Deep Learning (DL) models, widely used in several domains, are currently often used for posture recognition. This work researches four DL architectures for posture recognition: Convolutional Neural Network (CNN), Long Short-Term Memory (LSTM), hybrid CNN-LSTM, and transformer. Agriculture and construction working postures were addressed as use cases, by acquiring an inertial dataset during the simulation of their typical tasks in circuits. Since model performance greatly depends on the choice of the hyperparameters, a grid search was conducted to find the optimal hyperparameters. An extensive analysis of the hyperparameter combinations' effects is presented, identifying some general tendencies. Moreover, to unveil the black-box DL models, we applied the Gradient-weighted Class Activation Mapping (Grad-CAM) explainability method on CNN's outputs to better understand the model's decision-making, in terms of the most important sensors and time steps for each window output. An innovative combination of CNN and LSTM was implemented for the hybrid architecture, by using the convolution feature maps as LSTM inputs and fusing both subnetworks' outputs with weights, which are learned during the training. All architectures were successful in recognizing the eight posture classes, with the best model of each architecture exceeding 91.5% F1-score in the test. A top F1-score of 94.31%, with an inference time of just 2.96 ms, was achieved by a hybrid CNN-LSTM.Impact Statement-Work-related musculoskeletal disorders (WRMSDs) are the most reported work-related health problem in the European Union. To get a wider picture of the working tasks with a higher WRMSD risk, we aim to decompose them by determining the postures necessary for their accomplishment. However, a manual record by the worker is neither practical nor feasible. Accordingly, automated human posture recognition and, particularly, DL models have shown huge potential, reaching high accuracies, but they suffer from a lack of transparency. Thus, in addition to their classification performance, we are concerned about these models' capacity to support their decisions with explanations. Therefore, we implemented Grad-CAM-based explainable CNNs, which also demonstrated their capacity to reach high F1-scores. Besides, we combined CNN with LSTM in a hybrid model, and we let the network learn which subnetwork it should give more importance to decide the output.