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What are the cognitive benefits of aerobic training?

This is an excerpt from ABLE Bodies Balance Training 2nd Edition With HKPropel Access by Sue M. Scott.

Cognitive Changes With Aerobic Training

In terms of cognition, MICT and HIIT share similar overlapping benefits but there are also differences. The emerging consensus is that HIIT amplifies the cognitive effects of MICT. That is, overall, higher intensities more quickly facilitate cognitive benefits equal or superior to moderate intensities. This is especially true for measures of cognitive flexibility, perhaps due to faster processing speeds required by HIIT programs (Calverley et al. 2020; Hugues et al. 2021; Mekari et al. 2020; Robinson 2018). Finally, many studies have found that HIIT improved quality of life measures more than MICT (Calverley et al. 2020; Ito 2019).
The following sections discuss the principal mechanisms facilitating cognitive benefits from MICT and HIIT programs. All of these mechanisms contribute to the good health, function, and neuroprotection of the brain, central nervous system, and quality of life (Calverley et al. 2020; Dun et al. 2019; Hughes et al. 2021; Marriot et al. 2019; Yue et al. 2022).

Neurogenesis and Neuroprotection

Increases in brain volume, from the creation of new neurons, are widely credited with mediating improved cognition. Both gray and white matter (cell bodies and their axons) increase after aerobic exercise. Aerobic exercise strengthens the integrity of axons, the communicative part of a neuron (Calverley et al. 2020; Erickson et al. 2012; Hugues et al. 2021; Robinson 2018). Microglial cells, a system of glymphatic neurons, also increase in response to aerobic exercise. These cells form a supportive network in and around working neurons that nurtures, bathes, and boosts the survival rate of other neurons. HIIT was shown to increase microglia activity compared with MICT (Calverley et al. 2020). Finally, an increase in protein growth factors and their uptake boosts the development, function, and survival of neurons. Growth factor effects are greater with HIIT compared with MICT (Calverley et al. 2020; Hugues et al. 2021; Smith and Kravitz 2023). All of these changes in volume, integrity, growth, and survival of neurons shore up the brain’s long-term function.

Synaptogenesis and Neuroplasticity
Aerobic exercise, especially at higher intensities, forms new synapses and improves how well they function. New and improved synapses mean better connectivity between neurons and across the brain to enhance cognitive flexibility (neuroplasticity), learning, and memory (Hugues et al. 2021; Mekari et al. 2020; Robinson 2018).

Enhanced Cerebral Blood Flow and Perfusion
Within months of both moderate- and higher-intensity cardiovascular training, angiogenesis is underway throughout the body, including the brain. Angiogenesis boosts the formation, growth, and function of new capillaries. The new capillaries provide more sites where exchanges can happen that deliver fuel, pick up waste, and keep brain tissue healthier and energized. This reliable, neuroprotective result improves brain resilience and cognitive reserve (Arida and Teixeira-Machado 2021). Angiogenesis occurs at a faster, higher rate with HIIT compared with MICT (Calverley et al. 2020). Higher-intensity exercise also gives rise to greater pressures for brain blood perfusion. These mechanisms increase blood flow and oxygen supply in the brain (Arida and Teixeira-Machado 2021; Calverley et al. 2020; Kramer and Colcombe 2018).

Changes in Metabolism
MICT and HIIT both improve glucose tolerance, insulin sensitivity, blood sugar control, autonomic function (blood pressure effects), and lipid profiles. Here, MICT seems the better choice, perhaps because its protocol requires greater frequency that would be more helpful for blood sugar control. MICT protocols call for 3 to 5 training days per week versus 2 to 3 days per week for HIIT (Chodzko-Zajko et al. 2009; Kravitz 2021; Petrick et al. 2021). Robinson and colleagues (2018) found that HIIT, more than MICT, significantly increased brain glucose uptake in older and younger adults in certain brain regions.

HIIT and MICT both influence antioxidant and anti-inflammatory mechanisms that protect against brain tissue loss (especially in areas associated with neurodegenerative diseases). Previous studies suggest that results are better with HIIT (Calverley et al. 2020; Dun et al. 2019; Erickson et al. 2018; Hugues et al. 2021; Marriot et al. 2019; Yue et al. 2022).

Changes to the Hippocampus and Prefrontal Cortex
The hippocampus is located deep in the brain, in the medial part of the temporal lobe. It is important for memory, learning, spatial navigation, and emotion. Although the hippocampus is sensitive to aging and neurodegenerative diseases, it is also highly plastic and remains responsive to aerobic exercise throughout a lifetime. Aerobic exercise increases hippocampal volume (neurogenesis) and blood supply (discussed previously), which enhances memory and learning functions (Arida and Teixeira-Machado 2021; Erickson et al. 2012; Kramer and Colcombe 2018; Robinson et al. 2018).

The prefrontal cortex (PFC) sits in the front part of the frontal lobe. Through its many connections with other brain regions, it regulates emotions, behavior, and executive function (planning and decision-making). Greater PFC volume is widely credited as the link between higher fitness levels and better executive function (Arida and Teixeira-Machado 2021; Erickson et al. 2018; Voss et al. 2013a). Voss and colleagues (2013a) and Arida and Teixeira-Machado (2021) explored how aerobic exercise relates to brain resilience. They showed that aerobic exercise increased volume and activity in the PFC of older adults. Furthermore, Voss and colleagues showed a dose-response effect to challenge. More difficult tasks generated more activity and capillary formation in the PFC. In addition, greater cognitive effort in exercise facilitated greater changes to the PFC. Exercise that incorporates challenges and cognitive engagement benefits PFC function. More research on engagement is presented in chapter 4 and later in this chapter.

Enhancements of Executive Function
Greater improvement in selective attention, working memory, decision-making, task switching, and inhibition has been seen with HIIT than with MICT. These changes enhance cognitive flexibility and improve networking (neuroplasticity) across brain regions, including those normally affected by aging. Voss and colleagues (2013a) and Kramer and colleagues (2008) concluded that combined modes of exercise, and aerobic exercise in general, are vital for maintaining cognitive and executive functions and for reducing occurrences of age-associated neurodegenerative diseases, including mild cognitive impairment and Alzheimer’s disease. Furthermore, sedentary individuals and those at greater risk for Alzheimer’s disease stand to gain the most benefit from higher-intensity training (Kramer and Colcombe 2018; Mekari et al. 2020; Voss et al. 2013a).

Release of Myokines
As discussed in chapter 4, aerobic exercise stimulates the release of myokines from contracting muscles. Myokines act like hormones and influence other organs. They cross the blood-brain barrier and affect the activity of neurons in the central nervous system. These changes involve perception of the environment and other functions (Calverley et al. 2020; Consorti et al. 2021). Myokines are higher in plasma after HIIT than after MICT (Calverley et al. 2020).

Long-Lasting Results
The effects of regular cardiorespiratory training on cognition and brain health can be long lasting. Erickson and colleagues (2012) found that higher aerobic fitness was still associated with greater volumes of gray matter (neuronal cell bodies) 9 years later. A classic study published in JAMA in 2004 was done with more than 18,000 nurses aged 70 to 81 years. The investigators showed that neuroprotective effects could last decades with long-term regular physical activity, including walking but especially with higher levels of intensity (Weuve et al. 2004).

Enhances Other Therapies
Aerobic exercise, even acute bouts, stimulates brain regions involved in motor learning and cognitive processes. This stimulation creates a priming effect on the brain that enhances learning ability. For example, taking a brisk walk before taking a test can improve test performance. This priming effect of aerobic exercise applies to learning motor skills and to academics and behavioral therapies, such as for depression (Moriarty et al. 2019).

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