Classical control theory is often sufficient for dealing with changing loads, terrain and wear and tear. Rejecting unknown disturbances is what a control system does. No training is required. Perhaps somewhat less than impressive due to the choice of robotics platform, but:
Achieving natural behavior in a robot using neurally inspired hierarchical control Joseph W. Barter, Henry H. Yin Paper: https://www.biorxiv.org/content/10.1101/2021.01.22.427862v1
Movie 8: https://www.biorxiv.org/content/biorxiv/early/2021/01/25/202...
Movie 9: https://www.biorxiv.org/content/biorxiv/early/2021/01/25/202...