The aim of this study was to determine the time course of architectural adaptations in the biceps femoris long head (BFLH ) following high or low volume eccentric training. Twenty recreationally active males completed a two week standardized period of eccentric Nordic hamstring exercise (NHE) training, followed by four weeks of high (n = 10) or low volume (n = 10) training. Eccentric strength was assessed pre- and post intervention and following detraining. Architecture was assessed weekly during training and after two and four weeks of detraining. After six weeks of training, BFLH fascicles increased significantly in the high (23% ± 7%, P < .001, d = 2.87) and low volume (24% ± 4%, P < .001, d = 3.46) groups, but reversed following two weeks of detraining (high volume: -17% ± 5%, P < .001, d = -2.04; low volume: -15% ± 3%, P < .001, d = -2.56) after completing the intervention. Both groups increased eccentric strength after six weeks of training (high volume: 28% ± 20%, P = .009, d = 1.55; low volume: 34% ± 14%, P < .001, d = 2.09) and saw no change in strength following a four week period of detraining (high volume: -7% ± 7%, P = .97, d = -0.31; low volume: -2% ± 5%, P = .99, d = -0.20). Both low and high volume NHE training stimulate increases in BFLH fascicle length and eccentric knee flexor strength. Architectural adaptations reverted to baseline levels within two weeks after ceasing training, but eccentric strength was maintained for at least four weeks. These observations provide novel insight into the effects of training volume and detraining on BFLH architecture and may provide guidance for the implementation of NHE programs.