## 2 The AAL Prototype CARIMO for Home Care Service Users  
According to the online catalogue for AAL products, the majority of AAL systems address \"health & care,\" \"living & buildings,\" or \"safety & security.\" Only a few relate to supporting and strengthening \"vitality & abilities,\" particularly the \"physical abilities\" of older people [21]. Maintaining the abilities of older people by fostering physical activities, such as walking or exercising, promotes healthy aging, delays the onset of disabilities, and postpones frailty [22; 23]. Being physically active can maintain mobility and thus postpone the demand for long-term care. Hence, physical activity is an important factor for active aging, allowing older adults (even with dependencies) to age in place and participate in social life [22; 24; 25].  
On that account, the \"Active Assisted Living Programme\" project \"CareInMovement--CiM\" developed CARIMO, an ICT-based system to promote physical activities for home care service users in Austria and Italy. Home care service users are older, care-dependent people living at home and receiving professional support to better cope with (instrumental) activities of daily living, such as getting dressed, bathing, cooking, or shopping. The CARIMO system was tested and evaluated in an eight-month field trial in Austria and Italy with test and control groups [26].  
Contrary to most AAL systems that address care, safety, or mobility issues [21], the AAL prototype CARIMO was primarily designed to maintain the physical abilities of home care service users by fostering _physical activities_, such as walking or exercising. It complements the few apps available for seniors, such as \"Fitivity Senior Fitness\" or \"Daily Senior Fitness Exercise,\" as CARIMO was especially tailored to older, care-dependent people living at home. To assign suitable fitness exercises to this target group, sport scientists developed a test [27] to assess the physical abilities of the users. Amongst others, the data collection involved testing muscle strength (e.g., grip strength test) and endurance (e.g., chair rise test), as well as physical limitations. Based on the assessment conducted by care workers, sport scientists assigned the participants to one out of two training levels (physically frail, physically dependent) [27]. The customized training plans for each participant were derived from their training level, and if available, data on physical limitations. Unlike existing fitness apps, CARIMO additionally provided an information and entertainment section especially prepared for older, care-dependent people to provide stimuli for the body and the mind [26].  
CARIMO differed from other AAL physical training prototypes for older people in three areas: intention for use, devices used, and the size and duration of the trial. First, a low-threshold exercise program developed for care-dependent people living at home offered a multi-component training program to improve coordination, strength, balance, and endurance [27] rather than training selected parts of the body, such as training using a treadmill [28] or ergometer [29; 30]. Second, it applied two commercially available, comparatively low-cost components (with prices expected to fall over time) and thus did not require expensive fitness equipment, sensors, or computing hardware [28; 29; 30; 31]. Finally, compared to most of the previous work reporting on short-term tests and small sample sizes [29; 30; 31], CARIMO was tested in an eight-month field trial with about 100 participants.  
To incorporate the user requirements of home care service users, lead users of the target group were involved in all development phases according to the human-centered design (HCD) approach [32]. To ensure acceptable usability and user experience of this prototype, we especially paid attention to appropriate text and button sizes, labeling of icons, high contrast, text and audio output (for fitness exercises), and a simplified user interface (UI) [33].