Have you tried just changing your routine? I change my routine every 5 - 6 weeks so that by body does not get too stagnate with the same thing.
For instance right now I am doing strength training and then the next week strength training with super sets, then a easy week of mostly cardio and a light workout then back to strength training. I have found my strength has improved by about 20% with this latest push. I do this work out for another 2 weeks then i'll go to doing my regular workout... back and bi's chest and tri's legs but all at about 50 - 70% of my max instead of this strength workout which is 75 - 100% of my max.
With the strength training you are doing more weight less reps and maybe more rest in between sets. Some guys do not like this because they think that they are doing less of a workout when they are doing only 1 - 6 reps on a exercise, But I think it is fantastic and cannot wait till my next switch to this workout so I can see greater gains.
