Effects of Baseline Fitness and BMI Levels on Changes in Physical Fitness During Military Service

This is a self-archived version of an original article. This version may differ from the original in pagination and typographic details. Author(s): Title: Year: Version: Copyright: Rights: Rights url: Please cite the original version: CC BY-NC-ND 4.0 https://creativecommons.org/licenses/by-nc-nd/4.0/ Effects of Baseline Fitness and BMI Levels on Changes in Physical Fitness During Military Service © 2020 Elsevier Accepted version (Final draft) Pihlainen, Kai; Vaara, Jani; Ojanen, Tommi; Santtila, Matti; Vasankari, Tommi; Tokola, Kari; Kyröläinen, Heikki Pihlainen, K., Vaara, J., Ojanen, T., Santtila, M., Vasankari, T., Tokola, K., & Kyröläinen, H. (2020). Effects of Baseline Fitness and BMI Levels on Changes in Physical Fitness During Military Service. Journal of Science and Medicine in Sport, 23(9), 841-845. https://doi.org/10.1016/j.jsams.2020.02.006 2020 Journal Pre-proof Effects of Baseline Fitness and BMI Levels on Changes in Physical Fitness During Military Service Kai Pihlainen, Jani Vaara, Tommi Ojanen, Matti Santtila, Tommi Vasankari, Kari Tokola, Heikki Kyr¨ol¨ ainen PII: S1440-2440(19)31497-5 DOI: https://doi.org/10.1016/j.jsams.2020.02.006 Reference: JSAMS 2260 To appear in: Journal of Science and Medicine in Sport Received Date: 16 November 2019 Revised Date: 13 January 2020 Accepted Date: 7 February 2020 Please cite this article as: Pihlainen K, Vaara J, Ojanen T, Santtila M, Vasankari T, Tokola K, Kyr¨ol¨ ainen H, Effects of Baseline Fitness and BMI Levels on Changes in Physical Fitness During Military Service, Journal of Science and Medicine in Sport (2020), doi: https://doi.org/10.1016/j.jsams.2020.02.006 This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier. 1 Effects of Baseline Fitness and BMI Levels on Changes in Physical Fitness During Military Service Kai Pihlainen 1, Jani Vaara 2, Tommi Ojanen 3, Matti Santtila 2, Tommi Vasankari 4, Kari Tokola 4, and Heikki Kyröläinen 2,5 1 Training Division, Defence Command, Finnish Defence Forces, P.O. Box 919, 00131 Helsinki, Finland 2 Department of Military Pedagogy and Leadership, National Defence University, P.O Box 7, 00861, Helsinki, Finland 3 Finnish Defence Research Agency, Finnish Defence Forces, P.O. Box 5, 04401 Järvenpää, Finland 4 UKK Institute for Health Promotion Research, Kaupinpuistonkatu 1, 33500 Tampere, Finland 5 Faculty of Sport and Health Sciences, University of Jyväskylä, P.O. Box 35 (VIV), 40014 University of Jyväskylä, Finland Corresponding author Kai Pihlainen, MSc, Marunakuja 6 A 28, 00840 Helsinki Tel. +358 40 024 8910 E-mail. kai.pihlaine[email protected] Word count: 2994 Abstract word count: 239 Number of tables: 2 (+2 supplement tables) Number of figures: 1 Journal Pre-proof 2 ABSTRACT Objectives. The purpose of the present study was to investigate how aerobic fitness, muscle fitness and body mass index (BMI) change in relation to their baseline levels during 6-12 months of military service. Design: Retrospective longitudinal follow-up study. Methods. The study group consisted of 249 279 healthy young male conscripts (age 19.1±0.4 yrs.) who completed their military service between the years 2005-2015. Anthropometrics (body mass, height, BMI), aerobic fitness (12-minute running test) and muscle fitness (sit-ups, push-ups, standing long jump) were measured. Results. A 12-minute running test improved by 5% (107±292 m), standing long jump 1% (2.1±16.2 cm), 1-min sit-ups 19% (4±8 repetitions/min) and 1-min push-ups 33% (5±10 repetitions/min) (p<0.001 for all). Baseline fitness and baseline BMI levels were inversely associated with their changes (r= −0.37 - −0.47, p<0.001). Performance improved in conscripts in the lowest two baseline fitness quartiles in all tests, while it decreased in conscripts in the highest fitness quartiles. In addition, in conscripts who were obese at baseline, body mass decreased on average by 4.9±7.0 kg (p<0.001). Conclusions. On average, the physical fitness of conscripts improved during their compulsory military service. In particular, conscripts with a lower baseline fitness level or higher BMI showed the largest improvements, which may be significant findings from both a military readiness and national health perspective. However, the decline in physical performance of high-fit conscripts Journal Pre-proof 3 highlights the importance of individualization of physical training and military training load during military service. Keywords: Physical performance, exercise, readiness, public health, conscript. Journal Pre-proof 4 INTRODUCTION It is generally recognized that successful management of military duties requires high levels of aerobic fitness and muscular strength 1. Aerobic fitness is particularly important in prolonged military tasks consisting of physical activity at varying intensities 2. Muscular strength and power are also essential physical performance attributes during physically demanding tasks such as sprinting short distances, jumping over obstacles, and lifting, carrying or dragging heavy loads and materials 3. Adequate physical fitness level is also desirable since it may decrease the risk of musculoskeletal injuries and premature discharge from military service 4, 5. From a health perspective, physical fitness and physical activity have been linked to a number of central and peripheral adaptations that decrease the risk of cardiovascular diseases 6, which are currently the leading causes of death in males globally 7. In addition, physical activity is a significant contributor to reductions in excess body weight, which is a risk factor for all-cause mortality and disability 8. While some studies have observed positive adaptations to a standardized military training 9, 10, 11, many of them have focused on one training phase such as basic training 4, 12, 13. Currently, there are limited data concerning the effects of longer follow-ups, e.g. 6-12 months, which report physical performance and body composition changes with a large representative sample size and throughout the complete military service time 14, 15. Finland is one of the very few countries where conscription is compulsory for all healthy males, which results in about 75% of young men performing their military service annually. Currently, the military service is divided into three main phases, known as basic training, special training and unit training period. The length of each period is approximately 8 weeks. In addition, roughly one third of the conscripts are trained for noncommissioned officer and reserve officer tasks for 16 to 22 weeks. During the 6‒12 months of military service, conscripts perform progressive physical training that includes combat training and close-order drills, marching and sports-related training for more than 20 hours per week 9. However, Journal Pre-proof 5 the execution of optimal military training has become more challenging because an increasing proportion of young Finnish men are overweight and have poor aerobic fitness 16. With this in mind, the purpose of the present study was to investigate military service-induced changes in physical fitness and body mass index (BMI) of male conscripts in relation to their baseline levels. METHODS The present retrospective dataset consisted of individual fitness test and body anthropometry results of 249 279 healthy young male conscripts (19.1±0.4 yrs., 179.2±6.6 cm, 77.0±13.3 kg) during 2005‒2015 (Table 1). The baseline fitness tests were conducted during the first two weeks of military service by educated fitness instructors, while the post-measurements were performed approximately 4‒6 weeks before the end of service. The average duration of the military service was 38 (range 24-52) weeks. After the tests, fitness instructors imported the results to the central database according to the standards determined by the Training Division of the Defence Command. Results concerning temporal changes in the initial body anthropometrics and physical fitness of conscripts from the same dataset were recently published by Santtila et al. 16. Table 1 here The present fitness tests and anthropometric measurements were conducted as part of military service, after a physical examination by medical doctors. Safety instructions were given to conscripts before each fitness test, and they were advised of their right to voluntarily interrupt the test at any time. The test termination criteria included the following indications: onset of angina-like symptoms, shortness of breath, wheezing, leg cramps, claudication, light-headedness, confusion, or nausea 17. All subjects were fully informed of the procedures and possible risks associated with the Journal Pre-proof 6 fitness tests. This study was approved by the Defence Command Finland and conducted according to the 1975 Declaration of Helsinki. The data were anonymized before scientific use. The measurements of the present study have been described in detail by Santtila et al. 16. Briefly, anthropometric measurements were conducted by a physician during a standardized medical examination as part of the military service. Body mass was measured to the nearest 100 g and stature with an accuracy of 5 mm. Thereafter, BMI was calculated by dividing body mass (kg) by the square of stature (m2). Physical fitness tests, protocols and techniques were standardized according to the guidelines of the Defence Command Finland 17, and the tests were supervised and demonstrated by educated fitness instructors. Aerobic fitness of the conscripts was assessed using the 12-min running test. Conscripts were instructed to perform the test with maximal effort at a progressively increasing running speed and the results were recorded with an accuracy of 10 m. Separated from the 12-min running test by at least two days, muscle fitness was assessed using standing long jump, 1-min sit-up and 1-min push-up tests. Standing long jump (SLJ) was used to assess explosive power production of the lower extremities. The result of this test was expressed in centimeters from the longest jump of three trials. The sit-up test assessed dynamic performance of abdominal and hip flexor muscles, while the push-up test assessed arm and shoulder extensor muscle performance. The outcome measure of the sit-up and push-up tests was the number of repetitions in one minute. Journal Pre-proof 7 Commercial software (IBM Corp. Released 2017. IBM SPSS Statistics for Windows, Version 25.0. Armonk, NY: IBM Corp.) was used for statistical analyses. Data are presented as means and standard deviations (± SD) where appropriate. Significance of changes between baseline and follow-up measures were analyzed using paired samples T-tests. Pearson correlation coefficients were calculated to examine associations between body composition and physical fitness variables and their changes. The data were additionally pooled into combined BMI categories and quartiles for each fitness test result, and the group differences were tested using analysis of covariance (ANCOVA). In the ANCOVA models, the contributions of categorized baseline fitness and BMI levels to changes in a given fitness variable were examined. Similarly, the contributions of categorized baseline BMI and categorized baseline fitness test results to changes in BMI were determined. Further adjustment for service duration only had a very small effect on comparative values and is therefore not presented in this article. Statistical significance was defined as p<0.05. RESULTS The average changes in stature and body mass were 0.5±1.5 cm (p<0.001) and 0.0±4.9 kg (p=0.602), respectively, during the follow-up period. The respective change in BMI was −0.1±1.5 kg/m2 (p<0.001). Change in body mass explained 93% of the change in BMI (R2=0.93, p<0.001). Despite the modest overall changes, the most marked reductions in body mass were observed in initially obese conscripts. Whereas the underweight (BMI <18.5) conscripts gained body mass on average by 4.0±4.6 kg (p<0.001), their overweight (BMI 25−29.9) and obese (BMI≥30) counterparts lost −2.0±5.9 (p<0.001) and −4.9±7.0 kg (p<0.001), respectively. Conscripts in the normal BMI category (18.5-24.9) gained body mass by an average of 1.1±3.8 kg (p<0.001). Journal Pre-proof 14 strength training are encouraged, especially for conscripts who belong to the highest baseline fitness quartiles.  These adjustments may help to ensure that the fitness level of the abovementioned subgroups continues to improve or is at least maintained during military service. ACKNOWLEDGEMENTS There are no conflicts of interest, financially or otherwise, among any of the authors of this article. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. The views, opinions, and/or findings contained in this publication are those of the authors and should not be construed as an official position, policy, or decision of the Finnish Defence Forces, unless so designated by other documentation. Journal Pre-proof 15 REFERENCES 1. Sharp M, Patton J, Vogel J. A database of physically demanding tasks performed by U.S. army soldiers. 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Variable n (pre-post) mean±SD (pre) Body mass (kg) 63 366 77+13 Stature (cm) 56 803 179+7 BMI (kg/m2) 56 444 24.0±3.8 12-min run (m) 218 810 2461±366 Standing long jump (cm) 220 318 218±26 1-min sit-up (reps/min) 221 276 37±11 1-min push-up (reps/min) 220 028 32±14 Journal Pre-proof 20 Table 2. Pearson correlation coefficients between the baseline test results and their changes (∆) during military service Variable n R (baseline vs. ∆) p Body mass 60 102 −0.43 <0.001 Stature 56 679 −0.15 <0.001 Body mass index 56 444 −0.47 <0.001 12-min run 218 810 −0.46 <0.001 Standing long jump 220 318 −0.37 <0.001 1-min sit-up 221 276 −0.44 <0.001 1-min push-up 220 028 −0.39 <0.001 Journal Pre-proof 21 FIGURE LEGENDS Figure 1. Mean changes in 12-min running distance (a), standing long jump (b), 1-min push-up (c) and 1-min sit-up (d) performance of conscripts in the combined baseline BMI category and fitness quartile groups during military service. Journal Pre-proof