This article highlights the important role between physical activity and sleep, and utilised a common activity tracker to investigate this, which makes the ecological validity of this study very high, i.e. achievable for a large population. Moreover, the researchers also set a realistic walking goal, and found a positive correlation between sleep and activity, particularly in women.
However, this study did have some limitations: there was a disproportionate number of female participants, and the self-reported questionnaires for sleep quality and sleep duration were not described in detail. A standardised outcome measure, as well as using other technology (such as a sleep monitor, for instance) could have led to other or at least more detailed outcomes than just self-reporting.
All this aside, this article does make a compelling case for the importance of exercise for sleeping well, especially with the growing number of people worldwide who struggle with this each night.