Physical Therapy Korea

Patellofemoral pain syndrome (PFPS) is characterized by pain around the patella during activities such as squatting, stair climbing, running, and jumping [1]. The prevalence of this disease is 22.7% [2], and it occurs more frequently in females than in males [3]. Factors contributing to PFPS include anatomical abnormalities such as muscle imbalances around the knee joint, increased quadriceps angle, and repetitive microtrauma to soft tissues [4]. Atrophy of the quadriceps muscle and imbalances between the vastus medialis oblique (VMO) and vastus lateralis (VL) are the major biomechanical etiologies of PFPS [5]. Stability of the patellofemoral joint during gliding is maintained by the dynamic balance between the VMO and VL, with lateral gliding of the patella supported by the VMO and medial structures of the knee joint [6]. However, if the activity of the VMO weakens or its onset is delayed relative to that of the VL, excessive lateral gliding of the patella occurs [7]. Therefore, exercises focusing on selective strengthening of the VMO are necessary in patients with PFPS.

Common treatments for PFPS include electrotherapy, quadriceps muscle strengthening exercises, core muscle training, knee braces, and taping. Taping is a nonpharmacological therapy that involves the application of tape to specific body parts to treat muscle and ligament tension and relaxation, thereby facilitating muscle flexion and extension [8,9]. One prominent taping technique, McConnell taping, is used to correct medial glide or tilt of the patella and is effective in reducing knee joint pain [10,11]. This technique involves the initial application a fixing tape with a soft texture that contacts the skin to protect it from slipping, followed by the non-elastic tape is attached on it for realign the patella [12].

Another taping technique, Kinesio taping (KT), uses an elastic tape, which is commonly used in sports medicine to prevent and manage musculoskeletal disorders [13]. It was developed with consideration for muscle contraction, relaxation, and joint flexion and extension, distinguishing itself from non-elastic tapes that restrict body movement by not considering the range of motion of muscles and joints [9]. KT has evolved from a concept of muscle fixation and joint protection to a proactive treatment method applied clinically, and various taping techniques developed to enhance muscle strength and endurance. The reported effects of KT include enhanced joint and muscle sensory input, increased lymphatic activity, improved blood circulation, and pain relief via an endogenous analgesic mechanism [14-16]. Additionally, KT normalizes muscle tension, corrects abnormal patellar glide, and enhances proprioception by stimulating mechanoreceptors [17,18].

KT can induce either facilitation or inhibition, depending on the direction of application. When applied from the origin to the insertion of weakened muscles, it can promote muscle contraction, whereas when applied from the insertion to the origin of overused muscles, it can inhibit muscle contraction [19]. Sinaei et al. [20] reported a significant increase in the muscle activity of the VMO during heel-raise exercises with facilitatory KT. Furthermore, Chen et al. [21] found that patients with PFPS showed significant differences in VMO and VL muscle activity when facilitatory KT for the VMO and inhibitory KT for the VL were applied compared to groups without taping (WT) and with placebo taping. However, Choi and Lee [22] reported increased muscle torque regardless of the direction of KT application, and Serr^ão et al. [23] found no significant differences among the facilitation, inhibition, and placebo taping conditions. These conflicting results highlight the need for further research on the effects of the KT direction.

Combining KT with appropriate exercises can enhance muscle function more effectively than taping alone [24,25]. Closed kinetic chain exercises, such as wall squats, are effective in alleviating PFPS symptoms, with wall squats being one of the safest exercises during the early rehabilitation stages in patients with PFPS. Wall squats have been shown to increase the muscle activity of the VMO and VL more than open kinetic chain exercises such as knee extensions in the sitting position [26]. However, increasing the knee flexion angle during wall squats can exacerbate patellofemoral joint compression and stress, potentially worsening pain and decreasing the isometric contraction strength of the quadriceps muscle [27]. Studies on squats with various knee flexion angles in patients with PFPS have reported that the VMO is maximally activated between 0° and 60° of knee flexion and that using knee flexion angles between 0° and 50° can minimize the worsening of patellofemoral joint pain [28]. Another study indicated that knee flexion between 45° and 60° was the most effective for selectively strengthening the VMO in patients with PFPS [29].

A study comparing VMO and VL muscle activity during squats across groups with McConnell taping, placebo taping, and no taping found that the McConnell taping group had a significant increase in VMO activity and VMO vs. VL (VMO/VL) ratio [30]. However, while using non-elastic tape can temporarily reduce pain and correct abnormal patellar movement, its effects do not last until the next exercise session, and there are conflicting reports on its impact on VMO activity [31-33]. Additionally, non-elastic tape restricts the range of motion of muscles and joints, can be applied for up to 18 hours, and may cause allergic skin reactions if worn for extended periods. In contrast, KT, which can stretch up to 140% of its original length [34], can be worn for 3–5 days, making it more convenient to use [35].

Studies have reported that combining KT with various muscle strengthening exercises has a positively affects muscle strength. Kuru et al. [24] reported significant pain relief and increased knee extension strength when lower limb strengthening exercises were performed with KT applied to the patella and quadriceps muscles. Similarly, Nayanti et al. [25] found a significant increase in muscle strength when KT was applied to the quadriceps muscles during strengthening exercises compared with a placebo taping group. These studies suggest that combining KT with various strengthening exercises positively improves muscle strength. However, Lee et al. [35] found no significant differences before and after the intervention or between groups when applying KT to the patella, quadriceps tendon, and muscles during open and closed kinetic chain exercises for one month. Given the conflicting evidence on the effects of KT direction and its combination with exercise, further research is needed to determine the optimal KT technique and treatment method for selectively strengthening the VMO.

Therefore, the purpose of this study was to compare the muscle activities of the VMO and VL during wall squat exercises under four conditions: patellar medial glide taping (PMGT), vastus medialis oblique facilitatory taping (VMOFT), combined taping (CT) of PMGT and VMOFT, and WT. This study aimed to determine the most effective method for increasing VMO muscle activity and the VMO/VL ratio.

1. Subjects

Seventeen healthy female volunteers aged 19–30 years participated in the study (Table 1). We used G*power software to calculate the sample size. The sample size, calculated using the G*power (repeated measures ANOVA; effect size f: 0.6, α error probability: 0.05, power [1-β error probability]: 0.95) number of the measurements, was 17. Therefore, the estimated sample size for this study was 17 participants. The inclusion criteria were as follows: (1) individuals without hip or knee joint disorders; (2) individuals with no history of trauma or spinal disorders in the past 6 months; and (3) individuals able to perform wall squats without pain. The exclusion criteria were as follows: (1) individuals who experienced fractures, surgeries, or other musculoskeletal injuries in the legs within the past 6 months; (2) inability to perform exercises due to pain in the back, hip, or knee joints; and (3) individuals who exhibited abnormal reactions during a KT skin sensitivity test within the past 30 days [36]. The research protocol was thoroughly explained to all participants, and written informed consent was obtained from each participant prior to the study. This study was approved by the Institutional Review Board (IRB) of Inje University (IRB no. 2023-11-025-001).

Table 1 . General characteristics of the participants.

Variable	Value
Age (y)	23.47 ± 3.41
Height (cm)	162.23 ± 4.73
Weight (kg)	54.23 ± 6.90

Values are presented as mean ± standard deviation..

2. Instrumentation

1) Electromyography

The activities of the VMO (2 cm above the superior aspect of the patella) and VL (3–5 cm above the lateral aspect of the patella based on the midline of the femur) [37] were recorded using a 2EM instrument (4D-MT; Relive). The sampling rate was set to 1,000 Hz, and the frequency bandwidth was 0–500 Hz. The electromyography values collected for each muscle were processed using the root mean square. The dominant leg was selected as the test leg. A disposable Ag/AgCl surface electrode was attached horizontally to the direction of the muscle fibers.

Prior to this experiment, the maximum voluntary muscle activity was standardized by measuring the maximal voluntary isometric contraction (MVIC) for each muscle according to the Cram et al. [38]’s guidelines. All measurements were performed for 5 seconds and repeated 3 times for each muscle. The signals for the middle 3 seconds, excluding 1 second each from the start and end of the measurement, were analyzed.

2) Goniometer

A goniometer (Baseline) was used to ensure that knee joint flexion was maintained at 50° during wall squats. The goniometer was attached to the outside of the non-dominant leg and aligned the line connecting the greater trochanter of the femur and the lateral epicondyle, and the line connecting the lateral epicondyle of the femur and the lateral malleolus (Figure 1).

Figure 1. Goniometer attachment.

3. Procedures

The tape used in this study was a 5 cm wide 3NS Kinesio Taping (TS Co.). Before applying the tape, dust and dead skin cells were removed using medical alcohol. For the PMGT, one side of the tape was attached to the lateral border of the patella to fix the patella, and then stretched toward the medial border with maximum tension. The VMOFT was applied in a “Y” shape while the participant was in a supine position with knee flexed at 90°, starting from the medial side of the upper one-third of the femur to the medial edge of the patella. The tension of the tape was applied at 25%, and to objectify the amount of tension, the length of the paper from which the tape was removed was measured and set to 0%. The maximum length stretched until the elasticity of the tape disappeared was defined as 100%. Subsequently, one end of the tape was attached to the muscle, a length equal to 25% of the tape tension was marked, and the end was stretched by that length and attached [39]. For the CT, VMOFT was applied first, followed by PMGT (Figure 2).

Figure 2. Kinesio taping techniques. (A) Patellar medial glide taping, (B) vastus medialis oblique facilitatory taping, and (C) combined taping.

To become accustomed to the exercise, the participants practiced the exercise posture accurately for 5 minutes by performing wall squats with a knee flexion of 50°. The subjects stood with their trunk leaning against the wall at a distance of 2/3 of the length of the femur between their feet and the wall. The participants crossed their arms in front of their chest, maintained 50° knee flexion, and then returned to the starting position (Figure 3). All taping techniques were performed three times for 10 seconds each, followed by 10 repetitions. Participants were instructed to go down for 3 seconds, hold for 5 seconds, and return to the starting position for the remaining 2 seconds. The average value for 3 seconds, excluding the first and last 1 second of the 5 seconds during which knee flexion was maintained at 50°, was used for data analysis. To minimize muscle fatigue, a 10-second rest period was provided between trials and a 1-minute rest was provided between the different taping techniques. A metronome set at 60 beats/min was used to equalize the exercise time.

Figure 3. Wall squat task. (A) Starting position and (B) end position.

4. Statistical Analysis

All data were statistically processed using the IBM SPSS Statistics 29.0 (IBM Co.). The Shapiro–Wilk test was performed to determine whether the data were normally distributed. A one-way repeated measures ANOVA was used to compare the muscle activities of the VMO and VL during wall squats. Significant differences among the four conditions (PMGT, VMOFT, CT, WT) were analyzed using the Bonferroni post-hoc test. The statistical significance for all analyses was set at 0.05.

Compared to the WT condition during wall squats, the muscle activity of the VMO increased in the PMGT and VMOFT conditions, but the difference was not statistically significant (p > 0.05). However, the muscle activity of the VMO was statistically significant at 35.73% ± 12.81% in CT condition compared to the condition WT (p < 0.05). Additionally, the muscle activity of the VMO significantly increased when both taping conditions were combined compared to when each taping technique was applied individually (p < 0.05). There was no significant difference in the muscle activity of the VL under any conditions compared to the WT condition during wall squats (p > 0.05) (Table 2).

Table 2 . Comparison of muscle activities among the three taping techniques during wall squat (N = 17).

Muscle	MVIC				F	p-value
	WT	PMGT	VMOFT	CT
VMO (%)	31.50 ± 12.31	32.99 ± 13.21	32.03 ± 12.16	35.73 ± 12.81a,b,c	26.06	0.01*
VL (%)	36.89 ± 14.20	34.20 ± 12.25	35.29 ± 12.46	33.30 ± 9.65	1.21	0.34

Values are presented as mean ± standard deviation. MVIC, maximal voluntary isometric contraction; WT, without taping; PMGT, patellar medial glide taping; VMOFT, vastus medialis oblique facilitatory taping; CT, combined taping; VMO, vastus medialis oblique; VL, vastus lateralis. *Significant difference among taping techniques, p < 0.05. ^aSignificant difference between WT. ^bSignificant difference between PMGT. ^cSignificant difference between VMOFT..

During wall squats, the VMO/VL ratio was significantly higher (p < 0.05) in the CT and PMGT conditions than in the WT condition (p < 0.05). The CT showed the highest ratio of 1.06 ± 0.17. Furthermore, the VMO/VL ratio significantly increased when the two taping techniques were combined compared to the VMOFT condition alone (p < 0.05) (Table 3).

Table 3 . Comparison of %MVIC ratio among the three taping techniques during wall squat (N = 17).

Ratio	%MVIC				F	p-value
	WT	PMGT	VMOFT	CT
VMO/VL	0.86 ± 0.16	0.96 ± 0.18a	0.92 ± 0.23	1.06 ± 0.17a,b	12.23	0.01*

Values are presented as mean ± standard deviation. MVIC, maximal voluntary isometric contraction; WT, without taping; PMGT, patellar medial glide taping; VMOFT, vastus medialis oblique facilitatory taping; CT, combined taping; VMO/VL, vastus medialis oblique vs. vastus lateralis. *Significant difference among taping techniques, p < 0.05. ^aSignificant difference between WT. ^bSignificant difference between VMOFT..

This study compared the muscle activity of the VMO and VL and the VMO/VL ratio during wall squats in healthy female individuals under three taping conditions: PMGT, VMOFT, and CT. There was no statistically significant difference in the muscle activity of the VMO when each technique was applied individually; a significant increase was observed in the CT condition. Additionally, a significant difference was observed between CT with PMGT and CT with VMOFT. There was no significant difference in the muscle activity of the VL across all taping techniques, but a statistically significant difference in the VMO/VL ratio was found between the PMGT and CT.

During wall squats, PMGT increased VMO activity, although the difference was not statistically significant. According to a studies by Banejad et al. [40] and Lan et al. [41], which compared the effects of short and long-term taping in the PFPS group using the same method as the medial gliding taping of the patella in this study, statistically significant differences were observed in lateral patellar displacement, patellofemoral congruence angle, and lateral patellofemoral angle. This suggests that when KT is applied at maximum tension, it can effectively alter patellar positioning. This fine increase of VMO activity is likely attributed to the medial shifting of the patella medially to its optimal position under maximum tape tension, which optimizes the formation of actin and myosin cross-bridges through the length-tension relationship and enhances the mechanical advantage, thereby facilitating VMO activity. However, in a study by Christou [42] that compared the effects of patellar medial gliding with non-elastic tape in patients with PFPS and healthy subjects, PMGT was found to increase VMO activity and decrease VL activity in the PFPS group, whereas it decreased VMO activity and increased VL activity in the healthy group. This suggests that in patients with PFPS, who have more significant damage to the medial knee joint structures than healthy individuals, patellar medial gliding with non-elastic tape provides mechanical support to the medial side of the knee joint through patellar taping. However, in healthy individuals, where the balance between the medial and lateral ligaments and muscles that move the patella within the trochlear groove of the femur is adequate, PMGT may decrease VMO activation and increase VL activation to maintain normal patellar gliding. Therefore, the lack of a significant increase in VMO activity with PMGT in this study is likely due to the intervention being conducted on healthy females without abnormal patellar positioning.

During the wall squat, VMO activity with the VMOFT did not show a statistically significant difference compared to the WT. This result is likely due to the differences in the presence or absence of pain. In a study by Ataabadi et al. [43], which measured quadriceps muscle activity during knee extension in healthy individuals under conditions of facilitatory and inhibitory KT, placebo taping, and no taping, no significant differences were reported in any taping condition. Similarly, a study by Yam et al. [44] on facilitatory and inhibitory KT found no statistically significant results in individuals without pain or disability; however, significant effects were observed in individuals with chronic musculoskeletal pain or muscle fatigue.

These differing results can be attributed to the presence or absence of pain in the subjects, and can be explained by two mechanisms. First, taping lifts the skin, increasing the space between the muscle and skin, which enhances blood and lymphatic circulation, thereby reducing pain and swelling [45]. According to Artioli and Bertolini [46], KT significantly reduced pain levels compared to the control and placebo taping groups. The second mechanism is the gate control theory, which suggests that the tactile stimulation provided by taping is transmitted through the relatively larger diameter Aβ nerve fibers, compared to the Aδ and C nerve fibers that transmit pain sensations. Tactile stimulation traveling through larger-diameter nerve fibers is transmitted more rapidly, exciting substantia gelatinosa cells. This leads to presynaptic inhibition before synapsis with pain-transmitting T-cells, thereby inhibiting pain transmission [44]. Based on these mechanisms, KT can reduce pain and consequently increase VMO activation in patients with PFPS. Therefore, the lack of statistically significant differences in VMO activation with the VMOFT in this study is likely due to the intervention being conducted on subjects without pain or disability.

While performing wall squats, VMOFT led to an increase in VMO activity, although the increase was not statistically significant. This can be explained using the principles of KT. According to Kase et al. [13]’s theory, the facilitation and inhibition techniques for KT are influenced by the direction and tension of the tape application. The principle of KT for muscle facilitation involves the application of tape from the origin of the muscle to its insertion, which stretches the fascia in the direction of muscle contraction. The “recoil effect” of the tape attempting to return to its original length creates tension on the skin, thereby providing sensory stimulation [13]. Conversely, when tape is applied from the muscle insertion to its origin along the direction of the muscle fibers, it pulls the muscle fibers in the opposite direction of muscle contraction. This action stretches the Golgi tendon organs at the muscle ends and inhibit alpha motor neurons from inducing muscle relaxation. Studies reporting no statistically significant effects based on the direction of KT application in healthy subjects have been conducted [43,44]. However, according to research utilizing facilitatory KT techniques and conducting grip strength tests, significant increases in grip strength have been observed in pain-free healthy females, demonstrating the effectiveness of facilitatory KT techniques even in pain-free subjects. These results suggest that KT stimulates the mechanoreceptors in the skin, thereby increasing muscle excitability [47]. Furthermore, a study comparing the effects of facilitatory and inhibitory KT in athletes reported significant increases in the %MVIC for facilitatory taping and significant decreases for inhibitory taping [48].

There was a statistically significant difference in the muscle activity of the VMO in the CT that combined the PMGT and VMOFT. These results are believed to be due to the synergistic effects of the two taping techniques. Both techniques were not statistically significant; however, the muscle activity of the VMO increased compared to that in the WT condition. The PMGT optimizes the length of the VMO to generate maximum active tension, and the VMOFT enhances afferent sensory input through the skin, thereby increasing VMO activity. Consequently, the significant increase in VMO activity observed in the CT group was likely due to the combination of the PMGT and VMOFT.

During wall squats, the VMO/VL ratio increased significantly with the PMGT and CT. A VMO/VL ratio greater than 1 indicates greater VMO activity than VL activity, which is a critical measure in patients with conditions such as PFPS. Although there was no significant difference in VMO activity alone with the PMGT, there was a significant difference in the VMO/VL ratio. With the PMGT, the patella glides and is fixed medially. This lengthens VL and shortens VMO [49]. This change increases the motor unit activation of the VMO while decreasing that of the VL, thereby effectively increasing the VMO/VL ratio. Additionally, CT likely resulted in greater VMO activity than VL, significantly increasing VMO/VL.

Therefore, the results of this study indicate that combining the PMGT with the VMOFT during wall squats can effectively activate the VMO. This approach may also induce beneficial changes in patients with PFPS who experience patellar malalignment and pain.

This study had several limitations. First, the participants were limited to young healthy females, making it difficult to generalize the results to older individuals, males, and those with musculoskeletal and neurological disorders. Second, the wall squat was restricted to 50°; therefore, we could not assess changes in muscle activity at different angles. Third, it was not possible to accurately verify the patellar movement induced by the PMGT. Fourth, as this study examined only the immediate effects of KT on muscle activity, the long-term effects of taping could not be determined. Forth, the small number of subjects may not adequately reflect individual differences in response to the intervention, which could affect the consistency and reproducibility of the results. Therefore, future studies should include a larger sample size to enhance the generalizability of the findings.

This study compared the activities of the VMO and VL during wall squats under three taping conditions: PMGT, VMOFT, and CT. The results showed that VMO activity significantly increased with CT, and the VMO/VL ratio significantly increased with PMGT and CT. Analysis of the significant differences between the taping methods revealed that VMO activity and VMO/VL ratio were significantly higher with CT than with either technique alone. Therefore, to selectively increase VMO activity in healthy individuals, a combination of the PMGT and VMOFT is recommended.

None.

The authors received financial and administrative support from the 2023 Inje University Research Fund. The funders had no role in the study design, data collection, analysis, decision to publish, or manuscript preparation.

No potential conflicts of interest relevant to this article are reported.

Conceptualization: JP. Data curation: JP. Formal analysis: JP. Funding acquisition: DA. Investigation: DA. Methodology: JP. Project administration: DA. Resources: JP. Software: JP. Supervision: DA. Validation: JP. Visualization: JP. Writing - original draft: JP. Writing - review & editing: JP, DA.