isotension principle

you know the guy at your gym that flexes between sets? you look at him & think "whatever". Actually this is an important step in trainig. during your rest period dont just sit there breathing hard. flex & contract the muscles you have just execised. This is actually a benificial exercise & also keeps you pumped. flexing between sets is actually an isometric form of exercise. isotension also developes muscle control, very important in body building. Isometrics involves intense muscle contractions. Although done alone isometrics has little effect on building mass . Next work out give it a try, although i dont flex in the mirror , i will keep my muscles pumped by flexing between sets