Rashi (explaining the mishna at the bottom of Shabbos 93b, and elucidated by yours truly here .) says that חי נושא אה עצמו/a living being carries itself means that a living being lightens itself. You may be (and, I daresay, should be ) asking yourself: What in the world does that mean? Perhaps you think it means "a living thing feels lighter... it can adjust itself and stuff." I respectfully submit that you should think again. First, Rashi does't say "makes itself feel lighter", but "makes itself lighter". Moreover, R' Moshe (Igros Moshe, O. Ch. IV, 90) explains that Rashi means that the כבדות/heaviness is less that expected for something of that משקל/weight and volume. Again, not "seems", just "is". You may argue that the "seems" is self-understood and obvious. I disagree; respectfully. Lastly, I think a mean-tempered cat (and what cat is not mean-tempered) is much easier to carry when bound. But, wait, there...
This is a paraphrase of the pasuk in t'hillim 84:7 -- "mei'chayil el chayil" -- which means "from strength to strength". In this case, it is my thoughts and ideas to those who are strong enough to be interested :)