Preterm Children in Iceland: Neonatal Morbidities and Motor Development in the First Two Years, and Later Disability Diagnosis.

A physically active lifestyle is consistently recommended as an important strategy to maintain brain structure, especially for the hippocampus, and cognitive function in old age [, ]. The evidence for this stems mainly from observational studies reporting positive associations between physical activity and exercise on hippocampal volume and cognition in older adults [–]. Randomized controlled trials (RCTs) examining the effect of exercise versus a control condition on hippocampal volume in younger and older adults, however, show mixed results. Some studies support the findings from observational studies [–], while others do not find positive effects [–]. Overall, meta-analyses of RCTs report modest or no effects of exercise interventions on different quantitative measures of the hippocampus and other brain structural volumes [–]. Likewise, RCTs and meta-analyses examining the relationship between exercise and cognition report conflicting results [–]. Taken together, the positive effects of physical activity and exercise on brain health in older adults in observational studies seem difficult to replicate in intervention studies. The abovementioned RCTs lasted from 6 weeks to 2 years and, with the exception of Blackmore and colleagues [], lacked post-intervention follow-up assessments, which are necessary for understanding the long-term effects of exercise on brain structure. The most commonly applied intervention in these studies was moderate-intensity continuous training (MICT) compared with a sedentary or stretching control group, although several studies have shown that high-intensity interval training (HIIT) provides greater improvements in cardiorespiratory fitness [], which is considered an important mediating mechanism in the relationship between exercise and brain health []. In the RCT Generation 100 study, we performed a 5-year exercise intervention at two levels of exercise intensity (MICT and HIIT) compared with a control group performing physical activity according to the national guidelines []. This RCT also included a study on brain health in a subgroup of the participants ( = 106), where we found increased hippocampal atrophy in the HIIT group and increased thalamic atrophy in the MICT group during the intervention compared with the control group []. We were not able to uncover an effect of intervention group on any cognitive domain or on O over time in the subgroup [], or on global cognition assessed with the Montreal Cognitive Assessment (MoCA) test in the entire RCT sample [].