Acute effect of diagonal stretching using the posterior oblique sling system on contralateral ankle dorsiflexion

Abstract

BACKGROUND:

A significant increase in the dorsiflexion range of motion (DFROM) after calf muscle stretching has been widely studied. However, it has been shown that the upper body is connected to the ankle joint by passive connective tissues.

OBJECTIVE:

The purpose of this study was to examine the effect of upper-back stretching on the mobility of the contralateral ankle.

METHODS:

In the supine position, DFROM in the contralateral leg was measured. In the sitting position with and without trunk rotation, DFROM was measured in both legs. In the sitting position with trunk rotation, dorsiflexion was measured only in the contralateral leg. Static diagonal stretching combining trunk rotation with slight trunk flexion was performed in the sitting position with a neutral pelvis.

RESULTS:

After stretching, DFROM in contralateral and ipsilateral legs were measured in the sitting position with a neutral pelvis. In the contralateral leg, significant differences in $\Delta$ DFROM were observed between the sitting position with trunk rotation and the supine position and between the sitting position with trunk rotation and the sitting position after stretching.

CONCLUSION:

In clinical settings, diagonal stretching of the unilateral posterior trunk causes a significant increase in the DFROM of the contralateral lower limb.

Keywords

Lumbar fascia posterior oblique sling range of motion static stretching

1. Introduction

Table 1
Subject characteristics

Gender (male/female)	Age (years)	Weight (kg)	Height (cm)	Body mass index (kg/m ${}^{2}$ )
10/10	20.9 $\pm$ 1.8	61.8 $\pm$ 11.4	166.4 $\pm$ 8.3	22.2 $\pm$ 2.5

In lower-limb disorders such as Achilles tendinitis, plantar fasciitis, and lateral ankle sprain, lack of dorsiflexion resulting from anatomical tightness of the triceps surae is commonly observed [1, 2, 3, 4]. During gait, a restricted dorsiflexion range of motion (DFROM) can functionally influence the knee and hip joint kinematics, and induces early heel rise during mid stance [5, 6]. Additionally, from mid stance to the terminal stance, it hinders a person from achieving a close-packed position, reducing the mechanical stability within the mortise-shaped talocrural joint and causing ankle instability [7]. It is also known that loss of dorsiflexion leads to susceptibility to injury. In individuals with limited extensibility of the gastrocnemius, the risk of Achilles tendinopathy increases up to 3-fold [8, 9, 10]. Hence, increasing the DFROM is considered a primary goal when designing a rehabilitation program [3]. The most widely studied and verified approach is the stretching technique, which has been scientifically proven to increase flexibility [11]. Recently, besides stretching that applies direct tensile force to the soft tissues, new methods, such as the myofascial release method using the Graston or foam roller technique, have been proposed [12, 13]. However, previous studies have solely focused on the flexibility of the lower limbs, especially that of the calf muscle, for DFROM improvement. Anatomically, the calf muscle is composed of the soleus and gastrocnemius. First, the length of the soleus, as a one-joint muscle, is influenced only by the ankle range of motion (ROM) in the sagittal plane. Second, the gastrocnemius is divided into the medial and lateral parts, connected to the medial and lateral condyle of the femur, respectively. As a two-joint muscle, the muscle length can also be influenced by the knee ROM in the sagittal plane. In clinics, on the basis of anatomical properties, full knee extension with dorsiflexion is recommended to stretch these two muscles together. Although the calf muscle is a structure with a strong influence on the DFROM, previous studies showed that the DFROM does not solely depend on the calf muscle. Vleeming et al. suggested that load transfer across distant joints can occur through the fascia [14, 15]. Additionally, Barker and Briggs reported that the upper body and lower limb are cross linked by the thoracolumbar fascia (TLF) [16]. According to recent studies examining the relationship between the upper body and the contralateral lower limb, increased muscle activation in the contralateral upper body and upper extremity was observed during hip extension in the prone position [17, 18, 19]. Furthermore, it has been reported that, during alternating reciprocal gait, the upper and lower bodies are cross linked and have an influence on each other [20]. However, previous studies only showed the interaction between the upper body and the contralateral lower limb during active muscle contraction but did not show the properties of interlinked passive connective tissues. Anatomically, it has already been shown that the hamstrings are connected until the ankle joint by passive connective tissues [21, 22]. That is, the passive tension generated in the upper back when it is stretched is expected to be transmitted to the lower leg. However, to date, no studies have examined the effect of upper-back stretching on the mobility of the contralateral ankle.

In this study, the aim of this study was to investigate the following: 1) whether passive tension generated in the upper back when it is stretched is transmitted to the contralateral lower leg to restrict the DFROM; 2) whether an increase in the extensibility of soft tissues in the upper back caused by novel diagonal passive stretching influences the DFROM of the contralateral and ipsilateral lower legs; and 3) whether a change in extensibility has an influence on pain during dorsiflexion. Diagonal stretching was applied to the posterior trunk via unilateral trunk rotation with slight trunk flexion.

2. Methods

2.1 Participants

A total of 20 healthy adults participated in this study (Table 1). Participants were excluded if they had musculoskeletal disorders or pain in the spine, hip, knee, and ankle joint in the last 6 months. This study was approved by the Institutional Review Board of Woosong University (approval number: 1041549-200107-SB-82), and informed consent was obtained from all participants. G*Power version 3.1.9.7 (Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany) was used for sample size estimation using an effect size of 0.35, the estimated $\alpha$ error probability of 0.05, and a power of 0.90.

2.2 Procedures

Each position was adopted in random order. Stretching was performed after measurements in the supine position and in the sitting position with trunk rotation. In the case of simultaneous measurements in the right (contralateral side) and left legs (ipsilateral side), the measurement order was randomly assigned. In case of a position change, a 10-min break was provided.

With the participant lying supine, the pelvis was maintained in a neutral position on the treatment table and the knee was fully extended. Active maximum dorsiflexion in the contralateral leg was measured as DFROM by attaching a Bluetooth embed IMU sensor (Re-live Inc., Kimhae, Korea) aligned with the 5 ${}^{\text{th}}$ metatarsal; the axis of rotation was the center of the lateral malleolus. Pain was measured using a 100-mm (0-mm $=$ no pain, 100-mm $=$ worst pain imaginable) visual analog scale (VAS). In the sitting position, the knee was fully extended. The upper body was kept erect so that the pelvis was in a neutral position, and a support apparatus was placed behind the back to maintain the position and keep the pelvis perpendicular to the treatment table. In the sitting position without trunk rotation, DFROM and VAS were measured in both the contralateral and ipsilateral legs. In the sitting position with trunk rotation, DFROM and VAS were measured only in the contralateral leg. While applying trunk rotation, the thighs were tied with a belt to prevent the pelvis from being lifted from the treatment table. To prevent a pelvic tilt from lower trunk rotation, the rotation was applied only to the upper trunk. Stretching was performed after all measurements had been taken in the supine position and in the sitting position with trunk rotation. In the sitting position with a neutral pelvis (Fig. 1a), passive diagonal stretching combining trunk rotation with slight trunk flexion was performed (10 s/trial, for a total of three trials, with 5-s rest between trials). With the therapist’s right hand placed on the participant’s left shoulder, the therapist rotated and flexed the participant’s upper body diagonally (Fig. 1b). After passive diagonal stretching, DFROM and VAS in contralateral and ipsilateral legs were measured in the sitting position with a neutral pelvis. DFROM and VAS were normalized as $\Delta$ DFROM and $\Delta$ VAS by subtracting the measured values from the sitting position.

Figure 1.

Sitting with the pelvis in a neutral position before (a) and during diagonal stretching (b).

2.3 Data analysis

The Shapiro-Wilk test was conducted for normality assessment. In the contralateral leg, the Friedman test was used to test for the difference in $\Delta$ DFROM and $\Delta$ VAS between positions. Additionally, a post hoc Wilcoxon signed-rank test was conducted for pairwise comparisons with Bonferroni correction. The significance level was set at $p<$ 0.005/3. In the ipsilateral leg, the Wilcoxon signed-rank test was conducted to compare the DFROM and VAS in the sitting position and in the sitting position after stretching. Linear regression was conducted to predict the DFROM in other positions based on the DFROM value in the sitting position. The significance level was set at $p<$ 0.05. Data analysis was performed using IBM SPSS Statistics 25 (IBM Corp., Armonk, NY, USA). Values are reported as mean $\pm$ standard deviation.

Figure 2.

$\Delta$ DFROM and $\Delta$ VAS in different positions in the contralateral leg. Sup, Supine position; Sit-TR, sitting position with trunk rotation; Sit-Str, sitting position after stretching; DFROM, dorsiflexion range of motion; VAS, visual analogue scale. Bar charts show the $\Delta$ DFROM and dots with broken lines show the $\Delta$ VAS. ${}^{*}$ Statistically significant difference in $\Delta$ DFROM and $\Delta$ VAS.

Figure 3.

DFROM and VAS in different positions in the ipsilateral leg. Sit, sitting position; Sit-Str, sitting position after stretching; DFROM, dorsiflexion range of motion; VAS, visual analogue scale. Bar charts show DFROM and dots with broken lines show VAS. ${}^{*}$ statistically significant difference in DFROM and VAS.

Figure 4.

Linear regression plot between the DFROM in the sitting position and the DFROM in the supine position (a) and between the DFROM in the sitting position and the DFROM in the sitting position with trunk rotation (b). Sup, supine position; Sit-TR, sitting position with trunk rotation; DFROM, dorsiflexion range of motion. Black lines show the regression line, and short broken lines show the 95% confidence interval of the fit.

3. Results

In the contralateral leg, a significant difference in $\Delta$ DFROM was found depending on the position ( $\chi^{2}$ (2) $=$ 23.272, $p<$ 0.001) (Fig. 2). In pairwise comparisons, significant differences in $\Delta$ DFROM were observed between the sitting position with trunk rotation and the supine position ( $Z=-$ 3.582, $p<$ 0.001) and between the sitting position with trunk rotation and the sitting position after stretching ( $Z=-$ 3.922, $p<$ 0.001). A significant difference in $\Delta$ VAS was found depending on the position ( $\chi^{2}$ (2) $=$ 29.175, $p<$ 0.001). In pairwise comparisons, significant differences in $\Delta$ VAS were observed between the sitting position with trunk rotation and the supine position ( $Z=-$ 3.835, $p<$ 0.001) and between the sitting position with trunk rotation and the sitting position after stretching ( $Z=-$ 3.646, $p<$ 0.001).

Figure 5.

The posterior oblique sling consisting of the latissimus dorsi, thoracolumbar fascia and contralateral gluteus maximus.

In the ipsilateral leg, significant differences in DFROM ( $Z=-$ 2.782, $p=$ 0.005) and VAS ( $Z=-$ 2.727, $p=$ 0.006) were found between the sitting position and the sitting position after stretching (Fig. 3).

A linear regression established that the DFROM in the sitting position could significantly predict the DFROM in the supine position ( $F$ (1, 18) $=$ 7.779, $p=$ 0.012] and the DFROM in the sitting position with trunk rotation ( $F$ (1, 18) $=$ 94.992, $p<$ 0.001) (Fig. 4). The DFROM in the sitting position accounted for 30.2% of the explained variability in the DFROM in the supine position and for 84.1% of the explained variability in the DFROM in the sitting position with trunk rotation. The regression equation was as follows: predicted DFROM in the sitting position $=$ 6.182 $+$ 0.431*DFROM in the supine position and $-$ 9.808 $+$ 1.031*DFROM in the sitting position with trunk rotation.

4. Discussion

A restricted ankle DFROM can cause various lower-limb disorders and predisposes even athletes to injuries [23]. Clinically, interventions such as stretching, joint manipulation, and exercise are used to improve a restricted DFROM. Among them, stretching has been the most widely used technique, specifically for the calf muscle because this muscle is composed of the soleus (linking the calcaneus and tibia) and the gastrocnemius (linking the calcaneus and femur). Although the results varied across studies, most studies observed a significant increase in the DFROM after calf muscle stretching. However, previous studies limited the target region of intervention to the lower limb. According to anatomical studies, the passive connective tissues of the lower leg are connected to the upper leg. Additionally, they are cross linked to the upper body via the TLF [14, 21, 24]. This enables inferring the interactions between the upper body and the contralateral lower limb, which, in turn, suggests that therapeutic approaches should not be limited to the lower limb but extended to the upper body.

In the contralateral leg, the DFROM in the sitting position was increased by 7.0 ${}^{\circ}$ in the supine position, decreased by 9.9 ${}^{\circ}$ in the sitting position with trunk rotation, and increased by 11.8 ${}^{\circ}$ in the sitting position after stretching. First, an increased DFROM in the supine position indicates that hip flexion in the sagittal plane significantly influences the DFROM although the knee is at 90 ${}^{\circ}$ flexion. As the hamstring muscles, except for the short head of the biceps femoris, originate from the ischial tuberosity, hip flexion leading to an anterior pelvis tilt pulls out the hamstring muscles and subsequently might pull out the soft tissues in the posterior ankle. According to a previous anatomical study, the pelvis and feet are continually linked by fascial connections composed of different passive structures, including the fascia latae, femoral intermuscular fascia, and crural fascia [21]. That is, passive tension in the hamstring muscles caused by hip flexion can make soft tissues in the posterior leg taut. Second, decreased contralateral DFROM in trunk rotation in the transverse plane can be partly explained by the anatomical alignment and composition of the posterior oblique sling (POS) system. Trunk rotation stretches the soft tissues of the upper portion of the POS in the transverse plane and induces a tensile force that passes through the TLF and can be transmitted to the hamstrings of the contralateral lower limb. The passive tension transmitted to the hamstrings can additionally restrict the DFROM. The result that the contralateral DFROM decreased in trunk rotation confirmed that the POS obliquely links the upper body to the lower leg and, additionally, the passive tension produced by trunk rotation is successfully transmitted the end of the lower limb. Previous studies have already demonstrated that the human body can transfer passive tension between distant segments given a connective tissue linkage [25, 26]. According to the study by Vleeming et al., the tendon of the biceps femoris long head is connected to the sacrotuberous ligament, which, in turn, connects to the TLF [14]. Additionally, recent studies have demonstrated that movements in the lower limb interact with the muscle activity in the contralateral upper body [17, 18, 19]. Lastly, this study confirmed that increased extensibility of the unilateral upper portion of the POS resulting from diagonal stretching successfully induces an increase in the contralateral DFROM. This finding indicates that the DFROM, even in the sitting position with a neutral pelvis, is partly restricted by the extensibility of the upper portion of the POS. Most previous studies attempted to increase the DFROM through calf muscle stretching. Although a significant increase was achieved, the amount of increase was very limited. After calf muscle stretching, increases of 2.0 ${}^{\circ}$ , 2.2 ${}^{\circ}$ , and 1.6 ${}^{\circ}$ were reported by Youdas et al., Knight et al., and Bohannon et al., respectively [27, 28, 29]. This raises the question of whether calf muscle stretching is clinically meaningful. Although it is difficult to make a direct comparison between previous studies and this study, in which DFROM measurements were made in a sitting position on a treatment table, a larger DFROM was observed. Moreover, there was a significant decrease in the pain scale after stretching, which did not differ when in the supine position, as observed for the DFROM. In the case of a restricted DFROM, stretching applied to the contralateral upper portion of the POS along with the calf muscle would cause a clinically meaningful increase in the DFROM.

The DFROM in the sitting position was significantly correlated with the DFROM in the supine position and that in the sitting position after stretching. On the basis of the DFROM in the sitting position, the DFROM in the supine position can be moderately predicted and the DFROM in the sitting position with trunk rotation can be highly predicted. Despite individual differences in inherent flexibility, trunk rotation caused the predictable decrease in the DFROM. Together with the result showing that a substantial degree of tension worked in the ankle in the sitting position with a neutral pelvis, this finding indirectly suggests the role of the POS. In healthy adults, passive tension induced during a rotation in the transverse plane corresponds to the functional demand. Passive forces favorably work, in terms of the biomechanical aspect, in the human body during movements, especially gait. In a previous study, with an increased speed during gait, an increased muscle activity in the upper body and obliquely crossed lower limb was observed [20]. During gait, the upper limb and contralateral lower limb work together to move the body forward and cause the soft tissues of the obliquely paired posterior trunk and lower back to be lengthened, which stores the passive force generated by tension in stretched tissues. The stored energy is released in opposite direction and helps the initial movement. This mechanism for the storing and releasing of passive forces is essential for an efficient gait economy. Trehearn showed that collegiate distance runners with less flexibility showed more economical movement [30]. Efficient use of the elastic energy in the human body can lead to a more economical countermovement [31].

In the ipsilateral leg, the DFROM in the sitting position increased by 8.4 ${}^{\circ}$ after stretching. Interestingly, there was a significant increase in the DFROM and a significant decrease in VAS after stretching. This implies that unilateral POS stretching significantly increases the DFROM in not only the contralateral lower limb but also the ipsilateral lower limb. As the diagonal stretching used in this study includes trunk flexion, it could have caused an increase in ROM in the ipsilateral lower limb. During trunk flexion, tightness of the lower back muscles has an influence on the lumbopelvic rhythm and spine curvatures, including the thoracic and lumbar flexion [32, 33, 34]. Moreover, hip ROM is influenced by the ankle position. In dorsiflexion, hip flexion is restricted and the largest passive torque is observed [35]. A restricted DFROM can also be partially caused by neural tissues because the sciatic nerve running from the lower back to the back of each leg will be taut owing to a pelvic anterior tilt during hip flexion [36]. In a study by Coppieters et al., sciatic and tibial nerve tension was increased during dorsiflexion with hip flexion [37]. Ankle dorsiflexion can additionally increase symptoms of neural tension during trunk flexion [38, 39]. Taken together, elongation of passive tissues through the diagonal stretching used in this study can help increase the extensibility of the lower-limb muscles [40]. In addition to trunk flexion, trunk rotation could have had a direct influence on the ipsilateral DFROM. The TLF consists of posterior and middle layers, in each of which dense connective tissues travel in different directions to provide stability [41]. Motion restricted by resistance against tensile strength depends on collagen fibers. In particular, the posterior layer of the TLF consists of irregular dense collagen fibers and provides stability without being restricted to a specific pattern [42]. The observed significant decreases in the pain scale in both the contralateral and ipsilateral lower limbs suggest that the extensibility in the ipsilateral lower limb also increased after stretching. Clinically, diagonal passive stretching of the unilateral posterior trunk is expected to induce an increase in the DFROM in both the contralateral and ipsilateral lower limbs. In clinical settings, if movements in the unilateral upper body are restricted owing to damage or surgery, applying diagonal passive stretching in the contralateral upper body can help maintain or improve the mobility of both lower legs.

In many previous studies, the joint ROM increased after stretching, whereas the muscle performance decreased [43]. A significantly increased passive DFROM after stretching did not lead to electromyographic activity of the gastrocnemius [44]. As stretching was not performed in the lower leg per se in this study, a decrease in muscle performance may not have occurred. Further studies are required to examine muscle performance. In addition, this study had a limitation in that only the acute effect of stretching on the DFROM was measured without examining longitudinal changes. Because of the possibility of a placebo effect, it will be necessary to measure the passive DFROM as well.

5. Conclusion

Although many therapeutic methods for improving a restricted DFROM have been suggested, their target region tends to be limited to the lower leg. In this study, owing to the nature of the POS (cross linking the upper body and lower limb), it was hypothesized that the extensibility of connective tissues in the upper body is related to the mobility of the contralateral lower leg. Our results showed that diagonal stretching of the unilateral upper back causes a significant increase in the DFROM of the contralateral lower limb and has some effects even on the ipsilateral lower limb. In clinical settings, while taking into account the anatomical properties of the POS (Fig. 5), diagonal stretching using trunk rotation with slight trunk flexion in the contralateral upper back might be considered to improve a restricted DFROM. If the approach is difficult to apply to the contralateral upper body, a certain level of improvement can be expected from applying it to the ipsilateral upper body instead.

Footnotes

Acknowledgments

The author has no acknowledgments.

Conflict of interest

The author has no conflict of interest.

Funding

This research was supported by 2020 Woosong University Academic Research Funding.

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Acute effect of diagonal stretching using the posterior oblique sling system on contralateral ankle dorsiflexion

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

Table 1 Subject characteristics

2.1 Participants

2.2 Procedures

5. Conclusion

Footnotes

Acknowledgments

Conflict of interest

Funding

References

Table 1
Subject characteristics