Try adding in some weight-lifting. At 5'-10" and 158lb, if you've got excess fat around your midsection you can't have much muscle mass. Heck, at 5-11 when I got down to my lightest point (visible abs, probably right at 10% BF), I still weighed 178.
True. I don't have a lot of upper body muscle at all! My legs are lot stronger after a couple months of cycling, but it doesn't do much for my arms. Perhaps I should carry my bike more than ride it :-)
John