Glucose or Caffeine? What to Snort to Boost Your Exercise Performance? Glucose Spray Increases Avg. Power Sign.

Pre-workout drinks were yesterday, the modern athlete snorts his ergogenics.

No, I didn't mean the headline to be figurative. A recent study in the International Journal of Sports Physiology and Performance built on the observation that nasal sprays (NAS) containing caffeine (CAF) or glucose (GLUC) activate the sensory(motor) cortices in your brain.

In their latest study, Kevin De Pauw, et al. investigate whether this effect would translate to real-world increases in exercise and/or cognitive performance (reaction times).
For their study, the scientists recruited eleven non-smoking and moderately trained male subjects (age: 22±2 yrs) with a low daily caffeine consumption (23 ± 27 mg/day). All subjects were asked to maintain the same nutrition pattern before each experimental trial. The latter included a 30 s Wingate test and a 30 min time-trial (TT) performance test interspersed by 15 min of rest.

"The three experimental trials that were identical except for the NAS solution. Each trial started at the same time of the day and included two exercise performances, i.e. the 30 s Wingate test and a 30 min TT performance, always performed in the same order and separated by 15 min of passive rest. During the exercise performances no verbal encouragement or other motivational measures were provided" (De Pauw. 2017). 

Before they started to cycle, the subjects used a nasal spray that contained solutions with caffeine (CAF), glucose (GLUC) or placebo (PLAC) in randomized, double-blind, placebo-controlled, cross-over manner. The solutions were nasally administered with a standard insufflator and were prepared by an independent company an here's what was in the sprays:

• all nasal sprays contained 400 mL water, 40 mg benzalkoniumchloride as a preservative plus natrium chloride as a base, as well as hydroxypropyl methylcellulose (HPMC) and mannitol to modify the particle morphology and flowability 
• the caffeine spray (CAF) and glucose sprays (GLUC) contained a final concentration of 16mg/ml and 80mg/ml caffeine and glucose, respectively

The sprays were used before each exercise performance and at 25, 50 and 75% of the 30 min TT (see graphical overview in Figure 1 | they cleared their nose before each application to ensure optimal distribution and absorption). Each time the subjects sprayed the solution within the nasal cavity, they alternately sprayed twice in the right and twice in the left nostril in order to optimally disperse the solution within the nasal cavity. As the scientists point out, this nasal spray (NAS) strategy is in accordance with previous research using mouth rinse solutions (Chambers 2009; Doering 2014).

Figure 1: Graphical overview of the study design (De Pauw. 2017).

Mouth rinse? Yes, you read that right. After all, scientists who have been dabbling with mouth rinsing as a means to improve athlete performance believe that the effects are mediated by the very increase in brain activity that Phillips et al (2014) observed in their previously discussed study. And De Pauw et al. believed that the same mechanism would be responsible for any potentially observable performance increase in the study at hand (brain activity was not measured, though).
Performance increases that reached statistical significance only in the glucose, yet not in the caffeine group, where the 1.2% and 0.5% increase in power output during the Wingate test and time trial in the caffeine group did not achieve statistical significance. The average increase in power output during the time-trial in the glucose group, on the other hand, was statistically significant.

Figure 2: Peak power and average power in watt, relative change compared to placebo trial in % (De Pauw. 2017).

In a similar vein, the scientist's magnitude-based inference analysis showed that the use of the glucose nasal spray had a "very likely beneficial (98 %)" beneficial effect on average (time-trial) and a very unlikely/trivial (2 %) negative effect on the peak power output during the Wingate trial. Accordingly, the scientists' mechanistic inference, based on threshold chances of 5 % for substantial magnitudes, shows that the glucose spray exerts a very likely positive effect on endurance performance as a whole - albeit only compared to placebo, not compared to caffeine which yielded small, but statistically non-significant increases in both peak (Wingate) and average (time-trial) wattage, of which I simply have to ask myself whether they would have been more pronounced and statistically significant if the concentration of caffeine in the spray had been higher than the meager 15mg/ml (based on blood tests we know that it was not sufficient to affect the level of caffeine in the blood, but that's not what we wanted to achieve, anyway).
References:

• Chambers, E. S., M. W. Bridge, and D. A. Jones. "Carbohydrate sensing in the human mouth: effects on exercise performance and brain activity." The Journal of physiology 587.8 (2009): 1779-1794.
• De Pauw, Kevin, et al. "Do Glucose and Caffeine Nasal Sprays Influence Exercise and/or Cognitive Performance?." International Journal of Sports Physiology and Performance (2017): 1-22.
• Doering, Thomas M., et al. "The effect of a caffeinated mouth-rinse on endurance cycling time-trial performance." International journal of sport nutrition and exercise metabolism 24.1 (2014): 90-97.
• Phillips, Shaun M., et al. "The Influence of Serial Carbohydrate Mouth Rinsing on Power Output during a Cycle Sprint." Journal of sports science & medicine 13.2 (2014): 252.