“We found that if you did one year of resistance training with heavy weights, you were able to maintain the strength in your legs that you had when you began the study,” Bloch-Ibenfeldt said.

The other groups were found to have lost strength from their baselines. Four years after the start of the study, leg strength performance decreased on average among those in the moderate intensity training cohort and the non-exercising control group — although more significantly among the latter. Those who did the moderate program initially benefited from increased leg strength at the end of the one-year regimen, but those benefits did not endure: After four years, their strength was less than it had been at baseline.

Participants determined the most weight they could lift at one time using typical weight machines found in gyms. Then they calculated 70 to 85 percent of their one-rep maximum and used that weight in their training. So if the most they could lift at one time was 100 pounds, they used 70- to 85-pound weights in their training.

tl;dr: 70-85% of 1RM is the GOAT

https://www.washingtonpost.com/welln...trength-aging/