All I do is walk (and climb stairs) and my legs look like they are carved out of solid oak. I mean, I get whistles from the ladies when I don my shorts, and I am over 50 and heavy set. That being said, I do both a lot, walking 6 miles over hills (with a small pack) almost every Sat & Sun, and 3-4 20-30 minute walks every day during the work-week. And, there’s the 2 looong flights up to my apartment, etc. And I have doing both for a couple of decades. My legs have plenty of muscle mass and strength.
Pick up a copy of Starting Strength by Mark Rippetoe if you can. He goes into great detail about squat form in that book - an entire 50-page chapter.
I haven’t competed in a triathlon in about 4 years, after my daughter was born I didn’t have the time to do all the training. I’m just a distance runner now (primary focus is 10k to 1/2 marathon distance), because I can always find time to run. When I did tri’s, I lifted with an upper/lower body split, and arranged my schedule so that lower body fell on swim days and upper on bike or run days. I also didn’t lift as heavy as I do now, as I considered lifting to be supplimentary to everything else. Nowadays, I schedule so that weights are followed either by a rest day or an easy day of running. I also try to separate the running and the weightlifting on the same day as much as possible, preferably running in the morning and lifting in the evening if I can manage it.
Yeah, I should’ve mentioned that studies have been mixed, the research is still out on the subject.
Here’s a page of weightlifting performance standards that breaks down typical performance by gender, body weight, and experience. Also, it’s often said that a good goal to shoot for is to be able to overhead press 75% of your body weight, bench your body weight, squat 1.5x body weight, and deadlift twice your body weight. Although, those are just averages and real individuals vary depending on their physiology and will hit some numbers easier than others.