EcoGeoFemme mentioned the disadvantages of being small when trying to do fieldwork involving brute force. She's being coy about what activities were difficult, so I'll list a few that I ran across when I was doing fieldwork.
1. Hand augering
2. Lugging around 60+ pound sample coolers
3. Yanking generator pull cords (my arms are too short)
4. Lugging various awkward pieces of equipment (tanks, pumps, etc) long distances over bad terrain
5. Sampling or developing wells with a check valve (yanking water-filled tubing up and down) for a couple of hours
6. Opening flush-mounted wells that have been rusted shut
7. Cutting locks (often on wells, but sometimes elsewhere)
8. Unscrewing things that have been previously cranked on by Superman. And have rusted.
If you're doing fieldwork regularly, you tend to build up strength. I found that I got a lot stronger once I started hauling coolers around, as I've discussed. Also, I've discovered that I can do a lot more than I thought I was capable by simply gritting my teeth and throwing myself into it. Note that I don't recommend this method for lifting, but it works for almost everything else. But the #1 thing I use when I run into problems with stubborn wells/locks/gas regulators is leverage. Followed closely by a sledgehammer.
Drillers use "cheater bars" all the time - they grab a chunk of drill rod, slide it over the wrench they're using to break the rods or casing, and yank on the end. In a pinch, spare PVC piping, like the leftovers from well construction, will do. Similarly, I always try to have an extender for my socket wrench so that when I'm faced with a cross-threaded bolt on a flush-mounted monitoring well, I can really put my knee into it.
I'm not a masochist. If I spend more than a couple minutes flailing away at something, I'll get help if I can. But 95% of the problems that test my strength in the field can be overcome with persistence and a little engineering.