This has been discussed before: https://news.ycombinator.com/item?id=29849033
It's a very, very bad study. If you want to know how bad: it would lend equal support to the hypothesis "everyone's heart rate drops 4.8bpm in one day".
It's a very, very bad study. If you want to know how bad: it would lend equal support to the hypothesis "everyone's heart rate drops 4.8bpm in one day".
It seems completely unsurprising that one would be slightly more relaxed the second day than the first.
Edit: In another comment someone mentions that this study was split the way I would have expected so hopefully they did account for schedule at least. Unfortunately I'm not seeing an easy way to access the whole paper to verify.