The effect of pre-exercise carbohydrate intake in the morning on appetite regulation and subsequent resistance exercise performance
2019-10-23T14:09:19Z (GMT) by
Breakfast, which is typically consumed within 2-3 hours after waking up, is considered by many to be the most important meal of the day. Its carbohydrate (CHO) content ranges between 50-60% of its energy, meaning breakfast could replenish carbohydrate (glycogen) stores after a long overnight fast. A number of studies have shown the detrimental effect of omitting breakfast on endurance exercise, however, little is known about the effects on resistance exercise. Considering the prevalence of omitting breakfast among exercisers, commonly due to logistical/practical reasons, examining breakfast consumption versus omission on resistance exercise performance is of particular interest. To initially investigate this, the study reported in Chapter 3 compared performance in 4 sets to failure of back-squat and bench press at 90% of 10 repetition maximum (10-RM), between an ecologically valid breakfast (BC), containing 1.5 g carbohydrate/kg body mass, and a water only breakfast (BO). As hypothesised, total repetitions of back squat and bench press were less during BO compared to BC. Correspondingly, hunger was elevated, whilst fullness was decreased in the BC condition. These results demonstrate that omission of a pre-exercise breakfast might impair resistance exercise performance. However, it cannot be discounted that, as subjects were aware of when they were consuming breakfast or not, that the exercise performance responses were confounded by psychological factors (i.e. placebo/nocebo effects). Therefore, a double-blind study was conducted (Chapter 4), with the aim to compare resistance exercise performance after consuming a water only control breakfast (WAT) or two identical semi-solid breakfasts, one a virtually energy-free placebo (PLA), the other containing 1.5 g carbohydrate/kg body mass (CHO). CHO and PLA breakfasts were eaten with a spoon from a bowl and contained 4.25 mL/kg body mass water, 0.75 mL/kg body mass sugar-free orange squash and 0.1 g/kg body mass xanthan gum as a thickener, with addition of 1.5 g/kg body mass of maltodextrin in the CHO breakfast. Back-squat total repetitions were greater in both CHO and PLA compared to WAT. Correspondingly, CHO and PLA similarly suppressed hunger and increased fullness relative to WAT. This study indicated that breakfast likely exerted its effect on resistance exercise performance via a psychological effect. However, when higher volume resistance exercise was applied (Chapter 5), consisting of sets of 10 repetitions of leg extension to exhaustion at 80% 10-RM, an ergogenic role of carbohydrate was evident, as CHO produced greater total repetitions compared to PLA. Whilst the studies in Chapter 3 and 4 suggested that breakfast influenced performance via a psychological effect, appetite also responded correspondingly, raising the question as to whether appetite might influence resistance exercise performance. In a follow-up study (Chapter 6) two breakfasts containing 1.5 g carbohydrate/kg body mass were provided, but one included 0.1 g/kg body mass of xanthan gum (SEM), whilst the other did not (LIQ), with the aim of manipulating appetite without affecting carbohydrate intake. Interestingly, back squat total repetitions were greater following the SEM compared to LIQ and this correspond with decreased hunger and increased fullness in SEM compared to LIQ. In conclusion, the results from these experiments demonstrate that the perception of breakfast consumption, rather than carbohydrate/energy per se, improves resistance exercise performance. The ergogenic role of pre-exercise carbohydrate only seems to benefit extremely high-volume resistance exercise performance. Whether these effects are still apparent when pre-breakfast/meal glycogen stores are not optimal is unknown (i.e. if a not fully replaced from a previous training session). However, when subjects are well-fed, high-intensity intermittent exercise like resistance exercise might be influenced by sensation of fullness and a pre-exercise meal might exert its effects through this novel mechanism. In situations where the amount carbohydrate or the metabolic effects of the carbohydrate consumed before exercise are unlikely to influence performance (such as resistance exercise), consumption of meals that decrease sensations of hunger might be a simple strategy to enhance performance.