Muscle health and performance in monozygotic twins with 30 years of discordant exercise habits
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.
KeywordsFiber type Myosin heavy chain Maximal oxygen consumption Endurance training FN14 PAX7 Body composition AMPK Aerobic exercise Aging
Body fat percentage
5′ AMP-activated protein kinase
Bone mineral content
Bone mineral density
Muscular cross-sectional area
Diastolic blood pressure
Dual-energy X-ray absorptiometry
Forced expiatory volume in the first second
Forced vital capacity
Insulin-like growth factor a
Myosin heavy chain
Maximal voluntary isometric contraction
Myosin heavy chain gene
Endothelial nitric oxide synthase
Quantitative reverse transcriptase polymerase chain reaction
Respiratory exchange ratio
Resting heart rate
Rating of perceived exertion
Rotations per minute
Systolic blood pressure
Transcription factor A of the mitochondria
Tumor necrosis factor-α
Visceral adipose tissue
Vascular endothelial growth factor
Maximal aerobic capacity
Wingate anaerobic test
Weekly estimated energy expenditure
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.
JRB and AJG conceived and designed this work. KEB, JRB, EJ, RJT, IST, JAA, and AJG performed the experiments. All authors collected and analyzed the data. KEB, JRB, LEB, JWC, NLS, and AJG interpreted the results of experiments. KEB, AJG, and JRB drafted the manuscript. All authors read and approved the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declared no conflicts of interest.
All procedures performed in this study were in accordance with the ethical standards of the University’s Institutional Review Board for Human Subjects and with the 1964 Declaration of Helsinki and its later amendments.
Informed consent was obtained from all individual participants included in the study.
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