Appearance of... arm strength?

Last night I bought a cheap-o Sharpie knock-off in silver, and did my nails:

It worked only when I applied a top coat. Otherwise, it smeared/rubbed off with water.

I need a better white polish. This one was streaky. :/

In the morning, I went to my 30 Day Shakedown class and meeting. We did PiYo today, which is always a favorite. I had to don a band-aid on my foot (gross) and lunges aggravated the cut on my foot, but otherwise, it was amazing. Or rather, I was amazing!

I successfully did tricep push-ups/chaturangas! :) I was surprised since I couldn't do them very well last night. Maybe I was warmer today.

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Regular push-ups were doable too, on my toes!

*This picture makes me feel victorious. Look at her arms, and she's on her knees doing pushups.

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I stayed in this position, on my knee, the whole time. I looked up and the rest of the class, besides the instructor, were on their sides. I pushed through.

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I've never built up much arm strength so this is super exciting. Now only if I can figure out why my belly is not cooperating.

What's the strongest and weakest parts of your body?
What workouts do you do for your weakest parts?