Intensity of acute aerobic exercise but not aerobic fitness impacts on corticospinal excitability

Abstract

Aerobic exercise (AE) modulates cortical excitability. It can alter both corticospinal excitability and intra-cortical networks, which has implications for its use as a tool to facilitate processes such as motor learning, where increased levels of excitability are conducive to the induction of neural plasticity. Little is known about how different intensities of AE modulate cortical excitability or how individual-level characteristics impact on it. Therefore, we investigated whether AE intensities, lower than those previously employed, would be effective in increasing cortical excitability. We also examined whether the aerobic fitness of individual participants was related to the magnitude of change in AE-induced cortical excitability. In both experiments we employed transcranial magnetic stimulation to probe corticospinal excitability before and after AE. We show that 20 min of continuous moderate- (40% and 50% of heart rate reserve, HRR), but not low- (30% HRR) intensity AE was effective at increasing corticospinal excitability. We also found that while we observed increased corticospinal excitability following 20 min of continuous moderate-intensity (50% HRR) AE, aerobic fitness was not related to the magnitude of change. Our results suggest that there is a lower bound intensity of AE that is effective at driving changes in cortical excitability, and that while individual-level characteristics are important predictors of response to AE, aerobic fitness is not. Overall these findings have implication for the way that AE is used to facilitate processes such as motor learning, where increased levels of cortical excitability and plasticity are favourable.

Acute high-intensity and moderate-intensity interval exercise do not change corticospinal excitability in low fit, young adults

“…Although we intended to acquire data from 22 participants, only 19 were available to us. However, a recent study from MacDonald et al [9] observed an increase in MEPs after moderate intensity cycling in a sample of 15 participants who ranged from sedentary to fit. Therefore, it is unlikely that the lack of effect we observed is due to a limited sample size.…”

“…This is in line with previous work showing no change in corticospinal excitability following moderate- [3][4][5][6] and high-intensity exercise [10] in low fit individuals. Increases in corticospinal excitability following exercise have only been observed in high fit individuals after moderate intensity exercise [6,8,9], although some studies have reported to change after moderate intensity exercise [7,11]. Opie and Semmler (2019) also recently showed increased MEP amplitude after both high-intensity interval training and low-intensity continuous exercise, although fitness of the participant sample tested was not reported.…”

“…Numerous studies have used TMS to assess neuroplasticity within the motor system after an acute session of aerobic exercise in healthy individuals (Table 1). These studies have reported either no change [3][4][5][6][7] or an increase [6,8,9] in MEP amplitude following exercise. The discrepancy may relate to either the fitness level of the participants tested, or the intensity of the exercise performed.…”

“…For example, the International Physical Activity Questionnaire (IPAQ) is commonly used to assesses physical activity and not fitness per se, whereas a peak oxygen uptake (VO 2peak ) test provides an indication of cardiorespiratory fitness. Studies reporting an increase in MEP amplitude after acute exercise were generally performed using highly fit individuals as gauged by a VO 2peak test [8,9] or in highly active individuals as gauged by the IPAQ [6]. In PLOS ONE | https://doi.org/10.1371/journal.pone.0227581 January 24, 2020 1 / 12 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111…”

“…Further, improvements in motor skill retention are greater following high-versus low-intensity acute exercise [20]. Opie & Semmler [12] reported an increase in MEPs following both low-intensity continuous and high-intensity interval cycling exercise whereas MacDonald et al [9] demonstrated increased MEP amplitude following moderate-intensity but not low-intensity continuous cycling. In contrast, other studies have found no change in MEPs following lower versus higher intensity cycling [3,5,11].…”