Trunk muscle endurance in Chinese adults

Abstract

BACKGROUND:

Previous studies in non-Chinese populations have found a relationship between performance on isometric trunk muscle endurance tests and low back pain (LBP). However, the relationship between trunk muscle endurance and LBP in Chinese populations has received little attention and age-referenced data have not been reported.

OBJECTIVE:

Evaluate the relationship between age-referenced isometric trunk muscle endurance values and LBP in a Chinese cohort.

METHODS

: One hundred and eighty-eight participants (20–59-years) performed four timed-endurance tests (Biering-Sørensen, plank, left/right side bridge) in random order. Participants with a history of LBP completed an Oswestry Disability Index (ODI) and pain scale. Holding-times for the four tests were summed and receiver operating characteristic (ROC) curve analysis was performed to differentiate participants with and without LBP.

RESULTS:

Data were grouped by age. Analysis revealed similar endurance values to those reported in non-Chinese populations, except longer holding times were recorded in the 50–59 yr Chinese cohort. Pain scores were positively correlated with ODI scores. ROC curve analysis showed that the area under the curve was 0.723 and optimal cut-off was 288 sec (sensitivity and specificity both 0.75).

CONCLUSIONS:

This study is the first to describe trunk muscle endurance reference data in Chinese people. Individuals with a summed endurance time of $<$ 288 seconds appear more likely to suffer LBP.

Keywords

Chinese endurance isometric Biering-Sørensen plank test side bridge test

1. Introduction

Low back pain (LBP) is a problem that affects most populations with a life-time prevalence reported to be as high as 80% [1]. Low back pain and injury accounts for more time lost from work than any other musculoskeletal injury and imposes a heavy cost to the health care system [2]. In the United States, LBP in workers 40 to 65 years of age costs employers an estimated $7.4 billion/year with exacerbations accounting for 71.6% of these costs [3]. While data on health care costs associated with LBP are not available in China, in a recent ‘Global Burden of Disease’ Study, LBP was ranked second in terms of years lived with disability in China in 2016 [4]. The point prevalence of LBP in China was reported to be 34.1% (95% CI: 27.9–40.3%) with the 12-month prevalence being 41.9% (95% CI: 35.5–48.3%) [5].

Performance on tests of isometric trunk muscle endurance has been shown to predict future episodes of LBP in non-Chinese populations [6]. Additionally, the clinical guidelines produced by the American Physical Therapy Association in 2012 state that there is strong evidence that sufficient trunk endurance can reduce LBP and disability in patients with subacute and chronic LBP, particularly for those with movement coordination impairments [7]. Exercises aimed at improving a person’s trunk muscle endurance, rather than trunk muscle strength, are more effective at improving a person’s tolerance to daily activities [8, 9]. Achieving optimal trunk muscle activation to maintain a neutral spinal posture under load, and often for long periods of time, is an important component of a rehabilitation program [10, 11].

Trunk muscle endurance can be assessed using sophisticated instruments such as electromyography, magnetic resonance imaging scanning and isokinetic dynamometry [12, 13]. However, these methods are not readily available for many practitioners working with patients in clinical settings. Instead, methods for assessing trunk muscle endurance commonly employed by clinicians are “timed endurance tests” such as the Biering-Sørensen test, plank test and side bridge tests all of which have been shown to have good reliability [14, 15, 16]. The Biering-Sørensen test challenges the trunk extensors, while the plank test provides stimulus for endurance training of the rectus abdominis and external oblique abdominis [17]. Major muscles challenged during side bridge tests are quadratus lumborum, external oblique, internal oblique, rectus abdominis, gluteus medius muscle, longissimus thoracis, and lumbar multifidus [17, 18, 19]. People with LBP have a lower fatigue threshold compared to those without LBP [16, 20, 21]. These tests are simple to perform and require little time and equipment. Although there are a number of studies reporting holding times for different populations [15, 22, 23, 24], nearly all of the previous studies have obtained data from relatively young populations and from western countries. Only one study has reported holding times on the side bridge test for a small cohort ( $n=$ 28) of sedentary female Chinese participants but there was no information on the plank test or the Biering-Sørensen test [25], and the effect of age on isometric trunk endurance in this Chinese cohort was not reported. In addition to a person’s age, there are a number of factors that can influence holding times during isometric trunk muscle endurance tests. The amount of body fat, different lifestyles and exercise habits may affect performance on the tests and influence the risk of LBP [26, 27, 28, 29, 30, 31]. It was reported that Chinese people living in China spend more time in vigorous activity, sleeping and walking but less hours in sitting compared to Chinese people residing in North America [32]; while most Chinese people in China spend over 1 hour performing exercise activities per day [32], 75% of the population in Curaçao do not exercise regularly [33]. As exercise habits could affect performance on isometric endurance tests it is important to establish an age-referenced isometric trunk muscle endurance values and LBP, with consideration of exercise habits, in a Chinese cohort.

Reference values of these “core” endurance tests may provide information not only on one’s core stability and function, but on possible risk of LBP [6, 24]. The current study aimed to determine the reference values for the Biering-Sørensen, plank test, right and left side bridge test scores in different age groups of Chinese people living in China. The second aim of the study was to compare the endurance test scores between those participants with and without LBP. Lastly, the relationship between these scores and functional ability as determined by the Oswestry Disability Index (ODI) in participants with LBP was also explored.

2. Materials and methods

2.1 Participants

Participants were recruited through volunteer posters placed on hospital and university notice boards. Participants were invited to contact the investigator (FL) for further information and to visit the Department of Rehabilitation to determine eligibility and for testing. Ethical approval for this study was obtained from the Institutional Review Committee of the (involved) University.

2.2 Inclusion criteria and exclusion criteria

Male and female participants aged between 20 to 59 years old with no history of spinal, upper or lower limb fractures, major trauma, tumor, acute infection, cauda equina syndrome, current pregnancy, neurological or cardiovascular diseases, or any disability that may limit the ability to perform the trunk muscle endurance tests were eligible to participate in the study. Participants with LBP for more than three months were also recruited for comparison with age and body mass index (BMI) matched normal participants.

Figure 1.

Trunk muscle endurance tests. a) Biering-Sørensen test; b) plank test; c) right side bridge test

2.3 Procedures and methods

A total of 188 participants aged between 20 and 59 years (mean $\pm$ SD: 35.9 $\pm$ 13.3 years) consented to participate in the study over a 9-month period. Among these 188 volunteers, only 16 participants reported experiencing LBP for more than 3 months at the time of testing. Demographic data, including gender, age, weight, height, regular exercise (regular/no), occupation (sedentary or labor), years of work (for those working), and LBP history (current or previous) were recorded prior to testing. Participants with current LBP more than three months were asked to complete the ODI and the visual analog scale (VAS) of pain intensity. The ODI [34] consists of 10 sections and explores pain intensity as well as how activities are influenced by LBP. The total score is out of 50 points and is expressed as an overall percentage. The higher the percentage, the higher self-reported level of disability. The validity and reliability of the Chinese version of the ODI (version 2.1) were established with good internal consistency with Cronbach’s alpha as 0.903 and good test-retest reliability with intraclass correlation coefficient (ICC) as 0.89 [35]. VAS of pain intensity is an ungraduated 10-cm straight line, with words “no pain” anchored to one end and “worst possible pain” at the other end. The respondent is asked to place a line perpendicular to the VAS line at the point that represents their pain intensity [36].

Participants were then asked to perform the Biering-Sørensen test, plank test, left and right side bridge tests, in a random order (by drawing lots), with a rest period of 20 minutes between each test. All tests were conducted by the same investigator (FL). For each test, participants were encouraged to ‘hold’ (isometric contraction of trunk muscles) in specific positions as illustrated in Fig. 1a–c for as long as they could until fatigue. Verbal feedback was given if there was deviation from the test position. The test was terminated if the participant was unable to maintain the accepted position after twice verbal feedback, or if they complained of fatigue, pain or discomfort. Participants were not informed of the duration of time during the test [23].

2.3.1 Biering-Sørensen test

The Biering-Sørensen test [37] was used to test the endurance of the trunk extensor muscles (Fig. 1a). This test has been extensively studied and has been shown to have good reliability (ICC ${}_{1,1}=$ 0.83, 95% CI: 0.62–0.93) [16]. The upper body is “levered” over the end of a bed, with the pelvis, knees and hips securely attached to the bed by three straps. Participants were instructed to place their arms crossed over their chest and maintain the horizontal position as long as possible and the holding time was manually recorded (in seconds) with a stopwatch from the point at which the participant assumed the horizontal position.

2.3.2 Plank test

The plank test [38] has been shown to have excellent reliability (ICC ${}_{1,1}=$ 0.98, 95% CI: 0.98–0.99) [14]. Figure 1b illustrates the position for the plank test. Participants were asked to assume a prone position with their elbows and forearms under their chest, and then propped into a plank position using their toes and forearms for support, keeping their neck straight throughout the duration of the test. Participants were instructed to hold the plank position for as long as possible. When a flat back or proper neck alignment could not be maintained, despite verbal cueing from the investigator, the test was terminated.

2.3.3 Side bridge test

The side bridge test is used to assess the endurance of the lateral trunk muscles. It has excellent intra-rater reliability (ICC $\geqslant$ 0.97) [15]. Figure 1c illustrates the position adopted by a participant during the right side-bridge test on an exercise mat of 2.5 cm thickness. Participants were asked to support themselves on the right elbow with hips off the mat, legs extended and to maintain a straight line over their full body length. The top foot is placed in front of the lower foot on the mat for support. The left (uninvolved) arm was held across the chest with the hand placed on the opposite shoulder. The test ended when the hips return to the exercise mat.

2.4 Data analysis

All data were analyzed using IBM SPSS version 22 and MedCalc 13.0, with MedCalc 13.0 employed for ROC curve analyses. Measurements were repeated in 17 participants to establish the test-retest reliability using one-way random-effects model to calculate the intraclass correlation coefficients (ICC ${}_{1,1}$ ) [39]. The standard error of measurement (SEM) was calculated by taking the square root of the mean square error of the repeated measurements [31]. In order to construct gender and age reference value tables for each endurance test, participants were divided into four age groups on a 10-year interval basis: 20–29, 30–39, 40–49, 50–59 years, respectively. Mean age, height, weight, BMI, exercise habit, occupation, work duration (years) were summarized using descriptive statistics. Biering-Sørensen test scores (position holding time), plank test scores, side bridge test scores in each age group were summarized using the descriptive statistics of mean, standard deviation and percentile. Among these 188 volunteers, only 16 participants reported experiencing LBP at the time of testing. Therefore 16 healthy participants were age and BMI matched with the 16 participants with LBP to compare endurance scores. Paired sample t-tests were used to compare the differences of each of the endurance scores between healthy participants and matched participants with LBP. Correlation analysis was conducted using Spearman’s rho to determine the relationship between VAS, Biering-Sørensen test scores, plank test scores, side bridge test scores and the ODI in participants with LBP. Receiver operating characteristics (ROC) curve analysis [29] was performed to determine the optimal cut-off score of the summed holding times of the four endurance tests (total score) to differentiate participants with and without LBP. The ROC curve was constructed by plotting the sensitivity (true positive rate) and 1-specificity (false-positive rate) for each cut-off score of the summed total score of the four endurance tests. The area under the ROC curve (AUC) shows the ability of using the summed total score to differentiate participants who had LBP or not.

3. Results

The ICC ${}_{1,1}$ (95% confidence interval), SEM for the Biering-Sørensen test, plank test, left side bridge test and right side bridge test were 0.816 (0.572–0.929), 22 seconds; 0.907 (0.767–0.965), 15 seconds; 0.715 (0.380–0.885), 20 seconds; 0.636 (0.249–0.850), 15 seconds respectively; suggesting fair to good reliability of measurements.

Table 1
General characteristics of participants in different age groups (data in mean $\pm$ SD, unless otherwise stated)

Age (years)	20–59	20–29	30–39	40–49	50–59	LBP
Number	172	67	34	36	35	16
Age (yr)	35.9 $\pm$ 13.3	21.6 $\pm$ 1.9	35.1 $\pm$ 3.1	45.1 $\pm$ 3.0	54.7 $\pm$ 2.6	38.9 $\pm$ 8.7
Height (cm)	163.3 $\pm$ 7.1	163.3 $\pm$ 8.2	163.6 $\pm$ 6.3	162.6 $\pm$ 7.2	163.7 $\pm$ 5.5	164.1 $\pm$ 10.8
Weight (kg)	59.6 $\pm$ 9.7	56.4 $\pm$ 10.9	63.8 $\pm$ 9.0	59.8 $\pm$ 9.2	61.3 $\pm$ 6.4	61.0 $\pm$ 15.5
BMI (kg/m ${}^{2}$ )	22.3 $\pm$ 2.8	21.1 $\pm$ 2.9	23.8 $\pm$ 2.4	22.7 $\pm$ 2.3	23.0 $\pm$ 2.5	23.5 $\pm$ 2.7
Occupation
Sedentary (%)	55%	94%	29%	22%	20%	50%
Labor (%)	31%	6%	53%	58%	31%	31%
Others(%)	14%	0%	18%	20%	49%	19%
Exercise habit
Regular (%)	35%	58%	3%	3%	54%	13%
No (%)	65%	42%	97%	97%	46%	88%
Work duration/years	–	–	10.09 $\pm$ 4.50	15.81 $\pm$ 8.87	29.69 $\pm$ 5.61	13.69 $\pm$ 9.07

The mean age, height, weight, BMI, exercise habit, occupation, work duration (years) of healthy and LBP groups are summarized in Table 1. Interestingly, 54% of participants in the 50–59 year group, compared to only 3% in the 30–39 and 40–49 year groups, engaged in regular exercise. The BMI of the 50–59 year group was similar to the younger groups (Table 1). Descriptive statistics of mean, standard deviation and percentile of Biering-Sørensen test scores, plank test scores, side bridge test scores in each age category of the healthy group and in the LBP group are displayed in Table 3 to Table 6. Graphic presentation of the scores in each different age group is illustrated in Fig. 2.

Table 2

Holding times for each test in participants with LBP. Category of disability defined by ODI score. Data in mean $\pm$ SD

Disability	n	ODI score	Biering-Sørensen	Plank	Left side bridge	Right side bridge
		%	test score	test score	test score	test score
Minimal	8	13 $\pm$ 4	109 $\pm$ 44	81 $\pm$ 29	70 $\pm$ 33	65 $\pm$ 31
Moderate	5	33 $\pm$ 5	84 $\pm$ 23	78 $\pm$ 40	43 $\pm$ 10	45 $\pm$ 6
Severe	3	52 $\pm$ 5	62 $\pm$ 18	48 $\pm$ 27	25 $\pm$ 10	32 $\pm$ 10

Figure 2.

Scores (position-holding times in seconds) recorded from the four tests in the four different age groups.

Paired sample t-test analysis showed that there were no statistical differences in the endurance test scores between the 16 participants with LBP and the 16 age, gender and BMI matched healthy participants. However, the mean values of tests of the LBP participants were less than the 25th percentile values of tests of healthy participants, except for values for the plank test. Amongst the 16 participants with LBP, the ODI scores indicated that eight participants had minimal disability, five participants had moderate disability, and three had severe disability. Only the VAS score had a strong correlation with the ODI score; the correlation coefficients between the ODI with the VAS, Biering-Sorenson test, plank test, left side bridge test and right side bridge test were 0.845, $-$ 0.391, $-$ 0.116, $-$ 0.558, and $-$ 0.532 respectively. The holding times for each test was significantly lower in participants with increasing ODI scores (Table 2).

Table 3

Biering-Sørensen test score (mean $\pm$ SD and percentile) of all the participants by age and gender

Age	Gender	n	Mean	Minimum	25th	50th	75th	Maximum
group	M $=$ male		$\pm$ SD	(sec)	percentile	percentile	percentile	(sec)
(years)	F $=$ female		(sec)		(sec)	(sec)	(sec)
LBP	M $+$ F	16	92 $\pm$ 38	43	66	84	109	194
20–59	M	84	132 $\pm$ 43	60	98	118	166	240
	F	88	129 $\pm$ 48	47	93	119	154	296
	M $+$ F	172	130 $\pm$ 45	47	94	118	159	296
20–29	M	26	142 $\pm$ 54	60	86	147	191	240
	F	41	154 $\pm$ 52	80	118	144	180	296
	M $+$ F	67	150 $\pm$ 53	60	113	145	183	296
30–39	M	18	124 $\pm$ 40	60	88	131	148	212
	F	16	108 $\pm$ 34	47	84	103	134	178
	M $+$ F	34	117 $\pm$ 38	47	88	117	147	212
40–49	M	21	121 $\pm$ 31	86	96	113	160	176
	F	15	100 $\pm$ 31	68	72	90	125	158
	M $+$ F	36	113 $\pm$ 32	68	89	108	133	176
50–59	M	19	136 $\pm$ 36	94	105	115	173	197
	F	16	111 $\pm$ 31	75	93	104	119	196
	M $+$ F	35	125 $\pm$ 36	75	100	110	159	197

The result of the ROC curve analysis is shown in Fig. 3. The AUC was 0.723 (95% CI: 0.573–0.865). The optimal cut-off score of the summed score of the four tests to differentiate between participants with and without LBP was $\leqslant$ 288 seconds, with a sensitivity of 0.75 and a specificity of 0.75.

Table 4

Plank test score (mean $\pm$ SD and percentile) of all the participants by age and gender

Age	Gender	n	Mean	Minimum	25th	50th	75th	Maximum
group	M $=$ male		$\pm$ SD	(sec)	percentile	percentile	percentile	(sec)
(years)	F $=$ female		(sec)		(sec)	(sec)	(sec)
LBP	M $+$ F	16	74 $\pm$ 33	18	51	76	96	134
20-59	M	84	117 $\pm$ 51	46	77	107	140	358
	F	88	76 $\pm$ 41	22	48	67	91	289
	M $+$ F	172	96 $\pm$ 50	22	58	84	121	358
20–29	M	26	129 $\pm$ 70	46	75	116	139	358
	F	41	99 $\pm$ 47	23	71	90	118	289
	M $+$ F	67	111 $\pm$ 59	23	73	107	131	358
30–39	M	18	110 $\pm$ 35	62	94	104	132	208
	F	16	55 $\pm$ 15	33	44	51	69	82
	M $+$ F	34	84 $\pm$ 39	33	53	74	106	208
40–49	M	21	106 $\pm$ 32	57	82	107	122	162
	F	15	59 $\pm$ 16	39	48	56	62	107
	M $+$ F	36	86 $\pm$ 35	39	57	76	112	162
50–59	M	19	121 $\pm$ 50	60	75	138	148	219
	F	16	56 $\pm$ 21	22	43	54	71	110
	M $+$ F	35	91 $\pm$ 51	22	54	75	140	219

Table 5

Left side bridge test score (mean (SD) and percentile) all the participants by age and gender

Age	Gender	n	Mean	Minimum	25th	50th	75th	Maximum
group	M $=$ male		$\pm$ SD	(sec)	percentile	percentile	percentile	(sec)
(years)	F $=$ female		(sec)		(sec)	(sec)	(sec)
LBP	M $+$ F	16	50 $\pm$ 30	18	33	48	67	136
20–59	M	84	86 $\pm$ 29	26	65	80	103	157
	F	88	64 $\pm$ 27	21	46	60	79	186
	M $+$ F	172	75 $\pm$ 30	21	54	70	90	186
20–29	M	26	91 $\pm$ 35	26	64	87	121	156
	F	88	64 $\pm$ 27	21	46	60	79	186
	M $+$ F	67	78 $\pm$ 33	22	56	77	94	186
30–39	M	18	87 $\pm$ 23	43	71	86	98	143
	F	16	72 $\pm$ 24	40	53	66	93	120
	M $+$ F	34	80 $\pm$ 24	40	63	78	96	143
40–49	M	21	82 $\pm$ 31	45	62	72	104	157
	F	15	59 $\pm$ 17	35	52	56	68	94
	M $+$ F	36	73 $\pm$ 28	35	54	66	82	157
50–59	M	19	82 $\pm$ 25	47	65	75	100	151
	F	16	42 $\pm$ 15	21	30	39	56	77
	M $+$ F	35	64 $\pm$ 29	21	40	62	80	151

Figure 3.

The ROC curve of the summated total endurance time score of the 4 tests in differentiation of participants with and without LBP.

Figure 4.

A comparison of the Biering-Sørensen test score between data from the current study and the Nigerian study (Mbada et al., 2009).

4. Discussion

This study is the first to provide reference values of Biering-Sørensen test, plank test, left side bridge test and right side bridge test scores in a cohort of Chinese people aged between 20 and 59 years old. The comparison of the Biering-Sørenson data in four similar age groups between Chinese and Nigerian participants is shown in Fig. 4. The Nigerian study was chosen for comparison as this is the only study that has reported the holding times for each test and in participants from different age categories. The data suggest that the Biering-Sørensen scores recorded from our Chinese cohort were similar to a Nigerian cohort [22], except for the 50–59 year group, where the present Chinese cohort achieved much longer holding times on this test. Even within the present Chinese cohort, both the Biering-Sørensen and plank test scores recorded in the 50–59 year old group were higher than the scores from the 30–39 and 40–49 year groups. This is an interesting finding, as it was anticipated that trunk muscle endurance would decline with age. However, the phenomenon of ‘increased endurance time’ in Biering-Sørensen and plank test scores in the 50–59 year old group was not observed in the left and right side bridge times with the side bridge test scores in the older group remaining similar to those scores in the 40–49 year group. It is interesting to note that the majority of participants in the 50–59 year group (54%) engaged in regular exercise (Table 1) compared to only 3% in the 30–39 and 40–49 year groups. Further analysis of their exercise habits revealed that about one third were engaged in “square dancing” for a minimum of 3 years; another one-third were farmers engaged in labor work for more than 25 years and the remaining one third were engaged in Tai Chi exercises. Only a few, mainly women, were engaged in sedentary activities such as cooking and television watching. Tai Chi can improve physical fitness in terms of static and dynamic balance [30]. Other studies have suggested that individuals who maintain a regular exercise pattern can reduce the risk of LBP and improve their health and ability to perform daily activities [40, 41, 42]. It is therefore likely that the higher trunk muscle endurance times observed in our 50–59 year cohort resulted from their active participation in exercise or physical activities. It is also possible that the lower scores in the middle age group reflect a lack of opportunity to engage in exercise due to their heavy work commitment. In a study on Singaporean Chinese, it was found that most middle aged Chinese adults worked five days a week for about 9.5 $\pm$ 0.5 hours/day and spent the majority of their days in sedentary activities both on work days (76.9%) and non-work days (69.5%). In that study, the self-reported median sitting time at work was 420 $\pm$ 180 minutes. The authors suggested that workplace norms of sitting and environmental factors could be important barriers to exercise [43]. The lack of exercise may be an important risk factor for a reduction of trunk muscle endurance.

Table 6
Right side bridge test score (mean (SD) and percentile) of all the participants by age and gender

Age	Gender	n	Mean	Minimum	25th	50th	75th	Maximum
group	M $=$ male		$\pm$ SD	(sec)	percentile	percentile	percentile	(sec)
(years)	F $=$ female		(sec)		(sec)	(sec)	(sec)
LBP	M $+$ F	16	52 $\pm$ 26	20	37	46	57	120
20–59	M	84	88 $\pm$ 31	33	64	87	104	189
	F	88	65 $\pm$ 25	20	49	65	78	205
	M $+$ F	172	77 $\pm$ 30	20	56	72	94	205
20–29	M	26	95 $\pm$ 38	37	64	94	119	189
	F	41	74 $\pm$ 28	25	60	71	88	205
	M $+$ F	67	82 $\pm$ 34	25	62	72	97	205
30–39	M	18	87 $\pm$ 22	49	65	95	106	123
	F	16	70 $\pm$ 18	44	50	73	84	100
	M $+$ F	34	79 $\pm$ 22	44	62	80	97	123
40–49	M	21	83 $\pm$ 28	33	63	72	103	137
	F	15	61 $\pm$ 14	42	46	58	72	90
	M $+$ F	36	74 $\pm$ 26	33	56	68	89	137
50–59	M	19	85 $\pm$ 29	42	73	79	101	170
	F	16	43 $\pm$ 16	20	30	41	58	78
	M $+$ F	35	66 $\pm$ 32	20	42	59	86	170

Many studies reported that BMI, obesity, percent body fat, lean body mass and height could account for factors that affect trunk muscle endurance and influence the risk of LBP [26, 27, 28, 44, 45]; therefore, another possible reason to explain why the trunk muscle endurance time in our 50–59 year group remained good is perhaps a well-controlled body weight. Our data showed that the weight of this participant group was 61.3 $\pm$ 6.4 kg, which was less than the Nigerian participants reported in Mbada et al.’s study [22] (66 $\pm$ 13.3 kg). Moreover, the BMI of our participant group was 22 to 23 kg/m ${}^{2}$ , similar to the younger groups.

Surprisingly, our data showed no significant difference in the trunk endurance time between participants with and without LBP. This may have been due to the small number of participants with LBP. Although we were not able to demonstrate a statistical significant difference in trunk endurance scores between participants with or without LBP, the between-group difference in holding time for the Biering-Sørensen test was similar between our participants (32 s) compared to that reported by Tekin et al. (29 s) [46]; and the correlation between ODI and Biering-Sørensen holding time reported in Tekin’s study (0.85) was similar to our recorded data (0.845) [46]. Nonetheless, our data suggest a trend that participants in the LBP group had much lower scores than the healthy participants, and apart from the plank test data, all test scores were less than the 25th percentile values of the healthy participants. As suggested in Mbada et al’s study (2009), endurance with position-holding time below the 25th percentile was classified as “poor” lumbar stabilization endurance, endurance time ranged between the 25th and 75th percentile was considered medium, and those with position-holding time in the 75th percentile was classified as good lumbar endurance. Based on Mbada et al’s data and classification, the trunk muscle endurance in our Chinese cohort with LBP was poorer than those without LBP.

The ROC analysis was initially conducted for each of the endurance test scores. The AUC computed for the Biering-Sørensen test, plank test, left side bridge test and right side bridge test were 0.660, 0.504, 0.730, and 0.756 respectively. These results suggest that the plank test alone may not be an appropriate test to differentiate between LBP and healthy people. In the plank test, endurance time is mainly determined by the rectus abdominis, which may be the muscle least affected by back pain. Therefore, it is not useful to use the plank test to differentiate between those with and without LBP in our Chinese cohort. Anatomically, the stability of the torso is not maintained by a single group of muscles [47]; rather, the “core” is a “muscle box” with the abdominals in the front, paraspinals and gluteals in the back, the diaphragm as the roof, and the pelvic floor and hip girdle musculature as the bottom [48]. In view of this, it may be more accurate and meaningful to include information from different endurance tests to reflect overall trunk muscle endurance. Therefore, the ROC curve analysis was revised using the summed scores of all the four endurance tests. The results of our analysis showed that a total score of less than 288 seconds may be used to differentiate a participant with or without LBP. This information may assist clinicians to consider appropriate intervention for their client before the onset of LBP. This is the first report using a summed score of all endurance tests to differentiate participants with and without LBP.

4.1 Limitations of the study

There were several limitations of this study. The sampling of the participants was obtained only from population of one district in China and therefore the results may not be generalizable to other districts in China. Secondly, the sample size of people with LBP was small, and their number only accounted for 8.5% of the whole sample size. Lastly, we did not measure percent body fat and lean body mass of our subjects and thus we were not able to explore any relationship between body musculature and trunk endurance in our Chinese cohort. Nonetheless, this study achieved its major aims and provided reference values of four common trunk muscle endurance tests in the Chinese population.

5. Conclusion

This study established the reference values of Biering-Sørensen test, plank test, left side bridge test and right side bridge test scores in a cohort of Chinese participants. The unexpected high endurance times for our over 50-year-old participants perhaps was likely attributed to the habit of having regular exercises or having a long history of being engaged in physical activities. Our study also suggests that a combined endurance times of less than 288 seconds for the four tests may be used to differentiate participants with or without LBP.

Footnotes

Conflict of interest

None to report.

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Trunk muscle endurance in Chinese adults

Abstract

BACKGROUND:

OBJECTIVE:

METHODS

RESULTS:

CONCLUSIONS:

Keywords

1. Introduction

2. Materials and methods

2.1 Participants

2.2 Inclusion criteria and exclusion criteria

2.3.1 Biering-Sørensen test

2.3.2 Plank test

2.3.3 Side bridge test

2.4 Data analysis

3. Results

Table 1 General characteristics of participants in different age groups (data in mean ± SD, unless otherwise stated)

Table 6 Right side bridge test score (mean (SD) and percentile) of all the participants by age and gender

5. Conclusion

Footnotes

Conflict of interest

References

Table 1
General characteristics of participants in different age groups (data in mean $\pm$ SD, unless otherwise stated)

Table 6
Right side bridge test score (mean (SD) and percentile) of all the participants by age and gender