GPFD-Net: A Geometry-Pose Frequency Decoupling Network for Privacy-Preserving Human Action Recognition in Healthcare

Human Action Recognition (HAR) holds significant application value in healthcare informatics, facilitating tasks such as clinical diagnosis and rehabilitation monitoring. Point cloud sequences have emerged as a pivotal modality for balancing privacy preservation with high-fidelity geometric structural representation, ensuring anonymity while retaining critical 3D behavioral information. However, existing point cloud sequence encoding methods struggle to precisely encode micro-geometric details and macro-pose contours within the spatial dimension, as well as the dynamic heterogeneity of actions within the temporal dimension. These limitations impede the realization of high-precision clinical motion analysis. To address these challenges, we propose a Geometry-Pose Frequency Decoupling Network (GPFD-Net) for human action recognition. First, we design a Geometry-Pose Parallel-Collaborative Spatial Encoder (GPCSE). This module designs a parallel dual-stream architecture to explicitly capture and fuse complementary micro-geometric details and macro-pose contours, generating an informative geometry-enhanced pose feature sequence. Second, we introduce a Frequency-Decoupled Temporal Capturer (FDTC). This module adaptively decomposes the geometry-enhanced pose feature sequence into a smooth trend sequence and a transient detail sequence, which are subsequently processed by two parallel expert encoders via differentiated encoding to achieve robust human action recognition. Extensive experiments on four public benchmark datasets demonstrate that GPFD-Net achieves superior performance. The proposed method provides a novel paradigm for high-precision and privacy-preserving motion analysis in healthcare applications.