Among the tidbits of exercise physiology the average lifter knows is this: ingest protein within 30 minutes of ending a workout. In failing to do so, an athlete risks letting hard-won hypertrophic gains slip through their grasp; immediate post-workout protein within your anabolic window seals in muscle growth, or so the logic goes.
What Is the Anabolic Window?
The “anabolic window” has been touted as a short period of post-workout time during which your body is primed to use amino acids for muscle protein synthesis. “This has not been categorically determined,” says Donny Camera, PhD, a research fellow at Australian Catholic University who studies skeletal muscle metabolism. “Exercise is known to increase the sensitivity of muscle to the anabolic effects of protein, but how long this sensitivity lasts is not known.”
So while we know to use protein to foster anabolism and that protein should be involved sometime before or after the workout, the research on the exact timing for optimal uptake is murky at best. We combed through the literature and, with Camera’s help, tried to make sense of nutrient timing for the contemporary obstacle course racing athlete.
Why Nutrient Timing Matters
When we apply resistance stressors to our muscles, they break down, and the process by which they repair themselves is called muscle protein synthesis. “Protein ingestion, through its amino acid building blocks, is able to be incorporated into muscle proteins to facilitate growth,” Camera says. “Amino acids can also stimulate the muscle’s molecular machinery to increase rates of MPS that, over time, constitute muscle hypertrophy.”
Over the past few decades, researchers have shown that the timing of protein ingestion has a significant effect on muscle protein synthesis. A 2001 study led by Vanderbilt University, for instance, found that taking 10 grams of protein (the supplement also contained 8 grams of carbohydrates and 3 grams of fat) directly after a lower-body resistance workout increased whole-body protein synthesis by 12 percent, as compared to a control group who took the same supplement three hours after the workout.
A similar 2010 American Journal of Clinical Nutrition study took quadriceps biopsies of young men who were continuously infused with leucine (an essential amino acid) and discovered myofibrillar protein synthesis increases that peaked 45 to 90 minutes after initial infusion, which would seem to underscore the need for getting quick protein to stimulate post-workout muscle protein synthesis.
The Elusive Anabolic Window
A variety of research, on resistance training in the elderly, whey protein, and fortified milk, has referenced the “anabolic window,” according to a 2013 Journal of the International Society of Sports Nutrition meta-analysis. But the analysis, which referenced 85 studies related to nutrient timing, found a lot more evidence to refute a specific anabolic window than evidence to support its existence.
For starters, the evidence supporting the idea of an anabolic window largely comes from people who worked out in a fasted state. When you ingest protein before a workout, the results are vastly different. A 2007 study had one group of participants take 20 grams of whey protein before exercise. A second group had the protein right after. Amino acid uptake (which fuels the synthesis) remained the same, regardless of whether the protein was ingested before or after the workout.
Unless you’re hitting the weights without eating anything that day, the post-exercise protein time crunch isn’t so stressful. “It was recently shown that the amount of protein required to to maximally stimulate MPS [muscle protein synthesis] following resistance exercise was less—20 grams—if a breakfast meal containing protein was ingested beforehand,” Camera says, referencing a 2013 American Journal of Clinical Nutrition study. That means a modest protein shake, rather than a mountain of chicken breast, can sustain you until lunchtime after a morning lift.
These studies run contrary to the 30-minute “anabolic window” because nutrient timing has more to do with getting protein around the time of the workout, not within an exact window before or after. “Available literature indicates that consuming protein either pre- or post-workout induces comparable increases in MPS and anabolic cell signaling,” Camera says. “Provided amino acids are consumed around the time exercise is performed, MPS will be increased.”
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Despite the fact that you can actually get adequate protein entirely before the workout, there’s a decent reason why you’d spread it out. “The main difference or point of consideration is, if consuming protein prior to exercise performance, whether the capacity to perform at the required intensity can still be maintained considering the effects of actively digesting and metabolizing protein while concomitantly exercising,” Camera says. In short, too much pre-workout protein could mess up your gut.
Now that we’re past the basics of nutrient timing, here are three real-world solutions to improve your training.
1. Get Protein within an Hour of Resistance Training
“I would recommend consuming protein within an hour of exercise completion, as it needs to be remembered that the muscle has undergone some minor ‘stress’ through exercise,” Camera says. Introducing amino acids shortly after ending the stress stimulus will likely start muscle repair and growth sooner, he says, than delaying protein ingestion. As a general rule, the more protein you had before the workout, the longer you can wait to get protein after, but get it done sooner if possible.
2. If You Can, Make It Whey Protein
If you’re not vegan or allergic to it, whey protein is best. “Most literature overwhelming indicates whey protein to promote enhanced effects on MPS compared to soy and casein protein types,” Camera says, because it is of higher quality and easier to digest, allowing the amino acids to get into the bloodstream faster. Lastly, Camera says, whey protein has a higher leucine content than other protein types, and leucine is known to influence the anabolic response of muscle.
3. Adjust for Size and Age
“If your goal is to primarily increase muscle strength and size with resistance training, the ingestion of 0.3 to 0.4 grams of whey protein per kilogram of body mass has been shown multiple times to be optimal to maximize the muscle growth response to resistance exercise,” Camera says.
That said, at age 55, the protein requirement increases by 70 percent at each meal to “maximally stimulate MPS and achieve equivalent rates compared to younger (20 to 35 year old) adults,” Camera says. Use these facts to guide your protein intake and maximize the anabolic gain from your resistance efforts.