The benefits of physical activity and sport are extensively examined in the literature [1-13], whilst fundamental movement skills are important determinants of physical activity. In an attempt to improve infants’ health, development of fundamental skills has been examined. The infant's development of postural responses of her body is following a cephalocaudal progression starting from the head control and then the moving distally to the trunk, arms as well as finally the legs. It has also shown that the postural response organization in the 4 to 6 years old children’s synergies were more variable and longer in latency than in the 15-month- to 3-year-old children, the 7 to 10 years old children, even the adults [14]. The development of posture was influenced by the interaction of many variables which included muscle control, anthropometrics, sensory functioning and the environment [15]. In terms of the general sequence of development for newborn babies, their trunk extensor strength was gained and become balanced with flexor strength so that these gains in force were beneficial to develop the sitting and standing skill for them [16]. The process of developing and refining fundamental movement ability was involved for the preschool children aged 4-6 years old [17].

The fundamental movement phase which represents a time for young children exploring the movement actively started at two to seven years old [18]. For learning the fundamental movement skills (FMS), these composed loco motor skills which involved moving body through space (e.g. running, jumping, skipping, hopping and sliding) and object control skills which involved manipulating and projecting objects (e.g. throwing, catching, dribbling, kicking and striking balls) [19].

Achieving the well-developed FMS was the important factor in developing children's physical activity habits in the critical period of preschool years (aged from 3 to 5 years old) [20]. In this period, it was rapid growth for children’s brain and neuromuscular maturation [21] which were important for acquiring the motor skill so that the higher levels of physical activity and motor skill levels could be increased in future sport participation and self- efficacy [22]. On the other hand, the muscular control of trunk was the primary importance in the development of advanced locomotor skill [23]. The stability of spine would be also contributed to strength, endurance and neuromuscular of core musculature significantly [24]. To move forward with the defining the relationship between the core endurance and fundamental movement skills, the different views in the body of literature should be recognized. For the recent study, it has motioned that the some level of general mobility and overall function were related to core musculatures [25-27]. The primacy of truck control was underlain nearly all function which involved head control, eye-hand coordination, reach and hand function and respiratory support [28]. The CUT was a measure of abdominal strength endurance which was the significant components required for performing a curl-up [23,29].

Participants

Sixty kindergarten children in good health (33 boys and 27 girls, M age=4.5 years) were recruited from a local kindergarten to participate in the reliability and validity phrase of the study. The criteria for exclusion in the study were that the participants had a parents reported in regarding history of medical, neurological, orthopedic (including wore any type of orthotic device), balance or visual disorders or had ever been treated for neck pain/injury and any history of back pain/ injury within the past 6 weeks.

Procedures

The field test was operated with the following sequence: curl-up test, star excursion balance test and half hold lying test. The whole participants were arranged to watch the films or read the story books in the classroom for waiting the field test. Five participants were formed a group and asked to perform one test movement in each time and one instructor was responsible to one participant. The assessment with an accurate demonstration and verbal description of the movement were provided by the instructors. Then, the practice trials were also provided for assuring the participants understands what to do. Moreover, the additional demonstration was performed when the participants did not appear to understand the test. After performing the curl-up test, the participants were asked to go back to classroom and rest. The other group was asked to perform a test by the instructors when the one group was resting so that the groups were rotated after each test.

Curl up test

The participants lied in a supine position on the yoga mat and the knees were fixed to approximately 140 degree in which the examiner would measure the degree with a goniometer and the legs slightly apart as well as the feet was flat on the yoga mat. For using the goniometer, the midpoint of goniometer was aligned with the lateral side of knee joint; the arms of goniometer was aligned with longitudinal axis of thigh and the lateral malleolus of ankle [30]. Besides, the participant's arms were straight and parallel to the lateral side of trunk with palms of hands resting on the mat. The participant's fingers were stretched out and the head was in contact with the yoga mat. In addition, their feet were extended as far as possible from the hip while keeping the feet to remain flat on the yoga mat. The 3 inch measuring strip was placed on the yoga mat under the participant's leg so that their fingertips were just resting on the nearest edge of the measuring strip. Moreover, a piece of paper was placed under the participant's head and the paper would assist the examiners in determining whether the participant's head touched down on the yoga mat each repetition.

Half hold lying test

The participants lied in supine position on the yoga mat and supine with the arms extended anterior to the trunk. The participant's knees were flexed to 90° in which the examiner would measure it with a goniometer. For using the goniometer, the midpoint of goniometer was aligned with the lateral side of knee joint; the arms of goniometer were aligned with longitudinal axis of thigh and the lateral malleolus of ankle [30]. Besides, both feet were flat on the yoga mat and secured by a strap across the dorsa of the feet. Then, the participants raised their head slowly, followed by shoulders and upper chest until the examiners said 'Hold it' when their scapulae was totally off the yoga mat. Walking time on course tests involved without obstacle, with a low obstacle and with high obstacle.

The soft block acting as the obstacles (depth, 11.5 cm and width, 23.5 cm) with difference heights (5 cm and 10 cm) were set at the halfway point of a mat (10 cm width and 200 cm length). Besides, the starting line and turning line (length, 10 cm and width, 10 cm) were marked separately in the two extremities of the mat. The participants were asked to walk within the mat under three conditions involved without obstacle, low obstacle and high obstacle. The time was measured from when the participant crossed the starting line and then reached the turning line until returning to the starting point again. The participants were instructed that they should change the direction quickly after reaching the turning line and return to the starting line as well as walking as fast as possible during the walking test. The participants were performed the test again if they fell or touch the obstacle by their foot while walking.

Monitoring

To find out the validity and reliability of muscular endurance in abdominal of the participants, the curl-up test with knees flexed and feet unanchored [31,32] was adopted. The field test was operated with the following sequence: curl-up test, walking time on course test and half hold lying test. All participants were arranged to watch the films or read the story books in the classroom for waiting the field test. After performing the curl-up test, the participants were asked to go back to classroom and rest. The other group was asked to perform a test by the instructors when the one group was resting so that the groups were rotated after each test.

Statistical analysis

Test-retest reliability was estimated by calculating the intra-class coefficient(R). Pearson correlation analysis was used to determine the relationship between CUT, HHLT and WTC. Descriptive statistics including mean and standard errors of outcomes were reported.

Descriptive statistics of participants in the reliability phase of the study are present in Table 1. Test-retest intra-class R value is presented in Table 2. No significant positive correlation were found between trial one and trial two of curl-up test (R=0.13, p>0.01).

Table 1: Descriptive Results of age, exercise habits and interest in sport of all the participants (N=60).

Assessing the predictive validity of curl-up test by reviewing it’s the relationship with half hold lying test and walking time on course test. The curl-up test showed a moderate significant positive correlation with half hold lying test in trail one (r=0.449, N=60, p<0.01). Besides, the strong to moderate significant negative correlation were found in the curl-up test by the walking time on course test without obstacle (r=- 0.618, N=60, p<0.01), with low obstacle (r=-0.517, N=60, p<0.01) and with high obstacle (r=-0.558, N=60, p<0.01) in the trail one. The Tables 1 and 2 showed the correlation of the curl-up tests between half hold lying test and walking time on course test in trial one respectively. For the trial two of predictive validity, the curl-up test was weak significant positive correlation with half hold test (r=0.347, N=60, p<0.01). Besides, there was no significant negative correlation between curl-up test and walking time on course test without obstacle (r=-0.209, N=60, p>0.01), with low obstacle (r= -0.261, N=60, p>0.01) and high obstacle (r=-0.287, N=60, p>0.01). The Tables 1 and 2 showed the correlation of the curl-up tests between half hold lying test and walking time on course test in trail two, respectively.

Table 2: Test-retest intra-class reliability estimates and 99% confidence intervals for the curl-up test reliability study.

A partial correlation among curl-up test, half hold lying test and walking time on course test in trail one and trail two were conducted by controlling for age, gender, exercise habits and interest in sport. The partial correlation between curl-up test and half hold lying test was no significant in the trial one (r=0.121, p>0.01) but significant in trial two (r=0.347, p<0.01). The partial correlation between curl-up test and walking time on course without obstacle was significant (r=- 0.563, p<0.01) but no significant in trial two (r=-0.038, p>0.01). The partial correlation between curl-up test and walking time on course with low obstacle was significant in trail one (r=-0.342, p=0.01) but no significant in trail two (r=-0.201, p>0.01) while the partial correlation between curl-up test and walking time on course test with high obstacle in trial one was significant (r=-0.534, p<0.01) but no significant in trial two (r=-0.287, p>0.01).

The purpose of this study was to examine the validity and reliability of curl-up test by assessing the correlation among curl-up test, half hold lying test and walking time on course test.

A possible explanation is on curl-up test result which is in terms of the lack of enough resting times for participants performing the trial one and trial two of three tests. The only 1 h of resting time were provided for the participants among the tests so that the fatigue of core musculatures was not recovered. They would also feel painful due to the localized muscle fatigue probably. This discomfort was particularly evident affecting the results of the three tests. Therefore, the young participants might have poor performance because of the anticipation of pain when performing the retest.

The variables which involved motivation, muscle substitution and test administration were strongly associated with the scores of curlup test so the motivation of participants in this study was the other possible factor in affecting the correlation of three tests [33]. The kindergarten children were no idea or any cognition of those tests during the process of performance, although the verbal instruction was provided for participants before the test. In addition, those tests were repeated movement exercise so the participants showed no interest in trail two tests. Many K3 children aged 5 years old quickly lost the interest in the retest and need to be persuaded to continue their testing. The sticker would be given to the children by the examiners when they were the highest scores on each test. They were also difficult to pay attention and focus for performing the curl-up test and half hold lying test in both trails since that they would be disturbed and look around the near participants. Thus, the test results might have the difference if the children were tested without the other participants in the room and without a reward.

There were also the potential factors causing the error during the curl-up test for kindergarten children such as administering the measurement. The measuring strip would be moved easily when the participants lying down on the mat each time and they would catch the measuring strip when curling up with moving the hand forward so that the range of curl-up would be affected. The participants caught their knee in holding the upper body sometimes when they performing the half hold lying time so it would assist them holding longer time in this test and the results were influenced. A study was also mentioned that the stable body position on the mat was unable maintained for some college-age student due to the rapid body movement of them. Although the participants performed the curl-up test with the slow rhythm, the criterion position of the fingers on measuring strip would influence the results.

Reviewing of the settings of curl-up test, it was modified from 1 minute to 30 seconds since the difficulty of curl-up test would be simplified as a field test for kindergarten children. However, it was low coefficient with half hold lying test. It might be influenced by the two different types of muscular concentration in curl-up test and half hold lying test. The core muscles were attributed by concentric concentration in performing the curl-up test but in the half hold lying test was isometric concentration. The 1 min speed test was low correlation and a weak relationship with the isokinetic measures of abdominal strength [34]. The other study has mentioned that the reach criterion in curl-up test would have depended on shoulder girdle flexibility and the upper spine flexibility [35].

The strength of this study pertains to some objective measures used to increase the objectivity [36-38]. However, some in-depth statistical analyses [39,40] were not adopted due to the nature of data collected in this study. This may affect the validity of findings [41,42]. The total exercise of children which may affect the motor symptoms was not evaluated. In addition, the impact of gender was also not evaluated in this study.

These preliminary findings provide evidences into the CUT test cannot produces reasonably accurate and stable measures of core stability, core endurance and dynamic stability for kindergarten children. Further is done research to develop a reliable measurement for assessing the core endurance for kindergarten children in Hong Kong.