The present study was designed to investigate effects of KT with closed basket weave method and LB on the vTTS, PvGRF, and time to PvGRF in the forefoot and rearfoot as well as perceived stability during lateral landing performed by female college athletes with CAI before and after fatigue.
vTTS and psychological effects on perceived stability
TTS is commonly examined in research on postural stability and the functioning of lower extremity joints, such as ankles and knees. It is defined as the time required for an individual to return to baseline values from an unstable position . The results of this study showed that at pre-fatigue, the PASs had no effect on vTTS in the forefoot and rearfoot during lateral landing, whereas at post-fatigue, the use of LB negatively affected vTTS in the forefoot and rearfoot and generated a vTTS longer than that observed under the control and KT conditions. PASs are widely used among athletes to prevent injury, and the use of tape and braces has attracted the attention of many researchers [2, 3, 6, 10]. Various studies on KT derived different effects, including increased skin blood flow during exercise, modified lymphatic circulation, support for ligaments and tendons, and a stimulated subcutaneous skin receptor mechanism; these effects enhance the activity of mechanoreceptors through a feedback mechanism and improve joint performance [5, 7]. Two broad theories have been used to explain the mechanism of brace efficacy: the first features passive mechanical support, and the second revolves around the improvement of sensorimotor function through increased stimulation of cutaneous receptors and joint mechanoreceptors .
Our hypothesis was that a brace model with support for lateral parts of the ankle can help control this body part during lateral landing and thus improve balance. Ankle stability was predicted to increase because of the eight-like shape and heel-lock structure used in the completed closed basket weave taping method. In spite of the advantages attributed to these PASs in the literature and in contrast to the hypothesis that we formulated, we did not observe a significant difference in vTTS during lateral landing with KT usage; meanwhile, at post-fatigue, the use of LB increased vTTS in the forefoot and rearfoot. Studies have shown that fatigue clearly affects the biomechanics of landing on one foot and that the risk of injury is greater after fatigue. Fatigue may alter neuromuscular control and diminish the body’s ability to maintain stability [6, 11], thus driving the use of TTS in evaluating the impact of fatigue on proprioception and neuromuscular control. An increase in this variable indicates the body’s delayed response to stability and difficulty in postural control during landing [6, 27].
According to the results, LB usage did not improve vTTS and increased vTTS post-fatigue, which can increase the risk of injury. Brace weight potentially weakens postural control during fatigue and increases vTTS during lateral landing. Significant results were derived as regards psychological effects on the perceived stability of the participants. Unlike the LB and control conditions, KT usage resulted in greater perceived stability pre-fatigue. Such stability did not differ significantly under the LB and control conditions. Despite the increase in perceived stability during landing with KT use, the vTTS did not decrease significantly in this condition. Consistent with these results, Hunt and Short and Gear et al. reported an improvement in subjects’ feelings of stability and self-confidence in performing functional tests with KT fitting, even though no significant difference was found in the participants’ performance [21, 22]. In our study, the participants felt that the ankle was more stable post-fatigue when they used a PAS in executing landing than when no support was employed. In addition to the tape, the LB also significantly differed from the controls in terms of improvement to perceived stability.
The vTTS results increased with LB usage during lateral landing. Sawkins et al. stated that if athletes believe that PASs protect them from injury, they may participate in an activity more confidently . In the present work, the increase in vTTS with LB usage at post-fatigue may have enhanced the participants’ sense of stability—an outcome that did not arise before the onset of fatigue. According to expectancy theory, athletes rely on the effects of PASs in preventing injury. As a result, inducing the belief that a placebo is effective and increasing perceived stability are easy, as asserted by Sawkins et al. . However, the use of PASs seems to result in less precise lateral landing owing to the creation of a false feeling of safety and an increase in false self-confidence. This can increase the risk of injury, especially during fatigue, in more difficult situations, such as races and competitions or the performance of complex and high-speed tasks.
A notable finding in this work was that all the 30 subjects with CAI preferred using the PASs as supports in performing landing, with 23 favoring KT for the increased sense of ankle stability that it provided, and seven preferring to use LB.
PvGRF and time to PvGRF
At pre-fatigue, using LB increased PvGRF in the rearfoot but decreased the time to PvGRF. The use of KT augmented PvGRF in the forefoot during lateral landing after fatigue. PvGRF is a pivotal and desirable variable for evaluating landing because it eases measurement and generates accurate results . It can also indicate an athlete’s ability to effectively reduce landing effects. The lower PvGRF show the better landing strategy; strong force can lead to injuries to the ankle and knee joints . PASs are primarily intended to limit the excessive inversion of the ankle and foot complex while allowing normal plantar flexion and dorsiflexion to maintain function. However, studies showed that the range of motion (ROM) of plantar flexion and dorsiflexion will also be limited when an ankle brace or tape is used [3, 7, 10, 29]. Decreasing the normal ROM of the ankle can affect the entire lower extremity and normal movement patterns and thereby weaken the body’s ability to absorb energy upon landing and impose greater GRF on the body . Damage to structures such as the subchondral bone, cartilage, and soft tissue may also occur as a result of increased GRF .
Studies demonstrated that the use of PASs not only influences the ROM of joints but also reduces muscle activity, which may diminish the auxiliary role of some muscles in minimizing body acceleration during landing . Fatigue is an integral part of physical activity. When it occurs, reaction times against external stimuli are delayed, and the likelihood of injury increases . This risk of injury is exacerbated on initial contact because the body at this stage cannot move within an ROM to allow contact forces to be absorbed through active structures (such as muscles) [27, 29]. Previous studies reported an increase in PvGRF in forward drop landing with decreasing joint ROM and leg muscle activity due to PAS use [3, 20, 29]. Our results also indicated that PvGRF increased before and after fatigue in rear foot under the use of LB and KT, respectively. Similarly, the use of KT increased PvGRF in the forefoot post-fatigue. These results are consistent with those of Cordova et al.  and Distefano et al.  but inconsistent with those of Hodgson et al.  Note that the task performed in the present study was lateral landing, whereas that in most previous works was forward landing.
The findings likewise illustrated that ankle bracing reduced the time to PvGRF in the rearfoot to levels lower than those occurring under the control and KT conditions. The increasing PvGRF and decreasing time to PvGRF during lateral landing under LB usage suggested that under this condition, musculoskeletal structures are affected by greater loads imposed at a shorter time . These changes also implied that the ankle’s ability to absorb energy decreases when certain PASs are used; this effect, in turn, increases the load imposed on proximal joints, including the knee . In this regard, Cordova et al. showed that some ankle stabilizers impair the optimal performance of this joint in absorbing contact by restricting the ROM of the ankle . Our results are consistent with those derived by Henderson et al. and Hodgson et al.  on the increase in PvGRF during landing with braces. They are also compatible with the findings of Riemann et al.  on the reduction of time to PvGRF.
Because the LB used in this study covers a large area of the soles of the foot and provides support to the lateral parts of the ankle, its use likely reduced the ROM of the rearfoot and may have decreased the time to PvGRF in the rearfoot by shortening its contact with the ground. Contrary to studies on forward landing drops that found a PvGRF2 larger than PvGRF1, the current research uncovered a PvGRF2 larger than PvGRF1 during lateral landing and a PvGRF1 greater than PvGRF2 at all landing conditions before and after fatigue.
The literature discussed the effects of general fatigue on balance, which is why a general fatigue protocol was used in the present study. Nevertheless, a different mechanism and effect may arise with regard to functional fatigue. Given that only a lateral landing test was performed on the injuried leg, no data on the other leg was derived for comparison in regard to PAS effects. Findings may also differ depending on task type. Finally, the same shoes were used by all the participants for matching in the test, but using other types of footwear may generate different results.