Background
Protein ingestion prior to sleep has been shown to stimulate myofibrillar protein synthesis rates during overnight recovery from exercise. Whether pre-sleep protein ingestion can also be applied to augment mitochondrial protein synthesis rates remains to be established. Furthermore, the impact of the type of protein to modulate overnight myofibrillar or mitochondrial protein synthesis rates has not yet been addressed.The purpose of this study is to assess the impact of pre-sleep casein and whey protein ingestion on myofibrillar and mitochondrial protein synthesis rates during overnight recovery from a bout of endurance exercise.

Methods
Thirty-six healthy, young men performed a single bout of endurance-type exercise in the evening (19:45 h) after a full day of dietary standardization. Thirty min prior to sleep (23:30 h), subjects ingested 45 g casein protein, 45 g whey protein, or a noncaloric placebo. Continuous intravenous L-[ring-¹³C₆]-phenylalanine infusions were applied, with blood and muscle tissue samples being collected to assess overnight mitochondrial and myofibrillar protein synthesis rates. Overnight muscle protein synthesis rates were compared between treatments with a one-way ANOVA with a Bonferroni correction.

Results
Protein ingestion resulted in higher mitochondrial (0.087±0.020 vs 0.067±0.016 %·h-¹, P=0.005) and myofibrillar (0.060±0.014 vs 0.047±0.011 %·h-¹, P=0.012) protein synthesis rates when compared to placebo. Casein and whey protein ingestion did not differ in their capacity to stimulate mitochondrial (0.082±0.019 vs 0.092±0.020 %·h-¹, P=0.690) and myofibrillar (0.056±0.009 vs 0.064±0.018 %·h-¹, P=0.440) protein synthesis rates.

Conclusion
Protein ingestion prior to sleep stimulates both mitochondrial and myofibrillar protein synthesis rates during overnight recovery from endurance exercise. There is no apparent difference in the capacity of pre-sleep whey or casein protein ingestion on overnight muscle protein synthesis rates.