A customized AI-based machine learning model for evaluating participants' activities under a workshop setting

Human action recognition (HAR) in the workshop-style environment poses unique challenges due to class imbalance, fused action boundaries, and context dependence. This study proposes a multi-stage fine-tuning supervised framework for workshop-style HAR based on a 3D CNN, supplemented by an unsupervised post-assessment. A total of 208 clips (100 frames per clip) from two internal and two external datasets were used, along with 183 clips generated from 152 videos in a subset of the public UCF101 dataset for an add-on supplementary analysis. An I3D-ResNet50 (I3D_R50) backbone was used to examine a pilot model for domain adaptation and subsequently optimized for cross-context generalization. In Study 1, the I3D_R50 model with a customized 57-class prediction head was trained on the internal dataset, achieving a solid class- and cluster-level performance, however, spurious co-activations and limited separation among similar actions were observed. Study 2 refined sample allocation and data augmentation, and applied threshold tuning to evaluate within-context adaptation (Test 1) and cross-context generalization (Test 2). Multi-level analyses (class-, clip-, cluster-, and person-level) revealed moderate co-activation and semantic fusion within context, whereas cross-context generalization suffered from structure over-merging and semantic drift. As a post-assessment, Study 3 provided supplementary evidence that the model captured certain semantic co-occurrence relationships, although its performance remained constrained by limited IGE-TREE specific training samples and fine-grained behavioral categories. Limitations include insufficient samples, blurred temporal sequence, and context dependency. Future work could explore domain-adversarial alignment, pose-guided normalization, and temporal contrastive modeling, and selective merging of semantically similar actions to enhance semantic disentanglement and generalization.