Stress fractures are small microinjuries in a bone, usually in the areas that are used repetitively, more often in lower limbs. Stress fractures in the femur, typically in the neck part (hip) are common in women participating in sport – but there are some exercise strategies we can use to take care of our bone health!

Stress fractures are very particular types of injury, as bones typically break due to an acute rapid force – whereas stress fracture occurs due to repetitive, ongoing overload to a tissue that is not able to bear them (Astur et al., 2016).

Women, particularly those who do a lot of sports, are particularly susceptible to these types of fractures due to the fact that we have a dynamic level of estrogen throughout our lives – this level tends to decrease as we age, particularly after menopause. Additional factor that increases risk for bone stress injuries is susceptibility for the relative energy deficiency (RED-s – a multifactorial, complex combination of symptoms that has to do with lower energy intake compared to the outlet, over longer period of time) – which is again more common in athletic females (Nattiv et al., 2007).

Hip stress fractures are particularly common in women in sports (Wentz et al., 2011), can have some quite serious consequences, the road to recovery can be long and challenging, and return to sport rather tough (these fractures along the foot stress fractures take longest to return to sport (Hoenig et al., 2023)). So ideally we want these bones to be in good condition – and prevent any decrease of density when sporty women age, or have temporarily less energy (in which case the treatment should also include other elements – such as nutrition, loading management etc.).

In most general terms, working on increasing bone density follows the same rules of adaptation as any other tissue – the bone needs to be exposed to loads higher than usual, but not too high, in the desired directional forces, for short periods of time, and then left to adapt. But more than that – beyond the mechanical stimuli that need to be applied to stimulate bone growth, there are some physiological mechanisms that also occur locally (where the bone is loaded) and globally (in the whole body) that stimulate the bone growth where we exercise.

Of course, when the bone density is low, we need to keep safety in mind, and as always - good and appropriate load management, gradual exposure and progressive exercise plan is key, so planning the treatment, rehab or rehab session based on individual capacity is always a priority here.

There are some ways to increase the bone density in women, and it’s always good to have these ways in mind when working with a female athlete – also with a specific focus on a hip:

1. Start early

   Data shows that participation in sport as a teenager is associated with higher bone density in adult women (Lloyd et al., 2000). Sport participation in young people has great benefits, and brings a lot of advantages to every young person – but there are some specific challenges that young girls face when doing sports. These barriers are well described in Women in Sport charity report in 2022 (link here), and there are a lot of things we can do as a community to keep girls doing sports!

    

   Considering hip joint, it is good to encourage young girls to participate in sports that include a lot of lower limb movement in any planes – football, rugby, athletics etc. The challenge is in a dose – as data shows that too early specialisation and too high participation in ‘leg dominant’ sports may increase risk for other hip diagnoses (de Silva et al., 2016). Which further emphasises the important message of sports and movement variety, particularly in young people.

    

   Let’s create a community where not only we model participating in sports regardless of how our bodies look, but also encourage girls to do sports in any way we can!

2. Resistance training – at any age

Training large muscle groups with a relatively high resistance (approximately 75% of 1 maximum repetition of any given exercise) was shown to increase bone density in association with increased strength in women between 65-75 years (Rhodes et al., 2000).

So increasing the muscle strength and muscle mass increases bone density too – but data seems to focus more on big muscle groups and more compound exercises. The mechanism of this increase in bone density is thought to be mostly about the mechanical force of the muscle contraction through the tendon on the bone, and further transferred to the whole bone (Hong & Kim, 2018), but there are also some physiological local processes that stimulates the bone growth.

Focussing on hip joint specifically, training big muscle groups in loaded (standing up with weights) or unloaded way (on a machine) is advisable. Focus on relatively high resistance, and on muscles such as quardiceps, hamstrings, calf muscles and glutes – maximus and medius, to create this force through the tendons, that will then transfer to bone at the insertion and stimulate adaptation.

3. Axial loading – compressive forces & compound movements

Axial loading (so loading against gravity) is one of the strongest forces to increase bone density (researched well in upper (Troy et al., 2020) and lower limb, but not always specifically in women).  

These exercise include any movement in a standing up position, with enough weights to stimulate physiological processes in a body. How much that is exactly – we don’t really know as it is different for everyone and depends on our lifestyle. The easiest way to determine this is to define 1 maximum repetition (1 rep max – so maximum resistance that we can only do 1 repetition with at any given point), and start on working around/above 75% of that weight.

Axial loading exercises have a great advantage as they are exposing the body to tension (pulling) forces when the muscles are working, but also additionally to compressive forces  - of the weight carried. So the directions and vectors of forces are actually quite extensive in these types of exercises – which stimulates the bone growth and density adaptation in multiple directions!

Focussing on hip joint, exercises such as squats, lunges, deadlifts, RDLs or heel raises are always a great idea to implement. If this is impossible (due to injury, pain, or technical difficulty), even movements such as little steps, weight shifts, mini-squats or one leg lifts will do the job – as long as the body is loaded!

4. High velocity and high impact training

Another nice way to increase the bone density is high velocity and high impact training, particularly in variety of loading direction (Nikander et al., 2005). This is a great way to keep the training interesting and fun, and can include any type of running-related sport participation, HIIT training or other fun activities – jumping, agility drills etc.

Specifically for the hip bone density, this data encourages women of every age to participate in various sports – netball, handball, football, volleyball, which bring a lot of running, jumping, changing directions and sprinting.

Variety of training, and making it fun means that the exercise routine becomes more sustainable – which is so important in maintaining a long term bone health throughout lifespan!

All in all – we know that exercises are great for so many reasons – including long term bone health! Although the exact mechanisms of the osteogenic (so – bone building) properties of exercises are not clear, evidence is directing us toward these four strategies for low bone density treatment and prevention.

And if you are a woman who does sports, or someone who support women in sport, do keep the bone health in mind when engaging in physical activity – in short, medium and long term!

Astur, D. C., Zanatta, F., Arliani, G. G., Moraes, E. R., Pochini, A. de C., & Ejnisman, B. (2016). Stress fractures: definition, diagnosis and treatment. Revista Brasileira de Ortopedia (English Edition), 51(1), 3–10. https://doi.org/10.1016/j.rboe.2015.12.008

de Silva, V., Swain, M., Broderick, C., & McKay, D. (2016). Does high level youth sports participation increase the risk of femoroacetabular impingement? A review of the current literature. In Pediatric Rheumatology (Vol. 14, Issue 1). BioMed Central Ltd. https://doi.org/10.1186/s12969-016-0077-5

Hoenig, T., Eissele, J., Strahl, A., Popp, K. L., Stürznickel, J., Ackerman, K. E., Hollander, K., Warden, S. J., Frosch, K. H., Tenforde, A. S., & Rolvien, T. (2023). Return to sport following low-risk and high-risk bone stress injuries: A systematic review and meta-analysis. In British Journal of Sports Medicine (Vol. 57, Issue 7, pp. 427–432). BMJ Publishing Group. https://doi.org/10.1136/bjsports-2022-106328

Hong, A. R., & Kim, S. W. (2018). Effects of resistance exercise on bone health. In Endocrinology and Metabolism (Vol. 33, Issue 4, pp. 435–444). Korean Endocrine Society. https://doi.org/10.3803/EnM.2018.33.4.435

Lloyd, T., Chinchilli, V. M., Johnson-Rollings, N., Kieselhorst, K., Eggli, D. F., & Marcus, R. (2000). Adult Female Hip Bone Density Reflects Teenage Sports–Exercise Patterns But Not Teenage Calcium Intake. Pediatrics, 106(1), 40–44. https://doi.org/10.1542/peds.106.1.40

Nattiv, A., Loucks, A. B., Manore, M. M., Sanborn, C. F., Sundgot-Borgen, J., & Warren, M. P. (2007). The female athlete triad. Medicine and Science in Sports and Exercise, 39(10), 1867–1882. https://doi.org/10.1249/mss.0b013e318149f111

Nikander, R., Sievänen, H., Heinonen, A., & Kannus, P. (2005). Femoral neck structure in adult female athletes subjected to different loading modalities. Journal of Bone and Mineral Research, 20(3), 520–528. https://doi.org/10.1359/JBMR.041119

Rhodes, E. C., Martin, A. D., Taunton, J. E., Donnelly, M., Warren, J., & Elliot, J. (2000). Effects of one year of resistance training on the relation between muscular strength and bone density in elderly women. British Journal of Sports Medicine, 34(1), 18. https://doi.org/10.1136/bjsm.34.1.18

Troy, K. L., Mancuso, M. E., Johnson, J. E., Wu, Z., Schnitzer, T. J., & Butler, T. A. (2020). Bone Adaptation in Adult Women Is Related to Loading Dose: A 12-Month Randomized Controlled Trial. Journal of Bone and Mineral Research, 35(7), 1300–1312. https://doi.org/10.1002/jbmr.3999

Wentz, L., Liu, P.-Y., Haymes, E., & Ilich, J. Z. (2011). Females Have a Greater Incidence of Stress Fractures Than Males in Both Military and Athletic Populations: A Systemic Review. Military Medicine, 176(4), 420–430. https://doi.org/10.7205/MILMED-D-10-00322