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Interactive Effect of Obesity and Pronated Foot on the Frequency Spectrum of Lower Extremity Muscle Activity in Men During Running
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Zahra Farajzadeh Haris1    , Amir Ali Jafarnezhadgero *2 , Ebrahim Piri3 , Hossein Farzollahi1 , Nastaran Moradzade4 |
1- M.Sc in Sports Biomechanics, Department of Sports Biomechanics, University of Mohaghegh Ardabili, Ardabil, Iran.
2- Professor, Department of Sport Biomechanics, University of Mohaghegh Ardabili, Ardabil, Iran. , amiralijafarnezhad@gmail.com
3- Ph.D in Sports Biomechanics, Department of Sports Biomechanics, University of Mohaghegh Ardabili, Ardabil, Iran. Department of Molecular Medicine and Surgery, Karolinska Institutet, Solna, Sweden.
4- Ph.D in Sports Biomechanics, Department of Sports Biomechanics, University of Mohaghegh Ardabili, Ardabil, Iran. |
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Keywords: Pronation [MeSH], Foot [MeSH], Running [MeSH], Fatigue [MeSH], Electromyography [MeSH]
Article ID: Vol28-04 |
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Type of Study: Original Articles |
Subject:
Sport Biomechanics
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Abstract: (428 Views) |
Extended Abstract
Introduction
Foot pronation is frequently observed alongside ankle joint dysfunction occurring due to biomechanical alterations. Any biomechanical changes in the ankle structure increase the susceptibility to injury in this region of the body. A pronated foot is a deformity that causes a reduction in the height of the medial longitudinal arch during weight-bearing. Additionally, the ankle structural deformity is observed following this condition. Consequent to this anomaly, the heads of the talus and navicular bones deviate medially, which can ultimately lead to the manifestation of a pronated foot. Furthermore, the pronated foot condition is directly associated with the exertion of direct pressure on the ankle, knee, and pelvic girdle joints.
Obesity, as a key mechanical factor, increases the vertical load imposed on lower extremity joints (particularly the knee and ankle). This increased loading not only alters the distribution pattern of ground reaction forces (GRF) but also modulates neuromuscular activity to maintain stability and compensate for the imposed pressures. Research has demonstrated that obese individuals show heightened activity in the vastus lateralis and medial gastrocnemius muscles during the stance phase of running, which is likely due to the nervous system's effort to mitigate joint pressure and prevent biomechanical instability.
Running is recognized as a popular and effective activity for cardiovascular health; however, the occurrence of any lower extremity disorders and also conditions such as obesity is a major concern that can alter the mechanics of translational movements and result in injury. On the other hand, obesity is one of the primary factors contributing to the acquired flatfoot, which in turn impairs postural control and balance. Hence, the presence of any structural abnormalities in the foot and plantar region, combined with obesity, may adversely affect an individual's performance during static, dynamic, and locomotor tasks, particularly in body displacement. Furthermore, from a biomechanical perspective, one of the main complications of obesity is the reduction in navicular bone height and hindfoot valgus. Research has demonstrated that a pronated foot is associated with increased body weight. This condition is one of the causes of increased internal rotation of the lower extremity and the occurrence of injuries such as patellofemoral pain and increased anterior pelvic tilt. Given the increased range of foot pronation in obese runners with foot pronation, the likelihood of developing running-related injuries is heightened. Foot pronation is accompanied by a medial displacement of the center of pressure (COP) and an increase in medial-lateral shear forces. This structural abnormality leads to the hyperactivity of the tibialis anterior and peroneus longus muscles in order to maintain dynamic balance. In contrast, the activity of the arch-supporting muscles, such as the tibialis posterior, decreases, which can indirectly influence the activation pattern of proximal muscles (such as the rectus femoris and hamstrings). Moreover, when foot pronation is coupled with obesity, the synergistic effects of these two factors culminate in an increase in internal rotation torque at the knee and hip joints. This phenomenon significantly impacts the activity of the hip abductor muscles (such as the gluteus medius) and pronation-controlling muscles (such as the tibialis posterior). Electromyographic studies have demonstrated that these neuromuscular adaptations may lead to premature fatigue and an increased risk of musculoskeletal injuries over the long term. The present study aimed to determine the interactive effect of obesity and pronated foot on the frequency spectrum of lower extremity muscle activity in men during running.
Methods
This quasi-experimental study was conducted on 40 male students (age range: 21-35 years) using non-random assignment into four groups of 10, including normal weight with normal foot, obese with pronated foot, obese with normal foot, and normal weight with pronated foot, at University of Mohaghegh Ardabili during 2024.
The inclusion criteria consisted of participant selection based on a navicular drop rate of more than 10 mm, a foot posture index of more than 10 mm, a body mass index (BMI) greater than or equal to 25 kg/m², and the informed completion of the participation consent form. The exclusion criteria included the occurrence of any injury during data collection and the voluntary withdrawal of participants during the study.
During the soccer kicking test, the right leg was identified as the dominant leg for all participants. Subsequently, electrode placement was performed on the dominant leg. The electrode configuration was bipolar, with a center-to-center electrode spacing of 2 cm2. The surface electromyography (EMG) for the non-invasive assessment of muscles (SENIAM) protocol was utilized to determine the precise location and orientation of the electrodes. A total of 8 electrodes were placed on the dominant leg of the participants, targeting the following muscles: Tibialis anterior, medial gastrocnemius, vastus lateralis, vastus medialis, rectus femoris, biceps femoris, semitendinosus, and gluteus medius. The testing procedure was as follows: Each participant ran 6 times at a speed of 3.2 meters per second along a designated straight walkway with specifications of 10 m in length, 1.5 m in width, and 0.25 m in thickness (the thickness of the designed track). To familiarize the participants with the track prior to the test execution, the participants were requested to take successive strides along the running path. The median frequency values of the signals were recorded and calculated during two phases, namely loading response and push-off, during running.
The fatigue protocol included running on a flat treadmill, adjusted according to heart rate intensity. The Borg Rating of Perceived Exertion (RPE) scale was utilized to determine the participants’ final moment of fatigue. Once the participants reported a perception of 13 or higher on the RPE scale, the treadmill speed was maintained at a constant level to allow the participants to run at a steady state. During the steady-state running phase, the RPE was recorded every 30 seconds. The fatigue protocol was terminated after 2 minutes of steady-state running when the RPE exceeded 17 on the Borg 6–20 scale, or when the heart rate reached 80% of the maximal heart rate (HRmax). Subsequently, following the fatigue protocol, the participants were instructed to repeat the running protocol at the predetermined speed for 6 repetitions. To record muscle activity, a surface EMG system (DataLITE EMG, Biometrics Ltd, Bandwidth: 10–490 Hz, made in the UK) was utilized. The recorded data were analyzed across various stages and methods to ensure their validity. In the initial stage, following the completion of each trial by the participant, the recorded surface EMG signals were inspected using the designated software (Biometrics DataLITE). The characteristics of each signal (such as numerical variations for each muscle) were evaluated to confirm preliminary accuracy. Any inconsistencies in the recorded data that could potentially compromise their validity and reliability led to data exclusion, and the process was subsequently repeated. In this study, EMG data were filtered using a 500 Hz low-pass filter, a 20 Hz high-pass filter, and a 60 Hz notch filter (to eliminate power-line interference).
The normality of the data distribution was assessed using the Shapiro-Wilk test. A two-way repeated-measures analysis of variance (ANOVA) was employed to compare the two groups across the pre-test and post-test phases. The statistical significance level for all tests was set at less than 0.05.
Results
Regarding the frequency of muscle activity across the four groups during the loading response phase prior to the fatigue protocol, no significant differences were observed among the muscle frequency spectrum values during the first half of the stance phase of running.
The main effect of group for the frequency spectrum of the biceps femoris muscle during the loading response phase was significant (d=0.0790, P<0.004). Furthermore, pairwise comparisons demonstrated that the frequency of the biceps femoris muscle was statistically significantly higher in the “normal weight” and “normal feet” groups compared to the other two groups. The effects of fatigue and the fatigue-group interaction on the frequency spectrum values of muscle activity during the loading response phase were not statistically significant.
Considering the frequency spectrum values of muscle activity across the four groups during the push-off phase before and after the fatigue protocol, the main effect of fatigue on the frequency spectrum of muscle activity during the push-off phase was not statistically significant. However, the interactive effect of fatigue-group on the frequency spectrum of vastus lateralis muscle activity was statistically significant (P<0.041, d=0.613). The results of the post-hoc test revealed that the frequency of vastus lateralis muscle activity during the push-off phase significantly decreased post-fatigue compared to pre-fatigue in both the “normal weigh with pronated foot” and the “obese with pronated foot” groups.
The results regarding the main effects of group on the frequency spectrum of vastus lateralis muscle activity (d=0.766, P<0.005) and the frequency spectrum of rectus femoris muscle (d=0.742, P<0.008) during the push-off phase were statistically significant. Moreover, pairwise comparisons revealed that the frequency of vastus lateralis muscle activity was statistically significantly higher in the “normal weight with pronated foot” group, as well as the “normal weight with normal foot” group, compared to the other two groups. Based on the obtained results, the frequency of the rectus femoris muscle in the “normal weight with pronated foot” group was statistically greater during the push-off phase compared to the other three groups.
Conclusion
In the “obese with pronated foot” group, the observed increase in muscle activity may reflect the neuromuscular system's attempt to manage biomechanical loads. Furthermore, individual differences in movement patterns, fitness levels, and compensatory strategies may contribute significantly to variations in muscle activity.
Ethical Statement
This study was approved by the Research Ethics Committees of University of Mohaghegh Ardabili (IR.UMA.REC.1402.011).
Authors' Contributions
Zahra Farajzadeh Haris (M.Sc): Project execution, Data collection and Data analysis.
Amir Ali Jafarnezhadgero (Ph.D): Project administration and design, Project execution, Data collection, Interpretation of the results, Drafting of the initial manuscript and Approval of the final manuscript.
Ebrahim Piri (Ph.D): Project administration and design, Project execution, Interpretation of the results, Drafting of the initial manuscript and Approval of the final manuscript.
Hossein Farzollahi (M.Sc): Project administration and design, Data collection, Data analysis and Interpretation of the results.
Nastaran Moradzade (M.Sc): Data analysis and Interpretation of the results.
Conflicts of Interest
No conflicts of interest.
Acknowledgement
This article has been extracted from the master’s thesis of Ms. Zahra Farajzadeh Haris in Sports Biomechanics at University of Mohaghegh Ardabili. The authors would like to thank the study participants for their sincere cooperation.
Key Message: In the “obese with pronated foot” group, the observed increase in muscle activity may reflect the neuromuscular system's attempt to manage biomechanical loads. Furthermore, individual differences in movement patterns, fitness levels, and compensatory strategies may contribute significantly to variations in muscle activity.
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Farajzadeh Haris Z, Jafarnezhadgero A A, Piri E, Farzollahi H, Moradzade N. Interactive Effect of Obesity and Pronated Foot on the Frequency Spectrum of Lower Extremity Muscle Activity in Men During Running. J Gorgan Univ Med Sci 2026; 28 (1) :29-37 URL: http://goums.ac.ir/journal/article-1-4589-en.html
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