What did this study look at?
Whenever endurance exercise sessions are performed with short intervals in between, adequate repletion of muscle glycogen stores between sessions is crucial to maintenance of performance. Maximal rate of post exercise muscle glycogen resynthesis can be obtained by the ingestion of carbohydrates only. However, the addition of protein allows similar glycogen repletion rate at lower rate of carbohydrate intake.
But apart from allowing lower rate of carbohydrate intake, does the addition of protein really help to improving performance? With other words, if one refills muscle glycogen by the ingestion of carbohydrates only, or with a protein carbohydrate mixture, does it matter at all to performance in the next session?
In order to find an answer to this question the research group of Jørgen Jensen at Copenhagen University enrolled well-trained cyclists in a protocol involving 2 exercise sessions with a 5h rest interval in between. The first session only served to deplete muscle glycogen. During the next 1.5h subjects received either carbohydrates alone (1.2g×kg-1×h-1, CHO), or a whey protein (0.4 g×kg-1×h-1) + carbohydrate (0.8g g×kg-1×h-1) mixture (CHO+PROT). Another 3.5h later the cyclist participated in a performance test which consisted of cycling to exhaustion at a power output (Watt) corresponding to ~70% of VO2max. Also muscle glycogen content was measured before and after the test.
What did the study show?
The study showed that CHO and CHO+PROT resulted in similar muscle glycogen contents at the end of the 5h recovery period. Muscle glycogen utilization during the performance test also was similar between the two conditions. However, time to exhaustion was ~20% longer in CHO+PROT (~55 min) than in CHO (~46 min)
What is the importance of this finding for sports performance?
The combination of whey protein and carbohydrates in a recovery shake is ideal to facilitate rapid repletion of muscle glycogen, which is the primary fuel for high-intensity endurance exercise. Carbohydrate and protein co-ingestion is also important to stimulate muscle repair and long-term training adaptation.
The current ‘spot-on’ study shows that whenever recovery time between exercise sessions is short, the addition of protein ingestion to carbohydrate intake immediately after exercise improves endurance performance beyond the effect that could be obtained by high rate carbohydrate intake alone.