RELIABILITY OF MEASURING VARIOUS CONTRACTILE FUNCTIONS OF FINGER FLEXORS OF MEN OF VARIOUS AGES

e aim of the research is to determine the reliability of testing various contractile functions of a male hand based on motoric and functional dominance and age. e examinee takes a seat with their arm extended or mildly exed in a mildly abducted position. For the measuring purposes, dynamometric probe with isometric straining conditions xed to a special construction was used. e “Isometrics” (ver. 3.1.1) was used and frequency of data selection was realized on the level of 500 Hz. e sample includes 269 male examinees aged from 14.0 to 69.9. e results of descriptive statistics have shown that in relation to the tested sample for the non-dominant hand, values for maximum force (Fmax) range from 462.8 to 529.0 N, for explosive force (RFDmax) the range is from 1621.6 to 1972.8 N/s and for muscular force impulse (ImpF50%max) from 8203.9 to 15552.3 Ns, while Fmax values the dominant hand ranges from 478.1 to 566.2 N, for RFDmax it ranges from 1742.6 to 2119.0 N/s and for ImpF50%max 9516.7 to 16845.1 Ns. e results have shown that it is reliable to measure all three examined contractile hand characteristics where by ICC ranges from 0.938 to 0.977 for Fmax, from 0.903 to 0.971 for RFDmax and from 0.747 to 0.943 for ImpF50%max. e second try as the better result should be considered the representational value for Fmaxand RFDmax variables, regardless of the hand dominance or age group. While for the variable ImpF50%max, in the age groups from 35.0 to 49.9 and from 50.0 to 69.9, the rst tested try for both hands should be considered, in 14.0 to 19.9 years group the second try should be taken into consideration, and in 20.0 to 34.9 age range, the better result of the non-dominant hand is the rst try, and of the dominant is the second try.


INTRODUCTION
e complex anatomical and functional structure of the hand is mostly directed for the assignment of catching and holding as the dominant motoric function of this part of the hand (Fernandes et al., 2014).
Former research have dealt with various functional and motoric characteristics of the hand as a segment of the arm, as well as the attempt of identifying di erent biomechanical aspects of the production of the hand grip force characteristics (Bohannon, 2001;Nicolay and Walker, 2005;Допсај et al., 2011;Fernandes et al., 2014).It has been determined that the dominant hand is around 10% stronger than the non-dominant hand (Hager-Ros and Rosblad, 2002; Кљајић et al., 2012), and that men reach the abso-lute maximum force values in the forth decade of life, those values decrease a erwards (Massy- Westropp et al., 2011).It has been con rmed that the children's and adolescent's maximum hand grip force can be useful for tracking biological development as well as for function of total muscular development evaluation (Bohannon, 2001;Sartorio et al., 2002;Wind et al., 2010).In the elds of epidemiology and gerontology it is used for examining the e ect of older generation aging (Kerr et al., 2006), and it is also a signicant indicator of health parameters of the grown-ups, such as density of the bone mass or the protein loss (Foo et al., 2007).
By analyzing the data from the available literature, it can be concluded that the examined phenomena of the hand contractility are mostly linked to the maximum force (Müller et al., 2000;Dopsaj et al., 2007;Aadahl et al., 2011), and the small number of research were realized in accordance with the explosive force (Demura et al., 2003;Dopsaj et al., 2009a), as well as in accordance with the endurance characteristics when producing force (Кљајић et al., 2012).
e lack of scienti c information about the metrological characteristics of di erent contractile abilities of thehand muscles which are obtained through the mentioned "Hand Grip" test, compared to the age of the examinees, is noticeable, especially when taking into consideration the fact that during the process of growing up (preadolescent, adolescent and post-adolescent period) and during the aging process, the contractile abilities of the muscles are changing (Aadahl et al., 2011).
No matter which scienti c discipline it is being applied in, the fact is that the "Hand grip" test is extremely applicable, simple and informative when applying the standardized measuring procedure.It is necessary to de ne both the new innovative values of the very test as well as the contractile characteristics which are measured by its application, all in order to improve the technological procedures of obtaining the valid and reliable information that indicate the physical health and specialized muscular function of the upper part of the body, i.e. the general indication about the muscular functions of the entire body of the population of interest.For the needs of de ning such expert system, it is necessary to form a huge data base with referential values, where the methodological procedure of forming data base requires initial de nition of the healthy population conditions of both genders in every age category (Hager-Ros and Rosblad, 2002; Dopsaj et al., 2009b).Such piece of information is essential when it comes to criterion and normative values and it is used for the needs of deciding algorithms, as well as more precise interpretations of the testing results, in the sense of comparison of both top athletes and recreationists, but also of the rest of the population, no matter whether they are healthy, injured or ill people that don't do sports (Desrosiers et al., 1995;Müller et al., 2000;Bohannon, 2001;Kerr et al., 2006;Gallup et al., 2007;Dopsaj et al., 2007;Dopsaj et al., 2009а;Ivanovic et al., 2009;Dhara et al., 2009;Beloosesky et al., 2010;Carrasco et al., 2010).e subject of this research is to examine di erent contractile characteristics of a hand.e aim of the research was to determine the reliability and quantitative descriptive indicators of di erent contractile functions of the male hand in relation to the maximum and explosive force, as well as criterion endurance of producing force in the function of motoric and functional dominance and age.Considering the already tested space of contractile characteristics realiability of both lower muscles and upper extremities from the aspect of force and explosive force where the results showed the high level of reliability (Blazevich et al., 2002;Demura et al., 2003;Ivanovic and Dopsaj, 2013;Jenkins et al., 2014), similar results can be expected in the space of hand muscles force and explosive force, and positive results in the space of hand muscle force impulse can be assumed.

METHODS
In case of this research, for the purpose of measuring the contractile characteristics of the muscular force, the quantitative approach of sampling the information has been applied, by the dynamometry method and by testing in isometric conditions of straining (Допсај, 2010).As a primary research method, the laboratory testing with the usage of the "Hand Grip" standardized test has been used (Dopsaj et al., 2007;Ivanovic et al., 2009;Допсај et al., 2011).
e analytical and statistical methods would be applied as a basic cognitive method, as well as the method of induction,i.e. total induction.e research sample e sample included 269 male examinees ranging from 14.0 to 69.9 years old, out of which 59 examinees aging from 14.0 to 19.9 years old -group I (BH = 181.9±6.1 cm, BW = 77.9±10.57kg, BMI = 23.5±2.7 kg/m²), 123 examinees aging from 20.0 to 34.9 years old -group II (BH = 182.8±6.9 cm, BW = 86.1±14.4kg, BMI = 25.7±3.4kg/m²), 47 examinees aging from 35.0 to 49.9 years old -group III (BH = 181.7±7.2 cm, BW = 87.5±12.4kg, BMI = 26.5±3.41kg/m²) and 40 examinees aging from 50.0 to 69.9 years old -group IV (BH = 180.3±4.77cm, BW = 86.7±11.8kg, BMI = 26.6±3.16kg/m²).Twenty examinees reported their le hand as their dominant one.e examinees were chosen by a simple random sample from the sports and general population.ey all were familiar with the methods of testing and they voluntarily took part in the examination.e examination was carried out according to the terms of Helsinki declaration and with the approval of Ethic Committee of the Faculty of Sport and Physical Education University of Belgrade.

Measurament procedure
e examinees were tested by the application of the standardized measurement procedure which was previously described as follows: in a sitting position, with the arm either outstretched mildly exed which is placed in the easily abducted position (Допсај et al., 2011; Кљајић et al., 2012).e procedure was as follows -a er the singly basic 3-minute warm-up (shaping and stretching exercises) each of the examinees was explained the testing procedure.A er that, they were introduced to the test by realizing 3 to 4 initial tryouts of the hand grip on lower force intensities, i.e. they tried to realize the endurance of each hand alternately in duration of 10 seconds with the arbitrarily selected force ranging from 150 to 200 N.A er that, each examinee performed one try of the maximum hand grip (both with dominant and non-dominant hand) for the sake of getting familiar with the testing procedure and in the function of the nal and speci c warming up phase as well.
A er the 2 to 3-minute break, the examinees did the test following the protocol -rstly, they realized two alternate measurements of maximum muscular hand grip force of both hands, on the mark of the measurer (the examinee was free to choose which hand he would do the test with rst) in order to dene the level which is 100% of the given contractile ability (maximum contraction duration is 2 seconds).
e break between every testing tryout was at least 1 minute long.
A er that, in the latter part of the procedure, a er 2 to 3-minute break, the measuring of the production of the given force capacity ensued (durability of the isometric muscle force production), i.e. the time interval during which the examinees could maintain the given force level at 50% of the maximum was measured, according to the before mentioned procedure (Markovic et al., 2016).e assignment of the examinees was to keep the de ned level of the force in the longest time interval as possible up until willing to quit by looking at the monitor which showed the level of force.e realization time of the given force was measured by a so ware, and the task of the measurer was to watch the screen with the examinee and to correct the examinee according to the force realization level, as well as to verbally motivate the examinee to endure the given task in as longer time interval as possible.Once the examinee couldn't realize the de ned level of force anymore, i.e. when his performance fell below 45% of the maximum, the attempt was stopped, and the so ware recorded the total time of the endurance in the given range.A er the 5-minute break, the same test was realized with the other hand, and a er the break of at least 10 minutes, the endurance test for both hands was repeated, following the same procedure.
e dynamometric probe which is xed to the construction and specially intended for the realization of the "Hand Grip" testing was used (Markovic et al., 2016), while the frequency of the selection i.e. information sampling was realized on the level of 500Hz, and with the help of the so ware used for analyzing data, called "Isometrics" (ver.3.1.1).

Variables
e tested space was de ned in accordance with the three variables muscular hand force as follows: the aspect of maximum force (shown in N), maximum explosive force (shown in N/s), and the endurance in muscular force production, i.e. the temporal aspect of detecting the given force percentage (shown in Ns).
For the purpose of this examination, the following variables were used: 1. Maximum muscular hand grip force -F max : of the dominant hand (F max D) and the non-dominant hand (F max ND), through the rst (1) and the second (2) attempt, shown in Newtons (N); 2. Maximum value of the explosive force -RFDmax : absolute value of the dominant hand (RFD max D) and non-dominant hand (RFD max ND), through the rst (1) and second (2) attempt, shown in Newton per second (N/s).
3. e muscular force impulse, endurance of the hand grip force, achieved on the level of 50% of F max -I mp F 50%max (calculated as a product of the force level F 50%max and the performed time during endurance on the mentioned force level): of the dominant hand (I mp F 50%max D) and the non-dominant hand (I m- p F 50%max ND), through rst (1) and the second (2) attempt, which is shown in Newton-seconds (Ns).

Statistical analysis
All results were rstly analyzed by the application of the basic descriptive statistical method where the following was calculated: central tendencies measures (arithmetic mean) and the dispersion measures (standard deviation) and the variation coe cient (C V %). e data was processed by the Student's t test for the dependent samples.A er that, the linear regressive analyses, as well as the analyses of the similarities of the variable pairs, were calculated, i.e. the parameters of the reliability were calculated-Intraclass Correlation Coe cient (ICC) (Hair et al., 1998).All statistical analyses were carried out with the help of so ware package "SPSS 19.0", while for the level of the statistical signicance, the value p < 0.05 was used.

RESULTS
e average values of muscular hand grip characteristics for the dominant and non-dominant hand of the whole sample were 501.8±97.1 N and 534.4±100.2N for F max , 1837.0±446.2N/s and 1984.8±494.7 N/s for RFD max , and 13537.4±5511.4Ns and 14458.6±6600.8Ns for I mp F 50%max .
e Table 1.shows the results of the both attempts of the tested variables of both the dominant and non-dominant hand in the function of age groups of the examinees.It was noticed that the highest measured F max of the hand grip of the non-dominant hand which was obtained from the II group for variable F max ND2, while the lowest level of force was measured in the I group for the variable F max ND1.In accordance with the F max indicators of the dominant hand, it can be noticed that the highest measured hand grip force which was determined in the II group for the variable F max D2, while the lowest force measured in the I group for the variable F max D1.
When it comes to the RFD max variable, the results have shown that the highest explosive hand grip force of the non-dominant hand was measured in II group for variable RFD max ND2, while the lowest level was measured in the IV group for the variable RFD max ND2.In relation to the obtained RFD max values of the dominant hand one can point out that the highest level of the explosive hand grip force was measured in the II group for the variable RFD max D2, while the lowest measured results were found in IV group for the RFD max D1 variable.
In accordance with the I mp F 50%max variables, the results have shown that the greatest impulse of the hand grip force of the non-dominant hand of the 50% below maximum was measured in group III for the variable I mp F 50%max ND1, and the lowest level was measured in the I group for the variable I mp F 50%- max ND1. e highest measured impulse of the hand grip force of the dominant hand was pointed out in III group for the variable I mp F 50%max D1, while the lowest one was measured in I group for the variables I mp F 50%max D1.
In relation to the established variations of the results, as well as their homogeneity measures, the results of the variation coe cient of the reached levels of the maximum force are within the 16.8% to 20.7% range, while the explosive level ranges from 19.4% to 29.8% which shows that the measured results F max and RFD max belong to the homogenous group of examinees, no matter the age.However in relation to the variation of measured results of the endurance testing while producing the muscular force, the Cv% value ranges from 30.6 for I mp F 50%max D2 in the group IV, to the value of Cv% 58.0 for I mp F 50%max ND1 in the group I (Table 1).Although the determined level of the variation is about 30% above the optimal value, which means that it belongs to the non-homogenous category, it is placed below the value of 60%, which satis es the conditions for the usage of the statistical analysis in further phase of parametric statistics.In relation to the results of the di erences in average values of the tested variables in the function of the tested tryouts (Table 2), it is established that the di erences in results of the rst and the second measurement of ten couples of the variables is highly statistically signi cant no matter the age group, ranging from t = -2.015and p = 0.049 for F max ND for the III age group, to t = -4.115and p =0.000 for F max D for group I. e statistical signi cance wasn't established with thirteen variables i.e. their results range from t = -1.919and p = 0.061 for RFD max ND in III age group to t = -0.050and p = 0.961 for I mp F 50%max ND in IV age group.Table 3. shows the results of the reliability in accordance to the questioned variables and age groups.It has been determined that the reliability level of the each questioned contractive characteristic of the hand in the function of the age group is highly statistically signi cant (p = 0.000 for every variable pair tested).
e ICC value of F max ranges from 0.938 to 0.977, for RFD max from 0.903 to 0.971, and for I mp F 50%max from 0.747 to 0.943.By linear regressive analysis (Table 4, Charts 1 to 6), regressive models of the testing reliability are de ned i.e. models of the linear regressive equations of all the tested variables for all ages.Graphs show the results of the linear regressive analysis in relation to the testing (Test 1 and 2) for the F max variable in the function of the non-dominant (Chart 1) and dominant hand (Chart 2), for the variable RFD max in the function of the non-dominant (Chart 3) and dominant hand (Chart 4), and the I mp F 50%max variable in the function of the non-dominant (Chart 5) and dominant hand (Chart 6).For the F max variable the range of the determination coe cient (R²) for dominant hand is 0.826-0.903,and for non-dominant hand 0.811-0.912.e second variable RFD max ranges from 0.826-0.871for dominant hand and 0.692-0.910for non-dominant hand, while the I mp F 50%max variable of the determination coe cient R² ranges from 0.360-0.674for dominant hand, and 0.401-0.808for non-dominant hand (Table 4).All regressive models of reliability showed the high level of signi cance on the level of p = 0.000.

DISCUSSION
e examinations of the contractile characteristics of the hand muscles are of great importance in predicting the functional limitations and diagnosis of the neural disorders, and have a signi cant role in the evaluation of the general level of the contractile physical abilities development of both professional athletes and recreationists (Desrosiers et al., 1995;Rantanen et al., 1998;Bohannon, 2001;Wind et al., 2010;Koley et al., 2011).Research of this type present the permanently current eld of interest of the scienti c research in order to increase the fundus of the knowledge, and to perfect the testing procedures in diagnostics, therapeutic and professional means as well.
Besides higher statistically signi cant correlation when it comes to repetitive action of the testing, the statistically signi cant di erence of the average values of the F max variables of the rst and the second attempt of the dominant hand of all the age categories, and for the non-dominant hand as well in the rst three tested groups (I, II, III age group)(Table 2).Other statistical analyses used to examine the reliability of measuring, showed the extremely high level of given characteristics of detection of maximum force (F max ), of the hand grip of all the questioned groups on the ICC level from 0.944 to 0.977 for non-dominant hand, i.e. from 0.938 to 0.970 for the dominant hand (Table 3).e given results are in total con rmation with the previously determined standards in relation to the reliability of the standard tests of the hand grip force of 0.961 for the right hand and 0.950 for the le hand (Hamilton et al., 1994), and respectably in accordance with the higher reliability of the standard tests of force of other muscular groups ranging from ICC 0.97-1.00for isometric squat position and leg pushing from the standing position (Blazevich et al., 2002), as well as for the standard leg thrust on the Cronbach's Alpha level of 0.989 (Ivanovic and Dopsaj, 2013). is way, the results showed that the usage of the isometric testing, in relation to the maximum hand grip force measurement is also reliable in the function among the male sex examinees of di erent age.It ought to be mentioned that because of the estimated statistically signi cant di erence of the second measurement compared to the rst measurement, the result of the second attempt, i.e. the result of the stronger attempt should be considered as a nal result.
In the case of second tested variable, which measured the maximum level of explosive hand grip force -RFD max , the statistically signi cant di erence between attempts was estimated only in age group I, both in cases of dominant and non-dominant hand (Table 2). is can be explained by the omition of the previous experience of performing the same strainings and their initial unpreparedness for the task during their rst attempt i.e. the higher acute neuro-motoric adaptability during their second attempt.Further statistical analysis have shown extremely high level of reliability of the given contractile characteristic RFDmax of hand grip in all of the tested age groups on ICC level from 0.903 to 0.971 for non-dominant hand, and from 0.948 to 0.964 for dominant hand (Table 3).As in the case of F max these results are in con rmation with the early established standards in relation to the reliability of methods for testing the explosive hand grip force where the ICC levels from 0.870 to 0.930 (Demura et al., 2003;Jenkins et al., 2014) i.e. in accordance with the high reliability of the standard tests of force of the other muscular groups leveled from 0.808 to 0.945 Cronbach's Alpha for the standard leg thrist (Ivanovic and Dopsaj, 2013).Based on former research and the given results of these tests it is obvious that the usage of the isometric testing, in relation to the measures of the maximum explosive force of the hand grip test, is valid in the function of the various groups and ages of men.One should mention that the statistically signi cant di erence of the second measurement compared to the rst is detected only in age group I for both hands.However, absolute di erences in the average results obtain are seen in favor of the second attempt, and they are based on the descriptive statistics in all age groups, except for group IV for non-dominant hand, where the rst attempt was better (Table 1).With all this in mind, one can propose the measurement of the nal attempt of the explosive force, i.e. the result of the second attempt as the nal result.
While in the third tested variable which measured the impulse of the maintaining of the force on the 50% from maximum -I mp F 50%max the signi cant di erence between the rst and the second attempt o esting can be seen in I age group, but also in the IV age group for dominant hand only (Table 2).e important factor of this testis the usage of the sensory information i.e. the visual monitoring of maintenance of the assigned level of the force which is at 50% of maximum, and their compatibility (motoric control) with the muscular characteristic (muscular endurance), where in the disputed age categories one may come across the process of accelerated developmentor the degradation of the same, this being the cause of obtained results (Nicolay and Walker, 2005).Based on these results the statistically signi cant level of reliability of the detection of the I mp F 50%max hand grip can be seen in all tested age groups on the ICC level from 0.761 to 0.943 for non-dominant hand, and from 0.747 to 0.894 for dominant hand (Table 3).Functional muscular ability for manifestation of the assigned level of the force as a measure of endurance, expressed as a force impulse has not been much examined phenomena in the sports area (Nicolay and Walker, 2005; Кљајић et al., 2012).Besides statistically signi cant di erence between the testing attempts I mp F 50%max only in the I and IV age group for dominant hand (Table 2), the di erences in average accomplished results can be distinguished based on the results of the descriptive statistics (Table 1).Based on that, it can be recommended that the value which presents the higher endurance should be taken as anal result, but that in the III and IV age group the rst testing attempt mainly presents the better result for both hands, while in the I age group it is the second one, and in the II aging group the mark of the better result of the non-dominant hand is the rst, and of the dominant hand is the second attempt.
e high level of signi cance of the regressive models of testing reliability of the variables of all age groups has been established.One can say that the great amount of variety of the second measurement is explained through the rst one and that is for F max ranging from 81% to 91%, for RFD max ranging from 69% to 91% and for I mp F 50%max ranging from 36% to 80%.ere by it is notice able that the obtained results of the linear regressive analysis for F max and RFD max are for a bit lower than the values informer research which range from 96 % to 99 % for both variables (Giampaoli et al., 1999;Dopsaj et al.,2009b).Regressive models of reliability I mp F 50%max were not noticed as a matter of former interest, so the possibility of comparison is omitted.is way the possibility of the prediction of the optimal result of the measured contractile characteristics of the hand is enabled, as well as positioning of the actual examinee in the function of the de ned population standards.

CONCLUSION
e hand grip presents the important method which can be used to diagnose the level of the functional ability of tested contractile properties of the hand as a basic manipulative segment which shows the basic condition of the muscular functions of the whole organism.
In accordance with the aim of the research, quantitative descriptive indicators which can serve as a means of comparing and determining the levels of development of the stated abilities of people of various level of training, various functional and health condition as well as of people with di erent stadiums of motoric or some other disorders, and therefore can gain the vast practice from many cognitive and practical aspects.One can state that the "Hand Grip" test can measure all of the three contractive characteristics of the hand -maximum and explosive force, endurance of the force of males from the age of 14.0 to 69.9 years.
Of course, as a nal indicator of the contractive muscle characteristics, the value which shows the better score is taken into consideration.By omitting the previous experience of performing the similar straining and their initial motor in adaptability for the task, it is established that the representative value of the F max and RFD max variables is best shown by taking the second attempt into consideration, no matter the hand dominance or age group.For the variable I mp F 50%max , a er the 35 th year of age, it is common to take the rst attempt for both hands, while for the youngest tested group, the second attempt should be taken as a de nite means of testing.In the age of 20.0 to 34.9, the indicator of the better result of the non-dominant hand is the rst, and of the dominant hand is the second attempt.

Table 1 .
Descriptive statistics of the tested variables

Table 2 .
e results of the di erences analysis (t test)

Table 3 .
Results of the reliability (Intraclass Correlation Coe cient)

Table 4 .
e results of the de ned models of the linear regressive equations Chart 1Chart Linear regression F max for 1 and 2 attempt of non-dominant (Chart 1) and dominant hand (Chart 2) *Legend of the single result positions by age: ∆ -age group from 14.0 to 19.9 -I age group; ○ -age group from 20.0 to 34.9 -II age group; □ -age group from 35.0 to 49.9 -III age group; ◊ -age group from 50.0 to 69.9 година -IV age group, and the same color points out the regressive lines also, i.e. blue for age group I; red for age group II; yellow for age group III; green for age group IV.