Physical Therapy Korea

The logistics industry has rapidly grown as a new strategic position in the global economy since the pandemic, hiring increasing numbers of delivery workers [1-3]. Delivery workers manage various sizes, shapes, and weight of products from the logistics center to customers’ doorsteps. A general delivery system involves combined driving and walking distribution [4]. Allen et al. [5] reported that delivery workers walked an average of 8 km, excluding the round distance to a logistics center. Delivery workers repeatedly get in and out of the truck, walk, and run to deliver products during work. A case-control study demonstrated that occupations that require heavy lifting with kneeling or squatting are significantly associated with knee pain [6].

Iliotibial band syndrome (ITBS) is the major cause of lateral knee pain and the second cause of total knee pain, affecting 5%–14% of people who usually participate in activities such as running and cycling [7-9]. ITBS is a well-known non-traumatic overuse injury on the lateral side of the knee caused by frequent knee flexion and extension [10]. Repetitive knee flexion and extension lead to inflammation of the distal iliotibial band directly over the lateral femoral condyle [11]. Friction of the iliotibial band is irritated at approximately 20°–30° of knee flexion, resulting in discomfort and pain [12-14]. ITBS is commonly diagnosed using Ober’s test and the noble compression test in addition to surveys of pain onset and location and other clinical examinations [15,16]. In the noble compression test, the examiner applies manual force 1–2 cm proximal to the patient’s lateral condyle while the knee is passively extended [15]. If pain is provoked at 20° of knee flexion, the noble compression test result is positive [15].

The hip muscles stabilize the hip joint and the pelvis in the sagittal plane [10]. Hip muscle strength is among the factors that prevent lower extremity injuries [17]. The iliotibial band, positioned in the lateral thigh, descends from the intermuscular septum and supracondylar tubercle of the femur to the anterolateral aspect of the proximal tibia [18]. The intermuscular septum includes the tensor fascia latae, gluteus maximus, and gluteus medius [19]. Therefore, many studies have reported a correlation between hip muscle strengths with and without ITBS. One study demonstrated that people with ITBS have weaker hip external rotator strength than healthy people; however, it reported no difference in hip abductor strength [20]. Another study noted that the affected ITBS side group had significantly weaker hip abductor strength than the unaffected ITBS side group and the healthy group [21].

Thorborg et al. [22] demonstrated that the ratio of the adductor/abductor strength of the dominant and nondominant sides in elite soccer players was 1.04 ± 0.18 and 1.06 ± 0.17, respectively. Nicholas and Tyler [23] recommended that the hip adductor/abductor strength ratio be > 0.9 and that adductor strength be equal to that of the contralateral side before returning to sports activity. Furthermore, Donatelli et al. [24] found that the abductor/adductor torque ratio was < 0 in the overall angular velocity, while hip adductor strength was approximately 20% greater than hip abductor strength in normal adult subjects.

Although many studies have examined the relationship between ITBS and hip muscle strengths, there was no study comparing hip muscle strength and ratio between delivery workers who walk an average of 8 km daily, while few studies have measured hip internal rotator and hip adductor strength. Therefore, this study aimed to compare the hip internal rotator/external rotator and hip adductor/abductor strength ratios in delivery workers with and without ITBS. This study hypothesized that the hip adductor/abductor and hip internal/external rotator strength ratios and hip muscle strengths would differ between delivery workers with and without ITBS.

1. Subjects

Based on the pilot data of eight subjects, the sample size was estimated using G*power software (ver. 3.1.9.4; University of Trier, Trier, Germany). From the a priori analysis, a power of 0.80, an alpha level of 0.05, and an effect size of 1.174 were set. The required sample size was 28 subjects. Fourteen subjects with ITBS (male = 13; female = 1; age = 39.21 ± 9.08 years; height = 175.43 ± 5.45 cm; weight = 73.64 ± 11.62 kg) matched inclusion criteria in the present study among 20 participants. Because total sample size was required 28 subjects by G*power program, 14 subjects without ITBS (male = 13; female = 1; age = 46.86 ± 7.42 years; height = 174.43 ± 8.58 cm; weight = 76.29 ± 12.03 kg) was recruited. The inclusion criteria for delivery workers with ITBS were as follows: lateral knee pain for > 2 months but < 1 year, pain aggravated by running (visual analog scale score, ≥ 3/10), and a positive noble compression test result. The exclusion criteria were a history of knee surgery within 1 year and any other musculoskeletal injury of the lower extremity or spine. The participants’ general characteristics are presented in Table 1. Before the study, each subject was informed of the details of the experimental procedures and signed an informed consent form. This study was approved by the Institutional Review Board of Yonsei University Mirae campus (IRB no. 1041849-202207-BM-124-01).

Table 1 . General characteristics of the subjects (N = 28).

Variable	Without ITBS	With ITBS	p-value
Age (y)	46.86 ± 7.42	39.21 ± 9.08	< 0.05
Height (cm)	174.43 ± 8.58	175.43 ± 5.45	> 0.05
Weight (kg)	76.29 ± 12.03	73.64 ± 11.62	> 0.05
Body mass index (kg/m2)	24.97 ± 2.52	23.85 ± 3.12	> 0.05
Work duration (mo)	26.43 ± 12.46	25.07 ± 19.36	> 0.05
KWOMAC (score)	40.43 ± 13.97	71.86 ± 41.42	< 0.05

Values are presented as mean ± standard deviation. ITBS, iliotibial band syndrome; KWOMAC, the Korean version of the Western Ontario and McMaster Universities Arthritis Index..

2. Instruments

The Korean version of the Western Ontario and McMaster Universities Arthritis Index (KWOMAC) is used to assess disability and handicap levels in three separate dimensions: pain (five questions), stiffness (two questions), and function (17 questions) [25]. The questions were rated on a 5-point Likert scale: 0 (none), 1 (slight), 2 (moderate), 3 (very), and 4 (extremely). The higher the total score summing with each score, the more severe the disability. The KWOMAC has high comprehensibility in patients who have osteoarthritis (intraclass correlation coefficient [ICC] = 0.95) and high test-retest reliability between 0.79 and 0.89 for the KWOMAC subscales [26].

Hip muscle strength was measured with the participant in the side-lying position using a Smart KEMA pulling sensor (KOREATECH Co. Ltd., Seoul, Korea) (Figure 1). The Smart KEMA pulling sensor demonstrated excellent intra- and interrater reliability (ICC (3,1) > 0.95, and ICC (2,1) > 0.95, respectively) [27]. Both ends of the sensor were attached to a board designed to hang a ring and connected to the test side of the ankle using an adjustable belt. The initial tension was 3 kgf in the starting position. All subjects performed maximal isometric contractions for 5 seconds. Considering muscle fatigue, the resting time between measurements was 1 minute. The hip muscle strength was normalized by body mass ([strength (kg)/body mass (kg)] × 100) [28,29].

Figure 1. Smart KEMA pulling sensor (KOREATECH Co. Ltd.).

The subjects laid on the non-test side with slight hip and knee flexion. The ankle on the test side was connected to an adjustable strap. The initial tension of the strap was set to 3 kgf [30]. The subjects were instructed to avoid trunk side-bending and hip flexion during the measurement. The subjects performed hip abduction with slight hip extension against the strap to maximal isometric contraction for 5 seconds (Figure 2).

Figure 2. Hip abduction strength measurement.

The subjects laid on the test side with 0° of hip and knee extension. The ankle on the test side was connected to an adjustable strap. The leg of the non-test side with 90° hip and knee flexion was placed on the pillow to prevent anterior pelvic rolling and provide comfort. The initial tension of the strap was set to 3 kgf. The subjects raised the tested leg with 0° of hip extension against the strap to maximal isometric contraction for 5 seconds (Figure 3).

Figure 3. Hip adduction strength measurement.

The subjects laid on the test side with 0° of hip extension and 90° of knee flexion. The ankle on the test side was connected to an adjustable strap. The non-test leg hip and knee were flexed at 90° and placed on a pillow to keep the pelvis neutral. The initial tension of the strap was set to 3 kgf. The subjects were instructed not to rotate the trunk and roll the pelvis anteriorly, and the test side of the knee was attached to the bed. The subjects performed hip external rotation against the strap to maximal isometric contraction for 5 seconds (Figure 4) [27].

Figure 4. Hip external rotator strength measurement. (A) The inferior view, and (B) the posterior view.

The subjects laid on the non-test side at 0° of hip and knee extension. The subjects were positioned at 0° of hip extension and 90° of knee flexion on the test side. The pillow was placed between the knee to avoid ipsilateral pelvic drop. The ankle on the test side was connected to an adjustable strap. The initial tension of the strap was set to 3 kgf to support the leg parallel to the floor. The subjects were instructed not to roll the pelvis anteriorly, and the test side of the knee was attached to the pillow. The subjects performed hip internal rotation against the strap to maximal isometric contraction for 5 seconds (Figure 5).

Figure 5. Hip internal rotator strength measurement. (A) The inferior view, and (B) the posterior view.

All subjects completed self-report questionnaires (date of birth, weight, height, work duration, and KWOMAC score). The subjects were instructed to perform the correct movement to measure hip muscle strength. After randomization, each hip muscle was tested by picking a wooden stick marked with one of the hip muscles. The subjects performed two practice trials followed by three test trials. For all strength measurements, the subjects were instructed to gradually increase how much they pushed over 5 secodns without compensatory movement. The values of the three testing trials were averaged and analyzed.

The independent variables were with and without ITBS. The dependent variables were hip muscle strengths and hip muscle strength ratios. The hip muscle strength was normalized by body mass ([strength (kg)/body mass (kg)] × 100) [28,29]. The data analysis was performed using IBM SPSS (ver. 24.0; IBM Co., Armonk, NY, USA), and values of p < 0.05 were considered significant. The Kolmogorov-Smirnov normality test was conducted to confirm the assumption of a normal distribution. Descriptive statistics are presented as mean ± standard deviation. The independent t-test was used to compare hip muscle strengths and hip internal/external rotator and adductor/abductor strength ratios between subjects with and without ITBS.

The Kolmogorov-Smirnov normality test presented normally distributed data (p > 0.05). The adductor/abductor strength ratio was significantly greater in subjects without ITBS than in those with ITBS (1.83 ± 0.59 and 1.32 ± 0.61, respectively; p < 0.05) (Table 2). There were no significant differences in adductor, abductor, internal rotator, and external rotator strengths and internal/external rotator strength ratio between subjects with and without ITBS (p > 0.05).

Table 2 . Group differences in hip muscle strengths normalized to body mass.

Variable	Without ITBS	With ITBS	p-value
Adductor (kgf∙BW–1)	19.42 ± 6.03	15.79 ± 3.97	0.071
Abductor (kgf∙BW–1)	11.11 ± 3.51	13.59 ± 4.87	0.134
Adductor/abductor ratio	1.83 ± 0.59	1.32 ± 0.61	< 0.05
Internal rotator (kgf∙BW–1)	9.98 ± 3.84	12.77 ± 3.72	0.062
External rotator (kgf∙BW–1)	11.66 ± 3.21	12.26 ± 4.41	0.683
Internal/external rotator ratio	0.87 ± 0.25	1.13 ± 0.45	0.077

Values are presented as mean ± standard deviation. ITBS, iliotibial band syndrome; kgf∙BW^–1, kilograms of force by body mass..

Previous studies determined the relationship between ITBS and hip muscle strength in various subjects such as runners, cyclists, and other athletes [20,21,23,31]. This study aimed to compare abductor, adductor, internal rotator, and external rotator strengths and hip internal/external rotator and adductor/abductor strength ratios in delivery workers with and without ITBS. Subjects with ITBS had a significantly lesser adductor/abductor strength ratio than those with ITBS (p < 0.05). The other variables, such as abductor, adductor, internal rotator, and external rotator strengths and internal/external rotator strength ratio were not significantly different between subjects with and without ITBS (p > 0.05).

Muscle imbalance is considered a secondary factor in musculotendinous injuries during running [32]. According to Thorborg et al. [22], the adductor/abductor strength ratio was 1.04 ± 0.18 and 1.06 ± 0.17 in the dominant side and nondominant sides of elite soccer players, respectively. Hip adductor strength was significantly greater than hip abductor strength (p = 0.04). Donatelli et al. [24] found that the ratio of the abductor/adductor torque was < 0 in the overall angular velocity, while hip adductor strength was approximately 20% greater than hip abductor strength in normal adult subjects. Grau et al. [33] reported that the abductor/adductor strength ratio was < 0 in concentric and eccentric measurements, while the ITBS subjects had greater isometric measurement ratio than the control group. Although few studies have measured the adductor/abductor strength ratio, the difference between the abductor and adductor strengths can be assumed through the ratio. These results corresponded with our results, in which the adductor/abductor strength ratio was > 1 in both groups.

McClay and Manal [34] studied the significance of secondary planes of motion in a 3-dimensional kinetic analysis of runners with ITBS and reported that walking and running occurs in the sagittal plane and 18.9% of the movement in the sagittal plane occurs in the frontal plane movement [34]. The hip abductor muscle controls pelvic stability in the frontal plane. Delivery workers lift and carry products in one hand while transporting them forward using a cart and walking up and down stairs frequently in the frontal and transverse planes. Their movements during work are obviously different from those of runners and other athletes. This may be a reason why delivery workers with ITBS had a significantly lower adductor/abductor strength ratio than those without ITBS.

Previous studies reported different hip abductor and hip adductor strengths [21,35]. Previous researchers stated that hip abductor weakness aggravates the symptoms of lower extremity injuries, particularly ITBS. Hip abductor weakness eccentrically controls pelvic drop in the stance phase, resulting in increased tension of the iliotibial band [36,37]. Niemuth et al. [35] found the injured side with ITBS (11.47 ± 2.34) had a significantly weaker hip abductor strength normalized by body mass than the non-injured side with ITBS (12.83 ± 2.31) (p < 0.001); however, the hip adductor strength was contrary (injured side = 9.75 ± 2.30 versus non-injured side = 8.84 ± 1.66; p = 0.010). Fredericson and Weir [13] compared hip abductor strength normalized by percent body weight times height (%BWh) of the injured side with the non-injured side and control group. The hip abductor muscle of the injured side was significantly weaker than that of the non-injured side and in the control group of runners. However, Grau et al. [33] reported a similar result to our study in which the hip abductor strength was greater in the ITBS group than in the healthy group; however, adductor strength was greater in the ITBS versus healthy group. In this study, the abductor and adductor muscle strengths did not differ significantly between subjects with and without ITBS. In other words, consensus is lacking on this point.

The hip adductor is an important factor in sports; meanwhile, its importance in ITBS is unknown [23]. The hip adductor and abductor muscles are agonists and antagonists. One study of motor control asserted that antagonist muscles were also significant. Based on electromyography, the antagonist muscles are especially prominent during movements that are fast, self-terminating, and performed against heavy loads at short distances [38]. The hip adductor muscle contributes to lower extremity stability during daily activities, such as walking and descending and ascending stairs. In addition, the hip abduction/adduction strength ratio is responsible for challenging balance tasks that may require rapid changes in muscle strength to recover stability [39]. However, in the present study, the hip abductor and adductor strengths did not differ significantly between subjects with and without ITBS. Therefore, the hip adductor/abductor strength ratio should be evaluated for muscle balance. Furthermore, it is necessary to determine whether ITBS pain decreases when the ratio is normalized.

The hip internal and external rotators play a role in maintaining the femoral head in the hip joint during the stance phase. Hip external rotator weakness creates greater tension in the iliotibial band [20]. Noehren et al. [20] demonstrated that individuals with ITBS have weaker hip external rotator strength than healthy individuals. In this study, the internal and external rotator strengths did not differ significantly between subjects with and without ITBS. However, the internal/external rotator strength ratios of the subjects with and without ITBS were 1.13 ± 0.45 and 0.87 ± 0.25, respectively. A ratio > 1 indicates greater internal rotator strength than external rotator strength, while a ratio < 1 indicates contrary results. Despite no significant difference, the internal/external rotator strength ratio may be worth consideration in ITBS evaluation and treatment.

The different results of this study from previous studies may be due to differences in measurement devices, subjects, and measurement postures. Previous studies used the hand-held dynamometer for the break test [21,35]. However, this study was performed using a Smart KEMA pulling sensor as make test. Although the hand-held dynamometer is generally used to measure isometric strength, the tester cannot maintain constant strength for the entire measurement, and if the tester’s strength is weaker than the subject’s strength, the measurement will be imprecise. However, the Smart KEMA pulling sensor was not affected by tester’s strength.

In this study, hip abductor strength was measured with the participant in a side-lying position with slight hip extension to prevent hip flexion. Despite aligning the tested leg with the trunk and measuring the strength in the side-lying position in previous studies, compensatory movements such as hip flexion might be affected by the measurement. The tensor fascia latae acts as the hip flexor, hip abductor, and hip internal rotator muscles. Because the ITB is part of the tensor fascia latae, a slight hip extension would help avoid tensor fascia latae activity.

This study had some limitations. First, it had a cross-sectional design that could not identify causes and effects. Our results could not explain whether the greater adductor/abductor muscle ratio caused the ITBS or the change in the ratio was due to adaptations made to avoid knee pain during walking. Therefore, a prospective study is necessary to determine the cause-and-effect relationship. Second, pain from ITBS is generated in a closed-kinetic chain that consists of hip and knee flexion [40]. However, the hip muscle strength in this study was measured in the open-kinetic chain. Therefore, further studies should confirm whether ITBS pain decreases when the ratio is normalized.

This study compared hip muscle strengths and ratios among delivery workers with and without ITBS. Its results showed that subjects with ITBS had a significantly lesser adductor/abductor strength ratio, and the differences in hip abductor and adductor muscle strength were not significant. Therefore, our findings suggest that comparing the abductor and adductor strengths could be insufficient; therefore, the adductor/abductor strength ratio could be considered in evaluations and treatment of ITBS among delivery workers.

None.

This study was supported by the “Brain Korea 21 FOUR Project”, the Korean Research Foundation for Department of Physical Therapy in the Graduate School of Yonsei University.

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

Conceptualization: EL, OK. Data curation: HY, IA. Formal analysis: HY, IA. Investigation: EL. Methodology: EL, UH, OK. Project administration: IA. Resources: EL. Supervision: UH, OK. Validation: OK. Visualization: HY. Writing - original draft: EL. Writing - review & editing: UH, OK.