Bachelor Thesis
HALMSTAD
UNIVERSITY
Exercise Biomedicine, 180 credits
Changes in physical capacity and body composition from military basic training
Biomedicine, 15 credits
Halmstad 2020-05-27
Hannes Fransson
Changes in physical capacity and body composition from military basic training
Hannes Fransson
2020-05-27
Bachelor Thesis 15 credits in Exercise Biomedicine Halmstad University
School of Business, Engineering and Science
Thesis supervisor: Charlotte Olsson Thesis examiner: Åsa Andersson
Abstract
Background: Military basic training is important to prepare the recruits for the physical demands that will be put on them during their service. Recruits need to be both strong and have a high aerobic capacity, which requires well-designed exercise plans.
Aim: The aim of this study was to examine how lower-body power, aerobic capacity, and body composition changes during basic training, from start to end of basic military training and to the end of post training in male recruits in the Swedish Armed Forces.
Methods: Recruits (n = 199; age: 18-50 years) were tested before and after basic military training, and after post training. Lower-body power was tested with loaded vertical squat jumps, performed bilaterally with a load of 30 kg in a smith machine. Aerobic capacity was tested with FM-beep test. Body composition was assessed with bioelectrical impedance analysis.
Results: Lower-body power was not significantly affected during basic training. Aerobic capacity improved during both basic military training (5.4%) and post training (1.9%). Body composition improved during basic military training as body fat mass decreased (- 12.6%) while fat-free mass (2.2%) and skeletal muscle mass (2.3%) both increased. During post training, however, body composition deteriorated as body fat mass increased (10.3%) while neither fat-free mass nor skeletal muscle mass changed.
Conclusion: The results indicate that physical training during post training is suboptimal, as most of the improvements in physical capacity and body composition occurred during basic military training. The lack of improvements in lower-body power suggests that more strength training is desirable for optimal physical training during basic training.
Abstrakt
Bakgrund: Militär grundutbildning är viktig för att förbereda rekryterna för de fysiska kraven som kommer att ställas på dem under deras tjänstgöring. Rekryterna behöver vara både starka och ha en hög aerob kapacitet, vilket kräver väl utformade träningsplaner.
Syfte: Syftet med denna studie var att undersöka hur effektutveckling i underkroppen, aerob kapacitet, och kroppssammansättning förändras under grundutbildningen, från början till slut av grundläggande militär utbildning och till slutet av befattningsutbildningen hos manliga rekryter i Försvarsmakten i Sverige.
Metod: Rekryterna (n = 199; ålder: 18–50 år) testades före och efter den grundläggande militära utbildningen och efter befattningsutbildningen. Underkroppens effektutveckling testades med viktade vertikala squat jumps, vilka utfördes bilateralt med en belastning på 30 kg i en smithmaskin. Aerob kapacitet testades med FM Beep test. Kroppssammansättning fastställdes med bioelektrisk impedansanalys.
Resultat: Underkroppens effektutveckling påverkades inte signifikant under
grundutbildningen. Aerob kapacitet förbättrades under både den grundläggande militära utbildningen (5.4%) och befattningsutbildningen (1.9%). Kroppssammansättning förbättrades under den grundläggande militära utbildningen eftersom kroppsfettmassan minskade (- 12.6%) medan fettfri massa (2.2%) och skelettmuskelmassa (2.3%) båda ökade. Under befattningsutbildningen försämrades dock kroppsammansättningen eftersom
kroppsfettmassan ökade (10.3%) medan varken fettfri massa eller skelettmuskelmassa förändrades.
Slutsats: Resultaten indikerar att fysisk träning under befattningsutbildningen är suboptimal, eftersom de flesta förbättringarna i fysisk kapacitet och kroppssammansättning inträffade under den grundläggande militära utbildningen. Bristen på förbättringar i underkroppens effektutveckling, tyder på att mer styrketräning är önskvärt för optimal fysisk träning under grundutbildningen.
Table of Contents
Background ... 1
Power ... 1
Aerobic capacity ... 4
Body composition ... 6
Aim ... 6
Methods ... 7
Participants ... 7
Study design ... 7
Testing procedures ... 8
Loaded vertical squat jump ... 8
FM-beep test ... 9
Bioelectrical impedance analysis ... 9
Ethical and social considerations ... 10
Statistical analysis... 10
Results ... 11
Participants ... 11
Lower-body power ... 12
Aerobic capacity ... 13
Body composition ... 14
Discussion ... 14
Lower-body power ... 14
Aerobic capacity ... 15
Body composition ... 16
Limitations ... 17
Conclusions ... 17
References ... 18
1
Background
One important aspect of basic training in the military is to prepare the recruits for the physical demands which will be put on them during their service. Basic training in the Swedish Armed Forces consists of two phases (Försvarsmakten, n.d.). The first phase: basic military training (BMT) is performed by all recruits and lasts for twelve weeks. The second phase: post
training (PT) is specific to the recruits’ post within the military and varies in length from three to twelve months. During basic training recruits will be subject to a variety of physical
training (Försvarsmakten, n.d.).
Physical demands in the military requires the recruits to be both strong and have a high aerobic capacity (Santtila, Pihlainen, Viskari, & Kyröläinen, 2015). Many of the physically demanding tasks in the Swedish Armed Forces require both muscular strength and aerobic endurance (Larsson, Dencker, Olsson, & Bremander, 2020). Transport of wounded have been identified by Swedish ground combat soldiers as the most demanding task regarding both aerobic and muscle strength demands. Other physically demanding tasks involve movement in combat, attack in close country and carry of heavy loads (Larsson et al., 2020).
Studies on how military basic training affects physical capacity have been made in several countries, for example, in the Armed Forces of Australia (Groeller et al., 2015; Drain et al., 2015; Burley, Drain, Sampson, & Groeller, 2018), Finland (Santtila, Häkkinen, Nindl, &
Kyröläinen, 2012) and Norway (Dyrstad, Soltvedt, & Hallén, 2006). Burley et al. (2018) show that most Australian recruits improve their physical capacity after basic military training but if the recruit’s initial fitness level is high, a decline in performance might occur instead (Burley et al., 2018). Military basic training may differ between countries, and thus studies regarding the effects of basic training on Swedish recruits are of interest for the Swedish Armed Forces.
Physical capacity includes several qualities, both anaerobic (e.g. strength/power) and aerobic (e.g. aerobic endurance/muscular endurance) abilities and it is therefore important to look at multiple different parts.
Power
Power is a measurement of the rate at which work is performed and is an important factor for performance in many human movements (Hamill, Knutzen, & Derrick, 2014). Power is the product of force and velocity and varies with loading as heavier loads increase force
2 production, but also reduces velocity of concentric movement (Hamill, et al., 2014). Peak values of power during a movement typically occurs with loads representing 30-60% of 1 repetition maximum (Augustsson, Augustsson, Thomeé, & Karlsson, 2019).
Improvements in maximal force production (strength) leads to improvements in power output at a given load (Moss, Refsnes, Abildgaard, Nicolaysen, & Jensen, 1997) and are likely the most important factor for increasing power production (Peterson, Alvar, & Rhea, 2006). The primary mechanisms for improved strength with strength training involve adaptations in the nervous system and greater cross-sectional area of the muscle (hypertrophy), as shown in Figure 1 (Augustsson, et al., 2019).
Figure 1. The main adaptations to strength training which enhance maximal force production.
Doublets = two discharges occurring close together.
Adaptations in the nervous system to strength training involve several possible mechanisms, including greater activation of the muscle by recruitment of more motor units (meaning one motor neuron, and the muscle fibers it innervates), as shown in figure 2; increased discharge rate of nerve impulses to the muscles; increased number of doublets (two discharges occurring close together); improved synchronization between muscle groups (Augustsson, et al., 2019).
Maximum voluntary muscle contractions are lower than the maximal value that can be obtained with electrical stimulation of the muscle, which indicates that all motor units are not utilized (Babault, Pousson, Ballay, & Van Hoecke, 2001). Del Vecchio et al. (2019) show that the recruitment threshold of motor units decreases with strength training, enabling greater
Adaptations to strength training leading to enhanced maximal
force production
Neural adaptations - Increased motor unit recruitment
- Faster discharge rate of nerve impulses
- More doublets
- Better synchronization between muscle groups
Muscular adaptations
- Synthesis of more contractile units within the muscles
3 activation of the muscle. Furthermore, strength training increased the discharge rate of motor units, at the same relative force, which indicates strength gains because of greater neural activity (Del Vecchio et al., 2019). Strength training also increase the number of doublets, which quickly increase force production and speed of the muscle contraction (Cutsem,
Duchateau, & Hainaut, 1998). Lastly, reduced co-activation of antagonist muscle groups may occur as an adaptation to strength training (Gabriel, Kamen, & Frost, 2006). Antagonist muscle groups are active during movements to help stabilize the joint. With practice of a movement, co-activation of antagonist muscle groups is likely to be reduced, which increase force and power output as antagonist muscle activity also breaks the movement (Gabriel, Kamen, & Frost, 2006).
Figure 2. Simplified view of how recruitment of more motor units improve strength.
Hypertrophy occurs when muscle protein synthesis exceeds muscle protein breakdown so that muscle protein net balance is positive. Strength training elevates both muscle protein
synthesis and muscle protein breakdown, however, the elevation of muscle protein synthesis is greater, and muscle protein net balance is therefore increased (Phillips, Tipton, Aarsland, Wolf, & Wolfe, 1997). Unless amino acids are consumed however, muscle protein net balance remains negative (Tipton, Ferrando, Phillips, Doyle, & Wolfe, 1999). Hypertrophy improves strength simply because more contractile units are synthesized within the muscle fibers and contribute to force production (Hamill, et al., 2014).
Adaptations in the nervous system and the increase in contractile units within the muscle, as a response to strength training enhance maximal force production, which in turn leads to greater
4 power output. The effect of military basic training on strength have been examined in several previous studies from different countries (Dyrstad et al., 2006; Williams, Rayson, & Jones, 1999; Santtila et al., 2012; Piirainen, Salmi, Avela, & Linnamo, 2008). The results of these studies vary, with some studies showing improvements in strength and other studies not showing any change in strength during military basic training. The effect of military basic training on power output, however, is not clear as most previous studies on military basic training have not tested power output. Groeller et al. (2015), however, measured lower-body power output with bodyweight vertical jumps and did not see any change during neither basic military training nor continued military training in Australian Army recruits. More studies on the effect of power output is therefore needed. Power is an important quality for short-term, high-intensity activities, such as sprinting. The ability to continue to work for a longer duration, however, is largely dependent on the capacity of the aerobic energy system.
Aerobic capacity
Maximal aerobic capacity can be determined by measuring VO2max, which is a measurement of the body’s capacity to utilize oxygen for energy production and an important factor for endurance performance (McArdle, Katch, & Katch, 2014). Several physiological systems are involved in determining the maximum amount of oxygen that can be utilized by the body, including pulmonary ventilation, hemoglobin concentration, blood volume, cardiac output, peripheral blood flow and aerobic metabolism (McArdle, et al., 2014). Many adaptations occur both centrally and peripherally as a response to endurance exercise; the most important ones are listed in Figure 3.
The most important central adaptation to endurance exercise is an increase in maximal cardiac output, which is achieved by increases in stroke volume (Krip, Gledhill, Jamnik, &
Warburton, 1997). The increase in stroke volume is primarily achieved through an increase in end-diastolic volume in accordance with the Frank-Starling law. The primary cause of
increased end-diastolic volume is increased blood volume, primarily through an increase in plasma volume (Krip et al., 1997), which is an adaptation to endurance exercise (Warburton et al., 2004). The main peripheral adaptations to endurance exercise are increases in
capillarization (Andersen & Henriksson, 1977; Ingjer, 1978), mitochondria size (Meinild Lundby et al., 2018), and activity of enzymes involved in aerobic metabolism (Meinild Lundby et al., 2018; Andersen & Henriksson, 1977), in the trained muscles. Increased
5 capillarization increase the supply of blood and oxygen to the muscles, while the increase in mitochondria size and activity of enzymes involved in aerobic metabolism augments the muscles ability to utilize oxygen for energy production.
Figure 1. The main adaptations to endurance exercise which increase aerobic capacity.
The increase in maximal cardiac output and the increase in capillarization of the trained muscles, improves blood flow to the working muscles so that more oxygen is available. The increase in availability of oxygen for the working muscles, in combination with enhanced ability to produce energy through aerobic metabolism, increases aerobic capacity as an adaptation to endurance exercise. The effect of military basic training on aerobic capacity have been examined in several previous studies from different countries (Burley et al., 2018;
Groeller et al., 2015; Williams et al., 1999; Santtila et al., 2012; Williams, 2005; Dyrstad et al., 2006). In general, military basic training has a positive effect on the aerobic capacity of recruits, as it improves. No study has, however, examined the effect of basic training in the Swedish Armed Forces on aerobic capacity. While maximal aerobic capacity is a good measurement of one’s ability to perform in endurance activities, other factors is important as well. Body composition is an important factor as many activities involve movement of the body.
Adaptations to endurance exercise leading to increases in
maximal aerobic capacity
Central adaptations
- Increased maximal cardiac output - Increased stroke volume - Increased blood volume
Peripheral adaptations
- Increased capillarization - Increased size of mitochondria
- Increased activity of enzymes involved in aerobic metabolism
6
Body composition
Body composition describes the proportions of various components, such as water, bone density, fat mass, and fat-free mass, in the body. A body composition of high fat-free mass and low body fat mass is favorable for optimal physical capacity, as fat-free mass correlates well with strength (McArdle, et al., 2014), and low body fat mass correlates well with performance in weight-bearing activities such as running (Alvero-Cruz et al., 2019). Both endurance exercise and strength training have a positive impact on body composition.
Endurance exercise is effective for reducing body fat mass, while strength training is effective for both reducing body fat mass and increasing fat-free mass (Broeder, Burrhus, Svanevik, Volpe, & Wilmore, 1997). The effect of military basic training on body composition have been examined in several previous studies from different countries (Mikkola et al., 2009;
Williams et al., 1999; Williams, 2005; Santtila et al., 2012; Piirainen et al., 2008) and is generally positive, as body fat decreases, and fat-free mass and/or skeletal muscle mass increases. No studies have, however, examined the effect of basic training in the Swedish Armed Forces on body composition.
One of the aims of basic training is to prepare the recruits for the physical demands that will be put on them during their service in the military. Recruits need to be both strong and have a high aerobic capacity (Santtila et al., 2015), which demands well-designed exercise plans to best prepare the recruits. As military basic training may be different for each country, it is of interest to study how basic training in the Swedish Armed Forces affects the recruits’ physical capacity and body composition, which this study can contribute with. Also, the effect of military basic training on power output is not well studied and will be examined in this study.
Aim
The aim of this study was to examine how lower-body power, aerobic capacity, and body composition changes during basic training, from start to end of basic military training and to the end of post training in male recruits in the Swedish Armed Forces.
- How does the physical capacity of male recruits in the Swedish Armed Forces change during basic training regarding lower-body power and aerobic capacity?
7 - How does the body composition of male recruits in the Swedish Armed Forces change
during basic training regarding body weight, body fat mass, percentage body fat, fat- free mass, and skeletal muscle mass?
Methods
Participants
One hundred and ninety-nine Swedish male army recruits (age 18-50) from a regiment in western Sweden volunteered for this study. Recruits must pass both physical and
psychological tests to be accepted for basic training and were therefore considered healthy enough to perform the tests in this study. Participants with electrical or metal implants was excluded from the bioelectrical impedance analysis for health reasons.
Study design
The study consisted of three test occasions (Figure 4): before BMT (BMTpre), after BMT (BMTpost) and after PT (PTpost). BMT was the same for all participants and lasted for twelve weeks. PT varied in length from three to twelve months and thus, the duration between the second and third test occasion varied, as the participants were tested upon completion of PT. Three measurements were made at each test occasion to examine the physical status of the participants. Lower-body power, aerobic capacity and body composition were tested with loaded vertical squat jumps (LVSJ), FM (an abbreviation of Försvarsmakten)-beep test (FMBT) and bioelectrical impedance analysis (BIA), respectively. All tests were performed indoors. Time of day for testing varied except for BIA, which was performed in the morning.
Amount of days between the different tests varied as well except for LVSJ and BIA, which were performed within a two-day period at each test occasion. Test leader was the same for all measurements of LVSJ and BIA but varied for FMBT.
8 Figure 4. Timeline of the study. Lower-body power, aerobic capacity and body composition was tested at each test occasion.
Physical training during BMT consisted of general group training and military-specific training. General group training consisted of intense activities such as running and strength training and was performed three hours per week, as well as two to four micro-training sessions (approximately 15 minutes in duration) per day. Military-specific training consisted of activities such as marching and combat-training and was performed for approximately 120 hours spread across the 12-week period. After BMT the recruits were assigned to different posts and received their PT in different places. General group training during PT was two to three hours per week, depending on the position. Military-specific training varied greatly during PT.
Testing procedures Loaded vertical squat jump
Lower-body power was measured with LVSJ, performed in a smith machine where a barbell is fixed to a vertical steel rail, limiting the movement to vertical displacement only. The test was performed bilaterally with a load of 30 kg. A linear displacement sensor (MuscleLab Encoder, Ergotest, Porsgrunn, Norway) was attached to the bar to measure velocity of the bar in order to calculate peak power and average power of the jump. Relative values for peak power and average power were calculated as well by dividing the absolute values with body weight for each participant.
Participants were instructed to place the bar on their shoulders and distribute the weight evenly over both feet. The participant then squatted until knees were bent 90 degrees, briefly stopped in this position to limit the effect of stretch-shortening cycle (Walshe, Wilson, &
Ettema, 1998; Takarada, Hirano, Ishige, & Ishii, 1997) and jumped as explosively as possible.
Both feet must leave the ground, and, land on the ground again jointly. Each participant was given three tries and the jump with the highest value for peak power was used for analysis.
9 MuscleLab Encoder has proven to be valid (Bosquet, Porta-Benache, & Blais, 2010) and reliable (Ravier, 2011). A study that compared bench press one-repetition maxes with
estimated one-repetition maxes measured with MuscleLab Encoder showed a high correlation (r = 0.93) between the two values (Bosquet et al., 2010). Another study compared MuscleLab Encoder with a different linear displacement sensor (Myotest A.S., Sion, Suisse), showing a strong relationship between the values (Ravier, 2011).
FM-beep test
Aerobic capacity was assessed using the Swedish Armed Forces own version of a multistage 20-m shuttle run; FMBT. FMBT was performed by running back and forth 20 meters in decreasing time. Rhythm was set by a standardized auditory track. Before the test began, participants performed an easy test run to familiarize with the procedure. Failure to complete the distance in required time resulted in a warning. The test was terminated when the
participant could not maintain the pace necessary for three lengths in a row, or, upon volitional termination. Highest level and lap completed was noted and used to estimate VO2max. Both the score for FMBT and the value for VO2max were used for analysis.
FMBT is a modified version of multistage 20-m shuttle run. The difference between the two tests is that FMBT starts at a lower intensity. Multistage 20-m shuttle run have been validated against incremental treadmill test, which is the gold standard for measuring aerobic capacity, showing a strong correlation (r = 0.86; r = 0.87) between the two tests (Penry, Wilcox, &
Yun, 2011; Paradisis et al., 2014). Penry et al. (2011) observed 6% lower estimated values from multistage 20-m shuttle run compared to values from incremental treadmill test and Paradisis et al. (2014) observed almost identical values. FMBT was used instead of incremental treadmill test for practical reasons. In contrast to incremental treadmill test, FMBT does not require any advanced equipment and can test multiple participants at once.
Bioelectrical impedance analysis
Body composition was assessed using BIA (InBody 770, InBody Co., Seoul, South Korea).
Body fat mass, percentage body fat, fat-free mass, and skeletal muscle mass, along with body weight, was recorded. BIA have been validated against dual energy X-ray absorptiometry which is considered the gold standard for body composition analysis. The results show an
10 excellent agreement for measurements of body fat mass and fat-free mass (ICC ≥ 0.93) with an average overestimation of 8% for body fat mass and an average underestimation of 1.8%
for fat-free mass by BIA (Ling et al., 2011). BIA was used instead of dual energy X-ray absorptiometry for practical reasons, as the equipment for BIA is both easy to transport and use. The measurements were made first thing in the morning, before a meal and after a bathroom visit, and according to the manufacturer’s instructions, to ensure validity and reliability of the measurements.
Ethical and social considerations
The study was approved by Regional Ethical Review Board in Lund, Sweden (Dnr 2016/400).
All participants signed informed consent and were given the opportunity to ask questions before the study began. Participants were informed that they could cancel their participation at any time without having to state why and that their employment with the Swedish Armed Forces would not be affected by their decision.
There is always a risk associated with intense physical activities, like the ones performed in this study. However, for the participants in this study, the risks were minimal, as all
participants were considered healthy. Also, test leaders were present at each test occasion and participants were asked not to participate in the event of illness or injury that propose a health risk, to further reduce the risks with this study. Test results were treated confidentially so that collected data could not be derived to individuals and was only available to members of the research group.
The results of this study can contribute with knowledge about how basic training affects physical capacity and body composition of recruits in the Swedish Armed Forces. As several qualities were tested in this study, the results can be used to see if any specific quality needs improvement, and thus, plan exercise accordingly. Future studies can, with the results from this study, examine the effectiveness of altered exercise plans, to help optimize physical training during basic training.
Statistical analysis
Shapiro-Wilks test was used to test the data for normal distribution, showing that most of the data was not normally distributed. Nevertheless, results are presented as mean ± standard
11 deviation even though non-parametric statistical tests were performed, to enable comparison with results from similar studies. One extreme value was identified in the data set for peak power, after PT, and were removed from the data (Pallant, 2016). Friedman test was used to compare the recruits over time (three time-points) and if the result from Friedman test was statistically significant, the Wilcoxon signed rank test for pairwise comparisons was used as a post hoc analysis. Statistical significance was set at p ≤ 0.05. All statistical analyses were performed with SPSS Statistics (IBM SPSS Statistics version 25, IBM corp., Armonk, New York, USA).
Results
Participants
Out of the 199 recruits who participated in the study, a total of 97 recruits participated in all three test occasions for at least one of the three tests (Figure 5). The remaining 102 recruits did not participate in all three test occasions for any of the three tests and their data were therefore considered incomplete, and not included in the study. Incomplete data was the result of, for example, injury, illness, specialized training at another regiment, premature discharge, or failure to perform test in a platoon. Only sixteen recruits participated in all three test occasions for all the three tests (nine measurements in total), while a total of 40, 41 and 71 recruits had complete data for LVSJ, FMBT and BIA, respectively, and were thus included to increase the number of participants for each test. Data for age and height were available for 75 of the 97 recruits who had complete data for at least one of the three tests and are shown in Table 1.
12 Figure 5. The distribution of participants during the study. A total of 97 recruits participated in all three test occasions for at least one test and therefore had complete data for that test.
Table 1. Age and height at the start of basic training for 75 of the 97 recruits who participated in all three test occasions for at least one of the three tests.
n Mean ± Standard deviation Median (min-max)
Age (years) 75 20.4 ± 3.9 19 (18-50)
Height (cm) 75 182.0 ± 6.9 181 (165-196)
Weight (kg) 75 78.2 ± 11.5 77.9 (46.3-116.8)
Lower-body power
Peak power and average power did not change significantly during basic training (Peak power: p = 0.111; Average power: p = 0.103) as shown in Table 2. Relative values for peak power and average power were calculated by dividing the values for peak power and for average power with body weight, for each participant. There was no significant change in body weight during basic training for the recruits who participated in LVSJ (n = 40; p = 0.253). Relative peak power changed during basic training (p = 0.042) with an increase of 4.8% from BMTpre to BMTpost (p = 0.009) followed by a decrease of 5.4% from BMTpost
A total of 199 recruits volunteered for the study
40 recruits had complete data for loaded vertical
squat jump (LVSJ)
16 recruits had complete data for all three tests 41 recruits had complete
data for FM-beep test (FMBT)
16 recruits had complete data for all three tests
71 recruits had complete data for bioelectrical
impedance analysis (BIA)
16 recruits had complete data for all three tests 102 of these recruits did
not participate in all three test occasions for any of
the tests
13 to PTpost (p = 0.015). Relative average power did not change significantly during basic training (p = 0.098; Table 2).
Table 2. Physical capacity and body composition before basic military training (BMTpre), after basic military training (BMTpost) and after post training (PTpost).
Measurement n BMTpre BMTpost PTpost p-value
Loaded vertical squat jump
BW (kg) 40 79.7 ± 11.9 79.8 ± 10.7 80.4 ± 11.4 0.253 PP (W) 40 965.7 ± 220.4 1023.6 ± 156.1 974.5 ± 182.5 0.111 AP (W) 40 482.0 ± 109.2 510.2 ± 95.4 488.1 ± 94.8 0.103 PP/kg (W/kg) 40 12.4 ± 3.7 13.0 ± 2.4a 12.3 ± 2.7b 0.042
AP/kg (W/kg) 40 6.2 ± 1.8 6.5 ± 1.5 6.2 ± 1.4 0.098
FM-beep test
Score 41 10.8 ± 2.3 11.7 ± 2.1a 12.0 ± 1.7a+b < 0.001 Estimated
VO2max (ml/kg/min)
41 46.1 ± 6.7 48.6 ± 5.9a 49.5 ± 5.0a+b < 0.001
Bioelectrical impedance analysis
BW (kg) 71 78.8 ± 11.4 78.9 ± 9.9 79.7 ± 10.3b 0.043 BFM (kg) 71 11.1 ± 5.8 9.7 ± 4.3a 10.7 ± 5.1b 0.001
%BF (%) 71 13.6 ± 5.5 12.0 ± 4.2a 13.2 ± 4.9b < 0.001 FFM (kg) 71 67.7 ± 8.1 69.2 ± 7.5a 69.0 ± 7.7a < 0.001 SMM (kg) 71 38.5 ± 4.7 39.4 ± 4.4a 39.4 ± 4.5a < 0.001 BW = body weight; PP = peak power; AP = average power; PP/kg = relative peak power;
AP/kg = relative average power; BFM = body fat mass; %BF = percentage body fat; FFM = fat-free mass; SMM = skeletal muscle mass; n = number of participants. All values except n are mean ± standard deviation.
a = statistically significant at p ≤ 0.05 level compared to BMTpre
b = statistically significant at p ≤ 0.05 level compared to BMTpost
Aerobic capacity
Changes in aerobic capacity was observed as FMBT scores increased during basic training (p
< 0.001) with an increase of 8.3% from BMTpre to BMTpost (p = 0.001) and a continued increase of 2.6% from BMTpost to PTpost (p = 0.021) as shown in Table 2. The scores from FMBT were used to calculate estimated values for VO2max, which also increased during basic training (p < 0.001) with an increase of 2.5 ml/kg/min from BMTpre to BMTpost (p = 0.001) and a continued increase of 0.9 ml/kg/min from BMTpost to PTpost (p = 0.020; Table 2).
14
Body composition
Body weight increased during basic training (p = 0.043), with an increase of 0.8 kg from BMTpost to PTpost (p = 0.025) as shown in Table 2. Body fat mass changed during basic training (p = 0.001), with a decrease of 1.4 kg from BMTpre to BMTpost (p < 0.001)
followed by an increase of 1.0 kg from BMTpost to PTpost (p < 0.001). Percentage body fat changed during basic training (p < 0.001), with a decrease from 13.6% to 12.0% from BMTpre to BMTpost (p < 0.001) followed by an increase from 12.0% to 13.2% from BMTpost to PTpost (p < 0.001). Fat-free mass and skeletal muscle mass both increased during basic training (Fat-free mass: p < 0.001; Skeletal muscle mass: p < 0.001), with an increase in fat-free mass of 1.5 kg (p < 0.001), and an increase in skeletal muscle mass of 0.9 kg (p < 0.001), from BMTpre to BMTpost and no significant change from BMTpost to PTpost (Table 2).
Discussion
The main findings of the present study indicate that for male recruits completing basic training, the first twelve weeks (BMT) elicit the most improvements, as relative peak power, VO2max, and body composition measures of body fat, fat-free mass and skeletal muscle mass improved. During the second phase of basic training (PT), only VO2max continued to
improve while relative peak power decreased and body fat increased without any changes in fat-free mass or skeletal muscle mass, resulting in increased body weight compared to before PT.
Lower-body power
The results of LVSJ show that when looking at the total period of basic training (BMT + PT), lower-body power is not affected. These results are in line with previous research, which showed that lower-body power measured with bodyweight vertical jumps did not change following twelve weeks of basic military training and six to fifteen weeks of continued
military training in Australian Army recruits (Groeller et al., 2015). The limited effect of basic training on lower-body power could be the result of insufficient strength training or because of concurrent aerobic exercise. Research on concurrent training has shown that power is adversely affected by combining strength training and aerobic exercise, compared to strength
15 training alone (Wilson et al., 2012). As muscular strength was not measured in this study it cannot be concluded if the limited effect on lower-body power is the result of insufficient strength training, interference of concurrent training, or some combination of the two.
Interestingly, relative peak power increased during BMT even though neither peak power nor body weight were significantly affected during this period. As relative peak power is
calculated by dividing the value for peak power with the participants body weight, this result is surprising. Based on the results from the body composition measurements, an informed guess would be that improved body composition during this period, with an increase in fat- free mass and skeletal muscle mass, and a decrease in fat mass, augmented the increase in relative peak power. If this informed guess is correct, overweight participants most likely improved their relative peak power due to decreases in body weight as a result of lower body fat mass, while underweight participants most likely improved their relative peak power due to increases in peak power, as the result of increased fat-free mass and skeletal muscle mass.
Aerobic capacity
The results of FMBT show that aerobic capacity increases during basic training. Estimated VO2max increased by 5.4% during BMT and by another 1.9% during PT, for a total of 7.4%
during basic training. The increase during BMT in the present study is in line with results from several previous studies (Burley et al., 2018; Groeller et al., 2015; Williams et al., 1999;
Santtila et al., 2012; Williams, 2005), which have shown increases ranging from 5.6% to 9.7% during military basic training. In contrast to these studies, Dyrstad et al. (2006) did not see any change in aerobic capacity during military basic training. The continued increase during PT in the present study, however, is not in line with previous research. In the study of Groeller et al. (2015) aerobic capacity decreased by 1.8% during six to fifteen weeks of continued military training and Santtila et al. (2012) did not see any change during eight weeks of continued military training on aerobic capacity. The increase in aerobic capacity during both BMT and PT in the present study are not in line with the results from LVSJ and BIA, which either deteriorated or did not change during PT. This indicates that more
emphasis is being put on endurance exercise compared to strength training during PT in the Swedish Armed Forces. The increase in fat mass, however, contradicts this. Another possible explanation is the difference in exercise time within different PT, which may affect the results as the distribution of participants from different PT may vary for each test.
16
Body composition
The results of BIA show that body composition is affected during basic training. Body fat mass decreased by 12.6% during BMT and then increased by 10.3% during PT and
percentage body fat decreased by 11.8% during BMT and then increased by 10% during PT.
Previous studies regarding changes in body fat during military basic training show a decrease in body fat most of the time, with a decrease of 9.7% in body fat mass in one study (Mikkola et al., 2009) and a decrease in percentage body fat ranging from 1.2% to 20.3% in other studies (Williams et al., 1999; Williams, 2005; Santtila et al., 2012) with the length of the military training period varying from eight weeks to twelve months. In contrast to these studies, Piirainen et al. (2008) did not see any changes in body fat following eight weeks of military basic training. The results of the present study, with the decrease in body fat during BMT and the increase of body fat during PT are likely the result of reduced exercise during PT. Santtila et al. (2012) examined body fat changes from eight weeks of basic military training followed by eight weeks of continued military training and demonstrated a decrease during basic military training and no change during continued military training. In the study of Santtila et al. (2012), total hours of military training did not change from basic military training to continued military training, which could explain the difference in results compared to the present study. The 1% increase in body weight during PT is most likely the result of the increase in body fat mass during this period.
Fat-free mass and skeletal muscle mass increased during BMT by 2.2% and 2.3%,
respectively, and did not change during PT. These results are in line with previous research, which has shown increases in fat-free mass and/or skeletal muscle mass following military basic training (Mikkola et al., 2009; Williams et al., 1999; Williams, 2005). In contrast to these studies Piirainen et al. (2008) did not see any changes in fat-free mass following eight weeks of military basic training. Interestingly, fat-free mass and skeletal muscle mass did not deteriorate during PT like measures of body fat did. This could be explained by the low levels of exercise needed to maintain gains in muscle mass (Bickel, Cross, & Bamman, 2011). This indicates that PT offers enough stimulus to maintain muscle mass gains obtained during BMT, but not enough to induce further improvements.
17
Limitations
The study design did not allow individual comparisons of different PT, which would have been preferable as they all differed in duration, as well as exercise time. Grouping the
participants by their PT would have enabled examination of one or more specific PT. Another limitation of this study was that the participants were not the same for each test, which made between-test comparisons less reliable. Addition of a test for lower-body muscular strength would have been desirable in order to determine whether the lack of change in lower-body power was due to insufficient strength training or due to concurrent exercise.
Conclusions
This study shows that most of the improvements in physical capacity and body composition during basic training occurs during BMT, as only aerobic capacity continued to improve during PT. Body composition improved during BMT and deteriorated during PT. Lower-body power was not affected during neither BMT nor PT, which indicates that more strength
training is needed. These findings are important for the Swedish Armed Forces as one important aspect of basic training is to prepare the recruits for the physical demands which will be put on them during their service. More strength training, especially during PT, could counteract the deterioration of body composition during this period and improve power.
Future studies may aim to examine the effect of altered exercise plans, containing more strength training.
18
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