I am also trying to get this working, either locally or on colab. I have not succeeded yet.

I do not have enough karma to comment, so I post an answer.

It looks like mmpose was developed with PyTorch 1.8. Colab has a different PyTorch version.

Also, mmpose was developed with Python 3.8.

Going to the PyTorch old versions page (https://pytorch.org/get-started/previous-versions/), I noticed there is a version 1.8.2 with LTS support. See below for relevant commands to install the correct versions of all python packages.

Here is the command that I used (Conda on Linux):
conda install python=3.8 pytorch torchvision torchaudio cudatoolkit=11.1 -c pytorch-lts -c nvidia

(Snippet from: https://pytorch.org/get-started/previous-versions/)

v1.8.2 with LTS support

Conda

OSX

macOS is currently not supported for LTS.

Linux and Windows

# CUDA 10.2
# NOTE: PyTorch LTS version 1.8.2 is only supported for Python <= 3.8.
conda install pytorch torchvision torchaudio cudatoolkit=10.2 -c pytorch-lts

# CUDA 11.1 (Linux)
# NOTE: 'nvidia' channel is required for cudatoolkit 11.1 <br> <b>NOTE:</b> Pytorch LTS version 1.8.2 is only supported for Python <= 3.8.
conda install pytorch torchvision torchaudio cudatoolkit=11.1 -c pytorch-lts -c nvidia

# CUDA 11.1 (Windows)
# 'conda-forge' channel is required for cudatoolkit 11.1 <br> <b>NOTE:</b> Pytorch LTS version 1.8.2 is only supported for Python <= 3.8.
conda install pytorch torchvision torchaudio cudatoolkit=11.1 -c pytorch-lts -c conda-forge

# CPU Only
# Pytorch LTS version 1.8.2 is only supported for Python <= 3.8.
conda install pytorch torchvision torchaudio cpuonly -c pytorch-lts

# ROCM5.x

Not supported in LTS.

Wheel

OSX

macOS is currently not supported in LTS.

Linux and Windows

# CUDA 10.2
pip3 install torch==1.8.2 torchvision==0.9.2 torchaudio==0.8.2 --extra-index-url https://download.pytorch.org/whl/lts/1.8/cu102

# CUDA 11.1
pip3 install torch==1.8.2 torchvision==0.9.2 torchaudio==0.8.2 --extra-index-url https://download.pytorch.org/whl/lts/1.8/cu111

# CPU Only
pip3 install torch==1.8.2 torchvision==0.9.2 torchaudio==0.8.2 --extra-index-url https://download.pytorch.org/whl/lts/1.8/cpu

# ROCM5.x

Not supported in LTS.