Protein timing after training: how much the anabolic window matters

Protein timing means eating protein at a planned time relative to training, most often in the first hour afterwards. The idea rests on the anabolic window, a supposed short period after exercise when muscle makes the best use of protein. The research gives a clear answer: the window exists, but it is much wider than an hour. For most people who train in the gym, the total amount of protein eaten each day, and how it is spread across meals, has a larger effect on strength and muscle gain than the minutes between the last set and the first serving.

What happens in muscle after resistance training

Muscle tissue is constantly rebuilt. Muscle protein synthesis is the process of building new muscle proteins, and muscle protein breakdown is the process of dismantling old ones. When synthesis exceeds breakdown over days and weeks, muscle grows. When breakdown exceeds synthesis, it shrinks.

Resistance exercise and eating protein both raise muscle protein synthesis, and the International Society of Sports Nutrition (ISSN) position stand on protein describes the two as working together when protein is eaten before or after training. The same position stand notes that the effect of a training session on muscle lasts at least 24 hours, although it probably becomes smaller as time passes. That time course already suggests why a one-hour cut-off is too strict: the body stays responsive to protein for most of the following day.

What the timing research shows

The most direct test of the one-hour idea is a 2013 meta-analysis by Schoenfeld, Aragon and Krieger, which pooled 23 randomized trials on muscle growth and 20 on strength. Each trial compared protein taken within about an hour of resistance training with protein taken later.

A simple comparison showed a small advantage for early protein on muscle size and none for strength. Once the authors accounted for how much protein each group ate in total, the advantage disappeared. In many trials, the "timed" group had simply eaten more protein. Total protein intake was the strongest predictor of muscle gain.

One limitation sets the reach of this result. Control groups ate protein anywhere from two hours to many hours after training, so short and long delays could not be compared directly. The first hour is not critical, but that does not mean timing never matters.

How much protein per day

A 2018 meta-analysis by Morton and colleagues combined 49 trials with 1,863 healthy adults who did resistance training for at least six weeks. Protein supplements produced modest extra gains in strength and fat-free mass, meaning body mass excluding fat, which includes muscle. Those gains levelled off at a total intake of about 1.6 g of protein per kilogram of body weight per day.

That number is an estimate with wide uncertainty. Its 95% confidence interval ran from 1.03 to 2.20 g/kg, so the authors suggest about 2.2 g/kg for people who want to cover the upper end. Supplements had a larger effect in people with resistance-training experience and a smaller one with increasing age.

The ISSN position stand reaches a similar range. These are the main reference points:

Whole food can cover these amounts. The position stand describes protein shakes as a practical way to meet them, not a requirement.

How large each serving should be

The ISSN recommends servings of about 0.25 g/kg, or roughly 20–40 g of high-quality protein, spread evenly every three to four hours. Each serving stimulates muscle protein synthesis, so regular servings keep that process raised through the day.

The upper limit of a single serving is less certain than older advice suggested. In a 2023 study by Trommelen and colleagues, 36 healthy, recreationally active young men drank 0 g, 25 g or 100 g of milk protein after one whole-body resistance workout. The 100 g dose produced a larger anabolic response that was still present after 12 hours. Because it measured a single meal in young men, the study does not show long-term muscle gain and may not apply in the same way to women, older adults or people with health conditions. It does indicate that a large protein meal is not wasted, so three larger servings are a reasonable option when four or five meals do not fit a schedule.

Worked example: a 70 kg athlete

Illustration, not a prescription: a 70 kg athlete doing resistance training four times a week.

1. Daily target. 70 kg × 1.6 g/kg = 112 g of protein per day. The ISSN range gives 98–140 g.
2. Serving size. 70 kg × 0.25 g/kg ≈ 18 g, so servings of 25–30 g sit comfortably within the 20–40 g guidance.
3. Distribution. Four servings of about 28 g reach the target: breakfast, lunch, an afternoon snack and dinner.
4. Training at 18:30. If the session ends at 19:30 and dinner follows at 20:30, dinner already serves as the post-training meal. A shake straight after training adds convenience, not a measurable advantage.

A 6:00 session changes the picture. If the last meal was dinner the night before and breakfast comes mid-morning, the gap before and after training stretches well beyond the three-to-four-hour pattern. Eating protein soon after the session, as a shake or a quick breakfast, keeps intake within that pattern. In this case the timing matters because of the long gap, not because of a one-hour deadline.

Endurance and hybrid training

Most of the evidence above comes from resistance training. For long runs, rowing or HYROX-style sessions, the ISSN position stand puts adequate carbohydrate first for performance, with protein supporting recovery and possibly reducing muscle damage. Hybrid athletes can use the same daily protein range, as long as protein does not displace carbohydrate on long endurance days.

Key points

1. Set a daily target first. Multiply body weight in kilograms by 1.6 for a practical figure, within an evidence-based range of 1.4–2.2 g/kg.
2. Spread protein across three to five meals of roughly 20–40 g, about every three to four hours.
3. Count the next regular meal as post-training protein when it comes within a couple of hours of the session.
4. Eat protein soon after early-morning sessions when the previous meal was the night before.
5. Keep carbohydrate in place on endurance days. Protein supports recovery but does not replace fuel.

Sources

• Schoenfeld BJ, Aragon AA, Krieger JW. The effect of protein timing on muscle strength and hypertrophy: a meta-analysis. Journal of the International Society of Sports Nutrition, 2013.
• Morton RW et al. A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine, 2018.
• Jäger R et al. International Society of Sports Nutrition Position Stand: protein and exercise. Journal of the International Society of Sports Nutrition, 2017.
• Trommelen J et al. The anabolic response to protein ingestion during recovery from exercise has no upper limit in magnitude and duration in vivo in humans. Cell Reports Medicine, 2023.

Heart rate is a training signal, not medical advice, and this article offers general nutrition information rather than a personal plan. People with kidney disease or a medically prescribed diet should agree on protein intake with their doctor.