Half Marathon Training while Lifting

[kmosher1]

Alright so I first want to address to whomever reads this that I have been working out for 1.5 years and have gained considerable weight throughout this span. Senior year of highschool I was 132lbs and 5'10, I am now close to 160lbs and 6'0. I decided since I have loved running since I was a kid that I would start training for a half marathon in June (Lake Placid). Already in week 3 of the training, I feel that my core and legs are becoming stronger but that I am losing weight and mass on my arms that I have tried building for 1.5 years.

Question to the BB'ing forum, what workout with weights should I do to supplement for this "feeling of loss" in my arms/ shoulders?

Thank you
-Kevin

EDIT: I have never been to the gym, I have simply used free weights my entire life (2 45lb stackable weights)

[gatovolador]

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