Badminton players perform a range of badminton-specific movements, including jumps, lunges, sidestepping and changes in direction to reach the shuttlecock (Cabello Manrique & González-Badillo, 2003; Phomsoupha & Laffaye, 2015). The repetitive high-intensity actions do however place high demands on the players’ lower limbs. In fact, a recent study by Nagano et al. (2020) revealed that adolescent female badminton players perform 7.72 actions with trunk accelerations above 4g per minute during games, (Nagano et al., 2020). Generating body accelerations at this level is likely an important contributor in the high incidence of lower limb injuries, particularly the knee and ankle joints, are prevalent among elite and recreational badminton players (Goh et al., 2013; Miyake et al., 2016; Reeves et al., 2015).

The high loads experienced during single-leg landings, following forehand and overhead jump strokes, have been associated with increased risk of anterior cruciate ligament injuries (Kaldau et al., 2024; Kimura et al., 2010, 2012) and Achilles tendon ruptures (Fahlström et al., 1998; Kaalund et al., 1989), and may in general contribute to the high incidence of lower limb injuries in badminton (Goh et al., 2013; Miyake et al., 2016; Reeves et al., 2015). Thus, existing biomechanical literature have focus on differences in lower limb landing mechanics between genders (Hu et al., 2023; Zhang et al., 2023; Zhao & Gu, 2019), and playing level (Kaldau et al., 2022; Nedergaard et al., 2022; Zhao & Li, 2019). Whereas the impact of jump intensity levels and inclusion of pre-jump footwork are not represented in the existing literature, despite its potential influence on lower limb mechanics and injuries.

The scissor-kick jump (SKJ) is a frequently utilised technique among badminton players when returning the shuttlecock from the rear-court forehand side (Kaldau et al., 2022), but also a frequent ACL injury situation (Kaldau et al., 2024). The SKJ involves a backward jump with a 180 degrees body rotation along the player’s longitudinal axis, resulting in the characteristic crossing of the legs in mid-air. The in-air rotation allows players to generate more power in their stroke and the ability to swiftly push off the ground and return to the court’s center (Brahms, 2014). We have recently demonstrated that recreational badminton players can reduce Achilles tendon forces by 25% when employing the SKJ technique during forehand jump strokes (Kaldau et al., 2022) and that the knee joint loads, during the initial contact phase of SKJs with submaximal intensity, are similar between elite and recreational male badminton players (Nedergaard et al., 2022). Nevertheless, despite its frequent use in elite badminton, a comprehensive understanding of the lower limb joint loads experienced during the initial landing phase after a SKJ, and the impact of jump intensity and match-like footwork remains limited.

In this exploratory study, we aimed to evaluate the lower limb joint landing mechanics that elite badminton players experience following SKJs. Considering the dynamic nature of badminton, where players constantly adjust their movement patterns, such as altering jump height or footwork to reach the shuttlecock, we specifically aimed to explore how increased jump intensity and inclusion of chasse steps prior to the SKJ alter lower-limb landing mechanics.

The repeated measures ANOVA revealed that jump height was significantly different between the three SKJ variations (F_{(1.253, 11.273)} = 35.401, p < 0.001). Post-hoc analysis showed that jump height was significantly higher for SKJ_Max (48.6 ± 7.2 cm) compared to both SKJ_SubMax (30.6 ± 9.8 cm, p < 0.001) and SKJ_Chassé (33.9 ± 8.5 cm, p = 0.001). Furthermore, contact time for the landing phase was significantly different between SKJ variations (F_{(1.899, 17.088)} = 8.543, p = 0.003), with post-hoc analysis showing that the SKJ_Max (389 ± 56 ms) had significantly longer contact time than the SKJ_Chassé (342 ± 42 ms, p = 0.012) but not the SKJ_SubMax (368 ± 48 ms, p = 0.086). There was no significant difference in V_Forward (p = 0.639) between the three SKJ variations (SKJ_SubMax: 4.85 ± 0.46 ms; SKJ_Max: 4.93 ± 0.37 ms; SKJ_Chassé: 4.98 ± 0.40 ms).

Only minor differences were observed in the joint angles and moments across the three SKJ variations (Figure 2). In general, the SKJ_Max and SKJ_Chassé variations displayed greater hip and knee joint moments in the frontal and transverse plane, and greater plantar flexor moments compared to the SKJ_SubMax. Nevertheless, the one-way repeated-measures SPM ANOVA found no significant difference in hip, knee, ankle joint angles and moments between the three SKJ variations.

Figure 2 (A) Silhouette representation of the SKJ movement, with the sequence of movements shown from right to left, starting with the jump phase and transitioning to the landing phase. (B) Mean ± SD clouds for hip joint angles and moments across all planes. (C) Mean ± SD clouds for knee joint angles and moments across all planes. (D) Mean ± SD clouds for sagittal ankle joint angles, moments, and foot progression angles. The average waveform plots, displaying only the landing phase, include three SKJ variations: SKJ_SubMax (black line), SKJ_Max (orange line), and SKJ_Chassé (blue line). Below the waveform plots, Statistical Parametric Mapping (SPM{F}) results from the one-way repeated measures ANOVA are shown. Significant main effects between SKJ variations are indicated where the F-curve (grey line) exceeds the critical threshold (horizontal dashed line). All curves are normalized to the landing phase (%).

The total amount of joint work absorbed by the non-racket leg was significantly affected by SKJ variations (F_{(1.796, 16.167)} = 4.493, p = 0.031), but without any significant differences at a post-hoc level (Figure 3). The percentage of joint work absorbed at the knee was significantly affected by SKJ variations (F_{(1.915, 17.239)} = 7.895, p = 0.004). More specifically, the post-hoc analysis revealed that the work absorbed by the knee was significantly higher for the SKJ_Max (30.8 ± 5.3%) compared to the SKJ_SubMax (27.1 ± 3.7%, p = 0.011). Similarly, the percentages of joint work generated by the knee during the push-off phase were significantly different between SKJ variations (F_{(1.966, 17.694)} = 7.444, p = 0.005). More specific, the post-hoc analysis revealed that the work generated by the knee was significantly higher for the SKJ_Max (23.0 ± 3.5%) compared to the SKJ_Chassé (19.9 ± 4.3%, p = 0.017).

Figure 3 Mean ± SD clouds for the hip (A), knee (B), ankle (C) joint power for the landing phase (normalized to 100%) of the three SKJ variations. D) Average positive and negative joint work (absolute and percentage) for the three SKJ variations. * Indicates that the joint work is significantly different from the SKJ_SubMax (P < 0.0167).

In the present study we demonstrate that elite male badminton players exhibit great ankle plantar flexor moments together with large hip and knee extensor and adductor moments during landings following SKJs. Particularly the triceps surae muscles are exposed to high eccentric loads accounting for ~41% of the total joint work absorbed by the non-racket leg during the landing phase. Finally, our results illustrate that landing mechanics (joint moments, powers and work) of elite badminton players is largely unaffected by SKJ intensity or the inclusion of backward chassé steps.

Only the percentage of eccentric joint work absorbed at the knee, and concentric joint work generated at the knee significantly differed between SKJ variations in the presented study. The increased jump height in the SKJ_Max resulted in higher peak knee eccentric power (Figure 2B) compared to SKJ_SubMax, which is in line with previous studies that showed increased landing impacts and eccentric knee joint work with increased drop height (Ali et al., 2014). The greatest differences in concentric knee joint power (Figure 2B) were observed between the SKJ_Max and SKJ_Chassé which in turn can explain the significant difference observed in the concentric knee joint work between these two. Previously, it has been shown that single-leg horizontal jumps for distance significantly increased the percentage of eccentric work at the knee, compared to vertical jumps with maximal effort (Kotsifaki et al., 2021). Nevertheless, the inclusion of the horizontal chassé footwork component prior to the SKJ in the presented study did not alter the elite players landing mechanics, most likely because all SKJ variations included a horizontal component with the players jumping horizontally onto the force plate. The lack of differences between SKJ variations observed in the present study demonstrate that minor alterations in jump strategies do not alter landing mechanics in elite male badminton players.

The lower limb landing mechanics observed for the SKJ in the present study generally resemble those previously described for single-leg landings following overhead strokes (Hung et al., 2020; Kimura et al., 2012; Zhao & Gu, 2019). In short, the peak plantar flexor moments of the SKJ were within the range of those previously presented for overhead backhand strokes in male badminton players (Hung et al., 2020; Zhao & Gu, 2019). However, the knee and hip extensor moments observed in the present study were higher than those previously reported for male badminton players during single-leg landings following overhead strokes. (Hung et al., 2020; Zhao & Gu, 2019), likely because all players in the present study competed at the highest level in Denmark. The peak external knee abduction moments, a well-known risk factor for anterior cruciate ligament injury during single-leg landing in badminton (Kimura et al., 2010), observed in the present study exceed those previously reported during overhead strokes for female players (0.42 + 0.26 Nm/kg) (Kimura et al., 2012) and for a mixed group of male and females players (0.89 ± 0.46 Nm/kg/m) (Hu et al., 2022). This indicates the importance of strong and active knee adductors to counteract the high external knee abduction moment (Zebis et al., 2022). Nevertheless, the current literature on single leg landing mechanics in badminton lacks sufficient data on joint moments in the frontal and transverse planes. Hence, we strongly encourage researchers to incorporate the non-sagittal kinetics when exploring the loading demands of other badminton specific jump landings and their association with injury risk.

This study was conducted on 10 elite male badminton players; thus, the findings may not be generalizable to female or non-elite players. Previous research has identified gender differences in single-leg landings following a backhand overhead stroke from the rear-court. For instance, female badminton players show smaller ankle, knee, and hip flexion angles, and higher ground reaction forces during landing (Zhao & Gu, 2019). They also display lower leg and knee stiffness, indicating reduced dynamic stability (Zhang et al., 2023), and different lower-limb neuromuscular control strategies during the pre-landing phase (Hu et al., 2023). Similar differences may for the rear-court forehand SKJ examined in this study, which potentially could explain the higher incidence of ACL injuries reported among female players on the rear-court forehand side compared to males (Kaldau et al., 2024). Further research is needed to determine whether the differences in peak eccentric and concentric knee joint power observed across SKJ conditions here are gender specific.

A limitation with this study is that the players performed the SKJs without a racket and shuttlecock, due to the limited laboratory floor-to-ceiling height. Furthermore, we acknowledge that landing mechanics differ between shadow and actual hitting actions (Hung et al., 2020). Nevertheless, since all the players included in this study were familiar with the SKJ movement, we strongly believe the players were able to reproduce the movement pattern from practice/games. Another limitation with our study design and the joint mechanics presented is that ground reaction forces only was measured for the non-racket leg, though players had double support in the last part of the SKJ landing. We did however focus on joint kinetics of the non-racket leg in this study because it indisputably is exposed to the highest loads during the SKJ landing. Moreover, the non-racket leg is generally more exposed to severe injuries (e.g. knee injuries) during jump landings than the racket leg in badminton (Kaldau et al., 2024; Kimura et al., 2010).

The landing mechanics of the SKJ described in the present study is similar to that previously observed during side-cutting (Bencke et al., 2013). This highlights the importance of simultaneous muscle activation of the hip extensor, adductors, and external rotators to counteract the high loads forcing the hip into internal rotation and abduction. Also, knee extensor activation is necessary for absorbing impact forces and stabilizing the knee. Additionally, activation of the knee adductors (i.e., the medial hamstrings) before landing is crucial to counteract the high external knee abduction moment during the initial landing phase. These musculoskeletal loads may contribute to the high knee injuries rates in badminton players (Goh et al., 2013; Miyake et al., 2016; Reeves et al., 2015). Similarly, our findings highlight the significant workload undertaken by the plantar flexors, which may contribute to the high incidence of Achilles tendon injuries in badminton. Previously, we demonstrated that novice players experience greater Achilles tendon forces, which can be significantly reduced by adopting the SKJ landing technique used by elite players (Kaldau et al., 2022). This highlights the importance of proper landing mechanics in mitigating stress on both the Achilles tendon and the knee (Kaldau et al., 2022; Kimura et al., 2010). In recreational players with lower fitness levels, the high plantar flexor and Achilles tendon loads during intense movements impose a relatively greater strain, even with correct technique. Hence, coaches should consider moderating the intensity of such actions to prevent overuse injuries. Additionally, the high horizontal landing velocity of the SKJ challenges knee and ankle joint stability, especially in less fit or skilled players. This supports recommendations for a progressive increase in exercise intensity during badminton-specific jump skill development, such as the SKJ, alongside target strengthening of the stabilizing musculature around the knee and ankle.

Whilst the direct association between SKJ landing mechanics and lower limb injury incidence in elite badminton remains unknown, physiotherapists and strength and conditioning coaches can benefit from the information on lower limb muscle/joint loads found in this study when designing injury prevention programs for elite badminton players. Ultimately, contributing to the overall goal by reducing the high incidence of lower limb injuries in competitive badminton.