Multifidus muscle size and symmetry among elite weightlifters

Article Outline

• Abstract
• 1. Introduction
• 2. Methods
  • 2.1. Participants
  • 2.2. Procedures
  • 2.3. Statistical analysis
• 3. Results
• 4. Discussion
• 5. Conclusion
• Conflict of interest
• Ethical approval
• Funding
• Acknowledgements
• References
• Copyright

Abstract 

Objectives

To examine muscle cross-sectional areas (CSA) and symmetry of lumbar multifidus (LM) muscles in elite weightlifters.

Design

Cross-sectional observational study

Setting

Neuromuscular and Pain Research Unit.

Participants

Thirty-one elite weightlifters (15 males) participated in the study, representing the population of Thai weightlifters eligible for national selection.

Main outcome measures

Resting CSA of the LM muscle were assessed bilaterally at 4 lumbar vertebral levels using ultrasound imaging. The between side differences (relative to the side of the preferred hand) were used to determine the asymmetry.

Results

The between side differences (relative to the preferred hand) of the LM muscle CSA were less than 3% for all vertebral levels and suggested symmetry between sides (p > .05). No difference was found between weightlifters with unilateral or bilateral pain symptoms.

Conclusion

This study provides new information on resting CSA for the LM muscle in elite weightlifters. Future studies could investigate other aspects of neuromotor control of the LM muscle to determine if there are impairments which could be addressed in an attempt to decrease the high prevalence of LBP in this population.

Keywords: Low back pain, Ultrasound imaging, Weightlifting

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1. Introduction 

Competitive weightlifting is a sport that exposes the spine to extreme forces (Cholewicki, McGill, & Norman, 1991). Injury reports conducted over a six year period among weightlifters at Olympic Training Centers showed that the low back was the most commonly injured area (23.1%) of the body (Calhoon & Fry, 1999). The prevalence of LBP was shown to be even higher (41.67%) among Thai weightlifters (Paungmali et al., 2007). In addition, former weightlifters had a higher rate and more severe degenerative changes in the upper lumbar spine (Videman et al., 1995). It has been reported that weightlifters have a 36.2% incidence of spondylolysis (Rossi, 1978), in comparison with a rate of 3–7% in other sports and general populations (Calhoon & Fry, 1999). Weightlifting may predispose the athlete to spondylolysis (Goertzen et al., 1989, Granhed and Morelli, 1988, Mundt et al., 1993) due to high compressive loads on the spine. Cholewicki et al. (1991) measured forces at the L4-L5 motion segment in 57 competitive weightlifters. The average compressive loads were >17,000 N. Given the high incidence of low back pain (LBP) among weightlifters, it would seem appropriate to examine muscles which have potential for protecting the spine in this group.

During lifting, many muscles are recruited and good technique is required. It has been suggested that an emphasis should be placed on achieving correct motor patterns before substantial weight is attempted. Preserving a neutral lumbar spine is thought to be essential for safe lifting (McGill, 2002). In one study of the mechanics of power lifters spines’ (Cholewicki & McGill, 1992) during the execution of a lift, one lifter reported discomfort and pain. On examination of the video fluoroscopy records, one of the lumbar joints (L2-3) went into full flexion, while all other joints maintained their static position, resulting in a buckling of the spine and injury. It was hypothesized that an error in motor control of a segmental muscle such as the lumbar multifidus (LM) resulting in a temporary reduction in activation and rotation at that single joint.

There is considerable evidence for the role of the LM muscle in segmental stabilization of the lumbar spine. Biomechanical studies have highlighted the role of the LM muscle in provision of segmental stiffness (Panjabi, 1992a, Wilke et al., 1995) control of the spinal segment’s neutral zone (Panjabi, 1992b, Panjabi et al., 1989) and its capacity to stabilize the spine when spinal stability is challenged (Keifer et al., 1997, Keifer et al., 1998). Furthermore, the LM muscle has been shown to contribute to proprioception of the lumbar spine (Brumagne, Cordo, Lysens, Verschueren, & Swinnen, 2000).

Imaging studies have been used to document normal morphology (Hides et al., 1992, Hides et al., 2008b, Hides et al., 1994, Stokes et al., 2005), and impairments in terms of decreased cross sectional area (CSA) of the LM muscle in non-athletic populations (Barker et al., 2004, Danneels et al., 2000, Hides et al., 2008b, Wallwork et al., 2009), and athletic populations with LBP (Hides, Stanton, McMahon, Sims, & Richardson, 2008c). There is evidence that the CSA of the LM muscle is selectively decreased compared with other lumbopelvic muscles in patients with chronic LBP (Danneels et al., 2000). Atrophy of the LM muscle is a common radiological finding (Karder, Wardlaw, & Smith, 2000). Elite Cricketers with LBP demonstrated localized atrophy and between-side asymmetry of the LM muscle, despite continued strength and cardiovascular training (Hides et al., 2008c).

Between-side asymmetry in the LM muscle CSA could be an indication of atrophy from dysfunction or hypertrophy secondary to handedness and sport specific tasks. In weightlifting, hand dominance would be more relevant during pulling the weight. Most of the load goes through the arms and transfers to the trunk in which it needs to counter the force and stabilize rotation. However, no study has evaluated the resting CSA and symmetry of the LM muscle in weightlifters. The aim of this study was to compare the resting CSA and symmetry of the LM muscles among elite weightlifters.

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2. Methods 

2.1. Participants 

The participants in this study were 31 elite weightlifters (15 males and 16 females) who were selected to attend a national training camp. This sample represented the population of Thai weightlifters eligible for national selection. Participants performed regular weightlifting training programs which consisted of one hour of cardiovascular and strength training and three hours of skill training per day, 6 days per week. The sample mean ± standard error (SE) of age, weight and height were 21.42 ± 0.59 years, 72.32 ± 3.69 kg, 162.09 ± 1.91 cm. The exclusion criteria were observable spinal abnormalities, previous spinal or abdominal surgery and pregnancy. The study was approved by the Human Research Ethical Committee of the Institution. Informed consent was obtained from all participants.

2.2. Procedures 

All participants completed a self administered questionnaire. Hand preference was defined as the hand that was used for writing and tasks during activity daily living (Bishop, Ross, Daniels, & Bright, 1996). LBP was defined as pain localized between T12 and the gluteal fold (Mazanec, 2004). Participants who did not report LBP on a body chart and pain provocation on manual examination, were coded as ‘asymptomatic’. Weightlifters, who reported current LBP plus pain provocation on manual examination were allocated to the “LBP group”. Weightlifters with LBP rated their pain intensity on a Visual Analogue Scale (VAS, rated 0–10), reported the duration of symptoms (in months) and the site of LBP was drawn on a body chart. The grouping of cases as ‘bilateral’ or ‘unilateral’ pain was based on body chart reports of LBP.

The resting CSA of the LM muscles were measured using a Toshiba ultrasound scanner (Toshiba, Famio 8, SSA-530A) set in B-mode with a 5-MHz curvilinear transducer. Measurement of the LM muscle was performed with subjects in the prone position with a pillow placed under the abdomen to minimize the lumbar lordosis. The spinous processes of the L2-L5 vertebrae were palpated and marked on the skin with a pen. The electro-conductive gel was applied on the skin and the ultrasound transducer was placed longitudinally along the midline of the lumbar spine to confirm the location of each lumbar spinous process. The transducer was rotated in transverse section and placed in the middle of each spinous process. The left and right LM muscles were captured once, with both sides on the same image. The ultrasound images were taken from L2-L5 with subjects in a relaxed state and images were stored for offline analysis (Fig. 1).

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• Fig. 1 

  Bilateral transverse image at the L3 vertebral level showing the shadow of the spinous process in the center of the image and the lumbar multifidus muscle, with and without the CSAs traced.

The program Image J was used to calculate the resting CSA of the LM muscle (version 1.36b, http://rsb.info.nih.gov/ij) at the vertebral levels of L2-L5. The measurement was carried out 3 times on one image and averaged for each image.

Prior to the data collection of the main study, reliability of measurements (CSA of the LM muscle) were conducted in eight subjects. The CSA of the LM muscle were assessed bilaterally at L2, L3, L4 and L5 vertebral levels in the prone position. The same investigator performed repeated measurements of the same image after resetting the calipers.

2.3. Statistical analysis 

Analysis of variance (ANOVA) was used to initially test for group similarity in age, height, weight, BMI and maximum lifting performance. In addition, the duration of pain and level of pain (VAS) were compared across the groups with unilateral and bilateral LBP using ANOVA.

A repeated-measured analysis of covariance (ANCOVA) was used to examine resting CSA and asymmetry of the LM muscles. As there is a systematic increase in the resting CSA of the LM muscle across vertebral levels, analyses were conducted separately for each level. The variables of ‘age’, ‘weight’ and ‘height’ were entered as covariates in the analyses. The repeated measure was ‘asymmetry’ (ipsilateral or contralateral side relative to dominant hand). The between-subjects factors were ‘pain group’ (asymptomatic, bilateral, unilateral LBP) and ‘gender’ (male, female). Post-hoc contrasts (Bonferroni) were used to examine differences among the groups, using the unilateral pain group as the reference category. Due to the relatively small number of weightlifters, interaction effects in the analytical model have been restricted to ‘pain group’ by ‘asymmetry’.

The analysis of reliability across repeated measurements of the same image was calculated by intraclass correlation coefficients (ICC_3,1). Response stability was calculated using standard error of the measurement (SEM = pooled SD × ).

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3. Results 

The demographic characteristics of the weightlifters are shown in Table 1. There were no significant differences for age, height, weight, BMI and maximum lifting performance between the asymptomatic and LBP groups (p > .05). In addition, there were no significant differences between those with unilateral and those with bilateral distributions of LBP in terms of pain intensity and duration of pain (p > .05). Weightlifters with LBP (unilateral and bilateral distributions) reported a mean pain VAS score of 5.9 ± 0.3 and the mean duration of pain was 8.5 ± 3.1 months.

Table 1. Characteristics of elite weightlifters (mean ± SE) (n = 31).

Abbreviations: SE, standard error; M, male; F, Female; VAS, visual analogue scale.

Among the weightlifters, there were 5 who were asymptomatic, 9 with unilateral back pain and 17 with bilateral back pain. Based on duration of painful symptoms, there were 7 with acute LBP (less than 1 month), 7 with subacute LBP (less than 3 months) and 12 with chronic LBP (more than 3 months) (Mazanec, 2004).

Table 2 shows the resting CSA of the LM muscle (cm²) for each vertebral level and for hand preference for the weightlifters studied. Results of the analyses showed that LM muscle CSAs were not different among weightlifters with unilateral and bilateral pain symptoms (p > .05). Male weightlifters had significantly larger LM muscles only at the L4 (p < .01) and L5 (p < .001) vertebral levels compared to females. Asymmetry of the LM muscle was not different across unilateral and bilateral LBP groups at any vertebral levels (overall p = .492–.941). The LM muscle showed symmetry between sides (overall p = .131–.412). The between side differences (relative to the side of the preferred hand) were 2.68% (−14.10% to 26.71%), 1.25% (−13.63% to 21.39%), 1.11% (−30.29% to 22.80%) and 0.81% (−26.31% to 22.53%) respectively for the L2, L3, L4 and L5 vertebral levels.

Table 2. Marginal means^a of resting CSA of LM muscle (cm²) based on hand preference.

Variables	L2 (Mean (SE)) (cm2)		p	L3 (Mean (SE)) (cm2)		p	L4 (Mean (SE)) (cm2)		p	L5 (Mean (SE)) (cm2)		p
	Ipsilateral	Contralateral		Ipsilateral	Contralateral		Ipsilateral	Contralateral		Ipsilateral	Contralateral
Pain group
Asymptomatic	2.92 (0.23)	2.93 (0.24)	0.492	4.66 (0.28)	4.71 (0.30)	0.583	8.06 (0.62)	8.05 (0.52)	0.814	10.09 (0.59)	10.06 (0.42)	0.941
Bilateral	2.59 (0.12)	2.46 (0.13)		4.49 (0.15)	4.34 (0.15)		8.17 (0.321)	7.79 (0.27)		9.90 (0.31)	9.60 (0.23)
Unilateral	2.89 (0.18)	2.88 (0.19)		4.30 (0.22)	4.32 (0.23)		7.72 (0.48)	7.75 (0.39)		9.58 (0.46)	9.57 (0.32)
Gender
Males	2.96 (0.16)	2.89 (0.17)	0.258	4.61 (0.19)	4.54 (0.21)	0.501	9.05 (0.44)	8.45 (0.36)	0.010	11.14 (0.42)	10.76 (0.29)	0.001
Females	2.64 (0.16)	2.62 (0.17)		4.36 (0.20)	4.37 (0.22)		6.91 (0.44)	7.28 (0.37)		8.58 (0.43)	8.72 (0.30)
Sideb	2.80 (0.10)	2.75 (0.11)	0.131	4.48 (0.12)	4.46 (0.13)	0.399	7.98 (0.27)	7.86 (0.23)	0.279	9.86 (0.26)	9.74 (0.19)	0.412

Abbreviations: SE, standard error.

The ICC _3,1 in current study ranged from 0.95 to 0.99 (95% confidence intervals (CI): 0.68–1.00) with standard error of measurements (SEM) of 0.06–0.23 cm² across both sides and vertebral levels, indicating an acceptable reliability of the measurement.

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4. Discussion 

Atrophy of the LM muscle in subjects with LBP has been demonstrated in several studies of the non-athletic population (Barker et al., 2004, Danneels et al., 2000, Hides et al., 2008b, Wallwork et al., 2009) and athletic population (Hides et al., 2008c). Authors explained this atrophy phenomenon was possibly related to pain inhibition involving reflex loops (Hides, Richardson, & Jull, 1996), and disuse atrophy (Parkkola, Rytokoski, & Kormano, 1993). The results of the current study showed that Thai elite weightlifters with LBP did not show specific deficits in the resting CSA of the LM muscle. McGregor, Anderton, and Gedroyc (2002) also found that athletes with LBP did not show atrophy of the LM muscle. Interestingly, this study of elite oarsmen found that rowers with a history of LBP had a larger LM muscle. These results were in contrast to a later study by Hides et al. (2008c) where investigators found a deficit in LM muscle among elite cricketer athletes. It is possible that the elite athlete in powerful sports such as weightlifting have competing influences of pain (Hides et al., 1996, Parkkola et al., 1993) and increased physical demands (Hides et al., 2008a, McGregor et al., 2002).

Hypertrophy of the LM muscle in response to weightlifting can be confirmed by comparing the resting CSA of the LM muscle in weightlifters with those of normal healthy subjects. Various studies of the morphometry of the LM muscle in healthy, non-athletes have provided consistent data (Hides et al., 1992, Hides et al., 1994, Lee et al., 2006, Stokes et al., 2005). At the level of the 4th lumbar vertebra (L4), the mean resting CSA of LM in healthy subjects has been reported to be approximately 6 cm² in females and 8 cm² in males (Stokes, Hides, Elliot, Kiesel, & Hodges, 2007). The weightlifters measured in the current study had larger LM muscles (females: 7.09 ± 0.38; males: 8.75 ± 0.37 cm²) at the L4 vertebra level. At the L5 vertebra level in healthy subjects, the muscle becomes larger than at L4 (approximately 7 cm² in females and 9 cm² in males) (Stokes et al., 2007). Again, the weightlifters in the current study had larger muscles (females: 8.65 ± 0.32, males: 10.95 ± 0.31 cm²). These results would suggest that weightlifting hypertrophies the LM muscle or those that reach the elite levels of weightlifting tend to have larger multifidus.

In previous studies where LBP and decreased resting CSA of the LM muscle has been demonstrated, rehabilitation resulting in an increase in resting CSA of the LM has been commensurate with a decrease in painful symptoms, decreased disability levels and decreased recurrence rates of LBP (Hides et al., 2008b, Hides et al., 1996). The current study did not find a difference between those with unilateral or bilateral LBP for the resting CSA of the LM muscle. However, we cannot confirm that the LM muscle is functioning optimally. Other parameters are yet to be assessed in this population, such as proprioception (Brumagne et al., 2000) and the ability to voluntarily contract the muscle at individual vertebral levels (Wallwork et al., 2009). Neurophysiological investigations, such as timing using fine wire EMG (Moseley, Hodges, & Gandevia, 2002) and power spectral analysis of EMG activity (Roy et al., 1990) could also be undertaken in this group. It is possible that precise motor control of the vertebral segment, rather than just CSA of the muscle at each segment could be important parameters to assess in these athletes. This theory may be supported by the work of Cholewicki and McGill (1992), who showed using video fluoroscopy that during the execution of a lift, one lifter reported discomfort and pain associated with one of the lumbar joints moving into full flexion, while all other joints maintained their static position, resulting in buckling of the spine and injury.

There are some limitations of this study. The main limitation is the small subject sample size, which is common to studies on elite athletes. As the entire available sample (elite Thai weightlifters eligible for national representation) was included in the study, a larger sample was not possible. The lack of sufficient numbers of asymptomatic weightlifters may not be able to be addressed in other studies. However, the result indicating a lack of asymmetry in this sample of weightlifters needs to be replicated. Notably, the small number of asymptomatic subjects is representative of this group and limits comparisons to the LBP groups. We are unable to determine from this study whether weightlifting in itself hypertrophies the multifidus muscle or if individuals who are elite weightlifters have a specific morphology that suits the sport. Future studies could explore this relationship. Furthermore, only one trunk muscle was examined in this study. Other trunk extensor muscles can contribute to segmental control of the lumbar vertebrae, and numerous trunk muscles are recruited in the complex skill of professional weightlifting.

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5. Conclusion 

Elite Thai weightlifters with LBP did not show specific deficits in the resting CSA of the LM muscle when compared with those without LBP. In addition, the LM muscle shows symmetry between sides among elite weightlifters. The lack of asymmetry may be related to the type of training in elite weightlifters. The results suggest future studies could investigate other aspects of neuromotor control of the LM muscle to determine if there are impairments which could be addressed in an attempt to decrease the high prevalence of LBP in this population.

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Conflict of interest 

None declared.

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Ethical approval 

Ethical Approval Ethical approval was granted by the Human Experimental Committee, Faculty of Associated Medical Sciences, Chiang Mai University, Thailand approved this study (Reference number A510PNYF).

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Funding 

None declared.

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Acknowledgements 

The authors thank the subjects studied, and Asst. Prof. Suchart Kiatwattanacharoen and Dr. Hudsaleark Neamin for use of the ultrasound imaging equipment.

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References 

1. Barker KL, Shamley DR, Jackson D. Changes in the cross-sectional area of multifidus and psoas in patients with unilateral back pain: the relationship to pain and disability. Spine. 2004;29:E515–E519
   • View In Article
   • CrossRef
2. Bishop DVM, Ross VA, Daniels MS, Bright P. The measurement of hand preference: a validation study comparing three groups of right-handers. British Journal of Psychology. 1996;87:269–285
   • View In Article
3. Brumagne S, Cordo P, Lysens R, Verschueren S, Swinnen S. The role of paraspinal muscle spindles in lumbosacral position sense in individuals with and without low back pain. Spine. 2000;25:989–994
   • View In Article
   • MEDLINE
   • CrossRef
4. Calhoon G, Fry AC. Injury rates and profiles of elite competitive weightlifters. Journal of Athletic Training. 1999;34:232–238
   • View In Article
5. Cholewicki J, McGill SM. Lumbar posterior ligament involvement during extremely heavy lifts estimated from fluoroscopic measurements. Journal of Biomechanics. 1992;25:17–28
   • View In Article
   • MEDLINE
   • CrossRef
6. Cholewicki J, McGill SM, Norman RW. Lumbar spine loads during the lifting of extremely heavy weights. Medicine and Science in Sports and Exercise. 1991;23:1179–1186
   • View In Article
   • MEDLINE
7. Danneels LA, Vanderstraeten GG, Cambier DC, Witvrouw EE, De Cuyper HJ. CT imaging of trunk muscles in chronic low back pain patients and healthy control subjects. European Spine Journal. 2000;9:266–272
   • View In Article
8. Goertzen M, Schoppe K, Lamge G, Schulitz KP. Injuries and damage caused by excess strains in body building and power lifting. Sportverletzung Sportschaden. 1989;3:32–36
   • View In Article
9. Granhed H, Morelli B. Low-back pain among retired wrestlers and heavyweight lifters. The American Journal of Sports Medicine. 1988;16:530–533
   • View In Article
   • MEDLINE
   • CrossRef
10. Hides JA, Cooper DH, Stokes MJ. Diagnostic ultrasound imaging for measurement of the lumbar multifidus muscle in normal young adults. Physiotherapy Theory and Practice. 1992;8:19–26
    • View In Article
    • CrossRef
11. Hides JA, Fan T, Stanton WR, Stanton P, McMahon K, Wilson S. Psoas and quadratus lumborum muscle asymmetry among elite Australian football league players. British Journal of Sports Medicine. 2008;Published Online First: 18 September 2008, doi: 2010.1136/bjsm.2008.048751
    • View In Article
12. Hides JA, Gilmore C, Stanton WR, Bohlscheid E. Multifidus size and symmetry among chronic low back pain and healthy asymtomatic subjects. Manual Therapy. 2008;13:43–49
    • View In Article
    • CrossRef
13. Hides JA, Richardson CA, Jull GA. Multifidus muscle recovery is not automatic after resolution of acute, first-episode low back pain. Spine. 1996;21:2763–2769
    • View In Article
    • MEDLINE
    • CrossRef
14. Hides JA, Stanton WR, McMahon S, Sims K, Richardson CA. Effect of stabilization training on multifidus muscle cross-sectional area among young elite cricketers with low back pain. The Journal of Orthopaedic and Sports Physical Therapy. 2008;38:101–108
    • View In Article
15. Hides JA, Stokes MJ, Saide M, Jull GA, Cooper DH. Evidence of lumbar multifidus muscle wasting ipsilateral to symptoms in patients with acute/subacute low back pain. Spine. 1994;19:165–172
    • View In Article
    • MEDLINE
    • CrossRef
16. Karder DF, Wardlaw D, Smith FW. Correlation between the MRI changes in the lumbar multifidus muscles and leg pain. Clinical Radiology. 2000;55:145–149
    • View In Article
    • Abstract
    • Full-Text PDF (608 KB)
    • CrossRef
17. Keifer A, Shirazi-Adl A, Parnianpour M. Stability of the human spine in neutral postures. European Spine Journal. 1997;6:45–53
    • View In Article
18. Keifer A, Shirazi-Adl A, Parnianpour M. Synergy of the human spine in neutral postures. European Spine Journal. 1998;7:471–479
    • View In Article
19. Lee SW, Chan CK, Lam TS, Lam C, Lau NC, Lau RW, et al. Relationship between low back pain and lumbar multifidus size at different postures. Spine. 2006;31:2258–2262
    • View In Article
    • CrossRef
20. Mazanec D. Non operative treatment of low back pain. In:  Frymoyer J,  Wiesel S editor. The adult and pediatric spine. 3rd ed. Philadelphia: Lippincott Williams&Wilkins; 2004;p. 883–898
    • View In Article
21. McGill S. Low back disorders. Champaign, Illinois: Human Kinetics; 2002;
    • View In Article
22. McGregor AH, Anderton L, Gedroyc WM. The trunk muscles of elite oarsmen. British Journal of Sports Medicine. 2002;36:214–221
    • View In Article
    • MEDLINE
    • CrossRef
23. Moseley GL, Hodges PW, Gandevia SC. Deep and superficial fibers of the lumbar multifidus muscle are differentially active during voluntary arm movements. Spine. 2002;27:E29–E36
    • View In Article
    • CrossRef
24. Mundt DJ, Kelsey JL, Golden AL, Panjabi MM, Pastides H, Berg AT, et al. An epidemiologic study of sports and weight lifting as possible risk factors for herniated lumbar and cervical discs. The American Journal of Sports Medicine. 1993;21:854–860
    • View In Article
    • MEDLINE
    • CrossRef
25. Panjabi MM. The stabilizing system of the spine. Part I. Function, dysfunction, adaptation, and enhancement. Journal of Spinal Disorders. 1992;5:383–389
    • View In Article
    • MEDLINE
    • CrossRef
26. Panjabi MM. The stabilizing system of the spine. Part II. Neutral zone and instability hypothesis. Journal of Spinal Disorders. 1992;5:390–397
    • View In Article
    • MEDLINE
    • CrossRef
27. Panjabi MM, Abumi K, Duranceau J, Oxland T. Spinal stability and intersegmental muscle forces. A biomechanic model. Spine. 1989;14:194–200
    • View In Article
    • MEDLINE
    • CrossRef
28. Parkkola R, Rytokoski U, Kormano M. Magnetic resonance imaging of the discs and trunk muscles in patients with chronic low back pain and healthy control subjects. Spine. 1993;18:830–836
    • View In Article
    • MEDLINE
    • CrossRef
29. Paungmali A, Pirunsan U, Chamnongkich S, Sitilertpisan P, Pothongsunun P, Khamwong P, et al. Analysis of injuries and rehabilitation for excellence of Thai national weightlifters. Thailand: Department of Physical Therapy, Faculty of Associated Medical Sciences, ChiangMai University; 2007;
    • View In Article
30. Rossi F. Spondylolysis, spondylolithesis and sports. The Journal of Sports Medicine and Physical Fitness. 1978;18:317–340
    • View In Article
    • MEDLINE
31. Roy SH, Deluca CJ, Snyder-Mackler L, Emley MS, Crenshaw RL, Lyons JP. Fatigue, recovery and low back pain in varsity rowers. Medicine and Science in Sports and Exercise. 1990;22:463–469
    • View In Article
    • MEDLINE
32. Stokes M, Hides J, Elliot J, Kiesel K, Hodges P. Rehabilitative ultrasound imaging of the posterior paraspinal muscles. The Journal of Orthopaedic and Sports Physical Therapy. 2007;37:581–595
    • View In Article
33. Stokes M, Rankin G, Newham DJ. Ultrasound imaging of lumbar multifidus muscle: normal reference ranges for measurements and practical guidance on the technique. Manual Therapy. 2005;10:116–126
    • View In Article
    • CrossRef
34. Videman T, Sama S, Battie MC, Koskinen S, Gill K, Paananen H, et al. The long-term effects of physical loading and exercise life-styles on back-related symptoms, disability, and spinal pathology among men. Spine. 1995;20:699–709
    • View In Article
    • MEDLINE
    • CrossRef
35. Wallwork TL, Stanton WR, Freke M, Hides JA. The effect of chronic low back pain on size and contraction of the lumbar multifidus muscle. Manual Therapy. 2009;14:496–500
    • View In Article
    • CrossRef
36. Wilke HJ, Wolf S, Claes LE, Arand M, Wiesend A. Stability increase of the lumbar spine with different muscle groups: a biomechanical in vitro study. Spine. 1995;20:192–198
    • View In Article
    • MEDLINE
    • CrossRef