Training Frequency
 

Training frequency can actually be muscle group-specific. Since upper body muscles typically have a greater percentage of fast twitch fibers, they often experience more damage than lower body muscles when all things are equal. This increase in damage means that upper body muscles will take longer to recover than lower body muscles. I'd stick with the classic 2x/week on most upper body muscle groups as increasing weekly training frequency probably won't offer additional benefits.
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▪️ Source: Chen, T. C., Yang, T. J., Huang, M. J., Wang, H. S., Tseng, K. W., Chen, H. L., & Nosaka, K. (2019). Damage and the repeated bout effect of arm, leg, and trunk muscles induced by eccentric resistance exercises. Scandinavian Journal of Medicine & Science in Sports, 29(5), 725-735.