Exercise and Bones

2 types of bone cells + their functions

• Osteoclasts

• Osteoblasts

Osteoclast function + effect of function

• Demineralise bone

• Releasing calcium into the bloodtstream

Osteoblast function + how

• Lay down new bone (by secreting collagen + other minerals)

How often is compact bone replaced?

approximately every 10 years

How often is spongy bone replaced?

every 3 to 4 years

When is bone mass maintained?

When activity between osteoclasts and osteoblasts is balanaced

When is bone mass lost?

When the activity of osteoclasts exceeds that of osteoblasts

Osteopenia def + what it increases risk for

• Bone mineral loss but not yet severe enough to be considered osteoporosis

• Higher risk of fractures

Osteoporosis clinical def +

• Bone density is 2.5 standard deviations below the mean

• Bones become thin, weak + fragile

Bones susceptible to osteoporosis fractures (3)

• Hips, pelvis, spine + wrists

Prevalence of poor bone health (1)

Increasing

Gender differences, mortality + health outcomes

• Gender Risk: Women are at a higher risk, accounting for over 70% of hip fractures in patients aged 50 and over. However, men account for 30% of fractures, indicating it is not exclusively a female disease.

• Mortality: 10% of patients do not survive 30 days after a hip fracture; 25% die within one year of the injury.

• Morbidity: 78% of survivors do not regain their pre-fracture walking ability within three months of the accident.

Economic cost of osteoporosis

Overarching way to prevent bone health problems in later life (1)

• Accrue as much bone mass as possible in bone building years

Purposes of bone remodelling

• Meet shifting mechanical demands

• Repair micro damage (replace old, brittle bone)

• Maintains homeostasis of blood calcium levels → prevents mineral salts from crystallising and making bones brittle and susceptible to fractures

Factors affecting bone remodelling (3)

• Nutrition: sufficient calcium intake

• Mechanical stimulation

• Vitamin D + hormones

Interesting note on calcium impact in older age

• Additional intake has little impact on bone density in older age (although insufficient intake def increases osteoporosis risk)

Wolff’s Law (on mechanical influence) (2)

• Increased loading on bone → increases bone density to improve ability of bone to resist force

• Decreased loading → encourages catabolism of bone

Keeping in mind Wolff’s Law, what can be done to maintain bone strength/density?

• Regular exercise

  • Weight bearing exercise best (running/walking/weights), but non-weight bearing (cycling, swimming) can still be effective

Benefits of resistance training for bone health

• Highest degree of specificity in targeting bone strengthening of specific areas (many machines + exercises)

Strategies for creating resistance training program to optimise bone health

• Compound/multi-joint movements → force through spine + hips to use greater absolute loads

  • E.g. squats, cleans, deadlifts, press

• Axial Skeleton Loading: Placing weight over the shoulders (e.g., in a gym setting) stresses the spine and hips—the sites most commonly affected by osteoporosis and osteopenia.

• Multi-directional Loading: Ensuring bones are stressed from various directions to account for their anisotropic nature.

What does skeletal health also encompass? (3)

Tendons, ligaments, and cartilage

Impact of resistance training on tendons + ligaments (1)

• Resistance training → muscle growth → net growth of tendons + ligaments (which aerobic training doesn’t do) → can withstand greater force

How does cartilage get its nutrient supply?

From synovial fluid (no direct blood supply)

Effect of exercise on cartilage health

• Joint movement from exercise → O2 to cartilage

Effect of moderate vs strenuous exercise on joint health + note on activity involving repetitive high impact force

• Both generally beneficial for cartilage, strenuous exercise the not deleterious for joints as commonly thought

• However, repetitive high impact force can increase risk of joint injury → which can in turn lead to cartilage degeneration