NHTSA’s frontal tests are run at 35 m.p.h. (56 km/h) into a rigid barrier using a crash-test dummy optimized for a 50th-percentile male–about 172 lb. and 5 ft. 9 in.
http://time.com/3617681/the-air-bag-blowout/

Assess the performance of the Holden Commodore air bag in a frontal barrier crash test with two unbelted, 50th percentile adult male H-III dummies.
http://www.google.com/url?q=http://www.ircobi.org/wordpress/...

--------------------------------------------------
Note added at 1 hr (2021-01-21 13:58:26 GMT)
--------------------------------------------------

Strictly speaking there should be a hyphen in 50th-percentile.

--------------------------------------------------
Note added at 2 hrs (2021-01-21 14:37:27 GMT)
--------------------------------------------------

Depending on the context, it's probably better to leave out "dummy". I assumed this was about a crash-test rating, but it may not be.

--------------------------------------------------
Note added at 6 hrs (2021-01-21 18:37:38 GMT)
--------------------------------------------------

And in case it's not obvious, the 50th percentile is the median, ie an average-sized man.