The effect of arch-support insoles on the frequency spectrum of ground reaction forces during waking in adults with anterior cruciate ligament reconstruction (ACL) reconstruction and pronated feet

Piri, Ebrahim; Jafarnezhadgero, AmirAli; Dehghani, Mahrokh; Enteshari-Moghaddam, Afsaneh

doi:10.22034/27.3.25

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Volume 27, Issue 3 (10-2025)

EBNESINA 2025, 27(3): 25-41

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The effect of arch-support insoles on the frequency spectrum of ground reaction forces during waking in adults with anterior cruciate ligament reconstruction (ACL) reconstruction and pronated feet

Ebrahim Piri

, AmirAli Jafarnezhadgero ^*

, Mahrokh Dehghani

, Afsaneh Enteshari-Moghaddam

Department of Sports Biomechanics, Faculty of Educational Sciences and Psychology, University of Mohaghegh Ardabili, Ardabil, Iran , amiralijafarnezhad@gmail.com

Keywords: anterior cruciate ligament reconstruction, anterior cruciate ligament, gait, flatfoot, biomechanic, knee joint

Full-Text [PDF 1940 kb] (98 Downloads) | Abstract (HTML) (187 Views)

Type of Study: Original | Subject: Military Medicine
Received: 2025/09/8 | Revised: 2025/10/19 | Accepted: 2025/11/3 | Published: 2025/11/22

Extended Abstract: (79 Views)

Introduction

Walking is a fundamental human activity essential for maintaining health [1]. Structural deviations of the lower limb, such as foot pronation, can alter gait mechanics [2]. Foot pronation, marked by a reduced medial longitudinal arch, changes ankle and foot alignment [7]. Anterior cruciate ligament (ACL) rupture is a common knee injury often reconstructed with grafts such as hamstring autografts [8]. ACL injuries are frequent, and re‑injury rates can reach 15-20% within the first postoperative year [9]. Pronated feet may increase re‑injury risk, possibly via mechanisms like increased internal tibial rotation [10]. Foot orthoses, including arch‑support insoles, are commonly used to correct alignment and improve biomechanics [11, 14]. Frequency‑spectrum analysis of ground reaction forces (GRFs) is a sensitive tool for assessing neuromuscular control and gait stability, often revealing changes not evident in time‑domain measures [17, 23–25]. Despite the importance of GRF frequency content, the effects of arch‑support insoles on these components in individuals with prior ACL reconstruction (hamstring autograft) and pronated feet remain unexplored. Therefore, this study aimed to examine the effects of arch‑support and placebo insoles on the GRF frequency spectrum during walking in this population.

Methods

This quasi‑experimental pre‑test/post‑test study was conducted in a sports biomechanics laboratory. Sample size was calculated with G*Power 3.1 (α = 0.05, power = 0.8, effect size = 0.7), yielding a minimum of 10 participants per group. The study population comprised male patients with ACL reconstruction and pronated feet from Ardabil city, Iran. Forty men were recruited by convenience sampling and allocated by time since surgery into three groups: Group 1, <6 months post‑surgery (n=10); Group 2, 6–12 months (n=10); Group 3, >12 months (n=10). Ten healthy men without pronated feet or ACL injury formed a control group.
Inclusion criteria for patients were: age 18-45 years; unilateral ACL reconstruction with hamstring autograft; unilateral pronated foot (navicular drop >10 mm and Foot Posture Index >4); BMI 18.5-25 kg/m²; no pain in functional range of motion; ability to run without limitation; no history of lower‑limb fractures or deformities; no long‑term use of drugs affecting the musculoskeletal system; and willingness to participate. Exclusion criteria included other surgeries, other lower‑limb injuries, leg‑length discrepancy >5 mm, or withdrawal of consent. Healthy controls required absence of pronation and lower‑limb pathology.
GRF data were recorded with a Bertec force plate (USA) at 1000 Hz while participants walked barefoot at a self‑selected speed along a walkway. Three successful trials were collected for each of three conditions: no insole (barefoot), placebo insole (flat thin foam), and arch‑support insole (rigid polyurethane, 25 mm arch height, 15 mm posting). A treadmill fatigue protocol (Horizon Fitness, USA) began at 6 km/h, increasing by 1 km/h every 2 minutes until participants reported a Borg RPE ≥13 or reached 80% of maximum heart rate [29]. Speed was then held for >2 minutes before immediately repeating the walking trials.
GRF signals were filtered with a 4th‑order low‑pass Butterworth filter (cutoff 20 Hz). Frequency analysis used FFT in MATLAB R2016a. Variables analyzed were 99.5% Power Frequency (F99.5%), Median Frequency (Fmed), and Essential Harmonic Number (EHN) in vertical (Fz), mediolateral (Fy), and anteroposterior (Fx) directions. Statistical analyses were performed in SPSS‑23; normality was tested with Shapiro–Wilk. A two‑way repeated measures ANOVA (insole × time: pre vs. post fatigue) was applied within each group. Cohen’s d quantified effect size. Significance was set at p ≤ 0.05.

Results

Demographic data showed no significant differences between groups in age, height, weight, or BMI (p>0.05). As expected, navicular drop and foot posture index were significantly higher in patient groups compared to the healthy group (p<0.001) (Table 1).

Vertical Direction (Fz): The insole factor significantly increased the EHN from pre- to post-fatigue under the no-insole (p=0.044, d=0.42) and placebo insole (p=0.049, d=0.17) conditions. A significant insole × group interaction was observed for F99.5% under both placebo (p=0.012, d=0.97) and arch-support (p=0.030, d=0.82) conditions compared to no-insole. The arch-support insole also led to a significant decrease in F99.5% from pre- to post-fatigue (p=0.045, d=0.36).
Mediolateral Direction (Fy): The insole factor significantly increased EHN under placebo (p=0.048, d=0.75) and arch-support (p=0.005, d=0.62) conditions. F99.5% decreased significantly with arch-support insoles compared to no-insole (p=0.005, d=0.62). A significant interaction for Fmed was found under arch-support insoles (p=0.001, d=0.87). Furthermore, a significant reduction in F99.5% was observed only in Group 1 (<6 months post-op) when using arch-support insoles (p=0.049, d=0.11).
Anteroposterior Direction (Fx): The insole factor significantly increased EHN under no-insole (p=0.048, d=0.20) and arch-support insole (p=0.001, d=0.77) conditions. In contrast, it caused a significant decrease in F99.5% under the arch-support condition (p=0.001, d=0.77). A significant reduction in Fmed was also observed with arch-support insoles (p=0.013, d=0.37). The insole × group interaction for EHN was significant (p=0.005, d=0.45), and a significant decrease in F99.5% occurred only in Group 1 when using arch-support insoles (p=0.007, d=0.13).

Discussion and Conclusion

The results show that insoles, especially arch-support types, alter the frequency spectrum of GRFs in adults with ACL reconstruction and pronated feet, with effects most evident after fatigue. The increase in EHN in the vertical direction under no-insole and placebo conditions after fatigue indicates greater signal complexity and likely reflects increased demand on muscular control to maintain stability [24], possibly due to impaired shock absorption. In contrast, the stability of EHN with arch-support insoles post-fatigue suggests a protective effect in preserving movement-pattern integrity [25].
Arch-support insoles produced the largest reductions in high-frequency power (F99.5%) across all directions, particularly in the mediolateral and anteroposterior planes, implying a shift of spectral power toward lower frequencies. This shift is commonly associated with improved postural stability, fewer unnecessary body oscillations, and more efficient neuromuscular control [2, 3, 23]. The significant decreases in F99.5% and Fmed observed in Group 1 (<6 months post-surgery) indicate that the neuromusculoskeletal system is especially responsive to interventions during early rehabilitation, a period characterized by substantial neural adaptation and biomechanical recalibration, making external aids like insoles potentially more impactful [26, 36].
Mechanistically, arch-support insoles likely enhance dynamic stability by improving proprioceptive feedback, optimizing plantar pressure distribution, and modulating muscle activity around the ankle and knee [13, 34]. These changes can produce smoother movement control, reduced joint stiffness, and potentially lower re-injury risk [35]. The placebo insoles produced modest effects as well, suggesting that even non-specific tactile input can alter gait, though to a lesser degree than structured arch suppor.
In summary, arch-support insoles appear to improve dynamic stability in individuals with ACL reconstruction and pronated feet, with the greatest benefit during the early postoperative stage. These findings support the inclusion of foot biomechanics assessment and appropriate orthotic intervention in comprehensive rehabilitation programs for ACL-reconstructed patients, particularly those with concomitant foot pronation.

Ethical Considerations

This study was approved by the Ethics Committee of Mohaghegh Ardabili University (Code: IR.UMA.REC.1404.019) and was registered in the Iranian Clinical Trial Registry (code: IRCT20220129053865N2). Written informed consent was obtained from all participants. The study was conducted in accordance with the principles of the Helsinki Declaration.

Funding

There is no funding support.

Authors’ Contribution

All authors contributed equally to the conceptualization and writing of the article. Each author reviewed and approved the final manuscript, agreeing on all aspects of the work.

Conflict of Interest

Authors declared no conflict of interest.

Acknowledgments

The authors sincerely thank all participants who volunteered for this study. We also acknowledge the support of the biomechanics laboratory staff.

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Ethics code: IR.UMA.REC.1404.019

Clinical trials code: IRCT20220129053865N2

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Piri E, Jafarnezhadgero A, Dehghani M, Enteshari-Moghaddam A. The effect of arch-support insoles on the frequency spectrum of ground reaction forces during waking in adults with anterior cruciate ligament reconstruction (ACL) reconstruction and pronated feet. EBNESINA 2025; 27 (3) :25-41
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