Exercise
The hair follicle is one of the most energy consuming organs in humans. Especially in the anagen (growth) phase [2022].
While normally dormant, Hair Follicle Stem Cells (HFSCs) quickly become activated to divide during a new hair cycle. Lactate generation (produced during normal metabolism and exercise) appears to be critical for the activation of HFSCs. Promoting lactate production in HFSCs accelerated their activation and the hair cycle.
These data suggest that HFSCs maintain a metabolic state that allow them to remain dormant and yet quickly respond to appropriate proliferative stimuli [2017].
The last sentence sums it up well, the hair follicle remains resting, but can quickly respond when given the energy. So, you want more gains, exercise.