Research Subject Ngrams

Ngrams are a Google service that finds word patterns and tracks their popularity over time in the literature available on Google Books. My English teacher asked my class to use the Ngrams to see how terminology of our research topic has progressed in popularity over time.

Above is the first set of terms I searched. As you can see, all of these terms and phrases started being used more frequently around the same time--the mid to late 1940s. This makes sense to me because weightlifting and concern with serious muscle growth seems like a relatively new concept with increasing popularity. 'Muscle protein synthesis,' 'skeletal muscle mass,' and 'skeletal muscle hypertrophy' are phrases that are more scientific, so I would expect them to be used less frequently than 'weightlifting' and 'resistance exercise.'

The first question I would ask is why 'skeletal muscle hypertrophy' is even below 'muscle protein synthesis,' since the result of MPS is hypertrophy? It seems to me like they would be used together. However, I suppose that muscle protein synthesis does not have to be that of skeletal muscle, so the graph could be accounting for MPS of other kinds of muscle tissue in the body. 

Another question I have is why is 'weightlifting' used so much more often than 'resistance exercise?' I feel as though it would be the opposite because weightlifting hasn't always been encouraged for women, so it seems like it should have been more popular between the 1980s and early 2000s when discussing fitness and exercise.

My second set of terms I found very interesting. I used all of the same words and phrases as before, but added 'nutrition' to the sequence. It is very clear how popular the topic of nutrition has been throughout history. Of course, nutrition for the everyday person is a little different than for someone trying to put on muscle mass, so it makes sense that overall, nutrition is more commonly discussed than the other words. It is just surprising how little they appear to increase in popularity and even seem relevant because of how frequently nutrition is mentioned. It also shocked me how popular 'nutrition' has been for so long.

Something I wonder conclusively is: why is everything having to do with my research topic at such a high popularity now? Is it simply because people have more time to focus on these things now? Or is it more because of technological advances that allow us to research 'muscle protein synthesis' and 'skeletal muscle hypertrophy?'