Tips » Weight Training
My friend says it is essential to do opposing muscle groups (chest and back, biceps and triceps) etc. on the same day to get results. True?
It may be that she is excited about a portion of her class that was covering agonist/antagonist pairs. You'll have to ask her what she means by "essential" because she obviously doesn't have the same definition I do ... to me, essential is something that you won't get the results without. That means those splits are definitely not essential.
See, if this were "essential" then people who did not do a split that way simply would not be making gains. I know many people with incredible physiques and good health who do not do their splits like that. So what is "essential?"
Perhaps she hasn't yet reached the area of her class that discusses the law of individual differences. Let her know she'll be in for an eye-opener when she hits "periodization."
There are a handful of studies that suggest there are moderate strength benefits gained from working opposing muscle pairs, but there is nothing to imply this is a law or set in stone, and at times, the goal is not to have a strength, but rather a hypertrophy gain!
I have yet to find an experienced strength coach or personal trainer (by experienced I mean those who have been doing this for some time and get consistent results from clients) who say, "this is the way to train." Rather, they have several methods that they customize to the individual, and even those who create "systems" that are effective build some flexibility into those systems to account for individual differences.