The Pearson correlation coeffi cient (r) between the grip strength and hand-forearm anthropometry was found to determine either existing or not a linear relation among them. Collecting data of the variables was obtained from ten young adults in both, right and left hand-forearm, it was taken into account some qualitative variables: to be right-handed, the gender with fi ve (5) men and fi ve (5) women, and it was established as a condition that the individual was healthy and did not have a previous career as an athlete. A direct linear relationship with hand anthropometry and the grip strength is concluded, even though as expected, there was a strong difference between the force exerted by a male and a female individual, being the fi rst stronger. Respect to the forearm, an inverse relation was found between the maximum circumference of the forearm and the grip strength. Finally, the strongest relationships found were in the width and length of the palm, as well as in the circumference of the wrist. Results were validated comparing the results of this research against the results of specialized literature. Some considerations may be considered for future research. Grip strength can promote the risk of accidents and ergonomists should consider this factor appropriately for their design.

Keywords:Anthropometry, Forearm, Grip strength, Hanf, Pearson.

El coefi ciente de correlación de Pearson (r) entre la fuerza de agarre y la antropometría del antebrazo manual supone una relación existente o no lineal entre ellos. La recopilación de datos de las variables se obtuvo de diez adultos jóvenes, tanto en el antebrazo derecho como en el izquierdo, se tuvieron en cuenta algunas variables cualitativas: ser diestro, el género con cinco (5) hombres y cinco (5) mujeres, y se establecieron como condiciones que el individuo estaba sano y no tenía una carrera previa como atleta. Se concluye una relación lineal directa con la antropometría de la mano y la fuerza de agarre, aunque como se esperaba, existía una gran diferencia entre la fuerza ejercida por un individuo masculino y femenino, siendo la primera más fuerte. Respecto al antebrazo, se encontró una relación inversa entre la circunferencia máxima del antebrazo y la fuerza de agarre. Finalmente, las relaciones más fuertes encontradas fueron en el ancho y largo de la palma, así como en la circunferencia de la muñeca. Los resultados se validaron comparando los resultados de esta investigación con los resultados de literaturas especializadas. Algunas consideraciones pueden ser consideradas para futuras investigaciones. La fuerza de agarre puede promover el riesgo de accidentes y los ergónomos deben considerar este factor de manera adecuada para su diseño.

Palabras clave: Antropometría, Antebrazo, Fuerza de agarre, Mano, Persona.

One of the most signifi cant developments during the long period of early human evolution was man’s achievement of upright posture since hands become available for activities other than locomotion. The tremendous value of the human hand as a functional part for grasping, manipulating, writing, as well as other activities, need not be emphasized [1]. Therefore, dimensions or sizes of the human hand are important for two primary reasons: protection and function. Thus, dimensional information on the hands is required for the effective design of handles of tools or implements to be grasped with the hands such as cutting tools [2], as well as handwear.

Anthropometry of the hand plays an essential role in different fi elds, like aeronautics [3] medicine or criminology where hand anthropometry is used to determine the sex of a deceased person. Determination of sex is often considered as one of the simplest tasks in forensic analysis but become increasingly important in cases of mass disasters, where there is a likelihood of recovering feet and hands separated from the body [4].
Despite the application of high technology at work, there are still physically demanding occupations in fi elds such as automotive industries, manual material handling jobs, postal, emergency and military services [5]. Hand-grip strength is identifi ed as one limiting factor for manual lifting and carrying loads [6], [7], [8]. Manual lifting and carrying of loads are common types of exercise in everyday life at home and work. Studies of grip strength typically examine maximum force during a single repetition, but this type of exertion is relatively rare in the workplace, where tasks frequently involve repeated forceful, and dynamic grasping or prolonged static holding [6]. This study is of high relevance to industry: Grip strength and relative endurance may both contribute to the risk of work-related accidents and cumulative musculoskeletal injury. Because grip force and endurance are unrelated, ergonomists should consider which factor is most important and appropriate for their design and research goals. Measurements of the forearm and hand were found to be better predictors of grip strength than were height and weight [6] so that anthropometry of handforearm. The ability to predict strength was most accurate for the single-repetition and then declined with increasing duration of the experiment [8]. This research study the hand-forearm anthropometry and the grip strength trying to fi nd a correlation coeffi cient to attribute a linear relation as expected.

Selection of participants 10 no-athletes young adults between 20 and 25 years old were selected for this study. This study included participants being right-handed, the gender selected with fi ve (5) men and fi ve (5) women. Also, it was established as a condition that the individuals were healthy at the time of collecting data and there were no previous musculoskeletal disorders. The participants were informed previously about the study and they were willing to participate according to an informed consent (Nijhawan et al.). [9]. For an optimal data collection, the procedure to be followed was carefully explained to the participants. (Fig 1).

Flexures (joint lines) are the major markings found in hand commonly crease the skin across the fl exor surfaces of the wrist, palm, and digits and are the sites of folding of the skin during movement. These fl exures are useful landmarks for measurements from the hand [4]. Hand length - distance from the Interstylion (middle point of the line connecting the Stylion Radiale and the Stylion Ulnare) to the Dactylion (tip of the middle fi nger). The hand width - the distance between Metacarpal Radiale and the Metacarpal Ulnare. Palm length - the distance between the mid-point of the distal transverse crease of the wrist and the most proximal fl exion crease of the middle fi nger. Finger lengths are measured as the distance between proximal fl exion creases of the fi nger and the tip of that fi nger. Three other measurements were taken on each person’s forearms. Forearm length was measured as the distance from the tip of the olecranon process to the styloid process of the ulna (Fig. 3). Forearm circumference was taken 5 cm from elbow crease, and circumference of the wrist was taken at the wrist fold, just distal to the ulnar styloid process [6]. These measures were taken with a Vernier caliper.

Handgrip test For measuring grip strength, a Jamar hand dynamometer was used, the Jamar is small and portable but relatively heavy (1.5 lb) hydraulic dynamometer. The dial reads force in both kilograms and pounds, with markings at intervals of 2 kg or 5 lb and can determine a maximum force of 90 Kg, has fi ve adjustable positions, as well as, it is the most widely cited in the literature and accepted as the gold standard by which other dynamometers are evaluated and it has the highest accuracy of the instruments tested in [10]. It requires 3–4 pounds of force to make the indicator needle move, which may be inappropriate when measuring grip strength in very weak patients and the reading error is reported to be greater at lower loadings. The calibration accuracy should be checked on new machines, and the manufacturers recommend annual or more frequent calibration if used on a daily basis [8]. At the time of measuring the grip strength, people had to have the hands dry and clean, since these physical conditions could affect the strength of grip, and they had to form a 90-degree angle between the arm and forearm. Data were taken from both hands.

After ordering the data collected between anthropometry of the hand and arm together with the forces, a total of 240 data were obtained. For the data analysis, descriptive statistics are used, through which averages and deviations were calculated to fi nally proceed to fi nd a Pearson correlation coeffi cient to know if there is a relationship between the grip strength and the hand measurements. Likewise, the data were represented as discrete variables, also by inferential statistics [11], it is deduced that none of the individuals has exercise routines where it strengthens the hands and the forearm. The used formulas were: (eq 1,2,3).

Pearson correlation coefficient (PCC) r is a measure of the linear correlation between two variables X and Y that has a value between +1 and −1, where 1 is a total positive linear correlation, 0 is no linear correlation, and −1 is a total negative linear correlation. It is widely used in the sciences [12]. (tab 1).

Hand, wrist, and forearm measurements were taken to the participants (see Table III). Regarding table IV, the average handgrip strength measured in Jamar hand dynamometer shows a clear difference in gender as all men have a superior strength over women, although, measures on men have a higher standard deviation than women. (Tab 3).

As seen in Figure 1 and table V, regarding men, it was found in both, right and left hands similar results concerning hierarchy (weak) in the thumb and the middle fi nger. Likewise, all the fi ngers and hand have a direct relationship with grip strength since no measurement marked a null correlation. (Fig 2).

There is a discrepancy between hands as the width of the hand, and the length of palm has an increase in Pearson coeffi cient (r) in the right hand disagreeing with the opposite hand in both genders.
Regarding the length of the hand, in both genders, it is noticed that the correlation is weak and very weak in men and women. Although, in the right hand of women there is a signifi cant hierarchy, differing from the left hand that is very weak. In the analysis between genders, there are coincidences in the hierarchy in the right hand of men and women in three measures, the two previously mentioned and the middle fi nger, while in the left hand there are similarities in the length and width of the hand and the fi ngers F2 and F4.
According to the measurements on the forearm, it should be noticed that in men there is a negative correlation in the maximum circumference of the forearm, which tells us that there is an inverse relationship between both measures, as one increases another decrease, something that would make us frown because it seems illogical. In women, a negative relationship was also found in this measure.
Although they are not coincident, there is a correlation in the circumference of the wrist in men with a hierarchy moderate and signifi cant for right and left hand respectively. This correlation is very low in women (null and weak for right and left hand), as well as, Pearson coeffi cients are positive in the right hand and the left negative, thus, in women, this measure cannot be considered.
In men, there is a clear discrepancy in the length of the forearm, because in the right hand it shows a signifi cant relationship while on the left it is null. Between genders, a negative and weak relation was found in the measurement of the maximum circumference of the forearm.

It could be inferred that the way in which force is applied varies between the hands. Because the test was applied to righthanded individuals, there is a tendency in which the correlation increases in the right hand in some measures.
It seems that the hierarchy of finger by finger cannot find something completely defined, it is advisable to take other measures in considerations such as the taken into account in [13] where it is advisable to consider all the possible measures concerning the hand in different positions.
The average maximum strength of the hand showed an expected result, a clear difference between men and women as the force exerted by a male is stronger than a female individual. It is found in [5] that 90% of women produced less strength than men. Even the results of female national elite athletes indicate that the level of strength attainable by extremely high training will rarely exceed 50% of untrained men. These results are related to the existence of an appreciable difference due to the difference in body mass.
The results obtained by the fingers are not the same as those found in [9]. Since in this investigation it was found that the force exerted by the fingers they had the following order - Medium, Annular, Index and Pinky. - Instead, the results were randomized, without any clear trend.
Grip strength can contribute to the risk of work-related accidents and musculoskeletal injuries and the risk increase as age increase [14]. It is recommended to study the relationship between the risk of work-related accidents and relative endurance. Because of ergonomists must consider which factor is most important and appropriate for their design [15]. In summary, hand anthropometry has a direct linear relationship with the grip strength since no measurement was null in the results. As well as, the strongest relationships found were in the width and length of the palm, and the circumference of the wrist.
Future studies have to consider all possible measures of the hand anthropometry in all the relevant positions of the hand with the purpose of obtaining more accurate results. It is recommended to take into account standards to measure anthropometry [16] – [19] and to enlarge the number of variables in different studies like the role of muscle loss [20] and the effect of elbow position [21]. Finally, the standard deviation of average grip strength that the Jamar hand dynamometer shows have to be considered for the analysis of data.