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Related Concept Videos

Polygenic Traits01:18

Polygenic Traits

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When more than one gene is responsible for a given phenotype, the trait is considered polygenic. Human height is a polygenic trait. Studies have uncovered hundreds of loci that influence height, and there are believed to be many more. Due to the high number of genes involved, as well as environmental and nutritional factors, height varies significantly within a given population. The distribution of height forms a bell-shaped curve, with relatively few individuals in the population at the...
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Exercise and Muscle Performance01:27

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Exercise induces a range of adaptations in muscle tissue, depending on the type and duration of activity. Such physical training can be broadly categorized into two types: endurance exercises and resistance exercises.
Endurance exercises
Endurance exercises involve running, swimming, or cycling, which require repetitive movements with low force output. When a person engages in endurance exercise, a few noticeable changes occur in their skeletal muscles. For instance, the number of capillaries...
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Classification of Skeletal Muscle Fibers01:48

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Skeletal muscles continuously produce ATP to provide the energy that enables muscle contractions. Skeletal muscle fibers can be categorized into three types based on differences in their contraction speed and how they produce ATP, as well as physical differences related to these factors. Most human muscles contain all three muscle fiber types, albeit in varying proportions.
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Background and Environment Affect Phenotype02:27

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Although the genetic makeup of an organism plays a major role in determining the phenotype, there are also several environmental factors, such as temperature, oxygen availability, presence of mutagens, that can alter an organism’s phenotype.
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Genetic Variation01:25

Genetic Variation

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Genetic variation is the diversity in DNA sequences found among individuals of the same species. This diversity is crucial for a species' survival because it helps organisms adapt to environmental changes. Genetic variation begins with fertilization, where an egg and sperm cell merge. Each of these cells carries 23 chromosomes, up to 46 in the fertilized egg. Chromosomes are long DNA strands that contain genes, the basic units of heredity.
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Types of Skeletal Muscle Fibers01:32

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Skeletal muscles comprise various fibers, each with distinct characteristics and roles in movement and stability. They are mainly categorized into three types — fast-twitch, slow-twitch, and intermediate.
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Related Experiment Video

Updated: Oct 3, 2025

Skeletal Muscle Gender Dimorphism from Proteomics
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Phenotypic differences between people varying in muscularity.

Steven B Heymsfield1, Brooke Smith1, Elizabeth A Chung2

  • 1Pennington Biomedical Research Center, LSU System, Baton Rouge, LA, USA.

Journal of Cachexia, Sarcopenia and Muscle
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PubMed
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Skeletal muscle mass varies significantly among adults of similar size and age. Higher muscularity is linked to different body composition and metabolic traits, highlighting unrecognized population heterogeneity.

Keywords:
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Area of Science:

  • Human physiology
  • Body composition analysis
  • Metabolic health

Background:

  • Body mass is a key metabolic indicator.
  • Skeletal muscle (SM) is a major body component, but its variation in individuals of similar sex, weight, height, and age is poorly understood.
  • Understanding this variation is crucial for clinical predictions.

Purpose of the Study:

  • To quantify the variation in skeletal muscle mass (muscularity) among adults.
  • To investigate the association between muscularity and other body composition and metabolic measures.

Main Methods:

  • Defined muscularity as the residual between actual and predicted SM mass, controlling for sex, weight, height, and age.
  • Developed SM prediction models using data from 492 healthy non-Hispanic White adults.
  • Measured SM and appendicular lean soft tissue (ALST) using MRI and DXA.
  • Evaluated associations with other organ/tissue residuals and resting energy expenditure.

Main Results:

  • Skeletal muscle mass showed wide variation in both men and women, even after adjusting for body size and age.
  • Higher muscularity correlated with smaller waist circumference and visceral adipose tissue.
  • Increased muscularity was associated with larger liver, kidneys, bone mineral content, and higher resting energy expenditure.

Conclusions:

  • Muscle mass is highly variable in adults of similar body size and age.
  • Greater muscularity is associated with distinct body composition and metabolic profiles.
  • This unrecognized heterogeneity in muscularity has significant clinical and research implications.