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Bone-Stress Injuries – Causes, Mechanisms, and Why They Affect Runners

Bone-Stress Injuries – Causes, Mechanisms, and Why They Affect Runners

Introduction: An Invisible Danger for Runners

Running is one of the most popular sports worldwide. It promotes physical and mental health and is easy to access, as it requires neither expensive equipment nor special facilities. However, despite its many benefits, overuse injuries are widespread in running. Particularly insidious among these are Bone-Stress Injuries (BSI), which occur through repeated mechanical stress rather than sudden trauma (1).

Bone-Stress Injuries are among the most common and severe overuse injuries in running. They particularly affect long-distance runners and can lead to extended training breaks. In the worst-case scenario, they may progress to complete fractures, requiring months of rehabilitation (2). The critical issue is that BSIs develop gradually. Early warning signs are often dismissed or mistaken for normal running aches and pains. As a result, the injury can advance unnoticed and, in the worst case, evolve into a stress fracture (3).

The aim of this article is to raise awareness of Bone-Stress Injuries, explain their causes, and illustrate why they pose a significant challenge specifically for runners.

What Are Bone-Stress Injuries?

Bone-Stress Injuries occur when bone tissue is subjected to repeated mechanical loads without sufficient time for adaptation. Unlike acute fractures, BSIs develop from an accumulation of microtraumas that can lead to structural damage over time (1).

The Cycle of Microtrauma, Bone Resorption, and Remodeling

Bone is a dynamic tissue that continuously adapts to the mechanical demands placed on it. This principle, known as Wolff’s law, describes the bone’s ability to change its density and structure in response to mechanical stress. When running, impact forces caused by footstrike exert stress on the skeleton. These forces create microtraumas – tiny cracks in the bone structure (2).

Normally, bone undergoes a continuous process of breakdown and rebuilding to adapt to stress:

Resorption: Osteoclasts remove damaged bone tissue. In the dense cortical bone, this process takes about four weeks (4).
Formation: Osteoblasts produce new bone tissue. Full mineralization can take three to twelve months 55.
Adaptation: With sufficient recovery, the new bone structure enhances resistance to future stress (6).

Problems arise when new stress is applied to the bone before the remodeling processes are complete. An imbalance occurs where bone is broken down faster than it is rebuilt, weakening its structure and increasing the risk of BSI (2).

Carbohydrates for Athletes: How to Do It Right

For endurance athletes, the proper amount and timing of carbohydrate intake are especially important. Below are the current recommendations:

Before Training:
1–4 g of carbohydrates per kilogram of body weight (g/kg) should be consumed 1–4 hours before training. Meals with mixed carbohydrates like glucose and fructose are particularly helpful for replenishing overnight-depleted liver glycogen stores (5–7).
During Training:
For training sessions lasting over an hour, 30–60 g of carbohydrates should be taken in per hour. For particularly long sessions (over 2.5 hours), intake can be increased to as much as 90 g per hour. A combination of glucose and fructose (in a 1:0.8 ratio) improves absorption and performance (5,6,8).
After Training:
To optimize recovery, it’s recommended to consume 1.0–1.2 g/kg of carbohydrates per hour in the first four hours post-exercise. Combining glucose and fructose speeds up glycogen replenishment in both the muscles and the liver (6).
Daily Requirement:
Depending on training intensity, endurance athletes need between 6–12 g of carbohydrates per kilogram of body weight per day. High-intensity training requires more energy, which is why the upper limit can be 10–12 g/kg (5,6,9).

Why Runners Are Particularly at Risk

Bone-Stress Injuries are not uncommon in running. Studies show that between 30% and 60% of long-distance runners experience a BSI during their careers (1). Several factors make runners especially vulnerable to this type of injury:

High Repetition of Stress: Each running step exerts forces of up to three times a person’s body weight on the musculoskeletal system (3).
Monotonous Load: Unlike sports involving multidirectional movements, the repeated, linear footstrike in running places consistent stress on the same parts of the bone structure (1).
Lack of Muscular Support: Runners who do only running without supplementary strength training often have lower bone density and a higher risk of injury (4,7).
Relative Energy Availability: A deficit in calories or nutrients leads to increased bone breakdown and reduced bone formation, further elevating the risk of BSI (8).

The Role of Bone Mechanosensitivity

One frequently overlooked factor is the mechanosensitivity of bone cells. Research shows that osteocytes – the primary sensory cells in bone – lose their sensitivity to mechanical stimuli after just 20 loading cycles (6).

Interestingly, after a rest period of four to eight hours, mechanosensitivity is largely restored, meaning additional loading will once again trigger a stronger adaptive response (4). This indicates that runners should structure their training to maximize bone adaptation.

Conclusion: Why Bone-Stress Injuries Must Be Taken Seriously

Bone-Stress Injuries are an underestimated hazard for runners. They arise from a combination of excessive mechanical loading, insufficient recovery, and inadequate bone adaptation. The injury often develops gradually and is only taken seriously when it has already advanced significantly.

Because bone adaptation is a long-term process, preventing BSIs requires carefully managing both training stress and recovery. The mechanosensitivity of bone underscores the importance of not only adjusting volume but also considering recovery intervals when designing training programs. At the same time, proper nutrition, strength training, and multidirectional movements are essential to maintaining bone health in the long term.

In the second part of this article, we will describe in detail the specific measures that can help prevent and rehabilitate Bone-Stress Injuries, and how to strategically minimize their risk in training.

Sources

Warden SJ, Davis IS, Fredericson M. Management and Prevention of Bone Stress Injuries in Long-Distance Runners. J Orthop Sports Phys Ther. Oktober 2014;44(10):749–65.
Warden SJ, Edwards WB, Willy RW. Preventing Bone Stress Injuries in Runners with Optimal Workload. Curr Osteoporos Rep. Juni 2021;19(3):298–307.
Popp KL, Outerleys J, Gehman S, Garrahan M, Rudolph S, Loranger E, u.a. Impact loading in female runners with single and multiple bone stress injuries during fresh and exerted conditions. J Sport Health Sci. Mai 2023;12(3):406–13.
Gabbett TJ, Oetter E. From Tissue to System: What Constitutes an Appropriate Response to Loading? Sports Med [Internet]. 11. November 2024 [zitiert 6. Dezember 2024]; Verfügbar unter: https://link.springer.com/10.1007/s40279-024-02126-w
Orchard JW, Ranson C, Olivier B, Dhillon M, Gray J, Langley B, u.a. International consensus statement on injury surveillance in cricket: a 2016 update. Br J Sports Med. 2016;50(20):1245–51.
Burr DB, Robling AG, Turner CH. Effects of biomechanical stress on bones in animals. Bone. 2002;30(5):781–6.
Nussbaum ED, Bjornaraa J, Gatt Jr CJ. Identifying factors that contribute to adolescent bony stress injury in secondary school athletes: a comparative analysis with a healthy athletic control group. Sports Health. 2019;11(4):375–9.
Sale C, Elliott-Sale KJ. Nutrition and Athlete Bone Health. Sports Med. Dezember 2019;49(S2):139–51.

Bone-Stress Injuries – Causes, Mechanisms, and Why They Affect Runners

Introduction: An Invisible Danger for Runners

What Are Bone-Stress Injuries?

Carbohydrates for Athletes: How to Do It Right

Why Runners Are Particularly at Risk

The Role of Bone Mechanosensitivity

Conclusion: Why Bone-Stress Injuries Must Be Taken Seriously

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