Yes, of course. People who row, swim, run, and bike routinely build and maintain muscle as they practice. Competitors may also do heavy strength training with barbells and other equipment, but as long you’re eating nutritiously, a wide range of physical activities will contribute to the muscle mass needed for health, for balance and coordination, and to chase away flabbiness.
The gym-dominated fitness community often paints cardio as the dull, time-intensive stuff that only marathoners can love, and resistance training as nothing but maximal strength training — training up to lift as much as possible. But cardio contains a wide range of power-oriented activities, like sprinting and rowing. And resistance training includes a wide range of “intensities”, from “muscular endurance” workouts with lower weights and very high reps (niche training important for efficiency in endurance sports) to simple, basic strength training (important for health, coordination, and bone density).
Just as the range from walking to running has many levels — different speeds (intensities, “light” to “heavy”) and different distances (“reps”) — so too does resistance training. A sprint is a brief, hard effort, and a walk may be an extended, light effort. Maximal strength training works up to a few reps at a time at heavy weights, while other aspects of training use lighter weights for more reps. The exercise benefits overlap, too — people who mostly lift get some cardio benefit from their workouts; people who focus on cardio get some strength benefits.
Does That Mean Cardio Can Make People Huge?
Even focusing on maximal strength training won’t necessarily make someone huge, and cardio sports are even less likely to. The heavy lifting that bodybuilders and competitive lifters do involves a lot of hard work, careful programming, and special eating plans to gain size, and it doesn’t happen overnight.
I Just Want to Be in Better Shape and Look Nicer
You’re in luck — moderate cardio with some pace changes (a mix of faster and slower) combined with moderate strength training (no need to max out, just be sure to keep challenging yourself gradually) will help you do exactly that. If you don’t have to worry about competing, you can focus on the basics and find forms you enjoy. Make exercise a regular habit, and you’ll be healthier, at lower risk of injuries, sleeping better, and looking (and feeling!) better.