How does hunger influence resistance exercise performance? Original paper

Preexercise carbohydrate intake enhances endurance and intermittent exercise performance, but its effect on resistance exercise performance is less clear. A study published in 2019 found that the consumption of 1.5 grams of carbohydrate per kilogram of body mass increased resistance exercise performance compared to no breakfast.^[1] However, a follow-up study reported no difference between a high-carbohydrate breakfast and a viscous very-low-energy breakfast (30 kcal) for resistance exercise performance,^[2]and changes in hunger and fullness were similar between groups. This research suggests that hunger may mediate the effects of preexercise carbohydrate intake on resistance exercise performance rather than glucose availability.

In this randomized crossover trial, 16 resistance-trained men (average age of 27; five years of resistance exercise experience) completed a resistance exercise workout consisting of four sets of barbell bench press and back squat performed to failure at 90% of their 10-repetition maximum, with at least three minutes of rest between sets. Two hours before exercise, the participants consumed either a low-viscosity (LIQ) or high-viscosity semisolid meal (SEM; contained the same ingredients as LIQ, but xanthan gum was added to thicken the solution) containing 1.5 grams of carbohydrate per kilogram of body mass. The participants recorded their diet and physical activity for two days before the first trial and replicated these patterns before the second trial.

The primary outcome was squat performance. The secondary outcomes were bench press performance, subjective hunger and fullness (measured using visual analog scales), blood glucose, and plasma insulin, total ghrelin, and peptide YY. Subjective hunger and fullness were assessed at 10, 45, 60, and 105 minutes postmeal; blood glucose levels were assessed at 15, 30, 45, 60, and 105 minutes postmeal; and hormone levels were assessed at 45 and 105 minutes postmeal.

Total repetitions completed for the back squat were 11.6% higher (57 vs. 51 repetitions) in the SEM condition compared to the LIQ. However, there was no difference between groups in the number of total repetitions completed for the bench press. Hunger was lower and fullness was higher in SEM compared to LIQ at 45 minutes and 105 minutes. Additionally, compared to premeal, fullness was significantly increased at all time points in SEM, but only at 10 and 45 minutes in LIQ.

With respect to blood markers, compared to premeal, plasma insulin increased at 45 and 105 minutes in both LIQ and SEM; however, plasma insulin levels were higher in LIQ than SEM at these time points. Also, blood glucose was higher at 30 minutes in LIQ compared to SEM. There were no differences between groups for total ghrelin or peptide YY levels.

Back squat was performed before bench press, so it’s possible that the fatigue from back squats carried over into bench press and negated the effects of hunger. An alternative hypothesis is that hunger exerts a greater influence during exercises that require activation of larger muscle groups.