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Background:
Systematic Review

Effects of Various Foot Wedges on Thigh Muscle Activity during Squatting in Healthy Adults: A Systematic Review and Meta-Analysis

by
Mohammadhossein Ghasemi
1,
Behnam Gholami-Borujeni
2 and
Kristín Briem
1,3,*
1
Department of Physical Therapy, University of Iceland, 112 Reykjavík, Iceland
2
Department of Sport Biomechanics and Motor Behavior, University of Mazandaran, Babolsar 4741613534, Iran
3
Research Centre of Movement Science, University of Iceland, 112 Reykjavík, Iceland
*
Author to whom correspondence should be addressed.
Appl. Sci. 2024, 14(5), 2091; https://doi.org/10.3390/app14052091
Submission received: 23 January 2024 / Revised: 23 February 2024 / Accepted: 29 February 2024 / Published: 2 March 2024
(This article belongs to the Special Issue Advances in Foot Biomechanics and Gait Analysis)
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Abstract

:
Squatting is a common movement in daily activities, athletic training, rehabilitation programs, and even in the workplace. Identifying the effects of various foot wedges on thigh muscle activity during squatting can help specialists in terms of rehabilitation, injury prevention, physical preparation, and occupational optimization. In this study, systematic literature searches in six electronic databases (Cochrane Library, PubMed, Google Scholar, Web of Science, ScienceDirect, and Scopus) were conducted up to December 2023. Fifteen studies met the inclusion criteria (total n = 269 subjects). The results showed that posterior wedges significantly increased the overall activity of thigh muscles (p < 0.001, 12 studies). No significant change was observed for anterior (p = 0.730, six studies), medial (p = 0.169; three studies), and lateral wedges (p = 0.989, two studies). Compared with a non-wedge condition, the activity of the vastus medialis (p < 0.001, eight studies) was significantly higher using a posterior wedge during squatting, as was the activity of the rectus femoris (p = 0.021, five studies) using the anterior wedge. It seems that thigh muscle activation is modifiable with a change in footwear design, which may be useful during sports training, rehabilitation, or daily work routines.

1. Introduction

Squatting is a common movement in daily activities [1], athletic training [2], rehabilitation programs [3], and even within the workplace [4,5]. During this task, whether performed with one or two legs, the center of the body is lowered and raised by joint motion at the hip, knee, and ankle. Thigh muscles act on the hip and knee joints and have an essential role as primary movers during squatting [5,6]. Different types of squats are used according to the maximum angle of the knee joint, including shallow (about 45°), medium (about 90°), or deep (about 135°) [7,8]. Another classification is based on two types of executions, including static [9,10] or dynamic [5,11,12,13,14,15,16,17,18,19,20].
Many efforts have been made to identify the factors associated with the thigh muscle activation, with the specific goal of strengthening them during rehabilitation and within sports contexts [6,21,22], as well as the potential of reducing muscle loads to avoid the early onset of fatigue in work environments [5]. As squatting is a closed kinematic chain movement, changes in the position at one joint can influence the function of other joints [23]. Changes in ankle and foot positions can alter the lower limb kinematics [12,24] and muscle activity [12] during squatting. These changes have been used for muscle strengthening and rehabilitation purposes and can be useful as a clinical workout option [10]. Modifications in foot position may also aid in preventing or correcting deformities and improving performance [25,26]. A common and efficient strategy used to alter ankle and foot joint positions is the use of foot wedges [5]. This strategy has been used for changing lower limb biomechanics [12,27,28], muscle activity [5,10,11,12,13,14,15,16,17,18,19,20,29,30], and stability [31] during squatting. Based on the ankle joint position, foot wedges can be classified as anterior (dorsiflexion), posterior (plantarflexion), medial (inversion), and lateral (eversion).
The results of previous studies on the effect of foot wedges on thigh muscle activity are inconsistent [5,10,11,12,13,14,15,16,17,18,19,20], which makes clinical decision-making problematic. While some studies showed decreased [5,12,15] or increased [11,17,19,32] thigh muscle activity with foot wedges, others have reported no significant difference [16,18,33]. With regard to the effects of wedges on thigh muscle activation levels, previous studies examined the rectus femoris [10,15,18,19,27,32], vastus lateralis [5,12,14,16,17,18,19,20,32], vastus medialis [5,11,12,13,14,17,18,19,20,32], biceps femoris [10,11,13,14,18,19,27,32], and semitendinosus [19]. However, the types of wedges used varied between studies, which may be the source of conflicting findings. For example, the effect of anterior wedge on thigh muscle activity was studied in five studies [5,12,13,14,18], but this wedge was different from other wedges applied in other studies [5,10,11,14,15,16,17,18,19,20,27,32]. In order to clarify the effects and potential use of foot wedges, the aim of this study was to perform a systematic review and meta-analysis to identify the effects of four types of foot wedges on thigh muscle activation during squatting. We hypothesized that different types of foot wedges would selectively influence the activation levels of thigh muscles during squatting in healthy adults. The results can help specialists to achieve the desired effects in the areas of rehabilitation, injury prevention, physical preparation, and occupational optimization.

2. Materials and Methods

2.1. Search Strategies

A systematic review of the literature was performed using guidelines in the Cochrane Handbook for Systematic Reviews of Interventions (version 5.1.0) and following the checklist for the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2015 (PRISMA). Two investigators (M.G. and B.G.) independently searched six electronic databases, namely, the Cochrane Library, PubMed, Google Scholar, Web of Science, ScienceDirect, and Scopus, to avoid a biased literature sample. The searches covered all available literature data up to December 2023. Keywords were collected through expert opinion, a literature review, and controlled vocabulary (e.g., Medical Subject Headings [MeSH]) [34], with all the conceivable combinations utilizing “OR” and “AND” in and between these categorical terms: category 1—wedge, incline, decline, slope, degree, change, and position; category 2—foot, feet, heel, ankle, and leg; category 3—muscle, muscular, activity, activation, EMG, and electromyography; category 4—thigh, quadriceps, hamstring, lower limb, lower extremity; and category 5—squat and lifting. Non-English publications were excluded, as were review studies, as well as the following terms (using “NOT”): elderly, children, teenager, patients, abnormal, malalignment, and disorder. The search results were screened for titles, abstracts, and full texts by two investigators (M.G., B.G.), and the third investigator (K.B.) in the case of disagreement (Figure 1).

2.2. Inclusion and Exclusion Criteria

A PICOS (participants, intervention, comparator, study outcomes, and study design) strategy was used to rate the studies for eligibility [34]. Adulthood was defined as the age range of 15–65 years [35], although all the eligible studies were conducted on subjects within the age range of 18–50 years. The inclusion criteria were as follows: (1) participants—healthy adult individuals; (2) intervention—e.g., foot or feet wedges, and change in ankle position; (3) comparator—crossover studies comparing neutral position (non-wedge) with various foot position changes; (4) study outcome—studies that used electromyography to assess the activity (mean or peak) level of at least one of the thigh muscles, including the vastus medialis (VM), vastus lateralis (VL), rectus femoris (RF), semitendinosus (ST), and biceps femoris (BF); and (5) study design—within-group repeated-measures design.

2.3. Data Extraction

Two authors (M.G. and B.G.) independently extracted data from the included studies in a Microsoft Excel file (version 2015). To compute the effect sizes, we used averages and standard deviations of neutral (non-wedge) and wedge conditions for muscle activity indices. The correlation between non-wedge and wedge conditions was estimated wherever sufficient information was available, but as studies often reported no corrected Bonferroni or p-values, a default correlation coefficient of 0.50 was used in all the meta-analyses [36]. If the data were missing or graphically displayed, authors were contacted and kindly asked to provide the data. In the case of getting no response, we used a software tool WebPlot Digitizer (version 4.1, Austin, TX, USA) [37], which is an accurate and precise tool for the extraction of data from graphs [38].
The selected studies used different methods to calculate the level of muscle activity. Using maximum voluntary isometric contractions (MVICs), the normalized mean amplitude was calculated in six studies [5,12,13,16,19,20], the normalized mean of the root mean square (RMS) in four studies [9,14,27,32], and the normalized peak RMS [17,27] in two studies. A dynamic normalization method was used to calculate the normalized mean amplitude in one study [15]. The mean activity in the microvolt unit with no normalization process was calculated in two studies [11,18], and the muscle activity index was not specified in one study [10]. We calculated a “combination effect” when studies used more than one wedge for a particular wedge condition (e.g., 2.2° and 6.6° for posterior wedges) [5,10,13,32], when the muscle activity level was reported during more than one phase of squatting [5,16,18], with two variables (mean and peak activity) [15,27], for right and left muscles [13], or for two parts of a muscle (e.g., short and long heads of the BF) [32].

2.4. Risk of Bias Assessment

The risk of bias for eligible studies was assessed independently by two investigators (M.G., B.G.) using the quality appraisal tool developed by Galna et al. (2009) [39]. It focuses on the internal and external validity, as well as the study’s reproducibility. It has 14 items, each with a rating between 0 and 1. This tool has no particular classification (e.g., low, acceptable, high), but a higher total score shows a better quality of the respective study [34,39]. As Galna et al. used this tool for gait assessment (2009) [39], minor adaptations were made (question 5: squatting speed rather than walking speed; question 14: clinical implications or practical applications stated rather than only clinical implications stated).

2.5. Statistical Tests

In the present study, Comprehensive Meta-Analysis (CMA) software (version 2, Biostat Inc., Englewood, NJ, USA) was used to compute all the effect sizes. We examined the effects of various foot wedges on thigh muscle activity using a random-effects pooling model approach with Hedges’ g as the effect size index for non-wedge and wedge conditions (anterior, posterior, medial, and lateral). We deliberately used Hedges’ g index, as it prevents the overestimation of an effect size value for sample sizes of fewer than 20 studies, and a random-effects model, as it can control the effects of within-study error (sampling error) and between-study variance [40]. Two statistics, namely, the Qtotal (QT) and I-square (I2) values, were used to assess the homogeneity of variance for the overall effects of foot wedges on thigh muscle activity (p < 0.05), where, if the QT statistic was significant, then a procedure was used to conduct subgroup (moderator) analyses [40].
The CMA included descriptive measures, such as averages, standard deviations, correlations, and sample sizes to estimate effect sizes. Where insufficient data were available, the CMA provided options for the estimation of effect sizes with combinations of existing data (mean differences, T, p-values, etc.). Each study contributed one effect size calculation for each wedge condition in the overall CMA analysis. When a study contained more than one measurement for a wedge condition (e.g., two or more wedge angles, phases of squatting, various muscle activity variables, and muscles of both legs), the software calculated the combined effect (based on averaged outcomes) to calculate the overall effects of foot wedges [41].

3. Results

3.1. Participants’ Characteristics

The systematic search identified 1194 potential articles (Figure 1). After screening for eligibility, 15 studies with 269 participants remained. The reported characteristics of participants were not always provided for gender [9,10], age [10,12], and height and weight [10], but are otherwise shown in Table 1.

3.2. Study Characteristics

The characteristics of each of the included studies, namely, the authors/years, participants and their number, interventions (types of wedges), variables, tasks (types of squatting), the weights of loading, muscles assessed, movement phases, and results, are presented in Table 2.

3.3. Methodological Characteristics

The data analysis process was performed for all 15 studies at the individual level. Data used to compute effects sizes by CMA included means and standard deviations of non-wedge and wedge conditions for 13 papers [5,9,10,12,13,15,16,17,18,19,20,27,32] and combinations of the mean difference, T, and P values in the two remaining studies [11,14]. The weight of lifting was 0 kg (free weight) [9,10,12,13,14,15,17,18,19,20], 1.36 kg [5], 10 kg [11], 20 kg [27], and 80% 1-RM [16,32] during double-leg [5,9,11,12,13,14,15,16,27,32] or single-leg squats [10,17,18,19,20], performed either statically [9,10,17] or dynamically [5,11,12,13,14,15,16,18,19,20,27,32]. With the exception of one study [17], no specific abnormalities in the lower extremities or foot region were reported [5,9,10,11,12,13,14,15,16,18,19,20,27,32]. Knee flexion angles of 45° [10], 60° [17], and 90° [9] were implemented for static squats, while for dynamic squats, the knee flexion range varied from zero to <45° (shallow) [18,20], <90° (medium) [5,12,14,19], or >90° (deep) [11,13,15,16,27,32]. The thigh muscles under investigation included the vastus medialis [5,9,11,12,13,14,17,18,19,20,32], vastus lateralis [5,9,12,14,16,17,18,19,20,32], rectus femoris [9,10,15,18,19,27,32], biceps femoris [9,10,11,13,14,18,19,27,32], and semitendinosus [19]. Twelve of the fifteen eligible studies assessed the effects of the posterior wedge [5,9,10,11,14,15,16,17,18,19,27,32], while six assessed the anterior [5,9,12,13,14,18], three assessed the medial [5,18,20], and two studies assessed the lateral wedge [18,20].

3.4. Risk of Bias Assessment

The results for the risk of bias assessment show that the eligible studies scored between 7.5 and 11 out of the maximum total score of 14 (Table 3). In the case of disagreement between two authors (M.G., B.G.), another co-author (K.B.) was consulted for clarification.

3.5. Effects of the Posterior Wedge on the Activity Level of Thigh Muscles

Overall, the meta-analysis showed that the posterior wedge significantly influenced the thigh muscles’ activity levels (Hedges’ g = 0.398; SE = 0.095; 95% CI = 0.212, 0.584; Z = 4.184; p < 0.001; 12 studies). A significant heterogeneous distribution across muscles was observed (QT = 123.364, df = 30, p < 0.001, I2 = 75.682), indicating the need for a subgroup analysis assessment.
For the sub-group assessment, the meta-analysis showed that during squatting, the posterior wedge had a significant effect on the vastus medialis (Hedges’ g = 0.700; SE = 0.184; 95% CI = 0.339, 1.060; Z = 3.805; p < 0.001; eight studies) during squatting (Figure 2). No significant effect, however, was seen on the rectus femoris (Hedges’ g = 0.401; SE = 0.209; 95% CI = −0.009, 0.811; Z = 1.917; p = 0.055; seven studies), vastus lateralis (Hedges’ g = 0.352; SE = 0.195; 95% CI = −0.031, 0.735; Z = 1.803; p = 0.071; seven studies), biceps femoris (Hedges’ g = 0.257; SE = 0.178; 95% CI = −0.092, 0.605; Z = 1.444; p = 0.149; eight studies), or semitendinosus (Hedges’ g = −0.540; SE = 0.519; 95% CI = −1.558, 0.477; Z = −1.042; p = 0.298; one study) (Figure 2).

3.6. Effects of the Anterior Wedge on the Activity Level of Thigh Muscles

Overall, the meta-analysis showed no significant effect of the anterior wedge on the thigh muscles’ activity levels (Hedges’ g = −0.028; SE = 0.081; 95% CI = −0.188, 0.131; Z = −0.345; p = 0.730; seven studies), but, as a significant heterogeneous distribution was observed (QT = 38.402, df = 17, p = 0.002, I2 = 55.732), a subgroup analysis assessment was conducted.
For the sub-group assessment, the meta-analysis showed that the only significant effect of the anterior wedge during squatting was on the activity level of the rectus femoris (Hedges’ g = 0.399; SE = 0.190; 95% CI = 0.026, 0.771; Z = 2.098; p = 0.036; three studies) (Figure 3). No significant effect was seen on the activity level of the vastus medialis (Hedges’ g = −0.074; SE = 0.124; 95% CI = −0.318, 0.169; Z = −0.599; p = 0.549; six studies), vastus lateralis (Hedges’ g = −0.201; SE = 0.135; 95% CI = −0.466, 0.063; Z = 1.495; p = 0.135; five studies), or biceps femoris (Hedges’ g = −0.023; SE = 0.150; 95% CI = −0.318, 0.272; Z = −0.150; p = 0.881; four studies) (Figure 3).

3.7. Effects of the Medial Wedge on the Activity Level of Thigh Muscles

Overall, the meta-analysis showed neither a significant effect of the medial wedge on the thigh muscles’ activity levels (Hedges’ g = 0.181; SE = 0.132; 95% CI = −0.077, 0.440; Z = 1.374; p = 0.169; three studies) nor a significant heterogeneous distribution (QT = 10.148, df = 7, p = 0.180, I2 = 31.018), and thus, no subgroup analysis was done (Figure 4).

3.8. Effects of the Lateral Wedge on the Activity Level of Thigh Muscles

Overall, the meta-analysis showed neither a significant effect the lateral wedge on the thigh muscles’ activity levels (Hedges’ g = −0.002; SE = 0.119; 95% CI = −0.236, 0.232; Z = −0.014; p = 0.989; two studies) nor a significant heterogeneous distribution for overall assessment (QT = 3.507, df = 5, p = 0.622, I2 = 0.001), and thus, no subgroup analysis was done (Figure 5).

4. Discussion

This was the first systematic review and meta-analysis to examine the effect of foot wedges on thigh muscles’ activity during squatting. The results of the meta-analysis showed a significant effect of the use of posterior wedges on thigh muscles’ activity levels (p < 0.001). Importantly, sub-group assessments showed that these effects were selective during squatting, as the posterior wedge increased the activity level of the vastus medialis and the anterior wedge altered the activity of the rectus femoris (p < 0.05).
A biomechanical concept called the muscle length–tension relationship may, in part, explain changes in muscle activation due to using various foot wedges. This relationship states that muscle activity is significantly influenced by changes in joint position, muscle length, muscle contraction speed, and muscle action line [5]. Squatting requires concurrent movement of the hip, knee, and ankle joints [42]. Using a posterior wedge during squatting creates ankle joint plantarflexion, which reduces the passive tension and activity level of the triceps surae muscle group [9], resulting in higher activity in the knee extensor muscles, which was generally the case in the selected studies. Therefore, reducing the activity of the calf muscles can be considered as a mechanism for increasing the activity of the thigh muscles [43]. Proximal kinematic changes may be induced by altering the ankle joint position during the squat movement, such as a more erect trunk position with reduced hip flexion. This would shift the center of mass (COM) further back [19], which increases the knee extensor torque and thigh muscle activity [19,44]. Increased quadriceps muscle activity with the posterior wedge may also be due to a narrower level of support, which challenges stability [45]. Using the posterior wedge during squatting to induce higher activity levels of the vastus medialis, as observed in the present study, can be a useful option for rehabilitation or strength programs. For example, when the quadriceps muscle strength is impaired in people with patellofemoral pain syndrome [46], specific strengthening of this muscle can be done by using the posterior wedge during squats. Conversely, squat movements are widely used to lift loads in work environments [5], where the goal is to delay fatigue by reducing the activity of thigh muscles, in which case, the posterior wedge is not appropriate.
As noted above, the alignment of the lower limbs and joint angles, especially the knee, directly influences the muscles’ length–tension relationship, which can affect the level of muscle activity. The selected studies exclusively included healthy subjects with no documentation of remarkable abnormalities in the lower limbs, except for one study [17]. Although knee joint angles were reported, the influence of specific kinematics on changes in the muscle activation levels were not investigated. The selected studies used shallow [17,18,20], medium [5,9,10,12,14,19], or deep squats [11,13,15,16,27,32], and some of them controlled the posture of lower limbs during squatting between non-wedge and wedge conditions [5,9,10,14,17,18,19]. Therefore, caution should be made when relating the results of this meta-analysis with the muscle length–tension relationship.
The results of the meta-analysis showed that the anterior wedge only had a significant effect on the activity level of the rectus femoris during squatting (p < 0.05), as increased activity was reported in two studies [9,13], although a third study reported the opposite finding [18]. As noted above, lower-limb muscle activity is dependent on the knee flexion angle [13] and postural stability [47]. In the dorsiflexed position of the ankle joint, the triceps surae is lengthened [12], which increases the calf muscle activity and knee flexion angle, as they are two-joint muscles [12,24]. Increased knee flexion excursion may increase the tension in the rectus femoris [13]. Another plausible theory is that increased tension in the triceps surae muscles during squatting may prevent the shank from moving forward and keep the COM back; therefore, a higher tension in hip and trunk flexors (e.g., rectus femoris) is needed to keep the COM over the base of support. A higher ankle dorsiflexion angle and posterior COP position have been reported as predictors for a higher knee extensor moment during squatting [48]. Furthermore, as with the posterior wedge, using an anterior wedge may decrease the base of support and stability, leading to a slightly higher demand of the rectus femoris [13]. Ghasemi and Anbarian (2020) showed that using different wedges can change the stability of the body, where the highest instability was reported in the anterior–lateral wedge [31]. However, future studies are needed to investigate the relationship between the lower extremity muscle activity and body stability during squatting.
The results of the meta-analysis for the overall and subgroup assessments showed no significant effect of the medial and lateral wedges on the activity level of thigh muscles (p > 0.05). However, these results must be interpreted with caution due to the limited number of studies on the effects of the medial (n = 3) and lateral (n = 2) wedges on the activity of the thigh muscles.

5. Limitations

This study was not without limitations. No distinction was made between insole wedges [5] and outer wedges. However, all the studies used the squat task, which is a semi-dynamic movement that does not involve moving the base of support, and thus, the effect of insole vs. outer wedge is unlikely to influence the results. Another limitation was that the potential influence of wedge materials and thicknesses, which varied across the included studies, was not investigated and may have influenced the results. Moreover, the angles of the wedges were not identical across the studies, which may have also influenced the magnitude of the muscles’ response. Due to the variety of angles in the present meta-analysis, the criterion was only the wedge type. Also, while most studies recorded the muscle activity throughout the total phase of the squatting, some studies recorded the muscle activity in the holding phase of the squatting [9,10]. No systematic investigation was done to relate the biomechanical changes due to the use of foot wedges to changes in the muscle activation levels. Future studies might focus on the influence of wedge characteristics on biomechanics and muscles’ length–tension relationships and how these mediate muscle activation levels.

6. Conclusions

The results of this systematic review and meta-analysis demonstrated the selective influence of the posterior wedge to increase the activity of the vastus medialis and the anterior wedge to increase the activity of the rectus femoris during squatting, while the medial and lateral wedges had no significant effects on the thigh muscle activity. Thigh muscle activation may, therefore, be modified by manipulating footwear design. This finding can be useful for specialists in developing sports exercises and designing footwear.

Author Contributions

All authors contributed equally toward the project. All authors read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

Not applicable.

Conflicts of Interest

The authors declare no conflicts of interest.

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Applsci 14 02091 g001
Figure 1. Flow chart illustrating the search and selection process.
Figure 1. Flow chart illustrating the search and selection process.
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Figure 2. Sub-group effects of posterior wedge on the activity level of thigh muscles [5,9,10,11,14,15,16,17,18,19,27,32].
Figure 2. Sub-group effects of posterior wedge on the activity level of thigh muscles [5,9,10,11,14,15,16,17,18,19,27,32].
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Figure 3. Sub-group effects of anterior wedge on the activity level of thigh muscles [5,9,10,12,13,14,18].
Figure 3. Sub-group effects of anterior wedge on the activity level of thigh muscles [5,9,10,12,13,14,18].
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Figure 4. Forest plot for the sub-group effect of medial wedge on the activity level of thigh muscles [5,18,20].
Figure 4. Forest plot for the sub-group effect of medial wedge on the activity level of thigh muscles [5,18,20].
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Figure 5. Forest plot for the sub-group effect of lateral wedge on the activity level of thigh muscles [18,20].
Figure 5. Forest plot for the sub-group effect of lateral wedge on the activity level of thigh muscles [18,20].
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Table 1. Participants’ characteristics within the eligible studies.
Table 1. Participants’ characteristics within the eligible studies.
CharacterReported (Number of Participants)Mean (SD)
Gender229 (13 studies)140 men, 89 women
Age (years)219 (13 studies)24.87 (5.79)
Height (cm)249 (14 studies)171.73 (9.15)
Weight (kg)249 (14 studies)69.69 (13.16)
Table 2. Study characteristics.
Table 2. Study characteristics.
Author (Year)NPParticipantsInterventionVariableTaskWeightMusclePhaseResults
Lu et al. (2022) [32]20Healthy adults (men and women)Posterior (1.5 and 3 cm)Normalized mean RMSBarbell squats80% of 1-RMRF, VM, VL, and BFTotal phaseVM in PW ↑ (Δ2%)
VL in PW ↑ (Δ11%)
RF in PW ↑ (Δ3%)
BF in PW ↑ (Δ14%)
Cui et al. (2022) [9]20Young individuals (gender unknown)Anterior (10°)
Posterior (10°)		Normalized mean RMSDouble-leg static squat0 kgVM, VL RF, and BFHolding phaseVM in AW and PW ↑ (Δ12, 38%), VL in AW and PW ↑ (Δ4, 17%), RF in AW and PW ↑ (Δ50, 115%), BF in AW and PW ↑ (Δ10, 17%)
Sung et al. (2021) [14]37Young (men and women)Anterior (15°)
Posterior (15°)		Normalized mean RMSDouble-leg squat0 kgVM, VL, and BFTotal phaseVM in AW ↓ (Δ13%)
VM in PW ↑ (Δ4%)
VL in AW ↓ (Δ11%)
VL in PW ↓ (Δ3%)
BF in AW ↓ (Δ4%)
BF in PW ↓ (Δ10%)
Lee et al. (2019) [16]14Recreational weightlifter (men and women)Posterior (4.3°)Normalized mean amplitudesDouble-leg barbell back squat80% of 1-RMVLDown, terminal depth, and up phasesVL in PW ↓ (Δ3%)
Ghasemi et al. (2018) [5]9Young (only men)Anterior (2.2°) Medial (7.1°)
Posterior (2.2°) Posterior (6.6°)		Normalized mean amplitudesDouble-leg squat load lifting1.36 kgVM and VLEccentric, holding, and concentric phasesVM in AW ↓ (Δ4%)
VM in MW ↓ (Δ4%)
VM in PW ↑ (Δ10%)
VL in AW ↓ (Δ9%)
VL in MW ↓ (Δ5%)
VL in PW ↑ (Δ7%)
Cho et al. (2017) [13]17Young (men and women)Anterior (5°)
Anterior (10°)		Normalized mean amplitudesDouble-leg squat0 kgVM and BF (both sides)Total phaseVM in AW ↑ (Δ11%)
BF in AW ↑ (Δ15%)
Charlton et al. (2017) [27]14Trained malesPosterior (2.5 cm)Normalized peak and RMS amplitudesBarbell Squat20 kgRF and BFTotal phaseRF in PW ↓ (Δ4%)
BF in PW ↑ (Δ5%)
Bae et al. (2015) [10]20Adult (men and women)Posterior (10°)
Posterior (30°)
Posterior (50°)		Muscle activitySingle-leg static squat0 kgRF and BFHolding phaseRF in PW ↑ (Δ31%)
BF in PW ↑ (Δ22%)
Macrum et al. (2012) [12]30Young (men and women)Anterior (12°)Normalized mean amplitudesDouble-leg squat0 kgVM and VLTotal phaseVM in AW ↓ (Δ8%)
VL in AW ↓ (Δ13%)
Sriwarno et al. (2008) [15]8Adult (men)Posterior (15°)Normalized (dynamic) initial and peak values Double-leg squatting to standing0 kgRFTotal phaseRF in PW ↓ (Δ60%)
Frohm et al. (2007) [11]13Young (men)Posterior (25°)Mean EMG activityDouble-leg squat10 kgVM and BFTotal phaseVM in PW ↑ (Δ6%)
RF in PW ↑ (Δ1%)
Ribeiro et al. (2007) [18]8Young (men and women)Anterior (10°)
Posterior (10°)
Medial (10°)
Lateral (10°)		Mean activity (microvolt)Single-leg squat0 kgVM, VL, RF, and BFAcceleration and deceleration phasesVM (AW and LW), VL (AW) ↓ (Δ8, 1, 2%)
VM (PW and MW), VL (LW, PW, and MW) ↑ (Δ17, 10, 15, 14, 16%)
RF (AW), BF (AW and LW) ↓ (Δ7, 1, 5%)
RF (MW and PW), BF (MW) ↑ (Δ7, 13, 8, 14%)
RF (LW) ↔ (Δ ≈ 0%)
Kongsgaard et al. (2006) [19]13Young (men and women)Posterior (25°)Normalized mean amplitudes Single-leg eccentric squats0 kgVM, VL, RF, BF, and STTotalVM in PW ↑ (Δ14%)
VL in PW ↑ (Δ14%)
RF in PW ↑ (Δ63%)
BF in PW ↓ (Δ9%)
ST in PW ↓ (Δ12%)
Hertel et al. (2005) [17]30Young (men and women) (normal, pes cavus, and planus)Posterior (4*7°)Normalized peak RMS Single-leg squat0 kgVM and VLTotalVM in PW ↑ (Δ13%)
VL not reported
Hung and Gross (1999) [20]16Young (men and women)Medial (10°)
Lateral (10°)		Normalized mean amplitudes Single-leg Short squat0 kgVM and VLTotalVM in MW ↓ (Δ3%)
VM in LW ↓ (Δ9%)
VL in MW ↓ (Δ6%)
VL in LW ↑ (Δ2%)
NP stands for the number of participants. PW, AW, MW, and LW stand for posterior, anterior, medial, and lateral wedges, respectively. VM, VL, RF, BF, and ST stand for vastus medialis, vastus lateralis, rectus femoris, biceps femoris, and semitendinosus, respectively. RMS stands for root mean square. The downward arrow indicates a decrease, the upward arrow indicates an increase, and the horizontal arrow indicates no change.
Table 3. Quality appraisal of eligible studies.
Table 3. Quality appraisal of eligible studies.
PapersQ1Q2Q3Q4Q5Q6Q7Q8Q9Q10Q11Q12Q13Q14Sum
Lu et al. (2022) [32] 11110.1710.60.801111010.57
Cui et al. (2022) [9]10.750.510.1710.81001110.59.72
Sung et al. (2021) [14]11110.510.81001110.510.8
Lee et al. (2019) [16]10.75110.6710.51001110.510.42
Ghasemi et al. (2018) [5]110.50.50.510.81001110.59.8
Cho et al. (2017) [13]110.510.6710.60.8001110.510.07
Charlton et al. (2017) [27]110.510.1710.60.8001110.59.57
Bae et al. (2015) [10]10.250.5000.50.60.8001110.57.15
Macrum et al. (2012) [12]10.750.510.511100111110.75
Sriwarno et al. (2008) [15]110.50.50.170.50.60.4001110.58.17
Frohm et al. (2007) [11]1100.50.50.50.60.40011017.5
Ribeiro et al. (2007) [18]110.500.8310.81001110.59.63
Kongsgaard et al. (2006) [19]110.50.50.810.80.8101110.510.9
Hertel et al. (2005) [17]110.50.50.6710.8110111010.47
Hung and Gross (1999) [20]110.510.6710.8110111010.97
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Ghasemi, M.; Gholami-Borujeni, B.; Briem, K. Effects of Various Foot Wedges on Thigh Muscle Activity during Squatting in Healthy Adults: A Systematic Review and Meta-Analysis. Appl. Sci. 2024, 14, 2091. https://doi.org/10.3390/app14052091

AMA Style

Ghasemi M, Gholami-Borujeni B, Briem K. Effects of Various Foot Wedges on Thigh Muscle Activity during Squatting in Healthy Adults: A Systematic Review and Meta-Analysis. Applied Sciences. 2024; 14(5):2091. https://doi.org/10.3390/app14052091

Chicago/Turabian Style

Ghasemi, Mohammadhossein, Behnam Gholami-Borujeni, and Kristín Briem. 2024. "Effects of Various Foot Wedges on Thigh Muscle Activity during Squatting in Healthy Adults: A Systematic Review and Meta-Analysis" Applied Sciences 14, no. 5: 2091. https://doi.org/10.3390/app14052091

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