…by doing a set of flys or pec dec to failure before doing benchpress or incline bench press, you have “pre-exhausted” the pecs, meaning that the shoulders and tris are “assisting” the chest to further exhaustion, rather than baring the brunt of the weight and the chest not quite getting there…
Rob’s got it absolutely right. The point is to use an isolation exercise to pre-fatigue the target muscle of a compound movement. If you do it right, when you fail in the compound movement, you can be sure that the failure is caused by the target muscle getting fatigued before any of the supporting muscles. Pre-fatiguing supporting muscles makes no sense because you will make the compound movement even less stressful on the target muscle, as you will fail even earlier than you would normally.
i understand what rob and u are saying but i feel like ur proposing a different scenario… i am referring to if ur shoulders and triceps are overpowering ur pecs… u have both described a situation in which the pecs are stronger than the shoulders and triceps
perhaps i am misinterpreting my body and thinking that my delts and tris are taking over when in fact my pecs are just so strong (relatively) that they are not becoming fatigued at all in the bench
not to be a jerk, but i think it is a misinterpretation coming into play here. you could do a “normal” set of bench press, or even a few sets, and really pay attention to what forces you to end your set. i would bet that it would be your triceps, and not your chest.
for me, its definitely the triceps that end the set before my chest does. therefore, if your triceps are going to give out on say rep 10, you definitely wouldnt want to pre-fatigue them before a set of bench press, because then they might give out at rep 6 or something, further taking away from the activation of the chest in the bench, if for nothing else because you ended at 6 instead of 10. does that make sense?
in other words, if you really concentrate and find that its your triceps (or maybe the delts) that give out before the chest, then you have to assume something like this: you terminated the set after rep 10 because your triceps (and/or delts) simply couldnt push anymore. but, your chest could have had several more reps left before it would have been ready to give out. by doing a single joint/isolation movement for your chest, immediately before hopping onto the bench, you are taking away the advantage that your chest had over the tris and possibly delts. that way, when the tris and delts are fried and ready to end the set, your chest is also fried.