“…In addition, many HRSs utilize context-related features to determine opportune moments for delivering recommendations, of which location and time of day are the most prevalent (e.g., [24], [26]- [28], [33]), but calendar availability [27], [28] and users' momentary activities [24], [26] have also been used in a few examples. Considering user preferences (e.g., preferred PA modalities and times, dietary restrictions) [20], [25]- [27], [44], [45] and the usefulness or effectiveness of recommendations (either user-evaluated or inferred) [24], [28], [30], [35], [38], [43] are also quite common. Some HRSs consider mental state (e.g., stress level, mood) [28], [29], [47], social ties [27], [33], environmental conditions [22], [47], or personal traits [28]…”