Effectiveness of an innovative mattress overlay for improving rehabilitation in low back pain: A pilot randomized controlled study

Abstract

BACKGROUND AND OBJECTIVE:

Sleep disorders should be routinely evaluated and treated in low back pain (LBP) patients because they represent an important contributor to pain. However, no study thus far has investigated the potential benefit to LBP management of a device improving the sleep quality. Therefore, aim of this study was to assess the effectiveness of an innovative mattress overlay as add-on treatment to LBP rehabilitation.

METHODS:

Thirty eight LBP patients were randomized to standard rehabilitation plus mattress overlay use (cases) or standard rehabilitation only (controls). The intervention duration was 2 months and the following assessments were performed before and after: pain intensity; level of perceived back disability and sleep health; spine mobility; thickness and echo intensity of the lumbar multifidus.

RESULTS:

Significant pre-post-intervention improvements were observed in cases for resting and movement pain, perceived back disability, sleep, fingertip-to-floor distance, multifidus thickness ( $\sim$ 6% increase) and echo intensity ( $\sim$ 13% decrease). On the contrary, all these variables remained constant between the two experimental phases in controls.

CONCLUSIONS:

A combination of rehabilitation and mattress overlay use seems an effective approach for improvement of pain, perceived back disability, sleep, spine mobility, and lumbar multifidus size and structure of LBP patients.

Keywords

Low back pain lumbar multifidus muscle echo intensity muscle thickness sleep

1. Introduction

A complex and variable interplay among biological, psychological, and social factors underlies the development and progression of low back pain (LBP). Several previous studies have addressed the association of fatigability and weakness of paraspinal muscles with LBP [1, 2, 3, 4, 5]. In addition, recent evidences showed that decrements in sleep health (including insufficient sleep duration, irregular timing of sleep, poor sleep quality, and sleep-wake circadian cycle disorders), that are widespread in modern society, can be associated with an array of disease risks and outcomes, including those contributing to health disparities [6]. Consistently, clinical [7, 8, 9] and epidemiological [10, 11] studies found that sleep disorders should be routinely evaluated and treated in LBP patients because they represent an important contributor to pain and disability.

Although the management of LBP is always multifactorial and may include the use of foot orthotics to normalize lower limb, pelvis and trunk mechanics as the well the use of other devices (e.g., lumbar corset, belts and supports) to provide support to or reduce the load on the lower back and/or pelvic joints [12], no study thus far has investigated the potential benefit to LBP management of a device improving the sleep quality. Mattress overlays are commonly used to prevent pressure ulcers in patients at high risk such as elderly and immobilized patients [13]. Price et al. [14] have previously showed that 4 weeks of mattress overlay use in rheumatology patients with chronic pain and sleep disorders produced improvements of both sleep and pain. Consistently, it may be hypothesized that mattress overlay use could also improve the sleep quantity and/or quality in LBP patients, thereby contributing to improve the effectiveness of a rehabilitation protocol through a modulation of the vicious cycle between sleep impairment, fatigue, and pain. Therefore, the aim of this study was to assess the effectiveness of an innovative mattress overlay as add-on treatment to rehabilitation of LBP patients.

2. Methods

2.1 Study design and patients

Thirty eight LBP patients of both genders [16 males, 22 females; median (interquartile range) age: 58 (18.5) years; body mass index: 23.9 (3.9) kg/m ${}^{2}$ ] volunteered to participate in the randomized controlled study.

Chronic LBP was diagnosed as LBP (without radiation) for at least 6 months without a known pathological basis (neurological, trauma-induced, etc.) as the underlying cause. The established exclusion criteria were: major trauma documented from the medical history, pregnancy, widespread pain, inflammatory, hormonal, and neurological disorders, severe psychiatric illness, or if the patient was unable to speak or write Italian to complete the questionnaires. In addition, participants were excluded if they were under anti-inflammatory, analgesic, anticoagulant, muscle relaxant, or antidepressant medication use 1 week before the start of the study, had fibromyalgia syndrome, or had any contraindication to rehabilitation (infection, fever, hypothyroidism, cancer or other systemic disease).

Patients were randomized to one of the following two experimental groups: mattress overlay use plus standard rehabilitation for 2 months (cases: $n=$ 28 patients) or standard rehabilitation only for 2 months (controls: $n=$ 10 patients). A pseudo-random procedure (with unequal allocation ratio) was adopted for patient allocation to obtain comparable age, gender composition, body mass index, and LBP duration for the two groups (see Section 3).

The patients received a detailed explanation of the study and gave written informed consent prior to participation. The study conformed with the guidelines in the Declaration of Helsinki and was approved by the local ethics committee.

2.2 Interventions

The Aiartex device (Herniamesh srl, Chivasso, Italy) used in the study was a 0.9 cm-thick volumetric mattress overlay manufactured with polyester, with suspensory monofilaments that support the weight of a person lying in bed. It has also a moderate stiffness that allows natural movements during sleep. Patients were instructed to use the mattress overlay every night for a period of 2 months.

A multi-domain rehabilitation intervention consisting of supervised rehabilitation therapy to improve back strength, balance, and mobility utilizing reproducible targeted exercises was administered to each patient. Patients participated in the rehabilitation program for 1 hour daily, 3 days per week for 2 months.

2.3 Pre-post-intervention assessments

The following assessments were performed before and after the 2-month intervention: (1) pain intensity; (2) fingertip-to-floor test [15]; (3) Oswestry Disability Index; (4) Roland Disability Questionnaire; (5) Pittsburgh Sleep Quality Index; (6) thickness and echo intensity measurements of the lumbar multifidus muscle by ultrasonography.

2.4 Assessment of resting and movement pain intensity

Participants were asked to rate the pain using a 100-mm visual analogue scale (VAS) on a vertical, consisting of a 100-mm horizontal line with pain descriptors marked “no pain” on the left side and “the worst imaginable pain” on the right side.

Resting pain intensity was measured prior to any study procedures. Movement pain was measured during active trunk flexion and extension.

2.5 Self-report instruments

The level of perceived back disability was measured with well-known self-report instruments for the assessment of the condition specific functional status of LBP patients. The Italian versions of the Oswestry Disability Index [16] and of the Roland Disability Questionnaire [17], that were previously cross-culturally adapted and validated, were adopted.

The Italian Version of the Pittsburgh Sleep Quality Index (PSQI) [18] was adopted for the sleep health assessment. It is a 19-item self-report questionnaire that measures sleep quality over the previous month. Seven clinically derived domains of sleep difficulties (sleep quality, sleep latency, sleep duration, habitual sleep efficiency, sleep disturbances, use of sleeping medications, and daytime dysfunction) are assessed by the questionnaire. Taken together, these sleep domains are scored as a single factor of global sleep quality (i.e., PSQI global score). A global score higher than 5 is considered as an indicator of relevant sleep disturbances.

Finally, all cases were also requested to express their general preference for one of the following two conditions: mattress overlay use during sleep or conventional sleep without mattress overlay.

2.6 Lumbar multifidus ultrasound assessments

Ultrasound B-mode images of the lumbar multifidus muscle of both sides were acquired while the patients were prone with a pillow placed under the abdomen to minimise the lumbar lordosis. The same experienced examiner performed all of the assessments and acquired all images.

Six consecutive transversal scans (three for each side) were acquired from the L5 vertebral segment while the patient was relaxed, while twelve longitudinal scans (six for each side) were acquired from the L4–L5 facet joint according to the following protocol [19, 20, 21]: (a) the examiner first identified the L4 spinous process, (b) the examiner then placed the transducer parasagittally along the patient’s spine, with the midpoint over the L4 spinous process, sliding it laterally and tilting it medially until the images of the L4–L5 facet joint, of multifidus muscle, and of the thoracolumbar fascia could be identified, (c) the examiner acquired three consecutive longitudinal scans while the patient was relaxed, (d) the patient performed three times the prone hip extension test and the examiner acquired three scans when the multifidus muscle reached its maximal thickness. The prone hip extension test was selected to assess the multifidus muscle activation (see Section 3) because it has been previously documented that the hip extension is more effective for selective activation of lumbar multifidus muscle than trunk extension or the arm lift [22].

A suitable amount of ultrasound coupling gel was used to ensure optimal image quality and to minimize the transducer pressure on the skin. All measurements were taken using a RS80 ultrasound device (Samsung Electronics Italia, Milano, Italy) equipped by a convex transducer with variable frequency band (2–8 MHz). Gain was set at 50% of the range, dynamic image compression was turned off, and time gain compensation was maintained in the same (neutral) position for all depths. All system-setting parameters were kept constant throughout the study and for each subject. Pictures were stored as DICOM files and transferred to a computer for processing.

Muscle thickness was measured on the longitudinal images acquired for each side. As previously described [23, 24, 25, 26] and shown in Fig. 1 (upper panels), muscle thickness was measured in one point as the distance between the thoracolumbar fascia and the posterior-most portion of the L4–L5 facet joint. The mean of three measurements (one measurement per image) was considered to measure the lumbar multifidus thickness in each of the two experimental conditions (resting and active contraction conditions).

Figure 1.

Examples of ultrasound scans of the lumbar multifidus muscle acquired from a representative patient. Upper panels show the longitudinal scans used to measure muscle thickness (white continuous line) for the resting (panel A: 2.5 cm) and active contraction (panel B: 3.1 cm) conditions. Lower panels show the transverse scan used to calculate the echo intensity of the region of interest (panel C: white continuous line). Luminance histogram generated for the region of interest (and used to calculate the mean echo intensity) is reported in panel D.

Muscle echo intensity was measured on the transversal images acquired for each side. As previously described [21, 23] and shown in Fig. 1 (lower panels), a region of interest was chosen to include as much of the muscle as possible without any bone (i.e., the spinous and transverse processes) or surrounding fascia. The mean echo intensity (8-bit resolution, resulting in a number between 0 and 255, where black $=$ 0, white $=$ 255) was determined for each scan [27] and the mean of three measurements (one measurement per image) was considered.

Measurements of muscle thickness and echo intensity were performed by using Image J (National Institutes of Health, Bethesda, MD, USA).

2.7 Statistical analysis

Since the Shapiro-Wilk test for the normal distribution of the data failed, non-parametric tests were used. The Mann-Whitney U test was adopted for comparisons between the two groups (cases vs controls), while the Wilcoxon signed-rank test was adopted for comparisons between sides (right vs left), experimental conditions (resting condition vs active contraction), and experimental phases (pre- vs post-intervention). The Fisher’s exact test was adopted for comparisons between proportions.

Data are expressed as median (and interquartile range) and are represented as box-and-whisker plots. Threshold for statistical significance was set at $P=$ 0.05. Statistical tests were performed with Statistica 6 (Statsoft Inc., Tulsa, OK, USA).

3. Results

The two groups of LBP patients were comparable ( $P>$ 0.05 for all comparisons) for gender composition (cases: 12/28 males vs controls: 4/10 males), age [cases: 58.5 (17.0) years vs controls: 50.0 (28.7) years], body mass index [cases: 24.4 (4.0) kg/m ${}^{2}$ vs controls: 22.6 (2.9) kg/m ${}^{2}$ ], LBP duration [cases: 10.0 (17.5) years vs controls: 6.5 (15.7) years], pre-intervention resting pain intensity [cases: 3.0 (4.3) a.u. vs controls: 1.3 (2.4) a.u.], pre-intervention movement pain intensity [cases: 5.0 (3.0) a.u. vs controls: 4.5 (3.5) a.u.], and pre-intervention PSQI global score [cases: 5.0 (4.0) a.u. vs controls: 7.0 (6.0) a.u.].

All patients who received the mattress overlay were compliant with its use for the 2-month intervention period: the percentage of cases who preferred the mattress overlay use during sleep (71.5%) was significantly ( $P=$ 0.003) higher than the percentage of cases who preferred the conventional sleep without mattress overlay (28.5%).

Significant reductions were observed in cases for the post-intervention pain intensity for both resting ( $P<$ 0.001) and movement ( $P<$ 0.0001) experimental conditions compared to the pre-intervention values, while pain intensity remained constant between the two experimental phases for both resting ( $P=$ 0.53) and movement ( $P=$ 0.07) experimental conditions in control patients (Fig. 2, upper panel). Significant reductions ( $P=$ 0.02) were also observed in cases for the post-intervention finger-to-floor distance compared to the pre-intervention values, while the finger-to-floor distance remained constant ( $P=$ 0.48) between the two experimental phases in control patients (Fig. 2, lower panel).

Figure 2.

Upper panel: pre- and post-intervention values of resting and movement pain intensity obtained in cases (leftmost part of the panel) and controls (rightmost part of the panel). ${}^{**}$ : $P<$ 0.001; ${}^{***}$ : $P<$ 0.0001. Lower panel: pre- and post-intervention values of finger-to-floor distance obtained in cases (leftmost part of the panel) and controls (rightmost part of the panel). ${}^{*}$ : $P<$ 0.05.

Figure 3.

Pre- and post-intervention values of Oswestry Disability Index (upper panel) and Roland Disability Index (lower panel) obtained in cases (leftmost part of the panels) and controls (rightmost part of the panels). ${}^{*}$ : $P<$ 0.05.

Significant reductions were observed in cases for the post-intervention scores of both the Oswestry Disability Index ( $P=$ 0.02: Fig. 3, upper panel) and Roland Disability Questionnaire ( $P=$ 0.02: Fig. 3, lower panel) compared to the pre-intervention scores, while the scores of both questionnaires remained constant ( $P=$ 0.17 and $P=$ 0.31, respectively) between the two experimental phases in control patients.

The PSQI global score remained constant between the two experimental phases in both cases [pre- intervention: 5.0 (4.0) vs post-intervention: 5.0 (4.0), $P=$ 0.06] and control patients [pre-intervention: 7.0 (6.0) vs post-intervention: 5.0 (2.0), $P=$ 0.06]. Consistently, the percentage of patients presenting sleep disturbances (PSQI global score $>$ 5) remained constant between the two experimental phases in both cases (pre-intervention: 53.4% vs post-intervention: 39.3%, $P=$ 0.42) and control patients (pre- intervention: 80% vs post-intervention: 60%, $P=$ 0.63). However, a significant pre-post-intervention reduction was observed in the percentage of cases reporting frequent (3 or more times a week) sleep interruptions (pre-intervention: 18% vs post-intervention: 3%, $P=$ 0.04), while this percentage remained constant between the two experimental phases in control patients (pre-intervention: 30% vs post-intervention: 20%, $P=$ 0.58). Moreover, a significant pre-post-intervention increase was observed in the percentage of cases reporting no pain during sleep (pre-intervention: 25% vs post-intervention: 44%, $P=$ 0.04), while this percentage remained constant between the two experimental phases in control patients (pre-intervention: 44% vs post-intervention: 50%, $P=$ 1.00).

Lumbar multifidus thickness was comparable between the two sides ( $P>$ 0.05 for all comparisons) in both cases and controls for the two experimental conditions (resting and active contraction conditions). Significant increases were observed in cases for the pre-intervention multifidus thickness of both sides measured after active contraction compared to the resting condition (left side: $+$ 21.8%, $P=$ 0.03; right side: $+$ 17.3%, $P=$ 0.01) and for the post-intervention resting thickness of both sides compared to the pre-intervention values (left side: $+$ 6.9%, $P=$ 0.0001; right side: $+$ 6.1%, $P=$ 0.001) (Fig. 4, upper panel). Multifidus muscle activation was measured as the percent thickness difference between the active contraction and resting conditions: we found in cases post-intervention values of both sides [left: $+$ 19.5 (9.8)%; right: $+$ 14.0 (15.1)%] comparable ( $P=$ 0.06 and $P=$ 0.08 for the left and right side, respectively) to pre-intervention values [left: $+$ 21.8 (13.1)%; right: $+$ 17.3 (11.8)%].

Figure 4.

Pre- and post-intervention values of lumbar multifidus thickness obtained for the two sides (left and right) and for the two experimental conditions (resting and active contraction) in cases (upper panel) and controls (lower panel). ${}^{*}$ : $P<$ 0.05; ${}^{**}$ : $P<$ 0.01; ${}^{***}$ : $P<$ 0.001.

Significant increases were observed in controls for the pre-intervention multifidus thickness of both sides measured after active contraction compared to the resting condition (left side: $+$ 20.2%, $P=$ 0.005; right side: $+$ 18.6%, $P=$ 0.005), while no significant changes of multifidus thickness were observed between the two experimental sessions in control patients (Fig. 4, lower panel). Moreover, multifidus muscle activation of control patients was comparable ( $P=$ 0.39 and $P=$ 0.65 for the left and right side, respectively) between the pre-intervention [left: $+$ 20.2 (15.2)%; right: $+$ 18.6 (8.6)%] and the post-intervention [left: $+$ 22.2 (9.2)%; right: $+$ 23.7 (8.9)%] phase.

Figure 5.

Pre- and post-intervention values of lumbar multifidus echo intensity obtained for the two sides (left and right) in cases (upper panel) and controls (lower panel). ${}^{*}$ : $P=$ 0.001.

Significant reductions were observed in cases for the post-intervention multifidus echo-intensity (of both sides) compared to the pre-intervention values (left side: $-$ 13.1%, $P=$ 0.001; right side: $-$ 14.9%, $P=$ 0.001) (Fig. 5, upper panel), while no significant changes of multifidus echo intensity were observed between the two experimental sessions in control patients (Fig. 5, lower panel).

4. Discussion

The main findings of this study were that the mattress overlay use in combination with rehabilitation was associated with better and clinically meaningful results for resting and movement pain, level of perceived back disability, sleep, fingertip-to-floor test performance of LBP patients (cases) when compared with rehabilitation only (controls). These results obtained in cases were also paralleled by pre-post-intervention improvements in muscle size (i.e., multifidus thickness increase) and structure (i.e., multifidus echo intensity reduction) that were not observed in controls.

We found high percentages of LBP patients presenting sleep disturbances in the pre-intervention phase ( $\sim$ 50% in cases and 80% in controls) and, although to a lesser extent, in the post-intervention phase ( $\sim$ 40% in cases and 60% in controls). This result confirms previous studies indicating that disorders of the sleep-wake circadian cycle are associated with or contribute to a wide range of diseases including musculoskeletal disorders [9, 10, 28] and chronic pain conditions [11, 14, 29]. Although the exact mechanisms underlying the association between sleep impairment and pain still need to be elucidated, it has been suggested that this association is bidirectional [30]. In fact, pain can produce intrinsic changes in sleep architecture and the treatment of pain conditions may be helpful for sleep quality [30]. On the other hand, sleep changes can trigger painful conditions. In fact, acute reduction of sleep time in healthy pain-free individuals caused hyperalgesia in the following morning [29] and sleep deprivation impaired pain perception [31], while restorative sleep was a predictor of chronic pain resolution [32]. Consistently, we found that the mattress overlay use, in combination with a rehabilitation program, improved not only sleep but also resting and movement pain as well as the level of perceived back disability. The impairment of the vicious cycle between sleep disorder, fatigue, and pain could have implied an improved patient compliance towards rehabilitation with the consequent improved rehabilitation effectiveness resulting in back muscle strengthening (i.e., reduced muscle fatigue) and in the pre-post-intervention improvements (in fingertip-to-floor test performance, muscle size and structure) observed in cases but not in controls. We acknowledge that the pre-post-intervention sleep improvements observed in cases were limited to sleep comfort, sleep disturbances, sleep quality (i.e., absence of night-time pain), while other relevant PSQI components such as sleep duration, latency, efficiency were not affected by the mattress overlay use. However, it may be hypothesized that these PSQI self-report measures had poor responsiveness to change [33] and that objective sleep assessment methods (e.g., wrist actigraphy, polysomnography) may be required to unravel additional sleep improvements elicited by the mattress overlay use.

The pre-post-intervention increase of the lumbar multifidus thickness observed in cases resembles the physiological adaptations of muscle size in response to training [34, 35, 36] and could be the result of the muscle anabolic response. To our knowledge, this is the first study investigating the lumbar multifidus echo intensity and its pre-post-intervention changes in LBP patients. Muscle echo intensity is related to the fibrous and adipose tissue content of muscles (i.e., myosteatosis) [27, 37, 38]. Although no muscle biopsy was performed in this study, the post-intervention reduction of the muscle echo intensity observed in cases can be related to a reduction of myosteatosis that could, in turn, be underlain by post-intervention improvements of insulin sensitivity [39] and/or changes in muscle fiber type composition [39, 40]. The pre-post-intervention improvements of muscle size and structure observed in cases were paralleled by improvements in the fingertip-to-floor test performance, but not in multifidus muscle activation. It may be hypothesized that the selected duration and/or paradigm of the rehabilitation intervention were not enough to elicit muscle activation improvements. Alternatively, it may be suggested that the responsiveness to change [33] of the ultrasound-based muscle activation assessment was poor and that other techniques (e.g., EMG analysis, muscle strength assessment) may be required to unravel the multifidus muscle function adaptations elicited by rehabilitation.

From a clinical perspective, the present results have three relevant implications for the management of LBP patients. First, given the high percentages of LBP patients presenting sleep disturbances, it may be suggested that LBP evaluation in clinical practice should systematically include the sleep health assessment. Second, given the observed compliance (and preference) of cases who received the mattress overlay and given the differences in the pre-post-intervention changes observed between cases and controls, it may be concluded that a device improving the sleep quality was also useful to improve rehabilitation effectiveness, ultimately resulting in improvement of pain and other clinical outcomes. These findings support the device incorporation in clinical protocols for rehabilitation of LBP patients. However, further studies are required to confirm these preliminary findings and to assess the effects on sleep and pain of different types of mattress overlays (e.g., inflatable mattress overlay, viscoelastic foam overlay, gel foam overlay) commonly used for prevention of pressure ulcers [13]. Third, the ultrasound assessment of multifidus thickness and echo intensity was useful to track the progression of muscle size and structure over time and to monitor their responses to interventions. These findings support the incorporation of quantitative muscle ultrasonography in clinical research studies performed in LBP patients to assess longitudinally their responses to rehabilitation protocols.

In conclusion, we showed that a combination of rehabilitation and mattress overlay use seems an effective approach for improvement of pain, perceived back disability, sleep, spine mobility, and lumbar multifidus size and structure of LBP patients.

Footnotes

Acknowledgments

Authors thank Herniamesh srl (Chivasso, Italy) for proving the mattress overlays used in this study.

Conflict of interest

None to report.

References

Roy

De Luca

Casavant

. Lumbar muscle fatigue and chronic lower back pain. Spine (Phila Pa 1976). 1989; 14(9): 992-1001.

Roy

De Luca

Emley

Buijs

. Spectral electromyographic assessment of back muscles in patients with low back pain undergoing rehabilitation. Spine (Phila Pa 1976). 1995; 20(1): 38-48.

Mannion

Connolly

Wood

Dolan

. The use of surface EMG power spectral analysis in the evaluation of back muscle function. J Rehabil Res Dev. 1997; 34(4): 427-39.

Kankaanpää

Taimela

Laaksonen

Hänninen

Airaksinen

. Back and hip extensor fatigability in chronic low back pain patients and controls. Arch Phys Med Rehabil. 1998; 79: 412-7.

Villafañe

Gobbo

Peranzoni

Naik

Imperio

Cleland

Negrini

. Validity and everyday clinical applicability of lumbar muscle fatigue assessment methods in patients with chronic non-specific low back pain: a systematic review. Disabil Rehabil. 2016; 38(19): 1859-71.

Laposky

Van Cauter

Diez-Roux

. Reducing health disparities: the role of sleep deficiency and sleep disorders. Sleep Med. 2016; 18: 3-6.

Bramoweth

Renqvist

Germain

Buysse

Gentili

Kochersberger

Rodriguez

Rossi

Weiner

. Deconstructing Chronic Low Back Pain in the Older Adult-Step by Step Evidence and Expert-Based Recommendations for Evaluation and Treatment: Part VII: Insomnia. Pain Med. 2016; 17(5): 851-63.

Sribastav

Peiheng

Jun

Zemin

Fuxin

Jianru

Hui

Hua

Zhaomin

. Interplay among pain intensity, sleep disturbance and emotion in patients with non-specific low back pain. PeerJ. 2017; 5: e3282.

Kovacs

Seco

Royuela

Betegon

Sánchez-Herráez

Meli

Martínez Rodríguez

Núñez

Álvarez-Galovich

Moyá

Sánchez

Luna

Borrego

Moix

Rodríguez-Pérez

Torres-Unda

Burgos-Alonso

Gago-Fernández

González-Rubio

Abraira

. The association between sleep quality, low back pain and disability: A prospective study in routine practice. Eur J Pain. 2018; 22(1): 114-26.

10.

Roizenblatt

Souza

Palombini

Godoy

Tufik

Bittencourt

. Musculoskeletal Pain as a Marker of Health Quality. Findings from the Epidemiological Sleep Study among the Adult Population of São Paulo City. PLoS One. 2015; 10(11): e0142726.

11.

Kardouni

Shing

Rhon

. Risk Factors for Low Back Pain and Spine Surgery: A Retrospective Cohort Study in Soldiers. Am J Prev Med. 2016; 51(5): e129-e138.

12.

National Guideline Centre (UK). Low Back Pain and Sciatica in Over 16s: Assessment and Management. London: National Institute for Health and Care Excellence (UK); 2016.

13.

McInnes

Jammali-Blasi

Bell-Syer

Dumville

Middleton

Cullum

. Support surfaces for pressure ulcer prevention. Cochrane Database Syst Rev. 2015; (9): CD001735.

14.

Price

Rees-Mathews

Tebble

Camilleri

. The use of a new overlay mattress in patients with chronic pain: impact on sleep and self-reported pain. Clin Rehabil. 2003; 17(5): 488-92.

15.

Perret

Poiraudeau

Fermanian

Colau

Benhamou

Revel

. Validity, reliability, and responsiveness of the fingertip-to-floor test. Arch Phys Med Rehabil. 2001; 82(11): 1566-70.

16.

Monticone

Baiardi

Ferrari

Foti

Mugnai

Pillastrini

Vanti

Zanoli

. Development of the Italian version of the Oswestry Disability Index (ODI-I): A cross-cultural adaptation, reliability, and validity study. Spine (Phila Pa 1976). 2009; 34(19): 2090-5.

17.

Padua

Ceccarelli

Romanini

Zanoli

Bondì

Campi

. Italian version of the Roland Disability Questionnaire, specific for low back pain: cross-cultural adaptation and validation. Eur Spine J. 2002; 11(2): 126-9.

18.

Curcio

Tempesta

Scarlata

Marzano

Moroni

Rossini

Ferrara

De Gennaro

. Validity of the Italian version of the Pittsburgh Sleep Quality Index (PSQI). Neurol Sci. 2013; 34(4): 511-9.

19.

Kiesel

Uhl

Underwood

Rodd

Nitz

. Measurement of lumbar multifidus muscle contraction with rehabilitative ultrasound imaging. Man Ther. 2007; 12(2): 161-6.

20.

Wong

Parent

Kawchuk

. Reliability of 2 ultrasonic imaging analysis methods in quantifying lumbar multifidus thickness. J Orthop Sports Phys Ther. 2013; 43(4): 251-62.

21.

Wilson

Hides

Blizzard

Callisaya

Cooper

Srikanth

Winzenberg

. Measuring ultrasound images of abdominal and lumbar multifidus muscles in older adults: A reliability study. Man Ther. 2016; 23: 114-9.

22.

Kim

Kang

Kim

Lee

Yoon

. Selective Activation of Lumbar Paraspinal Muscles during Various Exercises in the Prone Position as Measured by EMG. J Phys Ther Sci. 2014; 26(8): 1223-4.

23.

Hides

Stanton

McMahon

Sims

Richardson

. Effect of stabilization training on multifidus muscle cross-sectional area among young elite cricketers with low back pain. J Orthop Sports Phys Ther. 2008; 38(3): 101-8.

24.

Koppenhaver

Hebert

Fritz

Parent

Teyhen

Magel

. Reliability of rehabilitative ultrasound imaging of the transversus abdominis and lumbar multifidus muscles. Arch Phys Med Rehabil. 2009; 90(1): 87-94.

25.

Teyhen

Childs

Stokes

Wright

Dugan

George

. Abdominal and lumbar multifidus muscle size and symmetry at rest and during contracted States. Normative reference ranges. J Ultrasound Med. 2012; 31(7): 1099-110.

26.

Nuzzo

Haun

Mayer

. Ultrasound measurements of lumbar multifidus and abdominal muscle size in firefighters. J Back Musculoskelet Rehabil. 2014; 27(4): 427-33.

27.

Caresio

Molinari

Emanuel

Minetto

. Muscle echo intensity: reliability and conditioning factors. Clin Physiol Funct Imaging. 2015; 35(5): 393-403.

28.

Smith

Togeiro

Tufik

Roizenblatt

. Disturbed sleep and musculoskeletal pain in the bed partner of patients with obstructive sleep apnea. Sleep Med. 2009; 10(8): 904-12.

29.

Roehrs

Hyde

Blaisdell

Greenwald

Roth

. Sleep loss and REM sleep loss are hyperalgesic. Sleep. 2006; 29(2): 145-51.

30.

de Oliveira

Hirotsu

Tufik

Andersen

. The interfaces between vitamin D, sleep and pain. J Endocrinol. 2017; 234(1): R23-R36.

31.

Schrimpf

Liegl

Boeckle

Leitner

Geisler

Pieh

. The effect of sleep deprivation on pain perception in healthy subjects: a meta-analysis. Sleep Med. 2015; 16(11): 1313-1320.

32.

Davies

Macfarlane

Nicholl

Dickens

Morriss

Ray

McBeth

. Restorative sleep predicts the resolution of chronic widespread pain: results from the EPIFUND study. Rheumatology (Oxford). 2008; 47(12): 1809-13.

33.

Hays

Hadorn

. Responsiveness to change: an aspect of validity, not a separate dimension. Qual Life Res. 1992; 1(1): 73-5.

34.

Cadore

González-Izal

Pallarés

Rodriguez-Falces

Häkkinen

Kraemer

Pinto

Izquierdo

. Muscle conduction velocity, strength, neural activity, and morphological changes after eccentric and concentric training. Scand J Med Sci Sports. 2014; 24(5): e343-52.

35.

Guilhem

Cornu

Maffiuletti

Guével

. Neuromuscular adaptations to isoload versus isokinetic eccentric resistance training. Med Sci Sports Exerc. 2013; 45(2): 326-35.

36.

Franchi

Longo

Mallinson

Quinlan

Taylor

Greenhaff

Narici

. Muscle thickness correlates to muscle cross sectional area in the assessment of strength training induced hypertrophy. Scand J Med Sci Sports. 2018; 28(3): 846-53.

37.

Reimers

Wagner

Paetzke

Pongratz

. Skeletal muscle sonography: a correlative study of echogenicity and morphology. J Ultrasound Med. 1993; 12(2): 73-7.

38.

Pillen

Tak

Zwarts

Lammens

Verrijp

Arts

van der Laak

Hoogerbrugge

van Engelen

Verrips

. Skeletal muscle ultrasound: correlation between fibrous tissue and echo intensity. Ultrasound Med Biol. 2009; 35(3): 443-6.

39.

Mastrocola

Collino

Nigro

Chiazza

D’Antona

Aragno

Minetto

. Accumulation of advanced glycation end-products and activation of the SCAP/SREBP Lipogenetic pathway occur in diet-induced obese mouse skeletal muscle. PLoS One. 2015; 10(3): e0119587.

40.

Collino

Mastrocola

Nigro

Chiazza

Aragno

D’Antona

Minetto

. Variability in myosteatosis and insulin resistance induced by high-fat diet in mouse skeletal muscles. Biomed Res Int. 2014; 2014: 569623.