| May 06, 2015
By Urho Kujala, M.D., Ph.D.
In exercise science, long-term intervention studies are challenging to accomplish, and observational follow-up studies, even in a longitudinal setup, also present problems in establishing cause and effect relationships. A monozygotic (MZ) twin-pair co-twin control study design presents a highly effective means to establish controls for genetic predisposition and largely controls for childhood home environment.
In our co-twin control study (part of the FITFATTWIN study), recently published in MSSE
, we investigated how physical activity level is associated with body composition, glucose homeostasis and brain morphology in young adult male MZ twin pairs – pairs that have been discordant for physical activity during the past three years. Identifying MZ co-twins who have long-term discordance in their physical activity habits is challenging because participation in physical activity has a rather high heritability.
First, 10 adult male MZ twin pairs whose members were clearly discordant for their leisure time physical activity during the past three years were comprehensively identified from a population-based Finnish twin cohort. As expected, active twins had higher cardiorespiratory fitness, a lower body fat percent and better glucose homeostasis compared to inactive co-twins. Findings on body composition show that long-term physical activity may clearly reduce percent body fat without having a significant effect on body weight. The pairwise difference in insulin resistance/sensitivity also was seen, as measured by both a steady state (fasting/HOMA) index and a dynamic (Matsuda) index.
Based on whole brain magnetic resonance imaging with voxel-based morphometry and use of preprocessing algorithms, we determined that physically active co-twins had larger striatal and prefrontal cortex gray matter volumes compared to their inactive co-twins. These regions are heavily involved in motor control networks. Other brain regions also may differ between active and inactive members of twin pairs, but the differences were not great enough to reach statistical significance in our “global” brain analysis. As MZ twins usually have a high-degree similarity in brain structure, our finding provides novel evidence for the structural region-specific effects of long term physical activity on the healthy adult brain.
The findings pointing toward enlarged areas involved with controlling motor abilities may have health implications in the long-term, such as possibly reduced risk of falling and mobility limitations at older age. As the study also showed beneficial effects on cardio-metabolic risk factors, exercising seems to have multidimensional, site-specific and systemic effects on health-related factors. Viewpoints presented on the ACSM blog reflect opinions of the authors and do not necessarily reflect positions or policies of ACSM.
Urho Kujala, M.D., Ph.D., is a specialist in sports and exercise medicine and professor at the Department of Health Sciences, University of Jyväskylä, Finland. His research focuses on different health benefits and adverse effects of sports and exercise. He has been a member of ACSM for 25 years.
This commentary presents Dr. Kujala’s views on the topic of a research article which he and his colleagues published in the March 2015 issue of
Medicine & Science in Sports & Exercise®
(MSSE). This research study also was covered in a recent article in The New York Times