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Accelerometer based assessment of daily physical activity and sedentary time in adolescents with idiopathic scoliosis

  • Swati Chopra,

    Roles Formal analysis, Resources, Software, Validation, Visualization, Writing – original draft, Writing – review & editing

    Affiliations Motion Analysis Laboratory, Mayo Clinic, Rochester, MN, United States of America, Leeds Institute of Rheumatic and Musculoskeletal Medicine, University of Leeds, Leeds, United Kingdom

  • A. Noelle Larson,

    Roles Conceptualization, Investigation, Methodology, Resources, Validation, Visualization, Writing – original draft, Writing – review & editing

    Affiliation Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, United States of America

  • Kenton R. Kaufman ,

    Roles Conceptualization, Data curation, Formal analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – review & editing

    Kaufman.kenton@mayo.edu

    Affiliations Motion Analysis Laboratory, Mayo Clinic, Rochester, MN, United States of America, Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, United States of America

  • Todd A. Milbrandt

    Roles Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Project administration, Resources, Validation, Visualization, Writing – review & editing

    Affiliation Department of Orthopedic Surgery, Mayo Clinic, Rochester, MN, United States of America

Accelerometer based assessment of daily physical activity and sedentary time in adolescents with idiopathic scoliosis

  • Swati Chopra, 
  • A. Noelle Larson, 
  • Kenton R. Kaufman, 
  • Todd A. Milbrandt
PLOS
x

Abstract

Background

Studies have shown a positive correlation between higher physical activity (PA) and health benefits. However, device-based assessment of PA and sedentary time (ST) in people with adolescent idiopathic scoliosis (AIS) has not been deeply investigated.

Objective

Analysis and comparison of weekend and weekdays PA and ST using multiple accelerometers in people with AIS with different curvature severity compared to healthy controls.

Methods

24 participants with AIS divided into 2 groups of 12 with Cobb angles < 40° and > 40°, along with 12 age and BMI matched healthy controls. Daily PA and ST during four consecutive days were measured using four tri-axial accelerometers. Clinical functional assessment was performed using the scoliosis research society (SRS-22) questionnaire.

Results

The combined weekend and weekdays average daily step count was found to be 22% and 29% lower in the AIS groups with Cobb angle < 40° and > 40°, respectively, compared to the controls. The average ST was also reported to be 5% and 7% higher in the AIS groups with Cobb angle < 40° and > 40°, respectively, compared to the controls. The reported differences were significant in the AIS group with higher Cobb angle (p≤0.05). No significant differences in PA or ST were reported between the AIS groups based on curvature severity.

Conclusions

Decreased PA and increased ST observed in patients with AIS may have long term health implications and may play a role in the disease process. The device-based assessment of PA to understand potential benefits in clinical practice is recommended.

1. Introduction

Scoliosis is the abnormal three-dimensional curvature of the spine including hypokyphosis, rotation and coronal deformities. Scoliosis in children can be rapidly progressive during the growing years [1]. Approximately 90% of scoliosis cases fall under the category of adolescent idiopathic scoliosis (AIS) with no clear underlying syndromic or neuromuscular cause [1]. The prevalence rate of AIS is 0.47% - 5.2%, with a female to male ratio of 2:1, and the gender ratio gap is seen to increase with disease severity and age [1]. The degree of spinal curvature identified on a postero-anterior radiograph is measured by the Cobb angle [2], the angle subtended by the two most tilted vertebrae. AIS patients diagnosed with a Cobb angle > 20° require treatment based on factors including the location of the curvature of the spine, skeletal maturity, and age. Radiographic images are used as an indirect measure of skeletal maturity which is presented in terms of the Risser sign [3]. The Risser sign has 6 stages from 0 to 5, where Stage 0 represents no ossification in the iliac apophysis, and Stage 5 represents complete ossification and fusion of the iliac apophysis [3]. Curves between 25° to 40° in growing children are treated with spinal bracing to reduce the risk of curve progression [4]. Curves greater than 50° are thought to be progressive throughout life; thus, surgery is usually the treatment of choice for curves over 45° to 50° [5].

A longitudinal study including 4640 participants has reported that children performing regular, objectively measured, moderate to vigorous PA (MVPA) are 30% less likely to develop scoliosis [6]. An objectively measured increase in the ST in healthy adolescents has also been found to be negatively associated with bone health [7]. Another study has reported negative effect of low level of self-reported PA on psychological wellbeing in adolescents [8]. Prolonged relaxed sitting in healthy children has shown to increase trunk asymmetry [9]. In AIS patients, prolonged relaxed sitting led to an even greater trunk asymmetry due to the habitual leaning on one side depending on the curvature type [10]. Knowing the health complications related to scoliosis (musculoskeletal, psychological and respiratory conditions) which seem to progress with an increase in the scoliosis curvature [1114] it is important to identify PA and ST as important factors in assessing health status of patients with AIS.

It is quite evident that participation in regular PA is important for patients with AIS for health benefits, including improved bone mineral density (BMD), strength, mobility, balance and controlled curve progression, thereby improving their quality of life [1518]. To achieve this successfully, it is important to have a valid and reliable method of assessment of PA. This will provide a more in depth understanding of the reduced exercise capacity and the factors affecting ST in patients with AIS in order to help design optimal interventions. However, studies reporting objectively measured PA and ST are uncommon in patients with AIS. In fact, only one survey-based study has compared PA in patients with AIS and their peers without AIS using the International Physical Activity Questionnaire Short Form (IPAQ-SF). The study concluded that patients with AIS have similar PA levels as their peers without AIS [19]. Notably, the IPAQ-SF questionnaire has been shown to exaggerate PA levels compared to the device-based measurements [20].

This study, therefore, aims to assess the daily PA and ST in patients with AIS objectively, based on the severity of their scoliosis curvature, and compare their activity status with healthy age and BMI matched controls. The working hypothesis of the study is that patients who have AIS with different severity levels will have similar PA levels when compared with the age and BMI matched healthy controls.

2. Methods

2.1. Participants

During the years 2015–2018, 51 patients, who referred to the Mayo Clinic tertiary referral center for treatment from various socioeconomic backgrounds, were screened to participate in the study. Out of 51, 14 patients declined and 37 agreed to participate. This cross-sectional study included 24 (17F/7M) consecutive patients with AIS, and 12 age, BMI and gender matched controls without AIS. The 24 patients with AIS included 12 patients with Cobb angles < 40° and a Risser’s stage between 0–2 who were advised to have spinal bracing treatment, and 12 patients with Cobb angles > 40° and Risser’s stages of 4 and 5 who were advised to have spinal fusion (Table 1). The control group consisted of children who were referred due to acute injuries that did not impair their mobility and also fulfilled the inclusion criteria of no prior or existing spinal or lower extremity deformities. The study protocol was approved by the Institutional Review board. Informed consent was obtained from all study participants in the presence of their parents/ guardians.

2.2. Assessment methods

Assessment was performed before any treatment was started. The subjective assessment of health, based on the patient reported outcome measure (PROM), was carried out using the commonly used SRS-22 questionnaire [21]. Scoring is based on the set of 22 questions related to pain, self-image, mental health, function and satisfaction. The final score gives the combined outcome of all 5 subsections and a higher score represents a better outcome. Although the validity and reliability of the SRS-22 questionnaire has only been proven among adults [22, 23], it is still widely used in studies assessing the outcome of treatments in AIS [2426]. This study utilized the SRS-22 questionnaire to compare the functional, pain and general health status of AIS patients with different curvature severity, to identify any differences between the groups.

The Cobb angle and Risser sign were calculated from the postero-anterior radiographic images. Radiographic imaging was not performed for the healthy controls. The PA of® all participants was assessed objectively based on the time spent being active or inactive. Field-based activity data was collected using four miniature tri-axial accelerometers (Actigraph GT3X+, Pensacola, FL, USA). All four activity monitor units (AMU) were calibrated to record +1g, 0g, -1g and were synchronized to each other based on a previously validated protocol [27].

The AMU were placed on both ankles, on the right thigh and at waist level, either over or under clothes. Activity data was collected at a frequency of 100 Hz. Based on the previous studies, device-based assessment of daily PA in children for least 10 hours/day and 4 days of monitoring including weekend and weekdays, is considered reliable [2830]. In this study, all participants, including the controls, were asked to wear the sensors for 4 consecutive days (2 weekdays and 2 weekend days) from the time they were out of bed and bathed in the morning until the time they returned to bed at night. Participants were asked to remove the sensors during any water activities e.g. bathing/ swimming.

2.3. Signal processing

Analysis, calibration and processing of the AMU data was carried out using the MATLAB R2015b (Version 7.11.0, Mathworks, MA, USA). A validated algorithm-based analysis of AMU data was used to detect movement and postural transitions during active and inactive periods [27]. More specifically, the waist AMU signals were used to differentiate between static and dynamic activity [27]. Dynamic activity is established by calculating when the signal magnitude areas (SMA) exceed a threshold of 0.135 g continuously for a period of 1s. SMA below the 0.135 g threshold were further analyzed via the application of a continuous wavelet transform using a Daubechies 4 Mother Wavelet [27]. Data, which fell within a range of 0.1–2.0 Hz and also exceeded a scaling threshold of 1.5 over each second, were also identified as dynamic activity [27]. SMA between 0.135 g and 0.8 g were considered light physical activity (LPA), including walking, while SMA exceeding 0.8 g were considered as MVPA, including jogging and running [31].

A step detection algorithm analyzed the ankle AMU data to identify heel strikes from the anterio-posterior signal, further differentiating into walking and jogging steps [27]. Finally, a postural orientation algorithm analyzed the thigh and waist AMU data to estimate the torso angle and differentiate between different postures (standing, sitting and lying down) as well as the transition between them [27]. A postural transition is recorded if a different position (standing, sitting or lying) is identified prior to and following a 2 second time-frame. Postural transitions are counted as active time periods [27].

2.4. Statistical analyses

AMU data and SRS-22 scores are presented as the group mean. The z score is assessed to test the distribution of data in each group [32]. The z score results showed normal distribution in our data set. Firstly, to compare PA and ST between the controls and the AIS groups, an analysis of variance (ANOVA) was performed to analyze the differences between the group means. The post hoc comparisons were performed using the Dunnett’s correction to control the Family-Wise Error Rate [33]. The effect size (d) was calculated to study the power of the analysis. Secondly, the differences in PA and ST were compared between the AIS groups with < 40° and > 40° Cobb angles after adjusting for age and BMI by using an analysis of covariance (ANCOVA). All the outcomes were presented as a mean with standard deviation (SD). The significance level for all statistical tests was set at p≤0.05.

3. Results

The recorded wear time of the AMU for all participants over weekdays and weekends was an average of 13.5±1.7 hours/day. The patient reported SRS-22 questionnaires, in both AIS groups, showed a comparable health status (Table 2).

The PA and ST outcomes during the two weekdays is given in (Table 3). The AIS group with Cobb angle > 40° reported a significantly less percentage of time spent physically active (p<0.02, d = 0.87), especially time spent in LPA (p<0.003, d = 1.2), as well as a significantly low daily step count (p = 0.02, d = 0.94) compared to the controls. The percentage of ST is also found to be significantly high (p = 0.02, d = 0.87) compared to the controls. While, the AIS group with Cobb angle < 40° also showed increased inactivity compared to the healthy controls, the difference was not significant. The only significant difference was reported in the percentage of time spent in LPA (p = 0.005, d = 1.66).

thumbnail
Table 3. Activity and sedentary behavior during weekdays.

Mean (SD).

https://doi.org/10.1371/journal.pone.0238181.t003

The PA and ST outcomes during the two weekend days is given in (Table 4). Reduced PA is reported in all three groups. However, a significant difference was only reported in percentage of time spent in MVPA in the AIS group with Cobb angle > 40°, compared to the controls (p = 0.005, d = 1.66).

thumbnail
Table 4. Activity and sedentary behavior during weekend days.

Mean (SD).

https://doi.org/10.1371/journal.pone.0238181.t004

The ANCOVA comparison between the two AIS groups, after adjusting age and BMI, reported no significant differences in PA or ST parameters. Fig 1 shows the relation between ST in % and age of the participants, in all three groups.

thumbnail
Fig 1.

Individual data plot representing the average sedentary time (%) in relation to age in (a.) AIS Cobb angle <40°, (b.) AIS Cobb angle >40°and (c.) Controls.

https://doi.org/10.1371/journal.pone.0238181.g001

4. Discussion

This study presents a device-based assessment of the daily PA levels and ST in patients with AIS. The quantification of PA levels was performed using accelerometers, applying validated methods [34]. A lower PA is observed in patients with AIS, irrespective of the curvature severity, compared to the controls. Therefore, the outcome of this study rejects the hypothesis that patients with AIS, irrespective of curvature severity, are as equally active as their peers without AIS.

Previous investigations have revealed 10,000 to 16,000 steps/day to be optimal for health benefits, which represents approximately ≥60 mins/day of MVPA in healthy adolescents [35, 36]. In our study, the patients with AIS, irrespective of the curvature severity, do not seem to achieve the recommended step counts, both during weekdays and weekends. The PA outcome aligns with the previous study assessing daily step count using a pedometer in AIS patients with Cobb angle <50° reporting lesser daily steps than the recommended for health benefits [37]. In AIS patients, during walking, a 30% increase in energy cost and a 20% -30% decline in muscle efficacy has been identified [38]. This could be one of the reasons behind the decreased number of daily steps and lower percentage of LPA reported in our cohorts with AIS, irrespective of curvature severity. Although, this not being an issue for healthy adolescents, our control group participants failed to achieve the recommended daily step count of 10000 steps during weekends. Previous studies, on healthy adolescents, reports that after school activity accumulates greater amount of PA [39, 40]. Therefore outcome of this study further confirms the importance of after school physical activity in all adolescents. Notably, the ST reported in this study also falls within the interquartile range of the ST reported in a previous study for healthy participants between ages 10 to 11 years [41]. Although, the average ST reported in this study, for the three groups, are on the higher end of the interquartile range, this could be due to the age range of the participants in our study (ages 11 to 16 years), knowing that ST seems to increase with age in adolescents [42].

Based on the above discussion, there is a need for a recommendation that patients with AIS, irrespective of curvature severity, are encouraged to participate in sports and regular PA. Unfortunately, most of the studies assessing the effect of therapeutic spinal exercises in patients with AIS only include mild severity cases [43, 44]. A recent meta-analysis based on the outcome of 15 studies has reported that the effect of therapeutic Schroth exercises is more beneficial for Cobb angles < 30° [45]. Furthermore, in idiopathic scoliosis, participation in sports which can strain the back leading to increased axial loading and hyperlordosis are not indicated if there is an underlying problem of back pain. It is also suggested that sports recommendation should be individualized in patients with curvature severity [46]. This could be one of the many reasons why patients with AIS are not encouraged to participate in sporting activities.

However, to achieve the health benefits, an increase in daily PA and a reduction in ST in patients with AIS are crucial. A study has shown the need to assess PA and ST in children objectively, to understand the factors affecting activity levels in order to develop tailored physical intervention [47]. There is also a clear need for health education regarding the risks and benefits of structured PA and the importance of an increase in PA and a reduction in ST for patients and their families in managing AIS. We suggest a device-based assessment of daily activity, similar to that carried out in this study, would provide accurate PA information, which in the future could help develop patient-specific PA guidelines, potentially preventing osteopenia and reducing other health problems related to AIS, perhaps even controlling progression of scoliosis.

The strength of the study follows the use of a validated AMU system capable of monitoring activity levels continuously over an entire day. PA levels were monitored for four consecutive days, including weekend and weekdays, to take into account the inherent differences. Furthermore, the utilized multi-sensor accelerometer array allows one to differentiate, not only between activity and inactivity, but also between different static position and postural transitions. The small study size is however a study limitation, though the significant differences showed an acceptable effect size. Another limitation of the study is the missing standardized method of grading leisure and sporting activities at the baseline. 90% of AIS patients in the study self-reported participation in regular organized PA. Based on the results of the study, this appears to be an overestimation.

5. Conclusion

The findings of our study illustrate the differences in PA and ST between patients with AIS and the healthy controls. Notably, curvature severity was not shown to have much effect on PA or ST when AIS groups with mild and severe Cobb angles were compared. The study suggests the use of device-based PA monitoring for more descriptive information on PA and ST in patients with AIS. In terms of improving treatment prognosis in AIS, it is important to include PA and exercise recommendations, based on the severity of the spinal curvature, in clinical practice.

References

  1. 1. Konieczny MR, Senyurt H, Krauspe R. Epidemiology of adolescent idiopathic scoliosis. Journal of Children's Orthopaedics. 2013;7(1):3–9. PMC3566258. pmid:24432052
  2. 2. Cobb JR. Outline for the Study of Scoliosis. In: Instructional Course Lectures. The American Academy of Orthopaedics Surgeons. 1984: 261–75.
  3. 3. Hacquebord JH, Leopold SS. In Brief: The Risser Classification: A Classic Tool for the Clinician Treating Adolescent Idiopathic Scoliosis. Clinical Orthopaedics and Related Research. 2012;470(8):2335–8. PMC3392381. pmid:22538960
  4. 4. Richards BS, Bernstein RM, D'Amato CR, Thompson GH. Standardization of criteria for adolescent idiopathic scoliosis brace studies: SRS Committee on Bracing and Nonoperative Management. Spine (Phila Pa 1976). 2005;30(18):2068–75; discussion 76–7. Epub 2005/09/17. pmid:16166897.
  5. 5. Maruyama T, Takeshita K. Surgery for Idiopathic Scoliosis: Currently Applied Techniques. Clinical Medicine Pediatrics. 2009;3:39–44. PMC3676291. pmid:23818793
  6. 6. Tobias JH, Fairbank J, Harding I, Taylor HJ, Clark EM. Association between physical activity and scoliosis: a prospective cohort study. Int J Epidemiol. 2019;48(4):1152–60. pmid:30535285.
  7. 7. Koedijk JB, van Rijswijk J, Oranje WA, van den Bergh JP, Bours SP, Savelberg HH, et al. Sedentary behaviour and bone health in children, adolescents and young adults: a systematic review. Osteoporosis international: a journal established as result of cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA. 2017;28(9):2507–19. Epub 05/26. pmid:28547135.
  8. 8. Ussher MH, Owen CG, Cook DG, Whincup PH. The relationship between physical activity, sedentary behaviour and psychological wellbeing among adolescents. Soc Psychiatry Psychiatr Epidemiol. 2007;42(10):851–6. Epub 2007/07/20. pmid:17639309.
  9. 9. Drza-Grabiec J, Snela S, Rykala J, Podgorska J, Rachwal M. Effects of the sitting position on the body posture of children aged 11 to 13 years. Work. 2015;51(4):855–62. Epub 2014/06/26. pmid:24962297.
  10. 10. Weiss H-R, Moramarco MM, Borysov M, Ng SY, Lee SG, Nan X, et al. Postural Rehabilitation for Adolescent Idiopathic Scoliosis during Growth. Asian Spine J. 2016;10(3):570–81. Epub 06/16. pmid:27340540.
  11. 11. Abdelaal AAM, Abd El Kafy E, Elayat M, Sabbahi M, Badghish MSS. Changes in pulmonary function and functional capacity in adolescents with mild idiopathic scoliosis: observational cohort study. The Journal of international medical research. 2017:300060517715375. Epub 2017/07/01. pmid:28661261.
  12. 12. Koumbourlis AC. Scoliosis and the respiratory system. Paediatric respiratory reviews. 2006;7(2):152–60. Epub 2006/06/13. pmid:16765303.
  13. 13. Martinez-Llorens J, Ramirez M, Colomina MJ, Bago J, Molina A, Caceres E, et al. Muscle dysfunction and exercise limitation in adolescent idiopathic scoliosis. The European respiratory journal. 2010;36(2):393–400. Epub 2009/12/25. pmid:20032022.
  14. 14. Sadat-Ali M, Al-Othman A, Bubshait D, Al-Dakheel D. Does scoliosis causes low bone mass? A comparative study between siblings. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society. 2008;17(7):944–7. Epub 04/22. pmid:18427842.
  15. 15. Zulfarina MS, Sharkawi AM, Aqilah SNZ, Mokhtar SA, Nazrun SA, Naina-Mohamed I. Influence of Adolescents' Physical Activity on Bone Mineral Acquisition: A Systematic Review Article. Iranian journal of public health. 2016;45(12):1545–57. Epub 2017/01/06. pmid:28053920; PubMed Central PMCID: PMC5207095.
  16. 16. Lee WT, Cheung CS, Tse YK, Guo X, Qin L, Lam TP, et al. Association of osteopenia with curve severity in adolescent idiopathic scoliosis: a study of 919 girls. Osteoporosis international: a journal established as result of cooperation between the European Foundation for Osteoporosis and the National Osteoporosis Foundation of the USA. 2005;16(12):1924–32. Epub 2005/09/16. pmid:16163440.
  17. 17. Fusco C, Zaina F, Atanasio S, Romano M, Negrini A, Negrini S. Physical exercises in the treatment of adolescent idiopathic scoliosis: An updated systematic review. Physiotherapy Theory and Practice. 2011;27(1):80–114. pmid:21198407
  18. 18. dos Santos Alves VL, Alves da Silva RJ, Avanzi O. Effect of a preoperative protocol of aerobic physical therapy on the quality of life of patients with adolescent idiopathic scoliosis: a randomized clinical study. Am J Orthop (Belle Mead NJ). 2014;43(6):E112–6. Epub 2014/06/20. pmid:24945482.
  19. 19. Diarbakerli E, Grauers A, Danielsson A, Gerdhem P. Adults With Idiopathic Scoliosis Diagnosed at Youth Experience Similar Physical Activity and Fracture Rate as Controls. Spine (Phila Pa 1976). 2017;42(7):E404–e10. Epub 2016/08/09. pmid:27496666.
  20. 20. Lee PH, Macfarlane DJ, Lam TH, Stewart SM. Validity of the International Physical Activity Questionnaire Short Form (IPAQ-SF): a systematic review. The international journal of behavioral nutrition and physical activity. 2011;8:115. Epub 2011/10/25. pmid:22018588; PubMed Central PMCID: PMC3214824.
  21. 21. Asher M, Min Lai S, Burton D, Manna B. Discrimination validity of the scoliosis research society-22 patient questionnaire: relationship to idiopathic scoliosis curve pattern and curve size. Spine (Phila Pa 1976). 2003;28(1):74–8. Epub 2003/01/25. pmid:12544960.
  22. 22. Bridwell KH, Cats-Baril W, Harrast J, Berven S, Glassman S, Farcy JP, et al. The validity of the SRS-22 instrument in an adult spinal deformity population compared with the Oswestry and SF-12: a study of response distribution, concurrent validity, internal consistency, and reliability. Spine (Phila Pa 1976). 2005;30(4):455–61. Epub 2005/02/12. pmid:15706344.
  23. 23. Karakaya I, Sismanlar SG, Atmaca H, Gok U, Sarlak AY. Outcome in early adolescent idiopathic scoliosis after deformity correction: assessed by SRS-22, psychometric and generic health measures. Journal of pediatric orthopedics Part B. 2012;21(4):317–21. Epub 2012/04/13. pmid:22495615.
  24. 24. Li N, Xu C, Shen MK, Luo M, Wang J, Xia L. Clinical outcomes of posterior pedicle screw instrumentation without osteotomy in the management of adolescent idiopathic scoliosis. Medicine. 2018;97(36):e12122. Epub 2018/09/12. pmid:30200098.
  25. 25. Erdem MN, Karaca S, Korkmaz MF, Enercan M, Tezer M, Kara AN, et al. Criteria for Ending the Distal Fusion at the L3 Vertebra vs. L4 in Surgical Treatment of Adolescent Idiopathic Scoliosis Patients with Lenke Type 3C, 5C, and 6C Curves: Results After Ten Years of Follow-up. Cureus. 2018;10(5):e2564. PMC6029740. pmid:29974019
  26. 26. Kwan KYH, Cheng ACS, Koh HY, Chiu AYY, Cheung KMC. Effectiveness of Schroth exercises during bracing in adolescent idiopathic scoliosis: results from a preliminary study-SOSORT Award 2017 Winner. Scoliosis Spinal Disord. 2017;12:32. Epub 2017/10/21. pmid:29051921; PubMed Central PMCID: PMC5641990.
  27. 27. Lugade V, Fortune E, Morrow M, Kaufman K. Validity of Using Tri-Axial Accelerometers to Measure Human Movement—Part I: Posture and Movement Detection. Medical engineering & physics. 2014;36(2):169–76. PMC3866210. pmid:23899533
  28. 28. Colley R, Connor Gorber S, Tremblay MS. Quality control and data reduction procedures for accelerometry-derived measures of physical activity. Health Rep. 2010;21(1):63–9. Epub 2010/04/30. pmid:20426228.
  29. 29. Hinkley T, O'Connell E, Okely AD, Crawford D, Hesketh K, Salmon J. Assessing volume of accelerometry data for reliability in preschool children. Medicine and science in sports and exercise. 2012;44(12):2436–41. Epub 2012/07/11. pmid:22776873.
  30. 30. Beck J, Chard CA, Hilzendegen C, Hill J, Stroebele-Benschop N. In-school versus out-of-school sedentary behavior patterns in U.S. children. BMC obesity. 2016;3:34. Epub 2016/07/21. pmid:27437117; PubMed Central PMCID: PMC4944493.
  31. 31. Fortune E, Lugade V, Morrow M, Kaufman K. Validity of Using Tri-Axial Accelerometers to Measure Human Movement–Part II: Step Counts at a Wide Range of Gait Velocities. Medical engineering & physics. 2014;36(6):659–69. PMC4030415. pmid:24656871
  32. 32. Kim H-Y. Statistical notes for clinical researchers: assessing normal distribution (2) using skewness and kurtosis. Restorative Dentistry & Endodontics. 2013;38(1):52–4. PMC3591587. pmid:23495371
  33. 33. McHugh ML. Multiple comparison analysis testing in ANOVA. Biochemia medica. 2011;21(3):203–9. Epub 2011/01/01. pmid:22420233.
  34. 34. Cain KL, Sallis JF, Conway TL, Van Dyck D, Calhoon L. Using accelerometers in youth physical activity studies: a review of methods. Journal of physical activity & health. 2013;10(3):437–50. Epub 2013/04/27. pmid:23620392; PubMed Central PMCID: PMC6331211.
  35. 35. Adams MA, Caparosa S, Thompson S, Norman GJ. Translating physical activity recommendations for overweight adolescents to steps per day. Am J Prev Med. 2009;37. pmid:19524391
  36. 36. Tudor-Locke C, Craig C, Beets M, Belton S, Cardon G, Duncan S, et al. How many steps/day are enough? for children and adolescents. The international journal of behavioral nutrition and physical activity. 2011;8.
  37. 37. Müller C, Fuchs K, Winter C, Rosenbaum D, Schmidt C, Bullmann V, et al. Prospective evaluation of physical activity in patients with idiopathic scoliosis or kyphosis receiving brace treatment. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society. 2011;20(7):1127–36. Epub 04/10. pmid:21479852.
  38. 38. Mahaudens P, Detrembleur C, Mousny M, Banse X. Gait in adolescent idiopathic scoliosis: energy cost analysis. European spine journal: official publication of the European Spine Society, the European Spinal Deformity Society, and the European Section of the Cervical Spine Research Society. 2009;18(8):1160–8. Epub 2009/04/25. pmid:19390877; PubMed Central PMCID: PMC2899505.
  39. 39. Arundell L, Fletcher E, Salmon J, Veitch J, Hinkley T. A systematic review of the prevalence of sedentary behavior during the after-school period among children aged 5–18 years. The international journal of behavioral nutrition and physical activity. 2016;13:93. Epub 2016/08/24. pmid:27549588; PubMed Central PMCID: PMC4994288.
  40. 40. Flohr JA, Todd MK, Tudor-Locke C. Pedometer-assessed physical activity in young adolescents. Res Q Exerc Sport. 2006;77(3):309–15. Epub 2006/10/06. pmid:17020075.
  41. 41. Fairclough SJ, Boddy LM, Mackintosh KA, Valencia-Peris A, Ramirez-Rico E. Weekday and weekend sedentary time and physical activity in differentially active children. J Sci Med Sport. 2015;18(4):444–9. Epub 2014/07/12. pmid:25011925.
  42. 42. Nelson MC, Neumark-Stzainer D, Hannan PJ, Sirard JR, Story M. Longitudinal and secular trends in physical activity and sedentary behavior during adolescence. Pediatrics. 2006;118(6):e1627–34. Epub 2006/12/05. pmid:17142492.
  43. 43. Ko K-J, Kang S-J. Effects of 12-week core stabilization exercise on the Cobb angle and lumbar muscle strength of adolescents with idiopathic scoliosis. Journal of Exercise Rehabilitation. 2017;13(2):244–9. PMC5412502. pmid:28503541
  44. 44. Borysov M, Moramarco M, Sy N, Lee SG. Postural Re-Education of Scoliosis—State of the Art (Mini-review). Current pediatric reviews. 2016;12(1):12–6. Epub 2015/11/18. pmid:26573166.
  45. 45. Park JH, Jeon HS, Park HW. Effects of the Schroth exercise on idiopathic scoliosis: a meta-analysis. European journal of physical and rehabilitation medicine. 2018;54(3):440–9. Epub 2017/10/05. pmid:28976171.
  46. 46. Gielen JL, Van den Eede E. Scoliosis and sports participation: FIMS position statements. International SportMed Journal. 2008;9(3):131–40.
  47. 47. Dolinsky DH, Brouwer RJ, Evenson KR, Siega-Riz AM, Ostbye T. Correlates of sedentary time and physical activity among preschool-aged children. Prev Chronic Dis. 2011;8(6):A131. pmid:22005624.