It is well known that taking carbohydrates before and during endurance exercise helps to increase both speed and endurance. It is not as well known that taking carbohydrates before and during resistance training for strength can increase intensity and duration of workouts. A review of 21 randomized controlled studies that included 226 young adults (ages 20-30, 95 percent men and five percent women) found that taking carbohydrates before or during lifting weights increased training volume, and caused higher peak blood lactic acid and sugar levels (Sports Med, Nov 2022;52(11):2691-2712). These are indirect measures of the intensity of workouts.
The athletes in the studies had been lifting weights from two months to more than five years and the studies did not separate the athletes by how long they have been lifting weights. This review found that taking carbohydrates during resistance exercises:
• was more effective in training sessions lasting more than 45 minutes and containing at least 8–10 sets
• did not prolong or improve workouts in sessions lasting less than 45 minutes
• was beneficial only when the athletes did not eat any food for several hours before each workout
• was most effective in sessions in which the athletes took such intense workouts that they went into failure or close to failure
• was not effective in workouts in which the athletes lifted only up to less than 85 percent of the maximum weight that they could lift
• was not effective when they took less than 0.3 to 2.5 grams of carbohydrate per kilogram of body weight
The carbohydrate dose is a matter of personal preference, because the amount of weight lifted and endurance increased as long as the lifter took at least 0.3 grams of carbohydrates per kilogram of body weight.
Why You Need Carbohydrates During Intense Exercise
Competitive weightlifters spend hours lifting weights, but they still follow the rules of “stressing and recovering”. On one day, they take very intense workouts that damage a specific muscle group and then on the next day, they go easy on that muscle group and take intense workouts stressing a different muscle group. The more intensely you can stress a muscle group without causing an injury, the stronger you become.
When you lift weights, your muscles use carbohydrates, fats and proteins as sources of energy. They need oxygen to convert food to energy. The limiting factor for how intensely you can exercise is the time it takes to move oxygen from your bloodstream into your muscles. Since the sugars from carbohydrates take less oxygen than fats and proteins to produce energy, sugar becomes the primary fuel from food to power your muscles. You have only a limited amount of sugar stored in your body, mostly in your liver and muscles. When you start to run low on sugar stored in your muscles and liver, you need more oxygen. If you are already working at your maximum, you have to slow down.
Lactic Acid Measures Intensity of Exercise
You can measure the intensity of a resistance workout by the weight that you can lift, but you can also measure intensity of a workout indirectly by seeing how high blood lactic acid levels rise during a workout. When you exercise as hard as you can, you use primarily carbohydrates for energy because carbohydrates require less oxygen than fats and proteins do. When you can’t keep up with your needs for oxygen, you start to accumulate large amounts of lactic acid in your muscles and bloodstream. The harder you exercise, the higher your blood lactic acid levels rise, so blood lactic acid levels are an indirect measure of how intensely you are exercising.
When you plan to exercise near your maximum intensity for endurance or resistance for 45 minutes or more, you need an adequate store of carbohydrates. Eat a full meal three hours before your exercise bout or competition, or take a sugared drink just before your workout or race. Almost all sugared drinks contain 10 grams of sugar per 100cc, because that is the concentration of sugar in drinks that tastes best. If your competition or intense workout takes more than 45 minutes, you may consider taking a sugared drink 30 to 45 minutes after you are into your race or intense workout. If your workout or race lasts longer than two hours, you should try to eat some food. This is very important, especially in hot weather. If your workout or race takes more than three hours, you should eat some salted foods.