The effect of energy-matched exercise intensity on brain-derived neurotrophic factor and motor learning

Abstract

Background: Pairing a bout of high-intensity exercise with motor task practice can enhance motor learning beyond task practice alone, which is thought, in part, to be facilitated by an exercise-related increase in brain-derived neurotrophic factor (BDNF). The purpose of the current study was to examine the effect of different exercise intensities on BDNF levels and motor learning while controlling for exercise-related energy expenditure.

Methods: Forty-eight young, healthy participants were assigned to one of three groups: high-intensity exercise [High], low-intensity exercise [Low], or quiet rest [Rest]. The duration of the exercise bouts were individually adjusted so that each participant expended 200 kcals regardless of exercise intensity. BDNF was measured before and after exercise or rest. After exercise or rest, all participants practiced a 3-dimensional motor learning task, which involved reach movements made to sequentially presented targets. Retention was tested after 24-h. BDNF genotype was determined for each participant to explore its effects on BDNF and motor learning.

Results: All participants equally improved performance, indicated by a reduction in time to complete the task. However, the kinematic profile used to control the reach movement differed by group. The Rest group travelled the shortest distance between the targets, the High group had higher reach speed (peak velocity), and the Low group had earlier peak velocities. The rise in BDNF post-exercise was not significant, regardless of exercise intensity, and the change in BDNF was not associated with motor learning. The BDNF response to exercise did not differ by genotype. However, performance differed between those with the polymorphism (Met carriers) and those without (Val/Val). Compared to the Val/Val genotype, Met carriers had faster response times throughout task practice, which was supported by higher reach speeds and earlier peak velocities.

Conclusion: Results indicated that both low and high-intensity exercise can alter the kinematic approach used to complete a reach task, and these changes appear unrelated to a change in BDNF. In addition, the BDNF genotype did not influence BDNF concentration, but it did have an effect on motor performance of a sequential target reach task.

Keywords: Acute exercise; Brain-derived neurotrophic factor; Exercise intensity; Motor learning.

Figure 1

Sequential Target Task (STT) setup. A. Side view of a participant sitting at the virtual display. Stereoscopic glasses provided a 3-dimensional view of the virtual environment. Virtual targets were sent from the projector, reflected off the mirror, and presented in the area below the glass. B. Representation of the nine possible target locations. Each target was 28 mm in diameter. Targets were presented in a circular array with a radius of 96 mm and a tangent distance between any adjacent targets of 75 mm. The repeated sequence consisted of targets 1, 8, 6, 5, 9, 4, 8, 2.

Figure 2

Response Time. A. Response time (sec) to complete a sequence across the acquisition phase and the retention phase for all groups. Each data point consists of an average of nine sequences. Error bars represent standard error. Error bars ascend from the marker for the random sequences and descend from the marker for the repeated sequences. No group differences in response time were evident. B. Response time for the High-intensity group. C. Response for the Low-intensity group. D. Response time for the Rest group.

Figure 3

Kinematic Variables. Distance of the hand path (A), peak velocity (B), and time to peak velocity (C) across the acquisition phase and the retention phase for all groups. Each data point consists of an average of nine sequences. Error bars represent standard error. Error bars ascend from the marker for the random sequences and descend from the marker for the repeated sequences. A. The Rest group travelled the shortest distance when completing a sequence compared to the High and Low groups (p < 0.001). B. The High group had the highest peak velocity compared to the Rest and Low groups (p < 0.001). C. The Low group had the earliest time to peak velocity compared to the Rest and High groups (p < 0.001).

Figure 4

BDNF exercise response by BDNF genotype. The Low-intensity group is represented by the gray bars and the High-intensity group is represented by the black bars. Each bar represents an individual participant. The BDNF response was not significantly different by BDNF genotype.

Figure 5

Response time and kinematic variables of performance by BDNF genotype. Response time, distance of the hand path, peak velocity, and time to peak velocity across the acquisition phase and the retention phase for both genotype groups. Error bars represent standard error. Error bars ascend from the marker for the random sequences and descend from the marker for the repeated sequences. A. The Val/Met genotype had significantly lower response times for both sequence types compared to the Val/Val genotype (p = 0.002). B. The Val/Val genotype had a significantly shorter distance when completing a sequence compared to the Val/Met genotype (p < 0.001). C. The Val/Met genotype had higher peak velocities when reaching to the targets compared to the Val/Val genotype (p < 0001). D. No difference in time to peak velocity was present between the genotypes (p = 0.05).