Would it be fair to say that most UNION jobs at UPS were never created for women, they have a thing call standards and considering the physical breakdown of ALL our bodies over time most women generally leave well before the men do. Truth is that no matter how safe you are, following the methods, men would have the advantage just by having the upper body strength. In my thirty years with the company I can remember only about three to five staying 25 or 30 years to collect a full time pension. The ladies who make it for any amount of time quit to start a family, find easier work or leave through the disability route.
For the most part during the 70's and 80's the vast majority of new hires were males of college age, the prime target or this kind of work. Admit that they adjusted their standards and the manual labor part of the work is not as hard as it was during those decades. Newer technology and more concern over safety practices among the part time workforce. In my hub we have over 150 package car drivers currently, of that group only 7 are women and the highest seniority is about 15 years, that in itself tells the physical battering that this position takes on both sexes.