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Developmental biology - Genetics|
Genes Do Not Determine Fitness
Because identical twins share over 99 percent of the same genes, studying them offers a perfect opportunity to gauge the importance of external influences on a person's health, explains Bagley.
To look at the effects of exercise on these two brothers, Bagley and his colleagues analyzed their physiques, blood profiles, cardiovascular and pulmonary health, skeletal muscle size, strength and power, and molecular markers of muscle health.
Not surprisingly, the athletic twin exhibited much better overall health: lower body fat, lower resting heart rate and blood pressure, lower cholesterol, triglycerides and blood sugar, and greater aerobic capacity and endurance. There was one surprise, however. The truck driver had larger, stronger leg muscles."The untrained twin had been carrying around more weight his whole life, which can build bigger muscles," explains Bagley.
Because the athletic twin was a runner, his muscles were leaner and built to move forward in space - to run. But, there is one measurement that tells you the most about a person's overall health - the "VO2 max," or the maximum rate of oxygen consumed during an exercise bike test. The athletic twin came out far ahead in the VO2 max test, which measures cardiovascular health, pulmonary health and muscle efficiency.
"VO2 max [the maximum rate of oxygen consumed during exercise] starts to drop off at age 65 or 70. When that rate hits a certain low you are probably going to become dependent on someone else. As people get older, we try to keep them over that dependency limit."
On the VO2 max test, the athletic twin's fitness was equal to that of a 30-year old, much better than that of the sedentary twin, whose VO2 max test was more typical. The athletic twin also had 55 percent more "slow-twitch" muscle fibers than the truck-driving twin, as he could run for hours without getting fatigued. "He was like a machine," Bagley adds.
Researchers plan to continue monitoring the twins every five years. While they could end up having the same life span, Bagley believes the athelete's "health span" - the ability to live longer independently and in good health - may become more significant.
Not everyone can be an Ironman athlete. But Bagley hopes the study will help researchers learn more about how much exercise a person needs and in what amount. Bagley: "It shows your genes aren't a cop-out. If your parents are overweight, for example, it might be harder for you to get fit, but this study shows that it's not impossible." As for the lesser-fit twin? He has started walking a lot more.
Physical health and function depend upon both genetic inheritance and environmental factors (e.g., exercise training).
To enhance the understanding of heritability/adaptability, we explored the skeletal muscle health and physiological performance of monozygotic (MZ) twins with > 30 years of chronic endurance training vs. no specific/consistent exercise.
One pair of male MZ twins (age = 52 years; Trained Twin, TT; Untrained Twin, UT) underwent analyses of: (1) anthropometric characteristics and blood profiles, (2) markers of cardiovascular and pulmonary health, and (3) skeletal muscle size, strength, and power and molecular markers of muscle health.
This case study represents the most comprehensive physiological comparison of MZ twins with this length and magnitude of differing exercise history. TT exhibited: (1) lower body mass, body fat%, resting heart rate, blood pressure, cholesterol, triglycerides, and plasma glucose, (2) greater relative cycling power, anaerobic endurance, and aerobic capacity (VO2max), but lower muscle size/strength and poorer muscle quality, (3) more MHC I (slow-twitch) and fewer MHC IIa (fast-twitch) fibers, (4) greater AMPK protein expression, and (5) greater PAX7, IGF1Ec, IGF1Ea, and FN14 mRNA expression than UT.
Several measured differences are the largest reported between MZ twins (TT expressed 55% more MHC I fibers, 12.4 ml/kg/min greater VO2max, and 8.6% lower body fat% vs. UT). These data collectively (a) support utilizing chronic endurance training to improve body composition and cardiovascular health and (b) suggest the cardiovascular and skeletal muscle systems exhibit greater plasticity than previously thought, further highlighting the importance of studying MZ twins with large (long-term) differences in exposomes.
Authors:Katherine E. Bathgate, James R. Bagley, Edward Jo, Robert J. Talmadge, Irene S. Tobias, Lee E. Brown, Jared W. Coburn, Jose A. Arevalo, Nancy L. Segal and Andrew J. Galpin.
The authors would like to thank Kathryn McLeland, Cassio Ruas, Nathan Serrano, Kara Lazauskas, and Colleen Gulick for their assistance with this project. This research was funded by a California State University Development of Research and Creativity (CSU-DRC) Grant to J.R. Bagley. The authors declared no conflicts of interest.
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A study of a pair of identical 52-year-old twins who had taken radically different fitness paths
over three decades, demonstrates the impact exercise can have on health over time.