The Effects of Acute Isometric Handgrip Exercise on Cognitive Function in Young Adults

Abstract

Acute whole-body exercise transiently improves cognitive function which may be mediated by increased cerebral blood flow (CBF) and arousal. Interestingly, small muscle mass exercise, like isometric handgrip exercise (IHG) may stimulate the same physiological responses as whole body-exercise and improve cognitive function. However, these effects are poorly understood, and whether sex-based differences exist in the cognitive response to IHG is unknown. Therefore, the purpose of this study was to investigate whether acute IHG improves cognitive function in young healthy adults and examine potential sex differences in the cognitive response to IHG. We hypothesized that acute IHG would improve cognitive function compared to a control condition, and that females would have greater improvements in cognitive function due to a lower exercise pressor response. To test this, 30 participants (n=15 females, mean age=23.8±3.3 years;BMI=25.3±4.1 kg/m2) completed either IHG or a control condition in a randomized-crossover design separated by at least 2 days. IHG consisted of four sets of 2-min unilateral squeezing a handgrip dynamometer at 30% maximal voluntary contraction separated by 3-min of rest. The control condition watched a nature documentary for 20-min. Hemodynamics (systolic blood pressure, diastolic blood pressure, mean arterial pressure, and heart rate) were assessed throughout. Executive function, working memory, and processing speed were assessed via the 4-Choice, Corsi Block, and N-Back tests. Arousal was assessed using the Felt Arousal Scale (FAS). Middle cerebral artery blood velocity (MCAv) was assessed using transcranial Doppler ultrasound. Compared to the control condition, IHG significantly increased MAP (∆ 26 ± 17 mmHg; P<0.001), HR(∆ 18 ±13 bpm; P<0.001), MCAv (∆ 5.27 ± 19.4 cm/s; P<0.001), cerebrovascular resistance (∆ 0.71 ±0.69 mmHg/cm/s; P=0.003), and arousal (∆ 2 ± 2 FAS score; P<0.001). Cerebrovascular resistance was calculated as MAP/MCAv. Overall, despite increases in MCAv and arousal, there was no effect of IHG on cognitive performance, and no sex differences were observed in the cognitive response to IHG. These findings stand in opposition to emerging work and suggests that increased CBF and arousal via acute IHG are an insufficient stimulus to enhance cognitive function in young adults. Furthermore, there seems to be no moderating effect of biological sex on the cognitive response to acute IHG.