Can impact exercise benefit bone health across the lifespan? Original paper

In this meta-analysis of randomized controlled trials, moderate-impact and high-impact exercises like running, dancing, and football improved structural bone health at the femur (thighbone) and tibia (shinbone). However, these outcomes varied widely across different age groups.

This Study Summary was published on February 5, 2024.

Quick Summary

In this meta-analysis of randomized controlled trials, moderate-impact and high-impact exercises like running, dancing, and football improved structural bone health at the femur (thighbone) and tibia (shinbone). However, these outcomes varied widely across different age groups.

What was studied?

The effect of moderate-impact and high-impact exercises on structural bone health across the lifespan.

Who was studied?

A total of 2,985 participants, including adults (ages 18–50), children and adolescents (under 18), and postmenopausal women (age not specified).

Individuals were excluded if they had a physical disability that could limit exercise ability, were postoperative, or were currently competing athletes.

How was it studied?

A systematic review and meta-analysis of 28 randomized controlled trials (RCTs) were conducted to assess the effect of moderate-impact and high-impact exercises on bone structure.

For this purpose, impact exercises with ground reaction forces equal to or greater than running (e.g., hopping, dancing, and football) were compared to no exercise, habitual recreational activities, or interventions not designed to influence bone structure (e.g., stretching). Interventions that combined impact activities with other forms of exercise such as resistance training were also included. The duration of the included studies ranged from 8 weeks to 4 years. The frequency of exercising ranged from 1 to 7 times per week, with exercise durations of 15 to 90 minutes.

The changes in bone structure were analyzed at several bones, including the tibia (shinbone), femur (thighbone), radius (forearm bone on the thumb side), and lumbar spine (lower back vertebrae). Moreover, the researchers assessed several locations within each of these bones, such as the distal and proximal sites (i.e., the parts of the bone closest and farthest away from the center of the body, respectively). These structures also included the trabecular bone, also known as cancellous or spongy bone, which is one of the two types of bone tissue in the human body. It has a porous, honeycomb-like structure, which makes it less dense and more flexible than cortical (compact) bone.

To analyze the changes in bone structures, the researchers assessed volumetric bone mineral density (vBMD). This metric measures the concentration of minerals (mainly calcium and phosphorus) in a specific volume of a bone. In contrast, areal BMD is more typically used to judge overall bone health because it measures mineral content over the area of the bone surface, not accounting for bone depth. As such, vBMD is a useful metric for bone structure, and it has been shown to predict fracture risk independent of areal BMD.[1]

Besides vBMD, the researchers also assessed cortical thickness, which refers to the thickness of the cortical bone, the dense, hard outer layer of bone tissue. This is another important factor in judging bone health and resistance to fracture.

Subgroup analyses were performed in children and adolescents (under 18), adults (ages 18–50), older men (over 50), and in postmenopausal women to investigate whether the effects of impact exercise on bone structure would differ during different stages of life.

What were the results?

Across all studies and age groups, impact exercise improved the vBMD at the proximal femur (the “upper” part of the thighbone) by 3.11% and the trabecular bone part at the distal tibia (the spongy bone structure at the “lower” part of the shinbone) by 0.54%. Moreover, impact exercise improved the cortical thickness at the mid/proximal radius (the thickness at the center of the wrist bone).

Subgroup analyses revealed that these effects differed for different age groups, particularly at the tibia. In adults, impact exercise decreased the vBMD of the cortical mid/proximal tibia (the “upper” part of the shinbone) by 0.2%. In children and adolescents, impact exercise improved vBMD of the tibia by 1.09%. In postmenopausal women, impact exercise improved total vBMD of the tibia by 1.35% and improved the vBMD at the distal tibia trabecular (the spongy bone structure at the “lower” part of the shinbone) by 0.79%.

Effect of impact exercise on bone density and bone area of the tibia (shin bone) by age group

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The big picture

The human bone is a dynamic tissue that constantly remodels itself. This continuous process of bone formation and resorption enables the human body to regenerate bones approximately every 10 years. This remarkable regeneration is profoundly influenced by physical activity, making exercise a crucial factor in maintaining bone health across the lifespan. Although moderate-impact and high-impact exercise can improve overall bone health (as measured by areal BMD), its effects on bone structure (as measured by vBMD) remain unknown.

The summarized meta-analysis was designed to shed more light on this topic, exploring how moderate-impact and high-impact exercises, such as running, dancing, and football, affect the structural aspects of bone health, specifically looking at vBMD. The choice of vBMD over the more commonly used measure of areal BMD is noteworthy. vBMD offers a three-dimensional perspective on bone density and also accounts for bone volume. This approach is especially beneficial for understanding the true strength and structure of bones, which is vital for assessing bone quality and predicting fracture risks. Specifically, this approach is particularly relevant in populations with unusual bone sizes, where areal BMD might not provide an accurate representation due to its two-dimensional nature.

Overall, the researchers demonstrated that impact exercises can significantly improve structural bone health, as indicated by increases in vBMD and cortical thickness at certain bone structures. Interestingly, these improvements varied at different bone sites and across different age groups. Most notably, the study found more pronounced effects on the trabecular bone, the more metabolically active and fracture-prone part of the bone. Although this finding is particularly relevant for conditions like osteoporosis, where trabecular bone’s integrity is a major concern, it raises questions about the underlying reasons behind these heterogeneous outcomes.

The reason some bone structures improved while others did not might be attributed to the distinct biological characteristics and functions of different types of bone tissue. Trabecular bone, which showed significant improvement, is known for its high metabolic activity and rapid turnover rate, regenerating about 7 times faster than cortical bone.[2][3] This makes it more responsive to mechanical stress induced by impact exercises. In contrast, cortical bone, which is denser and slower to remodel, may not exhibit immediate or noticeable changes with similar exercise regimes. Therefore, the type of exercise and the specific bone’s metabolic properties and remodeling rates could explain these varied outcomes.

Secondly, the differences in bone outcomes across the lifespan may be influenced by physiological changes associated with aging. Bone loss occurs when bone resorption (bone breakdown) exceeds bone formation.[4] Postmenopausal women experience accelerated bone loss largely due to an increase in bone resorption, rather than a decrease in bone formation.[5] Exercise seems to inhibit bone breakdown,[6][7] suggesting that it is especially beneficial after menopause because increased bone breakdown is the principal driver of bone loss in this population. The increased vBMD in this subgroup supports the idea that impact exercise is particularly effective in counteracting the rapid bone density loss typical in postmenopausal women.

However, it’s crucial to consider the study’s limitations and the need for further research. The evidence quality ranged from low to moderate, suggesting a need for more high-quality RCTs. Additionally, the clinical relevance of the observed changes in vBMD needs deeper exploration. As such, impact exercises vastly improved vBMD the proximal femur (by more than 3%) but had only marginal benefits at other bone sites (less than 1%). Therefore, the clinical relevance of these changes remains questionable.

Overall, this study emphasizes the complexity of bone biology and underscores the critical role of physical activity in maintaining and improving bone health. Moreover, it highlights the necessity for tailored exercise protocols that consider the unique bone remodeling dynamics at different life stages. Further research in this field is required to develop optimized exercise recommendations that maximize bone health benefits for all age groups.

Anything else I need to know?

High-quality RCTs in different age and sex subgroups are needed to identify optimal exercise protocols for improving bone structure across the lifespan.

This Study Summary was published on February 5, 2024.

References

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  2. ^Oftadeh R, Perez-Viloria M, Villa-Camacho JC, Vaziri A, Nazarian ABiomechanics and mechanobiology of trabecular bone: a review.J Biomech Eng.(2015-Jan)
  3. ^Manolagas SCBirth and death of bone cells: basic regulatory mechanisms and implications for the pathogenesis and treatment of osteoporosis.Endocr Rev.(2000-Apr)
  4. ^Santos L, Elliott-Sale KJ, Sale CExercise and bone health across the lifespan.Biogerontology.(2017-12)
  5. ^Ji MX, Yu QPrimary osteoporosis in postmenopausal women.Chronic Dis Transl Med.(2015-Mar)
  6. ^Alghadir AH, Aly FA, Gabr SAEffect of Moderate Aerobic Training on Bone Metabolism Indices among Adult Humans.Pak J Med Sci.(2014-Jul)
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