Deloading Tape Reduces Muscle Stress at Rest and during Contraction FRANÇOIS HUG1,2, ADAM OUELLETTE1, BILL VICENZINO1, PAUL W. HODGES1, and KYLIE TUCKER1,3 1 National Health and Medical Research Council Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Sciences, University of Queensland, Brisbane, Queensland, AUSTRALIA; 2 Laboratory ? Motricite´, Interactions, Performance X (EA 4334), UFR STAPS, University of Nantes, Nantes, FRANCE; and 3School of Biomedical Sciences, University of Queensland, Brisbane, Queensland, AUSTRALIA
ABSTRACT HUG, F., A. OUELLETTE, B. VICENZINO, P. W. HODGES, and K. TUCKER. Deloading Tape Reduces Muscle Stress at Rest and during Contraction. Med. Sci. Sports Exerc., Vol. 46, No. 12, pp. 2317–2325, 2014. Purpose: Taping techniques that aim to protect and reduce stress on an injured tissue during rehabilitation are common in sport. Called deloading tape, the mechanism of action is hypothesized to involve effects ranging from direct mechanical deloading of the underlying soft tissues to psychological effects on confidence. There is no evidence that deloading tape has direct mechanical effects. This study used an elastographic technique (supersonic shear imaging) to test the hypothesis that deloading tape applied to the skin over the rectus femoris would reduce stress within the taped area of this muscle. Methods: Thirteen healthy volunteers participated in this experiment. Muscle shear elastic modulus was compared between three treatments (no tape, deloading tape, and sham tape) in four conditions: three conditions without muscle contraction at different rectus femoris muscle–tendon unit lengths (moderately stretched, highly stretched, and shortened) and during submaximal isometric leg extension. Results: Although there was no effect of treatment when the muscle was shortened (P = 0.99), the shear elastic modulus was significantly affected by treatment for the three other conditions (all P G 0.002). Muscle shear elastic modulus was significantly less during application of deloading tape than that during both the no tape and sham tape conditions (all P e 0.001; e.g., vs no tape: moderately stretched, 8.4 T 2.7 vs 6.7 T 1.7 kPa; highly stretched, 25.2 T 8.2 vs 14.4 T 4.3 kPa; submaximal contraction, 21.3 T 4.8 vs 14.2 T 4.3 kPa). Conclusions: Through the use of elastography, this is the first study to support the hypothesis that deloading tape reduces stress in the underlying muscle region, thereby providing a biomechanical explanation for the effect observed during rehabilitation in clinical practice (reduce pain, restore function, and aid recovery). Further investigations are necessary to confirm these results in injured tissues. Key Words: SUPERSONIC SHEAR IMAGING, TAPING, STRESS, PASSIVE FORCE, FORCE TRANSMISSION
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Address for correspondence: Fran0ois Hug, Ph.D., National Health and Medical Research Council Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Sciences, University of Queensland, Brisbane, St. Lucia, Queensland 4072, Australia; E-mail: [email protected] and francois.hug@univ-nantes. Submitted for publication January 2014. Accepted for publication April 2014. 0195-9131/14/4612-2317/0 MEDICINE & SCIENCE IN SPORTS & EXERCISEÒ Copyright Ó 2014 by the American College of Sports Medicine DOI: 10.1249/MSS.0000000000000363
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physiotherapy/physical therapy. Their mechanism of action is hypothesized to involve direct mechanical deloading of the underlying soft tissues (e.g., skin, muscle, sensory receptors) or an effect secondary to changes in load sharing among synergist muscles (e.g., realignment of the patella secondary to increased activation of the vastus medialis relative to that of the vastus lateralis [13]). Psychological effects, such as altered confidence, have also been suggested (14). There is variable evidence of efficacy. Vicenzino et al. (37) demonstrated increased pain-free grip strength with taping of the wrist extensor muscles in patients with lateral epicondylalgia. However, O’Leary et al. (31) reported no effect of deloading tape, applied to the thoracic erector spinae muscles, on pressure pain thresholds in asymptomatic individuals. In terms of muscle activation, some studies show no effect of deloading tape on amplitude of muscle activity (23) whereas others report a decrease in muscle activity (36). The hypothesized mechanism of action of deloading taping is proposed to involve reduced tissue stress (load) within the taped area. However, changes in muscle stress during taping cannot be interpreted from EMG for several reasons related to the presumed effect of deloading tape on muscle
aping, in its many forms, is commonly used in sports for prophylaxis and/or management of musculoskeletal disorders. A range of techniques of tape application is used with the aim to achieve an array of effects such as inhibition (1) and facilitation (28) of muscle activation, restriction of range of motion (11), changes in posture (16,21), improvement of proprioception (7), altered timing of muscle activity (12,20), and reduced pain (8,20). Taping techniques that aim to reduce load on a painful/ injured tissue (often called deloading tape) are common in
length (30). First, change in muscle–tendon length distorts the relation between muscle activity and stress because of the well-known force–length relation (15). Consequently, the same muscle stress can be achieved at different muscle activation levels when the muscle operates at different lengths (3). Second, EMG does not account for passive force that also depends on the muscle length. Direct measures of tissue stress (or load) are thus necessary to test the hypothesis that deloading tape unloads the target tissues. Supersonic shear imaging (SSI) is a shear wave elastographic technique that quantifies the shear elastic modulus (stiffness) of a localized area of tissue (4,33). The shear elastic modulus is calculated from measurement of local shear wave velocity propagation from a remote mechanical vibration. Measures are made with a handheld ultrasound probe with two-dimensional maps of elasticity generated in real time. SSI provides a reliable measure of muscle shear elastic modulus (26), with a linear relation between muscle shear elastic modulus and muscle stress during passive stretching (10,25,29) and isometric contraction (5,6,10,38). This technique provides a unique opportunity to quantify the effect of deloading tape on muscle stress. This study aimed to use SSI to test the hypothesis that deloading tape applied to the skin over the rectus femoris (RF) would reduce shear elastic modulus (i.e., stress) within the taped area of this muscle at rest when the muscle– tendon unit is moderately and highly stretched and during contraction. We further hypothesized that deloading tape would not decrease muscle shear elastic modulus when the RF is shortened (i.e., when the muscle–tendon unit is already slack).
METHODS
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Participants Thirteen healthy volunteers (age, 34 T 6 yr; weight, 68 T 14 kg; height, 172 T 12 cm; six females) participated in this experiment. Participants were excluded if they had cuts, blisters, or bruises on the left anterior thigh, any lower limb musculoskeletal injuries in the previous 4 wk, or a history of allergy to adhesives. Participants provided an informed written consent. The Institutional Medical Research Ethics Committee (University of Queensland) approved the study, and all the procedures conformed to the Declaration of Helsinki. Measure of Muscle Shear Elastic Modulus An Aixplorer ultrasonic scanner (version 6.0; Supersonic Imagine, Aix-en-Provence, France), coupled with a linear transducer array (2–10 MHz, SL10-2), was used in shear wave elastography mode (general preset) to measure muscle shear elastic modulus. The method used to obtain the shear wave speed (V s) is described in detail elsewhere (4,35). Assuming a linear elastic behavior
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(4,9), the muscle shear elastic modulus (K) was calculated as follows: K ¼ QVs2
½1 j3
where Q is the density of muscle (1000 kgIm ). Maps of the shear elastic modulus were obtained at 1 sample per second, with a spatial resolution of 1 1 mm.
Experimental Procedure To aid tape adherence, the participants’ left anterior thigh was shaved. To standardize muscle conditioning, before testing, a physiotherapist passively stretched the RF into maximal hip extension with knee flexion for 30 s and repeated this three times with 20 s of rest between repetitions. Immediately after this procedure, the RF was visualized using the ultrasound (B-mode). The ultrasound transducer was placed longitudinally on the midbelly of the RF, and the location was marked on the skin using a waterproof felt-tip pen. Maximal voluntary contractions. At the beginning of the experimental session (before any application of tape), maximal isometric voluntary knee extensions (MVC) were performed with participants seated on a plinth and their back and upper legs supported. Their torso was reclined by 10from upright, and participants crossed their arms over their chest. A 5-cm-wide support strap was placed firmly around the pelvis and chair to minimize changes in body position throughout the MVC. Isometric knee extension force was measured with a force transducer (maximal range, 300 lb; FUTEK) attached via a strap around the test leg just above the ankle. Knee angle was set at approximately 65- from full extension. Maximal force was maintained for approximately 3 s and then returned to rest. This was repeated three times with 960-s rest between contractions. The highest force was considered the best performance (MVC) and was used to calculate the 20% MVC target force for subsequent submaximal isometric contractions. Treatments. Three treatments were tested in random order: control (no tape), sham tape, and deloading tape. For the two tape treatments, tape was applied with the participants seated upright on a standard plinth, with their arms supporting their upper body, hips flexed (approximately 80- from neutral), knees extended (0-), and legs supported. Participants were encouraged to relax their leg while the tape was being applied. The deloading tape consisted of a nonelastic therapeutic tape (Allcare Ridged Strapping Tape, 3.8 cm wide; Pharmacare, Australia) applied in a diamond formation over the midbelly of the RF (Fig. 1). The tape was applied around the location described previously for ultrasound transducer placement. The tissue inside the diamond was gathered to the center, creating an ‘‘orange peel’’ appearance (Fig. 1A) of the skin (31,37). The sham tape was applied in the same formation but without any tension applied to the tape, and there was no ‘‘orange peel’’ appearance (Fig. 1B).
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in a full extension. During the passive trials at different muscle lengths, participants were asked to remain as relaxed as possible. For the submaximal isometric contraction (contraction condition), participants adopted the same position used for MVC. They matched a knee extension target torque set at 20% of MVC for approximately 15 s. This target torque was chosen to induce a similar muscle stress to that induced by the highly stretched condition (as determined during pilot experiments). Data Analysis
FIGURE 1—Tape techniques tested in this study. To apply the deloading tape technique (using the diamond tape technique) (A), four pieces approximately 15–20 cm long were applied to the skin in a diamond shape with tension applied so that the skin was notably gathered to the center with an ‘‘orange peel’’ appearance. The strips overlapped at their ends and were secured with four additional tape strips. The sham tape (B) was formed in an identical diamond pattern but without any tension applied to the skin.
An example of the obtained shear elastic modulus map is shown in Figure 3. The software of the ultrasound scanner (Supersonic Imagine, France) was used to measure mean shear elasticity values across circular regions (from 1 to 2 cm in diameter, depending on the individual participant’s muscle thickness). Care was taken to avoid inclusion of hyperechoic regions (areas of dense connective tissue) within this circular region because this may affect the accuracy of estimation of shear elastic modulus. For each treatment and each condition separately, the 10 shear elastic measurements (corresponding to the 10-s recording) were averaged to obtain a mean value of muscle shear elastic modulus. Note that the Aixplorer scanner provides the Young modulus measurement. Because the Young modulus calculation requires the assumption of an isotropic material (which is not the case for muscle [32]), all the measurements were divided by three to convert the value to represent the shear elastic modulus, as classically undertaken in other experiments (22,26). Additional Control Experiments
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If the muscle–tendon unit length remains unchanged (same hip and knee angles) and if, as hypothesized, the application of tape shortens the muscle (reduced elastic modulus) within the taped area, then it follows that the muscle–tendon unit length outside this area must increase, resulting in increased shear elastic modulus. Thus, evaluation of opposite changes within and outside the taped area was considered to provide an additional method to rigorously test the hypothesis of this study. To this end, we performed an additional experiment in four participants (one newly recruited using identical criteria and three who participated in the main protocol) to quantify the change in RF shear elastic modulus within and distal to the diamond tape during each of the four conditions described previously. The protocol was identical to the one described previously, except that the sham tape treatment was not tested. It was considered that an alternative explanation for the observations in this study could be changes in tissue shear elastic modulus secondary to vascular engorgement, which would be consistent with the external appearance (discoloration) of the skin. To verify that vascular engorgement (if any) did not change muscle elastic modulus, an additional experiment was conducted in four participants (who participated in the main protocol) in which shear elastic modulus was measured with and without
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Experimental conditions. For each of the three treatments (control, sham tape, deloading tape), the muscle shear elastic modulus was measured, in a region of the RF muscle immediately below the center of the diamond, for 10 s (10 values were recorded at 1 sample per second). This was repeated for three passive conditions during which the RF muscle–tendon unit was placed at different lengths (moderately stretched, highly stretched, and shortened) and one active condition where the participants performed an isometric submaximal contraction with the muscle at a moderately stretched length (Fig. 2). The order of the experimental conditions was randomized (within each treatment). Hip and knee angles were measured using a goniometer, and adjustments to joint angles were made before each 10-s recording, as follows (Fig. 2). To moderately stretch the RF, which crosses the hip and knee, participants sat in the chair with their arms across their chest in a comfortable position, hips at approximately 80- flexion, knees at approximately 80- flexion, and leg freely hanging. To further stretch the RF (highly stretched condition), participants laid supine, with their hips in 5- flexion and the knees flexed over the edge of the bed. The left knee was held in 90- flexion by an experimenter. The shortened length of RF (shortened condition) was achieved with the participant sitting in the chair, their right leg hanging freely, and the left leg manually supported
FIGURE 2—Experimental conditions. Muscle shear elastic modulus was measured during four conditions: three passive conditions with the muscle at different lengths and the participants asked to remain as relaxed as possible and one active condition (contraction). To modify the length of the RF muscle (which crosses the hip and knee), the knee and/or hip angles were adjusted, as shown in the figure (and maintained by the experimenter in the same position between the treatments for the relaxed states).
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application of a tourniquet proximal to the recording site. For this experiment, measures were made on the biceps brachii (because blood flow is easier to inhibit within the arm) in two different positions, i.e., moderately stretched (elbow angle, 90-) and highly stretched (elbow angle, 180-). This tourniquet application (approximately 3 min) resulted in an increase of 7.5 mm (range, 5.0–10.0 mm) in arm circumference, which confirms significant vascular engorgement of the tissue. Statistical Analysis Statistical analyses were performed in Stata (StataCorp LP, College Station, TX). Data were normally distributed, and thus, the values are reported as mean T SD. To test the effect of muscle condition (moderately stretched, highly stretched, shortened, and contraction) on the shear elastic modulus in the control state (no tape), a repeated-measure ANOVA was used, with condition as a within-subject factor. The large effect of condition on shear elastic modulus (i.e., shear elastic modulus was 8 times greater in the highly stretched than that in the shortened muscle) induced a large variance in the sample. Thus, each condition was compared
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separately to determine whether the application of tape significantly affected muscle stress. A repeated-measure ANOVA (within-subject factor, treatment (no tape, sham tape, and deloading tape)) was performed for each condition. A Tukey post hoc test was used when significant main effects were observed. A P value G0.05 was considered significant.
RESULTS When shear elastic modulus was compared between conditions in the control (no tape) treatment only, there was a significant main effect (P G 0.0001). Post hoc analysis showed that the elastic modulus was greater when the muscle was highly stretched (25.2 T 8.2 kPa) than that when either shortened (3.7 T 1.0 kPa, P G 0.001) or moderately stretched (8.4 T 2.7 kPa, P G 0.001). Furthermore, the shear elastic modulus was significantly greater when the muscle was contracted (21.3 T 4.8 kPa) than that when at rest in both the shortened and moderately stretched states (P values G0.001). As intended by our methods, the shear elastic modulus did not differ (P = 0.18) between the highly stretched condition at rest and during contraction in the moderately stretched length. Despite a tendency indicating a greater
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FIGURE 3—Individual examples of shear elastic modulus maps with and without tape. The ultrasound images were obtained during the highly stretched (A) and contraction (B) condition for both the control and deloading tape treatment. The map of shear elastic modulus is superposed onto the B-mode image on the upper panel, with the color scale depicting graduation of shear elastic modulus (scale (kPa) at top right). To obtain a representative value, the shear elastic modulus (kPa) was averaged over a circular area.
MECHANICAL EFFECT OF DELOADING TAPE
the modulus was significantly less during application of deloading tape than that during the sham tape treatment for the highly stretched (j33.9% T 21.4%, P G 0.001) and contraction conditions (j28.6% T 23.7%, P = 0.002) but not when the muscle was moderately stretched (P = 0.11) (Fig. 4). No significant difference in the modulus was observed between the sham tape and the no-tape treatment for any condition (0.15 G P G 0.95). The additional control experiment with measures of muscle shear elastic modulus both within and distal to the taped area first confirmed the decrease in stress within the taped area compared with the untaped control state during the moderately stretched (j1.3 T 1.8 kPa, i.e., j16.3% T 22.4%), highly stretched (j5.7 T 3.8 kPa, i.e., j32.6% T 22.5%), and contraction conditions (j6.1 T 7.3 kPa, i.e., j24.7% T 30.1%). No change in shear elastic modulus was observed during the shortened condition (j0.1 T 1.7 kPa).
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elastic modulus when the muscle was moderately stretched than that when shortened, the P value (P = 0.09) did not reach the threshold for significance. The force produced during the contraction condition was not different across treatments (78.9 T 27.2, 78.9 T 26.8, and 78.8 T 26.9 N for control, deloading tape, and sham tape conditions, respectively; main effect of treatment, P = 0.91). There was no effect of treatment when the muscle was shortened (P = 0.99); however, the shear elastic modulus was affected by treatment in the three other conditions, as follows: moderately stretched (P = 0.002), highly stretched (P = 0.0015), and contraction (P = 0.009). Post hoc analysis showed that the shear elastic modulus was significantly less during application of deloading tape than that in the untaped control state (moderately stretched: j17.8% T 16.1%, P = 0.001; highly stretched: j39.0% T 19.0%, P G 0.001; contraction: j31.7% T 20.7%, P = 0.001) (Fig. 4). Similarly,
FIGURE 4—Effect of deloading and sham tape on the RF’s shear elastic modulus. Deloading tape reduced the modulus during the ‘‘moderately stretched,’’ ‘‘highly stretched,’’ and ‘‘contraction’’ conditions but not when the muscle was shortened. The sham tape did not affect the shear elastic modulus compared with the no-tape control. *P G 0.05 for comparison with the ‘‘control’’ (no tape) treatment; +P G 0.05 for comparison with the ‘‘sham tape’’ treatment.
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In addition, the shear elastic modulus measured distal to the deloading tape increased systematically during the moderately stretched (4.0 T 0.9 kPa, i.e., 55% T 7%), highly stretched (3.3 T 3.6 kPa, i.e., 23% T 23%), and contraction conditions (14.6 T 9.4 kPa, i.e., 139% T 85%). No change in shear elastic modulus was observed during the shortened condition (j0.1 T 0.4 kPa). These data provide further validation of our interpretation of the muscle stress changes within the taped area. The additional control experiment to study the effect of putative vascular engorgement showed that shear elastic modulus was not changed in the muscle after application of the tourniquet neither for the moderately stretched condition (from 5.2 T 2.6 to 5.1 T 2.2 kPa for before and after the tourniquet application, respectively) nor the for highly stretched condition (from 13.7 T 2.5 to 14.1 T 1.4 kPa for before and after the tourniquet application, respectively). This suggests that the results are unlikely to be explained by vascular changes from bunching of the tissues with tape application.
DISCUSSION Taking advantage of an elastographic technique, the present study is the first to quantify the effect of deloading taping on muscle stress during both passive and active conditions. Consistent with our hypothesis, the deloading tape applied to the skin directly over the RF muscle reduced muscle stress (measured inside the diamond-shaped area) for the muscle conditions where the RF was tensioned (moderately stretched, highly stretched, and contraction conditions). In contrast, when the muscle–tendon unit was slack (shortened condition), there was no effect of
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deloading tape on muscle shear elastic modulus. These results provide a better understanding of the mechanical effect of deloading taping on muscle tissues. Two observations support our argument that the changes in muscle stress are caused by changes in muscle length induced by tape application. First, stress was decreased by shortening the muscle–tendon length (to slacken the muscle) without application of tape. Second, stress was not reduced by tape when the muscle was already slack, i.e., in the shortened condition. Furthermore, results from additional experiments (n = 4) provide some evidence that 1) stress was increased distal to the area of tape, which would have to undergo lengthening if the muscle tissue within the taped area was shortened, and 2) changes in muscle vascular engorgement that might accompany the tape application did not replicate the decreased stress observed when the deloading tape was applied. It is accepted that the muscle shear elastic modulus is linearly related to muscle stress, as demonstrated in both in vivo (5,6,29) and in vitro (25) studies. Before interpretation of the observed changes in shear elastic modulus as a decrease in muscle stress (and thus as a mechanical effect of tape), other possible methodological explanations need to be considered. First, changed pennation angle (angle between the muscle fibers and the ultrasound transducer) alters the relation between shear elastic modulus and muscle stress (19). Because of the complex architecture of the RF muscle (bipennate), the putative change in pennation angle induced by tape could not be quantified from our B-mode images; however, they could be expected to be small. Gennisson et al. (19) reported a decrease of 20 kPa (from 60 to 40 kPa, i.e., j33%) in shear elastic modulus when the transducer was changed from an orientation parallel to the muscle fibers
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MECHANICAL EFFECT OF DELOADING TAPE
of our B-mode images (where the deeper RF aponeurosis was visible) suggests that the muscle thickness increased inside the diamond tape during the deloading tape treatment compared with that during the no-tape condition (Fig. 3). Because muscle tissues are considered an incompressible material (17), muscle volume does not change (24), and therefore, the increased muscle thickness should be directly linked to shortening of the muscle within the area bounded by tape. Because the muscle–tendon unit length did not change (hip and knee angles were matched between the treatments), shortening (i.e., reduced muscle stress) must be counterbalanced by lengthening (i.e., increased muscle stress) proximal and distal to the taped area. The additional control experiment confirmed this prediction. The mechanisms by which tape alters muscle length may include transmission of force by the fascia structure (34). Li and Ahn (27) described fascial bands as structural bridges that mechanically link the skin, subcutaneous layer, and deeper muscle layers. Application of deloading tape has been proposed to reduce pain either directly by unloading the injured/painful tissue (e.g., lateral epicondylalgia) (Vicenzino et al. [37]) or secondary to a change in factors such as joint position as a result of modification of muscle activity (e.g., patellofemoral joint position) (Tobin and Robinson [36]). The present study confirmed a direct effect of deloading tape on tissue stress. A decrease in muscle stress was measured inside the diamond-shaped area (n = 13), and the results of the additional experiments (n = 4) suggest that the effect is counterbalanced (at least in part) by increased stress distal to the taped area. Consequently, it is very likely that the global force produced by the RF muscle (directly linked to muscle stress [6]) was not reduced. This observation is important when the intended clinical effect is to decrease the force produced by an individual muscle to alter load sharing among synergist muscles. Although we demonstrated that deloading tape is effective to reduce stress in the underlying muscle region, this observation has been performed on healthy participants and is limited to the taping technique used (diamond shape, encompassing both longitudinal and transverse elements). This study does not confirm that the technique is clinically effective. For such an interpretation, deloading tape should be applied over injured tissues where the effects may differ because of edema, scarring, pain inhibition/facilitation, or heightened motoneuron excitability. In addition, studies are required to investigate the effect of taping on clinical outcomes (e.g., pain level) because this cannot be assumed from the identification of a reduction in muscle stress despite the plausibility of the effect. For a thorough comparison with results reported in the literature, other tape configurations (e.g., longitudinal/transverse tape [2,36]) need to be tested. Finally, the potential effect of training status on change in muscle stress has not been investigated in the present study and should be further explored. The present study quantified the decrease in muscle stress in the muscle tissue directly beneath the deloading tape using
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to a perpendicular orientation (mimicking an extreme— nonphysiological—change in pennation angle by 90-). We suggest that it is unlikely that the large changes in shear elastic modulus reported in the present study (range, 17.8%– 39% of the elastic modulus measuring during control, depending on the condition) can be explained by potential changes in the RF muscle’s architecture. Second, it is important to consider that unlike other elastographic techniques (18), SSI does not require external application of mechanical force (e.g., vibration) to generate shear waves but instead uses focused ultrasound beams. Consequently, the change in thickness of subcutaneous tissue with tape (due to the bunching of the skin (Fig. 1A)) is unlikely to alter the mechanical force applied to the tissues and, thus, the shear elastic modulus measurement. The mechanism by which tape modulates muscle stress is unclear. Taping along the length of a muscle can reduce the Hoffman reflex (H reflex, which is influenced by motoneuron excitability) in the trapezius (2) and triceps surae (1) muscles. However, it is very unlikely that the decrease in shear elastic modulus observed during the moderate and highly stretched conditions was due to decreased motoneuron excitability because the muscle was at rest (i.e., no voluntary muscle activity). It is important to note that although participants were asked to relax their muscle during these stretched conditions, the absence of muscle activation cannot be confirmed during these tasks because surface EMG was not recorded during this experiment. This was because the application of deloading tape increases the thickness of the superficial layers in the center of the area bounded by tape, which would increase the distance between the electrode and muscle and, thus, invalidate interpretation of changes in myoelectrical activity between treatments/ conditions. The validity of our conclusion related to the relaxed muscle state is strengthened by the fact that resting values of shear elastic modulus reported during the no-tape treatment are similar to those reported by Lacourpaille et al. (26) for the same resting muscle. Considering that some studies (1,2), but not all (23), reported a decreased motoneuron excitability with tape, we cannot exclude that the decrease in muscle shear elastic modulus reported during the contraction condition might in part be due to a decrease in muscle activation during contraction. If so, it likely accounts only in small part for the observed effects. The decrease in muscle stress observed during the moderately and highly stretched conditions and when the muscle was at rest provides evidence for a mechanical effect of deloading tape. As proposed by Morissey (30), tape could reduce muscle length and, therefore, passive force (i.e., unload the muscle). Consistent with this observation, our results showed a significant effect of tape for the three conditions in which the muscle–tendon unit was under tension (greater than the slack length) but failed to show any significant decrease in shear elastic modulus when the muscle–tendon unit was already shortened below the slack length, i.e., with no passive force. Further inspection of some
SSI. As the reliability (intrasession repeatability, interday reproducibility, and interobserver reliability) of this SSI technique to measure the shear elastic modulus of resting human muscles has been demonstrated (26), the technique offers opportunity to investigate the effects of different taping techniques or to determine the effectiveness of taping in clinical practice or for training purposes. Even if the clinical outcome (e.g., pain relief, joint realignment) is the most relevant measure of the taping effectiveness, the quantification of its mechanical effect may help to better understand
the controversial outcomes of mechanisms reported in the literature. The authors thank M4 Healthcare (Australia) for lending the ultrasound scanner and Jean Hug for drawing Figure 2. The study was funded by a program grant (ID631717) from the National Health and Medical Research Council of Australia. P. W. H. holds a Senior Principal Research Fellowship (APP1002190), and K. T., a Career Development Fellowship (ID 1009410), both from the National Health and Medical Research Council. The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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REFERENCES 1. Alexander CM, McMullan M, Harrison PJ. What is the effect of taping along or across a muscle on motoneurone excitability? A study using triceps surae. Man Ther. 2008;13(1):57–62. 2. Alexander CM, Stynes S, Thomas A, Lewis J, Harrison PJ. Does tape facilitate or inhibit the lower fibres of trapezius? Man Ther. 2003;8(1):37–41. 3. Altenburg TM, de Haan A, Verdijk PW, van Mechelen W, de Ruiter CJ. Vastus lateralis single motor unit EMG at the same absolute torque production at different knee angles. J Appl Physiol (1985). 2009;107(1):80–9. 4. Bercoff J, Tanter M, Fink M. Supersonic shear imaging: a new technique for soft tissue elasticity mapping. IEEE Trans Ultrason Ferroelectr Freq Control. 2004;51(4):396–409. 5. Bouillard K, Hug F, Gue´vel A, Nordez A. Shear elastic modulus can be used to estimate an index of individual muscle force during a submaximal isometric fatiguing contraction. J Appl Physiol (1985). 2012;113(9):1353–61. 6. Bouillard K, Nordez A, Hug F. Estimation of individual muscle force using elastography. PLoS One. 2011;6(12):e29261. 7. Callaghan MJ, Selfe J, Bagley PJ, Oldham JA. The effects of patellar taping on knee joint proprioception. J Athl Train. 2002; 37(1):19–24. 8. Campolo M, Babu J, Dmochowska K, Scariah S, Varughese J. A comparison of two taping techniques (kinesio and mcconnell) and their effect on anterior knee pain during functional activities. Int J Sports Phys Ther. 2013;8(2):105–10. 9. Catheline S, Gennisson JL, Delon G, et al. Measuring of viscoelastic properties of homogeneous soft solid using transient elastography: an inverse problem approach. J Acoust Soc Am. 2004;116(6):3734–41. 10. Chernak LA, DeWall RJ, Lee KS, Thelen DG. Length and activation dependent variations in muscle shear wave speed. Physiol Meas. 2013;34(6):713–21. 11. Cordova ML, Ingersoll CD, LeBlanc MJ. Influence of ankle support on joint range of motion before and after exercise: a metaanalysis. J Orthop Sports Phys Ther. 2000;30(4):170–7; discussion 178–82. 12. Cowan SM, Bennell KL, Hodges PW. Therapeutic patellar taping changes the timing of vasti muscle activation in people with patellofemoral pain syndrome. Clin J Sport Med. 2002;12(6): 339–47. 13. Crossley K, Cowan SM, Bennell KL, McConnell J. Patellar taping: is clinical success supported by scientific evidence? Man Ther. 2000;5(3):142–50. 14. Delahunt E, McGrath A, Doran N, Coughlan GF. Effect of taping on actual and perceived dynamic postural stability in persons with chronic ankle instability. Arch Phys Med Rehabil. 2010;91(9):1383–9. 15. Evans CL, Hill AV. The relation of length to tension development and heat production on contraction in muscle. J Physiol. 1914; 49(1–2):10–6.
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16. Franettovich M, Chapman A, Blanch P, Vicenzino B. A physiological and psychological basis for anti-pronation taping from a critical review of the literature. Sports Med. 2008;38(8):617–31. 17. Fung YC. Biomechanics: Mechanical Properties of Living Tissues. New York (NY): Springer-Verlag; 1993. 18. Gennisson JL, Cornu C, Catheline S, Fink M, Portero P. Human muscle hardness assessment during incremental isometric contraction using transient elastography. J Biomech. 2005;38(7): 1543–50. 19. Gennisson JL, Deffieux T, Mace´ E, Montaldo G, Fink M, Tanter M. Viscoelastic and anisotropic mechanical properties of in vivo muscle tissue assessed by supersonic shear imaging. Ultrasound Med Biol. 2010;36(5):789–801. 20. Gilleard W, McConnell J, Parsons D. The effect of patellar taping on the onset of vastus medialis obliquus and vastus lateralis muscle activity in persons with patellofemoral pain. Phys Ther. 1998; 78(1):25–32. 21. Greig AM, Bennell KL, Briggs AM, Hodges PW. Postural taping decreases thoracic kyphosis but does not influence trunk muscle electromyographic activity or balance in women with osteoporosis. Man Ther. 2008;13(3):249–57. 22. Hug F, Lacourpaille L, MaBsetti O, Nordez A. Slack length of gastrocnemius medialis and Achilles tendon occurs at different ankle angles. J Biomech. 2013;46(14):2534–8. 23. Janwantanakul P, Gaogasigam C. Vastus lateralis and vastus medialis obliquus muscle activity during the application of inhibition and facilitation taping techniques. Clin Rehabil. 2005; 19(1):12–9. 24. Kardel T. Niels Stensen’s geometrical theory of muscle contraction (1667): a reappraisal. J Biomech. 1990;23(10):953–65. 25. Koo TK, Guo JY, Cohen JH, Parker KJ. Relationship between shear elastic modulus and passive muscle force: an ex-vivo study. J Biomech. 2013;46(12):2053–9. 26. Lacourpaille L, Hug F, Bouillard K, Hogrel JY, Nordez A. Supersonic shear imaging provides a reliable measurement of resting muscle shear elastic modulus. Physiol Meas. 2012;33(3): N19–28. 27. Li W, Ahn AC. Subcutaneous fascial bands—a qualitative and morphometric analysis. PLoS One. 2011;6(9):e23987. 28. Macgregor K, Gerlach S, Mellor R, Hodges PW. Cutaneous stimulation from patella tape causes a differential increase in vasti muscle activity in people with patellofemoral pain. J Orthop Res. 2005;23(2):351–8. 29. MaBsetti O, Hug F, Bouillard K, Nordez A. Characterization of passive elastic properties of the human medial gastrocnemius muscle belly using supersonic shear imaging. J Biomech. 2012; 45(6):978–84. 30. Morissey D. Proprioceptive shoulder taping. J Bodywork Mov Ther. 2000;4(3):189–94.
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31. O’Leary S, Carroll M, Mellor R, Scott A, Vicenzino B. The effect of soft tissue deloading tape on thoracic spine pressure pain thresholds in asymptomatic subjects. Man Ther. 2002;7(3):150–3. 32. Royer D, Gennisson JL, Deffieux T, Tanter M. On the elasticity of transverse isotropic soft tissues (L). J Acoust Soc Am. 2011; 129(5):2757–60. 33. Shinohara M, Sabra K, Gennisson JL, Fink M, Tanter M. Realtime visualization of muscle stiffness distribution with ultrasound shear wave imaging during muscle contraction. Muscle Nerve. 2010;42(3):438–41. 34. Stecco C, Macchi V, Porzionato A, Duparc F, De Caro R. The fascia: the forgotten structure. Ital J Anat Embryol. 2011;116(3): 127–38.
35. Tanter M, Bercoff J, Athanasiou A, et al. Quantitative assessment of breast lesion viscoelasticity: initial clinical results using supersonic shear imaging. Ultrasound Med Biol. 2008;34(9):1373–86. 36. Tobin S, Robinson G. The effect of McConnell’s vastus lateralis inhibition taping technique on vastus lateralis and vastus medialis obliquus activity. Physiotherapy. 2000;86(4):173–83. 37. Vicenzino B, Brooksbank J, Minto J, Offord S, Paungmali A. Initial effects of elbow taping on pain-free grip strength and pressure pain threshold. J Orthop Sports Phys Ther. 2003;33(7):400–7. 38. Yoshitake Y, Takai Y, Kanehisa H, Shinohara M. Muscle shear modulus measured with ultrasound shear-wave elastography across a wide range of contraction intensity. Muscle Nerve. 2014;50(1):103–13.
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MECHANICAL EFFECT OF DELOADING TAPE
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ABSTRACT HUG, F., A. OUELLETTE, B. VICENZINO, P. W. HODGES, and K. TUCKER. Deloading Tape Reduces Muscle Stress at Rest and during Contraction. Med. Sci. Sports Exerc., Vol. 46, No. 12, pp. 2317–2325, 2014. Purpose: Taping techniques that aim to protect and reduce stress on an injured tissue during rehabilitation are common in sport. Called deloading tape, the mechanism of action is hypothesized to involve effects ranging from direct mechanical deloading of the underlying soft tissues to psychological effects on confidence. There is no evidence that deloading tape has direct mechanical effects. This study used an elastographic technique (supersonic shear imaging) to test the hypothesis that deloading tape applied to the skin over the rectus femoris would reduce stress within the taped area of this muscle. Methods: Thirteen healthy volunteers participated in this experiment. Muscle shear elastic modulus was compared between three treatments (no tape, deloading tape, and sham tape) in four conditions: three conditions without muscle contraction at different rectus femoris muscle–tendon unit lengths (moderately stretched, highly stretched, and shortened) and during submaximal isometric leg extension. Results: Although there was no effect of treatment when the muscle was shortened (P = 0.99), the shear elastic modulus was significantly affected by treatment for the three other conditions (all P G 0.002). Muscle shear elastic modulus was significantly less during application of deloading tape than that during both the no tape and sham tape conditions (all P e 0.001; e.g., vs no tape: moderately stretched, 8.4 T 2.7 vs 6.7 T 1.7 kPa; highly stretched, 25.2 T 8.2 vs 14.4 T 4.3 kPa; submaximal contraction, 21.3 T 4.8 vs 14.2 T 4.3 kPa). Conclusions: Through the use of elastography, this is the first study to support the hypothesis that deloading tape reduces stress in the underlying muscle region, thereby providing a biomechanical explanation for the effect observed during rehabilitation in clinical practice (reduce pain, restore function, and aid recovery). Further investigations are necessary to confirm these results in injured tissues. Key Words: SUPERSONIC SHEAR IMAGING, TAPING, STRESS, PASSIVE FORCE, FORCE TRANSMISSION
T
Address for correspondence: Fran0ois Hug, Ph.D., National Health and Medical Research Council Centre of Clinical Research Excellence in Spinal Pain, Injury and Health, School of Health and Rehabilitation Sciences, University of Queensland, Brisbane, St. Lucia, Queensland 4072, Australia; E-mail: [email protected] and francois.hug@univ-nantes. Submitted for publication January 2014. Accepted for publication April 2014. 0195-9131/14/4612-2317/0 MEDICINE & SCIENCE IN SPORTS & EXERCISEÒ Copyright Ó 2014 by the American College of Sports Medicine DOI: 10.1249/MSS.0000000000000363
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APPLIED SCIENCES
physiotherapy/physical therapy. Their mechanism of action is hypothesized to involve direct mechanical deloading of the underlying soft tissues (e.g., skin, muscle, sensory receptors) or an effect secondary to changes in load sharing among synergist muscles (e.g., realignment of the patella secondary to increased activation of the vastus medialis relative to that of the vastus lateralis [13]). Psychological effects, such as altered confidence, have also been suggested (14). There is variable evidence of efficacy. Vicenzino et al. (37) demonstrated increased pain-free grip strength with taping of the wrist extensor muscles in patients with lateral epicondylalgia. However, O’Leary et al. (31) reported no effect of deloading tape, applied to the thoracic erector spinae muscles, on pressure pain thresholds in asymptomatic individuals. In terms of muscle activation, some studies show no effect of deloading tape on amplitude of muscle activity (23) whereas others report a decrease in muscle activity (36). The hypothesized mechanism of action of deloading taping is proposed to involve reduced tissue stress (load) within the taped area. However, changes in muscle stress during taping cannot be interpreted from EMG for several reasons related to the presumed effect of deloading tape on muscle
aping, in its many forms, is commonly used in sports for prophylaxis and/or management of musculoskeletal disorders. A range of techniques of tape application is used with the aim to achieve an array of effects such as inhibition (1) and facilitation (28) of muscle activation, restriction of range of motion (11), changes in posture (16,21), improvement of proprioception (7), altered timing of muscle activity (12,20), and reduced pain (8,20). Taping techniques that aim to reduce load on a painful/ injured tissue (often called deloading tape) are common in
length (30). First, change in muscle–tendon length distorts the relation between muscle activity and stress because of the well-known force–length relation (15). Consequently, the same muscle stress can be achieved at different muscle activation levels when the muscle operates at different lengths (3). Second, EMG does not account for passive force that also depends on the muscle length. Direct measures of tissue stress (or load) are thus necessary to test the hypothesis that deloading tape unloads the target tissues. Supersonic shear imaging (SSI) is a shear wave elastographic technique that quantifies the shear elastic modulus (stiffness) of a localized area of tissue (4,33). The shear elastic modulus is calculated from measurement of local shear wave velocity propagation from a remote mechanical vibration. Measures are made with a handheld ultrasound probe with two-dimensional maps of elasticity generated in real time. SSI provides a reliable measure of muscle shear elastic modulus (26), with a linear relation between muscle shear elastic modulus and muscle stress during passive stretching (10,25,29) and isometric contraction (5,6,10,38). This technique provides a unique opportunity to quantify the effect of deloading tape on muscle stress. This study aimed to use SSI to test the hypothesis that deloading tape applied to the skin over the rectus femoris (RF) would reduce shear elastic modulus (i.e., stress) within the taped area of this muscle at rest when the muscle– tendon unit is moderately and highly stretched and during contraction. We further hypothesized that deloading tape would not decrease muscle shear elastic modulus when the RF is shortened (i.e., when the muscle–tendon unit is already slack).
METHODS
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Participants Thirteen healthy volunteers (age, 34 T 6 yr; weight, 68 T 14 kg; height, 172 T 12 cm; six females) participated in this experiment. Participants were excluded if they had cuts, blisters, or bruises on the left anterior thigh, any lower limb musculoskeletal injuries in the previous 4 wk, or a history of allergy to adhesives. Participants provided an informed written consent. The Institutional Medical Research Ethics Committee (University of Queensland) approved the study, and all the procedures conformed to the Declaration of Helsinki. Measure of Muscle Shear Elastic Modulus An Aixplorer ultrasonic scanner (version 6.0; Supersonic Imagine, Aix-en-Provence, France), coupled with a linear transducer array (2–10 MHz, SL10-2), was used in shear wave elastography mode (general preset) to measure muscle shear elastic modulus. The method used to obtain the shear wave speed (V s) is described in detail elsewhere (4,35). Assuming a linear elastic behavior
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(4,9), the muscle shear elastic modulus (K) was calculated as follows: K ¼ QVs2
½1 j3
where Q is the density of muscle (1000 kgIm ). Maps of the shear elastic modulus were obtained at 1 sample per second, with a spatial resolution of 1 1 mm.
Experimental Procedure To aid tape adherence, the participants’ left anterior thigh was shaved. To standardize muscle conditioning, before testing, a physiotherapist passively stretched the RF into maximal hip extension with knee flexion for 30 s and repeated this three times with 20 s of rest between repetitions. Immediately after this procedure, the RF was visualized using the ultrasound (B-mode). The ultrasound transducer was placed longitudinally on the midbelly of the RF, and the location was marked on the skin using a waterproof felt-tip pen. Maximal voluntary contractions. At the beginning of the experimental session (before any application of tape), maximal isometric voluntary knee extensions (MVC) were performed with participants seated on a plinth and their back and upper legs supported. Their torso was reclined by 10from upright, and participants crossed their arms over their chest. A 5-cm-wide support strap was placed firmly around the pelvis and chair to minimize changes in body position throughout the MVC. Isometric knee extension force was measured with a force transducer (maximal range, 300 lb; FUTEK) attached via a strap around the test leg just above the ankle. Knee angle was set at approximately 65- from full extension. Maximal force was maintained for approximately 3 s and then returned to rest. This was repeated three times with 960-s rest between contractions. The highest force was considered the best performance (MVC) and was used to calculate the 20% MVC target force for subsequent submaximal isometric contractions. Treatments. Three treatments were tested in random order: control (no tape), sham tape, and deloading tape. For the two tape treatments, tape was applied with the participants seated upright on a standard plinth, with their arms supporting their upper body, hips flexed (approximately 80- from neutral), knees extended (0-), and legs supported. Participants were encouraged to relax their leg while the tape was being applied. The deloading tape consisted of a nonelastic therapeutic tape (Allcare Ridged Strapping Tape, 3.8 cm wide; Pharmacare, Australia) applied in a diamond formation over the midbelly of the RF (Fig. 1). The tape was applied around the location described previously for ultrasound transducer placement. The tissue inside the diamond was gathered to the center, creating an ‘‘orange peel’’ appearance (Fig. 1A) of the skin (31,37). The sham tape was applied in the same formation but without any tension applied to the tape, and there was no ‘‘orange peel’’ appearance (Fig. 1B).
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in a full extension. During the passive trials at different muscle lengths, participants were asked to remain as relaxed as possible. For the submaximal isometric contraction (contraction condition), participants adopted the same position used for MVC. They matched a knee extension target torque set at 20% of MVC for approximately 15 s. This target torque was chosen to induce a similar muscle stress to that induced by the highly stretched condition (as determined during pilot experiments). Data Analysis
FIGURE 1—Tape techniques tested in this study. To apply the deloading tape technique (using the diamond tape technique) (A), four pieces approximately 15–20 cm long were applied to the skin in a diamond shape with tension applied so that the skin was notably gathered to the center with an ‘‘orange peel’’ appearance. The strips overlapped at their ends and were secured with four additional tape strips. The sham tape (B) was formed in an identical diamond pattern but without any tension applied to the skin.
An example of the obtained shear elastic modulus map is shown in Figure 3. The software of the ultrasound scanner (Supersonic Imagine, France) was used to measure mean shear elasticity values across circular regions (from 1 to 2 cm in diameter, depending on the individual participant’s muscle thickness). Care was taken to avoid inclusion of hyperechoic regions (areas of dense connective tissue) within this circular region because this may affect the accuracy of estimation of shear elastic modulus. For each treatment and each condition separately, the 10 shear elastic measurements (corresponding to the 10-s recording) were averaged to obtain a mean value of muscle shear elastic modulus. Note that the Aixplorer scanner provides the Young modulus measurement. Because the Young modulus calculation requires the assumption of an isotropic material (which is not the case for muscle [32]), all the measurements were divided by three to convert the value to represent the shear elastic modulus, as classically undertaken in other experiments (22,26). Additional Control Experiments
MECHANICAL EFFECT OF DELOADING TAPE
If the muscle–tendon unit length remains unchanged (same hip and knee angles) and if, as hypothesized, the application of tape shortens the muscle (reduced elastic modulus) within the taped area, then it follows that the muscle–tendon unit length outside this area must increase, resulting in increased shear elastic modulus. Thus, evaluation of opposite changes within and outside the taped area was considered to provide an additional method to rigorously test the hypothesis of this study. To this end, we performed an additional experiment in four participants (one newly recruited using identical criteria and three who participated in the main protocol) to quantify the change in RF shear elastic modulus within and distal to the diamond tape during each of the four conditions described previously. The protocol was identical to the one described previously, except that the sham tape treatment was not tested. It was considered that an alternative explanation for the observations in this study could be changes in tissue shear elastic modulus secondary to vascular engorgement, which would be consistent with the external appearance (discoloration) of the skin. To verify that vascular engorgement (if any) did not change muscle elastic modulus, an additional experiment was conducted in four participants (who participated in the main protocol) in which shear elastic modulus was measured with and without
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Experimental conditions. For each of the three treatments (control, sham tape, deloading tape), the muscle shear elastic modulus was measured, in a region of the RF muscle immediately below the center of the diamond, for 10 s (10 values were recorded at 1 sample per second). This was repeated for three passive conditions during which the RF muscle–tendon unit was placed at different lengths (moderately stretched, highly stretched, and shortened) and one active condition where the participants performed an isometric submaximal contraction with the muscle at a moderately stretched length (Fig. 2). The order of the experimental conditions was randomized (within each treatment). Hip and knee angles were measured using a goniometer, and adjustments to joint angles were made before each 10-s recording, as follows (Fig. 2). To moderately stretch the RF, which crosses the hip and knee, participants sat in the chair with their arms across their chest in a comfortable position, hips at approximately 80- flexion, knees at approximately 80- flexion, and leg freely hanging. To further stretch the RF (highly stretched condition), participants laid supine, with their hips in 5- flexion and the knees flexed over the edge of the bed. The left knee was held in 90- flexion by an experimenter. The shortened length of RF (shortened condition) was achieved with the participant sitting in the chair, their right leg hanging freely, and the left leg manually supported
FIGURE 2—Experimental conditions. Muscle shear elastic modulus was measured during four conditions: three passive conditions with the muscle at different lengths and the participants asked to remain as relaxed as possible and one active condition (contraction). To modify the length of the RF muscle (which crosses the hip and knee), the knee and/or hip angles were adjusted, as shown in the figure (and maintained by the experimenter in the same position between the treatments for the relaxed states).
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application of a tourniquet proximal to the recording site. For this experiment, measures were made on the biceps brachii (because blood flow is easier to inhibit within the arm) in two different positions, i.e., moderately stretched (elbow angle, 90-) and highly stretched (elbow angle, 180-). This tourniquet application (approximately 3 min) resulted in an increase of 7.5 mm (range, 5.0–10.0 mm) in arm circumference, which confirms significant vascular engorgement of the tissue. Statistical Analysis Statistical analyses were performed in Stata (StataCorp LP, College Station, TX). Data were normally distributed, and thus, the values are reported as mean T SD. To test the effect of muscle condition (moderately stretched, highly stretched, shortened, and contraction) on the shear elastic modulus in the control state (no tape), a repeated-measure ANOVA was used, with condition as a within-subject factor. The large effect of condition on shear elastic modulus (i.e., shear elastic modulus was 8 times greater in the highly stretched than that in the shortened muscle) induced a large variance in the sample. Thus, each condition was compared
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separately to determine whether the application of tape significantly affected muscle stress. A repeated-measure ANOVA (within-subject factor, treatment (no tape, sham tape, and deloading tape)) was performed for each condition. A Tukey post hoc test was used when significant main effects were observed. A P value G0.05 was considered significant.
RESULTS When shear elastic modulus was compared between conditions in the control (no tape) treatment only, there was a significant main effect (P G 0.0001). Post hoc analysis showed that the elastic modulus was greater when the muscle was highly stretched (25.2 T 8.2 kPa) than that when either shortened (3.7 T 1.0 kPa, P G 0.001) or moderately stretched (8.4 T 2.7 kPa, P G 0.001). Furthermore, the shear elastic modulus was significantly greater when the muscle was contracted (21.3 T 4.8 kPa) than that when at rest in both the shortened and moderately stretched states (P values G0.001). As intended by our methods, the shear elastic modulus did not differ (P = 0.18) between the highly stretched condition at rest and during contraction in the moderately stretched length. Despite a tendency indicating a greater
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FIGURE 3—Individual examples of shear elastic modulus maps with and without tape. The ultrasound images were obtained during the highly stretched (A) and contraction (B) condition for both the control and deloading tape treatment. The map of shear elastic modulus is superposed onto the B-mode image on the upper panel, with the color scale depicting graduation of shear elastic modulus (scale (kPa) at top right). To obtain a representative value, the shear elastic modulus (kPa) was averaged over a circular area.
MECHANICAL EFFECT OF DELOADING TAPE
the modulus was significantly less during application of deloading tape than that during the sham tape treatment for the highly stretched (j33.9% T 21.4%, P G 0.001) and contraction conditions (j28.6% T 23.7%, P = 0.002) but not when the muscle was moderately stretched (P = 0.11) (Fig. 4). No significant difference in the modulus was observed between the sham tape and the no-tape treatment for any condition (0.15 G P G 0.95). The additional control experiment with measures of muscle shear elastic modulus both within and distal to the taped area first confirmed the decrease in stress within the taped area compared with the untaped control state during the moderately stretched (j1.3 T 1.8 kPa, i.e., j16.3% T 22.4%), highly stretched (j5.7 T 3.8 kPa, i.e., j32.6% T 22.5%), and contraction conditions (j6.1 T 7.3 kPa, i.e., j24.7% T 30.1%). No change in shear elastic modulus was observed during the shortened condition (j0.1 T 1.7 kPa).
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elastic modulus when the muscle was moderately stretched than that when shortened, the P value (P = 0.09) did not reach the threshold for significance. The force produced during the contraction condition was not different across treatments (78.9 T 27.2, 78.9 T 26.8, and 78.8 T 26.9 N for control, deloading tape, and sham tape conditions, respectively; main effect of treatment, P = 0.91). There was no effect of treatment when the muscle was shortened (P = 0.99); however, the shear elastic modulus was affected by treatment in the three other conditions, as follows: moderately stretched (P = 0.002), highly stretched (P = 0.0015), and contraction (P = 0.009). Post hoc analysis showed that the shear elastic modulus was significantly less during application of deloading tape than that in the untaped control state (moderately stretched: j17.8% T 16.1%, P = 0.001; highly stretched: j39.0% T 19.0%, P G 0.001; contraction: j31.7% T 20.7%, P = 0.001) (Fig. 4). Similarly,
FIGURE 4—Effect of deloading and sham tape on the RF’s shear elastic modulus. Deloading tape reduced the modulus during the ‘‘moderately stretched,’’ ‘‘highly stretched,’’ and ‘‘contraction’’ conditions but not when the muscle was shortened. The sham tape did not affect the shear elastic modulus compared with the no-tape control. *P G 0.05 for comparison with the ‘‘control’’ (no tape) treatment; +P G 0.05 for comparison with the ‘‘sham tape’’ treatment.
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In addition, the shear elastic modulus measured distal to the deloading tape increased systematically during the moderately stretched (4.0 T 0.9 kPa, i.e., 55% T 7%), highly stretched (3.3 T 3.6 kPa, i.e., 23% T 23%), and contraction conditions (14.6 T 9.4 kPa, i.e., 139% T 85%). No change in shear elastic modulus was observed during the shortened condition (j0.1 T 0.4 kPa). These data provide further validation of our interpretation of the muscle stress changes within the taped area. The additional control experiment to study the effect of putative vascular engorgement showed that shear elastic modulus was not changed in the muscle after application of the tourniquet neither for the moderately stretched condition (from 5.2 T 2.6 to 5.1 T 2.2 kPa for before and after the tourniquet application, respectively) nor the for highly stretched condition (from 13.7 T 2.5 to 14.1 T 1.4 kPa for before and after the tourniquet application, respectively). This suggests that the results are unlikely to be explained by vascular changes from bunching of the tissues with tape application.
DISCUSSION Taking advantage of an elastographic technique, the present study is the first to quantify the effect of deloading taping on muscle stress during both passive and active conditions. Consistent with our hypothesis, the deloading tape applied to the skin directly over the RF muscle reduced muscle stress (measured inside the diamond-shaped area) for the muscle conditions where the RF was tensioned (moderately stretched, highly stretched, and contraction conditions). In contrast, when the muscle–tendon unit was slack (shortened condition), there was no effect of
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deloading tape on muscle shear elastic modulus. These results provide a better understanding of the mechanical effect of deloading taping on muscle tissues. Two observations support our argument that the changes in muscle stress are caused by changes in muscle length induced by tape application. First, stress was decreased by shortening the muscle–tendon length (to slacken the muscle) without application of tape. Second, stress was not reduced by tape when the muscle was already slack, i.e., in the shortened condition. Furthermore, results from additional experiments (n = 4) provide some evidence that 1) stress was increased distal to the area of tape, which would have to undergo lengthening if the muscle tissue within the taped area was shortened, and 2) changes in muscle vascular engorgement that might accompany the tape application did not replicate the decreased stress observed when the deloading tape was applied. It is accepted that the muscle shear elastic modulus is linearly related to muscle stress, as demonstrated in both in vivo (5,6,29) and in vitro (25) studies. Before interpretation of the observed changes in shear elastic modulus as a decrease in muscle stress (and thus as a mechanical effect of tape), other possible methodological explanations need to be considered. First, changed pennation angle (angle between the muscle fibers and the ultrasound transducer) alters the relation between shear elastic modulus and muscle stress (19). Because of the complex architecture of the RF muscle (bipennate), the putative change in pennation angle induced by tape could not be quantified from our B-mode images; however, they could be expected to be small. Gennisson et al. (19) reported a decrease of 20 kPa (from 60 to 40 kPa, i.e., j33%) in shear elastic modulus when the transducer was changed from an orientation parallel to the muscle fibers
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MECHANICAL EFFECT OF DELOADING TAPE
of our B-mode images (where the deeper RF aponeurosis was visible) suggests that the muscle thickness increased inside the diamond tape during the deloading tape treatment compared with that during the no-tape condition (Fig. 3). Because muscle tissues are considered an incompressible material (17), muscle volume does not change (24), and therefore, the increased muscle thickness should be directly linked to shortening of the muscle within the area bounded by tape. Because the muscle–tendon unit length did not change (hip and knee angles were matched between the treatments), shortening (i.e., reduced muscle stress) must be counterbalanced by lengthening (i.e., increased muscle stress) proximal and distal to the taped area. The additional control experiment confirmed this prediction. The mechanisms by which tape alters muscle length may include transmission of force by the fascia structure (34). Li and Ahn (27) described fascial bands as structural bridges that mechanically link the skin, subcutaneous layer, and deeper muscle layers. Application of deloading tape has been proposed to reduce pain either directly by unloading the injured/painful tissue (e.g., lateral epicondylalgia) (Vicenzino et al. [37]) or secondary to a change in factors such as joint position as a result of modification of muscle activity (e.g., patellofemoral joint position) (Tobin and Robinson [36]). The present study confirmed a direct effect of deloading tape on tissue stress. A decrease in muscle stress was measured inside the diamond-shaped area (n = 13), and the results of the additional experiments (n = 4) suggest that the effect is counterbalanced (at least in part) by increased stress distal to the taped area. Consequently, it is very likely that the global force produced by the RF muscle (directly linked to muscle stress [6]) was not reduced. This observation is important when the intended clinical effect is to decrease the force produced by an individual muscle to alter load sharing among synergist muscles. Although we demonstrated that deloading tape is effective to reduce stress in the underlying muscle region, this observation has been performed on healthy participants and is limited to the taping technique used (diamond shape, encompassing both longitudinal and transverse elements). This study does not confirm that the technique is clinically effective. For such an interpretation, deloading tape should be applied over injured tissues where the effects may differ because of edema, scarring, pain inhibition/facilitation, or heightened motoneuron excitability. In addition, studies are required to investigate the effect of taping on clinical outcomes (e.g., pain level) because this cannot be assumed from the identification of a reduction in muscle stress despite the plausibility of the effect. For a thorough comparison with results reported in the literature, other tape configurations (e.g., longitudinal/transverse tape [2,36]) need to be tested. Finally, the potential effect of training status on change in muscle stress has not been investigated in the present study and should be further explored. The present study quantified the decrease in muscle stress in the muscle tissue directly beneath the deloading tape using
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to a perpendicular orientation (mimicking an extreme— nonphysiological—change in pennation angle by 90-). We suggest that it is unlikely that the large changes in shear elastic modulus reported in the present study (range, 17.8%– 39% of the elastic modulus measuring during control, depending on the condition) can be explained by potential changes in the RF muscle’s architecture. Second, it is important to consider that unlike other elastographic techniques (18), SSI does not require external application of mechanical force (e.g., vibration) to generate shear waves but instead uses focused ultrasound beams. Consequently, the change in thickness of subcutaneous tissue with tape (due to the bunching of the skin (Fig. 1A)) is unlikely to alter the mechanical force applied to the tissues and, thus, the shear elastic modulus measurement. The mechanism by which tape modulates muscle stress is unclear. Taping along the length of a muscle can reduce the Hoffman reflex (H reflex, which is influenced by motoneuron excitability) in the trapezius (2) and triceps surae (1) muscles. However, it is very unlikely that the decrease in shear elastic modulus observed during the moderate and highly stretched conditions was due to decreased motoneuron excitability because the muscle was at rest (i.e., no voluntary muscle activity). It is important to note that although participants were asked to relax their muscle during these stretched conditions, the absence of muscle activation cannot be confirmed during these tasks because surface EMG was not recorded during this experiment. This was because the application of deloading tape increases the thickness of the superficial layers in the center of the area bounded by tape, which would increase the distance between the electrode and muscle and, thus, invalidate interpretation of changes in myoelectrical activity between treatments/ conditions. The validity of our conclusion related to the relaxed muscle state is strengthened by the fact that resting values of shear elastic modulus reported during the no-tape treatment are similar to those reported by Lacourpaille et al. (26) for the same resting muscle. Considering that some studies (1,2), but not all (23), reported a decreased motoneuron excitability with tape, we cannot exclude that the decrease in muscle shear elastic modulus reported during the contraction condition might in part be due to a decrease in muscle activation during contraction. If so, it likely accounts only in small part for the observed effects. The decrease in muscle stress observed during the moderately and highly stretched conditions and when the muscle was at rest provides evidence for a mechanical effect of deloading tape. As proposed by Morissey (30), tape could reduce muscle length and, therefore, passive force (i.e., unload the muscle). Consistent with this observation, our results showed a significant effect of tape for the three conditions in which the muscle–tendon unit was under tension (greater than the slack length) but failed to show any significant decrease in shear elastic modulus when the muscle–tendon unit was already shortened below the slack length, i.e., with no passive force. Further inspection of some
SSI. As the reliability (intrasession repeatability, interday reproducibility, and interobserver reliability) of this SSI technique to measure the shear elastic modulus of resting human muscles has been demonstrated (26), the technique offers opportunity to investigate the effects of different taping techniques or to determine the effectiveness of taping in clinical practice or for training purposes. Even if the clinical outcome (e.g., pain relief, joint realignment) is the most relevant measure of the taping effectiveness, the quantification of its mechanical effect may help to better understand
the controversial outcomes of mechanisms reported in the literature. The authors thank M4 Healthcare (Australia) for lending the ultrasound scanner and Jean Hug for drawing Figure 2. The study was funded by a program grant (ID631717) from the National Health and Medical Research Council of Australia. P. W. H. holds a Senior Principal Research Fellowship (APP1002190), and K. T., a Career Development Fellowship (ID 1009410), both from the National Health and Medical Research Council. The results of the present study do not constitute endorsement by the American College of Sports Medicine.
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MECHANICAL EFFECT OF DELOADING TAPE
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