Introduction

Flexible flatfoot, a prevalent biomechanical dysfunction, significantly impacts both athletic performance and musculoskeletal health. This condition alters load distribution in the lower extremities, resulting in compensatory changes throughout the kinetic chain, including tibial internal rotation, lateral knee deviation, and coxofemoral joint internal rotation during weight-bearing activities. These alterations can elevate the risk of sports-related injuries and diminish movement efficiency1,2. The foot, as the foundation for human movement, plays a pivotal role in various physical activities2. Although approximately 80% of the population contends with various foot ailments, flatfoot deformity stands out as the predominant disorder encountered throughout the lifespan3. Prior investigations have documented that the occurrence of flatfoot typically hovers around a quarter of the general population4,5. It is observed that this condition is more commonly found in women, individuals with increased BMI values, and those with larger foot sizes4,6. It is common for infants and young children to exhibit flat feet, with the arch of the foot progressively forming its typical structure as they age6. The medial longitudinal arch’s collapse, a hallmark of flexible flatfeet, is a frequent occurrence that can disrupt foot functionality and potentially hinder broader motor skills7.

Excessive foot pronation in individuals with flexible flatfeet modifies force distribution in the lower limb. This change increases load on the medial foot musculature while reducing load on the lateral musculature, leading to muscular imbalances. These imbalances can compromise the stability of the ankle and knee joints, thus increasing their susceptibility to overuse injuries8,9 . The alignment of skeletal components exerts a direct influence on neighboring anatomical structures9. Activities involving weight distribution necessitate the integration of interconnected kinetic and kinematic sequences across the lower extremity’s joint complex, encompassing the pedal, talocrural, tibiofemoral, and coxofemoral joints. Alterations in foot placement modify the posture and motion of joints located in the more superior segments of the limb8,10. Consequently, following flatfoot deformity, foot pronation induces tibial internal rotation, lateral knee deviation, and inward rotation of the coxofemoral joint during weight-bearing activities. This condition creates disturbances throughout the kinetic chain, resulting in alterations to the orientation of the pelvis, shifts in the curvature of the lower spine, and core stabilization10,11,12. Consequently, it is plausible that this compromised kinetic and kinematic sequence could impair individuals’ performance during the execution of basic movement patterns. Also, studies have reported that individuals with flatfeet may exhibit reduced balance, agility, and coordination in contrast to individuals with anatomically standard foot arches8,13,14,15. These limitations can affect daily activities, athletic performance, and overall quality of life. Furthermore, evidence indicates that the Functional Movement Screen (FMS) demonstrates strong correlations with various components of physical fitness, including agility, muscle strength, and balance16. Lower FMS scores, particularly in tests such as the deep squat and hurdle step, may reflect deficits in motor control and stability of the hip and knee joints, which are critical for individuals with flexible flatfeet. These deficits may stem from biomechanical alterations associated with excessive foot pronation and muscular imbalances16,17,18. Therefore, assessing FMS in individuals with flatfeet can reveal valuable insights into the primary movement impairments that contribute to their reduced physical fitness levels.

Treatments for flatfeet include both surgical and nonsurgical options, with the treatment dependent on severity. Nonsurgical options can include insoles, physical therapy, or arch-supporting muscle exercises to improve balance control, plantar pressure distribution, and to reduce the health risks associated with flatfeet. Many studies have focused on specific foot muscle exercise, such as short foot (SF) exercises, which have been shown to improve foot posture, muscle strength, and balance in individuals with flexible flatfeet19,20,21,22.However, the maintenance of the foot’s internal arch structure also depends on the muscles external to the foot, including the posterior tibial (TP) and peroneal longus (PL) muscles23. Consequently, strengthening the musculature located external to the foot, specifically the TP and peroneus longus tendon, is crucial for supporting the MLA and improving foot function.

It has been established that lower-extremity and core strengthening exercises, even those of a generalized nature, can positively influence gait biomechanics, muscle function, and overall performance in individuals with flatfoot or related conditions. For instance, a study by Goo et al. demonstrated that strengthening exercises targeting both the abductor hallucis and gluteus maximus were more effective in correcting pronated feet and improving gait than exercises for the abductor hallucis alone24. Similarly, a randomized controlled trial by Horsak et al. reported that a hip abductor and knee extensor strengthening program improved gait biomechanics and reduced hip adduction in obese adolescents, who often present with similar biomechanical challenges25. Furthermore, a study by Engkananuwat et al. found that lower-extremity strengthening exercises were more effective than foot orthoses in enhancing the medial longitudinal arch (MLA), improving static and dynamic balance, and increasing muscle strength in individuals with flexible flatfoot26. These findings underscore that interventions focusing on the proximal segments of the kinetic chain–such as the hip, knee, and core–can yield significant improvements in foot function and overall movement quality.

While earlier investigations have investigated the influence of elements of motor function, such as balance and nimbleness, and others have investigated the impact of custom orthotics on balance, nimbleness, and ankle proprioception in individuals with flatfeet27. Calisthenics, a form of bodyweight training, utilizes multi-joint and rhythmic movements to enhance muscular strength, endurance, and flexibility28. This training inherently targets major muscle groups of the lower limbs and core, which are directly involved in maintaining proper kinetic chain alignment and movement control. While not a targeted “corrective” program for flatfeet, calisthenics exercises can strengthen the stabilizing muscles of the ankle and knee, improve motor control and hip/knee stability, and improve overall movement pattern in individuals with flatfeet29,30,31,32. There is a need for further investigation into the role of generalized calisthenics in improving functional movement patterns, as assessed by the FMS, and overall health and motor performance in individuals with flatfeet. Based on the evidence that strengthening of the lower limbs and core can improve functional outcomes in individuals with biomechanical deficits, we developed two distinct hypotheses. First, we hypothesize that a well-designed calisthenics program will improve overall physical motor skills in both people with and without flexible flatfeet. Second, we further hypothesize that the relationship between FMS scores and measures of core strength, balance, and agility will be significantly different between individuals with and without flexible flatfeet following the intervention.

Methodology and resources

Framework and subject recruitment

The ethical directives specified in protocol IR/SSRI.REC.2022.13901.1950 were strictly followed in this cross-sectional clinical trial research. All experiments were performed in accordance with relevant guidelines and regulations. The study procedures were in accordance with the latest version of the Declaration of Helsinki. Human participants’ names and other HIPAA identifiers were removed from all sections of the manuscript, including supplementary information.

This study was designed to evaluate the efficacy of a 16-week calisthenics intervention on functional movement outcomes in female university students, specifically examining the impact of flexible flatfeet on these outcomes. The recruitment period for this study began on February 2, 2023, and ended on June 3, 2023. A cohort of ninety-six female students, ranging in age up to 25 years of age, willingly took part in the investigation and supplied formal consent. A convenience sample of female university students was recruited from Bhonar Teacher Training University through announcements posted on campus bulletin boards and flyers distributed in physical education classes. Of the 116 students who were initially screened for eligibility, 96 met the inclusion criteria and provided formal consent to participate. This corresponds to a participation rate of 82.7% (96/116). The detailed flow of participants through the study is visually represented in Fig. 1. The participants were categorized into two groups: those with flexible flatfeet (n = 25) and those with normal feet (n = 71), as defined by the navicular drop test (NDT) scores33. The NDT evaluation was completed utilizing an altered Brody method. With feet without shoes on the ground, and the navicular protuberance was indicated. The articulation was physically positioned into an equilibrium position. The space between the navicular bone’s tuberosity and the plantar surface was taken during bearing and non-bearing states. The navicular drop index was then derived from the difference of those measurement numbers. This process was conducted three separate times for each test subject to ensure accuracy34. Study population size determination was performed via G*power software, version 3.1.9.4 (from Franz Faul, Kiel, Germany), referencing data from a comparable trial35. An estimated treatment effect of 0.4, an alpha level of 0.05, and a sensitivity of 0.75 generated a required cohort size of 23. A power analysis was conducted to ensure adequate statistical power to detect clinically relevant changes in the measured variables.

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Flow diagram of study participants.

Given the higher prevalence of students exhibiting the normal feet standards, the population size in this group surpassed that of the group with mobile flatfeet. Yet, a sensitivity examination confirmed that this population size did not substantially influence the experiment’s conclusions. Sensitivity analysis was performed to validate the robustness of the statistical findings despite the unequal group sizes.

Entry parameters require participants ranging in age from 18 to 25 and free from neurological, musculoskeletal, or systemic conditions, with the exception of mobile flatfeet.

Elimination standards comprised non-pliable pes planus, expert athletic involvement, distal limb deformities (excluding mobile flatfeet), neurological, immunological, or nutritional impairments, vestibular dysfunction, postural control deficits, recurrent vertigo, and significant lateral and anterior spinal distortions36. These exclusion criteria were implemented to minimize potential confounding variables and to ensure a homogenous study population.

Assessment protocol

Each participant filled out a uniform survey to gather participant background data, including chronological age, stature, mass, and exercise engagement. Locomotor capabilities were evaluated using validated and dependable assessments, particularly chosen regarding the anticipated influence of bodyweight training on persons with pliable pes planus. These assessments were selected based on their relevance to evaluating functional movement and performance parameters that are likely to be affected by both flexible flatfeet and calisthenics training. These evaluations were conducted for all subjects in both groups.

For the measurement of abdominal and spinal extensor muscle endurance, a partial curl-up and a static plank position were implemented. The partial curl-up required participants to lie on their backs with knees bent at 140 degrees and feet flat on the ground. Participants were asked to perform controlled upper body flexions, lifting their shoulder blades from the mat and reaching their fingertips towards their knees and then returning to the initial position. The total number of successful repetitions was recorded. The test was stopped when the participant could not maintain proper technique or complete the required repetitions. Proper technique was defined as maintaining the controlled motion without using momentum and ensuring the fingertips reached the designated point. Verbal cues were provided to maintain correct form throughout the test37,38. The static plank position required participants to maintain a 90-degree angle between their body and arms, with forearms and toes as the only points of contact with the mat. The participant was required to maintain a straight body alignment (neutral position of the spine and pelvis). Any required adjustments to posture had to be made within a three-second period; otherwise, the assessment was terminated. Failure was specifically defined as the inability to maintain a straight back (e.g., hips sagging, raising the buttocks significantly, or losing a neutral spine position) or touching the mat with any body part other than the forearms and toes. The total duration of holding the correct position was used for analysis39. The ICC values for all measures, as presented in Table 1, indicated good to excellent test–retest reliability (ICC > 0.75), ensuring the consistency of the assessment protocol. The test–retest reliability ICC for the variant of the sit-up exercise and the static plank position is shown in Table 1. These tests were chosen based on their ability to assess core stability, which is essential for functional movement and potentially impacted by both flatfeet and calisthenics.

Table 1 The ICC for test–retest for variables.
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Static postural stability was evaluated using an altered Romberg procedure. Subjects were asked to stand without footwear on a flat plane, placing their dominant foot in front of their non-dominant foot in a heel-to-toe position. Their arms were folded across their chests, and their eyes were closed. The time the subject maintained this stance before losing stability was documented as their performance metric. Losing stability was defined as any of the following: moving the feet from the heel-to-toe position, stumbling, or opening the eyes40. The test–retest reliability ICC for the altered Romberg procedure is shown in Table 1. This test assessed static balance, which is often compromised in individuals with flatfeet and can be improved through targeted exercises.

Dynamic equilibrium was examined using the Y-balance evaluation. Participants were directed to stand on a designated starting point with one leg, the anchor leg, and use the opposing leg, the extension leg, to move a reach device to its maximum reach in the forward, lateral-posterior, and medial-posterior planes. The Y-balance test was performed using a commercially available Y-Balance Test Kit (Tavan Gostar Company, made in Iran). Each participant completed three scored trials in each direction for both legs after six preparatory attempts. Only the data from the three scored trials were used to calculate participant scores. Individual directional scores were calculated by dividing the mean reach distance (in cm) by the participant’s leg length (in cm) and multiplying by 100 to show the reach distance as a percentage of leg length. The total score was determined by adding the maximum reach distances in all three directions and dividing by three times the participant’s leg length41. The test–retest reliability ICC for the Y-balance evaluation is shown in Table 1. This test evaluated dynamic balance, a critical component of functional movement and potentially affected by flatfeet.

Agility was assessed using a 4 × 9-m sprint shuttle test. Participants began behind the start line and, upon verbal cue, initiated a 9-m sprint. At the 9-m mark, participants were required to halt with one foot past a designated marker, pivot, and sprint back towards the starting point, where a similar directional reversal was performed. Following the fourth 9-m segment, the timing was concluded as participants crossed the finish line. A digital handheld chronograph, accurate to the nearest 0.01 s (Q & Q, HS43, Japan), was employed to record sprint times. The minimum time obtained in two back-to-back runs was applied for statistical computation42. The test–retest reliability ICC for the 4 × 9-m sprint shuttle test is shown in Table 1. This test measured agility, which is relevant to performance in various physical activities and potentially impacted by flatfeet.

Functional movement capabilities were evaluated utilizing the Functional Movement Screening (FMS) protocol. This assessment employed a 0–3 ordinal scoring system, wherein a score of 3 represented flawless execution and a score of 0 implied pain-induced movement constraints. The FMS battery comprised the full squat, hurdle crossing, linear lunge, shoulder articulation, straight leg elevation, trunk stabilization push-up, and rotational steadiness. The sum of scores from all seven movements was logged. The Functional Movement Screening was conducted with the FMS Kit, which consisted of a measurement instrument, hurdle, resistance bands, and a length rod43,44,45. The test–retest reliability ICC for the FMS protocol is shown in Table 1. The FMS assessed fundamental movement patterns, which are crucial for overall physical function and may be influenced by both flatfeet and calisthenics training.

Post-test assessment

Post-intervention, all participants underwent the identical series of motor performance evaluations to determine the extent of functional changes. This repeated measures design allowed for the evaluation of the intervention’s impact over time.

Training procedures

Intervention group

For a 16-week period, both experimental cohorts engaged in a monitored calisthenics training regimen. The program comprised weekly sessions, each spanning 90 min. This protocol format was selected to optimize participant compliance and offer an attainable exercise routine. Given the logistical constraints and time commitments of the university student population, a once-weekly session was the most feasible option, as a two- or three-session-per-week schedule was not practical for the participants. While less frequent than standard exercise protocols, a 90-min session was intended to provide a potent stimulus to induce physiological changes, particularly in a sedentary population. This structure adheres to contemporary exercise recommendations put forth by the contemporary fitness guidelines of the American College of Sports Medicine (ACSM)46, which stipulate that adults should accrue a baseline of a total of 150 min of moderate or 75 min of vigorous cardio exertion weekly to realize appreciable health gains. Although the ACSM guidelines typically advocate for exercise distribution spread over the weekly cycle, a one-time weekly instance of a moderate-grade calisthenics workout might serve as a potent stimulus to boost somatic conditioning, particularly for individuals new to exercise protocols47. Recent findings indicate that even brief periods of physical exertion can yield health advantages, thus reinforcing the viability of a weekly training period46. This protocol format was selected to optimize participant compliance and offer an attainable exercise routine. The calisthenics program was designed to target key muscle groups relevant to foot stability and functional movement, including intrinsic and extrinsic foot muscles, core stabilizers, and lower limb musculature.

Workout layout

Each exercise period adhered to a standardized structure:

Warm-up (5 min) A combination of gentle aerobic activity (e.g., accelerated ambulation, light running) and dynamic flexibility movements was employed to prime the body for exertion and mitigate the potential for injury.

Calisthenics Exercises (80 min) The central component of the regimen comprised a variety of body resistance exercises, strategically selected to gradually stress main muscle groups, reinforce core stability, and improve lower limb strength, pliability, and movement proficiency. A thorough presentation of the calisthenics exercise development is shown in Table 2.

Table 2 Calisthenics training program.
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Cool-down (5 min) Static stretches maintained over time were employed to increase flexibility and decrease muscle discomfort after exercise.

Exercise progressions

The calisthenics movements were methodically escalated during the training phase to ensure continuous stimulus and physiological adaptation. A certified strength and conditioning expert oversaw all training periods to guarantee proper exercise execution and lower the probability of injury. Real-time feedback concerning correct technique was given during each exercise period, including direction on posture, breathing patterns, and movement sequences. Participants were asked to immediately inform the expert about any pain or discomfort they experienced during exercise. Program modifications were done to accommodate individual limitations and requirements.

Statistical analysis

The Shapiro–Wilk test was used to ascertain the data’s normality. Since the data were not normally distributed, medians and interquartile ranges are shown (Table 3). For most measured variables, two outliers were discovered and subsequently excluded from further processing, resulting in a final sample of 70 individuals in the normal feet group and 24 individuals in the flatfeet group. The Wilcoxon test was used to determine within-group changes from pre-to-post-test (Table 4) and the Mann–Whitney U test was applied to determine between-group differences at pre and post-test (Table 5). To address the significant baseline differences in BMI and to evaluate between-group differences post-intervention, linear regression analysis was performed for each dependent variable (FMS, core strength, balance, and agility), with the group (normal vs. flatfeet) and BMI serving as independent variables. To determine the potential relation between FMS and other performance variables at post-test, spearman’s rank-order correlation was used due to the non-parametric nature of the data. Additionally, due to the small sample size of the flatfeet group (n = 24), bootstrapping with 1000 resamples was performed to confirm the robustness of the spearman’s correlation finding and to provide more reliable confidence intervals for the correlation coefficients. Furthermore, a multiple regression analysis was performed for the normal feet group to determine which combination of significant predictors collectively predicted FMS scores. An evaluation of residual normality and residual independence was conducted. The effect size (r) was evaluated for variations between groups or shifts within groups. All statistical evaluations were conducted with SPSS 24, with a significance level of p < 0.05 being the standard for determining statistical significance.

Table 3 Demographic characteristics of subjects.
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Table 4 Comprehensive summary of outcome variables, within-group changes (Wilcoxon), and between-group comparisons.
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Table 5 Between-group post-intervention comparisons with BMI as a covariate.
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Results

Table 3 presents the descriptive data for the two participant cohorts. Individuals with flexible flatfeet (n = 24) exhibited a statistically significant increase in body mass (average = 65.92 ± 10.87 kg) and body mass index (average = 24.45 ± 3.45 kg/m2) when compared to participants with normal feet (n = 70) (average weight = 58.16 ± 9.32 kg; average BMI = 21.90 ± 3.42 kg/m2; p < 0.05). Conversely, no statistical variations were noted in age or stature between the two cohorts. These results indicate that the disparities in motor function observed between the two groups may be partially explained by the elevated body mass index in the flexible flatfeet cohort.

The full descriptive statistics (median and quartiles), within-group changes (Wilcoxon), and between-group comparison (Mann–Whitney) for all performance variables are consolidated and presented in detail in Table 4. Figures 2 and 3 provide a visual comparison of the pre- and post-test median scores.

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Comparison of pre-test and post-test median scores for performance variables in the flexible flatfeet group.

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Comparison of pre-test and post-test median scores for performance variables in the normal feet group.

Within-Group Changes: Non-parametric analysis (Wilcoxon Signed-Rank Test) revealed that the 16-week calisthenics intervention resulted in statically significant improvements in all key functional and performance measures for both the flexible flatfeet and normal feet groups (p ≤ 0.01 for all variables, as shown in Table 4).

Functional Movement Score (FMS): the participants with flexible flatfeet showed a 26.3% increase in FMS scores, compared to a 7.7% increase in the normal feet group.

Core Endurance: both cohorts displayed notable enhancements in the stamina of their abdominal and spinal extensor muscles. Specifically, the participants with flexible flatfeet showed a more pronounced improvement in both assessments, exhibiting a 20% augmentation in abdominal endurance and a 63.6% elevation in spinal extensor endurance, in contrast to the normal feet cohort, which demonstrated improvements of 16.7% and 29.1%, respectively.

Agility: both cohorts demonstrated substantial enhancements. Nevertheless, the degree of improvement was marginally higher among the participants with flexible flatfeet (0.54 s; 4.5%) than those with normal feet (0.43 s; 3.8%).

Balance: both participant cohorts exhibited marked enhancements in both static and dynamic equilibrium. Although improvements were evident in both groups, the flexible flatfeet group showed a more substantial gain in static balance, registering a 56% increase, as opposed to the 41.2% increase observed in the normal feet group. Similarly, the flexible flatfeet group demonstrated a slightly greater improvement in dynamic balance, with a 9.7% increase, compared to the 9.5% increase seen in the normal feet group.

Although both participant cohorts displayed notable enhancements across all assessed parameters, the extent of these improvements differed between the groups. These results imply that the intervention may have exerted a varying influence on motor function based on foot morphology (Table 4).

The Mann–Whitney U analysis (detailed in Table 4) revealed significant disparities between the flexible flatfeet and normal feet cohorts in the pre- and post-intervention measurements of abdominal and spinal extensor muscle stamina, as well as static equilibrium. The Mann–Whitney U test was selected for inter-group comparisons owing to the non-parametric distribution of data for these specific variables, as verified by the Shapiro–Wilk assessment. In the pre-intervention phase, abdominal muscle endurance in the normal feet cohort was observed to be 20% greater than that of the flexible flatfeet cohort, with a 16.6% difference noted post-intervention. Similarly, pre-intervention spinal extensor muscle stamina was 45% higher in the normal feet cohort compared to the flexible flatfeet cohort, decreasing to a 36% difference post-intervention. Regarding static equilibrium, the normal feet cohort exhibited a 53% advantage over the flexible flatfeet cohort pre-intervention, with this difference slightly diminishing to 50% post-intervention. A visual comparison of pre-test median scores between the groups is additionally presented in Fig. 4. The differences in the post-test median scores are also visualized in Fig. 5.

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Comparison of pre-test median scores for performance variables between the flexible flatfeet and normal feet groups.

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Comparison of post-test median scores for performance variables between the flexible flatfeet and normal feet groups.

However, to control for the significant baseline difference in BMI, linear regression analysis was performed on the post-intervention scores. In this analysis, the foot type variable was dummy-coded, with Normal Feet designated as 0 and Flexible Flatfeet as 1. The results showed a significant difference between the two groups in post-intervention abdominal muscle endurance (p < 0.05), spinal extensor stamina (p < 0.05), and static equilibrium (p < 0.05) even after accounting for the influence of BMI. Conversely, no significant between-group differences were observed in post-intervention FMS scores, dynamic equilibrium, or agility after controlling for BMI (p > 0.05) (Table 5).

In the flexible flatfeet group, spearman’s rank-order correlation was used to analyze the relationships between post-intervention FMS scores and core and back strength, agility, and dynamic and static balance. The data showed that the correlation coefficients for all these variables were not statistically significant (p > 0.05), indicating no significant relationship with FMS scores in this group. It must be noted that the post-hoc power analysis indicated the study was underpowered (power of 0.301) to detect a medium-sized correlation (ρ = 0.3) in this cohort, meaning that a moderate relationship cannot be definitively ruled out. To confirm the robustness of these findings, a bootstrapping analysis was performed with 1000 resamples. The results showed that 95% confidence intervals for all correlation coefficients included zero, further supporting the lack of a significant relationship between FMS and other performance metrics in this cohort. .

To address the potential for a Type II error due to the small sample size (n = 24), a post-hoc power analysis was conducted for the non-significant correlation findings. This analysis demonstrated that the study’s power to detect a medium-sized effect (ρ = 0.3) was 0.301, which is below the conventional threshold of 0.80. This suggests that the study was underpowered to find a medium correlation. However, the power to detect a large-sized effect (ρ = 0.5) was 0.729, which is considered sufficient. Therefore, while a strong, large correlation does not exist in this group, the absence of a medium or weak correlation cannot be definitively ruled out based on the current data (Table 6).

Table 6 The results of Spearman’s correlation between FMS and performance variables in the flexible flatfeet group.
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In the normal feet group, spearman’s rank-order correlation analysis revealed a significant positive correlation between FMS scores and core strength (ρ = 0.451, p < 0.05), static balance (ρ = 0.297, p < 0.05), and dynamic balance (ρ = 0.396, p < 0.05). Conversely, a significant negative correlation was found between FMS scores and agility (ρ = − 0.378, p < 0.05), suggesting that as agility increased (i.e., lower time scores), FMS scores also tended to increase (Table 7). A multiple linear regression was performed to determine the collective predictive value of core strength, agility, static balance, and dynamic balance on post-intervention FMS scores in the normal feet group. The model, which included these four variables, was statistically significant and explained a substantial portion of the variance in FMS scores (R2 = 0.320), f 4 = 7.64, p < 0.05). Specifically, the results indicated that core strength and dynamic balance were significant positive predictors of FMS scores. However, neither static balance nor agility significantly contributed to the model, suggesting that their predictive value for FMS scores is largely overshadowed by the other variables in the collective model. The regression coefficients for each predictor are presented in Table 8.

Table 7 The results of Spearman’s correlation between FMS and performance variables in the normal feet group.
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Table 8 Multiple Regression Analysis Predicting FMS Scores from Post-Intervention Performance Variables in the Normal Feet group.
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Discussion

This study found that calisthenics significantly improved agility, abdominal and spinal extensor muscle endurance, as well as static and dynamic balance in female students. Despite these positive effects of calisthenics on various fitness components, post-test results did not reveal a correlation between Functional Movement Screen (FMS) scores and these fitness parameters in the flexible flatfeet group.

Flexible flatfeet group

The study revealed significant improvements in Functional Movement Screen (FMS) scores among female students with flexible flatfeet following the calisthenics intervention. Given the complex kinetic chain reactions within the lower extremity, any structural impairment, such as flat feet, can lead to compensatory movements throughout the entire chain1. Calisthenics, involving multi-joint exercises that engage the entire body, likely promoted improved neuromuscular control and muscle activation, thereby enhancing the overall function of the lower kinetic chain, including the lumbopelvic region. Consequently, participants demonstrated improved performance on the FMS.

The beneficial impact of bodyweight training on core and back extensor muscle endurance in individuals with flatfeet observed in this investigation aligns with prior studies by Sakinah et al.48. The incorporation of exercises such as Russian twists and planks within calisthenics programs may be particularly beneficial for this population, given the potential biomechanical impairments associated with flatfeet49. These results suggest potential applications for the creation of targeted exercise interventions for individuals with flatfeet.

The findings of this study regarding the improvement in agility following calisthenics training in female students with flatfeet align with the results of Panihar and Rani50. The calisthenics program, which included exercises such as swings, twists, bends, push-ups, lunges, crunches, and mountain climbers, likely contributed to these improvements via neurological adjustments and heightened motor neuron activation, enhanced intermuscular coordination, and refined muscle activation sequencing29.

Furthermore, the current investigation revealed notable enhancements in both postural stability and movement control in female participants with flexible flatfeet following the calisthenics intervention. The ability to maintain balance on both stable and unstable surfaces requires dynamic control. In line with previous research by Lee and Choi, who found that activities focusing on the foot’s internal musculature and posterior tibialis resulted in greater improvements in dynamic balance compared to exercises targeting only the intrinsic foot muscles22, our findings suggest that the calisthenics program, which likely involved exercises that challenged balance and coordination, contributed to the observed improvements. Additionally, Sukprasert et al. reported that exercises targeting the posterior tibialis and fibularis longus muscle, integrated with brief foot maneuvers, improved posterior tibialis and peroneus longus muscle strength and dynamic balance in individuals with flatfeet51. The neural adaptations induced by calisthenics, involving improved neuromuscular control and motor output of the lower extremity, may have played a significant role in these improvements52.

Normal feet group

The observed improvements in Functional Movement Screen (FMS) scores among participants with normal foot arches align with the findings of Barcak and Buxton53,54. Previous studies have often employed corrective exercise interventions specifically targeting the movement deficits identified in the FMS55. However, the calisthenics program in this study likely challenged similar movement demands and stability requirements as those assessed in the FMS, such as through exercises like single-leg squats and lunges. This suggests that the improvements in FMS scores may be attributable to the generalized adaptations resulting from a comprehensive calisthenics program.

The findings of this study regarding the improvements in core and back extensor muscle stamina in female students with normal foot arches align with the results of Kojic et al.56. The enhanced core strength observed in this study can be attributed to the improved intramuscular and intermuscular coordination induced by whole-body calisthenics exercises57. Exercises such as lunges, squats, and burpees demand significant core stability, leading to adaptations in core muscle endurance.

The observed improvements in agility in female students with normal foot arches following the calisthenics intervention align with the findings of Panihar and Rani31. Sharrock and Cropper have previously demonstrated a direct correlation linking core stability and agility. The torso functions as the central link in the movement sequence, and improvements in core strength and endurance can lead to enhanced motor activation, neural adaptations, and coordination58. Thus, the calisthenics program, by challenging the core musculature, probably facilitated the noted enhancements in agility through improved neuromuscular control and functional efficiency.

The observed advancements in both postural stability and movement control within female participants with normal foot arches align with the findings of Mear et al. and Panihar and Rani31,59. The calisthenics program, encompassing a variety of exercises that activate multiple muscle groups, likely contributed to these improvements by enhancing proprioception and coordination. Additionally, the strengthening of the core musculature, which acts as the body’s central stability system, may have played a significant role in improving balance12.

Normal feet group vs. flexible flatfeet

While the calisthenics intervention improved agility, endurance, and balance in both groups, post-intervention FMS scores for strength and static balance were lessened in the flexible flatfoot population compared to the non-flatfoot population. Furthermore, our data showed that FMS scores could be predicted by core strength, agility, and balance in the non-flatfoot population (Table 6).

However, following the intervention, these relationships were not detected within the flexible flatfeet group (Table 6). These findings within the normal feet group aligned with Curbuz and Parpucu who highlighted the significance of trunk stabilization for movement functionality60. The core plays a crucial role in force transmission to the extremities during both fundamental and functional movements. Thus, even with good coordination, reduced core stability can negatively impact functional movement patterns. on the other hand, they failed to identify a link between FMS and movement equilibrium60, this variance could stem from the dissimilar populations studied. Our study included non-athletes, whereas their study focused on handball players. This suggests that in non-athletes, components like nimbleness and equilibrium might exert a greater influence on FMS performance, in addition to core strength.

The most significant finding of this study is the differential relationship between FMS scores and other performance variables in the flexible flatfeet and normal feet groups. While a clear correlation was observed in the normal feet cohort, these relationships were absent in the flexible flatfeet group, despite both groups showing marked improvements. This suggests that for individuals with flexible flatfeet, FMS may be measuring something fundamentally different.

Hypothesis 1 (compensatory movement strategy): It´s plausible that flatfoot morphology introduces a movement strategy that relies on compensatory patterns rather than true, fundamental movement proficiency61. In this scenario, improvements in isolated fitness components like core strength or balance may not directly translate to a higher FMS score because the underlying compensatory movement strategy remains unchanged. The FMS, therefore, may be capturing this unique “movement signature “that is decoupled from isolated measures of strength or balance.

Hypothesis 2 (measurement ceiling/floor effect): Alternatively, a “ceiling” or “floor” effect might be in play. For example, for example, those with a baseline FMS score already at the higher end of the scale may show smaller improvement, as noted by Clark et al.62, suggesting that even significant gains in strength or balance may not be enough to increase their FMS score further, as the screen´s limited scoring range could mask true gains in function that are only reflected in continuous variables (like strength or balance scores).

Several limitations should be considered when interpreting the findings of this study. The following structural and methodological constraints restrict the generalizability and definitive conclusions of our work:

  • Low Intervention Frequency and Lack of Control Group: The most significant structural limitation is the low intervention dosage and the absence of a true control group. The study relied on only a single weekly 90-min training session. While this frequency was implemented due to logistical constraints, it is highly unconventional for inducing optimal long-term neuromuscular adaptation for corrective purposes, meaning the observed improvements might be partly attributable to practice effects or maturation. This is compounded by the lack of a control group that did not participate in the exercise program, which prevents us from definitively isolating the effect of the intervention.

  • Unequal and small sample size The two groups were not equal in size, which limited the generalizability of the results, despite the use of statistical methods to adjust for unequal sample sizes. Furthermore, the small sample size in the flatfeet group (N = 24) resulted in low power for correlation analysis.

  • Baseline differences in BMI The significant baseline differences in BMI between the two groups could be a confounding factor. While we attempted to control for this in our linear regression analysis, its potential influence on our findings cannot be overlooked.

  • Homogeneous sample Our findings were utilized in a non-athletic sample of young females, which restricts the generalizability of our findings to other populations, such as athletes or older adults.

  • Absence of direct biomechanical measures A major limitation is the absence of objective biomechanical measures. We acknowledge that our study did not include metrics such as plantar pressure analysis, arch height measurements, or electromyography (EMG) of foot muscles. Therefore, our conclusions regarding the modification of flatfoot pathology or neuromechanical deficits are based on functional assessments rather than direct biomechanical evidence.

  • Absence of long-term follow-up Finally, the absence of long-term follow-up prevented us from assessing the durability of the observed improvements and the lasting impact of the intervention on the participants’ functional movement patterns.

Conclusion

This study concludes that calisthenics training appears to be a beneficial approach for enhancing functional movement, core strength, and balance in both individuals with normal feet and those with flexible flatfeet. However, the findings reveal a fundamentally different relationship between composite movement screening (FMS) scores and specific performance metrics in the flexible flatfeet group compared to the normal foot cohort. Specifically, the observed decoupling of FMS scores from isolated measures of strength and balance in the flatfeet group has significant clinical implications for rehabilitation, suggesting that FMS results in this population should not be interpreted as a direct reflection of underlying core strength or balance proficiency. Clinicians must, therefore, be cautious when using FMS as a primary determinant of functional capacity in individuals with flexible flatfeet, as it likely captures unique compensatory movement strategies.

To solidify these implications, future research is warranted and should utilize more robust methodologies, including: controlled designs (i.e., inclusion of a non-exercising control group), higher training frequency and larger sample sizes, and crucially, integrated biomechanical analysis (e.g., EMG and plantar pressure) to elucidate the underlying neuromuscular mechanisms responsible for this differential FMS relationship.