March 3, 2026Open Access

Development of preliminary validation of hitoe system: smartphone application and wearable device to monitor physical activity levels for cardiac rehabilitation

Key Points

The hitoe system shows satisfactory agreement with gas analyzer measurements for most physical activities.
High intraclass correlation coefficients indicate strong reliability for higher-intensity activities like cycling and lifting weights.

Structured PICO

Does the hitoe system accurately measure physical activity intensity compared to a standard gas analyzer in healthy adults?

Population

28 healthy adults (26 males, mean age 42.3 ± 11.2 years)

Intervention

hitoe system (smartphone application and wearable device) to monitor physical activity levels during 13 activities

Comparator

Standard gas analyzer

Outcome

Accuracy and reliability of exercise intensity measurement in metabolic equivalents (METs)surrogate

The hitoe wearable system provides reliable estimates of physical activity intensity during moderate-to-vigorous tasks, suggesting potential utility for personalized cardiac rehabilitation.

Abstract

This study aimed to develop and conduct a preliminary validation of the hitoe system, a novel smartphone application and wearable device designed to tailor exercise loads to individual exercise tolerance, with the goal of supporting personalized cardiac rehabilitation. A preliminary validation study was conducted involving 28 healthy adults (26 males, mean age 42.3 ± 11.2 years). Participants used the hitoe system to perform 13 activities, including sedentary tasks, household chores, walking, and cycle ergometer. Exercise intensity was measured in metabolic equivalents (METs) and compared with values obtained using a standard gas analyzer. Statistical analyses, including intraclass correlation coefficients (ICCs) and Bland-Altman analyses, were applied to assess the accuracy and reliability of the device. The hitoe system demonstrated satisfactory agreement with gas analyzer measurements across most activities. Bland-Altman analyses revealed that the majority of data points fell within ± 2.0 METs, indicating limits of agreement. High ICCs were observed for activities such as cycle ergometer (ICC = 0.797), vacuuming the floor (ICC = 0.693), and lifting a 5 kg weight (ICC = 0.614), reflecting strong reliability. In contrast, sedentary activities such as sitting (ICC = 0.033) and desk work (ICC = 0.144) showed lower ICCs, although the absolute differences between the two methods remained within approximately 1 MET. The preliminary findings suggest that the hitoe system may be useful for assessing physical activity intensity, particularly during higher-intensity activities. The system may offer a promising tool for real-time feedback and tailored exercise prescription in cardiac rehabilitation. Further studies involving patients with cardiovascular diseases are warranted to validate these preliminary results and enhance the system’s precision in clinical settings.

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