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13.1 Physical Fitness

13.1.1 Rationale and Definition

There exists no unique and clear definition of physical fitness although efforts have been undertaken for long to find one. Already Caspersen et al. (1985) saw the need of a standardised terminology to obtain comparable results and to gain a better understanding of the relation between physical fitness, physical activity, exercise and health. In contrast to physical activity (see Chap. 7, of this book) that seeks to survey the type, duration, frequency and intensity of an activity carried out as a process, physical fitness measures a status that is rather stable over a certain period of time. Physical activity and physical fitness are weakly associated (Martínez Vizcaíno et al. 2008). This weak association may be explained by the fact that the validity and reliability of the measurements vary strongly between physical activity and physical fitness (see Martínez Vizcaíno et al. 2008). Moreover, physical fitness is supposed to be primarily determined by physical activity, but is also influenced by non-modifiable factors such as age, sex and genotype, as well as by modifiable factors such as smoking, obesity and medication (Lee et al. 2010). Consequently, physical fitness and physical activity were measured independently in the IDEFICS (Ahrens et al. 2011) and I.Family (Ahrens et al. 2017) studies.

One well-accepted definition of physical fitness is given in the glossary of the Report of the Surgeon General on Physical Activity and Health (US Department of Health and Human Services 1996), which goes back to Caspersen et al. (1985). It defines physical fitness as “a set of attributes that people have or achieve that relates to the ability to perform physical activity.” The Report of the Surgeon General explicates physical fitness as the “ability to carry out daily tasks with vigour and alertness, without undue fatigue, and with ample energy to enjoy leisure-time pursuits and to meet unforeseen emergencies,” which follows the idea of Clarke (1971) as presented in the first issue of the Physical Fitness Research Digest. This annotation uses an undetermined wording, e.g. the measurement of undue fatigue, and therefore it is not very stringent.

In the 1990s, two consensus conferences have been held with the intent to find a standardised terminology and understanding of physical fitness, activity and health (Bouchard et al. 1990, 1994). In the latter reference, physical fitness is understood as a composition of morphological fitness, bone strength, muscular fitness, flexibility, motor fitness, cardiovascular fitness and metabolic fitness.

Recent efforts to standardise the terminology refrain from claiming to give the one and only definition but rather give one “definition that is consistent with experts” (Corbin et al. 2000). Corbin et al. (2000) thus present the following Table 13.1 describing the aspects of physical fitness and its multi-dimensional hierarchical nature which will be discussed in more detail in the following section.

Table 13.1 Components describing physical fitness.
Full size table

Skill- or performance-related fitness is typically associated with those fitness aspects that vary with a sport activity (e.g. distance running vs. weightlifting), i.e. that are necessary for a good sports performance, whereas health-related fitness comprises the components that are closely related to health (Howley 2001). Performance-related fitness is sometimes termed motor fitness. Obviously, health- and skill-related fitness aspects interact strongly and a general motor ability is required (Vedul-Kjelsås et al. 2012). Physiological fitness components are related to biological systems that are influenced by one’s level of habitual physical activity and do not measure performance (Bouchard et al. 1990; Corbin et al. 2000).

The classification of body composition as a health-related fitness component is debatable. Bouchard et al. (1994) classify body composition as a morphological fitness aspect as this covers body composition factors such as body circumferences, body fat content and regional body fat distribution whereas, e.g. Howley (2001) or Caspersen et al. (1985) categorise it as a health-related fitness component which is more common today.

However, the most recent position stand of the American College of Sports Medicine (ACSM) still follows the approach to find an expert consent and describes physical fitness as a “physiological state of well-being and that reduces the risk of hypokinetic disease, a basis for participation in sports and good health, which enables one to complete task of daily living. Components include cardiorespiratory endurance, muscle strength endurance, flexibility and body composition” (Donnelly et al. 2016). These rather broad definitions implicate a careful decision on what measures of physical fitness are included in study protocols, in particular, when children and adolescents are studied which is the case in the IDEFICS and I.Family studies. Consequently, the assessment of physical fitness in both studies is based on reference standards following the complex construct of physical fitness (De Miguel-Etayo et al. 2014).

13.1.2 Physical Fitness Components

This section describes briefly the components used above to assess the term of physical fitness. It is based on the glossary from the Report of the Surgeon General (US Department of Health and Human Services 1996) and the review by Corbin et al. (2000).

Health-related fitness components:

  • Body composition describes the relative amounts of the body components. These include muscle, fat, bone and other vital body parts (see also Chap. 3 of this book).

  • Cardiovascular fitness, cardiorespiratory fitness and cardiorespiratory endurance are often used synonymously in the literature. They describe the ability of the circulatory and respiratory systems to supply oxygen when being sustainably physical active.

  • Flexibility describes the range of motion available at a joint.

  • Muscular endurance covers the ability of the muscle to continue to perform without fatigue.

  • Muscular strength describes the ability of the muscle to exert force.

Skill-related fitness components:

  • Agility describes the ability to rapidly change the position of the entire body in space with speed and accuracy.

  • Balance describes the ability to maintain equilibrium while stationary or moving.

  • Coordination describes the ability to use the senses, such as sight and hearing, together with body parts in performing motor tasks smoothly and accurately.

  • Power is the rate at which one can perform work.

  • Speed is the ability to perform a movement within a short period of time.

  • Reaction time covers the time elapsed between stimulation and the beginning of the reaction to it.

Physiological fitness components:

  • Metabolic fitness describes the state of metabolic systems and variables that can be altered by an increased physical activity or regular endurance exercise without the requirement of a training-related increase of maximal oxygen uptake (VO2 max). This includes blood sugar levels, blood lipid levels and blood hormone levels (Corbin et al. 2000).

  • Morphological fitness describes fitness that is related to body composition, e.g. body fat content and distribution, waist-to-hip ratio.

  • Bone integrity or bone strength is described by the area of bone, bone mineral content or density and bone structural properties.

13.2 Importance of Physical Fitness

The most important purpose of physical fitness assessment in children and adolescents is its use as a predictor for later health outcomes. Ortega et al. (2008) give a detailed review on the association of physical fitness with obesity, cardiovascular disease, skeletal health, cancer and mental health. They focus on cardiorespiratory fitness, muscular fitness and speed/agility as physical fitness components. Ortega et al. (2008) report strong association of obesity and cardiorespiratory fitness levels, association of cardiovascular risk factors and cardiorespiratory and muscular fitness and association of skeletal health and muscular fitness and speed/agility. Cardiorespiratory fitness and muscular fitness support among other compensation of chemotherapy-induced neuropathy and muscular atrophies of cancer patients. In addition, association of cardiorespiratory fitness with depression, anxiety mood status and self-esteem is reported. Ruiz et al. (2009) published a systematic review that takes additionally into account quality of life and lower back pain. For lower back pain, no relationship with body composition can be established from the literature search and inconclusive evidence is available on the relationship of lower back pain and flexibility.

There is evidence that cardiovascular diseases are determined during childhood, i.e. risk factors track into adulthood (Raitakari et al. 2003; Andersen et al. 2004; Högström et al. 2014). As cardiovascular diseases are the most frequent causes of mortality in the European Union (EU) (Eurostat 2017), the assessment of health-related fitness components which are risk factors for cardiovascular diseases is most important (e.g. Ortega et al. 2008; Kvaavik et al. 2009).

However, it should not be forgotten that 3.5 million osteoporotic fractures occur in Europe every year, representing a substantial and increasing burden on healthcare systems in many countries (Kanis et al. 2017). Strength and speed are directly related to bone quality (Vicente-Rodriguez 2006). These fitness components can be enhanced by intervention, e.g. training, and prevention (e.g. Ruiz et al. 2009) and the promotion of a healthy lifestyle beginning during childhood is crucial (Terre 2008).

At the same time, it must be recognised that the genetic background and social factors largely determine physical fitness in children. Therefore, the modification of individual and social determinants of physical activity must be in the focus, even if this will not affect the level of physical fitness directly (Martínez Vizcaíno et al. 2008).

Moreover, surveying physical fitness of children offers the opportunity to monitor children’s health and the efficacy of prevention programmes (Ortega et al. 2008; Finger et al. 2014).

13.3 Measurement of Physical Fitness Components

The following section discusses the measurement of physical fitness components. We will focus on components that were included in the IDEFICS and I.Family studies (see Sect. 13.4). The measurement of health-related fitness aspects is highly developed as physiological dimensions are studied where these measurements can be obtained most exactly in a laboratory setting. However, laboratory methods typically require expensive equipment and are personnel intensive. They are therefore not feasible in large-scale population-based studies where appropriate surrogate measures have to be used instead. In contrast to physiological dimensions, laboratory methods to measure skills like balance or agility are rare. Hence, valid field methods have to be used and strict protocols for studies, General Survey Manuals (for access see Sect. 13.6) were worked out that provide detailed protocols for all examinations to be followed by trained field staff.

Cardiovascular endurance describes an individual’s aerobic capacity, e.g. the ability to supply oxygen to the working muscles during an activity (Morrow et al. 2000). It is captured best by the maximal oxygen consumption (VO2 max) that is measured during an exhaustive exercise. In a laboratory setting, an exercise is conducted, e.g. on a treadmill, cycloergometer or a step-bench and the expired gases are monitored, i.e. by a gas analysis system, to determine the maximum exhaustion reached. When laboratory testing is not feasible, e.g. in large epidemiological studies, field methods have to be applied. These methods aim to estimate the maximal oxygen consumption from other parameters as Morrow et al. (2000) report: From a step test, for example, VO2 max can be estimated by assessing the heart rate after exercise and the one-minute recovery heart rate, and exploiting the linear relationship between workload, heart rate and VO2 max. The Rockport one-mile walk test accounts for sex, weight, age and ending heart rate to obtain a valid VO2 max estimate. The 20 m shuttle run test (also known as the beep test) measures how often running between two lines 20 m apart in time to recorded beeps (in an increasing frequency) is accomplished. It can be performed by children and has a longstanding history (e.g. Tomkinson et al. 2003). The recorded shuttles are transformed to VO2 max values (e.g. Leger and Lambert 1982) or used as a score without transformation. Lang and colleagues demonstrate that the 20-m shuttle run test is a very useful and powerful indicator for population health in children and youth (Lang et al. 2018).

The gold standard to assess flexibility in a laboratory setting is radiography, although feasibility is limited due to radiation (Miller 1985). A flexometer allows direct assessment of the possible range of motion. Alternatively, the sit and reach test which specifically measures the flexibility of the hip back (mainly lower back) and hamstring muscles, by measuring how far forward an individual is able to bend, can be applied. The backsaver sit and reach test, a modified version, measures the flexibility of the right and left leg separately (Chillon et al. 2010). It can be easily accomplished by children. When analysing results, it should be borne in mind that a limitation of this procedure is that people with long arms and/or short legs would get a better result.

Muscular strength and endurance can be measured in a laboratory setting with the help of computerised dynamometers, which track force, work, torque and power generated throughout a range of motion. Controlling the speed of the movement can be realised by isokinetic dynamometers. Strength is defined as the peak force measurement whereas endurance is captured by fatigue rates in force production during a set of repetitions (Morrow et al. 2000). Field methods focus on particular muscle groups, e.g. the upper or lower body. Muscular endurance is typically assessed by counting the number of pull-up, push-ups or sit-ups an individual can accomplish which is not feasible for small children. Therefore, muscular strength instead of muscular endurance is measured to describe the muscular fitness of a child. The force that is generated by a contracting muscle can be measured with a cable tensiometer in a laboratory setting. A field method that provides equivalent information is a one-repetition maximum test. For example, weights for weightlifting or the bench press are increased such that the individual is able to perform one repetition only. Muscular isometric strength of children can be easily assessed using dynamometers; i.e. handgrip. The dynamic strength of the lower extremities can be measured withstanding broad jump or vertical jump tests. In both cases, the leg power can be calculated by the distance that was overcome, which can be transformed into Watts (e.g. Sayers et al. 1999).

Balance as one important skill-related fitness aspect can be measured either static or dynamic; that is the ability to maintain equilibrium when stationary, respectively, when moving. A laboratory method to assess balance is computerised dynamic posturography. Force plates or similar devices are used to measure ground reaction forces. From these ground reaction forces, among others, centre of pressure, displacements, sway of the centre of mass, equilibrium score, postural stability index (PSI) can be computed (for a review of methods see Chaudhry et al. 2011). The measurement obtained by performing a Flamingo or other balance tests is the time an individual can maintain static equilibrium on one leg. Protocols describe when equilibrium is lost, e.g. the supporting foot moves in any direction or the non-supporting foot touches the ground. It can easily be accomplished by children.

Agility is the ability to move quickly and to change directions while maintaining control and balance. It therefore has an important speed component. There exists no laboratory method to assess agility. A common field method that can be accomplished by children is a modified shuttle run (e.g. Ortega et al. 2008). The time elapsed while running as quickly as the individual can between two markers covers the speed aspect, the pick-up and dropping off an item cover the control and balance aspect. This method can be performed in groups. Protocols describe the exact distance between markers and the numbers of shuttles to be completed.

Table 13.2, an adaption and extension of the table presented in Caspersen et al. (1985), summarises the measurements that have been discussed in detail. Wood (2008) provides online an extensive list of fitness tests.

Table 13.2 Field and laboratory methods to assess aspects of physical fitness (Morrow et al. 2000)
Full size table

According to Castro-Piñero et al. (2010), the following conclusions on the validity of the field methods can be drawn:

  1. 1.

    The 20m shuttle run test is most appropriate to assess cardiorespiratory fitness. Equations by Barnett (1993, equation (b)) and Ruiz et al. (2008) yield best VO2 max estimates.

  2. 2.

    The backsaver sit and reach test has moderate validity to assess hamstring and low back flexibility.

  3. 3.

    The handgrip strength test with an extended elbow and adapted grip span is a valid test to assess upper body maximal strength. Due to the small number of studies available in the literature, there is limited evidence that the standing broad jump can assess explosive leg power validly.

Field methods for fitness testing often lack validity and reliability and further research is needed here (e.g. Ortega et al. 2008 and above).

13.4 Assessment of Physical Fitness in the IDEFICS and I.Family Studies

A number of physical fitness test batteries have been developed over the last four decades where the most popular test batteries that are applicable to children and/or adolescents are compared in the following. Table 13.3 covers the FitnessGram (Plowman and Meredith 2013), EUROFIT (Adam et al. 1988), the International Physical Fitness Test (Rosandich 2008) and the Movement Assessment Battery for Children (M-ABC, Henderson et al. 2007). Castro-Piñero et al. (2010) provide a systematic review on the criterion-related validity of existing field-based fitness tests used in children and adolescents, including components of FitnessGram, EUROFIT and the IPTF.

Table 13.3 Comparison of selected fitness test batteries for children and adolescents
Full size table

Obviously, all tests differ in the age groups they address and the exercises to be conducted. Only the M-ABC is suitable for the whole age range surveyed in the IDEFICS study but has a strong focus on motor abilities. It was therefore decided to use a modified EUROFIT test because the EUROFIT test offers a sound assessment of most physical fitness aspects. Furthermore, single to all items of the EUROFIT tests are widely used in other European studies investigating aspects of physical fitness and health, for example, in Spain (Fonseca Del Pozo et al. 2017) and Greece (Arnaoutis et al. 2018) which allows comparability of results. The following tests were included in the IDEFICS protocol:

  1. 1.

    Flamingo balance test

  2. 2.

    Backsaver sit and reach

  3. 3.

    Handgrip strength

  4. 4.

    Standing broad jump

  5. 5.

    40-m sprint

  6. 6.

    20-m shuttle run test

The reasons for using a shortened EUROFIT version were the limited time that was available for single measurements to not further increase the burden for the participating children, in particular, since the assessment of physical fitness was not the major focus of the IDEFICS study. Furthermore, only children 6 years and older were asked to participate in the physical fitness assessment. At a younger age, children are not able to understand and conduct some of the requested exercises correctly. The pre-test showed that children at kindergarten age were not able to complete the requested exercises in reasonable time (Suling et al. 2011). Only the handgrip item was continued in I.Family because it required the least amount of time and effort. Moreover, muscular strength has shown to be a valid and feasible predictor of all-cause mortality (Garcia-Hermoso et al. 2018) and is positively associated with blood pressure in youth (Zhang et al. 2018).

13.5 Practical Aspects When Assessing Children’s Fitness

Several recommendations can be given based on the experiences the field staff gained from the fitness tests, by this expanding the findings of the pre-tests published previously (Suling et al. 2011). In general, the children who participated in the IDEFICS study enjoyed the fitness tests, in particular, the 20-m shuttle run test. Some test items, such as the Flamingo balance test, were easy and quick to apply, whereas sufficient space was crucial to conduct the 20-m shuttle run test and the 40-m sprint test. It would be therefore highly recommendable to use a whole gym, if available, such that clearly defined stations are available for each test item.

Especially for the 20-m shuttle run test, ensuring maximal exhaustion is mandatory. From our practical experiences, we cannot recommend to have each child run the test individually. Instead, we highly recommend (a) to let the children run in groups of 5–10 children, each child on a separate track, and (b) to have an experienced pacemaker from the study team, running on a separate track alongside. Thus, it is possible to measure many children simultaneously, ensure a sound implementation of the test protocol and ensure maximum exhaustion of the children.

13.6 Provision of Instruments and Standard Operating Procedures to Third Parties

All standard operating procedures (SOPs) described in this chapter are provided by the General Survey Manuals that can be accessed on the following website: www.leibniz-bips.de/ifhs after registration.

Each third partner using the SOPs provided in this chapter is kindly requested to cite this chapter as follows:

Brandes M, Vicente-Rodríguez G, Suling M, Pitsiladis Y, Bammann K, on behalf of the IDEFICS and I.Family consortia. Physical fitness. In: Bammann K, Lissner L, Pigeot I, Ahrens W, editors. Instruments for health surveys in children and adolescents. Cham: Springer Nature Switzerland; 2019. p. 277–289.