Gait stability in postpartum runners: A pilot study to inform the development of evidence-based return-to-running guidelines following childbirth

Abstract

Introduction & Purpose

Only 75% of female runners return to running following pregnancy and childbirth (Moore et al., 2021). Reported barriers for returning to running postpartum include pelvic floor dysfunction, musculoskeletal pain, and fear of movement (Moore et al., 2021), all of which may trigger or be the result of compensatory running gait adaptations. Provenzano and colleagues (2019) showed limited transverse plane trunk and pelvis rotations during running in the first weeks of the postpartum period and speculated that this adaptation may be an attempt to compensate for lower gait stability and higher perceived injury risk. It is unknown, however, whether reduced gait stability is still present greater than four months post-birth when current Austrian physical activity guidelines consider a return to high-impact sports possible (Ring-Dimitriou et al., 2020).

Next to musculoskeletal and psychological rehabilitation, one possible approach to improve gait stability in postpartum runners may be through footwear interventions. This is based on evidence for an improved local dynamic joint stability during running with shoes of reduced midsole thickness – possibly due to superior sensory feedback from the running surface (Frank et al., 2019).

The goal of this pilot study was to test the hypothesis that gait stability, quantified by trunk rotation excursion and local dynamic gait stability during running, is lower in postpartum (PP) runners more than four months post-birth compared to nulliparous controls (CTR). Further, to explore the association between measures of gait stability, fear of movement, and the choice of running footwear to help inform return-to-running guidelines.

Methods

Twenty-one female runners (n = 12 PP, n = 9 CTR) self-reported their demographics, running habits, birth and postpartum history (PP only) and fear of movement according to a German version of the 11-item Tampa Scale of Kinesiophobia (TSK; Woby et al., 2005). Running kinematics were quantified using a 17-sensor inertial motion capture suit (Xsens Link, Movella, Enschede, NL). All runners ran on a treadmill at a self-selected speed for five minutes and in four running shoe conditions (their own running shoes plus three models varying in midsole thickness and stiffness). Trunk rotation excursion was quantified from the average range of motion of the thorax segment in the transverse plane for the last three minutes. Local dynamic gait stability was assessed using the local divergence exponent of the medio-lateral trunk velocity (Bruijn et al., 2013). Higher exponents indicate lower stability. Linear mixed effects models clustered by runner were used to investigate the influence of “group” (PP vs CTR), and “shoe condition” on the two measures of gait stability (α = .05) with “running speed” as a covariate. In addition, we explored the association between “fear of movement” (TSK-score) and the two measures of gait stability with “group” as a potential effect modifier.

Results

On average, PP runners returned to running five months [range 1-10 months] post-birth and were measured at eight months (range 4-18 months] post-birth. The mean age was slightly higher in PP runners (35 years) compared to the CTR group (30 years) but height and body mass were similar (PP: 176 cm, 63 kg vs. CTR: 169 cm, 64 kg). On average, the training frequency per week and distance per run were higher in the CTR group (2.2/week, 7.7 km/run) compared to PP runners (1.5/week, 5.3 km/run). Average fear of movement TSK-scores were marginally elevated in PP runners (19.1 [range 14-25]) compared to the control (CTR) group (17.4 [range 13-22]).

PP runners showed significantly elevated local divergence exponents compared to nulliparous runners (mean difference 95% CI = .07 [.01, .14], F(1, 17.6) = 5.202, p = .035, Figure 1a) indicative of lower local dynamic gait stability in PP runners. This effect was not significantly influenced by the type of running shoe (F(3, 54.9) = 0.282, p = .838) nor confounded by running speed (p = .160). In contrast, there was no significant influence of “group” (F(1, 18) = 0.672, p = .423) nor “shoe condition” (F(3, 56) = 1.125, p = .347) on the transverse plane trunk rotation excursion (Figure 1b) with a trend of confounding by running speed (p = .066). There was no significant association between the fear of movement (TSK-score) and local dynamic gait stability (p = .137) nor trunk rotation excursion (p = .550).

Discussion

Postpartum runners showed a reduced local dynamic gait stability during running compared to nulliparous runners in a time frame of 4-18 months post-birth. This effect was observed independently of the selected running speed and despite relatively low levels of fear of movement in the postpartum runners compared to other cohorts with musculoskeletal pain conditions (Chimenti et al., 2021). Local dynamic stability quantifies the ability of the neuromuscular control system to respond to and recover from small perturbations (Bruijn et al., 2013). Given the lack of association with the fear of movement (TSK-scores), we speculate that the lower gait stability in postpartum runners may result from persistent deficits in lumbopelvic muscle function postpartum (Christopher et al., 2020) or fluctuations in breast mass. This is because of the crucial role of the lumbopelvic region for force transmission between the ground, legs, and upper body during running (Schache et al., 1999) and thus the capacity to respond to perturbations. Since lumbopelvic muscle function and movement is notoriously difficult to measure (Schache et al., 1999), local dynamic gait stability indices may be an interesting marker for monitoring and guiding the rehabilitation and return to running postpartum. To understand its association with clinical and biomechanical measures of lumbopelvic muscle function should be the goal of future studies in this field.

In contrast to the findings of Provenzano and colleagues (2019), we did not observe a significant restriction of upper body rotation in postpartum runners, which may be owed to the longer time post-birth and low levels of fear of movement in the current PP group. Furthermore, we could not demonstrate a systematic influence of the shoe type on either measure of gait stability, which suggests that the optimal footwear characteristics regarding gait stability are likely runner-specific (Nigg et al., 2017).

Given the small sample size, this study must be considered a pilot study and should inform a more comprehensive assessment of postpartum runners including clinical and biomechanical markers of lumbopelvic function. One specific limitation is the heterogeneity of the PP group, which combined runners in a wide time frame post-birth, with one and more children as well as different birth modes, which may have masked effects present in more homogenous subgroups.

Conclusion

This pilot study suggests a reduced local dynamic trunk stability in postpartum runners 4-18 months post-birth compared to nulliparous runners. Local dynamic stability indices should be investigated as potential biomarkers for monitoring the rehabilitation and guiding the return to running process postpartum.

References

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