Effect of heel height on lower limb biomechanics during stair descent in young women: a laboratory study

Abstract

Background

Stair descent in high heels is risky for young women. Existing studies have focused on level walking, but research on stair descent biomechanics with different heel heights is limited. This study aimed to investigate the effects of heel heights on the biomechanical parameters of the lower limbs, joint stiffness and work pattern in young women during stair descent.

Methods

Twenty-five young women walked downstairs wearing high heels heights (1 cm, 3 cm, 5 cm, and 7 cm). Kinematic and kinetic data of the lower limb joints were synchronously collected using the Vicon infrared motion capture system and AMTI force plates.

Results

The ankle stiffness decreased at 3 cm (P = 0.035), 5 cm (P < 0.001) and 7 cm (P < 0.001), compared with a heel height of 1 cm. The ankle joint net work significantly decreased at 7 cm compared with 1 cm (P = 0.017) and 3 cm (P = 0.003). The work contribution of the ankle joint significantly decreased at 7 cm compared with 1 cm (P = 0.017) and 3 cm (P = 0.003).

Conclusion

Young women wearing 7 cm heels significantly affected ankle biomechanics during stair descent, reducing ankle net work, work contribution, and stiffness. Therefore, it is recommended that young women prioritize footwear with heel heights below 7 cm during stair descent.

Introduction

Stair negotiation is one of the most challenging daily activities, the risk of falls during stair descent is higher than other activities [1]. Surveys have shown that about 26% of falls occur during stair walking [2], with falls down stairs accounting for about 3/4 of stair walking falls [3]. Wearing high-heeled shoes can cause a more upright posture, but it can lead to gait abnormalities [4]. And long-term wear can lead to knee pain, foot pain and even deformity [5], which threatens the physical health of young women, and has also attracted widespread attention in the fields of clinical medicine and biomechanics.

A study found that compared with walking on a flat surface, stair walking requires greater lower limb joint torques and ranges of joint motion [6]. Compared with ascending stairs, the peak values of the maximum flexion torques of the hip and knee joints during the process of descending stairs increase significantly, and the contact force of the knee joint doubles [7]. Therefore, greater support torques of the lower limb joints are required.Studies have shown that joint stiffness may be related to the attenuation of the load transmitted by the body. Therefore, joint stiffness can indirectly reflect the risk of lower limb injuries [8]. Studies have shown that, in order to cope with various situations and avoid falling, the first activated movement protection mechanism of the human body is the regulation of the stiffness of the lower limbs, and this response is accomplished by relying on the dynamic interaction between joint displacement and force [9].

In recent years, numerous studies have extensively investigated the biomechanical effects of high-heeled shoes on the lower limb during level walking. The survey indicates that as heel height increases, there is a corresponding elevation in vertical ground reaction force sagittal plane of knee moments during flat ground walking in high-heeled shoes [10, 11]. Furthermore, Buddhadev et al. [12] found that walking in high-heel shoes decreases the overall plantar flexion range of motion (ROM), moments, powers and work of the ankle joint during walking. They also reported lower plantar flexor moments and the reduced contribution of plantar flexors during the stance phase of high-heel shoes walking [12].

However, current research on the effects of high heels on gait is limited to level walking [13, 14], and fewer on the biomechanics of lower limb joint angle, moment, stiffness, and joint work during stair descent. Descending stairs while wearing high heels is one of the most challenging and hazardous daily activities for young women [15, 16]. Walking in high-heeled shoes with high heels can impair the ability to control the stability of the foot, often resulting in discomfort and pain [15, 17]. Consequently, young women who choose to wear high heels encounter numerous challenges during stair descent [18]. Alterations in joint angles, moments, and joint work, along with adjustments in stiffness, can collectively contribute to a more intricate and potentially perilous gait pattern when descending stairs [19]. Joint angle, moment, work, and stiffness have been extensively studied in walking [20], running [21] and other sports, but its application to young women descending stairs at different heel heights is rare.

Therefore, it is important to investigate the changes in angle, moment, work, and joint stiffness when young women during stair descent in high heels to prevent falls and sports injuries. Given the scarcity of existing research in this field, it is crucial to undertake further studies to explore the comprehensive impact of heel heights on the biomechanics of stair descent among young women. Such research will enhance our understanding of the risks linked to high-heel use and guide the development of strategies to reduce these risks, thereby promoting safer and more stable movement patterns during stair descent. The present study aims to investigate the effects of different heel heights on lower limb joint angle, moment, stiffness and joint work during stair descent in young women. We hypothesized that change in joint angle, moment, work and contribution of three joints of lower limb (ankle, knee and hip) increase with elevated heel heights during descending stairs.

Materials and methods

Participants

Using G*Power 3.1 software, a one-way repeated-measures ANOVA was selected for statistical analysis. With the statistical power set to 0.8 and the alpha level at 0.05, the calculated minimum required sample size was 14 participants. Twenty-five healthy females (age: 20.88 ± 1.41 years old, height: 164.98 ± 3.55 cm, 53.69 ± 4.42 kg, body weight: 20.74 ± 0.19 kg/m²) were enrolled randomly and participated in this study. The study protocol was approved by the internal review board of Shandong Sport University (Approval No. 2023011). The participants enrolled voluntarily in this study and provided written informed consent before participation in this study.

Inclusion criteria: (1)healthy females aged between 18 and 25 years; (2)wearing shoe sizes of 38/39; (3)a body mass index (BMI) less than 23.9Kg/m² [18]. Exclusion criteria: (1)acute injuries to other lower limb joint musculoskeletal structures within the past six months, and foot orthotics; (2)having musculoskeletal diseases, cardiovascular diseases, and neurological and sensory system injuries [22]; (3) Prior Foot Orthopaedic Interventions.

Protocol

This study was conducted in the laboratory of Shandong Sport University. The participants were required to wear standardized tight-fitting clothing and shoes, and the personnel affixed reflective markers to the bony landmarks on the participants’ body according to the model provided by Visual 3D. The participants were also required to footwear in their respective size and descend the staircase three times for each heel height condition. The dominant leg was defined as the preferred leg for kicking a football [22]. After receiving instructions from the researcher, the participants started to descend the staircase with the non-dominant foot for the first step in a step-by-step manner at their comfortable speed under four heel height conditions. In total, each participant was asked to complete 12 stair descending trials (3 trials per shoe condition). A successful stair descending trial was defined as a trial in which the participant’s dominant foot had to strike within the boundaries of the force plates. Besides, a 1-min rest was given between consecutive trials.

The simulated staircase consists of 6 steps, with each step measuring 0.17 m in height, 1.5 m in width, and 0.3 m in length, and it has an inclination angle of 29.4 degrees (Fig. 1). Four shoes that varied in heel height (flat: 1 cm, low: 3 cm, medium: 5 cm, and high: 7 cm) were used in the study (Fig. 2). All shoes were made by the same manufacturer, using the same kind of material. Except for flat shoes as the baseline condition, all experimental shoes were dress shoes with stiletto heels (14 mm × 13 mm). The heel-height shoes order was randomly assigned to each participant.

Fig. 1.

Simulation Staircase, Force Plates and A twelve-camera motion analysis system

Fig. 2.

Four Experimental Shoes with 1, 3, 5, 7 cm Heel Height (All but flat shoes were 14 mm×13 mm).

Data collection

Ground reaction forces were collected at a rate of 1,000 Hz using two force plates (AMTI, Inc. Watertown, MA, USA), which were embedded in the third and fourth steps of the stairs [23]. A twelve-camera motion analysis system (Vicon, Oxford Metrics Ltd.,UK) (Fig. 3), was used to capture kinematic data at 100 Hz [22]. 43 reflective markers (14 mm) were placed on each participant’s anatomical landmarks to quantify lower extremity kinematics. Reflective markers were labeled and digitized using Visual 3D software (C motion, Inc., Germantown, MD, USA). Kinematic and kinetic data were filtered with a fourth-order Butterworth low-pass filter with a cutoff frequency of 6 Hz and 50 Hz [24].

Fig. 3.

The Application of Markers on The Frontal and Dorsal Aspects

The stance phase was determined from the contact of dominant leg on the fourth step to take-off the same step. The ground reaction force defined as the threshold for determining the contact and toe-off is at least 20 N in the vertical direction [25]. Lower limb joint angle in sagittal plane was obtained by calculation based on model data by Visual 3D software.

An inverse dynamics method was used to calculate the net moments in sagittal plane generated by the muscles around each joint of the lower limb [26]. The joint power in sagittal plane is the product of moment and angular velocity [27]:

where Pi is the power of frame i (W/kg), Mi is the joint moment of frame i (N-m/kg), and ωi is the angular velocity of frame i (rad/s).

Joint work was defining as the integral of joint power and time, and the net joint work in the dominant leg support phase is the sum of positive and negative work [28]:

In formula: joints do positive work when P > 0; joints do positive work when P < 0.

The net joint work contribution was defined as the ratio of certain joint work to the sum of all joint work in the lower limb during the support phase during stair descent [29]. The formula is(an example for knee joint):

Joint stiffness was defined as the change in joint moment divided by the change in joint angle during the stance phase [30]:

In formula:△M denotes the amount of change in joint moment, △θ denotes the amount of change in joint angle, K_Hip denotes hip joint stiffness, K_Knee denotes knee joint stiffness, and K_Ankle denotes ankle joint stiffness.

Statistical analysis

All statistical analyses were in IBM SPSS Statistics 27.0 software. All data are expressed as mean ± standard deviation. The normality of all outcome variables was tested using Shapiro-Wilk test, and all variables were found to be suitable for parametric analysis. One-way ANOVA with repeated measures was performed to compare the joint angle, moment, work and contribution. Post hoc comparisons consisting of paired t-tests with Bonferroni adjust were employed to detect difference of variables between shoes. The significance level was set at a P value less than 0.05. To refer to effect sizes as small (cohen’s d < 0.2), medium (cohen’s d = 0.5), and large (cohen’s d = 0.8) based on benchmarks [31]. The effect size of each variable was tested using partial eta squared (η²p), with values of 0.01, 0.06, and 0.14 used to indicate small, medium, and large effects, respectively [32].

Result

Joint angle, moments

One-way ANOVA showed that the significant differences were found in ΔKnee Angle(P = 0.028, η²_p = 0.042), ΔAnkle Angle (P < 0.001, η²_p = 0.150). Post-hoc comparison found that compared with 1 cm heels, the ΔAnkle Angle significantly decreased with 5 cm (P = 0.019, Cohen’s d = 0.38), 7 cm (P < 0.001, Cohen’s d = 0.76); compared with 3 cm heels, the ΔAnkle Angle significantly decreased with 7 cm (P = 0.001, Cohen’s d = 0.46); compared with 5 cm heels, the ΔAnkle Angle significantly decreased with 7 cm (P = 0.011, Cohen’s d = 0.37) (Fig. 4).

Fig. 4.

Comparison of Joint Angle, Moment, Stiffness and Net Work between different heel heights. (a) P < 0.05 compared with 1 cm heels; (b) P < 0.05 compared with 3 cm heels; c:P < 0.05 compared with 5 cm heels

Joint stiffness

One-way ANOVA showed that the significant differences were found in K_Ankle(P < 0.001, η²_p = 0.567). Post-hoc comparison found that compared with 1 cm heels, the K_Ankle significantly decreased with 3 cm (P = 0.035, Cohen’s d = 2), 5 cm (P < 0.001, Cohen’s d = 2.5), 7 cm (P < 0.001, Cohen’s d = 1.94); compared with 3 cm heels, the K_Ankle significantly decreased with 5 cm (P < 0.001, Cohen’s d = 0.55), 7 cm (P < 0.001, Cohen’s d = 0.278); compared with 5 cm heels, the K_Ankle significantly decreased with 7 cm(P < 0.001, Cohen’s d = 0.83) (Fig. 4).

Joint work

One-way ANOVA showed that the significant differences were found in ankle joint net work(P < 0.001, η²_p = 0.089). Post-hoc comparison found that compared with 1 cm heels, the ankle joint net work significantly increased with 7 cm(P = 0.017, Cohen’s d = 0.46); compared with 3 cm heels, the ankle joint net work significantly increased with 7 cm(P = 0.003, Cohen’s d = 0.63); compared with 5 cm heels, the ankle joint net work significantly increased with 7 cm(P = 0.048, Cohen’s d = 0.42) (Fig. 4).

One-way ANOVA showed that the significant differences were found in ankle joint work contribution (P = 0.009, η²_p = 0.056). Post-hoc comparison found that compared with 1 cm heels, the ankle joint work contribution significantly decreased with 7 cm(P = 0.017, Cohen’s d = 0.41); compared with 3 cm heels, ankle joint work contribution significantly decreased with 7 cm(P = 0.003, Cohen’s d = 0.50) (Fig. 5).

Fig. 5.

Lower Limb Contribution between Different Heel Heights. (a) ankle joint work contribution significantly decreased with 7 cm compared with 1 cm heels (P < 0.05); (b) ankle joint work contribution significantly decreased with 7 cm compared with 3 cm heels (P < 0.05)

Discussion

This study investigated the effect of different heel heights of the lower limb joint stiffness and work pattern during stair descent in young women. Our results showed as heel height increased, lower limb three joint stiffness decreased, moment and net joint work increased, hip and knee work contribution increased while ankle decreased in young women during stair descend, which partially supported our hypothesis.

This study observed that the range of ankle joint angle in the sagittal plane gradually decreases with the increase of the heel height, which is consistent with the results of Mika et al. [33]. Notably, compared with 1 cm heel height, Δjoint angle is significantly less in 3 cm, 5 cm, and 7 cm, which indicates that the lower joint moment that young women exhibited could not provide enough support moment during stair descent, which would further increase the risk of falls [34]. Moreover, as heel height increases, lower limb joint torque increases. This may be due to the instability caused by the increased heel height, which leads to an increased risk of falling during stair descent [35]. The observations provide partial corroboration for our hypothesis.

Joint stiffness, defined as the change in moment divided by the change in angle [36], can be related to the attenuation of loads transmitted through the body and can reflect the risk of lower limb injury [37]. Stiffness regulation and joint work mode play significant roles in assessing joint coordination, especially during complex activities such as stair descent [8]. As heel height increases from 1 cm to 3 cm, 5 cm, and 7 cm, young women actively adjust their biomechanics to maintain stability and safety while descent stairs. This adjustment includes reducing lower limb stiffness and adopting an ankle joint compensation work mode, which helps to lower the risk of falls during stair descent. However, the results showed an increase in heel height from 1 cm to 3 cm, 5 cm and 7 cm, led to a reduction in ankle stiffness, possibly due to the increased ankle joint vulnerability by changing the support structure and force distribution, which partially support our hypothesis. The decrease in ankle stiffness is likely to increase the risk of injury during stair descent. A previous study showed that energy absorption during touching the ground mainly rely on the knee and ankle joint [38, 39]. Therefore, the ankle stiffness reduction in this study might be an active strategy for enhancing shock absorption and improving joint stability in young women during stair descent [37].

The results also showed an increased contribution of hip and knee and less ankle joint work contribution with increase of heel height. Relative joint contribution magnitudes obtained in the present study differ from previous findings, we found higher knee and hip joint and lower ankle joint contributions compared to Fain, et al. [40]. Young women adjust their ankle joint kinetics during stair descent, a strategy that may reduce the risk of falls [41]. Accordingly, the females who often wears high heels should pay attention to developing ankle joint function during stair descent.

The studies also indicate that as heel height increases from 1 cm to 3 cm, 5 cm, and 7 cm, young women exert greater net work through their lower limb joints during stair descent. This increase in net work output is likely a strategy to enhance stability and reduce the risk of falls, as suggested by the higher joint moments observed in young women during stair descent. The results highlight an increased contribution from the hip and knee joints, with a relatively lesser contribution from the ankle joint. These findings contrast with previous study [40], they observed higher knee joint work and lower hip and ankle joint contributions. The adjustment in ankle joint kinetics by young women may be a strategic adaptation to minimize fall risk during stair descent [42]. Consequently, females who frequently wear high heels should be mindful of the potential impact on their ankle joint function and stability while descending stairs, and consider strategies to enhance ankle joint strength and control to mitigate this risk.

There are three limitations in this study. First, only a narrow age range was used for this study, and future studies should expand the age range and sample size [43]. Second, only kinematic and kinetic data were collected for this study, the absence of electromyography could not determine the effect of high heels on neuromuscular control during stair descent in young women. Thirdly, Future studies should further employ methods such as SPM1d to conduct a more comprehensive comparison and analysis of the effects of different heel heights throughout the entire gait cycle.

Conclusion

As heel height increases from 1 cm to 3 cm, 5 cm, and 7 cm, there is a significant decrease in ankle joint stiffness, net joint work, and joint work contribution during stair descent in young women. In our study, it was found that a heel height of 7 cm significantly reduced ankle net work, work contribution and joint stiffness, and may increase the risk of ankle injuries when walking down stairs descent. Therefore, it may be advisable that young women choose a heel height of less than 7 cm.

Abbreviations

ROM

Range of motion

Pi

The power of frame i

Mi

The joint moment of frame i

ωi

The angular velocity of frame i

W₊

Joints do positive work when P > 0

W₋

Joints do positive work when P < 0

W

The sum of positive and negative work

Con

The net joint work contribution

K

Joint stiffness

η²p

Partial eta squared

Author contributions

Y.W., W.S. and J.W. contributed to drafting the manuscript, participating in the conception and study design, revising the manuscript, and submitting it for publication. X.Y, G.M. contributed to data acquisitiondata acquisition, analysis and interpretation. H.X. provided guidance and suggestions for the revision of the manuscript. All authors read and approved the version of the manuscript to be published.

Funding

This work was supported by the Science and Technology Innovation Project of the General Administration of Sport of China under Grant (24KJCX065).

Data availability

Data availability The datasets used and analysed during the current study are available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

This study was conducted following the principles outlined in the Declaration of Helsinki. This study was approved by the ethics committee of Shandong Sport University (No.2023011). Participants were briefed about the study and signed an informed consent form prior to its commencement.

Consent for publication

The data in the paper were obtained with the participants’ Written informed consent for identifiable images publication.

Competing interests

The authors declare no competing interests.

Clinical trial registration number

Not applicable.