Comparison of High-Intensity Interval Training and Moderate-Intensity Continuous Training on Executive Functions, Cardiorespiratory and Physical Fitness in Older Adults With Mild Cognitive Impairment

Mild cognitive impairment is a syndrome defined as cognitive decline greater than expected for an individual's age and education level but that does not interfere notably with activities of daily life. Prevalence in population-based epidemiological studies ranges from 3% to 19% in adults older than 65 years. Some people with mild cognitive impairment seem to remain stable or return to normal over time, but more than half progress to dementia within 5 years. Mild cognitive impairment can thus be regarded as a risk state for dementia. The amnestic subtype of mild cognitive impairment has a high risk of progression to Alzheimer's disease, and it could constitute a prodromal stage of this disorder. One of the main causes of disability and dependency in older adults globally, dementia ranks as the seventh most common cause of all disorders. Globally, there were 55 million dementia sufferers in 2021; by 2030, that figure is expected to rise to 78 million, and by 2050, it will reach 139 million. Thankfully, there is a chance that postponing dementia onset by five years could cut its prevalence in half globally. Compared to just 3% of the age-matched group, 46% of people with mild cognitive impairment (MCI), an intermediate stage between normal cognition and dementia, will develop dementia within three years. As a result, MCI is a crucial phase in stopping dementia from getting worse. The multi-cognitive function of subjects with MCI declines.

HIIT can enhance cognitive performance through increased blood flow to the brain, promoting neurogenesis and synaptic plasticity, which are crucial for cognitive tasks. MICT also supports cognitive function. HIIT often produces superior results in a shorter time frame. HIIT involves short bursts of high-intensity exercise followed by rest or low-intensity periods, leading to significant cardiovascular adaptations such as increased VO2 max and improved heart efficiency. MICT, while beneficial, requires longer durations to achieve comparable gains in cardiorespiratory fitness (CRF). Engaging in regular physical exercise has been shown to delay age-related physiological and cognitive decline, reduce the risk of common diseases, and improve the subjective quality of life. Meanwhile, a large proportion of older adults are insufficiently physically active, potentially increasing societal health-related challenges connected to a growing older population. It is, therefore, important to provide both effective and attractive exercise methods adapted for this group. One of the proposed key factors in maximizing exercise effects is to exercise beyond moderate intensities, as in high-intensity interval training (HIIT). Although aerobic moderate-intensity continuous training (MICT) is performed at intensities below the anaerobic threshold, HIIT is broadly defined as short, repeated work intervals at an external intensity close to (80%-100%), or above (>100%) the intensity that elicits maximum oxygen uptake (Vo2 max), with passive or low intensity recovery between intervals.

While exercise is a promising intervention for cognitive health, the comparative efficacy of High-Intensity Interval Training (HIIT) and Moderate-Intensity Continuous Training (MICT) in older adults with MCI remains underexplored. This research seeks to provide useful insights examining the effects of HIIT and MICT on executive functions, cardiorespiratory fitness, and overall physical fitness. HIIT's potential time efficiency and physiological benefits may offer significant advantages over traditional exercise methods. The findings could inform clinical practice, shape public health guidelines, and lead to more effective exercise interventions, ultimately enhancing the quality of life for older adults at risk of cognitive decline.