Bone health in ageing and the role of physical activity

Describe the normal changes in bone turnover and bone strength during ageing

Explain the osteogenic adaptations induced by physical activity and training

Discuss the scientific evidence for training recommendations to improve bone health and reduce fracture risk in postmenopausal women

Bone strength:
reflects the integration of three main features
(1) bone mineral density
(2) bone geometry
(3) bone quality (material properties, microarchitecture, bone turnover rate)

Osteoporosis is a skeletal disorder characterised by:


  • compromised bone strength predisposing to
  • increased risk of fracture

Bone strength of osteoporosis bone is compromised by:

  • reduction in bone quality
    --> loss of horizontal struts
    --> loss of connectivity
    --> conversion of trabecular plates to rods
    --> resorption pits are "stress concentrators"

DXA BMD:


T-score

  • compared with mean peak bone mass for young adults
  • assesses what is desirable
  • used to assess fracture risk

Z-score

  • compared with age- and gender matched population
  • assesses what is expected
  • used to determine if bone mass is unusually low

Cause of inadequate peak bone mass:


  • genetic factors
  • inadequate nutrition during growth and development (particularly calcium, vitamin D, energy and protein intake)
  • limited physical activity
  • diseases or drugs (e.g. corticosteroids) during growth

Bone turnover (remodelling) is accelerated in osteoporosis and the net bone balance in each bone remodelling unit is negative

Osteogenic training:


  1. Mechanical stimulus = elastic bone deformation = strain
  • strain magnitude
  • strain rate
  • strain novelty

  1. Rest periods


  2. Forces

  • dynamic ground reaction forces (GRF) in weight-bearing: high impact, odd impact
  • dynamic muscle forces

Strain magnitude: The effect of low and high intensity resistance training on BMD and bone turnover


Strain rate: A comparison of the effect of strength versus power resistance training (PRT) on bone


Menopause and ageing involve hormonal changes and menopause is characterised by a decrease in oestrogen levels that negatively impacts body composition by increasing body fat and decreasing lean and bone mass.


This ultimately increases risk of musculoskeletal disorders such as osteoporosis.

A RCT involving 80 inactive postmenopausal women aged 49 to 79 years with menopause for at least 3 years found that recreational handball increased lumbar spine BMD and BMC, femur BMC by 1.5%, 2.3% and 2.2% respectively. As well as 7% improvement in terms of postural balance.


Additionally, bone remodelling to repair micro-fractures and replace old and fragile bone tissue with new bone is of significance for osteoporosis prevention. After menopause there is a greater increase in osteoclastic resorption than in osteoblastic activity leading to a negative net bone balance.


The handball group showed higher absolute delta values for biochemical bone formation markers after 16-weeks than the control group. Even though recreational handball resulted in an increase in bone resorption marker CTX, it was accompanied by an increase in the osteoblastic activity markers P1NP and OC, which seems to indicate an overall osteogenic change in bone turnover

The author of this study suggest that osteogenic response may take more time in older and in younger populations. Longer-term study may be required to understand whether training improves femur BMD.

1) Bone is sensitive to applied strain rate, with higher strain rates being more osteogenic. Static loading (strain rate=0) produces a state similar to disuse resulting in bone resorption. This indicates that loads should be applied relatively quickly during an exercise program

(2) Strain magnitude is highly related to the amount of new bone formation at the organ level.


The larger the generated deformation in the bone matrix the larger the overall response of the bone. Larger forces lead to larger strains in bone, and, possibly, large mechanical forces should be created during exercise. However, as stated earlier, the distribution of strain magnitude can be poorly related to the specific sites of bone formation for a given bone section. Thus, bone may not be sensitive to strain magnitude but rather to a parameter that is related to strain magnitude. Furthermore, the attempt to create large forces in bone may contribute to bone, joint, or soft tissue injuries.

(3) A threshold behavior exists for the number of loading cycles. The full response can be triggered after only a limited number of loading cycles. This suggests that an optimally designed exercise program could be short in duration. Also, an extremely large number of loading cycles may increase the risk for stress fractures in bone even though the loads generated in each loading cycle are small.

(4) Bone is sensitive to the applied strain distribution.


Simply imposing a strain distribution that produces the same peak strain magnitudes in a bone section – but at different locations within the section (i.e., rotating the strain distribution) – may initiate new bone formation. Consequently, “unusual” bone strain distributions could be produced during exercise. Running, for instance, may not be the osteogenically optimal exercise partly because it generates strain distributions that are very similar to strain distributions induced by normal walking. Additionally, compared to walking, running only slightly elevates peak bone strain magnitudes.

(5) Induced strains do not have to be large to be osteogenic. Even very small magnitude strains can initiate bone (re)modeling if they are applied at high frequencies (>10 Hz). Clinical trials with humans are in progress to confirm these preliminary data.

(6) Bone may be capable of distinguishing between different types of strains. Bone strains can be classified as normal strains and shear strains. Normal strains deform the bone matrix in the direction of bone's longitudinal axis or transverse to it and are generated primarily by axial loads and bending moments. Shear strains, which can be generated by shearing loads and torsional moments, cause angular deformations of bone matrix elements. Several studies suggest that shear strains have less osteogenic potential than normal strains but shear strains may be important to minimize (intracortical) bone turnover. Thus, a variety of exercises may be best to maximize bone mass.

(7) Strain gradients are correlated with specific sites of new bone formation. Because exercise-related new bone accretion is linked to specific sites within a bone, the structural enhancement of bone can be maximized if the new tissue is added to sites that are at greatest risk to fracture. Thus, it is critical to have a means of controlling the specific sites of new bone deposition. Recently, Judex et al. (1997) confirmed previous data (Gross et al., 1997) that circumferential strain gradients of longitudinal normal strain are highly correlated with periosteal sites of bone forming surfaces in adult bone. Generally, circumferential strain gradients are largest where strains (deformations) are the smallest. This suggests that exercises could be designed to generate the sites of minimal strain at locations most in need of enhanced structural integrity.