Carbohydrate Ingestion During Resistance Exercise Elevates Blood Glucose and May Improve Muscular Endurance but Not Maximal Strength or Power: A Randomised, Placebo-Controlled, Workload-Matched Crossover Trial
In a randomized, placebo-controlled crossover trial involving resistance-trained individuals, ingesting 60g of carbohydrates during resistance exercise significantly elevated blood glucose and modestly improved muscular endurance in the dominant leg, but did not enhance maximal strength, power, or affect the non-dominant leg.
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For decades, the gym has operated on a simple, widely held belief: if you want to push harder, lift heavier, or last longer, you need fuel. Carbohydrates, the sugars and starches found in bread, pasta, and fruit, are the body's preferred source of quick energy. In long-distance running or cycling, the science is clear; eating carbs during the event keeps the engine running and delays exhaustion. But in the world of weightlifting and resistance training, where the goal is often to move heavy loads for short bursts, the rules are less certain. Many people assume that sipping a sugary drink between sets of squats or bench presses will boost their strength or power, yet scientific evidence for this specific scenario has been thin. The question remains: does adding fuel mid-workout actually change how a muscle performs, or is it just a placebo effect for the person lifting the weight?
Researchers at Goethe University Frankfurt decided to settle this question with a careful, controlled experiment. They gathered fifteen people who were already experienced with resistance training and asked them to complete two full-body workout sessions. The workouts were identical in every way: the same five exercises, the same heavy weights, and the same number of repetitions. The only difference was what the participants drank. In one session, they consumed a beverage containing sixty grams of carbohydrates, a significant amount of sugar designed to flood the system with energy. In the other session, they drank a placebo that looked and tasted exactly the same but contained no carbohydrates. To ensure the comparison was fair, the researchers made sure the participants ate a standard breakfast three hours before each session, so their starting energy levels were consistent. The participants did not know which drink they were getting, but the researchers did, and they carefully matched the workload so that the physical effort required was the same in both trials.
The results painted a picture that was both clear and surprisingly specific. As expected, the carbohydrate drink did exactly what it was designed to do: it raised the participants' blood sugar levels significantly, increasing them by nearly twenty milligrams per deciliter compared to the placebo. However, this surge in fuel did not translate into a general boost in power. When the researchers tested the participants' maximum strength and explosive power after the workout, there was no difference between the two sessions. Whether they had drunk the sugar water or the placebo, their ability to jump high or squeeze a handgrip with maximum force remained unchanged. The study also found that the extra sugar did not make the participants feel like they were working harder or easier; their overall sense of effort and mood during the workout stayed the same.
There was, however, one narrow area where the carbohydrates seemed to make a difference, though it came with a caveat. When the participants performed an endurance test on a leg extension machine, lifting a heavy weight until they could no longer continue, those who had the carbohydrate drink managed to complete more repetitions with their dominant leg. On average, they did nearly three extra repetitions compared to the placebo session. This improvement was statistically significant for the dominant leg, but for the non-dominant leg, the improvement was similar in size but did not reach the threshold of statistical certainty. The researchers noted that this benefit appeared to be limited to muscular endurance rather than raw strength, and it did not seem to be driven by a change in how the body processed waste products like lactate, which remained the same in both conditions.
The study also uncovered an interesting detail about how different bodies handle the same amount of fuel. The rise in blood sugar was not uniform across all participants; it was more pronounced in individuals who were shorter and lighter. This suggests that body size plays a role in how the body responds to a fixed dose of carbohydrates during exercise. Despite this metabolic difference, the extra sugar did not directly correlate with the extra repetitions performed, meaning the mechanism behind the endurance boost is not simply about having more sugar in the blood. The researchers concluded that while drinking carbohydrates during a workout does raise blood sugar, it does not magically increase strength or power. Any benefit appears to be small and specific to endurance in certain muscle groups, and the findings are preliminary enough that they require further confirmation in larger studies before they can be turned into a universal rule for gym-goers.
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