I wanted to explore the relative importance people place on difference aspects of running, regardless of how important the really are. So here is a book-indexed trend for each of the terms "VO2max", "running economy", "neuromuscular training" and "lactate threshold".
NB: On an earlier version of this post I had entered "Vo2max" and found a different, erroneous, trend. All sorted out now.
The term "VO2max" has been steadily rising from the 1980s to the early 2000s, where we may or may not be witnessing an ultimate peak around 2005. Though much smaller in book frequency, both "lactate threshold" and "running economy" reached their maximum values in 2002 and have been edging downward. Meanwhile "neuromuscular training" has been growing slowly but steadily. Since as Ngrams only reaches to 2008, I searched Google trends for more recent (search-based) differences.
The trend for these four variables has been quite stable between 2005 to present, with VO2max beating out the others by a fair margin. Therefore I included barefoot running as a more dynamic variable (NB: the phrase 'barefoot running' is quite flat during the pre-2009 ngram timespan). It is interesting to observe the sudden jump in barefoot searches in 2009, followed by a steep decline in 2014 to levels below those of VO2max.