It's impossible to manually add activities. For example, if I add a swim I took and press save, nothing happens. It isn't added at all. Even if it's just tracking my steps, it's dodgy. If I go for a 20 minute walk then stop for 5 minutes, then do another 20 minutes, it stops at the first 20 minutes. Sometimes a day later the second 20 minutes will be included, but not always.