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Related Concept Videos

Changes in the Appendicular Skeleton with Age01:09

Changes in the Appendicular Skeleton with Age

The upper and lower limb initially develops as a small bulge called a limb bud, which appears on the lateral side of the early embryo. The upper limb bud appears near the end of the fourth week of development, with the lower limb bud appearing shortly after.
Initially, the limb buds consist of a core of mesenchyme covered by a layer of ectoderm. The ectoderm at the end of the limb bud thickens to form a narrow crest called the apical ectodermal ridge. This ridge stimulates the underlying...
Growth of Cartilage and Bone Tissue01:27

Growth of Cartilage and Bone Tissue

Chondrocytes form a temporary cartilaginous model by dividing and secreting a thick gel-like extracellular matrix. Once the chondrocytes undergo programmed cell death, osteoblasts enter the site of the cartilaginous model. The process of replacing the temporary cartilaginous model with bone in an ordered manner is called endochondral ossification. In endochondral ossification, not all of the cartilage is replaced by bone tissue. Some cartilage that performs a protective and supportive function...
Hormones and Bone Tissue01:17

Hormones and Bone Tissue

The endocrine system produces and secretes hormones, which interact with the skeletal system. These hormones control bone growth, maintain bone once it is formed, and remodel it.
Hormones That Influence Osteoblasts and/or Maintain the Matrix
Several hormones are necessary for controlling bone growth and maintaining the bone matrix. The pituitary gland secretes growth hormone (GH), which, as its name implies, controls bone growth. This happens in several ways: first, it triggers chondrocyte...
Bone Remodeling01:40

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Bone remodeling is a continuous and balanced process of bone resorption by osteoclasts and bone formation by osteoblasts. In adults, it helps maintain bone mass and calcium homeostasis. While mechanical stress can stimulate turnover as part of the normal maintenance and reparative process, several hormones also regulate bone remodeling.
Bone Formation by Endochondral Ossification01:24

Bone Formation by Endochondral Ossification

Bone formation, or ossification, begins around the sixth to seventh week of embryonic development. Most bones develop from a cartilaginous template through the process of endochondral ossification. Cartilage formation begins when clusters of mesenchymal cells differentiate into chondrocytes. These chondrocytes proliferate rapidly and secrete an extracellular matrix that becomes encased in a membrane called the perichondrium. The resulting cartilage model provides a template that resembles the...
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Bone Formation by Intramembranous Ossification

Intramembranous ossification is one of the two processes involved in the development of bones within an embryo. The flat bones of the face, most of the cranial bones, and the clavicles are formed via this process. During intramembranous ossification, the bones develop directly from sheets of undifferentiated mesenchymal connective tissue.
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Related Experiment Video

Updated: May 13, 2026

Visualization of Intensity Levels to Reduce the Gap Between Self-Reported and Directly Measured Physical Activity
05:59

Visualization of Intensity Levels to Reduce the Gap Between Self-Reported and Directly Measured Physical Activity

Published on: March 7, 2019

Ten-year objective physical activity tracking: Iowa Bone Development Study.

Shelby Lane Francis1, Joanna L Morrissey, Elena M Letuchy

  • 1Department of Health and Human Physiology, University of Iowa, Iowa City, IA 52242, USA. shelby-francis@uiowa.edu

Medicine and Science in Sports and Exercise
|March 9, 2013
PubMed
Summary

Physical activity tracking is more consistent in girls than boys from childhood to adolescence. Boys

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Physical Activity Measurement in Children Accepting Table Tennis Training
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Physical Activity Measurement in Children Accepting Table Tennis Training

Published on: July 27, 2022

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Last Updated: May 13, 2026

Visualization of Intensity Levels to Reduce the Gap Between Self-Reported and Directly Measured Physical Activity
05:59

Visualization of Intensity Levels to Reduce the Gap Between Self-Reported and Directly Measured Physical Activity

Published on: March 7, 2019

Physical Activity Measurement in Children Accepting Table Tennis Training
06:51

Physical Activity Measurement in Children Accepting Table Tennis Training

Published on: July 27, 2022

Area of Science:

  • Pediatric Exercise Science
  • Growth and Development Studies
  • Public Health and Physical Activity

Background:

  • Tracking physical activity (PA) from childhood into adolescence is crucial for lifelong health.
  • Understanding sex differences in PA trajectories is essential for targeted interventions.
  • Maturity-based alignment may offer a more accurate assessment of PA stability than age-based alignment.

Purpose of the Study:

  • To examine the 10-year tracking of physical activity (PA) from childhood to adolescence.
  • To investigate if sex differences in PA trajectories change when aligned by biological maturity versus chronological age.
  • To identify critical periods for intervention in boys' physical activity patterns.

Main Methods:

  • Utilized accelerometer data from the Iowa Bone Development Study (140 girls, 128 boys) at ages 5, 9, 11, 13, and 15 years.
  • Employed logistic regression and Spearman correlation to assess PA tracking and stability.
  • Estimated biological age relative to peak height velocity (PHV) using the Mirwald prediction equation for maturity-based analysis.

Main Results:

  • Girls demonstrated significant 10-year PA tracking (r = 0.27), while boys did not.
  • Girls in the lowest PA tertile at age 5 were significantly more likely to remain in the lowest tertile at age 15.
  • PA tracking stability was moderate to high in girls when aligned by biological age, and low to moderate in boys, particularly around PHV.

Conclusions:

  • Physical activity tracking from childhood to adolescence is more robust in girls than in boys.
  • Intervention programs for boys should concentrate on the pubertal period when activity patterns are most dynamic.
  • Aligning PA analysis with biological maturity provides deeper insights into developmental trends and sex-specific differences.