Most sports injuries occur in the middle and late stages of competition or practice and are correlated with some extent of fatigue [1, 2]. Fatigue reduces an athlete’s neuromuscular control [3], in turn decreasing balance.
Balance is an essential ability for athletes. Techniques in sports such as gymnastics, ball games, and track and field are particularly demanding with respect to balance quality, making it essential for athletic performance [4]. Most people rely on dynamic or static balance while standing, walking, or running. Static balance can maintain a stable posture, whereas dynamic balance enhances movement quality [5]. Balance is controlled by two systems in the human body and four factors: vision, the vestibular system, proprioception in the nervous system, and the influence of muscle strength in the musculoskeletal system [6]. Balance is achieved by adjusting the relative position of the center of gravity and base of support to achieve stability. The body must continuously correct and adjust the angles of the ankle and hip joints to maintain static balance while standing. The ankle joint muscles are used primarily in the forward and backward directions, whereas the hip joint muscles are mainly responsible for left–right adjustments. The information sources for these adjustments rely on the continuous input of proprioceptive signals [7].
With respect to static balance, standing is the most functional for postural assessment. The ability to control the ankle joint while standing is an essential factor affecting standing balance [8]. The standing static balance test can be used to determine the test subject’s sensory and muscle coordination [9]. The gastrocnemius is the most important stabilizing muscle for standing. Previous studies suggested that subjects with poor proprioception have poor standing quality, thereby increasing their risk of falls or reducing their activities of daily living [10]. In the clinical setting, constant stimulation is used to compensate for and enhance the sources of proprioception. Stimulation can re-train the nervous system to re-establish neuronal connections, and proprioceptive inputs can be increased by enhancing external signals, such as through sensory stimulation [11], braces [12], and tapes [13].
Kinesio tape (KT) is a widely available auxiliary device with proven ability to enhance proprioceptive input in many studies [14]. KT was experimentally shown to stimulate tactile input when applied to the skin, affect mechanoreceptors, enhance proprioception in the joints, muscles, and tendons [14, 15], improve myoelectric activity and recruitment [16–19], and improve ankle joint position sense in healthy individuals and individuals with sports injuries [20].
Further studies have found that KT can improve proprioception in subjects [20–22] and enhance dynamic balance in athletes [13, 23]. Different taping methods can result in different effects, so users have employed different KT shapes, tensions, and directions as needed [24]. Taping methods can be classified based on direction. In the facilitation method, the goal is to support muscle contraction, whereas in the inhibition method, the goal is to relax the muscles and increase flexibility or joint mobility. Some studies suggest that facilitation taping can increase muscle strength, power, and tension [25, 26], but some researchers believe that facilitation and inhibition methods do not affect muscle contraction or coordination [21,27−29]. However, previous studies focused primarily on the coordination of a single muscle and did not test the overall contraction performance and coordination of the muscle group simultaneously. In addition, opinions differ about facilitation and inhibition taping methods [21,25−29].
Although KT has been proven to improve proprioception, such as the joint position sense and force sense [13, 20], the sensation system in the human body can be divided into three categories: superficial, deep, and combined cortical. Superficial sensation is produced from stimulating the skin and subcutaneous tissues, such as light-touch thresholds [11,30−32]; deep sensation is produced from stimulating muscles, tendons, ligaments, joints, and fascia, such as vibratory sense, joint position sense, and force sense; and combined cortical sensation is produced from the combination of superficial and deep sensations [13, 14, 20, 30], such as two-point discrimination. Muscle taping may produce interaction among these three sensation systems, thus influencing proprioception. However, current studies suggest that KT can improve deep sensation (joint position sense and force sense) [13, 20, 33], but many researchers hold the opposite view [29, 34, 35], and the effects of other sensations have not been sufficiently studied. Therefore, this study aimed to use two different taping directions on the gastrocnemius muscle, the most important muscle for stance stability, to further investigate the effect of different taping directions on overall balance and sensation systems before versus after muscle fatigue.