I quit going to the gym a few years ago. I could never get motivated enough to get there more than once a week, and I ended up spending a lot of money on a membership I seldom used. I liked the cross elliptical trainers best; those are the machines that work your legs and your arms (in a cross-country skiing way). But they were always in use, so that you ended up having to wait to use them. So, I'm now biking and walking as much as I can, having integrated those exercises into my daily life and routines--walking to and from work, biking to and from work, biking instead of taking the bus, walking instead of taking the car or the bus--those kinds of things. That's what works for me. I realize that I don't miss the gym at all. In fact, I wouldn't go back, because I realize that I enjoy being outdoors while I'm walking and biking. I missed being out in nature.
I decided recently that in addition to these activities, I wanted to strengthen my arms since I've never had much arm strength. Serendipitously, I came across a video and a website link that inspired me to start doing push-ups. Normally, I am a bit skeptical when it comes to books or shows that promise that after 30 days, you'll be in great shape, for example. But I decided to start doing push-ups. Over one month later, I actually do have muscles in my upper arms that weren't there before I started the push-ups. I can tell you that push-ups do work to build up arm muscles and to make your arms stronger. I don't know that I'll get to the point that the young lady got to in the video after 100 days of push-ups (I'd like to), but after one month, I have muscles that I never thought I'd have. She did it as part of the Give It 100 movement (https://giveit100.com/), and documented her progress on video each day. I'm challenging myself without documenting my progress each day. I'll keep on going, because I got results, and because I want to see how far I can actually go.
Here is the website link to Womanitely: 7 Exercises that will transform your body---http://womanitely.com/exercises-transform-your-body/. I'm doing some of the other recommended exercises as well. I can do them at home, whenever I want, and there's no pressure. Just do a few of them once a day. You'll see a difference after one month.
And here's the video that originally inspired me to try doing push-ups: