Hey Neil I am a personal trainer and I specialize in sports performance and injury prevention. At this point weightless training would put you at a calorie deficit that will lead to poor performance or injury. So don't worry about it!!

What you need to focus on is doing a small amount of work on each body part. Do not get extra sore!! You don't have the time needed to recover properly. The other aspect of training is the cardio. You should try doing some treadmill running, running in a field or track (it will be similar to some of your running at tough mudder), swimming, and biking.

Don't over do any aspect and rotate them so you aren't pounding joints or over using muscles.

3 days workout 1 day rest 2 days workout 1 day rest = 7 day cycle.

Believe it or not to push your output you need to eat more good carbs and proteins, specifically chicken or beef and rice or pasta. Fruits and veggies will also help a ton. And check out my page on how to hydrate.

If you want some exercises I have some basic ones on the page that will help you with your core strength.

The 2-3 days before you should load up on carbs, protein, and water.... not because you will store it but because you will repair the most right before the race so the body is the best it could be.

If you want more help let me know. I will offer online training.

Goodluck