BackgroundOlder adults are the fastest growing segment of the world‘s population. Recent evidence indicates that excessive sitting time is harmful to health, independent of meeting the recommended moderate to vigorous physical activity (PA) guidelines. The SITLESS project aims to determine whether exercise referral schemes (ERS) can be enhanced by self-management strategies (SMSs) to reduce sedentary behaviour (SB), increase PA and improve health, quality of life and function in the long term, as well as psychosocial outcomes in community-dwelling older European citizens from four countries, within a three-armed pragmatic randomised controlled trial, compared with ERS alone and also with general recommendations about PA.MethodsA total of 1338 older adults will be included in this study, recruited from four European countries through different existing primary prevention pathways. Participants will be randomly allocated into an ERS of 16 weeks (32 sessions, 45–60 min per session), ERS enhanced by seven sessions of SMSs and four telephone prompts, or a control group. Outcomes will be assessed at baseline, month 4 (end of ERS intervention), month 16 (12 months post intervention) and month 22 (18 months post intervention). Primary outcomes will include measures of SB (time spent sedentary) and PA (counts per minute). Secondary outcomes will include muscle and physical function, health economics’ related outcomes, anthropometry, quality of life, social networks, anxiety and depressive symptoms, disability, fear of falling, executive function and fatigue. A process evaluation will be conducted throughout the trial. The full analysis set will follow an intention-to-treat principle and will include all randomised participants for whom a baseline assessment is conducted. The study hypothesis will be tested with mixed linear models with repeated measures, to assess changes in the main outcomes (SB and PA) over time (baseline to month 22) and between study arms.DiscussionThe findings of this study may help inform the design and implementation of more effective interventions to reduce SB and increase PA levels, and hence improve long-term health outcomes in the older adult population. SITLESS aims to support policy-makers in deciding how or whether ERS should be further implemented or restructured in order to increase its adherence, impact and cost-effectiveness.Trial registrationClinicalTrials.gov, NCT02629666. Registered 19 November 2015.Electronic supplementary materialThe online version of this article (doi:10.1186/s13063-017-1956-x) contains supplementary material, which is available to authorized users.

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[1] The characteristics of the capture and freezing of supercooled water droplets by falling ice crystals were quantitatively investigated in a vertical supercooled cloud chamber of 10 m length at temperatures from À5 to À25°C. We present evidence that ice crystals can start the riming process at smaller sizes than previously reported. The results obtained show that the minimum dimension of ice crystals involved in riming is around 60 mm in diameter for hexagonal plates and 30 mm width and 60 mm length for columnar ice crystals. No substantial difference has been observed between the size distribution of the droplets accreted on the crystals and the cloud droplet size distribution, indicating that this process should not produce significant changes in the cloud droplet spectrum. The time elapsed between the ice crystal nucleation and the collection of crystals with droplet accretion was typically around 60 seconds. Citation: Á vila,