In part one of this post on refueling and recovery, I discussed rehydration strategies with water and sports drinks and now we turn our focus to glycogen re-synthesis and protein synthesis.
Normal glycogen restoration occurs within between 24 and 36 hours whereas a more aggressive approach can regenerate glycogen stores within 20 hours. Aggressive strategies therefore become an important consideration for those participating in more frequent, vigorous training programs and less important for those participating in moderate-to-vigorous bouts of cardio every 24 – 48 hours who need nothing more than their regular diet.
If contemplating an aggressive strategy, the following factors will influence the rate of glycogen re-synthesis:
- Timing of carbohydrate ingestion following exercise.
- Type of carbohydrate ingested.
- Quantity of carbohydrate ingested.
- Inclusion of protein (to accelerate glycogen re-synthesis).
Glycogen re-synthesis rates (glycogen synthetase activity) are most active in first hour following exercise, becoming progressively less active with each passing hour. In fact, rates are approximately 100 % greater in the first hour than two hours post-exercise. If one waits two hours after exercise to begin eating carbohydrates, muscle glycogen stores at the 4-hour mark (post-exercise) will be 45 % lower than levels where eating began within the hour following exercise.
Glycogen re-synthesis rates are approximately 50 % slower from fructose than from glucose for several reasons. Glucose undergoes a more rapid, active absorptive process versus fructose, which is absorbed via a slower, more passive process. Glucose is also absorbed higher up (sooner) in the GI tract and fructose generally requires conversion to glucose within liver cells before it becomes biologically available to the muscle cells. As glucose and fructose are absorbed via different mechanisms and at different location, consideration of multiple-source carbohydrate foods may potentially increase muscle delivery. However, the issue of glycemic load and the body’s insulin response may require some consideration. Not only do high-glycemic load foods trigger greater insulin responses and the classic post-prandial blood sugar crash, but high levels of circulating insulin also inhibit the action of Hormone Sensitive Lipase (HSL), the enzyme responsible for mobilizing fats from storage for use as energy. Traditionally, the post-exercise window (EPOC) is a period where the body typically favors strong utilization of fats as a fuel.
Volumes of research have investigated the effects of feeding different quantities of carbohydrates on glycogen re-synthesis rates and while positive results are associated with 0.7 – 1.5 g carbohydrates / kg BW / hour for the first 4 hours, the consensus appears to be around 1.0 – 1.2 g / kg BW / hour. This amounts to significant quantities of carbohydrates (e.g., 175 lb (79.5 kg) runner would consume 80 – 95 g / hour or 320 – 380 kcal / hour for the first 4 hours. While the first hour is most critical, total calories needed should always be considered when planning post-exercise dietary strategies. The inclusion of some protein (≤ 20 g) can accelerate glucose uptake for first 40 – 60 minutes after exercise, but only if carbohydrate intakes are < 1.0 g / kg BW.
Recent research demonstrates that quality protein consumed before exercise (containing 6 g of essential amino acids = approximately 15 – 18 g of whey isolate) appears to create the largest increase in protein synthesis rates in recovery (~ 150 – 200% increase in rates over resting levels versus ~ 150 % increase in rates when feeding after exercise). While 15 – 18 g of quality whey isolate appears to optimize the post-exercise anabolic effect, many questions exist over the ideal quantity of protein that should be consumed within 30 – 45 minutes after exercise. Various studies have investigated this effect by comparing quantities as small as 5 g to over 60 g and it appears that 20 g of quality protein consumed within 30 – 45 minutes is generally considered optimal (averages around 0.23 – 0.27g / Kg BW for average male and female). A whey isolate is suggested given how quickly it’s assimilated into the body and given the fact that it is a rich source of Leucine, an amino acid associated with protein synthesis. Casein on the other hand, while cheaper, and contains less Leucine than whey isolate, and takes considerably longer to empty from the stomach. However, it is a protein of choice to take a few hours after your workout to sustain continued protein synthesis, long after the whey isolates have been utilized.
For individuals with goals to replenish both glycogen stores and build protein, a 4:1 mixture of carbohydrates-to-protein is indicated from research (approximately 1.0 g / Kg BW of carbohydrates; 0.25 g / Kg BW for protein). Accelerade™ is a commercially-available product that meets this recommendation, whereas the new line of recovery products from Gatorade™ only deliver a 1-to-1 or 2-to-1 ratio. Regardless of your goal however, hydration must always be your first consideration before adopting strategies for glycogen and protein synthesis – always factor total caloric quantity and protein intake for the day. To learn more on this topic, see ACE’s online course for Nutrition Strategies for Fitness and Performance.