two main categories, namely general fitness tests and occupational performance tests (Hauschild et al. 2017). Traditionally, the physical performance of soldiers has been tested using population-based aerobic and muscular fitness tests such as a 12-minute running test and the maximum number of push-ups in one or two minutes (Knapik et al. 2006; Santtila et al. 2006). According to a systematic review by Herrador-Colmenero et al. (2014), the most common fitness component assessed in the military and security forces was aerobic fitness (81% prevalence among studies included in the review), with the 2.4 km run being the most commonly used test. Muscular fitness (e.g. sit-up and push-up tests) and body composition (e.g. BMI, percent body fat) were the second and third most commonly assessed components of fitness, with prevalence of 69% and 64%, respectively (Herrador-Colmenero et al. 2014).
2.6.1 General physical fitness tests
Regarding general physical fitness components, Hauschild et al. (2017) reported that the highest correlations with performance on twelve common physical military tasks, including load carriage, numerous manual materials handling tasks, combative movements and their combinations, were found in tests assessing aerobic fitness, lower body strength and upper body muscular endurance. The most valid and reliable field assessments of aerobic fitness included timed 2.4‒4.8 km running tests, vertical and horizontal jump tests to assess lower body strength and power, and push-up tests to evaluate upper body muscular endurance (Hauschild et al. 2017).
As already noted, assessment of aerobic fitness in soldiers is important due to its associations with performance in several military tasks (Hauschild et al.
2017; Nindl et al. 2015). Based on the guidelines of the American College of Sports Medicine (ACSM), direct assessment of aerobic capacity (VO2max, commonly expressed relative to body mass) requires measurement of oxygen and carbon dioxide from the expired air during a graded endurance test until exhaustion (ACSM 2014, 73-75). This method requires a well standardized environment (e.g.
laboratory), and is therefore often not feasible for large study samples, such as in the military. Several indirect methods have been developed for military purposes.
In the Finnish Defence Forces, the most commonly used method of assessing aerobic fitness in conscripts and professional soldiers is the 12-min running test, and performance on this test is strongly correlated (r = 0.90) with relative VO2max (Cooper 1968). Similar relationships have been found between distance-based running tests (e.g. 3.2 km running test) and relative VO2max among soldiers (Mello et al. 1988; U.S. Army Public Health Command 2014, 35).
Muscular (maximal) strength has been acknowledged as the most relevant component of fitness from a military performance perspective (Nindl et al. 2015).
However, while fitness test batteries used by the armed forces extensively focus on muscular endurance, methods of assessing muscular strength are very rarely included in their test batteries (Nikolaiditis et al. 2019). Traditional measures of dynamic muscular strength within civilian as well as military populations include 1-5RM squat, leg press, deadlift and 1RM bench press or shoulder press (ACSM 2014, 96; Foulis et al. 2017b). While less sophisticated equipment is needed for the dynamic tests, reliable 1RM performance requires a good, safe technique and practice (ACSM 2014, 96-98). Isometric devices have been developed to increase accuracy and standardization of muscular strength measurements. In general, methods of measuring isometric peak force produc-tion of the lower extremity extensor muscles have shown good reliability and construct validity among trained and untrained males (Drake et al. 2017).
The current test battery for assessing muscular fitness in the Finnish Defence Forces consists of standing long jump, 1-min sit-ups and 1-min push-ups (Defence Command, 2019). Standing long jump has been shown to assess explosive strength (power) of the lower extremities with a similar reliability as vertical jump tests (Markovic et al. 2004). Since standing long jump performance has also been shown to strongly correlate with performance on military tasks
such as single lift and stretcher carry (U.S. Army Public Health Command 2014, 30), it has been recommended as a field-expedient option for assessing muscular power in soldiers (Nindl et al. 2015). Regarding muscular endurance of the upper body and trunk, repeated push-ups and sit-ups (or curl-ups) have been identified as simple field tests by the ACSM (2014, 99-101). Vaara et al. (2012) found a moderate correlation (r = 0.61) between 1-min push-up and maximal isometric bench-press performance. Moderate relationships have also been reported between upper body muscular endurance test results and military tasks such as crawl (pooled r = 0.66), repeated lift and carry (pooled r = 0.62) and stretcher carry (pooled r = 0.58), while correlations between core/trunk muscular endurance and military tasks seem to be weaker (Hauschild et al. 2017).
Body composition is included as a component of health-related physical fitness in some definitions (ACSM 2014, 3; Nindl et al. 2015). Anthropometric measures such as body mass and stature can be used to calculate BMI. In addition, the amounts and distributions of muscle or fat can be assessed indirectly by measuring body part circumferences or skinfolds (ACSM 2014, 63-69), or more accurately by using more advanced technology. While the most precise criterion methods such as computed tomography and dual-energy X-ray absorptiometry (DXA) are very expensive and require laboratory conditions with highly trained personnel, there are indirect but more feasible options for military use. Multi-frequency bioelectrical impedance analysis (BIA) is based on differences in electric conductivity of tissues. The electrical current is conducted differently through the extracellular (ECW) and intracellular (ICW) water as a function of the current frequency. According to Ling et al. (2011), six different electrical fre-quencies are used to predict the ICW and ECW components of total body water (TBW). While the low-level frequencies (≤ 50 kHz) rely on the conductive prop-erties of extracellular fluid, high-level frequencies (≥ 250 kHz) are conducted through both ICW and ECW. Thus, muscle mass can be estimated as TBW (ICW + ECW)/0.73. Fat mass is calculated as the difference between total body mass and muscle mass. A general overestimation of muscle mass and underestimation of fat mass, as well as fat percentage, has been reported in studies comparing BIA and DXA methods (Aandstad et al. 2014; Antonio et al. 2019; Sillanpää et al. 2014).
However, good reliability values have been reported for multi-frequency BIA against DXA for the assessment of muscle mass, fat mass and fat% in adult males within the normal BMI range, especially when the measurement standardization (e.g. timing of measurement, clothing, fasting) has been performed properly (Aandstad et al. 2014; Antonio et al. 2019; Ling et al. 2011; McLester et al. 2020).
2.6.2 Occupational physical performance tests
While the most commonly used physical fitness tests among the armed forces assess aerobic capacity and muscular endurance, army soldiers engaged in combat situations require an adequate level of anaerobic capacity to perform high-intensity assignments in rapidly changing, life-threatening situations (Kraemer & Szivak 2012). Such high-intensity tasks typically include sprinting,
rushes, climbing, quick changes in direction, jumping, crawling, lifting and carrying loads, and casualty evacuation (O´Neal et al. 2014).
The relevance of general fitness tests for assessing combat readiness has been questioned in a number of studies, and it has been argued that such health-related fitness tests performed in light sports clothing and using the person´s own body mass as resistance favour soldiers with low body mass and high relative endurance capacity (Vanderburgh & Crowder 2006; Vanderburgh 2008). Yet, operative military duties are often performed whilst wearing combat gear and body armor, which increase the amount of load being carried (Knapik et al. 2004;
O´Neal et al. 2014; Taylor & Groeller 2003). The increase in the weight of the carried load negatively influences the physical performance of soldiers during tasks of longer (Crawford et al. 2011) and shorter (Billing et al. 2015; Jaworski et al. 2015; Laing-Treloar & Billing 2011; Larsen et al. 2012) duration (Charlton &
Orr 2014). Previous studies have collectively demonstrated that less body fat (Crawford et al. 2011; Kusano et al. 1997; Lyons et al. 2005) and more fat free mass (Kusano et al. 1997; Lyons et al. 2005) are beneficial body composition factors in such tasks.
These findings have led to the development of more occupationally relevant tests that evaluate military task-specific physical performance (Hauschild et al.
2017; Richmond et al. 2008; Payne & Harvey 2010; Vanderburgh & Crowder 2006).
Typical occupational physical performance tests include walking or running various distances with combat load (Billing et al. 2015; Nindl et al. 2015; Santtila et al. 2010; Taylor & Groeller 2003), manual materials handling (Richmond et al.
2008), lifting and carrying loads (Carstairs et al. 2016), and obstacle courses (Jaworski et al. 2015; Larsen et al. 2012) that include mimicking of tactical movements used in combat situations. Foulis et al. (2017a) reported relatively high reliability measures, including intra-class correlations (ICCs) of 0.76-0.96 and standard errors of measurement (SEM) of 3-16% among several occupational tests including sandbag carry, casualty evacuation, move under fire, carrying and manual handling of tank ammunition, and a 6.4-km march. The highest reliability values were observed in the casualty drag test and the 6.4-km march, while longer lasting learning effects were observed especially in tests requiring manual materials handling (Foulis et al. 2017a). Collectively, these simulations consist of various military-specific test protocols for assessing anaerobic capacity and maneuver abilities of soldiers. Furthermore, such tests can be used to develop optimized physical training programs for soldiers preparing for a specific aim such as a military occupational specialty or an international military operation (Carlson & Jaenen 2012; Frield et al. 2015; Mala et al. 2015).
2.7 Physical training to maintain or improve military