This is why a runner who performs another steady-state activity such as cycling will be gasping for air.

Maybe that's why I gasp and feel like I'm dying every time I try to run, despite being in supposedly good shape. On the other hand, conditioning my body to run efficiently would be very useful in terms of transportation (using your own body to walk or run places is free!)

Your heart and lungs cannot tell whether you’re working your muscles intensely for thirty seconds on a stationary bike or working them intensely on a leg press.

Can your muscles tell? I'm often sore the day after doing weights in the gym, but also the day after biking, or running, or playing tag with children (if I haven't done any of these things in a while.) I swam with one of my friends who doesn't swim regularly, and pushed her hard, and she was pretty sore the next day.