Breast Support Requirements for Badminton Players to Minimize Breast Movement

Abstract

Exercise-induced breast pain may be caused by excessive breast movement, which can negatively affect athletic performance. As a common asymmetric exercise, playing badminton may produce different breast motion and require different breast support from symmetric exercise such as running. This study aimed to characterize breast displacement during two typical badminton movements and determine breast support requirements for playing badminton. Three-dimensional displacement of left and right breasts for female participants (75B, Chinese bra sizing) was calculated. Breast displacement on the hitting side was significantly greater than that on the other side. Trunk rotation and breast displacement during forehand stroke were greater than that during side-hand stroke. Breast displacement was predominantly mediolateral during forehand strokes. Findings suggest that further research is required to focus on mediolateral breast displacement during badminton forehand strokes. The present findings will be useful for controlling breast motion during playing badminton and in turn avoiding exercised-induced breast pain.

Keywords

Asymmetric Exercise Breast Motion Breast Pain Playing Badminton Sports Bra

Introduction

Wearing a high quality of sports bra is an appropriate way to provide firm breast support effectively, based upon the reduction of exercise-induced breast motion and pain,^1–4 and the improvements in female athletes’ performance and breast comfort.^5,6 The majority of published literature investigating breast motion and comfort has been conducted during symmetric exercise, including treadmill running,^1,7–9 deep water running,⁷ front crawl,¹⁰ breaststrokes swimming,¹⁰ horse riding¹¹ and two-step star jumping.¹² These findings have significantly optimized bra design for symmetric exercise. However, breast motion and discomfort during asymmetric movements have been neglected. One previously published research has examined breast motion during agility tasks that required participants to run along the shape of a T, to explore three-dimensional breast displacement, velocity, and acceleration. The T-shaped movement routes involved in the experiment were asymmetric, potentially generating asymmetric postures, but the running itself was still a regular symmetric movement.¹³

Many forms of exercise in daily life are asymmetric, including playing badminton, table tennis, basketball, golf, and so on. As trunk motion has been previously reported as a driving force of breast motion, asymmetric trunk motion in asymmetric exercise may induce different breast motion from symmetric exercise. The difference in trunk motion between symmetric exercise and asymmetric exercise was also reflected in the rotation angle of the trunk. Previous research has measured trunk rotation during badminton to be 46.9 ± 11.2° for skilled players and 36.7 ± 8.2° for novice players,¹⁴ which are both greater than trunk rotation measured in running (measured to be 30.75 ± 4.05°).¹⁵ Breast movement induced by trunk rotation could therefore be greater in badminton compared to running. Even a novice badminton player’s trunk rotation angle was greater than that of a runner. This means that existing sports bras designed based on breast biomechanics data during running may not fulfill the requirements of female badminton players.

Playing badminton is one of the most popular sports in the world, with 200 million adherents.¹⁶ However, competitive badminton players are prone to overuse injuries of the upper limb, axial skeleton, and lower limb.¹⁷ Repetitive overhead forehand and backhand strokes are executed with a very short hitting action, applying excessive stress on the upper extremity.¹⁷ Breast motion has also been associated with upper limb muscle activity,¹⁸ as increased upper body extremity velocities and ranges of motion could elicit greater magnitudes of breast movements. Therefore, excessive movement on the upper limb during playing badminton may also cause increased breast motion and potential exercise-induced breast pain. A sports bra designed for badminton based on breast kinematic data can help limit excessive breast motion and prevent the risk of breast injury.

The overhead forehand strokes and side-hand strokes were selected as two typical badminton movements for this research, as they are the most common and frequently investigated movements in previous research.^19,20 These two movements require the badminton player to serve vigorously, with a large amplitude of movement and a large radius of swing, which generates a great force at the moment of hitting to ensure that the shuttle cock has enough power to fly both high and far.²¹

The aim of the current investigation was to quantify the difference in three-dimensional breast displacement between two typical badminton movements, to compare the breast displacement in no bra condition and sports bra condition, and to assess the breast displacement in three directions. It was hypothesized that there would be

trunk rotation during forehand strokes is different from that during side-hand strokes; and

greater trunk rotation results in greater breast displacement.

Methods

Following institutional ethical approval, seven female volunteers (age = 23.0 ± 4.7 years, body mass = 56.5 ± 4.6 kg, height = 166.2 ± 2.4 cm) were selected to take part in this study. The participants were recruited through campus campaigns and leaflets. Participants were selected if they had experienced no surgical procedures to the breasts, had not gone through pregnancy within the last year, and were a China 75B breast size, as the average breast size of Chinese women is 75B. B-cup women experience breast discomfort during exercise.²² All participants gave written informed consent to participate. Participants in this experiment were amateurs.

The participants’ breast size was measured by a trained bra fitter. The participants stood bra-less with their arms relaxed by their side. The lower bust girth was measured underneath the breasts. The bust girth was determined with a girth measurement taken over the fullest part of the breast. The cup size was determined by subtracting the lower bust from the bust size. Two kinds of breast support conditions were used in this experiment, namely bare-breasted and wearing sports bra (Daskin brand of Li Ning Company, China) conditions (Figure 1).

Figure 1.

The design of the sports bra. The sports bra was composed of a cup cushion. (a) The design of the sports bra and (b) the design of the cup cushion. The whole shape of the cup cushion is a water drop. The cup cushion is thinner at the top and thicker at the bottom, so it can support the breasts better.

Participants completed a warm-up using their own bras, playing forehand and side-hand strokes (Figure 2) for 5 min each against another badminton player. This kind of familiarization period ensured that participants were comfortable with exercise activities and were performing them correctly, thus guaranteeing the accuracy of the two typical badminton movements. All participants held the racket in their right hand, and then the right side was defined as the “hitting side.” Following the familiarization, the bra was removed and five infrared light-emitting diodes markers were attached with hypoallergenic skin tape to the P₁, P₂ and P₃, P₄ and P₅ (Figure 3; P4 and P5 were on the nipple for the bare-breasted condition). During the sports bra condition, markers were repositioned on the bra, over the nipple. After each forehand stroke and side-hand stroke, participants were asked to rate their perceived breast motion and breast discomfort using a visual analog scale (from 0 to 10), with 0 indicating no movement or discomfort, and 10 indicating extreme movement or discomfort. The participants were all right-handed.

Figure 2.

Two typical badminton movements. There was no landing phase but a tiptoe phase during playing badminton forehand strokes in this study. (a) Forehand stroke and (b) side-hand stroke.

Figure 3.

Markers’ positions. P₁ was on the sternal notch, P₂ was 4 cm down from P₁ and 1 cm to the left, P₃ was 4 cm down from P₁ and 1 cm to the right, P₄ and P₅ were on the left and right nipples.

A shuttle cock was suspended by a rope at a fixed point on the ceiling in front of the participants, and the height of the shuttle cock was adjusted according to the adaptive height of each participant (Figure 4) to ensure the subjects were comfortable and hit the ball accurately. Following this, the participants swung the racket in a standard position (Figure 2) and hit the shuttle cock up to the ceiling. At the same time, the decibel detector (version1.3.0, Beijing Anecdote Society Technology Co. Ltd, China) monitored the maximum sounds during each hitting process. Racketing with a maximum sound less than 60 dB was excluded. The maximum sounds in the final results range from 62.5 to 69.8 dB, which were are comparable with the maximum sound (64 dB on average) measured outdoors. This part of the process is to maximize the consistency and repeatability of each badminton movement of the participants.

Figure 4.

Position diagram in the experiment.

Marker coordinates were recorded during two typical badminton movements. Three-dimensional displacements of the markers were tracked using two infrared tracking systems with six cameras sampling at 200 Hz (Optotrak Investigator, NDI, Canada), positioned in an arc in front of the participants. Data were collected for 3 s during playing two typical badminton movements. The laboratory coordinates systems during playing badminton identified x as mediolateral (m/l), y as the line of progression (a/p), and z as vertical (Figure 5).

Figure 5.

Axes were established using the right-hand screw rule. Point A was processed as point A′, to make the Z-axis of the trunk coordinate system consistent with the trunk segment vertical axis of the human body. Vectors X, Y, Z were perpendicular to each other.

Markers were identified and 3-D data were exported into Microsoft Excel 97-2003 (Excel, Microsoft, USA). The Cartesian x, y, and z coordinates for the five markers were exported into Microsoft Excel 97-2003 (Excel, Microsoft, USA). To establish relative breast movement independent to the motion of the trunk, a local coordinate system converted absolute breast coordinates to relative coordinates using a transformation code. Point A was processed as point A′ by running the code using python (version 3.9.6, Google, Netherlands), to make the Z′-axis of the trunk coordinate system consistent with the trunk segment vertical axis of the human body. Vectors X′, Y′, Z′ were perpendicular to each other (Figure 5).

The distribution of breast displacement in three directions was determined by the ratio of the displacement in each direction to the total displacement in three directions. Trunk rotation of each test was calculated by the max change of the angle between the projection of P₃P₂ vector in the xOy plane (Figure 5) and X axis. Trunk rotation was averaged during playing forehand strokes and side-hand strokes in each bra condition.

Playing badminton is an asymmetric motion; therefore, three-dimensional displacements of the left and right breasts were analyzed separately below. Vertical, m/l, and a/p relative displacement of the breast were then calculated during playing two typical badminton movements. Overall breast displacement in each plane was calculated by adding the left and right breast displacement together. The distribution of all data was checked for normality using the Kolmogorov–Smirnov. As it does not conform to the normal distribution, the Wilcoxon test was conducted for the non-parametric difference between forehand and side-hand strokes and between two breast support conditions. As it conforms to a normal distribution, one-way ANOVA and a paired sample t-test were used to determine the difference between three directions to the left breast and the right breast. An alpha level of 0.05 was adopted. All statistical analyses were completed using SPSS for Windows software (Version 21.0, SPSS Inc, Chicago, USA).

Results

Trunk Rotation During Forehand Strokesand Side-hand Strokes

The angle of trunk rotation during badminton forehand strokes was 34.0 ± 6.7° in the no bra condition and 16.6 ± 5.2° in the sports bra condition. Trunk rotation measured during side-hand strokes was 27.9 ± 9.6° in the no bra condition and 20.5 ± 11.5° in sports bra condition. Trunk rotation was significantly greater in no bra condition compared to the sports bra condition during forehand strokes (t = 5.353, p = 0.002). There was no significant difference between forehand strokes and side-hand strokes in trunk rotation in the no bra condition (t = 1.291, p = 0.244) and the sports bra condition (t = −1.197, p = 0.276).

Trunk rotation refers to the angle of rotation of the trunk around the z-axis. The angle of trunk rotation is calculated the same for forehand and side-hand strokes:

\vec{u} = (x_{4} - x_{3}, y_{4} - y_{3}, z_{4} - z_{3})

(1)

\vec{u^{'}} = (x_{i} - x_{i - 1}, y_{i} - y_{i - 1}, z_{4} - z_{3})

(2)

\cos θ = \frac{x_{1} x_{2} + y_{1} y_{2} + z_{1} z_{2}}{\sqrt{x_{1}^{2} + y_{1}^{2} + z_{1}^{2} * \sqrt{x_{2}^{2} + y_{2}^{2} + z_{2}^{2}}}}

(3)

\begin{matrix} α = θ_{\max} - θ_{\min} \end{matrix}

(4)

where x₄, x₃, y₄, y₃, z₄, z₃ are the 3D coordinates of the marker points P₂ and P₃ in the laboratory coordinate system, respectively; x_i, x_i−1, y_i, y_i−1 are the x- and y-axis coordinates of P₂ and P₃ in the i-th row of data collected, respectively; x₁ = x₄₋x₃, x₂ = $x_{i}$ − $x_{i - 1}$ , y₁ = y₄₋y₃, y₂ = $y_{i}$ − $y_{i - 1}$ , z₁ = z₄₋z₃, z₂ = z₄₋z₃; $\vec{u}$ is the initial vector of the first row of data; $\vec{u^{'}}$ is the projection vector of each row of data; $\cos θ$ is the cosine of the angle between the projection vector and the initial vector of each row of data; and α is the angle of trunk rotation around the z-axis.

Breast Displacement During the Forehand Strokes and Side-hand Strokes

Greater breast displacement was found during forehand strokes than during side-hand strokes in the bare-breasted condition irrespective the left breast and the right breast (Figure 6). However, no significant difference was found in three-dimensional breast displacement between forehand strokes and side-strokes in the sports bra condition (Figure 6). There were significant differences between the forehand strokes and side-hand strokes in m/l (Z = −2.023, p = 0.043) and vertical breast displacement (Z = −2.023, p = 0.043) for the left breast and m/l breast displacement (Z = −2.023, p = 0.043) for the right breast in the bare-breasted condition. It can be seen that the maximum breast displacement value was 47.2 mm during the forehand strokes in the no bra condition in m/l direction for the right breast, while the minimum breast displacement value was only 7.2 mm during side-strokes in the sports bra condition in the vertical direction for the left breast (Figure 6). In the no bra condition, overall breast displacement for the right breast was 20.4 mm greater than that for the left breast during forehand strokes (Z = −2.023, p = 0.043) and 21.6 mm greater during side-hand strokes (Z = −2.023, p = 0.043). In the sports bra condition, displacement for the right breast was 12.4 mm greater during forehand strokes (Z = −2.023, p = 0.043) and 12.3 mm during side-hand strokes (Z = −2.023, p = 0.043). There exists no significant difference in three-dimensional breast displacement between forehand strokes and side-strokes in sports bra condition.

Figure 6.

Breast displacement during the forehand stroke and side-hand stroke: (a) no bra condition and (b) sports bra condition. “*” means significant difference. “XL” means m/l breast displacement for the left breast, “YL” means a/p breast displacement for the left breast, “ZL” means vertical breast displacement for the left breast, “XR” means m/l breast displacement for the right breast, “YR” means a/p breast displacement for the right breast, “ZR” means vertical breast displacement for the right breast, “Rela” means relative breast displacement. All participants held the racket bat in their right hand.

Breast Displacement in Two Breast Support Conditions

The maximum difference was found in mediolateral direction of the right breast, with a maximum value of 15.1 mm during the forehand strokes (Figure 7). For the left breast, significant less breast displacement existed in the vertical direction (Z = −2.023, p = 0.043) during forehand strokes and in a/p direction (Z = −2.023, p = 0.043) during side-hand strokes in the sports bra condition compared to the no bra condition. For the right breast, significant less breast displacement was found in the m/l direction (Z = −2.023, p = 0.043) during forehand strokes in the sports bra condition compared to the no bra condition.

Figure 7.

Breast displacement in two support conditions: (a) forehand stroke and (b) side-hand stroke. “XL” means m/l breast displacement for the left breast, “YL” means a/p breast displacement for the left breast, “ZL” means vertical breast displacement for the left breast, “XR” means m/l breast displacement for the right breast, “YR” means a/p breast displacement for the right breast, “ZR” means vertical breast displacement for the right breast, “Rela” means relative breast displacement. All participants held the racket in their right hand.

Breast Displacement in Three Directions

Distribution of Breast Displacement

Breast displacement was predominantly mediolateral during both forehand strokes and side-hand strokes (Figure 8). In the no bra condition, the distribution of mediolateral left and right breast displacement was greater during the forehand strokes (50.7%) than that during the side-hand strokes (41.9%), while the distribution of vertical displacement remained similar during two badminton movements (21.1% for forehand strokes vs 23.8% for side strokes). However, the distribution of anterioposterior breast displacement was increased from 28.3% during the forehand strokes to 34.3% during the side-hand strokes (Table 1). In the sports bra condition, breast displacement demonstrated a similar distribution of vertical (forehand strokes: 24.1%; side-hand strokes: 25.8%), m/l (forehand strokes: 47.7%; side-hand strokes: 42.6%), and a/p (forehand strokes: 28.2%; side-hand strokes: 31.6%) components between the forehand strokes and side-hand strokes. The percentage of the right breast displacement in mediolateral direction was greater than that of the left breast in bare-breasted condition during the two strokes (Table 1).

Figure 8.

Breast displacement in three directions: (a) no bra condition and (b) sports bra condition. “*” means significant difference. “XL” means m/l breast displacement for the left breast, “YL” means a/p breast displacement for the left breast, “ZL” means vertical breast displacement for the left breast, “XR” means m/l breast displacement for the right breast, “YR” means a/p breast displacement for the right breast, “ZR” means vertical breast displacement for the right breast, “Rela” means relative breast displacement. All participants held the bat racket in right hand.

Table 1.

Mean percentage contribution of anteroposterior, mediolateral, and vertical breast displacement in two breast support conditions during forehand stroke and side-hand stroke.

Mean percentage contribution	Direction	No bra (%)	Sports bra (%)
Displacement of the left breast during forehand stroke	Forehand-XL	45.0	52.4
	Forehand-YL	31.1	29.9
	Forehand-ZL	23.9	17.7
Displacement of the right breast during forehand stroke	Forehand-XR	55.0	44.0
	Forehand-YR	26.1	26.8
	Forehand-ZR	18.9	29.2
Overall breast displacement during forehand stroke	Forehand-X	50.7	47.7
	Forehand-Y	28.3	28.2
	Forehand-Z	21.1	24.1
Displacement of the left breast during side-hand stroke	Side-hand-XL	39.3	47.9
	Side-hand-YL	41.1	33.9
	Side-hand-ZL	19.5	18.2
Displacement of the right breast during side-hand stroke	Side-hand-XR	43.7	38.5
	Side-hand-YR	29.3	29.8
	Side-hand-ZR	27.0	31.7
Overall breast displacement during side-hand stroke	Side-hand-X	41.9	42.6
	Side-hand-Y	34.3	31.6
	Side-hand-Z	23.8	25.8

No Bra Condition

There were significant differences between three directions during side-hand strokes in no bra condition for the left breast (F = 6.938, p = 0.010). Post-hoc analysis revealed significant differences in breast displacement between m/l direction and vertical direction (p = 0.01 < 0.05), and between a/p direction and vertical direction (p = 0.006 < 0.05) during side-hand strokes. However, there existed no significant difference in three-dimensional breast displacement in no bra condition during the forehand strokes. There were significant differences between three directions during forehand-strokes (F = 15.582, p < 0.01) and side-hand strokes (F = 10.324, p = 0.002) in the no bra condition for the right breast. Post-hoc analysis revealed significant differences in breast displacement between m/l direction and a/p direction (p = 0.001 < 0.05; p = 0.004 < 0.05), and between m/l direction and vertical direction (p = 0.000 < 0.05; p = 0.001 < 0.05).

Sports Bra Condition

There were significant differences between three directions during forehand strokes (F = 8.110, p = 0.006) and side-hand strokes in sports bra condition (F = 6.031, p = 0.015) for the left breast. Post-hoc analysis revealed that the differences between m/l and a/p breast displacement (p = 0.024 < 0.05), between m/l and vertical breast displacement (p = 0.002 < 0.05) were significant during the forehand strokes. Furthermore, a significant difference between m/l and vertical breast displacement (p = 0.005 < 0.05) was found during side-hand strokes. For the right breast, however, no significant difference was found between three directions irrespective forehand strokes and side-hand strokes.

Breast total displacement equals to left breast displacement plus right breast displacement:

T = L + R

(1)

Where T means breast total displacement, L means displacement of the left breast, R means displacement of the right breast.

The distribution of breast displacement (fore and side strokes) in three directions was determined by the ratio of the displacement in each direction to the total displacement in three directions.

a = \frac{x}{x + y + z}

(2)

b = \frac{y}{x + y + z}

(3)

c = \frac{z}{x + y + z}

(4)

where a, b, c are the distributions of breast displacement in m/l, a/p, and vertical directions, respectively, and x, y, z are values of breast displacement in m/l, a/p, and vertical directions, respectively.

To determine vertical relative breast displacement, Select vertical coordinate data were selected in the original data and vertical coordinates of the breasts subtracted from vertical coordinates of human trunk to obtain vertical relative breast displacement.

γ = α - β

(5)

where $γ$ means vertical relative displacement, $α$ means absolute vertical breast displacement, and $β$ means trunk vertical displacement.

Perceived Breast Motion and Breast Discomfort

Participants reported lower perceived breast motion and breast discomfort in sports bra condition compared to the no bra condition, for both forehand and side-hand strokes (Figure 9). Greater perceived breast motion was found during forehand strokes (4.6 ± 1.0 for the no bra condition and 3.3 ± 1.1 for the sports bra condition) than during side-hand strokes (3.4 ± 1.0 for the no bra condition and 2.6 ± 0.5 for the sports bra condition). Similarly, greater breast discomfort was perceived during forehand strokes (2.1 ± 0.7 for the no bra condition and 2.0 ± 0.8 for the the sports bra condition) compared to during side-hand strokes (2.0 ± 0.8 for no bra condition and 1.6 ± 0 for the sports bra condition). No significant difference in perceived breast motion and breast discomfort was found between bra conditions, and between forehand strokes and side-hand strokes. The path of breast motion during playing badminton is shown in Figure 10.

Figure 9.

Perceived breast motion and breast discomfort of each participant in no the bra and the sports bra conditions during badminton forehand and side-hand strokes. Each dot represents a participant, and the intensity of the dot increases as more participants report that level of movement and discomfort. All participants held the bat racket in their right hand. (a) Forehand stroke and (b) side-hand stroke.

Figure 10.

The path of breast motion during playing badminton. Xr_coordinate means the coordinates of right breast displacement in m/l direction, yr_coordinate means the coordinates of right breast displacement in a/p direction, zr_coordinate means the coordinates of right breast displacement in vertical direction. XR_T coordinate means the coordinates of right breast displacement in m/l direction relative to the trunk, YR_T coordinate means the coordinates of right breast displacement in a/p direction relative to the trunk, ZR_T coordinate means the coordinates of right breast displacement in a vertical direction relative to the trunk.

Discussion

This article explored breast displacement in three dimensions during badminton forehand strokes and side-hand strokes. Greater trunk rotation and breast displacement were found during forehand strokes than during side-hand strokes in the bare-breasted condition. The sports bra was effective to decrease three-dimensional breast displacement in each plane during forehand strokes and side-strokes compared to the bare-breasted condition. The maximum difference in breast displacement between the no bra condition and the sports bra condition was found in the mediolateral direction of the right breast. Furthermore, breast displacement was predominantly mediolateral during both forehand strokes and side-hand strokes, with a maximum of 50.70% during the forehand strokes. The implications of these findings are discussed below.

Trunk Rotation During Forehand Strokes andSide-hand Strokes

Trunk rotation measured during forehand strokes was greater than that during side-hand strokes in the no bra condition, accepting hypothesis 1. This indicated that forehand strokes require the badminton player to have a greater swing and body twist, which causes greater breast displacement compared to side-hand strokes. The angle of trunk rotation during forehand strokes was 25.8 ± 7.5° in no bra condition, lower than the data reported in previous research,¹³ in which trunk rotation was measured to be 36.7 ± 8.2° for novice players and 46.9 ± 11.2° for skilled players. This suggests that competitive badminton players have a high trunk rotation compared to badminton amateurs. Trunk rotation in the sports bra condition was lower than that in the no bra condition during forehand strokes. This suggests that the sports bra was able to control trunk motion, thereby controlling breast movement and relieving breast discomfort.

Breast Displacement During the Forehand Strokes and Side-hand Strokes

The results showed that breast displacement in the no bra condition during forehand strokes was significantly greater than that during side-hand strokes in m/l and vertical direction for the left breast and in m/l direction for the right breast, indicating that the forehand strokes is more severe than the side-hand strokes, accepting hypothesis 2. This suggests that breast motion research in the no bra condition during playing badminton should focus on forehand strokes as they may result in larger breast displacement. Furthermore, no significant difference in three-dimensional breast displacement was observed during the sports bra condition. This finding indicated that the sports bra reduced the difference in breast displacement between the two movements. Thus, although only forehand strokes are preferred for breast motion research in the no bra condition, both forehand and side-hand strokes could be used in sports bra condition. In addition, breast displacement for the right breast was greater than that on the left breast, highlighting that displacement on the hitting side is greater than that the non-hitting side. Playing badminton is an asymmetric motion, with an imbalance of forces generated in the left and right upper limbs, which may explain the difference in displacement of the left and right breasts. Future research on asymmetric movements, including playing badminton, should distinguish between left and right breast displacement to obtain characteristics of breast movements under asymmetric motion.

Breast Displacement in Two Breast Support Conditions

The maximum difference in breast displacement between two support conditions was found in the mediolateral direction for the right breast during the forehand strokes. This finding was different from that reported during running in previous research in which the maximum difference was found in the vertical direction.⁹ Significantly less breast displacement was found in three dimensions in the sports bra condition compared to the no bra condition. This finding indicates that the sports bra was effective to decrease three-dimensional breast displacement in each plane during forehand strokes and side-strokes compared to the bare-breasted condition.

Breast Displacement in Three Directions

In comparison with vertical breast displacement, there was significantly greater m/l displacement during both forehand strokes and side-hand strokes, followed by a/p displacement. Breast displacement in the m/l direction accounted for an average of 41.9–50.7% of during two strokes. This large proportion of m/l breast displacement clearly indicates that during playing badminton, the vast majority of female athletes’ breast displacement is in the mediolateral direction, which may be caused by trunk rotation during badminton smash technical action. This conclusion was inconsistent with the results of previous investigations in which breast displacement was mainly in the vertical direction during treadmill running, with the proportion as high as 50%.⁹ Previous studies on jumping movement also found that the proportion of breast displacement in the vertical direction was largest (35%).¹²

The proportion of breast displacement in mediolateral direction was reduced during side-hand strokes compared to the forehand strokes, while the proportion in the anterioposterior direction was increased and the vertical component remained similar. A maximum numerical difference in breast displacement between forehand strokes and side-hand strokes was shown in the mediolateral direction compared with vertical and a/p. This possibly implied that this difference in mediolateral breast displacement is due to the main breast displacement in m/l during playing badminton, while the vertical breast displacement dominates during treadmill running.^8,9 The m/l variables accounted for an average of 47.7–50.7% of breast displacement during forehand strokes and 41.9%–42.6% during side-hand strokes. This finding indicates that breast displacement in the m/l direction should be not ignored when designing products to reduce breast motion during playing badminton.

Perceived Breast Motion and Breast Discomfort

Participants perceived lower breast motion and breast discomfort in sports bra condition compared to the no bra condition, indicating that the sports bra used in this study can effectively control breast movement during playing badminton, and in turn relieve exercise-induced breast discomfort. The perceived breast motion and breast discomfort during forehand strokes were higher than that during side-hand strokes irrespective of the no bra condition and sport bra condition, implying that forehand strokes may be more violent than side-hand strokes, and thus induce greater breast movement and discomfort.

Strengths and Limitations

It is acknowledged that the marker position used in this experiment was a limitation of this study. The markers were close to the midline to measure trunk and breast motion in the a/p and m/l plane, and thus possibly caused bias. Furthermore, participants in this study were homogenous in age, BMI and breast size, which may limit the application of the findings. Despite these limitations, this study was the first to explore breast displacement during two asymmetrical badminton movements in three directions in no bra and sports bra conditions, different from previous research in which symmetrical movements were examined. In addition, trunk rotation was measured in the no bra condition and sports bra condition, to predict breast displacement during forehand and side-hand strokes.

Conclusion

Breast displacement and trunk rotation for the forehand strokes were greater than that for the side-hand strokes in the no bra condition during playing badminton. Future research may focus on forehand strokes to investigate the effect of playing badminton on three-dimensional breast biomechanics. Breast displacement on the hitting side was greater than that on the non-hitting side during playing badminton. Future research should investigate breast biomechanics on both sides to optimize bra design. Breast displacement during playing badminton is predominantly in the m/l direction, unlike the dominant vertical breast displacement during running. Further research is therefore required to focus on m/l breast displacement during playing badminton.

Practical Implications

In the context of the rise of female sports, breast movement during exercise is one of the important factors affecting women’s sports participation. This study explored breast movement characteristics under two badminton asymmetric movements.

As a driving force of breast movement, trunk rotation is greater in forehand strokes than in side-hand strokes, and breast movement in the m/l direction is greater in forehand strokes than in side-hand strokes, implying that forehand strokes need more breast support in the m/l direction than side-hand strokes. Breast displacement in badminton is mainly in the mediolateral direction, unlike running, in which it is concentrated in vertical direction. Therefore, bra design for badminton players should focus on the control effect in mediolateral direction.

Breast displacement on the hitting side is greater than that on the non-hitting side; however, previous studies usually explored breast movement on one side only. Sports bras designed according to those studies may not be suitable for badminton players, thus, future bras should perhaps be designed for “handedness”—right-handed and left-handed bras.

Footnotes

Author contributions

Yingying Zhang carried out the experiment. Yingying Zhang wrote the manuscript with support from Xiaona Chen and Guangwu Sun. Xiaona Chen and Guangwu Sun helped supervise the project. Tiantian Sun and Lulu Shang conceived the original idea.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Natural Science Foundation of China (grant number 11802171) and Hainan Provincial Natural Science Foundation of China (grant number 223MS054).

ORCID iD

Xiaona Chen

Data availability statement

All data included in this study are available upon request by contact with the corresponding author.

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