The reason is probably that there is a significant eccentric component to walking downhill in a weighted vest, and your elderly ass exceeded its recovery capacity therewith.
Rip,
I am in my early 50s and a couple of months ago I started adding some Prowler work along with weighted vest walking for conditioning on days I lifted. Doing the Prowler never seemed to affect my squat however everytime I walked with the vest my squat seemed to suffer either in form or in difficulty in lifting the weight. I laid off the vest and the lifts went well. I started back with the vest they started to suffer again.
I have quit using the vest and sticking to the Prowler ( no big deal) however I am curious as if there any reason physiologically that walking with a weighted vest (45 lbs) for about 30 minutes in some hilly areas that would have a negative on squats.
The reason is probably that there is a significant eccentric component to walking downhill in a weighted vest, and your elderly ass exceeded its recovery capacity therewith.