Isokinetic evaluation of the trunk flexors and extensors in women with and without scoliosis: A comparative study

Abstract

BACKGROUND:

Scoliosis affects mainly women and even if its diagnosis relies on clinical evaluation and radiographic assessment, muscular involvement is undeniable impacting possibly on strength and daily activities.

OBJECTIVE:

To assess the strength of sagitally operating trunk muscles in women with scoliosis (WwS) and apparently healthy women (AH) with a similar mean age.

METHODS:

The two groups consisted 114 WwS and 42 AH women. The concentric isokinetic evaluation related to the peak moment (PM) of the trunk flexors and extensors at 30 and 90 ${}^{\circ}$ /s. Division into subgroups was based on the location of the scoliosis and magnitude of the Cobb angle.

RESULTS:

The PM of both muscle groups was not correlated with the location of the scoliosis. However, these muscles manifested a highly significant weakness in WwS compared to the AH group, in both test velocities. In terms of the general severity of the weakness, the PM scores in WwS with Cobb angle $>$ 30 ${}^{{\circ}}$ were significantly lower compared to their healthy counterparts in both ‘muscle’ and ‘velocity’ whereas save the flexors at 90 ${}^{\circ}$ /s, there was no difference between the lesser compromised WwS (Cobb $\leqslant$ 30 ${}^{\circ}$ ) and AH women. The PM-based extension/flexion ratios in WwS were respectively 1.34 $\pm$ 0.28 and 1.23 $\pm$ 0.27 at 30 ${}^{\circ}$ /s and 90 ${}^{\circ}$ /s, with no significant difference between subgroups, nor with control values.

CONCLUSION:

In view of the results, trunk muscles strength should definitely be taken into account when planning therapeutic options for WwS.

Keywords

Idiopathic scoliosis isokinetic evaluation trunk muscles

1. Introduction

Table 1
Impact of curve type on maximal force expressed by the peak moment (PM) in Nm/kgbw, for trunk flexors (FL), trunk extensors (E) at 30 ${}^{\circ}$ and 90 ${}^{\circ}$ /s. Results are presented by means (m) $\pm$ standard deviation

	Dorso lumbar $N=$ 18		Double major $N=$ 38		Thoracic $N=$ 35		Lumbar $N=$ 23		$p$ -value
Age	31.7	$\pm$ 8.3	28.8	$\pm$ 6	30.1	$\pm$ 7.4	29.3	$\pm$ 7.8	0.6
Weight	57.2	$\pm$ 8	57.2	$\pm$ 7.6	58.5	$\pm$ 7.9	53.6	$\pm$ 4.8	0.38
PM_FL_30	1.74	$\pm$ 0.31	1.86	$\pm$ 0.35	1.88	$\pm$ 0.38	1.91	$\pm$ 0.27	0.43
PM_FL_90	1.65	$\pm$ 0.29	1.75	$\pm$ 0.34	1.74	$\pm$ 0.43	1.80	$\pm$ 0.32	0.42
PM_E_30	2.37	$\pm$ 0.69	2.44	$\pm$ 0.58	2.53	$\pm$ 0.59	2.28	$\pm$ 0.60	0.45
PM_E_90	1.98	$\pm$ 0.70	2.14	$\pm$ 0.51	2.17	$\pm$ 0.59	2.02	$\pm$ 0.63	0.64
Ratio PM 30	1.36	$\pm$ 0.26	1.35	$\pm$ 0.25	1.37	$\pm$ 0.23	1.24	$\pm$ 0.36	0.18
Ratio PM 90	1.19	$\pm$ 0.32	1.27	$\pm$ 0.25	1.26	$\pm$ 0.21	1.13	$\pm$ 0.31	0.20

Significance thresholds: ${}^{*}<$ 0.05, ${}^{**}<$ 0.01, ${}^{***}<$ 0.001%.

The prevalence of adult spinal deformity and scoliosis is not well established, with estimates of more than 8% in adults over the age of 25 [1] and up to 68% in the age of over 60 years [2], caused by degenerative changes in the aging spine. Adults with scoliosis were sometimes adolescents with idiopathic scoliosis, which is a common disease with an overall prevalence of 0.47–5.2% [3]. The female to male ratio ranges from 1.5:1 to 3:1 and increases substantially with increasing age. In particular, the prevalence of curves with higher Cobb angles is substantially higher in girls than in boys [3]. Primary degenerative scoliosis is also a highly prevalent condition, especially in females [4]. Young adult women are therefore particularly troubled by the problem of scoliosis.

Diagnosis and surveillance of adult scoliosis are based on clinical examination of the trunk, and radiographic assessment. The monitoring is justified in view of the evolution of scoliosis in adulthood, which has been known for a long time [5] and even better described more recently in adults [6]. It may be the aggravation of idiopathic scoliosis in adulthood, the occurrence of degenerative phenomena such as discopathy, posterior osteoarthritis, alteration of muscle quality in degenerative scoliosis or de Novo scoliosis, deformations/disorders of the spine which appear in adulthood.

The control of the evolution of scoliosis is based on Cobb’s angle [7] obtained from the tangent of the upper plateau of the upper limit vertebra and the lower plateau of the lower limit vertebra. This angle allows classification of the scoliosis according to its location and severity, to assess its evolution and to propose therapeutic approaches.

This completely underestimates the muscular component of the trunk, its role in scoliosis evolution and its impact on functional daily activities as well which is of particular interest. Measuring trunk muscles strength is possible and the use of isokinetic dynamometers has been shown to be valid and reliable in healthy subjects [8, 9] and patients with scoliosis [10, 11, 12, 13]. These devices are frequently used in spinal retraining programs, and may also be used for monitoring and training the trunk muscles in patients with scoliosis.

The primary aim of this study was thus to measure, in WwS, the concentric strength of the trunk flexors and extensors using an isokinetic dynamometer, and to explore their relationship with the topography and angular variations of this disorder. The second aim was to compare the observed outcome parameters to those in apparently healthy women of a similar age range.

2. Methods

2.1 Participants

Participants had to be female, over 18 years and under 45 years of age with a main Cobb angle $>$ 10 ${}^{\circ}$ in order to be included in the scoliosis group. Their mean age and weight are outlined in Table 1 and following. Scoliosis had to be idiopathic, without surgical history, and patients could not be included if they were in pain, or if they had a cardiac condition contraindicating the use of the isokinetic device.

2.2 Study design

This is a prospective study conducted between 2008 and 2018 in our rehabilitation center. All patients who came for medical consultation (1 ${}^{\text{st}}$ consultation or follow-up consultation) were included if they met the inclusion criteria and gave consent for inclusion in the study. Data was collected in the course of routine medical examination, and the Institutional Ethics Committee gave its approval for the study.

At the same time, healthy subjects of equivalent age and gender were recruited on a voluntary basis from hospital staff to form the control group.

2.3 Evaluation procedure

Participants were given an overall 20-minute warm-up on a treadmill beforehand. The isokinetic evaluation was then carried out on the CON-TREX ${}^{\@setsize{\scriptsize}{8pt}{\viipt}{\@viipt}\textregistered}$ TP 1000 isokinetic dynamometer in the standing position with the subject’s pelvis, thighs and lower legs firmly strapped to the support device. The resistance arms were placed below the tip of the sternum and at the level of the tip of the scapula, and the center of rotation was placed at 3 cm below the iliac crest. As isokinetic dynamometers put subjects in very different conditions from natural movement, participants were provided with a time of familiarization with the isokinetic device to avoid initial weakness possibly linked to fear [14]. Four repetitions in maximal concentric effort were carried out, first at 30 ${}^{\circ}$ /s and then at 90 ${}^{\circ}$ /s in flexion and extension of the trunk, with a reciprocal protocol. The angular sector was set between 0 and 70 ${}^{\circ}$ of trunk flexion. Each subject was verbally encouraged to give her best and use the full range of motion available.

The results of the evaluation are given in terms of the peak moment (PM), without gravity correction, and all values are related to the body weight (in Nm/kg of body weight) [15].

2.4 Statistical analysis

The analysis was performed using the R software (version 3.4.2, R Foundation, Vienna) [16]. Characteristics of the participants are described through their age, weight, type of scoliosis according to Ponsetti classification [17], and Cobb angles. Comparisons of the 2 groups was made using Student’s $t$ tests in case of normality and Wilcoxon-Mann-Whitney tests, otherwise. For more than 2 groups, ANOVA were used in case of normality and Kruskal-Wallis test otherwise.

Within the WwS population, patients were compared according to the scoliosis types and the angulation (below or above 30 ${}^{\circ}$ ). The patients with low performances (under the first quartile of PM measures) have also been compared to the rest of the WwS population. The WwS and AH populations were compared, and for statistically significantly differences between WwS and AH, post hoc pairwise tests were performed, comparing the different types of scoliosis to the AH population. In this case, a Holm’s multiplicity correction was applied. The links between angulation and measurements have also been evaluated by Spearman nonparametric correlation coefficient. All comparisons were 2-sided, with a significance level of 0.05.

3. Results

3.1 Characteristics of participants

Of the 114 WwS, 43 patients presented with an angulation of less than 30 ${}^{\circ}$ (10–30 ${}^{\circ}$ ) while 71 hada Cobb angle of between 31 and 78 ${}^{\circ}$ . According to Ponsetti’s classification [17], there were 35 patients (31%) with thoracic scoliosis, 18 patients (16%) with a dorsolumbar curve, 38 patients (33%) with a double major scoliosis and 23 patients (20%) with a lumbar one.

The control group consisted of 42 women recruited from hospital staff. The two groups were similar in age but differed in weight: women with scoliosis weighted on average 1.4 kg more than AH women ( $p=$ 0.047) but this difference was not clinically significant and has no impact on results as isokinetic values are adjusted to weight.

3.2 Relationships between strength and scoliosis parameters

3.2.1 Impact of curve type

The isokinetic strength of the WwS group was studied as a function of the scoliosis topography according to Ponsetti’s classification, and no difference was found in the strength levels among the various sub-groups (Table 1).

3.2.2 Impact of angulation

The subgroup with an angulation of less 30 ${}^{\circ}$ was compared to the one with over 30 ${}^{\circ}$ and the results are presented in Table 2. No significant differences were found.

Table 2
Impact of scoliosis angulation on peak moment (PM) expressed in Nm/kgbw, for trunk flexors (FL), trunk extensors (E) at 30 ${}^{\circ}$ and 90 ${}^{\circ}$ /s. Results are presented by means (m) $\pm$ standard deviation

	Angle $\leqslant$ 30 $N=$ 43	Angle $>$ 30 ${}^{\circ}$ $N=$ 71	$p$ -value
Age	$m=$ 28.2 $\pm$ 5.6	$m=$ 30.7 $\pm$ 7.8	0.14
Weight	57.8 $\pm$ 8.1	56.7 $\pm$ 7.2	0.58
PM FL 30	1.89 $\pm$ 0.35	1.84 $\pm$ 0.33	0.43
PM FL 90	1.76 $\pm$ 0.36	1.73 $\pm$ 0.36	0.83
PM E 30	2.51 $\pm$ 0.60	2.37 $\pm$ 0.59	0.22
PM E 90	2.18 $\pm$ 0.62	2.05 $\pm$ 0.57	0.55
Ratio PM 30	1.35 $\pm$ 0.26	1.33 $\pm$ 0.29	0.73
Ratio PM 90	1.26 $\pm$ 0.28	1.21 $\pm$ 0.26	0.34

Spearman’s non-parametric correlations illustrated in Fig. 1 also show no correlation between the Cobb angle and the PM neither in terms of movement pattern nor in velocity.

Figure 1.

Link between scoliosis angle and isokinetic peak moment ( $=$ maximal force (MF)) expressed in Nm/percentage of body weight, in flexion (FL), extension (E), at 30 and 90 degrees/sec. None of the associated Spearman’s non-parametric correlations coefficients were statistically significantly differently than 0.

3.2.3 Characteristics of WwS with low strength values

Table 3 shows that for all parameters, patients with the lowest values had significantly higher weights. They were also significantly older, except for the 90 ${}^{\circ}$ extension PM measure.

Table 3
Characteristics of WwS who presented the lowest PM values (1st quartile of PM results), regarding age, weight and type of scoliosis according to Ponsetti’s classification

		Total WwS group	Low (1 ${}^{\text{st}}$ quartile)	Normal (2 ${}^{\text{nd}}$ and 3 ${}^{\text{rd}}$ quartiles)	$p$ -value
PM_FL_30	Age	29.9 $\pm$ 7.1	32.8 $\pm$ 7.6	28.8 $\pm$ 6.7	0.011 ${}^{*}$
	Weight	57.1 $\pm$ 7.6	59 $\pm$ 8	56.5 $\pm$ 7.4	0.046 ${}^{*}$
	DL scoliosis	40 (35.1%)	13 (44.8%)	27 (31.8%)	0.097
	DM scoliosis	38 (33.3%)	8 (27.6%)	30 (35.3%)
	L scoliosis	12 (10.5%)	0 (0%)	12 (14.1%)
	T scoliosis	24 (21.1%)	8 (27.6%)	16 (18.8%)
PM_FL_90	Age	29.9 $\pm$ 7.1	32.6 $\pm$ 8	28.9 $\pm$ 6.6	0.028 ${}^{*}$
	Weight	57.1 $\pm$ 7.6	59.9 $\pm$ 7.3	56.2 $\pm$ 7.5	0.0046 ${}^{**}$
	DL scoliosis	40 (35.1%)	10 (34.5%)	30 (35.3%)	0.29
	DM scoliosis	38 (33.3%)	9 (31%)	29 (34.1%)
	L scoliosis	12 (10.5%)	1 (3.4%)	11 (12.9%)
	T scoliosis	24 (21.1%)	9 (31%)	15 (17.6%)
PM_E_30	Age	29.9 $\pm$ 7.1	33.4 $\pm$ 8.5	28.6 $\pm$ 6.1	0.0083 ${}^{**}$
	Weight	57.1 $\pm$ 7.6	61.5 $\pm$ 9.4	55.7 $\pm$ 6.3	0.0017 ${}^{**}$
	DL scoliosis	40 (35.1%)	10 (34.5%)	30 (35.3%)	1
	DM scoliosis	38 (33.3%)	10 (34.5%)	28 (32.9%)
	L scoliosis	12 (10.5%)	3 (10.3%)	9 (10.6%)
	T scoliosis	24 (21.1%)	6 (20.7%)	18 (21.2%)
PM_E_90	Age	29.9 $\pm$ 7.1	31.2 $\pm$ 7.9	29.4 $\pm$ 6.8	0.45
	Weight	57.1 $\pm$ 7.6	60.9 $\pm$ 9.1	55.8 $\pm$ 6.5	0.0033 ${}^{**}$
	DL scoliosis	40 (35.1%)	13 (44.8%)	27 (31.8%)	0.42
	DM scoliosis	38 (33.3%)	8 (27.6%)	30 (35.3%)
	L scoliosis	12 (10.5%)	4 (13.8%)	8 (9.4%)
	T scoliosis	24 (21.1%)	4 (13.8%)	20 (23.5%)

T: thoracic, DL: dorsolumbar, DM: double major, L: lumbar.

The type of scoliosis does not seem to be related.

3.3 Patients with scoliosis vs healthy subjects

Table 4 presents the results and comparisons between the WwS sugroups and the AH group. The concentric PMs were significantly lower in the scoliosis group, for movement and speed. It was 12% and 13% lower for flexors at 30 and 90 ${}^{\circ}$ /s, respectively, and 13% lower for extensors at 30 and 90 ${}^{\circ}$ /s.

Table 4
Comparison of scoliotic and control participants for maximal force expressed by peak moment (PM) in Nm/kgbw, of trunk flexors (FL), trunk extensors (E) at 30 ${}^{\circ}$ and 90 ${}^{\circ}$ /s. Results are presented by means (m) $\pm$ standard deviation

	Total $N=$ 156		Scoliosis group $N=$ 114		Control group $N=$ 42		$p$ -value
Age	29.4	$\pm$ 6.8	29.7	$\pm$ 7.2	28.6	$\pm$ 5.6	1
Weight	57.1	$\pm$ 7.6	59.6	$\pm$ 7.2	57.1	$\pm$ 7.5	0.047 ${}^{*}$
PM FL 30	1.92	$\pm$ 0.35	1.85	$\pm$ 0.34	2.10	$\pm$ 0.31	0.001 ${}^{***}$
PM FL 90	1.81	$\pm$ 0.36	1.74	$\pm$ 0.36	1.99	$\pm$ 0.28	0.001 ${}^{***}$
PM E 30	2.52	$\pm$ 0.60	2.42	$\pm$ 0.60	2.77	$\pm$ 0.52	0.01 ${}^{**}$
PM E 90	2.19	$\pm$ 0.58	2.10	$\pm$ 0.59	2.44	$\pm$ 0.50	0.01 ${}^{**}$
Ratio PM 30	1.33	$\pm$ 0.26	1.34	$\pm$ 0.28	1.33	$\pm$ 0.23	0.86
Ratio PM 90	1.23	$\pm$ 0.25	1.23	$\pm$ 0.27	0.23	$\pm$ 0.21	0.91

The PM-based extension/flexion ratios in WwS were respectively 1.34 $\pm$ 0.28 and 1.23 $\pm$ 0.27 at 30 ${}^{\circ}$ /s and 90 ${}^{\circ}$ /s, with no significant difference between subgroups, nor with control values.

With respect to the differences between sub-groups of WwS according to Ponsetti’s classification, the results show also significant differences for the PM of the flexors at 30 ${}^{\circ}$ and 90 ${}^{\circ}$ /s in dorsolumbar and double major scoliosis, and for the PM of the extensors in lumbar scoliosis at the higher speed (Table 5).

Table 5

Comparison of scoliotic Ponsetti’s sub-groups and control participants for maximal force expressed by peak moment (PM) of trunk flexors (FL), trunk extensors (E) at 30 ${}^{\circ}$ and 90 ${}^{\circ}$ /s

	Control vs dorso-lumbar	Control vs double major	Control vs thoracic	Control vs lumbar
PM FL 30	0.0028 ${}^{**}$	0.034 ${}^{*}$	0.071	0.092
PM FL 90	0.0018 ${}^{**}$	0.017 ${}^{*}$	0.092	0.092
PM E 30	0.092	0.09	0.092	0.02 ${}^{*}$
PM E 90	0.057	0.092	0.092	0.071

$P$ -values are presented with the significance threshold: ${}^{*}<$ 5%, ${}^{**}<$ 1%, ${}^{***}<$ 0.1%.

Regarding the different sub-groups of patients according to the angulation ( $<$ or $>$ 30 ${}^{\circ}$ ), there were significant differences between WwS and control participants as shown by Table 6. In the group $>$ 30 ${}^{\circ}$ , there was a significant difference for all values tested, whereas only the flexion at 90 ${}^{\circ}$ /s was significantly different in the subgroup with Cobb angle $<$ 30 ${}^{\circ}$ .

Table 6

Comparison of scoliotic angulation sub-groups (Cobb angle $\leqslant$ 30 ${}^{\circ}$ or Cobb angle $>$ 30 ${}^{\circ}$ ) and control participants for peak moment (PM) of trunk flexors (FL), trunk extensors (E) at 30 ${}^{\circ}$ and 90 ${}^{\circ}$ /s

	Control vs angle $\leqslant$ 30 ${}^{\circ}$	Control vs angle $>$ 30 ${}^{\circ}$
PM FL 30	0.057	0.0018 ${}^{**}$
PM FL 90	0.027 ${}^{*}$	0.004 ${}^{**}$
PM E 30	0.092	0.011 ${}^{*}$
PM E 90	0.092	0.01 ${}^{*}$

$P$ -values are presented with the significance threshold: ${}^{*}<$ 5%, ${}^{**}<$ 1%, ${}^{***}<$ 0.1%.

4. Discussion

The results for AH women are completely in line with previous studies [18, 19, 20] although the tests were performed using a different isokinetic dynamometer, a fact that significantly enhance the validity of isokinetic trunk testing. Regarding WwS, the results show a significant 12–15% reduction compared to AH women in all parameters and irrespective of movement pattern or speed. These results support those previously reported [21]. Studies have also been published in adolescents, and show that there was a deficit of isokinetic strength in young people with low back pain [22] and in young people with scoliosis [15, 23] and in patients with low back pain, although in the latter the deficit was mainly in extension [24, 25]. Yuan et al. explored posterior muscle strength in a group of young women with non-specific low back pain, with and without lumbar scoliosis, and found that the muscular deficit was specifically in the posterior muscles in non-scoliotic patients, whereas it did not specifically affect the posterior muscles in patients with scoliotic [26]. This finding is in line with our results attesting to general sagittal muscular weakness.

The smaller groups notwithstanding, it is interesting to consider the results for the different locations of curvature. It appears that compared to the AH group, thoracolumbar scoliosis and double major ones led to weaker flexion tested at 30 and 90 ${}^{\circ}$ /s, whereas lumbar scoliosis led to weaker extension at 30 ${}^{\circ}$ . However, in all cases there was a trend for weakness in all subgroups compared to the controls. Thus, regardless of topography, the scoliosis group has a lower isokinetic sagittal strength of the trunk than the control group.

With regard to angulation, it was not possible to find a relationship between the angle of scoliosis and isokinetic parameters; this is somewhat surprising because it could be expected that a strong angulation of scoliosis could hinder the production of muscle moment in performing these movements. There appears to be a trend for the extensors’ strength at 30 and 90 ${}^{\circ}$ /s, where small angulations have high values and large angulations have low values, but a larger population would be necessary to better analyze this trend.

A second approach was made by separating the population with scoliosis between the milder (Cobb $<$ 30 ${}^{\circ}$ ) and more severe scoliosis (Cobb $>$ 30 ${}^{\circ}$ ) to obtain two groups of 43 and 71 women respectively. There was no significant difference on any of the values between the two populations; but if one compares each population to the control population, it appears that the scoliosis $>$ 30 ${}^{\circ}$ group had lower values for all the values tested, and the scoliosis $<$ 30 ${}^{\circ}$ group showed a significant deficit compared to the controls only for 90 ${}^{\circ}$ /s flexion. Therefore, it seems as if scoliosis with high angulation does induce a lower maximum muscular force.

The WwS who presented the lowest trunk muscles strength were slightly older and weighted with a higher body mass compared to those who obtained higher values. This finding complies with the work of Danneskiold-Samsøe et al. [20], who found that muscle strength in women is dependent on weight and is only related to age from around 40 years of age.

One limitation of this works clearly lies in the lack of data regarding the level of physical activity of both scoliotic and healthy participants. It is indeed difficult to conclude if the trunk muscles weakness in the scoliotic group is due to a poor physical activity level, or only due to the presence of scoliosis. Further studies should take this aspect into account [27].

5. Conclusion

This study is the first to unveil a general flexion and extension weakness in WwS. The severity of scoliosis appears to be related to the variation in muscle strength. On the other hand, the location of the scoliosis does not seem to cause a very significant variation in strength parameters. It appears from this work that the evaluation of the strength of the trunk is important, as this parameter can vary from one type of scoliosis to another, especially as a function of its angulation. This work highlights the importance of muscular evaluation of patients with scoliosis, along the radiological assessment, in order to better analyze this disorder and to propose adapted therapeutic solutions, especially targeting the inherent muscular weakness [28, 29, 30].

Author contributions

For every author, his or her contribution to the manuscript needs to be provided using the following categories:

CONCEPTION: Grégoire Le Blay.

PERFORMANCE OF WORK: Anne Pujol.

INTERPRETATION OR ANALYSIS OF DATA: Stéphane Verdun.

PREPARATION OF THE MANUSCRIPT: Rachel Bard-Pondarré.

REVISION FOR IMPORTANT INTELLECTUAL CONTENT: Jean-Claude Bernard.

SUPERVISION: Emmanuelle Chaléat-Valayer.

Ethical considerations

This study was exempt from Institutional Review Board approval.

Funding

None.

Footnotes

Acknowledgments

The authors wish to warmly thank the Association de Recherche Médicale du Centre des Massues, for its support and help in designing the manuscript.

Conflict of interest

The authors have no conflicts of interest to disclose.

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Isokinetic evaluation of the trunk flexors and extensors in women with and without scoliosis: A comparative study

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

Table 1 Impact of curve type on maximal force expressed by the peak moment (PM) in Nm/kgbw, for trunk flexors (FL), trunk extensors (E) at 30 ∘ and 90 ∘ /s. Results are presented by means (m) ± standard deviation

2.1 Participants

2.2 Study design

2.3 Evaluation procedure

2.4 Statistical analysis

3. Results

3.1 Characteristics of participants

3.2 Relationships between strength and scoliosis parameters

3.2.1 Impact of curve type

3.2.2 Impact of angulation

Table 2 Impact of scoliosis angulation on peak moment (PM) expressed in Nm/kgbw, for trunk flexors (FL), trunk extensors (E) at 30 ∘ and 90 ∘ /s. Results are presented by means (m) ± standard deviation

Table 3 Characteristics of WwS who presented the lowest PM values (1st quartile of PM results), regarding age, weight and type of scoliosis according to Ponsetti’s classification

Table 4 Comparison of scoliotic and control participants for maximal force expressed by peak moment (PM) in Nm/kgbw, of trunk flexors (FL), trunk extensors (E) at 30 ∘ and 90 ∘ /s. Results are presented by means (m) ± standard deviation

5. Conclusion

Author contributions

Ethical considerations

Funding

Footnotes

Acknowledgments

Conflict of interest

References

Table 1
Impact of curve type on maximal force expressed by the peak moment (PM) in Nm/kgbw, for trunk flexors (FL), trunk extensors (E) at 30 ${}^{\circ}$ and 90 ${}^{\circ}$ /s. Results are presented by means (m) $\pm$ standard deviation

Table 2
Impact of scoliosis angulation on peak moment (PM) expressed in Nm/kgbw, for trunk flexors (FL), trunk extensors (E) at 30 ${}^{\circ}$ and 90 ${}^{\circ}$ /s. Results are presented by means (m) $\pm$ standard deviation

Table 3
Characteristics of WwS who presented the lowest PM values (1st quartile of PM results), regarding age, weight and type of scoliosis according to Ponsetti’s classification

Table 4
Comparison of scoliotic and control participants for maximal force expressed by peak moment (PM) in Nm/kgbw, of trunk flexors (FL), trunk extensors (E) at 30 ${}^{\circ}$ and 90 ${}^{\circ}$ /s. Results are presented by means (m) $\pm$ standard deviation