Effects of Basic Training on Acute Physiological Responses to a Combat Loaded Run Test

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1 MILITARY MEDICINE, 175, 4:273, 2010 Effects of Basic Training on Acute Physiological Responses to a Combat Loaded Run Test LTCOL Matti Santtila, MSc * ; Keijo Häkkinen, PhD ; William J Kraemer, PhD ; Heikki Kyröläinen, PhD ABSTRACT The purpose of the study was to examine the effects of an 8-week basic training (BT) with added strength training (ST) or endurance training (ET) on both the performance of a 3K-combat loaded run test and the acute neuromuscular and hormonal responses. All training groups improved ( p < 0.001) their run-test times: ST by 12.4%, ET by 11.6%, and normal training (NT) by 10.2%. Significant acute decreases were observed in maximal isometric force of leg extensors ( p < ) in all subject groups following the run. Increases were observed in acute testosterone responses ( p < 0.001) after the test in all groups both at pre- and post-training. However, ET and NT demonstrated lower ( p < ) acute post-training serum cortisol responses than ST. In conclusion, the present results indicate that within a demanding BT, the added training for ET and especially ST may be compromised in their adaptation potential due to interference from the demands of BT. INTRODUCTION Military training and field exercises consist of many different challenging tasks such as prolonged physical activity and lifting or carrying heavy loads that require high endurance and/ or strength capacities. 1,2 Nindl et al. 3 have shown that higher physical fitness levels in soldiers can offset the detraining that can occur with harder military training and combat operations. Therefore, military basic training has as one of its fundamental tenets, improving physical fitness. In fact, in a study by Sharp et al. 4 they observed that a 9-month military operation in Afghanistan caused a significant decrease only in the U.S. Army soldier s aerobic performance and upper body anaerobic power possibly due to the low training frequency during the operation and resulting detraining.5 In that study by Sharp et al., 4 they examined a wide array of tests including body composition measurements, lifting strength measured by an incremental lifting machine, lower and upper body explosive power measurements (vertical jump, medicine ball put), and aerobic capacity measurement. One type of field test, which taxes both the aerobic and strength capabilities of a soldier, is the loaded running or marching test. 2,3 Typically load tests reflect heavier demands and a lighter combat loaded run test has not been used to evaluate physical training programs in the military. Such tests would reflect some of the operational demands in combat field operations. The effects of combined strength and endurance training have been shown to enhance heavy 2-mile load carriage performance more than strength or endurance training alone.2 * Personnel Division of Defence Command, Finnish Defence Forces, P. O. Box 919, Helsinki, Finland. Department of Biology of Physical Activity, University of Jyväskylä, P. O. Box 35 (VIV), Jyväskylä, Finland. Department of Physiology and Neurobiology, University of Connecticut, Storrs, Connecticut Department of Biology of Physical Activity, University of Jyväskylä and National Defence University, P. O. Box 7, Helsinki, Finland. A field-specific run test with a combat load will allow the evaluation of the various physical training programs of its performance and changes in physiological stress responses (e.g., hormonal responses). Testosterone (TES) and cortisol (COR) have been used as primary hormonal markers representing the predominance of anabolic and catabolic activity, respectively. Acute and chronic hormonal responses induced by exercise and/or training have been widely reported. 6 It has been shown that strength training can induce acute and in some cases chronic changes in total serum TES, COR, and immunoreactive growth hormone (GH), which are strongly related to volume, intensity, and duration of exercise session. 6,7,8 Changes in the resting and acute responses to an exercise protocol with training can provide insights into the physiological mechanisms involved with the stress adaptations of the exercise training protocol. 6 Endurance exercise usually induces acute increases in serum TES, GH, insulin-like growth factor-1 (IGF-1), and COR. 8 However, endurance exercise of a prolonged duration (>2 h) can lead to acute decrease in TES. 9 With endurance training no changes or decreases are observed in serum basal TES, IGF-1, GH, or COR. 6,10 Nindl et al. 3 have additionally demonstrated that 8 weeks of intensive military training caused chronic increases in COR and decreases in TES concentrations. These changes were associated with energy deficit and losses in fat and fat-free mass. The endurance part of concurrent endurance and strength training could, however, induce a more catabolic response and therefore, may interfere with strength development. 11 Although concurrent endurance and strength training has not been shown to reduce TES, a significant increase has been observed in serum COR level. 8 In the present study, we evaluated the effects of different basic training protocols using a new 3K-combat loaded running field test to evaluate soldiers field running performance corresponding to operational combat loaded requirements. Therefore, the primary purpose of the present study was to investigate the effects of three different 8-week basic training MILITARY MEDICINE, Vol. 175, April

2 courses: normal basic training (NT), basic training with added strength training (ST), or basic training with added endurance training (ET) on a novel 3K-combat run test. A secondary purpose was to examine the acute neuromuscular force production capabilities and hormonal responses to the 3K-combat run test before and after basic training. METHODS Subjects A total of 72 male conscripts volunteered for the study after passing the medical examination and were randomly assigned to one of three training groups: NT ( n = 24); ST ( n = 24), or ET ( n = 24). However, after group assignment, there were nine dropouts (four in the ET group, three in the ST group, and two in the NT group) due to cessation of military service for mental health reasons, sick leave of over 14 days, missing information from training diaries, or a change of garrison. The mean age of the subjects was 19.2 ± 0.9 years, height 1.79 ± 0.06 m, initial body mass 73.8 ± 12.4 kg, and body mass index 23.0 ± 3.8. No significant initial differences between the groups were observed with respect to age, height, body mass, muscle strength, aerobic capacity, or physical activity. Subjects were carefully informed about the design of the study with special information given on possible risks and discomfort that might occur, and subsequently they signed an informed consent document before the study. This study was conducted according to the Declaration of Helsinki 1975 and was approved by the Ethical Committee of the Central Finland Health Care District and the University of Jyväskylä, Finland. Experimental Design The duration of the present study (BT season) was 8 weeks, including a total of 300 h of military training. The subjects were tested during the first and ninth service weeks before and after the training period using the identical protocols. The detailed description of the training program has been published earlier. 12 The BT standard program for all groups consisted of combat simulations and marching with a load of kg including clothing, as well as marksmanship training, material handling, general military and theoretical education, skill training, and sport-related physical training (SRPT). SRPT refers to running, nordic walking (using walking poles), walking, cycling, strength training, ball games, orienteering, and other sport activities. The SRPT program during basic training of each group differed with regard to specific training sessions. The SRPT program of the ST group contained three strength training sessions a week with a duration of min for a total of 44 h. A whole body linear periodized strength-training program consisted of gym and circuit training and each training session always included two exercises for leg extensor muscles. During the first 3 weeks of preparatory training, the subjects trained with loads of 30 50% or 60 70% of one repetition maximum (1 RM) for 2 3 sets and or repetitions (muscle endurance), during weeks 4 and 5 with loads of 60 80% of 1 RM for 2 4 sets and 6 10 repetitions (hypertrophy cycle), and finally during weeks 6 to 8 with loads of % for 5 7 sets and 1 6 repetitions (maximal strength/ power cycle). Additionally, explosive strength training was also performed during the last training cycle. The ET group had three additional endurance sessions a week with a duration of min with a total of 51 h, which included nordic walking, walking, running, bicycling, and some other endurance exercises. The training intensity was mainly aerobic (50 70% of maximal heart rate). The NT group served as a control group and trained according to the basic training standard program. The SRPT program of NT consisted of endurance-type sport activities such as ballgames and muscle fitness exercises for a total of 33 h. Experimental Testing 3K-Combat Loaded Run Test A 3-kilometer field running test with maximal effort was performed twice on the same cross-country track while carrying the 14.2-kg combat load (battle dress, running shoes, rifle with a sling, and combat gear), approximately 19.2% of body weight. All subjects were instructed to complete the test in the shortest possible time. Heart rate (HR) was recorded continuously using heart rate monitors (Suunto T6, Suunto, Vantaa, Finland). Blood samples, maximal isometric force of leg extensors, and maximal hand grip were assessed before and after the 3K-combat run test. Aerobic Capacity Peak oxygen uptake was measured using the bicycle ergometer (Ergoline GmbH, Ergoline, Germany). Oxygen uptake (VO 2 peak) was measured continuously using an automated gas analysis system (SensorMedics, Yorba Linda, California). The detailed description of the protocol has been reported earlier. 12 The pretest for the loaded run and VO 2 peak tests were performed during the first training week and the post-test during the ninth training week, respectively. Blood Analyses Blood samples were obtained from the antecubital vein. Serum total immunoreactive classical 21 kda (191 aa) growth hormone (GH) was analyzed (1235 WallacAutoDelfia, Wallac Oy, Turku, Finland) using time-resolved fluoroimmunoassay (Auto-DelfiahGH, Wallac Oy, Turku, Finland). The sensitivity and intra-assay variance for this assay was up to <0.026 miu l 1 and 4.9%, respectively. Serum total testosterone (TES tot ) and COR were analyzed by Vitros ECi (Ortho Clinal Diagnostic, New York) using respective commercial luminoimmunoassays (Ortho-Clinical Diagnostic, Amersham, UK). The sensitivity and intra-assay coefficient of variance for these assays were 0.5 nmol l 1 and <5.7%, 5.5 nmol l 1 and <5.8%, respectively. 274 MILITARY MEDICINE, Vol. 175, April 2010

3 Blood lactate (B-La) was analyzed from fingertip blood samples (Lactate Pro, Arkray, Japan). Its coefficient of variance (CV) was 3%. Muscle Strength Measurements Maximal isometric force of the bilateral leg extensor muscles (knee and hip angles of 107 and 100, respectively) was measured using an electromechanical dynamometer. 13 The force signal was recorded, digitized, and analyzed with a Codas TM computer system (Dataq Instruments, Inc, Akron, Ohio). Maximal peak force was defined as the highest value of the force.13 Maximal isometric grip strength was measured by the dynamometer (Saehan, Saehan Corporation, Masan, South Korea) in a sitting position. The elbow was flexed at a 90 position. The best result of the right and left hands was chosen as the outcome. 14 Statistical Analyses These data are presented as means and standard deviations (± SD). Pearson product-moment correlation coefficients were calculated to determine bivariate pairwise relationships. The data were then analyzed by utilizing measures for Univariate ANOVA (with least significant difference [LSD] and Bonferroni multiple comparisons) or Kruskal-Wallis nonparametric test (with Mann-Whitney U -tests as pairwise comparisons) when assumptions were not met. Also paired t-tests and nonparametric Wilcoxon tests were used for testing differences in dependent variables. An level of p 0.05 was defined as being statistically significant in this study. RESULTS During the 8-week basic training period, all training groups decreased significantly (i.e., improved) their 3K-loaded combat run test time as follows: ST by 12.4% ( p < 0.001), ET by 11.6% ( p < 0.001), and NT by 10.2% ( p < 0.001) ( Fig. 1 ). No differences were observed between the groups. Table I shows that no significant changes were observed for HR. When compared to pre- and post-tests during the last 400 s of the 3K-combat run test, significant increases were observed in the average HR of all training groups as follows: ST from 174 ± 6 to 179 ± 4 bpm ( p < 0.001), ET from 179 ± 5 to 182 ± 3 bpm ( p < 0.001), and NT from 179 ± 6 to 184 ± 3 bpm ( p < 0.001) ( Fig. 2 ). No differences among the groups were observed. The B-La post value decreased from 10.5 ± 2.2 to 9.5 ± 2.0 mmol L 1 ( p < 0.01) in NT when comparing the preand post-tests, whereas no significant changes were observed in the ST or ET groups (see Table I ). Figure 3 demonstrates that the 3K-loaded combat run test induced significant decreases in maximal isometric force of leg extensors ( p < ) of all subject groups. Also a significant decrease was observed in hand grip force ( p < 0.01) of the ET group, whereas no significant decreases were noticed in the ST and NT groups. Examining the changes in strength from pre to post basic training, no differences were observed between the groups. Acute pre to post run tests for serum TES responses were significantly increased both at pre- and post-training test time points in all training groups as follows: ST by 25.1% ( p < 0.001) and 16.4% ( p < 0.001), ET by 26.5% ( p < 0.001) and 30.0% ( p < 0.001), and NT by 24.4% ( p < 0.001) and 31.1% ( p < 0.001) (see Figure 4 ). Serum TES post-training acute response of NT was significantly higher ( p < 0.05) when compared to that of the pretraining testing time point. However, no significant differences in the response patterns among the different training groups were observed. Figure 4 shows that serum GH concentrations increased significantly ( p < 0.001) after the 3K-loaded combat run test in all basic training groups at both the pre- and post-training testing time points. The acute posttraining responses in both the ST and ET groups were significantly higher in the post-test time point compared to the pretest FIGURE 1. Mean (± SD) times of the field running tests in the strength (ST), endurance (ET), and normal training (NT) groups before (white bars) and after (black bars) the 8-week training period (*** p < 0.001). TABLE I. Mean (± SD) Maximal Heart Rate (HR max ), Average Heart Rate, and B-La post Values of the Field Running Test Measured Pre and Post the 8-Week Training Period Pretraining (0 weeks) Post-training (8 weeks) Strength ( n = 21) Endurance ( n = 20) Normal ( n = 22) Strength ( n = 21) Endurance ( n = 20) Normal ( n = 22) HR max (beats/min) 188 ± ± ± ± ± ± 8 Average HR (beats/min) 168 ± ± ± ± ± ± 8 B-La post (mmol l 1 ) 10.1 ± ± ± ± ± ± 2.0 ** **p < MILITARY MEDICINE, Vol. 175, April

4 FIGURE 2. Average heart rates (mean ± SD) during the field running tests in the strength (ST), endurance (ET), and normal training (NT) groups pretest (gray line) and post-test (black line) during the 8-week training period including HR max (mean ± SD) values measured during the first VO 2 max test. Average heart rates during the last 400 s represented by short parallel lines with asterisk at the right side of graph (*** p < 0.001). time point. In addition, NT differed in terms of the traininginduced GH responses in the ET and ST groups. Acute serum COR responses were significantly increased following exercise in both pre- and post-training testing time points in all training groups as follows: ST by 45.3% ( p < 0.001) and 44.2% ( p < 0.001), ET by 45.7% ( p < 0.001) and 14.1% ( p = 0.10), and NT by 70.5% ( p < 0.001) and 49.0% ( p < 0.001). The post-training acute responses to exercise for the ET and NT groups were significantly lower than those of pretraining testing time points ( Fig. 4 ). Furthermore, ST differed in the acute COR responses induced by training in the ET and NT groups. The total group of subjects improved their averaged VO 2 peak by 10.5% ( p < 0.01) during the 8-week training period. The ET group increased their VO 2 peak by 8.5% ( p < 0.05), ST by 12.0% ( p < 0.01), and NT by 13.4% ( p < 0.001). Significant correlations were observed between the initial level of VO 2 peak and decreases in field running test time during the 8-week training period in ST ( r = 0.63, p < 0.01) and ET ( 0.46, p < 0.05), whereas no significant correlation was observed in NT ( r = 0.36, p = 0.14). However, a significant correlation was observed for the total subject population in this study ( r = 0.49, p < 0.001) between the initial level of VO 2 peak and decreases in field running test time (see Figure 5 ). A significant correlation was also observed between the initial VO 2 peak values and initial field running test times ( r = 0.66, p < 0.001) in a total subject group. However, the correlation was low ( r = 0.22, p = 0.10) between individual changes in VO 2 peak values and changes in the field running test times of a total subject group during the 8-week training period. Furthermore, a significant correlation was observed between the initial level of maximal isometric force production of leg extensors and decreases in field running test time during the 8-week training period in the ST group ( r = 0.66, p < 0.01), whereas no significant correlation was observed in the ET group ( r = 0.38, p = 0.13) or the NT group ( r = 0.39, p = 0.21). DISCUSSION The primary findings in this study were that the demands of the 8-week basic training with the additional strength or endurance training did not add to the training adaptations on performance in a novel 3K-combat loaded run test because all groups improved to a similar level. This could be due to initial incompatibility of the demands of the basic training course with additional specific exercise training or a redundancy of aerobic stimuli as 3K-combat run times were all similar post-training. It has been demonstrated earlier that concurrent endurance and strength training is an important and may even be an essential training method needed to achieve optimal improvements in a demanding military load carriage (i.e., 2-mile run with 45-kg pack) performance. 2 Kraemer et al.2,8 have shown that only the groups performing concurrent training (i.e., total body strength training and upper body strength training along with endurance training) significantly decreased their run times despite other variables that were found to be incompatible with such simultaneous training (e.g., type I muscle fiber 276 MILITARY MEDICINE, Vol. 175, April 2010

5 FIGURE 3. Mean (± SD) relative changes (%) in maximal voluntary force (N) of bilateral isometric leg extension and in hand grip (kg) of the strength (ST), endurance (ET), and normal training (NT) groups pre- (white bar) and post- (black bar) field running tests (* p < 0.05, ** p < 0.01). growth, anaerobic power). 8 Interestingly, the groups that did only strength or endurance training programs did not see any real improvements in the load carriage task after 3 months of training four times per week. In stark contrast to the current study where untrained soldiers were undertaking a full basic training course, it must be noted that these soldiers in the study by Kraemer et al. 2 were only training and no other training demands or additional exercise were required of them, making this a very pristine study as to a stimulus and response pattern relationships. Furthermore, the soldiers in this study were fit airborne rangers. In the present study, the NT group participating in the normal basic training program similarly improved the soldiers 3K-loaded combat run performance as did the programs in the ST and ET groups, indicating that for this military relevant task, the training stimulus was adequate for the activities of the normal basic training program. The addition of more strength training or more aerobic training did not contribute to improvements in this military relevant task and this might be due to the significantly lower load being carried by the soldiers in this test. Alternatively, it is possible that the challenging demands of the BT course itself prevented the needed short-term training adaptations that would be able to contribute to a faster pace in the test. It is unclear whether more individualized training programs might have yielded different results when combined endurance and strength training is undertaken. In the current study, we did not see this additive effect on the military relevant task of a 3K-loaded combat run test. Furthermore, the aerobic stimuli needed for this improvement could be achieved by a 15 20% lower amount of endurance training as was the case in the ST group. These improvements may be a consequence of improved VO 2 max and partly by improved maximal force production of the lower body extremities in relation to better running economy. Earlier, Kyröläinen et al. 15 have suggested that higher or strengthened neuromuscular functions may have a positive effect on running economy during a demanding running performance. Furthermore, the 3K-loaded combat run test caused minor responses to hand grip force, while soldiers carried their rifles with a sling. This may indicate lower muscle activation in arm extensors during the field running test. The significant reduction (about 10%) in maximal force production of the lower extremities further suggests that the 3K-loaded combat run test caused a weakened neuromuscular performance. Finally, a reduction in the number of endurance training activities in a BT program with more focused concurrent strength and endurance physical training programs might allow for more optimal combat readiness for operations. In a study by Williams et al. 16 they evaluated the typical 11-week basic training course in the British Army, consisting of various military loading and marching tasks but no formalized specific strength training program. To test their prior hypothesis that a modified BT course with a specific strength training program would be more effective to improved military task performances, Williams et al. 17 conducted a follow-up study to see whether such a program could enhance a soldier s material-handling ability and other aspects of physical fitness. Their findings that a modified 11-week basic training course including a focused strength training program with the elimination of other extraneous exercise tasks could result in improved military task performances that were greater than the normal basic training program. In the present study, the initial VO 2 peak level was the main determinant of the improved field running performance. This is partly in line with the findings of Rosendahl et al., 18 who have reported that a 12-week military training course led to significant improvements in running test times and in VO 2 max values in untrained soldiers but not in the well-trained ones. However, in the study by Kraemer et al. 8 even the highly trained soldiers not involved with any basic or advanced course all improved in their treadmill VO 2 max values even if they were concurrently strength training, demonstrating that strength training does not interfere with aerobic improvements. The improvements in the 3K-loaded combat run test by all groups was apparently due to the availability for training adaptation in this variable with the minimal stimulus of normal basic training effective in this type of short-term training period. MILITARY MEDICINE, Vol. 175, April

6 FIGURE 4. Mean (± SD) relative changes in field running performance of serum TES, COR, and GH concentrations in the strength (ST), endurance (ET), and normal training (NT) groups during the 8-week training period (pretest white and post-test black bars, * p < 0.05, *** p < 0.001). In the latter part of the 3K-loaded combat run test, heart rate was significantly higher in all subject groups when compared to pretraining testing. This clearly indicates that the soldier s field running performance and VO 2 max had significantly improved, allowing a greater cardiovascular output to achieve a faster run time by the end of the 8-week basic training program. Such data indicate that whereas the performance times were faster, the expected cardiovascular vagal tone achieved over the 8-week FIGURE 5. Relationship between the initial maximal oxygen uptake (VO 2 max) and absolute changes in field running times during the 8-week basic training period in the total group of subjects. basic training course was not observed. The lack of a decided advantage in the ET group to perform better in the 3K-loaded combat run test shows some type of interference from the basic training course when combined with a specific endurance training program as employed in this study. This may well be due to all of the additional physical and psychological demands of a challenging basic training course in young men who are unaccustomed to physical training and the military. Yet greater tolerance for cardiovascular strain was achieved in all groups allowing for enhanced performances. This finding of incompatibility in the early weeks of a basic training and endurance training program is a novel finding and has not been shown before in the scientific literature in military physiology. In the present study, the higher initial levels of maximal isometric force production of leg extensors were associated with the faster 3K-loaded combat run testing times in a before/ after training comparison. Again, strength training three times a week did not lead to interference with the development of running performance, which is in line with prior studies. 8,19 However, Bell et al. 19 did caution that long-term concurrent training may lead to an elevated catabolic state and decreased skeletal muscle hypertrophy, which may in turn impair the magnitude of strength gains. With only 8 weeks of training, the changes observed in this study were in the early phase of an adaptation response and the demands and activities in the basic training program (i.e., drills, carrying and lifting heavy loads) were by themselves effective in producing the run time improvements in all groups. 278 MILITARY MEDICINE, Vol. 175, April 2010

7 The acute exercise-induced hormonal responses observed in the present study are consistent with earlier classical findings of Galbo, 20 Bunt et al., 21 and Kraemer et al., 8,22 since significant increases were demonstrated in acute serum responses of GH, TES, and COR. The hormonal responses to the 8-weeksof-resistance-training study by Kraemer et al., 22 in untrained young men offer some interesting comparisons to the responses and adaptations observed in the current study and may well underscore the dramatic impact of addition of basic training to a strength training program. In that study, TES, COR, and GH all increased in response to an acute resistance exercise stress. Different from the current study, the men increased their resting total TES after 6 weeks of training and reduced their resting COR after 8 weeks of training. However, they saw no changes in the GH response to exercise or with training. In comparison, while exercise-induced increases were observed in GH in all of the groups, the present study demonstrated a significant post-training increase in serum GH in response to the acute 3K-loaded combat run in the ST and ET groups. In conclusion, significant improvements were observed in the novel 3K-loaded combat run test in all training groups after the 8-week military basic training course. However, the magnitude of training-specific gains from an endurance training program added to the ET group and a periodized strength training program added to the ST group was blunted by the challenges and demands of the basic training alone as few differences existed among the three groups. This indicates an interference with the normal physiological adaptations that are associated with endurance and strength training. The NT group saw similar if not identical adaptations to the tests conducted. The underlying mechanisms for these responses remain speculative but could be based in the high levels of endurance demands in the basic training course augmented by the psychological demands of military training. Thus, the equivalence of the training groups might well be a consequence of too high an amount of endurance-based military training. Thus, it seems that some individualized training program, based on initial physical fitness, is needed to achieve more specific training responses. ACKNOWLEDGMENTS We express our special thanks to Ms. Elina Maria Kokkonen for her assistance in the statistical analysis. This study was supported in part by grants from the Scientific Advisory Board for Defence, the Ministry of Education, Finland, the Foundation of Sport Institute, and the Foundation of Werner Hacklin. REFERENCES 1. Nindl BC, Leone CD, Tharion W, et al : Physical performance responses during 72 h of military operational stress. 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