Resistance exercising on unstable surface leads to Pupil Dilation

Abstract

Background: Chronic resistance training and acute resistance exercises improve physical performance and can enhance cognitive performance. However, there is still uncertainty about the mechanism(s) responsible for cognitive improvement following resistance training and exercise. Recent findings suggest that resistance exercise has metabolic as well as cognitive demands, which potentially activate similar neural circuitry associated with higher-order cognitive function tasks. Exercising on unstable devices increases the coordinative and metabolic demands and thus may further increase cognitive activation during resistance exercise. The measurement of pupil diameter could provide indications of cognitive activation and arousal during resistance exercise. Pupil dilation is linked to the activity in multiple neuromodulatory systems (e.g., activation of the locus coeruleus and the release of the neurotransmitter norepinephrine (LC-NE system)), which are involved in supporting processes for executive control. Therefore, the purpose of this study was to compare the cognitive activation measured by pupil diameter during an acute bout of resistance exercise on stable and unstable surfaces.

Methods: 18 participants (23.5 ± 1.5 years; 10 females) performed ten kettlebell squats in a preferred repetition velocity in stable and unstable (BOSU® Balance Trainer) ground conditions. Pupil diameter was recorded with eye tracking glasses (SMI ETG) during standing (baseline) and during squatting. Raw pupil data were cleaned of artifacts (missing values were linearly interpolated) and subjected to a subtractive baseline correction. A student t-test was used to compare mean pupil diameter between ground conditions.

Results: The mean pupil diameter was significantly greater during squats in the unstable condition than in the stable condition, t (17) = -2.63, p =.018, Cohen's d_Z = -0.62; stable: 0.49 ± 0.32 mm; unstable: 0.61 ± 0.25 mm).

Conclusion: As indicated by pupil dilation, the use of unstable devices can increase the cognitive activation and effort during acute bouts of resistance exercise. Since pupil dilation is only an indirect method, further investigations are necessary to describe causes and effects of neuromodulatory system activity during resistance exercise. Resistance training with and without surface instability can be recommended to people of all ages as a physically and cognitively challenging training program contributing to the preservation of both physical and cognitive functioning.

Keywords: Mental effort; Metastable resistance training; Pupil size; Pupilometry; Surface instability; Task complexity.

Fig. 1

Study procedure with pretesting and testing session

Fig. 2

Raincloud plot of the mean pupil data during squatting on stable and unstable ground conditions

Fig. 3

Raincloud plot of the rating of perceived exertion (RPE) in stable and unstable ground conditions