Abstract. Aim: The purpose of this study was to investigate the effects of physical characteristics including; age, gender, mass, height, body mass index (BMI) and waist-hip ratio on trunk muscles endurance in healthy subjects. Methods: In the current work, 111 females and 89 males, totally 200 healthy subjects with mean age of 31.58±13.78 years without any acute disease participated. Trunk muscles endurance was examined using curl up, static back endurance and horizontal side bridge tests. Subjects were classified into four different, equal age groups such as; 10 to 19 years (group 1), 20 to 29 years (group 2), 30 to 39 years (group 3), and 40 to 65 years (group 4). Results were statistically analyzed by Kruskal-Wallis test, Mann-Whitney U test with Bonferroni correction and Spearman’s correlation coefficient. Results: When the subjects were analyzed; the first group (age<20 years) had the best scores concerning the physical characteristic measures and endurance tests. And the fourth group (age>40 years) had the lowest scores. There was a significant negative correlation between all the test scores and age (p≤ 0.05). When all subjects were analyzed in terms of gender; males had better scores than females except for static back endurance test (p≤ 0.05). There was a significant negative correlation between mass, BMI and the test scores (p 0.05). We found a significant positive correlation between height and all trunk endurance test (p 0.05).Conclusion: We conclude that increasing age, mass, BMI and waist- hip ratio are important factors which cause a decrease in trunk muscles endurance in healthy subjects.

Keywords: Physical characteristics, endurance, trunk muscles

Introduction

Physical fitness is a growing field. Endurance is one of the important parameters of health-related physical fitness. Endurance is the time limit of person’s ability to maintain prolonged stressful effort or activity [9]. It is analyzed in two parts as cardiovascular endurance and muscular endurance.

Muscular endurance is the ability to sustain muscle contraction over a period of time without undue fatigue. Muscular endurance is also defined as the ability to produce work over time or the ability to sustain effort [11].

Muscular endurance of the lumbar extensors is assessed less frequently than muscular strength, although the endurance capabilities of these muscles may be as important as or even more important than strength in the prevention and treatment of low back pain [28].

There are few studies investigating the relationship between physical characteristics and muscular endurance performance [15,23]. Therefore we planned current study to detect effects of physical characteristics including age, gender, mass, height, body mass index (BMI) and waist-hip ratio on trunk muscles endurance in healthy subjects.

Methods

This study was performed in Pamukkale University Department of Physical Therapy and Rehabilitation Department and Turkish Red Crescent Society Denizli Medical Center in Turkey.

In the current work, prospectively 200 healthy subjects (111 females and 89 males, with mean age of 31.58±13.78 years; 166.41±9.09cm height, 68.21±14.69kg body mass, 24.62±5.06kg/m² BMI, 0.81±0.009 waist to hip ratio) without any acute disease participated. The experimental design and testing protocol for this study were approved by the institutional review board of the Health Sciences Institute of Pamukkale University.

Subjects were classified into four different groups in terms of age; first group subjects’ ages were younger than 20 years old, second group’s ages were between 20–29 years, third group’s were between 30–39 years and fourth group’s ages were 40 years and more. Each group consisted of 50 subjects.

Physical Characteristics

The subjects’ physical characteristics were determined as age (years), gender, body mass (kg), body length (cm), body mass index (BMI) (kg/ m²), waist to hip ratio.

The BMI was calculated as body mass (kg)/ (body length (m)) ². Waist to hip ratio was calculated as waist circumference (cm)/hip circumference (cm). Waist circumference was measured with a tape around the narrowest point between ribs and hips. Hip circumference was measured at the point where the buttocks is maximally extended, when viewed from the side.

Muscle endurance tests

Trunk muscles endurance was examined using curl up, static back endurance and horizontal side bridge tests.

Curl-up Test: This test measures muscular endurance of abdominal muscles. To begin the test subjects lied on their back on the floor with their feet flat on the floor about shoulder width apart and held by the physical therapist. Subjects fold their arms across their chest, and moved the top of their head as far forward as possible while pressing their chin against their chest. Subjects curled up until their elbows touch the upper part of their thighs, and then returned until their low back is in contact with the floor. They performed as many curl-ups as in 1 minute [12, 17].

Static Back Endurance Test: This test measures the muscular endurance of the back muscles. Subjects lied face down on the test bench with the inguinal region at the end of the table, upper body extending out over the end of the bench and arms at sides, ankles fixed and holding horizontal position. The goal was to hold the upper body in a straight horizontal line with the lower body as long as possible. Test ended when the subject could not hold the position or fall down the horizontal position. The position can be held timed (max. 240 sec) [2,12,19, 22].

Horizontal Side Bridge Test: This test measures the endurance of the spinal stabilizing muscles. The subject is side lying, supported on forearm and crossed ankles. The subject raises up on forearm and ankles until pelvis and trunk are nearly horizontal. The duration the position can be held until the subject's pelvis returns to the floor. This test is made for the right side of the subjects [17,19, 23].

Data Analysis

Data were presented as mean ± SD. Statistical analysis was performed by using SPSS 10.0 for Windows. Significance was defined as p≤ 0.05. Statistical analysis was performed with Kruskal- Wallis Test, Mann-Whitney U test with Bonferroni correction, Spearman’s correlation coefficient using a commercial statistical package (SPSS/PC).

Results

When we evaluated the overall subjects without concerning age and gender differences, averages of curl up, horizontal side bridge endurance, and static back endurance tests were 20.09±12.10 repeat/min, 41.96±27.96 sec, and 83.40±48.76 sec, respectively.

In the study statistically significant negative correlation was found between subject’s ages, body mass, BMI and all the endurance tests (p0.05). Also statistically significant positive correlation was found between body length and all the endurance tests (p0.05). Besides, statistically significant negative correlation was found between waist to hip ratio, curl up and static back endurance tests (p0.05). No correlation was found between waist to hip ratio and horizontal side bridge test (p>0.05).

There was a significant negative correlation between all trunk muscle endurance tests scores and age (p≤ 0.05). In the study statistically significant differences were found between age groups for endurance tests (p≤0.05). In terms of curl up there were significant differences between first group and third and fourth groups and also between second group and other groups except the first group. There were also significant differences between third, fourth groups. For horizontal side bridge test there were statistically significant differences between fourth group and other groups. For static back endurance test we found significant differences between first group and other groups except the second group, and also between second group and third, fourth groups.

Subject’s physical characteristics were analyzed in terms of gender. Women’s mean age was found 31.01±12.53 years, body mass was 63.82±14.36 kg, body length was 161.68±6.16 cm, BMI was 24.53±5.95 kg/m² and waist to hip ratio was 0.76±0.07. Men’s mean age was found 32.29±15.25 years, body mass was 73.67±13.27 kg, body length was 172.31±8.73 cm, BMI was 24.74±3.67 kg/m² and waist to hip ratio was 0.88±0.06. There were statistically significant differences between genders in terms of body mass and body length (p≤0.05). There was no statistically significant difference in terms of age and BMI between genders (p>0.05). When all subjects were analyzed in terms of gender; males had better scores than females concerning the curl up and horizontal side bridge tests (p≤ 0.05). However there was no correlation between gender and static back endurance test (p>0.05). There was a significant negative correlation between mass, BMI and trunk muscles endurance tests (p 0.05). We found a significant positive correlation between height and all trunk endurance test (p 0.05). And also there was a significant negative correlation between waist- hip ratio and curl up, static back endurance test (p 0.05). No correlation was found between waist- hip ratio and horizontal side bridge test (p>0.05).

Table 2. Physical Characteristics of the subjects according to gender.

Table 4. Endurance Test Score of the Subjects According to age groups (n=200)

Discussion

The purpose of this study was to investigate the effects of physical characteristics such as age, gender, mass, height, body mass index and waist-hip ratio on trunk muscle endurance.

The validity and reliability of endurance tests that were approved in was shown in many studies in literature. These tests are practical tests that can be used previously, at the end of or any time of treatment in rehabilitation programmes. The first test for evaluating the isometric endurance of trunk extensor muscles was described by Hansen in 1964[10]. In 1984 following a study by Biering-Sorensen this test became known as the “Sorensen Test” and gained considerably popularity [5]. Since then this test has been used in many studies either in its original version or variants. The Sorensen test allows for a rapid, simple and reproducible evaluation of isometric endurance of the trunk extensor muscles and its discriminative validity, reproducibility and safety is good [8].

When the literature was reviewed there were few studies about the relationship between physical characteristics and muscle endurance [1, 8, 9,18]. Gonzales E. studied muscle endurance of the females and males in different age groups. Similar to our study curl-up scores showed decrease with increasing age. There is an age related decrease in muscle strength, muscle mass and fatigue. Histochemical studies of striated muscle showed evidence of fiber size variation, hyaline or granular degeneration, increased fat and connective tissue. Muscle spindles undergo capsular thickening, lamellar fibrosis and a mild degree of intrafusal fiber loss. There is a one-third to one-half reduction in total muscle mass between ages 30–80. Between 50–80 years, there is %30 decrease in cross-sectional area of muscles [9]

In our study the first group (age< 20 years) had best scores and the fourth group (age>40 years) had lowest scores concerning physical characteristic measures and trunk muscle endurance test. There was a significant negative correlation between all trunk muscle endurance tests and age. In a previous study reported that age had a moderately significant influence on paraspinal muscle fatigability. The results of the studies indicated that muscle fatigue was slightly greater in young men than in older men [8, 9]. On the other studies investigators showed that back muscle endurance capacity decrease slightly with aging [1,18]. Although it is well known that muscle endurance decrease with increasing age because of poor muscle function as a result of decreasing muscle mass, age related decline in strength which appears to be greater in back and lower extremity muscles, decreasing aerobic capacity avarage of approximately %1 per year after third decade, the potential influence of age and stature remains debated [1, 8, 9, 18].

In the results of our study we did not find any correlation between gender and static back endurance test. In the study of Alaranta et al., which they used non dynamometric trunk performance tests, men showed greater muscle endurance in all muscle tests [1]. Conversely, Kankaanpaa M. et al’s study showed that women fatigue more slowly than men in the Sorensen back endurance test [16]. Also many previous studies showed that men have had longer position-holding times compared with females[5, 20, 21].

Spectral analysis of EMG signals recorded during test supported greater muscle fatigue in males[16]. The gender differences in paraspinal muscle fatigue during the Sorensen test may be due to muscles’ anatomic and functional characteristics. Back muscles in woman have a greater relative cross-sectional area of fatigue resistant type І fibers than men [26]. Another suggestion is that the greater degree of lumbar lordosis in females may afford a mechanical advantage by lengthening the lever of the spinal erector muscles [27]. Influence of sex hormones can be another factor [13]. As it can be understood from the samples of literature and results of our study, the effect of gender on trunk muscle endurance is not clear and further studies are needed [26, 27].

There are numerous suggestions that subject weight may influence the Sorensen test results. But no earlier studies have investigated suggestion systemically. Kankaanpaa M. et al. found moderately high negative correlation between paraspinal fatigue and BMI and this indicated that women with high BMI fatigue faster then women with normal or low BMI [16]. There was a significant negative correlation between mass, BMI and trunk muscle endurance tests too in our study.

Waist circumference is used in determining the abdominal fat ratio and it is an important health indicator [3, 4]. As it is known and supported by literature the increase of waist to hip ratio over the definite values is found to by risk for cardiopulmonary diseases [25].

Well then, how is the relationship between waist hip ratio and muscle endurance which is shown highly correlated with lumbar disorders especially LBP?

In a study, 24 males (between 25–50 ages) muscle endurance and fat distribution was analyzed by Seidell et al. They found negative correlated relationship between waist to hip ratio and muscle endurance which is similar to the results of our study [24]. The subjects with higher waist hip ratio had lower muscle endurance. More recently, investigators have shown that endurance can be used as a predictor for first time low back injury. Low levels of static endurance in the back extensor muscles are associated with higher rates of low back pain, decreased awareness and decreased producibility in work place [14].

Brill et al. studied the relations between muscle strength and endurance and potential functional limitations. 3069 males 589 females participated to the study.

A clinical assessment and then participants reassessed after five years. One or more limitation occurred in the participants for participants concerning the age, aerobic physical fitness and BMI assessment who had low levels of muscle strength and endurance. At the results of the study they concluded that levels of muscle strength and endurance were important factors for decreasing functional limitations[9].

We conclude that increasing age, mass, BMI and waist- hip ratio are important factors which cause decrease in the trunk muscles endurance in healthy subjects. The effects of physical characteristics on trunk muscles endurance should be taken into account while planning endurance programmes for healthy subjects. As there are few studies about physical characteristics and muscle endurance further studies are needed. And regarding this we have started a study that analyses the subjects’ trunk endurance capacity who have LBP. We planned to compare the endurance capacity of LBP subjects with healthy subjects.

We suggest that as decrease in trunk muscle endurance is one of the important causes of LBP it is important to design protective endurance training programmes for people with low trunk muscle endurance in order to prevent from LBP. Also physical therapists who deal with LBP patients should evaluate trunk muscle endurance properly for planning effective treatment programmes.

References

1. Alaranta H, Hurri H, Heliovaara M et al. (1994). Nondynamometric trunk performance tests: reliability and normative data. Scand J Rehabilitation Med.; 26; 211–5
2. Alaranta H, Luoto S, Heliovaara M, Hurri H. (1995). Static back endurance and the risk of low-back pain. Clin Biomech (Bristol, Avon). Sep;10(6):323–324.
3. Appropriate body-mass index for Asian populations and its implications for policy and interventionstrategies WHO expert consultation. (2004). Lancet; 363: 157–63.
4. Barker D, Livingstone C. (1998). Mothers, Babies and Diseases in Later Life. 1st Citation 2nd. London.
5. Biering-Sorensen F. (1984). Physical measurements as risk indicators for low back trouble over a one-year period. Spine 9; 106–1
6. Brill PA, Macera CA, Davis DR, Blair SN, Gordon N. (2000). Muscular strength and physical function. Med Sci Sports Exerc. Feb;32(2):412–6.
7. Chad E, Bart N, Green DC, Johnson CD, Moreau SR. (2001). Isometric Back Extension Endurance Tests: A Reviev of Literature. Journal of Manipulative and Physiological Therapeutics, Volume 24, issue 2, February; 110–122.
8. Demoulin C, Vanderthommen M, Duysens Cl, Crielaard JM. (2006) Spinal Muscle Evaluation using the Sorensen test: a critical appraisal of the literature. Joint Bone Spine 73 43–50
9. Gonzales E. (2001). Physiological Basis of Rehabilitation Medicine. Butterworth-Hehemen, Wasen USA, Chapter 24 P: 563–564
10. Hansen JW. (1964). Postoperative management in lumbar disc protrusions. І. Indications, method and results. П. Follow up on a trained and untrained group at patients. Act a Ortop Scand; 17 (suppl 71): 1–47
11. Heyward VH. (1997). Advanced fitness and exercise prescription. 3^th ed. New Mexico: Human Kinetics
12. Ito T, Shirado O, Suzuki H, Takahashi M, Kaneda K, Strax TE. (1996). Lumbar trunk muscle endurance testing: An inexpensive alternative to a machine for evaluation. Arch Phys Med Rehab 77:75-9
13. Jorgensen K, Nicolaisen T. (1987). Trunk extensor endurance: determination and relation to low back trouble. Ergonomics 30:259–67.
14. Jorgensen K, Nicolaisen T. (1987). Trunk extensor endurance: determination and relation to low back trouble. Ergonomics 30:259–67.
15. Kankaanpaa M, Loaksonen D, Taimela S. et al. (1998). Age, sex and body mass index as determinants of back and hip extensor fatigue in the Isometric Sorensen Back Endurance
16. Kankaanpaa M, Laaksonen D, Taimela S, Kokko SM, Airaksinen O, Hanninen O. (1998). Age, sex and body mass index as determinants of back and hip extensor fatigue in the Isometric Sorensen Back Endurance Test. Arch. Phys Med Rehabil Vol 79, September; 1069–1074
17. Kell RT, Bhambhani Y. (2005). Relationship between erector spine static endurance and muscle oxygenation-blood volume changes in healthy and low back pain subjects. Eur J Appl Physiol. Nov 1;1–8.
18. Letikka P, Bethie MC, Videmen T et al. (1995). Correlation of isokinetic and phychophysical back of and static back extensor endurance tests in men. Clinic Biomech (Bristol, Avon);10:323–30
19. Liebenson C. (2000). Documentation of physical capacity: It’s purpose in rehabilitation. Dynamic Chiropractic, Volume 18,issue 08.
20. Mannian AF, Dolen P. (1994). Electromyographic median frequency changes during isometric contraction of the back extensors to fatigue. Spine;19: 1223–9
21. Mc Gill Sll, Childs A, Liebenson C. (1999). Endurance times for low back stabilization exercises: clinical targets for testing and training from a normal database. Arch Phys Med. Rehabilitation;80:841-4
22. McGill. (2002). Low Back Disorders: Evidence Based Prevention and Rehabilitation. Champaigne, III.: Human Kinetics.
23. Robergs RA, Robert SO. (1997). Exercise physiology. Performance and Clinical Applications. Boston:520–539, 600–631, 764–779
24. Seidell JC, Bjorntorp P, Sjostrom L, Sannerstedt R, Krotkiewski M, Kvist H. (1989). Regional distribution of muscle and fat mass in men-new insight into the risk of abdominal obesityusing computed tomography;13(3):289–303.
25. Smith DA, Ness EM, Herbert R, Schechter CB, Phillips RA, Diamond JA, Landrigan PJ. (2005). Abdominal diameter index: a more powerful anthropometric measure for prevalent coronary heart disease risk in adult males. Diabetes Obes Metab. Jul;7(4):370–80.
26. Thorstensson A, Calson H. (1987). Fiber types in human lumbar back muscles. Acta Physial Scand;131: 195-202
27. Tvelt P, Doggfeldt K, Hetland S et al. (1994). Erector spine lever arm length variations with changes in spinal curvature. Spine;19:199–204
28. Uderman BE, Mayer JM, Graves JE, Murray SR. (2003). Quantitative Assessment of Lumbar Paraspinal Muscle Endurance. Journal of Athletic Training. September; 38 (3):259–262