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An Empirical Study on a Domain Adaptation Framework for Personalized Exercise Intensity Prediction Using Smartwatch Sensing

  • Journal of Internet of Things and Convergence
  • Abbr : JKIOTS
  • 2026, 12(2), pp.79~85
  • Publisher : The Korea Internet of Things Society
  • Research Area : Engineering > Computer Science > Internet Information Processing
  • Received : March 3, 2026
  • Accepted : April 11, 2026
  • Published : April 30, 2026

JaeHyuk, Lee 1

1서울과학기술대학교 IT융합기술연구소

Accredited

ABSTRACT

This study investigated cross-subject generalization in smartwatch-based exercise intensity classification and proposed a lightweight domain adaptation framework under constrained sampling conditions. Exercise intensity was defined relative to individual peak heart rate (%HR_peak) using wrist photoplethysmography and inertial signals. A lightweight 1D-CNN was trained and evaluated using a subject-wise hold-out design to assess cross-subject domain transfer. An unsupervised test-time batch normalization (BN) recalibration strategy was applied to mitigate distribution mismatch. The model achieved strong validation performance (macro-F1 = 0.88, accuracy = 0.87). However, macro-F1 declined to 0.31 under cross-subject evaluation, indicating substantial degradation in detecting moderate- and high-intensity segments. BN adaptation improved macro-F1 to 0.35 and enhanced moderate-intensity detection. These findings demonstrate that cross-subject domain shift fundamentally constrains model generalization and that normalization-based lightweight adaptation can partially mitigate distribution mismatch. The proposed framework provides a scalable foundation for robust model development in wearable-based exercise monitoring.

Citation status

* References for papers published after 2024 are currently being built.

This paper was written with support from the National Research Foundation of Korea.