Carbohydrate Loading – Maximize Your Performance (#35)

Carbohydrate loading is essentially straightforward: the aim is to ensure your glycogen stores are well-filled.

But… don’t overcomplicate it!

Training and competing with full glycogen stores offer several advantages, and research largely agrees that full stores enhance performance compared to depleted ones. Besides the immediate performance boost, you as an athlete can train more often, longer, and harder without risking the negative physiological and psychological impacts of training (1). The outcome is simply higher quality training.

Your body efficiently replenishes glycogen stores. Typically, you can store about 400 g of glycogen in your muscles and roughly 100 g in your liver. Additionally, about 5 g (5.5 mmol/L) circulates in your bloodstream as free glucose, known as “blood sugar.” Maintaining liver glycogen helps balance blood glucose levels. A significant depletion in these stores can trigger several signals, including a central fatigue signal that simply makes you feel tired.

The approximate 400 g stored in your muscles are sufficient for about 60–90 minutes, so if you plan to train for over 1.5 hours, you might consider carbohydrate intake—depending on the intensity, of course. If you're walking for 90 minutes, you'll likely manage just fine.

Research is also exploring whether a reduction in brain glycogen stores contributes to fatigue. In mice, a reduction of 34–60 percent in brain glycogen stores was observed after two hours of running, possibly explaining more significant central fatigue during longer sessions (2). However, this has not yet been studied in humans. But who wants to take the SAT right after crossing the finish line?

However, you don't need to overcomplicate it. Make sure to increase your carb intake during the three days leading up to the race or tough training session. All types of carbohydrates eventually lead to muscle glycogen as long as the stores aren't already maxed out. Let taste and habit guide your carbohydrate sources, but avoid complex, fibrous carbs on the last day — you don't want your gut full at the start line; you want the energy in your stores. Don't see carb loading as an excuse for junk food, but aim for easily digestible carbohydrates on the last day.

In a study, participants were given 500 g of simple carbohydrates in the form of white bread, jam, and juice in a single meal. Their blood sugar levels peaked at 6.6 mmol/L after 90 minutes but reverted to baseline (5.5 mmol/L) and remained there for eight hours. All the carbohydrates they consumed were either stored as glycogen or used as fuel immediately. No carbohydrates turned into fat; instead, they were primarily stored as glycogen — very important for endurance athletes (source).

An overview of carbohydrates in various forms. Image borrowed from Train Strength (in case someone misses it :))

At the start line, it's crucial to be as energized as possible. Here's a valuable tip: by eating your last meal a few hours before the race, your glycogen stores will be full, but the levels slightly decrease each time the muscles contract. So, at the start line, you're likely not 100 percent full. A smart strategy is to drink a small amount of the sports drink or energy source you intend to use during the race around 15 minutes before the start. These carbohydrates won't be saved as muscle glycogen but will "activate" the absorption mechanisms in the stomach — keeping the body ready to receive more energy right from the beginning. From there, it's your decision on how to manage your energy intake.

I also want to recommend creatine in conjunction with carbohydrate loading. Creatine is perhaps the most commonly used supplement in the strength training world because it helps replenish ATP, the body's explosive fuel for anaerobic (without oxygen) heavy or fast muscle work. Newer studies show exciting effects for glycogen storage as well (link). In a study, a group of exercisers did a glycogen-depleting session followed by six days of carbohydrate loading. The group that consumed carbohydrates after the depleting session and also took creatine (20 g per day for five days) increased the amount of glycogen in the muscles by 82 percent compared to the placebo group that consumed the same amount of carbohydrates (8 g/kg body weight) but did not take creatine.

The participants initially had 400–450 mmol/kg muscle mass (dry weight) without glycogen. They did a depleting session and dropped to about 80 mmol. Immediately afterward, they started replenishing with 8 g of carbohydrates/kg body weight in the form of carbohydrate-rich food and sports drinks. The diet during the test consisted of 80 percent carbohydrates, which led to very rapid replenishment and recovery.

The black bars represent the participants who took creatine. After the first day, the creatine group had 82 percent more glycogen re-stored in the muscles and were already back, even slightly above the starting level. During the following five days, this increased glycogen level was maintained so that they were consistently above the control group.

Carbohydrates are essential when it's race time, regardless of your previous training strategy. Training adapts the body to certain conditions, but on race day, there's no debate: you don't run a marathon on an empty stomach just to "optimize" fat utilization after crossing the finish line. If you're at the start line, be 100 percent prepared for what's ahead.

Experiment with and learn how your body reacts to higher amounts of carbohydrates. It may take time for your body to adjust to handling larger volumes, so gradually increase your intake to avoid stomach issues.

Large amounts of carbohydrates also bind some extra water in the body, which can be beneficial in hot weather or for long-lasting performance. But if you're concerned about weight categories, keep in mind that carb-loading can add a couple of extra kilos.

For more reading, we recommend Professor Jeukendrup's blog: http://www.mysportscience.com/single-post/2016/05/12/Carb-loading-what-is-new

1. 1 – Higher dietary carbohydrate content during intensified running training results in better maintenance of performance and mood state.
2. 2 – Brain glycogen decreases during prolonged exercise
3. 3 – Nutrition and Athletic Performance
4. 4 – Carbohydrate availability and exercise training adaptation: Too much of a good thing?