Refueling: When, What, and How Much?

Key Recovery Points:

1. Use your post-workout window - eat some carbohydrates and protein as soon as possible post workout.
2. Ensure that you are recovering appropriately after the initial post-workout window by meeting caloric and protein needs.
3. Use the 4 R’s framework to make sure you are ticking all the recovery boxes.
4. Recovery is as much about acute adaptation to the session you just finished as it is about preparing well for your next session.

The recent boom in recovery-centric devices, practices, and protocols says everything in regards to how important recovery is to performance.

It always has been. And nowadays  athletes are really prioritizing their recovery more, and seeking ways to improve it.

Why? Because they’re increasingly appreciating the importance of recovery for both performance improvement and prevention of injury and illness.

As in all aspects of training, the basics are the most important, and the rest is a nice addition even for a marginal additional benefit.

What are the basics of recovery nutrition?

Recovery, in its most basic form, can be defined as the return to readiness following a workout or competition. Among the variables impacting recovery, nutrition is one of the pillars of it.

Whether it’s a magic drink or a new space-based molecule, we’re eager for a good sales pitch, especially one that promises that it can make us better than we were before.

Existing literature helps define the essential elements of a good nutritional strategy to recover after exercise. It’s a guide to figure out what really works:

The 4 R’s: Refuel, Repair, Rehydrate, Rest

Refuel: Eat enough macronutrients (specifically carbohydrates), micronutrients and prioritize energy intake in general.

Repair: Eat enough protein.

Rehydrate: Drink enough to replace fluid losses.

Rest: Get good sleep and have nutrition that facilitates this.

When it comes to nutrition, the research in the field is quite robust with good guidelines available as to what, how much, and when to eat. We also understand the physiology of this quite well. That means standard recommendations are feasible to implement.

Before we get into the when, what, and how much, it is important we start with the ‘why’ to ensure the importance of this is not underestimated. Especially because despite this and the willingness of athletes to embrace recovery, athletes are often under fueling their recovery still

The Why:

When exercising, we are breaking down muscles and using our fuel stores. These are catabolic (breaking down) processes. When recovering (via the 4R’s) we are doing the opposite, repairing and replenishing, these are anabolic (building and storage) processes.

But why does the body need to quickly go into an anabolic state?

This is because the primary importance after exercise is glycogen replenishment.

Glycogen acts as a central glucose repository that the entire body can access via conversion of glycogen into glucose both in the liver and in the muscles. Muscle glycogen acts as a local storage site for the working muscles. On average, there are 100g of glycogen in the liver and 400g in the muscle, and the body's glycogen stores hold about 2000-3000 calories of energy, depending on the individual.

As we know, glucose utilization by the working muscle can go up by 10-fold during exercise, and yet after one hour, glucose is maintained at 4g at the expense of these muscle and liver glycogen reservoirs. The amount of glucose in the blood can still be constant after two hours of exercise in well-nourished athletes. Tapping into these stores is important for exercise performance, but depleting these stores prematurely may cause premature fatigue or a drop in glucose leading to hypoglycemia. This is why replenishing these glucose stores is key immediately after exercise especially when the next workout is close.

The process of glycogen synthesis is also supported by other interesting metabolic changes that occur after exercise. During the recovery (anabolic) window, in contrast to the predominant reliance on carbohydrate metabolism seen during a bout of moderate intensity exercise, the rate of lipid oxidation is accelerated and carbohydrate oxidation is reduced, even under conditions of high carbohydrate feeding.(Van Loon et al, 2001) Such a scenario following prolonged aerobic exercise has been shown to persist to the following morning.

This shift in substrate metabolism demonstrates a state of high metabolic priority for muscle glycogen resynthesis, whereby lipid oxidation from intra and extra muscular sources is elevated to meet fuel requirements to sustain other processes not directly involved in recovery. The importance of this is evidenced by the fact that there is a strong relationship between replenishment of liver and skeletal muscle glycogen stores and subsequent exercise performance. Commencing a bout of exercise with reduced muscle glycogen levels impairs exercise capabilities, meaning that restoration of muscle glycogen is vital if optimal performance is desired.

The primary trigger for glycogen synthesis (refueling) is carbohydrate ingestion. This can be fine-tuned to help refuel or leveraged to create a low or high carbohydrate availability training situation in a ‘train low’ approach (training with low carbohydrate availability and low glycogen stores) or a “train high” approach aiming for the opposite.

In addition to replenishing carbohydrates-based stores, the body also has in place a set of processes to quickly repair the muscle damages induced by exercise. The biggest triggers of muscle protein synthesis (repairing and building muscles) are eating protein. Appropriate doses of protein can maximally stimulate muscle protein synthesis. Given the main focus of this article we refer the interested reader elsewhere for further readings.

The When:

The simple answer to this? ASAP.

The more correct answer? Within the first 2 hours, there is a key recovery window that can be used to maximize recovery and delaying ingestion of carbohydrates results in a reduced rate of muscle glycogen storage.

A bout of exercise influences glycemia both during and after, and this can persist for up to 48 hours post exercise due to changes in insulin sensitivity and muscle glucose uptake. Therefore, the post-exercise period includes everything from immediately post-exercise until 48 hours post-exercise (and potentially longer if there is severe muscle damage or after exhaustive endurance exercise). It is important to note, that in the real world, athletes compete or train much more regularly than every 48 hours, sometimes competing multiple times per day, depending on their event. Therefore, the athlete must have a good understanding of which aspects of recovery they prioritize so that glycemia is optimal and energy substrates have recovered to facilitate future performance.

The process of muscle glycogen synthesis begins immediately following exercise and is the most rapid during the first 5-6 hours of recovery. Glycogen synthesis after a bout of exercise occurs in a biphasic pattern, the insulin dependent and independent phases.

Insulin independent phase of muscle glycogen synthesis:

In the initial post-exercise phase, there is a rapid increase in glycogen synthesis for 30-60mins. This is independent of insulin and reflects the initial recovery phase post exercise. This initial rapid glycogen synthesis will slow if carbohydrates are not ingested. Glucose and lactate are the primary substrates for glycogen synthesis, with lactate accounting for at least 20% of post exhaustive exercise glycogen synthesis. Yes, that’s right, lactate is farm from a waste product, it is a key aspect of metabolism and aids in the redundancy of the system.

The above described insulin-independent phase, is suggested to occur when glycogen is depleted at the end of an exercise bout. It seems that the mechanism responsible for the initial rapid phase of glycogen synthesis is the same contraction mediated glucose transporter type 4 (GLUT4) translocation that turns glucose rushes into glucose rises when walking post meal. Additionally there is augmented glycogen synthase activity.

Insulin dependent phase of glycogen synthesis:

The second phase of glycogen synthesis has been defined as the insulin-dependent phase.(Scott et al, 2021)  Insulin increases blood flow to the muscle, GLUT4 translocation to plasma membrane, hexokinase II and glycogen synthase activity, which all contribute to increased glucose uptake by the muscle and glycogen synthesis. Research in athletes has shown that the rate of carbohydrate delivery potentially can be augmented via certain strategies such as use of alternative carbohydrates, congestion of protein and caffeine.

What:

Protein and carbohydrates work together in the post exercise window, allowing for improved protein metabolism as well as improved glycogen synthesis when compared to carbohydrates alone. Glycogen storage is not impacted by source of carbohydrates when comparing liquids and solids.

In addition to carbohydrates, insulin secretion can also be induced through ingestion of certain amino acids. Studies have also shown that there is a synergistic effect of combined amino acids and/or protein and carbohydrate ingestion on insulin release. This evidence led to the strategy of accelerating post-exercise muscle glycogen synthesis with the co-ingestion of carbohydrate and protein. Indeed, there is evidence that when amino acids and/or protein are co-ingested with carbohydrate postprandial insulin levels are augmented leading to an increase in glycogen synthase activity, when carbohydrate intake is below the threshold for glycogen storage (e.g. 0.5-0.8g CHO/kg/h). However, when carbohydrate intake is adequate (e.g. >1g CHO/kg/h), the co-ingestion of protein has no additional effect on glycogen synthesis.

Interestingly, inducing a glucose rush (if this is in response to a carbohydrates-based meal) can be an indication that your body is in an anabolic state, ensuring that glycogen stores are being refilled. During this time phase, insulin is secreted to support glucose uptake by the cells but also protein synthesis in the muscles.

This is perhaps why the co-ingestion of protein and carbohydrates have synergistic effects above caloric matched ingestion of one or the other individually. Yes, you read that right, whilst generally you want to stay in the blue zone, and this is possible even with higher carbohydrate intakes when changing meal order or altering meal composition a little to include fibre and some fat, for example, a bit of a spike post meal in the window of time post workout is probably not detrimental.

How Much:

Your carbohydrate requirements are at least in part related to your intake prior and during training – in your Prime and Perform windows. Beyond this, they are dictated by the intensity and duration of your activity, with consideration given to whether you want to optimize recovery or intentionally not do so.

It should be recognized that these recommendations are in the context of total output for a week as well as after one training session, as is the nutritional intake.

In terms of carbohydrate requirements, the following is suggested:

• Moderate duration/low-intensity training (e.g., 2–3 h/day of intense exercise performed 5–6 times/week): 5–8 g/kg body mass/day
• Moderate to heavy endurance training (e.g. 3–6 h /day of intense training in 1–2 daily workouts for 5–6 days/week): 8–10 g/kg body mass/day
• Extreme exercise programs or competition (+6 h per day or high competition frequency during the week): 10–12+ g/kg body mass/day 11

With respect to protein, dosing is more related to maximal muscle protein synthesis than total dosing requirements. As caloric intake increases, protein will naturally go up. The requirements of protein to ensure maximal muscle protein synthesis vary based on age, energy intake (more protein is needed in times of energy restriction) and recent training stimulus (resistance training increases muscle protein synthesis).

Protein requirements are as follows:

0.5 g/kg of body mass, or an absolute dose of 40g total.

Protein per meal should be between 0.25-0.40g/kg of body mass, or absolute values of 20g total.

When planning multiple sessions per day or multiple sessions with a short time between, rapid restoration of glycogen stores may be required. If this is the case and recovery time is less than 4 hours, you may consider the following right after your workout:

1.2g/kg body mass//hour of carbohydrates, aiming for a high glycemic index carbohydrates OR combining carbohydrates in a lesser dose of 0.8g/kg body mass/hour with 0.2-0.4g/kg body mass/hour of protein.

Potentially adding 3-8mg/kg body mass of caffeine (if appropriate given time of day).

When looking to optimize recovery without another session in a short time frame, it has been suggested that ongoing, regular intake of carbohydrate and protein every 2-3 hours will maintain a rapid rate of muscle protein synthesis and glycogen synthesis, provided this starts relatively soon after exercise.

This may not always be logistically possible or appropriate, given training time, goals etc.

Refueling Conclusions and Recommendations

The good news is that your post training session social meal might be the perfect recovery protocol (even perhaps with the addition of a good coffee). Make sure you eat enough protein and carbohydrates in the post workout window.

The challenge is to ensure this is soon enough after your training session and you keep refueling properly afterwards.

Remember, recovery from one session is aiding in your preparation for the next one within your Prime-Perform-Recover endless energy cycle (see below).

References:

1. Bonilla DA, Pérez-Idárraga A, Odriozola-Martínez A, Kreider RB. The 4R's Framework of Nutritional Strategies for Post-Exercise Recovery: A Review with Emphasis on New Generation of Carbohydrates. Int J Environ Res Public Health. 2020 Dec 25;18(1):103. doi: 10.3390/ijerph18010103. PMID: 33375691; PMCID: PMC7796021.
2. Ivy JL, Ferguson-Stegall LM. Nutrient Timing: The Means to Improved Exercise Performance, Recovery, and Training Adaptation. American Journal of Lifestyle Medicine. 2014;8(4):246-259. doi:10.1177/1559827613502444
3. VAN LOON, L. J., GREENHAFF, P. L., CONSTANTIN-TEODOSIU, D., SARIS, W. H. & WAGENMAKERS, A. J. 2001. The effects of increasing exercise intensity on muscle fuel utilisation in humans. J Physiol, 536, 295-304.
4. EGAN, B. & ZIERATH, J. R. 2013. Exercise metabolism and the molecular regulation of skeletal muscle adaptation. Cell Metab, 17, 162-84.
5. ALGHANNAM, A. F., JEDRZEJEWSKI, D., TWEDDLE, M. G., GRIBBLE, H., BILZON, J., THOMPSON, D., TSINTZAS, K. & BETTS, J. A. 2016. Impact of Muscle Glycogen Availability on the Capacity for Repeated Exercise in Man. Med Sci Sports Exerc, 48, 123-31.
6. BERGSTRÖM, J. & HULTMAN, E. 1967. A study of the glycogen metabolism during exercise in man. Scand J Clin Lab Invest, 19, 218-28.
7. Hawley JA, Burke LM. Carbohydrate availability and training adaptation: effects on cell metabolism. Exerc Sport Sci Rev. 38(4):152-60, 2010.
8. Saunders, M.J.; Luden, N.D.; DeWitt, C.R.; Gross, M.C.; Dillon Rios, A. Protein Supplementation During or Following a Marathon Run Influences Post-Exercise Recovery. Nutrients 2018, 10, 333.
9. Churchward-Venne, T.A.; Pinckaers, P.J.M.; Smeets, J.S.J.; Betz, M.W.; Senden, J.M.; Goessens, J.P.B.; Gijsen, A.P.; Rollo, I.; Verdijk, L.B.; van Loon, L.J.C. Dose-response effects of dietary protein on muscle protein synthesis during recovery from endurance exercise in young men: A double-blind randomized trial. Am. J. Clin. Nutr. 2020, 112, 303–317.
10. Ivy JL, Katz AL, Cutler CL, Sherman WM, Coyle EF. Muscle glycogen synthesis after exercise: effect of time of carbohydrate ingestion. J Appl Physiol (1985). 1988 Apr;64(4):1480-5. doi: 10.1152/jappl.1988.64.4.1480. PMID: 3132449.WOJTASZEWSKI, J. F., HANSEN, B. F., KIENS, B. & RICHTER, E. A. 1997. Insulin signaling in human skeletal muscle: time course and effect of exercise. Diabetes, 46, 1775-81.
11. Scott SN, Fontana FY, Cocks M, et al. Post-exercise recovery for the endurance athlete with type 1 diabetes: a consensus statement. Lancet Diabetes Endocrinol. 2021;9(5):304-317. doi:10.1016/S2213-8587(21)00054-1
12. JENTJENS, R. & JEUKENDRUP, A. 2003. Determinants of post-exercise glycogen synthesis during short-term recovery. Sports Med, 33, 117-44.
13. IVY, J. L. & KUO, C. H. 1998. Regulation of GLUT4 protein and glycogen synthase during muscle glycogen synthesis after exercise. Acta Physiol Scand, 162, 295-304.
14. BANGSBO, J., GOLLNICK, P. D., GRAHAM, T. E. & SALTIN, B. 1991. Substrates for muscle glycogen synthesis in recovery from intense exercise in man. J Physiol, 434, 423-40.
15. KARLSSON, H. K., CHIBALIN, A. V., KOISTINEN, H. A., YANG, J., KOUMANOV, F., WALLBERG-HENRIKSSON, H., ZIERATH, J. R. & HOLMAN, G. D. 2009. Kinetics of GLUT4 trafficking in rat and human skeletal muscle. Diabetes, 58, 847-54.
16. Thomas, D.T.; Erdman, K.A.; Burke, L.M. Position of the Academy of Nutrition and Dietetics, Dietitians of Canada, and the American College of Sports Medicine: Nutrition and Athletic Performance. J. Acad. Nutr. Diet. 2016, 116, 501–528.
17. Reed, M. J., Brozinick, J. T., Lee, M. C., & Ivy, J. L. (1989). Muscle glycogen storage postexercise: effect of mode of carbohydrate administration. Journal of Applied Physiology, 66(2), 720–726. doi:10.1152/jappl.1989.66.2.720
18. FLOYD, J. C., JR., FAJANS, S. S., CONN, J. W., KNOPF, R. F. & RULL, J. 1966. Stimulation of insulin secretion by amino acids. J Clin Invest, 45, 1487-502.
19. FLOYD, J. C., JR., FAJANS, S. S., PEK, S., THIFFAULT, C. A., KNOPF, R. F. & CONN, J. W. 1970a. Synergistic effect of certain amino acid pairs upon insulin secretion in man. Diabetes, 19, 102-8.
20. FLOYD, J. C., JR., FAJANS, S. S., PEK, S., THIFFAULT, C. A., KNOPF, R. F. & CONN, J. W. 1970b. Synergistic effect of essential amino acids and glucose upon insulin secretion in man. Diabetes, 19, 109-15.
21. HOWARTH, K. R., MOREAU, N. A., PHILLIPS, S. M. & GIBALA, M. J. 2009. Coingestion of protein with carbohydrate during recovery from endurance exercise stimulates skeletal muscle protein synthesis in humans. J Appl Physiol (1985), 106, 1394-402.
22. Jeukendrup AE. Periodized Nutrition for Athletes. Sports Med. 2017 Mar;47(Suppl 1):51-63. doi: 10.1007/s40279-017-0694-2. PMID: 28332115; PMCID: PMC5371625.
23. Kerksick CM, Arent S, Schoenfeld BJ, Stout JR, Campbell B, Wilborn CD, Taylor L, Kalman D, Smith-Ryan AE, Kreider RB, Willoughby D, Arciero PJ, VanDusseldorp TA, Ormsbee MJ, Wildman R, Greenwood M, Ziegenfuss TN, Aragon AA, Antonio J. International society of sports nutrition position stand: nutrient timing. J Int Soc Sports Nutr. 2017 Aug 29;14:33. doi: 10.1186/s12970-017-0189-4. PMID: 28919842; PMCID: PMC5596471.
24. Kerksick, C.M.; Wilborn, C.D.; Roberts, M.D.; Smith-Ryan, A.; Kleiner, S.M.; Jäger, R.; Collins, R.; Cooke, M.; Davis, J.N.; Galvan, E.; et al. ISSN exercise & sports nutrition review update: Research & recommendations. J. Int. Soc. Sports Nutr. 2018, 15.
25. Jager R., Kerksick C.M., Campbell B.I., Cribb P.J., Wells S.D., Skwiat T.M., Purpura M., Ziegenfuss T.N., Ferrando A.A., Arent S.M., et al. International Society of Sports Nutrition Position Stand: Protein and exercise. J. Int. Soc. Sports Nutr. 2017;14:20. doi: 10.1186/s12970-017-0177-8.