Human Anatomy — all lessons
Foundations of Anatomy
Anatomical terminology, planes, axes and movement directionsThe Skeletal System
Skeletal system: structure and functionsBone structure, remodelling and adaptation to loadingJoints and the Muscular System
Joint types and classificationJoint mechanics: arthrokinematics and stabilityThe muscular system: organisation and major muscle groupsMuscle architecture: pennation, length and cross-sectional areaMuscle fibre typesRegional Functional Anatomy
Spine and postureThe shoulder complexThe hip complexThe knee complexThe ankle and foot complexCore and pelvic stabilityElbow and wrist functional anatomyCervical and thoracic spine functional anatomyBone structure, remodelling and adaptation to loading
Compact and spongy bone, the cells that build and remove bone, how remodelling works, and what kinds of exercise load bone effectively.
Learning objectives
- Label the parts of a long bone and distinguish compact from spongy bone
- Describe the roles of osteoblasts, osteoclasts and osteocytes
- Explain remodelling and the mechanostat concept
- Identify the loading characteristics that are most osteogenic and apply them safely
Before this lesson
Why this matters
Bone strength determines fracture risk across life. Peak bone mass is built in youth, and from mid-life onward bone is gradually lost, faster in women after menopause. Exercise is one of the few non-drug influences on bone — but only certain kinds of loading work.
Fundamental concepts: anatomy of a long bone
- Diaphysis — the shaft; a tube of dense compact (cortical) bone around the medullary cavity (yellow marrow).
- Epiphyses — the ends; spongy (trabecular) bone — a lattice of struts aligned with typical stresses — containing red marrow.
- Articular cartilage — hyaline cartilage capping joint surfaces.
- Periosteum — the outer membrane, rich in nerves and blood vessels, supplying cells for growth and repair.
- Epiphyseal line — remnant of the growth plate where length increased until adulthood [openstax2022bone].
Compact bone is organised into osteons — concentric layers around a central canal carrying vessels and nerves.
The science: bone cells and remodelling
| Cell | Role |
|---|---|
| Osteoclasts | Large cells that resorb (dissolve) bone matrix |
| Osteoblasts | Lay down new bone matrix (collagen + mineral) |
| Osteocytes | Former osteoblasts trapped in bone; a network that senses strain and signals remodelling |
Remodelling occurs in a cycle: activation → resorption (osteoclasts) → reversal → formation (osteoblasts). In adults, a substantial fraction of the skeleton is replaced over several years. When resorption exceeds formation — as with oestrogen loss, ageing, inactivity or low energy availability — bone mass declines.
The mechanostat
Frost proposed that bone keeps its strain within a set range: strains above a threshold trigger formation (modelling); strains below another threshold trigger loss [frost2003]. Practical consequences:
- Magnitude matters: heavier loads produce larger strains.
- Rate matters: rapid, impact-type loading is more osteogenic than slow loading.
- Novelty matters: bone responds to unusual strain distributions and becomes less responsive to repetitive, familiar loading.
- Short bouts suffice: relatively few loading cycles per session can stimulate bone.
Evidence in practice
In the LIFTMOR randomised trial, post-menopausal women with low bone mass performed supervised, progressive high-intensity resistance and impact training (deadlifts, overhead press, back squats and jumping chin-ups with drop landings) twice weekly for eight months. They improved lumbar spine and femoral neck bone density and physical function compared with a low-intensity home programme, with no serious adverse events [watson2018]. This challenged the older belief that people with low bone mass should avoid heavy loading — but supervision, technique and gradual progression were central.
Common mistakes and misconceptions
- “People with osteoporosis must avoid all loading.” Appropriately supervised loading is recommended; what changes is exercise selection and progression (e.g., avoiding loaded spinal flexion with high fracture risk).
- “More training always means stronger bones.” High training volume with low energy intake can reduce bone density.
Assessment and practical tools
DXA reports give a T-score (comparison with young adults): ≥ −1.0 normal, between −1.0 and −2.5 low bone mass (osteopenia), ≤ −2.5 osteoporosis. These are clinical classifications; trainers use them only to inform, not to diagnose.
Case study
Client: Mrs D’Souza, 62, T-score −2.1 at the hip, no previous fractures, cleared by her doctor. Over 12 weeks, the trainer teaches hip-hinge and squat patterns with light loads, then progresses to moderately heavy sets of 5 with excellent form, adds heel drops progressing to small jumps, and includes balance work for falls prevention (falls prevention).
Further learning: video lessons
Video links are only marked “verified” after a human has watched them. Unverified entries open a YouTube search for that channel and topic rather than a guessed link.
Bone remodelling: osteoblasts, osteoclasts and osteocytes
Armando Hasudungan
You will understand: how bone is continually broken down and rebuilt
Why: Clear hand-drawn physiology explanations.
Exercise for bone health — what works
Royal Osteoporosis Society
You will understand: safe loading strategies for bone
Why: Patient-education material from a national charity.
Knowledge check
Knowledge check · 0/5
1. Which cell type senses mechanical strain and signals remodelling?
2. Spongy (trabecular) bone is mainly found…
3. Which loading pattern is most likely to stimulate bone gain?
4. In the LIFTMOR trial, women with low bone mass who did supervised high-intensity resistance and impact training…
5. The epiphyseal line represents…
Short-answer & application questions
- Explain why a young endurance athlete with very low energy intake may have low bone density despite high training volume.
- Describe how you would progress impact loading for a beginner aged 60 with normal bone density.
- Why does trabecular bone tend to be affected earlier than cortical bone by oestrogen loss?
Key takeaways
- Long bones have a compact-bone shaft around a marrow cavity and spongy-bone ends capped with articular cartilage.
- Osteoclasts resorb bone, osteoblasts form it, and osteocytes sense strain and coordinate remodelling.
- Bone responds to strain magnitude, rate and novelty more than to repetition count.
- Supervised high-intensity resistance and impact training has improved bone density in post-menopausal women with low bone mass.
- Low energy availability, low calcium/vitamin D and certain hormones impair bone regardless of training.
Connected topics
Osteoporosis
Resistance and power training for sarcopenia
Energy availability and RED-S
Understanding pain science and tissue healing
References
- Betts JG, Young KA, Wise JA, et al. (2022). Anatomy and Physiology 2e — Chapter 6: Bone Tissue and the Skeletal System. OpenStax, Rice University. · Link Textbook check pending
- Frost HM (2003). Bone's mechanostat: a 2003 update. The Anatomical Record Part A, 275(2):1081–1101. doi:10.1002/ar.a.10119 Narrative review check pending
- Watson SL, Weeks BK, Weis LJ, et al. (2018). High-intensity resistance and impact training improves bone mineral density and physical function in postmenopausal women with osteopenia and osteoporosis: the LIFTMOR randomized controlled trial. Journal of Bone and Mineral Research, 33(2):211–220. doi:10.1002/jbmr.3284 RCT check pending
Educational content only — not medical advice. Consult a qualified clinician for diagnosis or treatment.