONCLUSIONS Actigraphy of the wrist or ankle by a one-axis or a three-axis device accurately estimates mean TST in groups of subjects and mean TST over several nights in individuals traveling to altitude. Therefore, actigraphy is valuable for assessing effects of altitude and other environmental influences on sleep duration during field studies over extended periods.