Been to China many times on a 14 hour flight over the years. The secret is the following:

- Do lunges & pushups every few hours to prevent butt from getting sore

- Workout/Run the day before or morning. Don't oversleep, lean on having less sleep before the flight (6-7 hours)

- Don't bother doing any work. Find that book you've wanted to read for some time, read that.

- Pick an aisle or window seat, middle seat sucks

When you get to your destination, do the following:

- Take a 1 hour nap in the middle of the day. This resets jetlag so you can sleep on a normal schedule

Additionally, noise cancelling headphones are amazing for helping sleep.

If a chemical method is your thing, I've heard good things about motion sickness medication, but I've never used it.

where do you do your pushups?

near the toilet in the back, where flight attendants grab food entrees. Almost every airplane has a larger footspace around this area.

Frequent flyers fly business class. It would be insane to fly a full work flight schedule in long-haul economy.

The occasional SFO-NYC in economy where my upgrade doesn't clear is torture. I can't fathom doing my usual 10h weekly flight in economy seats. I fly 150k miles a year, on about 80 flights or so. Pretty much all in business or first. Paid by myself. It's really not as expensive as people think… I spend maybe $15,000 annually on flights. Optimizing judiciously is key.

For what it’s worth I did find that I adapted to long flights and jet lag. The first time I did the NYC to LON redeye I was a mess the first day. After doing it every other week for awhile it was no problem. Then I did a Dallas to Sydney flight and found I had no trouble. I moved my sleep around a couple days before so that I would sleep for the middle 8 hours of the 16 hour flight. Being awake for four hours on either side of a night of sleep and getting up to walk around a lot made it a breeze.