I can identify with Katrina, although I've never sorted fat cattle and (heaven forbid) I've never taken my shirt off.
The old cowboss of a big outfit in W. Montana taught me to use my jacket and shake it at the cattle. You don't have to yell. That jacket shaking will usually do the trick when you are on foot. Just hold it so it is wide and shake it or if you have too, snap it at the cattle.
Mr. FH takes his hat off and holds it real high and that causes our cattle to move foreward if he is behind them on foot, such as in an alley, etc. He refuses to yell or make a lot of noise. Amazing how well they respond in quiet situations. Our cattle don't do well with a lot of noise BEHIND them.