Relationship of Digit Ratio With Cardiovascular Endurance

This first chapter represents a review of the conducted study. In this chapter, there are several subtopics that have been reviewed. The following topics provide the descriptions regarding to background of the study, statement of the problem, research questions, hypotheses involved, conceptual framework, significance of the study, and definition of terms that been used in this study. Lastly, the structure of this study is outlined in the last part of the chapter.


Application of digit ratio which is known to be related to prenatal testosterone hormone had been used widely across the world and its submission in the area of sports, health and fitness had attracted a swarming interest among practitioner and generated many interesting findings. However, in the midst of discovering the application of digit ratio which mainly focused on adults, interest towards the children is still lacking which bring towards the establishment of this study.

Digit ratio have stirred considerable amount of research in relation with various traits of putatively linked to sex hormone (Putz, Gaulin, Sporter, & McBurney., 2004). Known as the ratio between the second digit, which is the index finger and the fourth digit, the ring finger had shown diversified results with several researcher reported significant correlations between digit ratio and such diverse traits as fertility, sexual attitudes and orientation, status, cognitive abilities, health and athletic prowess (Manning, Churchill & Peters, 2007; Coates, Gurnell & Rustichini, 2009; Manning, 2002a; Manning, 2007; Williams, 2000).

The association between pattern formation and numbers of prenatal testosterone and estrogen may lie in the actions Homeobox or Hox genes in vertebrates, including humans, the Hox gene family is vital for the differentiation of both the urinogenital system (including the testes and ovaries) and the digit (Herault, Fradeau, Zakany & Ulnaless., 1997). The sexual dimorphism is determined as early as the 14th week of fetal life, and remains unchanged at puberty.

In children, digit ratio has been reported to be associated with measures of fetal growth, congenital adrenal hyperplasia, developmental psychopathology, autism and Asperger’s syndrome (Manning, 2004). Hence, if digit ratio is associated to prenatal testosterone and oestrogen then the differences such as finger ratio should also be determined in utero. Thus indicate that children should reflect differentiation of digit ratio which is fundamentally the same as in adults.

Preceding information of major health problems and their threat factors towards children, abundant field based fitness test batteries have been developed to assess fitness in this population. In conjunction with the issues, major reviews covering the matter involved in obtaining accurate and reliable measurements have been published and this include the application of relative length of 2nd (index finger) and 4th (ring finger) as a predictive intervention to be used in diagnosis, prognosis, and in early life-style interventions which may delay onset of disease or facilitate its early detection (Manning & Bundred., 2000)

Precise measurement of children’s activity is thought-provoking, as the application is characteristically irregular and recurrent; consist of regular, short sessions. However, health related fitness is notoriously difficult to measure and these difficulties are particularly exacerbated when assessing activity in children. Numerous methods exist for the measurement of health related fitness. Selection of a measurement method depends on the purpose of the evaluation, the nature of the study population, and the resources available. The various components of health related fitness can be assessed accurately in the laboratory and, in many cases, in the field by using a composite of performance tests.

Valid and reliable assessment measures are critical for identifying relevant trends in the activity patterns of young people and for determining the impact of intervention programs and curriculum implementation. Measures of health related components have been used for many years with children; however, these measures may not accurately reflect levels of their health.

Prenatal testosterone has been shown to stimulate anabolic process in skeletal muscle and appears to be principal hormone responsible for the development of strength. Testosterone level increases during early stage of puberty to rapid increase in mid-late puberty in boys whereas high level of oestrogen causes inhibition of muscle growth as a result of skeletal maturation (Manning, Trivers, Thornhill & Singh., 2000). Muscular strength improvement among children are negatively associated with changes in overall adiposity (Ruiz, 2009). Clinical and invasive muscle strength measurement of different muscle group is time consuming and a quick and simple measurement might provide a good indication of general muscle strength. Therefore, in this study the implementation of digit ratio is predicted could be used as measuring tools for muscle strength as it had been found to be correlate with prenatal testosterone which is found to be significant with strength among adult male (Fink, 2006).

Furthermore, prenatal testosterone exposure is believed to have an impact on the fetal cardiovascular system with higher levels of testosterone possibly assisting in the development of more efficient running economy (Manning et. al., 2007). There is a strong evidence signifying that cardiorespiratory fitness in childhood and adolescence is a predictor of cardiovascular disease risk factors such as abnormal blood lipids, high blood pressure and overall and central adiposity later in life (Ruiz,2009). Adverse CVD (Cardiovascular Disease) risk factors during childhood also seem to track into adulthood (Andersen, 2004) with evidence indicating that the main cause of CVD has their origin in childhood and adolescence (Mc.Gill, 2000; Strong, 1992). Therefore application of digit ratio measurement will be used in this study as a predictor to assess cardiovascular endurance among school.

Rapid advancement in socioeconomics situation in many countries in Asia, including Malaysia, has resulted in significant changes in the lifestyle of communities which also affect children in this country. Obesity is associated with adverse health outcomes among both children and adults (Freedman et. al., 2001) and overweight status tends to track from childhood into adulthood (Must, 1992). Due to the treatment of obesity is unsuccessful frequently; primary prevention of obesity has become an important public health priority. Many experts have recommended that public health initiatives to prevent obesity should begin with our youngest children. Therefore, digit ratio which is closely related to prenatal testosterone hormone is predicted in this study to have direct relationship towards body composition physical level among school children.


In studies investigating the primary or secondary prevention of cardiovascular diseases, the major component of physical fitness that has been related to cardiovascular health or risk has been cardiorespiratory fitness or capacity (also referred to as cardiovascular, aerobic, or endurance fitness or capacity). Although other components of physical fitness, such as muscle strength or endurance, may relate to some aspects of cardiovascular health, few data document these relations.

One of the major reasons for measuring cardiovascular fitness in studies of the relation between physical activity and health is that habitual physical activity status is one of the major determinants of cardiovascular fitness. Other determinants include age, sex, heredity, medical status, and selected health-related behaviours (Malina & Bouchard, 1989). Thus, tests of cardiovascular fitness can be used as objective, surrogate measures of physical activity status with the understanding that factors other than activity influence the results. The magnitude of the effects of these other factors is generally reduced when changes in fitness are measured to verify changes in activity status.


Muscle strength can be measured during performance of either static or dynamic muscle contraction (Wilmore, 1989). Like muscle endurance, strength is specific to the muscle group, and therefore the testing of one muscle group does not provide accurate information about the strength of other muscle groups (Clarke, 1973). Thus, to be effective, strength testing must involve at least several major muscle groups, including the upper body, trunk, and lower body. Standard tests have included the bench press, leg extension, and biceps curl with free weights. The heaviest weight a person can lift one time through the full range of motion is considered the person’s maximum strength.


Obesity in children and adolescents is both predominant and increasing in developed and developing countries and is therefore deemed a major international public health issue. Moreover, obesity tracks from adolescent to adulthood with obese adolescents at increased risks of morbidity and mortality in adulthood, irrespective of adult weight status. Obesity caused by chronic energy imbalance resulting in the storing of excess energy adipose tissue. Measuring physical activity following obesity treatment is important to elucidate how treatment has impacted on behaviour that influences energy balance.


During the last decades, a great deal of attention has been devoted to the fitness of children and adolescents. As a result, numerous field based test batteries have been developed to assess fitness in this population. Field test provide reasonable alternative since they are time-efficient, low in cost and equipment requirement can be easily administered to a large number of people simultaneously. However, in order for the assessment to be considered, it should measure what it is supposed to measure. Therefore, digit ratio which is found to be negatively correlating with prenatal testosterone levels in humans could be established as a valid predictor to assess health related fitness and physical activity level will be discovered in this study.

Many reported relationships of digit ratio are restricted to adult population. Small amount of research relating digit ratio with children had restricted the application of this method to act as an alternative field test. Biologic development of school age children occurs intensely, unevenly and differently among individuals. Greater sensitivity to detect biological sources of variation in children ability to exert maximum muscular effort (muscular strength) and the ability of heart to deliver oxygen to working muscle and sustain for long period of time (cardiovascular endurance) is believe could be predicted by digit ratio (prenatal testosterone hormone). If digit ratio in adults correlates with prenatal testosterone, it is expected to be presented in young children as the digit ratio among individuals should not change with growth and digit ratio should show little absolute change with growth in children (Manning et. al., 1998).


The purposes of this study were threefold. First was to identify the relationship of digit ratio with cardiovascular endurance among school children. A secondary purpose of this study was to identify the relationship of digit ratio with muscular endurance among school children among school children. Lastly, the purpose of study was to provide current scientific evidence based data related with digit ratio in relation with body composition among school children that could be implemented as a new measurement intervention on measuring cardiovascular endurance, muscular strength and body composition among school children.


Muscular strength, cardiovascular endurance and body composition are predicted through digit ratio are the main objectives of this study. Therefore, the objectives of this study are:

  1. To determine the relationship between digit ratio and muscular strength among public school children in Selangor.
  2. To measure the relationship between digit ratio and cardiovascular endurance among public school children in Selangor.
  3. To determine the relationship between digit ratio and body composition among public school children in Selangor.

Based on the issues regarding muscular strength, cardiovascular endurance and body composition with digit ratio measurement that need to be addressed, the following hypotheses were formed to identify the outcome of this study. Therefore, for the purpose of this study, the hypotheses are:

Ho1 : There is no significant relationship between digit ratio and muscular strength

among public school children in Selangor.

Ho2 : There is no significant relationship between digit ratio and cardiovascular

endurance among public school children in Selangor.

Ho3 : There is no significant relationship between digit ratio measurement and body

composition among public school children in Selangor.


The outcome of this study is hope could act as an alternative approach on predicting muscular strength, cardiovascular endurance and body composition among children through implementation of simple, quick and reliable digit ratio measurement.

Besides that, this study also hopes could be part of a measurement application for talent identification consideration among children especially school children. Lastly, the significance of this study is hope to provide additional information with relationship of biological marker to identify muscular strength, cardiovascular endurance and body composition among children as current biological testing to identify biological condition among children require laboratory testing only.


The scope of this study is to provide new alternative and reliable method in predicting muscular strength, cardiovascular endurance and body composition among school children in Selangor. This however will limit to only selected physical fitness test and not applicable for comparison with other physical test.

Number of subjects will be used in this study is based on current student intake throughout public school in Selangor with consideration of age. Therefore, from 645 primary school in Selangor, a different amount of subject from different numbers of school may render different outcome.

    1. Digit Ratio

In this study, digit ratio is a relative length between the second finger (index finger) and the fourth finger (ring finger). It is sexually dimorphic with male having a lower mean compared to female and shown to be positively correlated with oestrogen and negatively correlated with prenatal testosterone.

  1. Cardiovascular Endurance

A health-related component of physical endurance fitness that relates to the ability of the circulatory and respiratory systems to supply fuel during sustained physical activity and to eliminate fatigue products after supplying fuel which in this study indicate through bleep test.

  1. Muscular Strength

Muscular strength is another health-related component of physical fitness that relates to the amount of external force that a muscle can exert. It is important as every human body movement require certain amount of strength in order to execute certain activities. This will be determine in this study through handgrip strength test.

  1. Body Composition

Body composition refers to the combination of lean tissue and fat tissue in the body. In this study, body composition among school children will be determine through several measurement method which were the two sites skinfold measurement and body mass index in order to identify which method could be a valid predictor of body composition.

  1. Physical Activity

Physical activity is defined as any bodily movement produced by the contraction of skeletal muscle. Physical activity can be categorized by several variables including type and intensity. In this study, every school children physical activity level will be predicted through series of fitness testing as well as digit ratio measurement in order to determine current health related component level of school children especially in Selangor.

  1. Obesity

Obesity is defined as abnormal or excessive fat accumulation that may impair health. Fundamental cause of obesity is an energy imbalance between calories consumed and calories expended. Changes in dietary and physical activity patterns are often the results of health and fitness implication among children which is also mainly the reasons why this research is conducted.

  1. Body Mass Index (BMI)

Body mass index is a simplify calculation of weight-for-height that is usually used to classify overweight and obesity in adult and children. A BMI greater than or equal to 25 is oversight while BMI greater than or equal to 30 is obesity.

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