Cognitive Performance during Aerobic Exercise: Do Exercise Modality and Fitness Level Matter?

Background: Exercise training represents a promising approach for mitigating cognitive impairment in persons with multiple sclerosis (MS). Treadmill walking has recently been identified as the exercise modality that might exert the greatest beneficial effects on cognitive performance in this population. However, the mechanisms as to how treadmill walking exercise improves cognition in persons with MS are not well understood. It has been hypothesized that treadmill walking is essentially a complex cognitive task that requires more attentional resources than other modalities of aerobic exercise (i.e., cycle ergometry), and repeated exposure trains the person in cognitive-motor processing. If this hypothesis is true, persons with MS should demonstrate worse cognitive performance during treadmill walking exercise than cycle ergometry, as more attentional resources would presumably be devoted to walking on a treadmill than cycling on a stationary bicycle. It further is unknown if having better aerobic fitness attenuates such cognitive-motor interference in persons with MS.

Objectives: This pilot study examined cognitive performance before and during acute bouts of treadmill walking exercise, stationary cycling exercise, and seated quiet rest in 12 fully-ambulatory persons with MS with high or low aerobic fitness using a within-subjects, repeated-measures design.

Methods: Participants underwent a baseline incremental exercise test to exhaustion for measurement of aerobic fitness (i.e., VO_2peak). Participants further completed three experimental conditions that consisted of 20 minutes of moderate-to-vigorous intensity treadmill walking exercise, moderate-to-vigorous intensity cycle ergometer exercise, and seated quiet rest in a randomized, counterbalanced order. Participants underwent the 3-second Paced Auditory Serial Addition Test (PASAT) as a measure of cognitive performance prior to and during each condition. 

Results: Overall, there were not larger decreases in PASAT performance during treadmill walking (d=−0.25) than during cycle ergometry (d=−0.40) relative to quiet rest (F(2,20)=0.80, p=.46, η_p²=.07). However, decreases in PASAT performance were larger for those with lower aerobic fitness during treadmill walking exercise than cycle ergometry compared with quiet rest (F(2,20)=3.24, p=.06, η_p²=.24).

Conclusions: The present results provide preliminary data on a potential mechanism whereby a single bout of treadmill walking exercise might affect cognitive processing to a greater degree than stationary cycling exercise, particularly among those with MS who demonstrate low aerobic fitness. This highlights the importance of targeting those with low aerobic fitness in treadmill walking exercise training interventions for improving cognition in persons with MS, as improving aerobic fitness may be beneficial for reducing MS-related cognitive-motor interference.