Rowing builds primarily biceps, shoulders and lats while being a cardiovascular workout if you are rowing at an intense speed. You may lose weight, but you'll be losing fat rather than muscle man. I don't know if it matter if you workout before or after rowing. What are you doing in addition to rowing. Also here's some tricks on getting fit.
Walk around as much as possible with your ab muscles flexed. It will speed up the time to get a six pack.
Eat 6 small meals a day, preferably lean proteins, fruit, and vegetables. 6 meals will speed up your metabolism and help shed fat quicker.
Drink lots of ice cold water. Drinking water speeds up metabolism, and if it is ice cold the body's metabolism speeds up even more to keep your body temperature even in light of the ice cold water.
It's better to do short interval high intensity aerobics (ie sprints) than long drawn out low intensity aerobics (ie a mile jog).
I'm going to recommend healthy supplements. Research them for yourself. Take CLA, creatine, NOX, fish oil, cytolean, and green tea extract. Creatine and NOX may be questionable for you, but the rest are naturally found in a lot of food we eat in lower doses.
Get better at picking up women to have lots of balls to the wall sex. High intensity sex is one of the highest calorie burners around and it feels great.
CHAT