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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.

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Body fat percentage


5′ AMP-activated protein kinase




Bone mineral content


Bone mineral density


Total cholesterol


Citrate synthase


Muscular cross-sectional area


Diastolic blood pressure


Dual-energy X-ray absorptiometry


Enhanced chemiluminescent


Echo intensity

FEV1 :

Forced expiatory volume in the first second


Fat mass


Forced vital capacity


Glycosylated hemoglobin


High-density lipoprotein


Insulin-like growth factor a


Mechano-growth factor




Low-density lipoprotein


Lean mass


Myosin heavy chain




Muscle thickness


Maximal voluntary isometric contraction


Myosin heavy chain gene




Endothelial nitric oxide synthase


Peak power




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




Trained twin


Untrained twin


Visceral adipose tissue


Vascular endothelial growth factor


Vastus lateralis


Maximal aerobic capacity


Wingate anaerobic test


Weekly estimated energy expenditure


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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.

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Authors and Affiliations



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.

Corresponding author

Correspondence to Andrew J. Galpin.

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Conflict of interest

The authors declared no conflicts of interest.

Ethical standards

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

Informed consent was obtained from all individual participants included in the study.

Additional information

Communicated by William J. Kraemer.

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Bathgate, K.E., Bagley, J.R., Jo, E. et al. Muscle health and performance in monozygotic twins with 30 years of discordant exercise habits. Eur J Appl Physiol 118, 2097–2110 (2018).

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  • Fiber type
  • Myosin heavy chain
  • Maximal oxygen consumption
  • Endurance training
  • FN14
  • PAX7
  • Body composition
  • AMPK
  • Aerobic exercise
  • Aging