*Article* **The Influence of a Shoe's Heel-Toe Drop on Gait Parameters during the Third Trimester of Pregnancy**

**Xin Li <sup>1</sup> , Zhenghui Lu 1 , Dong Sun 1 , Rongrong Xuan 2 , Zhiyi Zheng 3, \* and Yaodong Gu 1, \***


**Abstract:** Background: Changes in physical shape and body mass during pregnancy may increase the risk of walking falls. Shoes can protect and enhance the inherent function of the foot, helping to maintain dynamic and static stability. Methods: Sixteen women during the third trimester of pregnancy participated in this study to investigate the effect of negative heel shoes (NHS), positive heel shoes (PHS), and normal shoes (NS) on spatiotemporal parameters, ground reaction force (GRF), and stability. Differences in spatiotemporal parameter, GRF, and center of pressure (COP) between footwear conditions were examined using Statistical Parametric Mapping (SPM) and repeated measures analyses of variance (ANOVA). Results: The walking speed and step length increased with the increase in heel-toe drop. The anterior-posterior (AP)-COP in NHS decreased significantly (*p* < 0.001). When wearing NHS, peak posterior angles were significantly lower than NS and PHS (*p* < 0.05). Conclusions: The results show that changing the heel-toe drop can significantly affect the gait pattern of pregnant women. Understanding the gait patterns of pregnant women wearing shoes with different heel-toe drops is very important for reducing the risk of injury and equipment design.

**Keywords:** negative heel shoes; positive heel shoes; gait; pregnant women; OpenSim; IDEEA

#### **1. Introduction**

Pregnancy induces tremendous changes in the body to accommodate a growing fetus [1]. During pregnancy, hormonal, anatomical, and physiological changes occur in the female body. These changes due to pregnancy include mass redistribution, an anterior shift in the center of gravity location, and increased joint and ligament flexibility [2–6]. These changes during pregnancy can cause physical pain and an increased risk of falls, especially in the third trimester [4,7]. During pregnancy, nearly a quarter of employed women sustain a fall [8]. This fall may result in musculoskeletal injury and maternal or fetal death [9–11].

Walking is the most commonly chosen type of physical activity during pregnancy [12]. The gait parameters, balance, and center of mass of pregnant women changes during walking and leads to a higher risk of falling [1,6,13,14]. The rate of falls during pregnancy is similar to that of women over 65 [6,8]. A decreased step length and cadence, increased base of support, and longer double support time are seen with the progression of pregnancy [15,16]; these changes provide a safer and more exploratory way for pregnant women to walk. However, results point toward excessive deviations from the optimal habitual spatiotemporal gait pattern as a pivotal factor that may contribute to falls in pregnant women [16]. Mei et al. studied pregnant women's gait biomechanics, which revealed lower limb kinematic and foot pressure alterations, and found that mean pressure in the forefoot increased. The center of pressure (COP) trajectory highlights a fall risk, particularly in the third trimester [4]. To improve their walking stability, pregnant women often use specially designed products, such as daily wearing shoes.

**Citation:** Li, X.; Lu, Z.; Sun, D.; Xuan, R.; Zheng, Z.; Gu, Y. The Influence of a Shoe's Heel-Toe Drop on Gait Parameters during the Third Trimester of Pregnancy. *Bioengineering* **2022**, *9*, 241. https://doi.org/10.3390/ bioengineering9060241

Academic Editors: Christina Zong-Hao Ma, Zhengrong Li and Chen He

Received: 1 May 2022 Accepted: 29 May 2022 Published: 31 May 2022

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Shoes can protect and enhance the inherent function of the foot, helping to maintain dynamic and static stability [17,18]. Many previous studies have focused on changing the shape and materials of a shoe sole to reduce pregnant women's foot discomfort [19,20]. Jang et al. designed balanced incline shoes [21] and reported that the balanced incline shoes corrected the postures and stabilized the gait pattern.

Research about the effects of different heel-toe drop shoes on pregnant gait parameters is lacking. Heel-toe drop is the height difference between the heel and the forefoot of the shoe [22]. In positive heel shoes (PHS; Table 1 includes a description of abbreviations and acronyms used), the heel is higher than the toe part. In contrast, in the negative heel shoe (NHS), the toe part is higher than the heel [23]. Advocates of shoes with negative inclination believe that negative heel inclination decreases lumbar lordosis, causing the center of gravity to shift backwards [24,25]. As a result, back and hip pain can noticeably be reduced [19]. However, the American College of Obstetricians and Gynecologists (ACOG) recommends wearing positive heel shoes (PHS) to relieve back pain during pregnancy [26]. However, few studies have investigated the effect of different heel-toe drops on spatiotemporal parameters, ground reaction force (GRF), and the dynamic balance in the third trimester of pregnancy. It is necessary to know the effects of the different heel-toe drops to design maternity shoes and keep pregnant women healthy.

**Table 1.** List of abbreviations and acronyms used in this article.


This study aimed to use a musculoskeletal simulation and Statistical Parametric Mapping (SPM)-based approach to investigate the effect of different heel-toe drops (negative 1.5 cm, 0 cm, positive 1.5 cm) on the spatiotemporal parameter, GRF, and dynamic balance during the third trimester of pregnancy. The results can provide a theoretical basis and ideas for the design of shoes for pregnant women in the third trimester.
