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Journal of Back and Musculoskeletal Rehabilitation 28 (2015) 635–644 DOI 10.3233/BMR-140559 IOS Press

Ultrasound assessment of trunk muscles and back flexibility, strength and endurance in off-road cyclists with and without low back pain Mohsen Rostamia,b , Majid Ansaria , Pardis Noormohammadpoura,∗, Mohammad Ali Mansourniac and Ramin Kordia,b a

Sports Medicine Research Center, Tehran University of Medical Sciences, Tehran, Iran Spine Division, Noorafshar Rehabilitation & Sports Medicine Hospital, Tehran, Iran c Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Science, Tehran, Iran b

Abstract. OBJECTIVES: To compare the thickness of lateral abdominal muscles and Cross Sectional Area (CSA) of lumbar Multifidus Spinae (LM) muscles of competitive off-road cyclists with and without Low Back Pain (LBP). We also aimed to compare the maximum isometric back strength and endurance, as well as flexibility of lower back in cyclists with LBP and in the controls. METHODS: The thickness of Transversus Abdominis (TrA), Internal Oblique (IO) and External Oblique (EO) along with the CSA of LM muscles of 14 professional competitive off-road cyclists with LBP and 24 controls were measured by ultrasound (US) in hook-lying position on the examination table, and mounted on the bicycle. In addition, the back strength and endurance of the subjects and the flexibility of the participants were measured. RESULTS: Data showed a significantly lower thickness of Transversus Abdominis (TrA) and CSA of LM muscles in cyclists with LBP comparing to controls in all positions. No significant result regarding the flexibility of the subjects in case group comparing with the controls was found (p = 0.674). In addition, it was found that there is no significant difference in isometric back strength of the subjects between the groups (p = 0.105). However, we found that subjects with LBP have a lower endurance in back dynamometry with 50% of their maximum isometric back strength (p = 0.016). CONCLUSION: In this study, useful information regarding possible factors associated with low back pain in off- road cyclists was found (lower thickness of TrA and LM muscles and decreased back endurance). Keywords: Ultrasound, flexibility, strength, lateral abdominal muscle, lumbar multifidus spinae, cycling

1. Introduction International attention to mountain biking (also known as off-road cycling) is increasing since its inception in 1970s [1]. Parallel to growing popularity of ∗ Corresponding author: Pardis Noormohammadpour, Sports Medicine Research Center, Tehran University of Medical Sciences, No 7, Al-e-Ahmad Highway, Tehran, P.O. Box: 14395-578, Iran. Tel.: +98 21 88630227 8; E-mail: [email protected].

recreational and competitive mountain biking in different communities [2,3], higher numbers of cycling related injuries and complaints could be expected. Therefore, some efforts were done to run research studies on injuries and medical complaints of off-road cyclists, but these studies continue to lag behind progress of the sport [4]. Incidence and prevalence of spinal pain in athletes have been shown to vary, depending on the physical demands necessary for different sports. Spinal pain

c 2015 – IOS Press and the authors. All rights reserved ISSN 1053-8127/15/$35.00 

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is among the most common overuse injuries in cyclists [5,6] and it is reported that cyclists are vulnerable to LBP [7]. Callaghan and his colleagues reported LBP as the most common problem encountered by elite British riders (60%) [8]. In another study, Clarsen and colleagues reported that 58% of the elite road cyclists participating in their cross-sectional cohort had experienced LBP during the past 12 months and 22% of all time-loss injuries were due to LBP. While only 6% of all cyclists had missed competition due to LBP, 41% had sought medical attention to treat LBP [6]. They also suggested that the different prevalence of injuries among recreational and competitive cyclists can be due to differences in exposure rate of the two groups to the sport [6]. However few studies have addressed the risk factors of low back pain among off-road cyclists. Most of available information on risk factors of LBP in off-road cyclists comes from the few epidemiological studies which have suggested improper bicycle fit, riding technique and training methods as exacerbating factors of LBP and dysfunction in the cyclists [7]. Similarly, data on therapeutic interventions for treatment of cyclists with LBP are also scarce and to our knowledge no specific therapeutic approaches are still developed for cyclists with LBP. However in recent decades, many studies aimed to find an effective therapeutic intervention for general population with LBP and an extensive list of treatments are already suggested [9]. Core stability exercises is one of these treatments which its effectiveness in the treatment of patients with LBP has been widely investigated over the past decade. In this regards, the lateral abdominal (particularly TrA) and Lumbar Multifidus (LM) muscles are known to play an important role in lumbopelvic stabilization and strengthening of these muscles is one of the major goals of the treatment which can lead to improvement of LBP in the patients. The early evidence of biomechanical involvement of TrA in patients with LBP comes from findings which showed a delayed TrA muscle activation prior to limb movement in patients with LBP [10]. Therefore, it was suggested that TrA may play an essential role in the stability of spinal column, and thereby in LBP [11]. These findings were further confirmed by finding that TrA strengthening exercises reduce the pain intensity in patients with LBP [12]. LM muscles also play a unique role in lumbopelvic stabilization and contribute to majority of lumbar spine stability especially in the lower lumbar section [13]. LM is the predominantly affected paraspinal muscle in patients with LBP [14] and its atrophy is a common finding (around 80%) in patients with chronic LBP [15].

Measurement of changes in lateral abdominal and LM muscles thicknesses (which are associated with LBP) can lead to development of selective interventions to reverse the identified impairment. For example, retraining contraction of the transabdominal (particularly TrA) and LM muscles may be considered as one of the cardinal constituents of an exercise-therapy approach for patients with current LBP [16]. Although the changes of LM and lateral abdominal muscle thickness of general population with LBP have been extensively studies, there are still limited data on the thickness of these muscles among the athletes. Therefore, in this study we aimed to compare the thickness of lateral abdominal and LM muscles in competitive off-road cyclists with and without chronic LBP in different positions such as hook-lying (at rest and during abdominal drawing-in maneuver) and functional mounted positions. In addition, based on some clinical findings, several factors such as the flexibility and back muscle strength are associated with the development of LBP in subjects; however, inconclusive results regarding the role of these mechanical factors have been reported [17–19]. To the best of our knowledge, the relationship of flexibility and back muscle strength of competitive cyclists with LBP have not been studied yet. Therefore, as a secondary objective of this study, back and hamstring flexibility and isometric back muscle strength and endurance of the subjects in symptomatic and control groups were measured and compared.

2. Method 2.1. Participants In this study, fourteen professional competitive offroad cyclists who had actively competed in the national and international cross-country mountain bike races during the past 12 months, and had bilateral non specific low back pain for more than 12 months were recruited. Also, 24 control healthy subjects who met the inclusion criteria of the study and were relatively matched with cases regarding the age and BMI [20] were recruited. Based on the previous studies, we used a standard definition for LBP. In this regards, LBP was defined as “Pain limited to the area between the twelfth rib and the inferior gluteal fold and was bad enough to limit the usual activity or change the daily routine of the subjects for more than one day during the past 4 weeks” [21]. Only male mountain-bikers between

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18 and 50 years of age who were screened for medical and medication history that could adversely affect muscle health or contraindicate testing included in the study. Also the criteria to select professional mountain bikers were as follow: 1) total cycling distance more than 100 kilometers per week. 2) Off-road cycling distance of more than 25 kilometers per week. In addition, cyclists who participated in road or triathlon bicycle races without participation in mountain biking competitions were not included. Those with obvious red flags of low back pain or prior history of cardiovascular, metabolic and pulmonary diseases were excluded from the study. Because we had just a few cyclists with low back pain, to maintain the study power, we had to increase the number of healthy cyclists. All subjects received written and oral information about the study procedures before participation. Also the study protocol was approved by the Ethical Committee of university. 2.2. Procedures All recruited subjects of the study were invited to the Sport Medicine Research Center for performing ultrasonic measurements. At the beginning, general information of the subjects was asked. Then, body weight and height of the cyclists were measured according to standard protocols [22,23]. Also the characteristics of the bicycle that the subjects usually use were all measured and recorded. Afterwards, the ultrasonic measurements of the lateral abdominal muscles thicknesses and Cross Sectional Area (CSA) of Lumbar Multifidus muscle as well as measurement of hamstring flexibility and also back strength and endurance of the subjects were performed respectively. 2.3. Ultrasonic measurements The Diameters of lateral abdominal muscles (TrA, IO and EO), were measured on both sides of the subjects while resting at hook-lying position (supine position with 30 degrees of hips flexion), and in the same position during abdominal drawing-in maneuver (ADiM) as described by Mannion and colleagues [24]. A Sonosite Micromaxx (Sonosite Inc., Bothell, WA, USA) ultrasound machine with a linear transducer (6– 13 MHz) was employed to record the thickness of abdominal muscles in B-mode format. A point 25 mm anteromedial to the midpoint between the inferior rib and the iliac crest on the mid-axillary line was set for transducer position. This point was selected on the ba-

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sis of previous studies to measure abdominal muscles thickness [22,25]. The transducer was positioned in the transverse plane and measurement of muscle thickness was made at the center point of the image using the caliper of the machine [22]. Prior the assessment of lateral abdominal muscles in ADiM, all subjects were taught to activate their TrA muscle via the drawing-in maneuver. They were instructed to draw in their lower abdominal muscles gently toward their spine as they exhaled and held for 10 seconds, while maintaining a neutral posture of the lumbar spine and continuing to breathe normally. Then the subjects were asked to repeat 5 contraction attempts each side for training, while using ultrasound for feedback and controlling the drawing in maneuver before obtaining ultrasound measurements. Finally, for minimizing the effect of fatigue, 15 minutes of rest was provided after the training session and prior to assessment of the lateral abdominal muscles thickness [20,26]. In addition to the thickness of muscles at rest and during ADiM, the contraction value which was calculated by subtracting the resting values from thickness of the muscles during ADiM, was also recorded for each subject and included in the final analysis of the study. The Cross Sectional Area (CSA) of LM muscle of both sides of the subjects was also measured at rest and during contraction using a curve transducer (5 MHz). To measure CSA of this muscle, the protocol developed by Hides et al. [27] was used. In this regard, the subject was positioned in prone lying, and to minimize the effect of lumbar lordosis of the subjects a small pillow was placed under the abdomen. An assessor with 3 years of musculoskeletal US experience palpated the lumbar vertebral levels and marked the location of the spinous process of L4 vertebrae of the cyclists on the skin with a pen. After finding the LM muscle into the monitor and capturing the image, the researcher traced around the muscle border to measure the CSA of the muscle. To measure the CSA of LM muscle in contracted condition, while the subjects were in prone lying position, they were asked to lift up their ipsilateral thigh and contralateral upper extremity. The thickness of lateral abdominal muscles and also CSA of LM muscles were also measured while the subjects were positioned on the bicycle (Fig. 1). In this regard, each of the subjects was positioned on a standard mountain bike that was fixed on a stationary trainer fit for him. The cyclists were asked to look forward and not to hold the bar-ends. Then, ultrasonic measurements of the thickness of lateral abdominal

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A

B

Fig. 1. The experimental set up of the study while the subjects were mounted on the bicycle is shown. The thickness of lateral abdominal muscles (A) and the Cross-Sectional Area of Lumbar Multifidus muscles (B) were measured by the assessor.

and CSA of LM muscles of both sides of the subjects were performed while the ipsilateral crank of the bicycle was fixed at following positions: 1) Top Dead Center (TDC) position: the bicycle crank was fixed at 12 o’clock. 2) Full Front (FF) position: the bicycle crank was fixed at 3 o’clock and 9 o’clock positions for the right and left sides respectively. 3) Bottom Dead Center (BDC) position: the bicycle crank was fixed at 6 o’clock. 4) Full Rear (FR) position: the bicycle crank was fixed at 9 o’clock and 3 o’clock for the right and left sides respectively. In course of US measurements following instructions were considered to improve the accuracy of the measurements: 1) To prevent feedback effects, subjects could not see the scanner screen. 2) Adequate ultrasound gel was used between the transducer and the skin to increase the area of contact and to minimize the need for inadequate inward probe pressure [22,25]. 3) The assessor was allowed to adjust the angle of the probe (< 10 degrees) until a clear image of muscles was achieved [27]. 4) Freezing of the view for the measurement was timed to coincide with the end of normal expiration [29]. 5) The ultrasound assessor was blind regarding the allocation of the cyclists into LBP and control groups. 2.4. Flexibility The flexibility of the subjects was assessed using the box sit-and-reach test. Following American Col-

lege of Sports Medicine (ACSM) recommendations, the participants performed a 5-minute identical warmup, including light to moderate aerobic exercises and modified hurdler’s stretches prior to sit-and-reach test. They were advised against any jerky, rapid movements including ballistic stretches. Also three practice tries were undertaken before this test [30]. Afterwards, they sat on the floor with knees fully extended and the feet on the vertical side of the test box. Then they were instructed to curl smoothly forward, with hands extended forward in parallel, to reach the maximum possible low-back flexion. Another researcher who was blinded towards the groups, recorded the distance the tip of subjects’ fingers could reach. To minimize the error of the measurements, the subjects repeated the test three times and the highest value was recorded as their final flexibility score. 2.5. Dynamometry Using a back dynamometer (Lafayette Instrument Company, Lafayette, IN, USA) the back strength of the subjects was tested by two assessors blinded to the subjects’ groups. The subjects were asked to keep their knees extended and lift the bar upward with alternate grip on the bar while they kept their knees fully extended, feet flat on the dynamometer plate and the back almost straight. The data was recorded by a researcher while another researcher monitored the subjects to per-

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Table 1 Baseline characteristics of participants in the study Variables Demographic findings Age (years) Height (cm) Weight (Kg) BMI (Kg/m2 ) Body Fat Percentage (%) Bicycle Features Frame size (cm) Crank Size (cm) Stem Size (cm) Professional Level of the Subjects Cycling Distance/week (Km) Road Cycling Distance/week (Km) Off-Road Cycling Distance/Week (Km) Pre-test questions Fasting Time (Hours) Current Intensity of Pain (VAS 0-10)

Case (n = 14)

Control (n = 24)

95% confidence interval (95%CI)

P value

27.2 (4.74) 172.7 (5.45) 71.5 (11.99) 24.0 (4.12) 20.1 (7.39)

27.8 (5.26) 179.7 (5.66) 80.2 (10.51) 24.9 (3.49) 18.95 (6.38)

−4.0 to 2.9 −10.8 to −3.1 −16.2 to −1.1 −3.4 to 1.7 −3.5 to 5.7

0.737 0.001 0.026 0.488 0.620

44.8 (2.32) 172.5 (2.59) 112.1 (6.99)

46.8 (3.41) 174.4 (2.68) 115.4 (7.21)

−4.0 to 0.1 −3.7 to −0.1 −8.1 to 1.6

0.064 0.043 0.181

236.1 (116.16) 165.0 (88.82) 71.1 (40.96)

299.6 (169.13) 240.4 (161.82) 58.7 (20.50)

3.8 (1.84) 1.6 (2.03)

3.7 (1.58) 0.00

−167.3 to 40.3 −170.8 to 20.0 −7.8 to 32.5

0.223 0.118 0.223

−107 to 1.22 −

0.892 −

Current Intensity of Pain (VAS 0–100): Intensity of low-back pain based on Visual Analogue Scale (0–10) at the time of the study.

form the test correctly. After 3 minutes of active rest of the subjects, they were asked to hold the bar of the dynamometer at 50% of their maximum strength as long as they could [31]. This time, the duration of holding the bar by the subjects was recorded in seconds, as a measure of low-back muscular endurance. Subjects performed these procedures for two times and assessors recorded the mean of values regarding the strength and endurance of back muscles, respectively. 2.6. Statistical analysis Data analysis was performed using SPSS 16 (SPSS Inc, Illinois, USA). Data normality was assessed using 1-sample Kolmogorov-Smirnov test. Independent 2-sample t-test was carried out for inter-group comparison of the continuous variables. Data are expressed as Mean ± SD and statistical significance was determined at P < 0.05.

ues of TrA muscle between the groups, it was found that although the thickness of TrA muscles of both sides of the athletes were less increased in symptomatic group comparing to the controls, the difference was statistically significant only for the left side measurements (p = 0.011). Comparing the thickness of external oblique (EO) and internal oblique (IO) muscles between the groups, no significant relation was found, except the left Int Obl muscle which in contracted position was significantly thicker in control group comparing to the symptomatic cyclists (p = 0.044). Regarding the LM muscle, it was found that the thickness of the left LM in resting condition and right LM in contraction was significantly lower in the case group comparing with the controls (p = 0.014 and 0.01 respectively). Also, the contraction value of right LM was significantly less than the controls (p = 0.009). 3.2. Functional mounted positions

3. Results In total, 14 male competitive off-road cyclists with LBP and 24 controls participated in this study. Demographic data of the participants is presented in Table 1.

In all 4 positions, the mean thickness of TrA and CSA of LM muscles of both sides of the subjects in case group were significantly lower than the controls (Table 3).

3.1. On bed position

3.3. Flexibility

As it is shown in Table 2, the thickness of TrA muscles in hook-lying position in both resting and during ADiM were significantly lower in LBP group compared to the controls. Comparing the contraction val-

Comparing the Mean ± SD scores of the sit and reach test between the case (38.92 ± 8.95 cm) and control groups (40.06 ± 5.59 cm), no significant difference was found (p = 0.674).

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Table 2 Thickness of Transabdominal muscles and Cross Sectional Area (CSA) of Lumbar Multifidus Muscles while the subjects were positioned on the bed Side EO (cm) Right

Left

IO (cm) Right

Left

TrA (cm) Right

Left LM (cm2 ) Right

Left

Condition of measurements

Case

Control

Mean difference (95% of confidence interval) −0.01 (−0.12 to 0.09) 0.006 (−0.10 to 0.11) −0.02 (−0.08 to 0.04) −0.04 (−0.14 to 0.04) −0.004 (−0.10 to 0.09) −0.04 (−0.10 to 0.01)

P value

Resting ADiM Contraction value Resting ADiM Contraction value

0.68 (0.15) 0.69 (0.16) 0.01 (0.05) 0.64 (0.16) 0.68 (0.15) 0.04 (0.05)

0.69 (0.15) 0.68 (0.15) −0.006 (0.11) 0.69 (0.12) 0.68 (0.14) −0.001 (0.09)

0.793 0.896 0.519 0.307 0.928 0.14

Resting ADiM Contraction value Resting ADiM Contraction value

0.83 (0.14) 0.94 (0.16) 0.11 (0.06) 0.75 (0.13) 0.86 (0.18) 0.10 (0.06)

0.85 (0.16) 0.94 (0.16) 0.09 (0.05) 0.84 (0.16) 0.97 (0.15) 0.13 (0.05)

−0.02 (−0.13 to 0.08) 0.002 (−0.11 to 0.11) −0.02 (−0.06 to 0.01) −0.09 (0.50 to 0.01) −0.11 (0.05 to −0.003) 0.02 (−0.01 to 0.06)

Resting ADiM Contraction value Resting ADiM Contraction value

0.28 (0.05) 0.43 (0.10) 0.14 (0.09) 0.29 (0.06) 0.45 (0.10) 0.15 (0.09)

0.37 (0.07) 0.59 (0.10) 0.21 (0.10) 0.36 (0.06) 0.60 (0.10) 0.23 (0.08)

−0.09 (−0.13 to −0.04) −0.15 (−0.22 to −0.08) −0.06 (−0.13 to 0.002) −0.06 (−0.11 to −0.02) −0.15 (−0.22 to −0.08) −0.08 (−0.14 to −0.02)

< 0.001∗ < 0.001∗ 0.057 0.002∗ < 0.001∗ 0.011∗

Resting Contracted Contraction value Resting Contracted Contraction value

5.59 (0.59) 6.47 (0.94) 0.88 (0.45) 5.67 (0.52) 6.72 (0.85) 1.04 (0.47)

6.01 (0.67) 7.30 (0.87) 1.28 (0.41) 6.17 (0.59) 7.19 (0.91) 1.02 (0.58)

−0.41 (−0.85 to 0.01) −0.82 (−1.4 to −0.20) 0.40 (0.10 to 0.69) −0.49 (−0.88 to −0.10) −0.47 (−1.07 to 0.13) −0.02 (−0.40 to 0.35)

0.060 0.01∗ 0.009∗ 0.014∗ 0.124 0.897

0.647 0.960 0.189 0.077 0.044∗ 0.219

Data is presented as Mean (SD) for case and control groups. TrA, Transversus Abdominis; IO, Internal Oblique; EO, External Oblique; ADiM, Abdominal Drawing-in Manuever; Contraction value, The difference between contracted thickness and resting thickness; ∗ Statistically Significant: (p-value < 0.05).

3.4. Back dynamometry Maximum force generated by back extensor muscles, did not significantly differ between the groups, however, the 50% of maximum strength endurance time was significantly lower in subjects with LBP in comparison to controls (Table 4).

4. Discussion 4.1. Ultrasound measurements The results of this study show that TrA muscle thickness of cyclists with LBP is significantly lower than the controls while the subjects were positioned on bed or bicycle. These findings are similar to the results obtained from comparison of the TrA muscle thickness between non-athletic subjects with and without LBP [25]. Different responses of the lateral abdominal and LM muscles to different postures were previously reported by other authors [11,32,33], therefore

in this study we also compared the thickness of lateral abdominal muscles and CSA of LM muscles of the cyclists with and without LBP while they were positioned on the bicycle. However, results showed that similar to “on bed” positions, at the time of positioning of the subjects on the bicycle, the thickness of TrA and CSA of LM in subjects with LBP is lower than the controls. Hides et al. [16] previously reported an altered ability in drawing-in maneuver in elite Australian footballers with LBP. This study findings also showed that the TrA contraction value of the subjects while they were positioned on bed is lower in subjects with LBP comparing to controls, although this difference was statistically significant only on the left side. The results of this study also showed a lower CSA of LM muscles in cyclists with LBP comparing to the controls. This finding supports the hypothesis that the flexionrelaxation phenomenon (FRP) may be a possible contributor to LBP in cyclists [34,35]. According to this phenomenon, deactivation of the paraspinal muscles which occurs following prolonged flexed position of the spine, may lead to increased strain on posterior ele-

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Table 3 Thickness of transabdominal and cross sectional area (CSA) of lumbar multifidus muscles while the subjects were positioned on the bicycle Side TDC Right

Left

FF Right

Left

BDC Right

Left

FR Right

Left

Case (n = 14)

Control (n = 24)

Mean diff (95% of CI)

TrA (cm) IO (cm) EO (cm) LM (cm2 ) TrA (cm) IO (cm) EO (cm) LM (cm2 )

0.30 (0.06) 0.98 (0.24) 0.60 (0.16) 4.91 (0.55) 0.28 (0.05) 1.00 (0.32) 0.66 (0.13) 4.80 ( 0.52)

0.41 (0.10) 1.11 (0.21) 0.71 (0.20) 5.39 (0.71) 0.38 (0.04) 1.19 (0.25) 0.74 (0.16) 5.48 (0.76)

−0.11 (−0.17 to −0.04) −0.129 (−0.28 to 0.02) −0.106 (−0.23 to 0.02) −0.47 (−0.92 to −0.02) −0.10 (−0.13 to −0.06) −0.18 (−0.38 to 0.005) −0.07 (−0.18 to 0.03) −0.68 (−1.15 to −0.21)

0.001∗ 0.099 0.101 0.039∗ < 0.001∗ 0.057 0.179 0.006∗

TrA (cm) IO (cm) EO (cm) LM (cm2 ) TrA (cm) IO (cm) EO (cm) LM (cm2 )

0.29 (0.05) 1.05 (0.24) 0.61 (0.16) 4.85 (0.50) 0.29 (0.07) 0.97 (0.33) 0.59 (0.20) 4.77 (0.59)

0.43 (0.11) 1.21 (0.25) 0.73 (0.20) 5.46 (0.71) 0.40 (0.06) 1.22 (0.27) 0.74 (0.16) 5.51 (0.76)

−0.13 (−0.20 to −0.06) −0.16 (−0.33 to 0.009) −0.11 (−0.24 to 0.01) −0.61 (−1.05 to −0.17) −0.11 (−0.16 to −0.06) −0.24 (−0.44 to −0.04) −0.15 (−0.28 to −0.03) −0.73 (−1.22 to −0.25)

< 0.001∗ 0.063 0.078 0.008∗ < 0.001∗ 0.019∗ 0.015∗ 0.004∗

TrA (cm) IO (cm) EO (cm) LM (cm2 ) TrA (cm) IO (cm) EO (cm) LM (cm2 )

0.31 (0.06) 1.13 (0.21) 0.65 (0.18) 4.86 (0.50) 0.29 (0.06) 1.03 (0.29) 0.61 (0.17) 4.80 (0.48)

0.43 (0.11) 1.33 (0.29) 0.71 (0.22) 5.58 (0.71) 0.38 (0.04) 1.32 (0.29) 0.70 (0.17) 5.41 (0.68)

−0.11 (−0.18 to −0.05) −0.20 (−0.38 to −0.02) −0.05 (−0.19 to 0.08) −0.71 (−1.15 to −0.27) −0.09 (−0.12 to −0.05) −0.28 (−0.48 to −0.08) −0.09 (−0.21 to 0.02) −0.61 (−1.03 to −0.18)

0.001∗ 0.029∗ 0.412 0.002∗ < 0.001∗ 0.007∗ 0.118 0.006∗

TrA (cm) IO (cm) EO (cm) LM (cm2 ) TrA (cm) IO (cm) EO (cm) LM (cm2 )

0.30 (0.05) 1.07 (0.24) 0.67 (0.18) 4.88 (0.46) 0.29 (0.07) 0.96 (0.31) 0.61 (0.03) 4.84 (0.54)

0.43 (0.11) 1.20 (0.23) 0.71 (0.19) 5.43 (0.65) 0.38 (0.04) 1.23 (0.28) 0.75 (0.18) 5.31 (0.73)

−0.13 (−0.20 to −0.06) −0.13 (−0.29 to 0.03) −0.03 (−0.17 to 0.09) −0.54 (−0.95 to −0.13) −0.09 (−0.13 to −0.05) −0.26 (−0.46 to −0.06) −0.14 (−0.26 to −0.01) −0.47 (−0.93 to −0.01)

< 0.001∗ 0.112 0.561 0.010∗ < 0.001∗ 0.010∗ 0.028∗ 0.044∗

Time of measurements

P-value

TDC, Top Dead Center Position; FF, Full Front; BDC, Bottom Dead Center; FR, Full Rear; TrA, Transversus Abdominis; IO, Internal Oblique; EO, External Oblique; LM, Lumbar Multifidus; CI, Confidence interval. ∗ Statistically significant, p < 0.05.

ments of the spinal column, which by itself may lead to increased chance of LBP in the cyclists [34]. The decreased CSA of LM in LBP group of cyclists may have played an additional role by decreasing the support of posterior elements following this phenomenon. On this basis, development of selective interventions to reverse the identified impairment of the paraspinal muscles in cyclists could be targeted by the clinicians.

ing the relation between the lumbar flexibility of the subjects and LBP could be found [17,19]. This might be related to the enhanced level of flexibility of the athletes in comparison to general population and use of different designs and testing procedures in different studies.

4.2. Flexibility

To the best of our knowledge, this study is the first to report significantly lower back muscle endurance in off-road cyclists with LBP, while there was no significant difference between the groups regarding the maximal force of their backs. Some longitudinal studies have previously reported a significant relationship between endurance of back muscles and prevention of LBP [36] and low endurance of trunk muscles could

Comparing the lumbar flexibility of the subjects, results showed no significant difference between the groups. This result is in concordance with the previous studies that found no significant difference in flexibility of athletes with and without LBP [36,37]. Reviewing the existing literature, inconclusive findings regard-

4.3. Dynamometry

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M. Rostami et al. / Ultrasound assessment of trunk muscles and back flexibility, strength and endurance Table 4 Comparison between the results of back dynamometry of subjects with and without Low Back Pain

Back dynamometry Maximal Force of the subjects (kg) Time of holding the bar at 50% of maximum strength (Seconds)

Case group (n = 14) 84.46 (8.41) 38.61 (12.76)

Control group (n = 24) 88.69 (5.13) 50.54 (14.81)

Mean difference (95% of CI) −4.22 (−9.41 to 0.97) −11.93 (−21.55 to −2.31)

P-value 0.105 0.016∗

CI, Confidence Interval; ∗ Statistically significant, p < 0.05.

be a discriminating factor between healthy subjects and those with a history of LBP [39]. Also, a recent study has shown that dancers with low back pain have a lower level of trunk muscles endurance [40]. Several studies have also discussed regarding the difference between the maximum back muscle strength of patients with LBP and controls. Because they have reported controversial results [41,42], the issue of association of maximal back strength to LBP development may be moot, although according to long term follow up studies, the power of back muscles is not a risk factor of low back pain [18,19]. It can also be suggested that back endurance in cyclists with LBP might be more important than strength alone in the prevention and treatment of LBP. Regarding the role of improvement of back muscle endurance in treatment of cyclists with LBP, further studies are needed.

seat [5,50] are other suggested parameters that might affect the position of the cyclist and thereby lead to LBP. However, in the current study we did not evaluate these parameters which are related to the set-up of the bicycle. Lack of control on the posture of the subjects on the bicycle could be considered as a limiting factor of the study. In addition, exclusion of cyclists with unilateral symptoms was helpful in more homogeneity of the subjects which leads to more consistent results. Also a larger number of control subjects than the symptomatic group and inclusion of only male cyclists could be considered as another limitations of the study. Although the previous studies have shown a good to high reliability for ultrasound assessment of lateral abdominal muscles and multifidus, there is limited data regarding the reliability of such measurements in cycling position.

4.4. Reliability of measurements

5. Conclusion

In this study we used ultrasound for measurements of the lateral abdominal muscle thickness and Cross Sectional Area (CSA) of LM muscles. The reliability of Ultrasonography (US) in such measurements has extensively been tested. According to these studies, it has been found that US is a reliable way in measuring the transabdominal muscles thickness in controlled contraction and resting condition [43,44]. Also the reliability of using US to measure the size of paraspinal musculature has been shown to be fair to excellent (ICC = 0.72–0.98), which is acceptable for clinical application [45–47]. In this regard, validity studies have shown that CSA of LM muscles can be considered as the indicator of muscle size. In addition, it is reported that there is no significant difference regarding CSA measurements between US and MRI findings [48].

This study results showed a significantly lower thickness of TrA and CSA of LM muscles and lower back muscle endurance in cyclist with the LBP comparing with the controls. This finding could be beneficial to develop sport-specific clinical guidelines for approach to LBP in athletes.

4.5. Limitations Excess lordosis of the lumbar spine which might be due to low height of the handle bars is previously mentioned as a possible cause of LBP in cyclists [34]. Also, downward saddle angle [49] and incorrect distance between the handle bar of the bicycle and center of the

Acknowledgements The authors of this manuscript would like to express their gratitude towards Mr. Afshin Ramezani, Mr. Mohsen Mohammadi and Mr. Benyamin Aghassi (the official coaches of the cycling federation of Iran) for their kind help in motivation of cyclists for participation in this study. We also acknowledge Dr. Farzin Farahbakhsh for his assistance in preparing the figure of the study. The authors also wish to thank the contribution of Mr. Hadi Amani towards providing the bicycles for running of the study. Funding This research has been supported by Tehran University of Medical Sciences & health Services grant.

M. Rostami et al. / Ultrasound assessment of trunk muscles and back flexibility, strength and endurance

Conflict of interest None to declare.

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