Aloha & Howzit!
Changing your "focus" comes by a strong interest of something else but you need to be able to see the "big picture."
Your outside fitness activity can be asociated with your livelihood, this being a fireman in terms of maintaining an optimum fuctional capacity that can adhere to the demands the body needs to withstand.
You use the same body for work and the same body for your physical activities. Keep in mind, "the tools of your labor is your body...the source of its energy is called Health."
Okay - Losing Weight and Losing Strength?
Your goal of losing bodyweight and maintaining proper strength is not a hard task but no walk in the park either.
In Hawaii, we are taught that a key element in perpetuating good stength comes by "enduring". All that endures, gains and perpetuates strength.
Endurance is what prolongs one's physical-mental-emotional strength.
Endurace is liken to breathing for it be life giving it surely needs to be taken and taken in consistently. This is why we breathe to endure.
Anyway...
The more we endure the more we stay strong. (This does apply to your dualthon experience.)
As for losing the weight and decreasing strength, is actually illusionary-conditioning. Our mental strength does affect our actual physical strength.
How's this?
There is something called "training-weight", that, which helps to fuel the body through early strages of one's general training sessions and allows the "natural" inborn health mechanisims to gradually build, gain and increase to the level of the participant's primary goal(s).
A good example of this are olympic weightlifters, powerlifters and even gymnast who need to compete in their bodyweight catergory.
I have witnessed these various competitors start off with excessive bodyweight/good strength and by the time of competition, lose the training-weight and at the same token gain better strength. They did not let their "chattering mind" intefere with the translatation of their body's language regarding "losing weight means losing strength."
When we are truly connected to why and what it is we do we our inner bodies health and outer fitness application we then recongize the "the bigger picture" of the right kind of physical exercise routine works.
Now before ending this, you being a fireman knows that what perpetuates fire is oxygen consumption. The more air the more the fire lives.
When there is no oxygen/air, the fire cannot survive.
When you take to your exercises and there is incorrect breathing pattern, your inner bodies become "oxygen-deprived" and your body's ability to endure is cut short.
Be aware of what is going on inside of you as well as what is happen outside of you. This will be vital and benefiting with the goals you set and wish to achieve.
Oh by the way, I use to teach Fire Science students and firemen Health Education and Physical conditioning courses and work with various athletes on their general and specific training methods.
Alrighty, I do hope my babbling on did at least give you some awarenss and ideas about your training.
Be Safe Out there & Good Health To You!
ALOHA!
mikey q.