The effect of menstrual cycle on inter-joint coordination variability during roundhouse kicks in taekwondo

Abstract

Background

This study aimed to investigate the effect of the menstrual cycle on the coordination variability of the lower-limb joints during the taekwondo roundhouse kick in professional athletes.

Methods

Twenty professional taekwondo female athletes voluntarily participated in the study. The participants visited a laboratory thrice during their menstrual cycles’ follicular, ovulation, and luteal phases. The lower-extremity kinematic data were collected during the roundhouse kick. Range of motion (ROM) and coordination variability of the lower-extremity joints in sagittal plane were calculated and compared for different menstrual cycles.

Findings

The results did not show significant differences in the ROM of the joints for the different menstrual cycles. Moreover, the results of a vector analysis using the repeated measures ANOVA did not show significant differences in joint coordination patterns and variability for different menstrual cycles. However, there were fluctuations in the coordination variability during the ovulation phase in the hip–ankle coupling, but this was not statistically significant.

Interpretation

The results suggest that female taekwondo players must be cautious of training during the ovulation phases of their menstrual cycles. However, more research is needed to better understand the effect of menstrual cycle on the coordination patterns of joints and segments.

Introduction

Taekwondo, a globally recognized martial art and an official Olympic discipline, boasts a substantial following among millions of athletes worldwide [1]. Renowned for its dynamic kicking techniques, Taekwondo requires an optimal combination of strength, speed, endurance, balance, flexibility, and coordination [2]. Within Taekwondo practice and competition, a variety of maneuvers are executed against an opponent, with the roundhouse kick holding a prominent position [3]. Renowned for its versatility in both offensive and defensive strategies, the roundhouse kick is extensively utilized in sparring contests due to its rapid execution, scoring potential, and crucial role in competitive point scoring, contributing to approximately 89% of all points [4–10].

The roundhouse kick, typically initiated within the sagittal plane and concluding in the lateral plane, involves a sequence of coordinated movements, including flexion, internal rotation, abduction, and knee flexion and extension [10–12]. Over the past decade, research has delved into the biomechanics of this technique, analyzing aspects such as impact force dynamics [13, 14], target distance effects on movement timing and force [5, 15], muscle activation profiles [3, 8], kinematics, and more recently, coordination, and coordination variability [9, 10]16 – [19].

Coordination refers to the organization and control of body segments to achieve a specific movement goal. Coordination variability, on the other hand, captures natural fluctuations in these movement patterns and reflects the system’s capacity to adapt to task demands or environmental perturbations [20–23]. While stable coordination patterns can indicate consistent performance, variability in coordination is thought to play a dual role—offering flexibility to adapt or signaling instability depending on the context [20–23]. In this regard, angle/angle coupling analyses, such as those based on continuous relative phase (CRP) and continuous relative phase variability (CRPV), are valuable tools for assessing how two joints or segments interact dynamically. These methods not only reveal patterns of inter-joint coordination but also provide insight into how variability in these patterns may enhance or compromise performance and injury risk.

The significance of coordination and coordination variability is particularly pronounced in dynamic sports like Taekwondo, where precise inter-joint synchronization is vital for executing complex techniques. Studies have shown that variability is often altered in injured versus uninjured individuals, where either excessive or diminished variability may increase the likelihood of injury [21, 23–25]. Within Taekwondo, researchers have examined coordination patterns under various conditions, such as different kicking styles [10], stances [17], and jump variations [19]. However, the relationship between menstrual cycle phases and coordination variability during Taekwondo kicks remains unexplored.

A notable physiological distinction between men and women is the menstrual cycle, a recurring process spanning an average of 28 days, with a typical range of ± 3 days, and lasting approximately 30 to 35 years in a woman’s life [26]. Menstrual cycle phases, characterized by fluctuations in estrogen and progesterone levels, are known to influence various physiological, biomechanical, and neuromuscular parameters [26, 27]. The cycle comprises three primary phases: the follicular phase (days 1–13), marked by rising estrogen and low progesterone levels; the ovulatory phase (days 13–15), where estrogen peaks; and the luteal phase (days 15–28), characterized by elevated progesterone and moderate estrogen levels [28–31]. These hormonal variations have been associated with changes in knee joint laxity, balance, and neuromuscular control. For instance, increased knee valgus angles have been observed during the late follicular phase due to elevated estradiol levels [28], while heightened knee laxity has been reported during the ovulation phase compared to the luteal phase [31, 32].

Although existing literature highlights hormonal influences on female movement biomechanics, findings remain inconsistent. Some studies suggest that menstrual cycle phases significantly impact athletic performance and injury risk [28, 29]31 – [34], while others report negligible effects [26, 35]. Notably, most studies employ linear methodologies, which may not fully capture the dynamic nature of movements, particularly in sports like Taekwondo. Nonlinear approaches, such as the analysis of coordination variability, could offer deeper insights into how hormonal fluctuations during the menstrual cycle affect joint coordination and movement adaptability [10, 17, 23, 36].

Considering the high prevalence of lower-extremity injuries in Taekwondo, which account for 54.7% of all injuries and are notably higher in women compared to men [37–41], understanding these dynamics is crucial. Hormonal fluctuations during the menstrual cycle may affect joint stability, coordination, and variability, potentially altering movement biomechanics and influencing injury risk. Thus, this study aims to investigate how menstrual cycle phases impact inter-joint coordination variability during the execution of the roundhouse kick in Taekwondo. We hypothesize that: (1) the range of motion in lower-extremity joints differs in different menstrual cycles, (2) inter-joint coordination patterns during roundhouse kick are different for different menstrual cycles, and (3) inter-joint coordination variability during roundhouse kick decreases during the ovulation phase, and increases in the follicular and luteal phases.

Methods

Participants

Twenty professional taekwondo female players with regular menstrual cycles (28–31 days) voluntarily participated in this study from 20 May 5/2022 to 20 July 2022 based on a statistical power of 95% and an effect size of 0.70 (age: 18.25 ± 3.69 years, mass: 52.700 ± 3.66 kg, and height: 169.37 ± 5.75 cm). For the purposes of this study, “professional” taekwondo players are defined as athletes who actively compete at the national level and receive systematic training under the guidance of certified coaches. This classification includes individuals who participate in elite national competitions. The inclusion criteria were as follows: (1) female Taekwondo athletes aged between 18 and 25 years, (2) a minimum of five years of competitive Taekwondo experience, (3) regular participation in Taekwondo training sessions at least three times a week, and (4) self-reported regular menstrual cycles (average length of 28 ± 3 days). The exclusion criteria included: (1) any history of lower extremity musculoskeletal injuries in the last six months, (2) any medical conditions that might affect movement performance, and (3) use of hormonal contraceptives or medications that could influence the menstrual cycle. All participants had no injury in their lower limbs and had not used hormonal contraceptives for at least six months before the testing. Menstrual cycle information was recorded for each participant before the main test. The menstrual cycle of each participant was defined and tested during three different menstrual phases. First, the follicular phase occurred between the 1st and 3rd days of the bleeding; second, the ovulatory phase occurred between the 13th and 15th days; and third, the luteal phase occurred between the 21st and 23rd days. Each participant was asked to visit the laboratory on a given day. This study was performed following the Helsinki declaration. All participants signed an informed consent form, and the research protocol and details were approved by the Institutional Review Board of the Sport Science Research Institute (IR.SSRI.REC.1401.1572). All experiments were performed in accordance with relevant guidelines and regulations.

Experimental setup and data collection

An eight-camera motion capture system (Vero 2.2, VICON, Oxford, UK) was used to record the kinematic data. After five minutes of warm-up, 16 reflective markers were placed on participants lower extremities based on Plug-in-Gait model. The participants stood in an anatomical position to record the static test. They were positioned barefoot in the middle of the calibration area. A target was placed at the distance of the lower-limb length of each participant in order to perform a roundhouse kick. The height of the target was individualized for each participant. The target was adjusted to match the participant’s waist level to ensure consistent conditions across all participants. Each participant performed nine roundhouse kicks in three phases of the menstrual cycle, and kinematic data were recorded at a sampling rate of 240 Hz during the roundhouse kicks. The speed of the kick was self-selected by each athlete to reflect their natural and comfortable kicking speed during performance.

Data processing and calculations

Marker data were low-pass filtered by zero-lag Butterworth filtering with a cut-off of 6 Hz and then labelled and gap filled. The angles and angular velocities of the lower-limb joints were then calculated. The processing was performed using the Nexus 2.4.2 software (VICON, Oxford, UK), and the kinematic data were analyzed by the MATLAB R2015a software (The Math Works, Natick, MA, USA). To ensure natural movement execution and avoid imposing artificial constraints on kicking velocity, we instructed the athletes to perform the roundhouse kick at a self-selected speed. This approach aligns with previous biomechanical studies that emphasize the importance of allowing participants to execute movements in a natural and unconstrained manner to maintain ecological validity. After data collection, each kick was separated by the Z-coordinate (superior–inferior) of the lateral malleolus marker. we standardized the kicking cycles by interpolating all data points to 100 frames, ensuring consistency across participants and facilitating meaningful comparisons Each kicking was divided into four phases: the swing phase (the time from lifting the leg to maximum knee bending; 0–25%), the impact target phase (the time of maximum knee bending to the impact moment [maximum knee extension]; 26–50%), kicking return phase (the time from kicking the target to the return of maximum knee bending; 51–75%), and putting leg down (the time from maximum knee bending to putting leg down; 76–100%). Nine continuous kicking cycles from the kicking leg in each menstrual cycle were chosen to calculate the coordination and coordination variability. In our study, kicking leg was defined based on the athletes’ self-reported preferred kicking leg. Based on previous studies, the continuous relative phase (CRP) and CRP variability (CRPV) were used to calculate the joint coordination and coordination variability, respectively. The calculations were reported previously [20, 22, 42].

The CRP angles were calculated for three couplings of hip flexion/extension–knee flexion/extension (hip FL/EX–knee FL/EX), hip flexion/extension–ankle plantarflexion/dorsiflexion (hip FL/EX–ankle PF/DF), and knee flexion/extension–ankle plantarflexion/dorsiflexion (knee FL/EX–ankle PF/DF). The CRPV was calculated as the between-kicking cycle standard deviation of the CRP data points in all trials. This study utilized CRP method to measure the coordination and variability of lower-extremity joints. CRP is a biomechanical method for analyzing the relative timing and phasing of two oscillatory movements. when the CRP angle is 0°, the two oscillators (in this case two joints) are perfectly in-phase, meaning they move in the same direction (e.g., both rotating clockwise or counterclockwise). A CRP angle of 180° indicates that the joints are perfectly antiphase, meaning they move in opposite directions (e.g., one joint rotates clockwise while the other rotates counterclockwise). Any CRP value between 0° and 180° represents an out-of-phase relationship: movements closer to 0° are relatively in-phase, while those closer to 180° are relatively antiphase. Additionally, the sign of the relative phase values provides further insight into the coordination dynamics. Positive relative phase values indicate that the distal segment is ahead of the proximal segment in phase space, while negative relative phase values indicate that the proximal segment is ahead. The slope of the relative phase curve reveals movement speed: a positive slope shows the distal segment moves faster, while a negative slope indicates the proximal segment moves faster. Local minima and maxima in the curve mark transitions or changes in coordination dynamics during the movement [43, 44].

In this study, we calculated the ROM of the lower limb joints primarily in the sagittal plane due to limitations in the data collection methods. Specifically, we used the plug-in gait model for lower extremity markers, which does not provide accurate kinematic analysis in the coronal and transverse planes during roundhouse kicks in taekwondo, given the complexity of this movement. Nonetheless, ROM in the coronal and transverse planes offers valuable insights, and future studies could expand this analysis by incorporating ROM data from all three planes to achieve a more comprehensive assessment. The hip, knee, and ankle joints angle in sagittal plane in kicking leg are presented in Fig. 1.

Fig. 1.

Hip, knee, and ankle joints angle in sagittal plane in kicking leg

Statistical analysis

The joint ROM was analyzed using repeated-measures ANOVA in SPSS (IBM SPSS Statistics 22, SPSS Inc., Chicago, IL). Before conducting the repeated-measures ANOVA, the data were tested for normality using the Shapiro-Wilk test for each dependent variable. The results indicated that all joint ROM followed a normal distribution (p˃0.05). These results confirmed that the data met the assumptions required for repeated-measures ANOVA (The effect sizes were reported using Partial Eta Squared (η²p)). One-dimensional statistical parametric mapping (SPM) one-way repeated-measures ANOVA was used to compare the CRP and CRPV in the three menstrual cycle’s phases. Before performing the SPM1d analysis, the Shapiro-Wilk test was conducted to assess the normality of the time-averaged data. Additionally, the homogeneity of variance across conditions was evaluated to ensure the assumptions of the analysis were met. Furthermore, the smoothness of the time-series data was examined to confirm compliance with the random field theory assumptions underlying SPM1d. Alpha set at 0.05 for statistical significance level, and all SPM analyses were performed using the open source spm1d code (v.M0.1, www.spm1d.org) in MATLAB R2015a software (The Math Works, Natick, MA, USA).

Results

The results of the one-way repeated-measures ANOVA did not show significant differences in joint ROM for the three menstrual cycles (p > 0.05). The hip, knee, and ankle ROMs in sagittal plane during the three menstrual cycles are presented in Table 1.

Table 1.

Hip, knee, and ankle ROM in sagittal plane during the roundhouse kick of Taekwondo in three menstrual phases

Joint	Movement	Follicular phase	Ovulation phase	Luteal phase	P-value	F	Effect size (η²p)
Hip	Flexion/Extension	48.84 ± 5.03	49.76 ± 9.83	52.83 ± 11.22	0.63	2.013	0.223
Knee	Flexion/Extension	74.76 ± 12.38	77.71 ± 14.01	68.84 ± 24.45	0.81	0.205	0.028
Ankle	Plantar/Dorsi Flexion	40.84 ± 10.56	44.86 ± 13.61	43.86 ± 15.88	0.91	0.871	0.111

The results of the vector analysis using one-way repeated-measure ANOVA in SPM did not show significant differences with respect to all the calculated CRPs (Figs. 2a and 3a, and 4a) and CRPVs (Figs. 2b and 3b, and 4b) during the three phases of the menstrual cycle (P > 0.05).

Fig. 2.

Hip FL/EX–knee FL/EX (a) CRP and (b) CRPV in different phases of the menstrual cycle

Fig. 3.

A. Hip FL/EX–ankle PF/DF (a) CRP and (b) CRPV in different phases of the menstrual cycle

Fig. 4.

Knee FL/EX–ankle PF/DF (a) CRP and (b) CRPV (b) in different phases of the menstrual cycle

Discussion

This study aimed to examine the effect of the menstrual cycle on inter-joint coordination variability of the lower extremities during a roundhouse kick in taekwondo. Our results showed that the ROM in the hip, knee, and ankle joints did not vary significantly between the three menstrual cycle phases, thereby rejecting our first hypothesis. However, we observed slight increases in knee flexion/extension and ankle plantar/dorsiflexion during the ovulation phase (Table 1). While these findings are non-significant, they should be interpreted with caution, as the observed differences may be due to chance, particularly given the limited sample size. These variations do not necessarily indicate a higher risk of acute injuries to the knee and ankle during the ovulation phase, although they may suggest a potential association.

Previous studies have examined the effects of the menstrual cycle on knee-joint laxity, which refers to the passive motion or looseness of the knee joint [31, 32]45 – [47], as well as ACL injury risk [28, 45, 48, 49] and knee valgus [28, 50], with some suggesting correlations with changes in the knee joint loads [24]. Although our study did not directly assess these variables and focused instead on the ROM of the lower extremity joints during the roundhouse kick- a measure of functional joint mobility rather than ligamentous laxity- our findings on ROM provide complementary insights in the mechanics of joint movement. Furthermore, Beynnon et al. (2005) [51] and Hoffman 2008 [52] reported no significant changes in knee-joint laxity across the menstrual cycle, findings that align partially with our observations. These mixed results highlight the complexity of the interplay between menstrual cycle phases, joint mechanics, and potential injury risk warranting further investigation with more specific analyses.

According to our results, the different phases of the menstrual cycle did not affect the coordination patterns of the lower-extremity joints statistically. The results of our study did not confirm our second hypothesis. The results showed that taekwondo players have an out-of-phase coupling pattern with knee dominancy in hip FL/EX–knee FL/EX (Fig. 2a) at the moment of the impact. Moreover, a negative slope in the hip–knee coupling (Fig. 2a) at the moment of impact indicates an increase in the velocity of the knee relative to the hip. It is based on the law of conservation of angular momentum and the fact that the knee joint has a higher angular velocity than the hip at the moment of impact [11, 18]. Estevan et al. (2015) observed that the proximal segment accelerated, while the distal segment lagged behind during the first phase of the kick, and the proximal segment decelerated, while the distal segment accelerated during the second phase of the kick [9]. Our results for hip–knee coupling (Fig. 2a) also demonstrated the dominance of hip speed during the swing phase and the dominance of knee speed during the impact phase and at the moment of impact. According to a study by Kim (2011), the hip and knee joints are in the same direction at the moment of impact when performing a roundhouse kick [10]. However, we examined the hip–knee coupling in sagittal plane and found out-of-phase coupling pattern in hip FL/EX–knee FL/EX. The difference in the method of calculating the coordination is possibly a reason for the difference between the results.

The hip FL/EX–ankle PF/DF coupling pattern was out of phase with ankle dominance (Fig. 3a) at the moment of impact. The knee FL/EX–ankle PF/DF coupling pattern was in phase with knee dominance (Fig. 4a) at the moment of impact as the velocity in the knee joint was higher than in the ankle; however, in studies on segments, the speed of the foot in the three planes was faster than that of the shank and thigh [9]. In addition, we observed fluctuations in the coordination pattern shortly after the moment of impact, possibly due to a change in the dominant joint.

Coordination variability in different phases of the menstrual cycle was not significantly different, and the third hypothesis was not confirmed. Our findings showed that CRPV was increased in the luteal phase in the hip FL/EX–knee FL/EX coupling (Fig. 2b); this increase could potentially enhance athletic performance by providing the flexibility required to adapt to perturbations or constraints, as suggested in studies on individuals without injuries [17, 22, 47]. Increased variability has been linked to the ability to adapt to changing movement demands or environmental constraints [17, 47]. In contrast, the CRPV decreased in the hip FL/EX–ankle PF/DF coupling during the ovulation phase (Fig. 3b). While this reduction in CRPV could potentially reflect changes in joint stability [40], caution is warranted in interpreting this result, as the differences were not statistically significant. Changes in CRPV may be associated with increased estrogen levels during ovulation, as estrogen broadly influences the development of bones, muscles, and connective tissue [33, 53]. Estrogen receptors are present in human connective tissues, including the ACL, muscle, pelvic ligament, and ankle. Fluctuations in sex hormones could theoretically influence dynamic joint movements, although this study did not directly measure such effects. Another possible explanation for observed changes is increased joint laxity during the evolution phase, as suggested in previous literature [32]. However, our study did not directly assess joint laxity, and this remains a speculative explanation that requires further investigation.

A decrease in coordination variability was also observed in the knee FL/EX–ankle PF/DF coupling across all three menstrual cycle phases at the moment of impact (Fig. 4b). While reduced CRPV has been linked to an increased risk of overuse injuries in activities like running [25, 54], the current findings should not be interpreted as evidence of increased injury risk. Given the absence of statistical significance and the exploratory nature of this study, these observations should be viewed as preliminary and interpreted cautiously. Future studies with larger sample sizes and more direct injury-related metrics are needed to further investigate the potential implications of reduced coordination variability.

Study limitations

Our conclusions should be interpreted in light of the following limitations. First, the study included only twenty-two taekwondo players, and two participants were unable to complete all experiments due to unforeseen circumstances. A larger sample size would enhance the statistical power of the findings and provide more generalizable results. Second, we did not utilize hormonal assays, such as blood sampling, to determine the concentration of sex hormones. Instead, menstrual cycle phases were classified based solely on self-reported cycle days. While this approach is commonly used in similar studies, hormonal assays could provide a more accurate and objective confirmation of menstrual cycle phases, reducing the potential for misclassification due to variations in individual cycle lengths or hormonal profiles. Future studies should incorporate hormonal testing to strengthen the reliability of phase classification. Third, we acknowledge the absence of balance assessments, joint range of motion tests, and clinical knee stability tests in each menstrual cycle phase as a limitation of this study. Our primary focus was on examining inter-joint coordination variability during the roundhouse kick in Taekwondo athletes. Future research incorporating these additional assessments could provide a more comprehensive understanding of the effects of menstrual cycle phases on movement mechanics and injury susceptibility.

Conclusions

Based on the findings of this study, we did not observe statistically significant differences in the coordination patterns or coordination variability of lower-extremity joints across the three phases of the menstrual cycle. While trends in coordination variability were noted, particularly during the ovulation phase, these findings were not statistically significant and should be interpreted with caution. These results highlight the need for further research to explore the potential influence of the menstrual cycle on joint and segment coordination using larger sample sizes and more robust methodologies, such as hormonal assays for precise phase determination. Female taekwondo players may benefit from monitoring their training and performance during the ovulation phase, but further evidence is required to establish definitive recommendations.

Abbreviations

ROM

Range of Motion

CRP

Continuous Relative Phase

CRPV

Continuous Relative Phase Variability

SPM

Statistical Parametric Mapping

ACL

Anterior Cruciate Ligament

PF/DF

Plantarflexion/Dorsiflexion

FL/EX

Flexion/Extension

η²p

Partial Eta Squared

3D

Three-Dimensional

hip FL/EX–knee FL/EX

hip flexion/extension-knee flexion/extension

hip FL/EX–ankle PF/DF

hip flexion/extension-ankle plantarflexion/dorsiflexion

knee FL/EX–ankle PF/DF

knee flexion/extension-ankle plantarflexion/dorsiflexion

Author contributions

S.S.S., A.A., M.K.T., Z.S., conducted the study design, measurement procedure, and data analysis. S.S.S., A.A. have contributed original organization of the manuscript literature. S.S.S., A.A., M.K.T., Z.H., and Z.S. participated in the discussions about the clinical issues and proofreading and contributed to the right interpretation of the clinical studies from the literature. All authors read and approved the final version of the manuscript.

Funding

There is no funding source regarding this research to declare.

Data availability

Data would be available on a request from corresponding author.

Declarations

Ethics approval and consent to participate

This study was performed following the Helsinki declaration. All participants signed an informed consent form, and the research protocol and details were approved by the Institutional Review Board of the Sport Science Research Institute (IR.SSRI.REC.1401.1572). All experiments were performed in accordance with relevant guidelines and regulations.

Consent for publication

The authors declare their consent for publication of this research article in BMC Women’s Health.

Competing interests

The authors declare no competing interests.