When it comes to weight training, I never know how long I will be using the same weight increase. Using my excel sheet as my example, my thinking was, I would have to manually change the cell reference when the weight increase changes.

C5 - 100
D5 - =SUM(C5+E$2$)
E5 - =FORMULATEXT(D5), get cell that references the weight increase (E$2$)
F5 - =SUM(E5+F$2$), weights are getting heavier, so I have to increase weight slower
G5 - =FORMULATEXT(F5), get cell that references the weight increase (F$2$)
H5 - =FORMULATEXT(F5), get cell that references the weight increase (F$2$)
I5 - =FORMULATEXT(F5), get cell that references the weight increase (F$2$)
J5 - =SUM(I5+F$2$), weights are getting heavier, so I have to increase weight slower

Obvious, I would need something a function to turn the text into an expression of some sort.