Lower step rate is associated with a higher risk of bone stress injury: a prospective study of collegiate cross country runners

Key Points

1. 54 collegiate cross country runners were included in this prospective study.
2. Running biomechanics and bone mineral density were assessed in pre-season then bone stress injuries (BSI) were analyzed in the following 12 months, over 3 consecutive seasons.
3. Step rate was the strongest predictor of BSI risk, with a lower step rate associated with increased risk.

BACKGROUND & OBJECTIVE

Bone stress injuries (BSI) present a triple threat for clinicians – they’re challenging to diagnose, difficult to treat, and have a tendency to recur. Identifying modifiable risk factors for these injuries could be hugely beneficial in reducing their prevalence and impact.

Multiple factors are thought to be involved in BSI development including training load, diet and energy availability, previous BSI, body mass index, stress, and sleep (1). This study aimed to determine if running biomechanics and bone mineral density were associated with BSI in collegiate cross country runners.

Multiple factors are thought to be involved in bone stress injury development.

A lower step rate is often seen in combination with ‘over-striding’, which is thought to increase load on a number of tissues including the tibia, knee and hip.

METHODS

This prospective study included 54 healthy cross country runners (33 female, 21 male) who were followed over 3 consecutive seasons. Data was collected in the annual pre-season period, and all medically diagnosed BSIs up to 12 months following data collection were recorded.

Whole body kinematics were assessed using 3D gait analysis and ground reaction force (GRF) data was also collected. Dual X-ray absorptiometry (DXA) scans were performed to determine bone mineral density (BMD).

The primary outcome measure was BSI occurrence during the 12 month calendar year coinciding with the beginning of the cross country season.

RESULTS

This study performed a univariate analysis (examining the role of individual variables) and a multivariate analysis (analyzing how multiple variables may relate to influence injury risk).

A number of univariable associations with BSI risk were identified. The risk of BSI was 2.22 times greater in athletes with a previous BSI compared to those without, which is consistent with previous research. Among the kinematic running gait variables, only centre of mass (COM) vertical excursion was associated with BSI. The risk of BSI increased by 17% for each 0.5 cm increase in COM vertical excursion. Furthermore, BSI risk decreased with an increased step rate.

In the multivariable model, low step rate was identified as a predictor of BSI (after adjusting for known BSI risk factors - prior BSI and sex). Step rate was the only variable significantly associated with BSI risk, and a 1 step per minute increase in step rate was associated with a 5% decreased risk of BSI. BMD was an important covariate in the model, with higher BMD indicative of lower BSI risk, however this relationship was not statistically significant.

LIMITATIONS

• This study had relatively small numbers for a prospective design. This may have made it underpowered to detect statistically significant differences, for example in determining the role of BMD.
• Collegiate cross country runners are a specific population and age group and so these findings may not be applicable to other populations (e.g. older athletes).
• Training volume, intensity and progression were not assessed, and these are likely important factors in the development of BSI (2).

CLINICAL IMPLICATIONS

Step rate, often known by runners as ‘cadence’, is the total number of running steps per minute. It can be increased, typically by 5 to 10%, by using a metronome and instructing a runner to ‘run to the beat’. This study suggests that such an approach may reduce the risk of BSI in collegiate athletes.

Previous research (3) had similar findings - that high school runners with a low step rate (164 steps per minute or less) were more likely to develop shin pain than those with a high step rate (174 or above). This mirrors clinical findings - that those with an already high step rate (e.g. 174 or above) are unlikely to benefit from further increases. We should bear in mind that while such an approach may reduce peak tissue load, it does increase the number of loading cycles per minute.

A lower step rate is often seen in combination with ‘over-striding’, which is thought to increase load on a number of tissues including the tibia, knee and hip. Conversely, a higher step rate may reduce load on these tissues.

It does appear that an increased step rate would be effective in decreasing the risk of BSI, but further research is required to test this theory. BSI risk is known to be multi-factorial and influenced by training load, diet, previous injury, and several other factors. It’s unlikely that one intervention, such as increasing step rate, would be effective in isolation unless some of these other factors are considered.

We’re not yet at a point where we should be increasing the step rate of collegiate athletes as a protective measure, but it may be a small piece in the complex puzzle of BSI development.

+STUDY REFERENCE

Kliethermes S, Stiffler-Joachim M, Wille C, Sanfilippo J, Zavala P, Heiderscheit B (2021) Lower step rate is associated with a higher risk of bone stress injury: a prospective study of collegiate cross country runners. Br J Sports Med, Epub ahead of print. PMID: 33990294.

SUPPORTING REFERENCE

1. Nussbaum ED, Bjornaraa J, Gatt CJ Jr. 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 Jul/Aug;11(4):375-379. doi: 10.1177/1941738118824293. Epub 2019 Jan 15. PMID: 30645183; PMCID: PMC6600585.
2. Warden SJ, Edwards WB, Willy RW. Preventing Bone Stress Injuries in Runners with Optimal Workload. Curr Osteoporos Rep. 2021 Feb 26. doi: 10.1007/ s11914-021-00666-y. Epub ahead of print. PMID: 33635519.
3. Luedke LE, Heiderscheit BC, Williams DS, Rauh MJ. Influence of Step Rate on Shin Injury and Anterior Knee Pain in High School Runners. Med Sci Sports Exerc. 2016 Jul;48(7):1244-50. doi: 10.1249/MSS.0000000000000890. PMID: 26818150.