Hi jdog,
There haven't been a lot of official studies done that showed anything definitive but there have been a few.
The one that most people refer to when they talk about mattress firmness was a
2003 Spanish study
that involved 313 people. They were each given either a firm and medium-firm mattress. There was no soft choice. Because the medium-firm mattress relieved pain more than the firm and gave more freedom of movement during the day, it was generally accepted that medium firm mattresses were better. There is some further commentary about the
study here
(among a million other places). From this point on the study results were interpreted as meaning that a medium firm mattress was the best ... unfortunately there was no real definition of medium firm and the study only used 2 different mattresses. The main value here is that the idea that firmer was not better began to be seriously considered.
Sleep to Live also did a more
recent study in 2011
which was much more interesting. While the study makes very interesting reading and certainly is much better thought out and includes movement measurements in addition to 7 different mattress firmnesses ... it also leads to more questions than answers. The basic results are that both ends of the scale are the worst and the middle range seems statistically to be the best ... however there are many areas where further study seems to be indicated. It also seems to indicate that a "best" mattress can be anywhere in between the two extremes.
They are also sponsoring another
study here
.
In my conversations with health professionals, mattress manufacturers, and many others and in my online travels, there seems to be a growing consensus ... at least among those who aren't immersed in the "old school" and have put real thought into this ... who will agree that a mattress that supports natural spinal alignment (the natural double S curve of the spine) and whatever helps achieve that is the "best" for each individual.
There has also been a lot of at least anecdotal evidence published ... mostly in regard to various pressure relieving materials ... that good pressure relief also has clear benefits including better circulation, less movement during the night, and deeper sleep. Of course anyone who has had the discomfort of pressure points and the numbness and pain that can be connected with this doesn't have to read a scientific study or research to know that pressure relief or lack of it can dramatically affect sleeping comfort.
So my own thoughts on all of this is that all of these studies are flawed as it relates to mattress firmness because the idea of rating a mattress with a single "firmness rating" seem to me to be somewhat nonsensical. For example (to make the point) if you have a mattress with 6" of 15 ILD foam and put this over 6" of 85 ILD foam you would have an average ILD of 50 which by any accounts would have a rating of ultra firm. On the other hand if you put the firm foam over the soft foam you would have the same rating. Even worse if you put a sheet of flexible firm plastic over 6" of ultra soft foam you would have an ultra soft mattress ... and yet all of these would be disastrous in one way or another. Both "firm on top" versions would clearly create pressure points for most people in addition to probable alignment issues and back pain and the "soft on top" version would certainly create alignment issues even if the pressure relief was better.
It seems pretty clear to me ... and almost anyone who deals with sleeping issues or who makes mattresses and has feedback from what they build will generally agree ... that a mattress has 2 main functions not just one (pressure relief and alignment) and that a mattress needs to deal with both by being both soft on top to differing degrees and firm underneath also to differing degrees. It also seems clear that a mattress that helps some with back pain issues can make back pain worse for others. To rate a mattress with a single rating (such as medium-firm) once this is realized or to think that a certain type of mattress is "better" for certain conditions without taking the individual into account defies common sense. This is the main message IMO of the Sleep to Live study.
So while it is generally recognized in almost every area that is involved with sleep and/or mattress construction that the idea of "firmer is better" is a flawed concept, and that the mattress that is best for each person depends on many things, the industry itself is way behind in the way they describe their mattresses and in helping people to understand how to find what is best for their own individual needs in terms of pressure relief and alignment.
I could go on at length about this as it gets into different materials, layer thicknesses, mattress constructions, and how each can fit different individual body weights and shapes and sleeping positions ... but there is already lots of information on the site and in the forum about this.
The bottom line is that it just makes sense (at least to me) and that not only different studies and research (as limited as they may be) but each person's own sleeping experience can validate it. All we have to do is help more people who sell mattresses to understand this "revolutionary" idea (that a mattress needs to be both soft and firm to different degrees and that an overall rating is meaningless) so they can better fit a mattress to the needs of their customers.
Phoenix