Hernandez has enjoyed a superb first season since arriving at Manchester United from Mexican club Chivas in the summer.
His double against Marseille on Tuesday took his tally to 16 goals so far this season, a total well in excess of what he anticipated at this stage of his United career.
But Hernandez has revealed he is having to put in extra work behind the scenes to ensure he is strong enough to deliver the goods in front of goal.
The 24-year-old striker said: "I have done better than I thought I would.
"But I wouldn't say it has been easier, nothing in life is easy. Physically I have got a lot stronger, I go to the gym a lot
"It is not because I like it, It is something I needed to do because the English league is quicker and more physical."
Hernandez has turned into the perfect partner for Wayne Rooney due to his pace and willingness to run behind defenders.
That in turn allows Rooney more space in which to operate and is one of the major reasons why United are now starting to find their form.
And that is all that matters to Hernandez — regardless of how many goals he scores.
He added: "It has helped my confidence a lot to score so many goals.
"But the most important thing for me has always been the results of the team. Goals are merely a consequence of the work everyone does.
"Of course I am very happy to score but if Manchester United win all their games, it doesn't matter who gets the goals."