Cutting Doesn't Change
Your Training.

Most lifters change their training when they change their diet. Start a cut and the sets come down, the reps go up, the "toning" starts. Start a bulk and the volume balloons because more food must mean more growth. Both moves are wrong, and for the same reason.

The amount of muscle you build is set by how many hard sets each muscle gets a week. Food decides what happens to your fat. Those are two different dials, and the phase you're in should move the second one, not the first.

The growth dial is weekly sets

The biggest dose-response analysis to date pooled 67 studies and 2,058 participants and found what every smaller one found: muscle growth rises with the number of hard sets a muscle gets each week, with returns that keep coming but shrink past the mid-teens.^[1] An earlier meta-analysis put the first clear step at ten or more sets a week.^[2] Nothing in either analysis depends on whether the lifters were eating a surplus or a deficit. The dial is the dial.

More food doesn't move it

This is the half most people get wrong on a bulk. A randomised trial in trained lifters compared maintenance, a 5% surplus and a 15% surplus for eight weeks. The bigger surplus mostly bought fat. Weight gain predicted skinfold gain strongly and muscle thickness barely at all.^[3] In elite athletes, a guided surplus produced five times the fat gain of eating to appetite, with no difference in lean mass or strength.^[4]

So adding sets because you're "bulking" is doubling down on the wrong lever. The extra food does not raise the ceiling on how fast you can build, and the extra sets push you toward the point where recovery fails rather than the point where growth is maximised.

Less food doesn't lower it either

On a cut the mistake runs the other way: people train lighter because they feel weaker, and they lose muscle they didn't need to lose. A meta-regression of training in an energy deficit found that lifting preserved strength across the board and that lean-mass gains only fell off as the deficit got large, around 500 kcal a day.^[5] Keep the sets, keep the effort, and in young men with high protein, a deficit with hard training has produced lean-mass gain.^[6]

What the phase does change

Recovery. A deficit lowers it, a surplus raises it a little. So the phase moves where you sit inside each muscle's productive range: toward the lower end on a cut, toward the upper end on a bulk. The range itself, the exercises, the split and the effort don't change. That's the whole adjustment, and it's small.

Cut: the lower end of each muscle's range. Bulk: the upper end. Same exercises, same effort, same program.

What the app does

Coast gives every muscle its own weekly range, taken from the dose-response work above, and the phase sets your position inside it. When you move from a cut to a build, the sets step up within the same program. Nothing is regenerated, nothing is swapped, and your progression carries across. Eating more never adds sets, and eating less never takes the hard ones away.