This decline raises concerns given the established associations between physical fitness and various health outcomes, including obesity, cardiometabolic risk factors, and both skeletal and brain health. While prior research has linked physical fitness to specific brain regions and structures in adolescents, there is a notable gap in understanding the association between physical fitness and gray matter (GM) volume of the cerebellum—a region crucial for coordination and cognition, and subject to health-related influences during adolescence.
The Significance of the Cerebellum in Adolescence: The cerebellum, a rapidly developing brain area during adolescence, plays a vital role in coordination and cognition. Certain cerebellar lobules, such as VI, VIIb, Crus I, and Crus II, are implicated in various cognitive functions, including working memory, language tasks, and emotional processing.
Importantly, GM volume development in these lobules occurs at different rates, and the cerebellum’s maturation may differ between sexes during adolescence. Hormonal modulation through estrogen and progesterone receptors adds another layer of complexity to cerebellar development.
Research Gap and Hypothesis: Despite the positive associations observed between physical fitness and neocortical volume, white matter structure, and cognition in adolescents, no study has delved into the relationship between physical fitness and cerebellar GM volume, particularly in cerebellar lobules related to cognition. The existing gap in knowledge is underscored by the need to explore potential sex-specific differences in these associations during the crucial adolescent period.
Building on previous cross-sectional evidence in children and adults, the hypothesis posits that various measures of physical fitness, including cardiorespiratory fitness (CRF), lower limb muscular strength, speed-agility, coordination, and overall neuromuscular performance, are positively associated with the GM volume of the cerebellum in adolescents.
Objectives of the Study:
- Investigate the association between CRF, lower limb muscular strength, speed-agility, coordination, and overall neuromuscular performance with total cerebellar GM volume.
- Examine the relationship between these physical fitness measures and GM volume in cognition-related cerebellar lobules (VI, VIIb, Crus I, and Crus II).
- Explore the potential impact of 8-year cumulative exposure to various physical fitness measures on cerebellar lobules, considering the prolonged development of physical fitness-induced cerebellar alterations, often starting in childhood.
- Assess whether these associations differ between male and female adolescents, recognizing the sex-specific changes in the adolescent cerebellum.
Discussion: Unraveling the Complex Associations Between Physical Fitness and Cerebellar Gray Matter Volume in Adolescents
In this study, we embarked on a detailed exploration of the associations between various measures of physical fitness and the gray matter (GM) volume of the cognitive cerebellum in adolescents, with a nuanced examination of sex-specific differences. Our findings challenge some prevailing hypotheses, while also presenting novel insights into the intricate relationship between physical fitness and cerebellar structure during the crucial adolescent years.
Contradictory Associations: Contrary to our initial hypothesis, a greater peak oxygen consumption (V̇O2 peak) relative to lean mass was associated with a smaller GM volume of the cerebellum. This unexpected negative association prompts speculation on potential mechanisms underlying this phenomenon. One possibility is that individuals with larger cerebellar GM volumes may not undergo adequate neural pruning during development, adversely affecting physical fitness in adolescents.
Another hypothesis suggests that improved physical fitness might be linked to the partial recovery of specific brain pathologies, such as shifts in cerebral fluids. However, these theories necessitate further investigation, particularly focusing on shifts in cerebral fluids, as this aspect was not explored in the present study.
Notably, caution is warranted in interpreting this negative association, as the results did not survive false discovery rate (FDR) correction.
Positive Associations: In contrast, our study revealed a positive association between cumulative neuromuscular performance index (NPI) and the GM volume of Crus I, aligning with previous findings in children.
This suggests that superior performance in tasks requiring neuromuscular skills is related to a larger GM volume of Crus I in children and adolescents. While speculative, previous studies indicating connections between the premotor cortex, primary motor area, and Crus I provide potential mechanistic explanations.
Furthermore, the impact of aerobic exercise on structural and synaptic proteins in the cerebellar cortex, as demonstrated in rodent studies, raises intriguing possibilities. Nevertheless, these mechanistic hypotheses necessitate further exploration, especially regarding cerebral-cerebellar tracts and brain plasticity, which were not investigated in our study.
Sex-Specific Associations: A unique aspect of our study was the examination of sex-specific associations, revealing differential findings.
In females, superior performance in speed-agility tasks was linked to a larger GM volume of Crus I, aligning with prior research in children with overweight or obesity.
However, in males, a greater cumulative NPI was associated with a smaller GM volume of Crus II, contradicting previous studies demonstrating a positive association between physical fitness and cerebellar GM volume in children and young adults.
These disparities may be attributed to variations in age, study populations, and methodologies employed for measuring neuromuscular performance. Nevertheless, caution is warranted in interpreting the negative association between NPI and GM volume of Crus II in males due to the lack of significance following FDR correction.
Limitations and Strengths: Several limitations merit consideration. The relatively small sample size, especially in sex-stratified analyses, might impact statistical power and increase the risk of accepting null hypotheses incorrectly. Despite this, comparable sample sizes with other relevant studies were maintained. Additionally, temporal disparities in the collection of peak oxygen consumption (VO2peak) data and other physical fitness measures may introduce confounding factors, particularly considering the differential growth patterns between males and females. Furthermore, the cross-sectional design limits our ability to infer causality, as reverse causation cannot be entirely excluded.
On the positive side, our study utilized validated and reliable research methods, including the gold-standard VO2peak laboratory test and validated measures of lower limb muscular strength, speed-agility, and coordination. Moreover, this study, to the best of our knowledge, is among the first to comprehensively investigate associations between different measures of physical fitness and the GM volume of the cerebellum in adolescents, filling a critical gap in the literature.
Conclusion and Future Directions: In conclusion, our study adds a layer of complexity to the understanding of the relationship between physical fitness and cerebellar GM volume in adolescents. While some associations align with existing literature, others defy conventional expectations. Future research, encompassing larger, more diverse populations and employing direct CRF measurements alongside advanced brain imaging techniques, will be pivotal in unraveling the intricate web of associations and establishing causality. Such endeavors will not only enhance our understanding of the interplay between physical fitness and brain structure but also inform targeted interventions to optimize both physical and neurological well-being in adolescents.
reference link : https://onlinelibrary.wiley.com/doi/10.1111/sms.14513