Advances in Exercise, Fitness, Performance Genomics in 2011
Advances in Exercise, Fitness, Performance Genomics in 2011
The year 2011 was a quiet one in terms of genetic studies on physical activity level, with the exception of a study comparing habitual activity behaviors in mitochondrial disease patients and healthy controls. Although the contribution of mitochondrial DNA mutations to exercise intolerance has been well documented, less is known about habitual physical activity level and sedentary behavior in these patients. Apabhai et al. recruited 100 mitochondrial disease patients with confirmed mitochondrial DNA mutations and 100 individually matched (by age, sex, and body mass index (BMI)) healthy controls. The patients were categorized in four groups on the basis of the type of mutations: 47 patients had at least one point mutation, 28 had multiple deletions, 21 had single large-scale deletions, and 4 had uncharacterized genetic defects with ragged red fibers and Cox-negative staining from skeletal muscle biopsy. Physical activity level and sedentary behavior were quantified with a multisensor array that was worn for 3 d.
The results showed that although all patients were ambulatory, their activity level was significantly lower than that of controls: the patients walked more than 3000 fewer steps per day than the controls. Moreover, the patients had sedentary periods of significantly longer duration than the controls. Finally, although clinical rating of the disease severity was inversely associated with physical activity level, there were no differences in activity level between different types of mitochondrial DNA mutations. Disease severity explained 4% to 15% of the variance in activity and sedentary traits after adjusting for age, sex, and BMI.
Although this study is the first one to report lower habitual physical activity levels in mitochondrial disease patients, the findings are not surprising given the clinical spectrum of their diseases. However, the study represents an excellent illustration of the multifactorial and polygenic nature of complex traits such as habitual physical activity level and sedentary behavior. Interestingly, if the authors had tested each mutation individually, they probably would not have seen any significant associations with activity traits. However, combining a wide range of mutations that all produce a relatively uniform clinical condition provided adequate power to detect the effects on physical activity level. These particular mutations are less relevant for physical activity behavior in the general population (i.e., in individuals apparently free of mitochondrial diseases), but it is likely that multiple genes and DNA sequence variants (nuclear and perhaps even mitochondrial) affect activity and sedentary traits in the population at large.
Physical Activity Level
The year 2011 was a quiet one in terms of genetic studies on physical activity level, with the exception of a study comparing habitual activity behaviors in mitochondrial disease patients and healthy controls. Although the contribution of mitochondrial DNA mutations to exercise intolerance has been well documented, less is known about habitual physical activity level and sedentary behavior in these patients. Apabhai et al. recruited 100 mitochondrial disease patients with confirmed mitochondrial DNA mutations and 100 individually matched (by age, sex, and body mass index (BMI)) healthy controls. The patients were categorized in four groups on the basis of the type of mutations: 47 patients had at least one point mutation, 28 had multiple deletions, 21 had single large-scale deletions, and 4 had uncharacterized genetic defects with ragged red fibers and Cox-negative staining from skeletal muscle biopsy. Physical activity level and sedentary behavior were quantified with a multisensor array that was worn for 3 d.
The results showed that although all patients were ambulatory, their activity level was significantly lower than that of controls: the patients walked more than 3000 fewer steps per day than the controls. Moreover, the patients had sedentary periods of significantly longer duration than the controls. Finally, although clinical rating of the disease severity was inversely associated with physical activity level, there were no differences in activity level between different types of mitochondrial DNA mutations. Disease severity explained 4% to 15% of the variance in activity and sedentary traits after adjusting for age, sex, and BMI.
Although this study is the first one to report lower habitual physical activity levels in mitochondrial disease patients, the findings are not surprising given the clinical spectrum of their diseases. However, the study represents an excellent illustration of the multifactorial and polygenic nature of complex traits such as habitual physical activity level and sedentary behavior. Interestingly, if the authors had tested each mutation individually, they probably would not have seen any significant associations with activity traits. However, combining a wide range of mutations that all produce a relatively uniform clinical condition provided adequate power to detect the effects on physical activity level. These particular mutations are less relevant for physical activity behavior in the general population (i.e., in individuals apparently free of mitochondrial diseases), but it is likely that multiple genes and DNA sequence variants (nuclear and perhaps even mitochondrial) affect activity and sedentary traits in the population at large.
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