Objectives. This study investigated the effects of prolonged use of a protein (casein hydrolysate) supplement on perceived muscle soreness and fatigue, in international level Sevens rugby players (n=23) during a pre-season training camp. Methods. A randomised, double-blind, placebo-controlled design was used. Players were assigned to a carbohydrate-only or an isocaloric carbohydrate and protein supplement and ingested the assigned supplement after each training session (17 field training sessions over a 23-day period). Before each training session a questionnaire and 10-point visual analogue scale was completed that assessed muscle soreness and muscle fatigue in the calf, hamstring, and quadriceps. Results. No significant differences were observed in leg fatigue in any of the muscle groups. However, muscle soreness was significantly lower in the experimental group in the quadriceps at Week 3, Day 5 (p=0.04) and calves at Week 4, Day 2 (p=0.02) and Day 3 (p=0.04). Additionally, no significant differences were found during the Heart rate Interval Monitoring System Test (p=0.350) used to determine training load recovery. Conclusion.The results suggest that prolonged use of a protein hydrolysate supplement may be beneficial in reducing muscle soreness, but not muscle fatigue, during periods of continuous high training loads. Keywords. Supplement, protein feeding, recovery S Afr J Sports Med 2015;27(4):102-107. DOI:10.17159/2078DOI:10.17159/ -516X/2015 With the increased emphasis on achieving success in both recreational and professional sport, nutritional strategies to improve performance and enhance recovery have been the focus of considerable research. Previous studies have shown that protein supplementation during or post exercise positively affects several factors related to recovery, such as a reduction in the subjective rating of muscle soreness and fatigue. [1][2][3] Delayed Onset Muscle Soreness (DOMS) can compromise performance and training due to pain and a reduction in joint range of mostion, shock attenuation and peak torque. [4] Muscle fatigue following hard training is common, and if not managed correctly, can result in overreaching or overtraining syndromes. [4] A period of reduced training load between hard training sessions is therefore necessary to allow recovery. This, however, limits the number of key workouts that an athlete can perform each week. Enhancing recovery through nutritional means by reducing either DOMS or muscle fatigue, or both, would permit an athlete to recover faster and be able to train at a high intensity more frequently.Previous studies have shown that protein supplementation either during or post exercise positively affects several factors related to recovery, including a reduction in the subjective rating of muscle soreness. [5,6] On the other hand, a number of studies have failed to show any potential beneficial effect on muscle soreness or muscle fatigue. [3,7,8] Despite these inconsistencies in findings related to DOMS and fatigue, when performance has been investigated,...