Activity data provided by the Whistle device includes the total activity in minutes per day and a visual activity intensity display (Fig. 2). This study revealed a strong correlation for total activity obtained by the two accelerometers. TAW is a single number and can be recorded (but not exported) from the Whistle application. TAW is also emailed weekly to the ‘owners’ of a specific dog which may provide another means of obtaining this data in clinical research. We also found a strong correlation for activity intensity data between the two devices. However, the method used to derive the intensity data from the Whistle is time-consuming and cumbersome, limiting the use of this feature.
The Whistle device pairs with any smartphone/tablet via a free application allowing dog owners to create a profile for their dog, set daily PA goals, track their dogs PA, log food consumption, track medication administration (as well as receiving medication reminders), add photos, and enter notes throughout the day. The application also allows for multiple owners to log in, track, and manage activity through their mobile device. PA data collected from the Whistle is synced hourly with the owners’ smartphone or tablet which the Whistle is linked to. This eliminates the need for device-removal for data retrieval and allows real-time monitoring of PA. Real-time monitoring and the collection of objective and subjective data in one location offers a wide variety of opportunities for future research/clinical use. This may include tracking of post-operative clinical progression, response to specific treatments (since all data is ‘time-stamped’) and two-way communication with veterinarians including the sharing of pictures (such as for evaluation of wound healing etc.). Furthermore, measurement of joined activity between people and dogs is feasible using the Whistle device and Jawbone wristband. This may be of interest for evaluation of the impact of the human-animal bond and activity on both, human and dog health [15–17].
We chose the Actical activity monitor for comparison since it is a widely researched accelerometer that has been previously validated for the use in dogs [2–4, 6, 10, 11] and cats . A recent study that evaluated the Actical in dogs found that there was 100 % specificity and 100 % sensitivity in distinguishing sedentary activity from walking activity and a 92 % specificity and 92 % sensitivity in distinguishing trotting activity from walking activity . Another study found that the Actical is highly effective in differentiating sedentary activity from various degrees of activity in healthy dogs moving on a treadmill . If the Whistle were to be used for activity intensity data collection, further investigations determining cut points between light, moderate, and vigorous activities may be indicated. Limitations of the Actical include its cost (at the time of writing priced at $450), the lack of real-time monitoring and the restriction to PA/energy expenditure measurement only. To access Actical data, the device must be physically removed from the protective housing/collar and placed onto the ActiReader, which must be connected to a PC. The data is then imported into the proprietary Actical Activity and Energy Expenditure analysis software and can be interpreted using this software or be exported into Microsoft Excel for further analysis. There are several disadvantages of the Whistle device including the lack of exportable data and battery life. As mentioned previously, to record TAW the researcher has to manually record this number either from the smartphone app or the weekly email sent to ‘owners’. The Whistle also uses proprietary software and the algorithms behind the data calculation are unknown. The battery life of the Whistle is approximately 7 days (compared to 240 days of the Actical), however, the device comes with a USB-charger for at-home use and charges within approximately 2 h. For long-term clinical studies the short battery life proposes a significant challenge for multiple reasons: Firstly, if owners forget charging their respective device, PA activity data recording is interrupted. Secondly, the dog’s activity during charging is not recorded. Lastly, while real-time data acquisition is a potentially useful feature, it eliminates the possibility of owner ‘blinding’ to their dog’s PA. Blinding would be feasible if owners were not allowed to pair their dog’s device, however, owner access to the smartphone app is necessary to check the device’s battery status. Since the battery lasts only a week, a study design where owners would be provided with a fully charged device would not allow for long-term outcome measurement. Furthermore, real-time monitoring is only feasible if the device is paired to the owner’s Wi-Fi network which requires some technical knowledge and a Bluetooth connection. This may limit participation of owners without Wi-Fi availability or the technical knowledge to perform the set-up.
The current study has several limitations. The Actical epoch length was set to 1 min whereas the Whistle is pre-set for an epoch length of 3 min. Since raw data was not available for the Whistle device, it is difficult to evaluate whether activities are recorded at the exact same moment. Data exploration suggested that less active dogs showed higher Whistle scores, however, this is difficult to confirm without availability of raw data. A second limitation is that all dogs participating in this study were large breed dogs. Therefore the results of this study may not apply to smaller dogs or cats. Only one device was used for this study, hence we can not comment on inter-device variability. Data evaluation for total activity data was performed over a 24-h time period. Previous studies have suggested a 7-day sampling interval for long-term clinical studies to account for differences in activity observed between week-days and weekend-days . However, the purpose of this study was comparison of the two devices rather than evaluation of the study participants themselves. Lastly, data evaluation was only performed for a 17-h time period for the intensity data evaluation. However, this is consistent with previous canine  and human studies  and since each time point is evaluated individually, this should not affect our results.