The effect of protein ingestion immediately following exhaustive endurance exercise on muscle glycogen resynthesis and performance

Abstract

Introduction: Endurance athletes often train two times at the same day. Energy intake during recovery may influence glycogen resynthesis and subsequent performance. The aim of the present study was to compare glycogen synthesis and performance 5 hours (h) after a bout of exhaustive exercise when carbohydrate (CHO) or an isocaloric amount of carbohydrate + protein (CHO+Pro) was ingested during the first 2 h after exercise. Methods: The study was performed with a double-blinded crossover design. Nine male subjects completed two dietary intervention days consisting of an initial glycogen depleting exercise to exhaustion at a workload corresponding to 70 % VO2peak, followed by a performance test after 5 h of recovery. The first 2 h after exhaustion, either CHO (1.2 g CHO·kg-1·h-1) or CHO+Pro (0.8 g CHO and 0.4 g Pro ·kg-1·h-1) was consumed in a randomized order. Energy intake was standardised and similar between CHO and CHO+Pro the remaining 3 h. Performance was tested by time to exhaustion (TtE) at the same workload as during the initial glycogen depleting exercise. Biopsies were harvested from vastus lateralis after the initial glycogen depleting exercise, the 5 h recovery period and after TtE. Performance was only assessed with five subjects. Results: Glycogen resynthesis during recovery was similar between CHO (41.3±5.8 mmol·kg dw-1·h-1) and CHO+Pro (46.8±23.9 mmol·kg dw-1·h-1). After the performance test, muscle glycogen was equally reduced in CHO and CHO+Pro. Nitrogen balance based on urine was positive in CHO+Pro (19.6±7.6 mg N·kg-1, p<0.05) and higher than CHO (-10.7±6.3 mg N·kg-1, p<0.05). TtE was only assessed with five subjects, and was improved by CHO+Pro (54.6±11.0 minutes (min)) compared to CHO (46.1±9.8 min) (p<0.01). Conclusion: CHO+Pro, compared to the isocaloric CHO diet, improved performance after 5 h recovery from an exhaustive exercise. The study shows that CHO+Pro intake immediately after exercise accelerates recovery of endurance capacity compared to CHO. There was no difference in rate of glycogen resynthesis, and we suggest that there are other mechanisms explaining the enhanced performance after intake of CHO+Pro compared to CHO. Increased protein synthesis is a possibility, as nitrogen balance was positive during CHO+Pro.