Abstract: A swim stroke exercise device including an adjustable resistance mechanism is provided. The resistance mechanism is attached to one end of the exercise device and includes a roller assembly having a roller clutch and a drive shaft extending from one end and a spring rewind assembly attached opposite the drive shaft. The drive shaft supports a drive pulley including a number of concentric engagement areas having different diameters. Adjustably disposed above the roller assembly, a resistance device includes an output shaft terminating in a mag pulley opposite the resistance device formed similarly to the drive pulley with a number of concentric engagement areas having different diameters that are aligned with the engagement areas on the drive pulley. The concentric engagement areas allow a belt trained about the pulleys to be moved to various positions on both the drive pulley and mag pulley to increase or decrease the amount of resistance provided to the drive shaft by the clutch.