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 Table of Contents  
ORIGINAL ARTICLE
Year : 2020  |  Volume : 29  |  Issue : 4  |  Page : 680-687

Comparative analysis of the effects of abdominal crunch exercise and dead bug exercise on core stability of young adults


1 Department of Medical Rehabilitation, College of Medicine, University of Nigeria, Enugu Campus, Nsukka, Enugu State, Nigeria
2 Department of Anatomy, College of Medicine, University of Nigeria, Enugu Campus, Nsukka, Enugu State, Nigeria
3 School of Rehabilitation Science, McMaster University, Hamilton, Ontario, Canada

Date of Submission23-May-2020
Date of Decision24-Jun-2020
Date of Acceptance25-Aug-2020
Date of Web Publication24-Dec-2020

Correspondence Address:
Dr. Chidiebele Petronilla Ojukwu
Department of Medical Rehabilitation, University of Nigeria, Enugu Campus, Nsukka, Enugu State
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/NJM.NJM_85_20

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  Abstract 


Background: Poor core stability is a known risk factor for musculoskeletal injuries. The utilization of abdominal crunch exercises for improving core stability has been discouraged by some authorities considering its risks for low back pain. Evaluating the efficacy of other core exercises is necessary for implementing them as safe alternatives. Aims: This study compared the effects of abdominal crunch and dead bug exercises on core strength, endurance, and flexibility of young adults. Materials and Methods: Twenty-nine untrained young adults participated in this study, comprising of three exercise groups [abdominal crunch group (ABG), dead bug group (DBG) and a control group (CG)]. Pre- and post-intervention (at 6 weeks) core strength, endurance, and flexibility were measured. ANOVA and ANCOVA were used to test for differences at baseline and between groups, respectively. Sidak's multiple-comparison test was used for post hoc analysis between groups. The effect size was reported using partial Eta-squared (η2p). Alpha level was set at 0.05. Results: The highest mean differences were observed within DBG (5.3 [1.67], 63.6 [23.10], and 2 [0.5] for core strength, endurance, and flexibility, respectively). Core strength, endurance, and flexibility varied significantly across groups (P = 0.0111, 0.000, and 0.0090, respectively). Estimated marginal mean (EMM) for core strength for DBG (EMM [ Standard error (SE)], 25.31 [1.38]) was significantly higher than ABG (20.57 [1.24]) and CG (19.37 [1.30]). For core endurance (EMM [SE], DBG (4.62 [0.12]) and ABG (4.2 [0.11]) were significantly higher than CG (3.8 [0.12]). EMM for core flexibility for the DBG (EMM [SE], 9.47 [0.48]) was significantly higher than the CG (7.28 [0.45]) and not ABG (8.27 [0.44]). Conclusions: The efficacy of dead bug exercise in improving core stability was revealed in this study. It is biomechanically efficient and suggested as an alternative to abdominal crunch exercise.

Keywords: Abdominal crunches, core, dead bug exercise, endurance, flexibility, stability, strength


How to cite this article:
Ikele CN, Ikele IT, Ojukwu CP, Ngwoke EO, Katchy UA, Okemuo AJ, Mgbeojedo UG, Kalu ME. Comparative analysis of the effects of abdominal crunch exercise and dead bug exercise on core stability of young adults. Niger J Med 2020;29:680-7

How to cite this URL:
Ikele CN, Ikele IT, Ojukwu CP, Ngwoke EO, Katchy UA, Okemuo AJ, Mgbeojedo UG, Kalu ME. Comparative analysis of the effects of abdominal crunch exercise and dead bug exercise on core stability of young adults. Niger J Med [serial online] 2020 [cited 2021 Nov 29];29:680-7. Available from: http://www.njmonline.org/text.asp?2020/29/4/680/304771




  Introduction Top


Core stability is “the ability to control the position and motion of the trunk over the pelvis to allow optimum production, transfer, and control of force and motion to the terminal segment in integrated athletic activities.”[1] The core musculature provides support to the lumbopelvic hip complex to balance the spine and pelvis during functional movement.[2] The core muscles are divided into local muscles (stabilization system) and global muscles (movement system). The local muscles are further categorized into primary stabilizers (transversus abdominis, multifidi) and secondary stabilizers (internal oblique, medial fibers of the external oblique, quadratus lumborum, diaphragm, pelvic floor muscles, lumbar portions of iliocostalis, and longissimus). The global muscles include rectus abdominis, lateral fibers of the external oblique, psoas major, erector spinae, and thoracic portion of iliocostalis.[3],[4],[5] The action of these muscles also protect the spine from excessive force and plays an essential role in body stabilization and force generation during sporting activities.[6] The contraction of these core muscles together keeps the spine in its most stable position (the neutral zone) and aids injury prevention. They contract before any limb movement, to keep the core of the body rigid during all movements.[2]

Suggested core stability components include strength, endurance, flexibility, motor control, and function.[7] Core endurance is the ability to maintain a position or perform multiple repetitions,[8] while core strength relates to the muscles' ability to produce force through contractile force and intra-abdominal pressure.[9] Flexibility refers to the range of motion possible around a specific joint or a series of articulations.[10] Maintaining balance in these muscles is vital because malfunctioning of these local muscles will cause inefficiency in movements due to the compensation of the global muscles, thus altering stability.[3] A weak core or reduced trunk stability is considered a risk factor for acute and chronic low back pain (LBP), lower extremity injuries, and affects athletic performance.[11],[12],[13],[14] Evidence has found that in people with LBP, these muscles fail to contract before limb movement, so retraining these muscles to contract is the fundamental theory of core stability.[2] Comprehensive strengthening of these core muscles can be used for injury prevention, rehabilitation, and sports performance enhancement. Core training has been commonly used as a modality in physical rehabilitation, promotion of general health, and improvement of sports performance. It can also facilitate recovery from injury and relief of chronic lower back pain.[13],[15],[16],[17]

Abdominal exercises are commonly employed as a result of their effects on improving core strength and endurance, reduction of LBP, and enhancement of sports performance as well as improvement of body image. For effective outcomes of core training, a combination of exercises targeting all the core muscles is employed. However, it is common to engage the abdominals more in core training programs. To this effect, the abdominal crunch exercise is commonly utilized.[18],[19],[20] Abdominal crunch is considered to be the gold standard abdominal exercise.[20] The abdominal crunch is done supine, lying with the knees flexed approximately 90°, the hips flexed approximately 45°, and the feet placed flat. The head and shoulders are then raised to clear the surface. The position of the upper extremities can be placed by the sides of the trunk, crossed on the chest, or with the upper extremities in full flexion over the head.[21],[22] When performed correctly, it activates the rectus abdominis and internal and external obliques, while limiting the activation of the accessory muscle (sternocleidomastoid, erector spinae, rectus femoris, and iliopsoas).[20] Wrong and consistent performance stagnates the processes of its expected outcomes and may lead to undesirable effects.[21] Despite its widespread inclusion in strength training programs, the crunch has recently come under scrutiny as a potentially dangerous movement that should be avoided by the public. This exercise was also considered to have tendencies of activating the hip flexor and lumbar paraspinal muscles, resulting in increased lumbar lordosis and risks of LBP.[22] More exercises and exercise machines have become popular for training the abdominal muscles.[20] Due to the abdominal crunch risk of injury, other alternatives are currently recommended and utilized. Some of these abdominal exercises include dead bugs, planks, etc.

Dead bug exercise is considered an effective exercise for promoting stabilization of the trunk and pelvis. Its performance involves alternately moving the arms and legs in supine lying when maintaining the abdominal draw-in maneuver. This activates the erector spinae, multifidus, rectus abdominis, and oblique muscles.[23],[24],[25] It is used to train stability and control around the trunk region, primarily focusing on the core musculature and hip adductor muscle groups.[26] It is also classified into static holds and slow movements in a stable environment and characterized by static isometric contraction with controlled simultaneous limb movements.[27] Dead bug as an isometric exercise challenges the core through braced positions, which may reduce the risk of injury, and eliminates excessive or undesirable movements while focusing more on spinal stability.[28],[29]

This exercise can enhance strength and endurance in the muscles of the core, which are essential for providing trunk stabilization and effective in promoting proper lumbopelvic functioning during motor skills.[29] During the performance of the dead bug exercise, resistance is applied through the weight of the arms and legs.[23]

Dead bug exercise has been suggested as a safer and useful alternative to abdominal crunch[28],[29] because of the associated risk of injury after abdominal crunch exercises. However, there is a paucity of data on their compared effects on core endurance, strength, and flexibility. This study, therefore, intends to compare the efficacy of both exercises in improving core strength, endurance, and flexibility of young adults.


  Materials and Methods Top


Study design

This study was a pretest-posttest experimental research design that employed a simple random sampling technique (balloting) to assign the participants to the three different groups. This involved picking a piece of paper labeled with an abdominal crunch group (ABG), dead bug group (DBG), or control group (CG).

The Health Research and Ethics Committee of The University of Nigeria Teaching Hospital, Ituku/Ozalla, Enugu State, approved this study: NHREC/05/01/2008B-FWA00002458-1RB00002323.

Target population, inclusion, and recruitment

Participants were students recruited from the University of Nigeria Enugu Campus, Enugu State, Nigeria. The researchers advertised the study in the school premises; individuals who were interested in participating were asked to contact the researchers. Participants were included if they did not have any history of physical activity or exercise training (untrained healthy), 18 years and older. Participants were excluded if had known cardiovascular, neurological, or musculoskeletal conditions of the low back or spine or currently participating in any form of physical activity or exercise programs.

Sample size

Sample size calculations assumed a moderate standard effect size of 0.40, while accounting for baseline scores, α = 0.05, power = 0.80. Sample size calculations determined that a minimum sample of 36 (with 25% adjustment) participants will provide ample power for ANCOVA.[30] A balanced design was adopted, and participants were randomized into the three groups.

Procedure

After completing informed consent to participate in the study, participants underwent a baseline assessment (see outcome measure). This study utilized a pretest-posttest experimental research design. To compare the effects of abdominal crunch and dead bug exercise on core strength, endurance, and flexibility, participants completed a 6-week core exercise training program. Participants did not engage in any other core-specific exercises during the 6 weeks of this study. The study design and flowchart of the experiment are presented in [Figure 1].
Figure 1: Study design

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Physical measures including the body weight (kg) and height (m) of all the participants were measured, and body mass index (BMI) was calculated. Physical activity readiness questionnaire was also used to screen participants for eligibility. Participants completed a 3-min warm-up exercise by walking at a self-selected pace up and down a level surfaced hallway before commencing the pretest. The pretest involved core strength, endurance, and flexibility testing to obtain baseline data.

Interventions

Participants were randomly assigned to one of the three groups: ABG, DBG , or CG (Control). The protocol flowchart [Figure 2] shows the protocol of the dead bug and abdominal crunch exercises (progressive) administered 3 times per week, for 6 weeks. Warm-up, cool down and stretch exercises were administered to the CG 3 times per week for the 6 weeks. Four participants did not complete the exercise protocol and were not included in the posttest.
Figure 2: Protocol for abdominal crunches and dead bug exercises

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Abdominal crunch exercise

The abdominal crunch exercise [Figure 3] started with the participant in supine, lying with the knees flexed to 90°, the hips flexed to 45°, and the feet placed flat on a mat. The sides of the trunk placed the upper extremities. The participant was then asked to raise the head and shoulders to clear the surface while maintaining craniocervical flexion in order to prevent excessive activation of superficial cervical flexors (sternocleidomastoid), hold for the stipulated time, and then return to the starting position.[22]
Figure 3: Abdominal crunch exercises

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Dead bug exercise

Dead bug exercise [Figure 4] started with the participant in supine, lying on a mat with shoulders, hip joints and knees flexed to 90°. With the lumbopelvic region being maintained in the neutral position, the participant was then instructed to draw in the abdomen, lower two contralateral limbs (opposite arm and leg) toward the floor, hold for the stipulated time, then return to starting position. The same movement was repeated with the opposite limbs. In the DBG, both pairs of limbs were moved an equal number of times within the stipulated time.[23]
Figure 4: Dead bug exercises

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Outcome measures

Core strength testing

Core strength was tested using an isoinertial strength test. It is a timed sit-up test [Figure 5], to perform as many full sit-ups as possible within 1 min. This sit-up test protocol was developed by the American Alliance of Health, Physical Education, Recreation, and Dance.[31] The test was initiated in the hook-lying position, with the participant's arm held across the chest, knees flexed at 90°, and feet secured. To complete a full sit-up, the participant's scapula touched the mat in the lying position; and in the upright position, the elbows made contact with the knees.
Figure 5: Timed sit-up test

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Core endurance testing

Core endurance was assessed using a trunk flexion endurance test [Figure 6]. The test started with the subject in a hook-lying position with the trunk supported manually with a wedge angled at 60° of trunk flexion. With the aid of a goniometer, the hips and knees were flexed to 90°. The feet were held securely. The arms were folded across the chest with the hands placed on the opposite shoulder. Subjects were instructed to hold the isometric posture as the wedge was removed. Time started when the wedge was moved 10 cm backward, and the participant held the isometric posture for as long as possible. Time stopped when any part of the participants back touched the wedge. The test was scored individually. Time was recorded in seconds (to the nearest 0.1 s).[32] This protocol for the flexor endurance test was established by McGill et al.[8]
Figure 6: Flexion endurance test

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Core flexibility testing

Active trunk extension range of motion measurement [Figure 7] was used as the trunk flexibility assessment based on Norkin and White.[33] The trunk extension range of motion was measured by first recording the distance between C7 cervical vertebra and S1 sacral vertebra when standing upright. The participant was then asked to bend backward as far as possible with the pelvis stabilized. The distance between the C7 and S1 was measured again, and the length decrease was documented as the trunk flexibility.[33]
Figure 7: Trunk flexibility test (extension)

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Data analysis

Descriptive analysis with mean and standard deviation (SD) for continuous variables and frequency and percentages for noncontinuous variables was conducted. Intention-to-treat analysis with multiple imputation techniques for missing values was used for between-group comparisons for outcomes. All continuous data were checked for normality prior to analysis using Shapiro–Wilk's test and histogram. Nonnormally distributed data were log-transformed for ANOVA or ANCOVA. Other assumptions for ANOVA and ANCOVA were met. Baseline differences were compared between groups with ANOVA for continuous and normally distributed data or Kruskal–Wallis analysis of variance for categorical variables. Three one-way ANCOVAs were used to examine differences between groups for core strength, endurance, and flexibility at 6 weeks postintervention. Baseline parameters (core strength, endurance, and flexibility) were used as covariates and groups (ABG, DBG, and CG) as fixed factors. Sidak's multiple-comparison test was used post hoc to examine means when the F-ratio was significant. The effect size was reported using partial Eta-squared (η2p), (a proportion of variance that a variable explains that is not explained by other variables in the analysis).[34] Partial Eta-squared (η2p) effect size was used to estimate the magnitude of the difference within each group; the thresholds for small, moderate, and large effects were defined as 0.01, 0.06 and 0.14, respectively.[35] Data were analyzed using STATA/IC (v14), with a P- value for significance set at <0.05.


  Results Top


A total of 33 untrained healthy young adults aged between 18 and 28 years participated in this study, but only 29 (12 men and 17 women) completed the exercises and qualified to take the posttest [Figure 1].

The physical characteristics of the participants are shown in [Table 1]. The mean age of the 33 participants that met the inclusion criteria, gave consent, and were randomly assigned to the three groups (ABG = 12, DBG = 10 and CG = 11) was 23 (SD = 2.92) years. Two participants each from ABG and CG withdrew from the study for personal reasons after baseline assessment. A total of 29 participants were assessed at posttreatment [Figure 1].
Table 1: Physical characteristics of participants (n=33)

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At baseline, there was no significant difference in age, sex, BMI, core strength, endurance, and flexibility scores between groups [Table 2]. [Table 3] shows core strength, endurance, and flexibility means, mean differences, and SD at baseline and postintervention. The highest mean differences in core strength, endurance, and flexibility were observed in DBG.
Table 2: Comparison of baseline differences in age, sex, body mass index, strength, endurance, and flexibility between groups (mean [standard deviation])

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Table 3: Core strength, core endurance, core flexibility at baseline and postintervention, means, mean differences and standard deviation

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After adjusting for baseline strength, ANCOVA showed a significant difference in mean core strength at 6 weeks postintervention (F [2, 29] =5.38, P = 0.0111; η2p [95% confidence interval (CI)] =0.26 [0.017, 0.461]). Post hoc comparison showed that estimated marginal mean (EMM) for core strength for the DBG (EMM [SE], 25.31 [1.38]) was significantly higher than the ABG (20.57 [1.24]) and the CG (19.37 [1.30]). There was no significant difference between ABG and CG.

Similar finding was noted in core endurance (F [2, 29] = 10.10, P = 0.0005; η2p [95% CI] = 0.41 [0.112, 0.580]). Post hoc comparison showed that EMM for core endurance for the DBG (EMM [SE], 4.62 [0.12] and ABG [4.2 (0.11)]) was significantly higher than the CG (3.8 [0.12]). There was no significant difference between DBG and ABG.

There was significant group differences in core flexibility (F [2, 29] = 5.56, P = 0.0090; η2p [95% CI] = 0.29 [0.022, 0.471]). Post hoc comparison showed that EMM for core flexibility for the DBG (EMM [SE], 9.47 [0.48]) was significantly higher than the CG (7.28 [0.45]) and not ABG (8.27 [0.44]). There was no significant difference between ABG and CG. Effect sizes were noted and interpreted as largely based on the Cohen's[35] guideline for interpreting partial Eta-squared. [Table 4] shows t-test and adjusted mean difference across groups for intention-to-treat analysis. The graphs show the plot of time by group-based baseline and postintervention means. [Figure 8], [Figure 9], [Figure 10] show graphs of core strength, endurance, and flexibility, respectively.
Table 4: Adjusted mean differences between groups, 95% confidence interval and post hoc analysis for core strength, endurance, and flexibility

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Figure 8: Differences in core strength across groups

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Figure 9: Differences in Core endurance across groups

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Figure 10: Differences in flexibility across groups

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  Discussion Top


This study compared the effects of abdominal crunch and dead bug exercises on core stability (strength, endurance, and flexibility) among young adults. The findings revealed that after 6 weeks, abdominal crunch exercises significantly improved only core endurance while dead bug exercises improved all the components of core stability measured.

Abdominal crunches are known to activate the rectus abdominis, internal and external obliques,[20] while dead bug exercises are known to activate the multifidus, rectus abdominus, internal and external obliques, and erector spinae.[24],[25] The internal oblique and medial fibers of the external oblique which are categorized as secondary stabilizers of the spine[9] are activated by both exercises. These muscles have shorter muscle lengths and attach directly to the spinal vertebrae.[5],[36],[37] They function primarily to stabilize the spine, but also function secondarily to move the spine.[38] Rectus abdominis and lateral fibers of the external oblique are also activated by both exercises. These are global muscles and are primarily in charge of producing movement and torque of the spine.[9] Training these muscles must have resulted in the improvements observed in core strength and endurance.

Core strengthening exercises enhance flexibility, aim to correct muscle tightness, and provide for the assumption of a neutral position so that strength can be developed.[39] The increase observed in flexibility may be a result of the eccentric contraction of the core muscles, possibly leading to an overall increase in muscle length. Core stability exercises may also reduce facet joint compression forces and provide stretch to the lumbar muscles, ligaments and myofascial structures.[40] Dead bug activates the erector spinae which is another global muscle. These global muscles possess long levers and large moment arms, making them capable of producing high outputs of torque, with emphasis on speed, power, and larger arcs of multiplanar movement, while countering external loads for transfer to the local musculature.[5],[37] This may explain the higher improvements recorded in flexibility in the DBG.

Multifidus which is categorized as a primary stabilizer of the spine[37],[38],[41] because of its short moment arms and lack of involvement with gross movement[9],[42] is also activated by dead bug exercise. The multifidi provide the largest contribution to intersegmental stability. They attach from the vertebral arches to the spinous processes spanning from sacral to the cervical spine and each muscle spans between 1 and 3 vertebral levels.[5] Before limb movement, they are activated in an attempt to stabilize the spine for that movement.[43] This may have contributed to the highest improvements observed with core strength and endurance in the DBG because strength training influences biomechanical functions and stability of the spine and pelvis.[40] Resistance exercises stress the body's musculoskeletal system, which enlarges muscle fibers and improves neural control of muscle function which results in greater muscular strength.[39]

The findings of this study may also be consequent to the fact that dead bug exercise activates both local (primary and secondary) and global core stabilizers.[24],[25] It had been reported that the abdominal muscle activity is highly increased with the upper and lower extremity dead bug exercise because, during the performance of the dead bug exercise, resistance is applied through the weight of the arms and legs.[23] Another report[44] also revealed a significant increase in rectus abdominis and oblique muscle activity when subjects performed the dead bug exercise with the additional weight of the upper and lower extremities. The reciprocal limb movement patterns associated with dead bug exercise resemble certain motor skills like walking, running, and swimming. This use of reciprocal arm and leg motions during dead bug exercises and functional motor skills places increased demands on muscles of the core to maintain trunk and pelvic (lumbopelvic) stability.[29] This challenges the activated muscles through braced positions, thereby improving their function and reducing the risk of injury associated with unwanted movements.[29] This further explains the highest mean differences observed in all the core stability measures in the DBG.

The abdominal crunch was considered to be the gold standard abdominal exercises based on the reports of a study[20] that found that traditional crunch exercises were more effective in activating the abdominal musculature when compared to some other exercises and exercise equipment. This, however, did not include dead bug exercise. Based on the findings of this study, the dead bug may be considered a greater contributor to core stability than abdominal crunch exercises. This provides an opportunity for avoiding repetitive bending and degenerative changes resulting from prolonged use of crunch while building a stronger core. This will improve the ability to maintain a stiff and stable trunk and pelvis and can aid in the transfer of forces across the extremities during activities such as throwing, striking, kicking, pushing, pulling, swinging, and running as suggested by Leatherwood et al.[45] The results of this study also support the report that the use of the dead bug core exercises is also considered an effective exercise to implement during the early phases of rehabilitation for some individuals with LBP.[29]

One of the limitations of this study is that intermediate measurements were not taken within the interventions. This would have given a clearer picture of the observed changes. Gender-based differences were also not assessed and some participants did not complete their treatment sessions. Small sample size required to power this study was not reached; therefore, Type I error may have been introduced. Clinicians may choose to consider this finding a hypothesis-generating result rather than a confirmative result. Further studies with larger sample sizes are recommended to refute or support these findings.


  Conclusions Top


Dead bug exercise was more efficient in improving core strength, endurance, and flexibility and may be used as an alternative to abdominal crunch exercise. Further research is, however, recommended on the effects of dead bug and abdominal crunch exercises on the muscles of the core. It is also recommended that gender-based and anthropometric differences in the effects of dead bug and crunch exercises be studied.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]
 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4]



 

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