Female athletes are at higher risk of knee injuries, particularly non-contact anterior cruciate ligament (ACL) injuries, often caused by dynamic knee valgus during landing. Proper landing techniques and neuromuscular training are crucial for injury prevention. Attentional focus strategies, such as external focus (EF) and internal focus (IF), can influence movement patterns, muscle activation, and skill transfer during landing tasks. EF generally promotes safer and more controlled landings, while IF offers certain kinematic benefits. However, real-world sports often require a combination of attentional strategies, and the effects of combined EF + IF instructions on landing mechanics and muscle activation have not been fully studied.

This study will investigate the effects of EF and combined attentional focus instructions on lower extremity and trunk movement, muscle activation, and skill transfer in young female athletes with asymptomatic dynamic knee valgus. The investigators aim to determine whether combined attentional focus training provides greater improvements in landing mechanics, muscle activation, and skill transfer than EF training alone.

Female athletes experience knee injuries significantly more often, with an incidence rate approximately 3.5 times higher than that of their male counterparts. One of the most common knee injuries is anterior cruciate ligament (ACL) injury, with the risk being particularly high in female athletes, who have a reported incidence of non-contact ACL injuries of 63%.

Approximately 70% of ACL injuries occur without contact, with one of the most frequent causes being dynamic knee valgus which can result in high abduction (valgus) loads during landing after a jump. Dynamic knee valgus describes the frontal-plane knee angle during dynamic tasks such as landing or stepping down, typically occurring in conjunction with femoral internal rotation, contralateral pelvic drop, and hip adduction. Female athletes exhibit significantly greater valgus angles than male athletes, with only 22% of female players classified as having good knee control during jump landing, compared with 80% of male players.

The initial landing phase after a jump requires special attention from injury-prevention professionals, as 31% of ACL injuries occur during this phase. Common biomechanical features during single-leg landing include decreased flexion angles of the ankle, knee, hip, and trunk; increased knee internal rotation and abduction (valgus) angles and moments; lateral trunk flexion; as well as exaggerated ground reaction forces. An important clinical implication of these findings is that athletes need to be taught safer landing techniques.

Recently, the importance of integrating cognitive strategies into injury prevention programs has been emphasized. One such cognitive strategy involves the external and internal focus of attention, in which instructions for executing the movement aim to improve neuromuscular performance and motor learning. In external focus (EF), the athlete's attention is directed to objects or the environment external to the body (e.g., "stand on one leg and slowly bend your knee while keeping your knee over your foot"), while in internal focus (IF), attention is directed toward the performer's own movements (e.g., "stand on one leg and reach slowly toward the cone with your knee while bending your knee").

Previous studies reported that EF and IF instructions have different effects on athletes' kinematic, kinetic, and muscle activation parameters. EF instructions enhance safer and more controlled movement patterns during jump-landing by increasing knee and hip flexion, reducing knee valgus moments, and increasing the overall range of motion compared to IF. IF instructions, on the other hand, may provide certain kinematic improvements, such as reducing knee varus moments and controlling medial-lateral displacement. Recent meta-analyses support these findings, showing that although EF is generally more effective in jumping tasks, both attentional focus types can improve knee flexion.

However, real-world sports environments are complex, requiring athletes to dynamically shift attention between IF and EF or use both simultaneously. Evidence supports the effectiveness of dynamic attentional use and highlights the need for further research investigating combined attentional focus strategies. The acute and one-week effects of combined attentional focus and video-based instructions, finding that verbal combined focus instructions produced greater improvements in DK and landing performance. Since female athletes demonstrated higher incidence rate of ACL injury and more commonly present with dynamic knee valgus, there is a need for sex-specific studies investigating the effects of combined attentional focus training on kinetic and kinematic parameters in individuals with dynamic knee valgus.

Previous studies also reported that EF and IF instructions result in difference muscle activation. It is reported that EF not only increases knee and hip flexion but also enhances the feedforward activation of the gluteus medius and gluteus maximus muscles, resulting in safer and more controlled landing mechanics. Although IF provides certain kinematic improvements and can enhance quadriceps activation in isokinetic settings, its effects on EMG activation are less pronounced than those observed with EF. Therefore, EF seems to offer clearer advantages in terms of both motor efficiency and muscle activation. However, to our knowledge, no study has examined the effects of combined attentional focus instructions on muscle activation outcomes, highlighting an important area for future research.

Skill transfer, or the ability to generalize learned motor patterns to new or more complex tasks, is a critical indicator of effective motor learning and real-world performance. Improvements in jump-landing technique successfully transferred to a sidestep cutting task when athletes were trained with EF or video-based instructions, suggesting that EF facilitates safer and more efficient motor performance in dynamic conditions. More research is needed to determine how skill acquisition interventions can optimize the generalization of learned motor skills and to understand the influence of combined attentional focus instructions on skill transfer outcomes.

In this study, The investigators aimed to investigate the effects of EF and combined attentional focus (EF + IF) instructions on lower extremity and trunk kinetic, kinematic, muscle activation parameters and skill transfer ability in young asymptomatic female athletes with dynamic knee valgus. The investigators hypothesized that combined attentional focus training would yield greater improvements in dynamic knee valgus and other associated biomechanical parameters, muscle activation and skill transfer than external focus training.

Inclusion Criteria:

Females aged between 18-30 years old

BMI between 18.5-25 kg/m²

Dynamic knee valgus >10° during single-leg squat test (Richardson et al., 2020)

Being recreationally active (engage in moderate physical activities at least 3 times a week, with each session lasting at least 30 minutes in the past 4 weeks) (Heinert, 2008)

Exclusion Criteria:

Trunk, lower back, or lower extremity pain greater than 3/10 on numeric pain rating scale (0-10) in the past 6 months

History of surgeries in the lower extremity or lower back that may affect the landing mechanism

Currently participating in any lower extremity biomechanics modification program

Any medical or physical condition that would prevent safe jumping from a 20-cm box