some research favored two or three sets and some favored single sets as superior...
That in itself is cancellation through elimination. In other words (and without having to delve into which research favoured what), the mere fact that the results were not conclusive, nullifies all these studies.
but the vast majority of studies revealed no significant differences between doing one set and doing multiple.
That is great news for lifters (and coaches) who live by studies, I am not one of those.
They were all equally effective
More reason to be suspicious.
what does this mean to you and why do you justify multiple set protocol?
I justify a multiple set protocol because that's what has been working in real life (with real lifters) since day one. Why would a sane lifter put himself through hell in order to make progress, when he could just as easily apply the one set method and get his training over and done with.
In my response to your post Andy, I've chosen a totally different approach from the norm. That is (as is evident) by my reply, I've kept it
real. No science, no fancy words, no "this research or this Doctor of physiology etc. says so", nothing like that. If a single set works, Olympic weightlifters world wide would have jumped onto that scientific discovery, but it obviously doesn't. And it doesn't for many more reasons than just one.
This whole thing reminds me a bit of a muscle contraction. We've all seen those commercials where someone (usually a scientist/doctor/"expert"), is trying to sell us a machine that causes our muscles to contract, without having to do any work. No one is even talking about one set or multiple sets here, not even a weight to be lifted or an arm to move from point a to point b no. Simply attach those probes and let them send those electrical impulses that cause a shock to our nerve endings and cause them to fire, sending a signal for a muscle fiber to contract. Oh, if it was so easy huh!
So it's obvious from the above example re muscle contraction, that it takes more than simply muscle contraction to make a muscle stronger, bigger, or both. It takes stress, and not just stress, but stress that is applied either continuously (as in TUT), or stress that is applied multiple times as in a heavy set done multiple times.
Let's look at real world training, both bodybuilding and strength/power orientated.
In bodybuilding , you have two major camps, both (arrogantly) claim to have the holly grail when it comes to their method of training. On the one hand you've got the high volume camp, and on the other hand you've got the high intensity group. Yet when it comes to the topic of this OP, both of this camps would agree on multiple sets to get the job done.
Moving on to Olympic weightlifting, you've also got two camps, one following the former Soviet Union method of periodisation based on the lifter's 1RM, whilst the other camp following the Bulgarian system where your 1RM is based on your daily's 1RM, applying what is now termed as self-autoregulation, and maintaining that only the two competition lifts are to be performed, with only one strength specific exercise for assistance work, namely the formant squat. Again we see an agreement between this two vastly different camps, where more than just the one set is applied in training to get the job done. Even if the lifter is restricting himself to single lifts, he does a multiple sets of that single lift, over and over again for about 6x/day 6x/week (if you're a Bulgarian or a Bulgarian system follower) as i am (in favour of over the Russian system). But that's another topic.
Point is, with all these diversities,
all agree on a multiple set over a single set method.