Foreground Detection of Mouse on Background Issues

Hello,

I have been trying my best to get an object tracking feature of Matlab to work on some video of a mouse that I have. It works decently at the moment, but it is not as accurate as I would like. Often the mouse appears misshapen or has some other deformities when analyzing the foreground mask. Attached are gifs of an example mouse video I was using, as well as an example of what the foreground produced. Below is some of my code I am using to create the foreground:

videoReader = vision.VideoFileReader(filename);
  videoPlayer = vision.VideoPlayer('Position',[200,200,500,400]);
  foregroundDetector = vision.ForegroundDetector('NumTrainingFrames', 500, ...
                  'InitialVariance', 0.05);
  blobAnalyzer = vision.BlobAnalysis('AreaOutputPort', false, ...
                  'MinimumBlobArea', 70);

    while ~isDone(videoReader)
        colorImage = step(videoReader);
        bw_file = rgb2gray(colorImage);

        % get background approximation of surface (lighting and stuff)
        background = imopen(bw_file,strel('disk',35));

        % Display the Background Approximation as a Surface
        ax = gca;
        ax.YDir = 'reverse';

        % Remove Background Approximation
        bw2 = bw_file - background;

        foregroundMask = foregroundDetector(bw2);
        foregroundMask = bwareaopen(foregroundMask, 15);
        foregroundMask = imfill(foregroundMask, 'holes');

Does anyone have any idea of how I can get the foreground to be more accurate?