# Relationship between Unilateral Leg Extension Strength and Dynamic Balance in Healthy Young Men
## 1 Introduction  
Muscle strength and balance are necessary to move independently and safely in the activities of daily living [1, 2]. It is mentioned that there is a relationship between balance and strength and that these parameters can explain each other [3]. It has been stated that muscle stiffness caused by force output can improve neuromuscular control by reducing the electromechanical delay associated with the spinal stretch reflex [4]. Balance requires the ability to integrate inputs from different sensory systems (i.e., somatosensory, visual, vestibular) and can be affected by musculoskeletal injuries, some neurological conditions, or ageing [5, 6]. Falls are a common problem in general health andactivities of daily living, especially in older people. It has been stated that understanding the relationship between strength and balance in older people and studies on this topic can contribute to the development of fall prevention and appropriate rehabilitation programs [7]. However, studying predominantly older populations leads to less scientific knowledge about the relationship between balance and strength in young adults. In balance and strength studies with adolescents and children, mostly individuals with certain specific disorders [8; 9] or patients after ACL reconstruction [10] were studied. Along these lines, a recent review noted that there is a need for more research examining balance and strength performance in healthy young people [11]. The rationale for this statement is that there are conflicting findings regarding the interaction between balance and strength in healthy active adults and athletes. One study found a significant positive relationship between lower body strength and balance (\(r\) = 0.360, \(p\) \(<\) 0.05) [12], while another study found no significant relationship between normalized reach scores and knee extensor strength of the dominant leg in professional football players (\(r\) = 0.06, \(p\) \(>\) 0.05) [13]. This heterogeneous information has led us to investigate the interaction between basic athletic performance skills such as balance and strength. Dynamic balance can be defined as the ability to meet postural demands in changing situations or successive conditions or to restore balance [14]. The Y Balance Test is the most commonly used dynamic balance test that measures the ability to control the body while maintaining stabilization of one leg. It is used to determine the possibility of injury in athletes, to identify bilateral asymmetries, and to identify functional limitations [15]. However, the Y Balance Test shows different results in terms of the scores obtained from three directions and the strength values for different muscle groups. For example, one study mentioned that there is a significant relationship between peak isokinetic knee extension torque and anterior reach asymmetry measured during the Y Balance Test, and that strength and balance performance can be used as important feedback for return to sport after ACL reconstruction [16]. Another study examined the relationship between concentric hip abductor strength and Y Balance Test scores. The authors found that hip abductor strength determined with an isokinetic dynamometer had a stronger correlation with posterior directions [17]. Furthermore, the results of the anterior Star Excursion Balance Test (SEBT) showed a positive correlation with the strength of the isometric hip flexors and extensors, while the results of the posterolateral SEBT were positively correlated with the strength of the hip abductors, extensors, and flexors [18]. So we can say that the type of contraction used during the strength test (isokinetic, isotonic, eccentric, etc.) and the different regions (knee, hip, etc.) directly influence the relationship between dynamic balance and strength. For the above rational reasons, the aim of this study was to investigate the relationship between unilateral leg extension strength and dynamic balance performance in healthy young men.