Metabolic window

The metabolic window (also called the anabolic window or protein window) is a term used in strength training to describe the 30-minute (give or take, dependent on the individual) period after exercise during which nutrition can shift the body from a catabolic state to an anabolic one. Specifically, it is during this period that the intake of protein and carbohydrates can aid in the increase of muscle mass.[1]

Currently there is not sufficient scientific evidence to support the metabolic window theory.[2]

The metabolic window is based on your bodies anabolic response (Stark, 2012). Anabolism is when small molecules grow into bigger complex molecules. This is the opposite to catabolism, when larger molecules break down in the body. During anabolism, the molecules form into new larger cells and tissues.

After strength training, your body is anabolic. This physical state requires a lot of cellular processes to take place for muscle repair and growth. These processes are fuelled by nutrients called protein and carbohydrates. The associated benefits to hitting the metabolic window of 30 minutes or less include increasing protein synthesis, reducing muscle protein breakdown and replenishing muscle glycogen. These are all processes that take place at a slow rate in the body and by pumping your body full of nutrients immediately after a workout, allows your body to increase the rate of repair and hopefully bigger muscle gains.

The evidence is somewhat on the fence regarding whether the metabolic window exists. The most well proven variable to muscle building is progressive overload, which involves lifting more resistance over time, to which the muscles adapt.

The evidence for replenishing depleted energy levels only relates when they are completely gone at the beginning of training, such as during fasted exercise (Witard, 2014). This is where large amounts of the day go by without any eating to spike and deplete energy levels to trick the body, followed by a training session (with low levels of nutritional energy) to force the body to be uncomfortable. Following this, the body is at an abnormally low level of various nutritionist (such as carbohydrate and proteins), which are then put back into the body to force an even higher adaptation in the body. During fasted exercise, an increase in muscle protein breakdown causes the pre-exercise negative amino acid level to continue in the post exercise period despite increases in muscle protein synthesis. This is why it would make sense to provide immediate nutritional replenishment after exercise as there was already such a low level before training started (Aragon & Schoenfeld, 2013). This would turn the catabolic state of the body into an anabolic one and therefore, promote the metabolic window as desirable. This means more or less that the body is so used to receiving food that when you starve yourself, the body does not know what to do, so it enters a panic mode where you push yourself through a depleted state, and then finally feed yourself and the body absorbs even more of the nutrients and only takes the ones needed. For more on this look up fasting and intermittent fasting.

Types of nutrition - Glycogen is one of the primary replenishments after exercise. Glycogen is considered essential to training at levels needed for muscle hypertrophy, responsible for as much as 80% of ATP production during workouts (Aragon & Schoenfeld, 2013). Due to such involvement of glycogen in the body during training, it is suggested that we replenish these levels after training. Glycogen comes in the form of carbohydrates such as potatoes, rice, bread and pasta. This can also be taken care of with a post training drink such as a recovery shake. These glycogen stores do recover over time though because they are already high enough after training to not cause any serious effect on the bodies production if following a regular eating plan (3-4 meals a day).

Protein is perhaps the most preached nutrient to be consumed after training because it is said to increase in muscle protein synthesis. Unfortunately the evidence here is lacking, since the biggest promoter of muscle protein synthesis is actually the resistance training taking place every time training takes place (Aragon & Schoenfeld, 2013).

Some theorists believe the metabolic window begins to close within minutes of the end of a workout. They claim the same nutrients taken two hours later result in significantly reduced protein synthesis and muscle glycogen storage.[1] Further research is needed into the effects of food and exercise timing, but methodology has to be considered in these experiments.[3]

Since there is so much information out there, young athletes and people who are new to fitness and strength often turn to the pros for advice. Unfortunately there are lots of celebrities and fitness influencers in the market who can advertise products for the young and naive. Little research is put into products when people think they can buy whatever the professionals take and look like them as well. Unfortunately it’s not that easy, and most of the athletes and professionals don’t use the products they’re advertising, such as refuel bars, protein shakes and nutrition supplements .