Several studies over the years have shown that peak growth hormone production occurs during deep sleep, but this study shows that sleep quality is also very important for testosterone production during the night. Sleep is incredibly important for gains – make sure you’re dedicating at least 8-hours/night to sleep!
Reference: Luboshitzky, R., Zabari, Z., Shen-Orr, Z., Herer, P., & Lavie, P. (2001). Disruption of the nocturnal testosterone rhythm by sleep fragmentation in normal men. The Journal of Clinical Endocrinology & Metabolism, 86(3), 1134-1139.