The current study shows that active duty soldiers compared with trainees performed significantly better in push-ups, sit-ups, the SBC, and the CD. Compared with active duty soldiers, trainees performed the 2-mile run significantly faster. Overall, IET seems to provide sufficient physical training because most trainees (>90%) were able to meet the MAPSs for the 3 CPDTs.
Recently, it was determined that U.S. Army male active duty soldiers performed significantly better on the APFT events across all age groups in comparison with male trainees in the first 3 weeks of their IET (6). It was assumed the differences on the APFT were likely due to the active duty soldiers having more experience performing the test along with more intense physical training. Because the trainees' APFT data in the current study were retrieved from the end of their IET rather than the beginning, the trainees had already become familiarized with the APFT events. The active duty soldiers performed significantly more push-ups and sit-ups, whereas trainees had faster 2-mile run times. The faster 2-mile run times by the trainees could be due to the greater emphasis placed on cardiorespiratory fitness during IET, related to the forms of running, road marching, obstacle courses, and other strenuous modes of physical activity (15,21). Although strong correlations have been previously reported between self- and unit-reported APFT data, slightly inflated performance values have been shown in self-report data (23). The potential inflation may have led to higher push-up and sit-up scores in the active duty soldiers; however, they still reported slower 2-mile run times compared with the trainees in this study.
The SBC is a repetitive lift-and-carry task that requires a combination of muscular strength and muscular endurance. It has been shown that expert and novice workers perform manual materials handling tasks differently in terms of body position during loading/unloading phases, foot movements during the transfer, and grip on the material (1). The active duty soldiers had a longer mean service time (i.e., 3 years) and reported performing the task more frequently, which may have allowed refinements in techniques to improve performance and efficiency of the task; however, the current study did not use visual aids (e.g., video recording) to analyze or evaluate technique differences between trainees and active duty soldiers. Other variables such as muscular strength levels and muscle mass may also have been responsible for performance differences in particular manual materials handling task (29).
Lean body mass and physical fitness have been shown to be modifiable factors that can improve occupational carrying performance. It has been reported that body composition, muscular strength, muscular power, and sprint time are all strong predictors of a manual carrying task performance (4,19). Beck et al. (2) reported leg lean mass as the most influential contributor for performance on 2 military carrying tasks. Unfortunately, we were unable to adjust for body composition in our subjects to determine the effect of lean body mass on SBC performance.
There were no differences in MUF performance between trainees and active duty soldiers. Foulis et al. (7) reported performance improvements in MUF from only the first to second trial. This indicates that an additional trial may have been necessary to familiarize subjects to the task simulation compared with how they would normally perform it during training. Furthermore, our results showed a 1.8-second (0.03 minutes) difference, which is less than the 3.6-second detectable difference reported in the reliability study (7). The 2-second or approximately a 1% difference between the trainees and active duty soldiers in the current study may not seem very substantial; however, one could contend this difference could mean life or death in a combat environment.
Performing combat rushes (e.g., MUF) while carrying an external load (extra weight to move) and holding a weapon (upper-body restriction for sprinting) require specific physical conditioning in order for significant improvements in performance (33). Billing et al. (3) found that maximal velocity did not change in repeated 6-meter sprint repetitions with varying external loads in experienced soldiers. Although a slower sprint time would be expected when wearing an external load, 51.7% of total performance loss during a prone start sprint with an external load occurred in the first 5 meters (33). The requirement of rising from a prone position with an external load into a sprint slows the momentum of performance at the start. The current study required the subjects to assume a prone position at every third marker. Rising from a prone position under a heavy load multiple times and the difficulty to improve sprint performance in a short distance (6.6 meters) are 2 possible explanations for the lack of performance differences between trainees and active duty soldiers. The 2 groups likely had equivalent skills performing this task because there were no differences in the reported performance frequency of task. Further research should investigate training modalities to improve performance on repeated sprint ability with an external load.
Finally, an important factor must be addressed regarding the task frequency questionnaire because there was not an equivalent timeframe between the trainees and active duty soldiers. The active duty soldiers based their answers on their entire military career (mean time in service of 3 years), whereas the trainees' careers consisted of only their time in IET (12–14 weeks). Harman et al. (10) state that short training periods (such as 8–10 weeks in basic combat training) may not elicit large improvements in physical performance of military tasks. Others have suggested task-specific physical training, and more exposure to the task is effective in improving performance of a single task (17,26). It is speculated that one of the explanations for better SBC and CD performance by the active duty soldiers is that they had more experience performing the tasks due to a longer time in service. This factor highlights the importance of having sufficient time to practice the tasks to improve performance.
This study highlights physical fitness and occupational task performance differences between trainees and experienced active duty soldiers. Most trainees met the MAPSs at the end of their IET, indicating that IET was successful in preparing the trainees to perform the physically demanding tasks of their MOS. Although the trainees may have met the minimal physical requirements at the end of their IET, performance differences were still apparent between the trainees and active duty soldiers, possibly in part to physical fitness and experience differences. Refinements should be continuously made to ensure that IET is optimizing performance in soldiers and other tactical athletes. This may include more task-specific practice of physically demanding tasks and the development of conditioning programs to enhance muscular strength and power.
The authors thank all the researchers and soldiers who participated in the data collection. The research team adhered to the policies for protection of human subjects as prescribed in Army Regulation 70-25, and the research was conducted in adherence with the provisions of 45 Code of Federal Regulations (CFR) Part 46. This research was supported in part by appointments to the Postgraduate Research Participation Program at the U.S. Army Research Institute of Environmental Medicine administered by the Oak Ridge Institute for Science and Education. The opinions or assertions contained herein are the private views of the author(s) and are not to be construed as official or as reflecting the views of the Army or the Department of Defense. Any citations of commercial organizations and trade names in this report do not constitute an official Department of the Army endorsement or approval of the products or services thereof.
1. Authier M, Lortie M, Gagnon M. Manual handling techniques: Comparing novices and experts. Int J Indust Ergon 17: 419–429, 1996.
2. Beck B, Carstairs GL, Billing DC, Caldwell JN, Middleton KJ. Modifiable anthropometric characteristics are associated with unilateral and bilateral carry performance. J Strength Cond Res 31: 489–494, 2017.
3. Billing DC, Silk AJ, Tofari PJ, Hunt AP. Effects of military
load carriage on susceptibility to enemy fire during tactical combat movements. J Strength Cond Res 29: S134–S138, 2015.
4. Bilzon JL, Scarpello EG, Bilzon E, Allsopp AJ. Generic task-related occupational requirements for Royal Naval personnel. Occup Med (Lond) 52: 503–510, 2002.
5. Boye MW, Cohen BS, Sharp MA, Canino MC, Foulis SA, Larcom K, et al. U.S. Army Physical Demands Study: Prevalence and frequency of performing physically demanding tasks in deployed and non-deployed settings. J Sci Med Sport 20: S57–S61, 2017.
6. Dada EO, Anderson MK, Grier T, Alemany JA, Jones BH. Sex and age differences in physical performance: A comparison of Army basic training
and operational populations. J Sci Med Sport 20: S68–S73, 2017.
7. Foulis SA, Redmond JE, Frykman PN, Warr BJ, Zambraski EJ, Sharp MA. U.S. Army Physical Demands Study: Reliability of simulations of physically demanding tasks performed by combat arms soldiers. J Strength Cond Res 31: 3245–3252, 2017.
8. Foulis SA, Sharp MA, Redmond JE, Frykman PN, Warr BJ, Gebhardt DL, et al. U.S. Army Physical Demands Study: Development of the occupational physical assessment test for combat arms soldiers. J Sci Med Sport 20: S74–S78, 2017.
10. Harman EA, Gutekunst DJ, Frykman PN, Nindl BC, Alemany JA, Mello RP, et al. Effects of two different eight-week training
programs on military
physical performance. J Strength Cond Res 22: 524–534, 2008.
12. Jones SB, Knapik JJ, Sharp MA, Darakjy S, Jones BH. The validity of self-reported physical fitness test scores. Mil Med 172: 115–120, 2007.
13. Knapik J, Staab J, Bahrke M, O'Connor J, Sharp M, Frykman P, et al. Relationship of Soldier Load Carriage to Physiological Factors, Military
Experience and Mood States. Technical Report T17-90. Natick, MA: U.S. Army Research Institute of Environmental Medicine, 1990. Available at: http://www.dtic.mil/dtic/tr/fulltext/u2/a227007.pdf
. Accessed November 15, 2017.
14. Knapik JJ. The importance of physical fitness for injury prevention: Part 1. J Spec Oper Med 15: 123–127, 2015.
15. Knapik JJ, Graham BS, Rieger J, Steelman R, Pendergrass T. Activities associated with injuries in initial entry training
. Mil Med 178: 500–506, 2013.
16. Knapik JJ, Hauret KG, Arnold S, Canham-Chervak M, Mansfield AJ, Hoedebecke EL, et al. Injury and fitness outcomes during implementation of physical readiness training
. Int J Sports Med 24: 372–381, 2003.
17. Knapik JJ, Sharp MA. Task-specific and generalized physical training
for improving manual-material handling capability. Int J Indust Ergon 22: 149–160, 1998.
18. Knapik JJ, Sharp MA, Steelman RA. Secular trends in the physical fitness of United States Army recruits on entry to service, 1975–2013. J Strength Cond Res 31: 2030–2052, 2017.
19. Leyk D, Rohde U, Erley O, Gorges W, Essfeld D, Erren TC, et al. Maximal manual stretcher carriage: Performance and recovery of male and female ambulance workers. Ergonomics 50: 752–762, 2007.
20. Lindberg AS, Oksa J, Antti H, Malm C. Multivariate statistical assessment of predictors of firefighters' muscular and aerobic work capacity. PLoS One 10: e0118945, 2015.
21. Lisman PJ, de la Motte SJ, Gribbin TC, Jaffin DP, Murphy K, Deuster PA. A systematic review of the association between physical fitness and musculoskeletal injury risk: Part 1-cardiorespiratory endurance. J Strength Cond Res 31: 1744–1757, 2017.
22. Mala J, Szivak TK, Flanagan S, Comstock BA, Laferrier JZ, Maresh CM, et al. The role of strength and power during performance of high intensity military
tasks under heavy load carriage. US Army Med Dep J Apr-Jun: 3–11, 2015.
23. Martin RC, Grier T, Canham-Chervak M, Anderson MK, Bushman TT, DeGroot DW, et al. Validity of self-reported physical fitness and body mass index in a military
population. J Strength Cond Res 30: 26–32, 2016.
24. Pihlainen K, Santtila M, Häkkinen K, Kyröläinen H. Associations of physical fitness and body composition characteristics with simulated military
task performance. J Strength Cond Res 32: 1089–1098, 2018.
25. Reilly T, Olinek S. Predicting casualty evacuation performance for the Canadian land forces command. Occup Ergon 11: 1–9, 2013.
26. Roberts D, Gebhardt DL, Gaskill SE, Roy TC, Sharp MA. Current considerations related to physiological differences between the sexes and physical employment standards. Appl Physiol Nutr Metab 41: S108–S120, 2016.
27. Roy TC, Knapik JJ, Ritland BM, Murphy N, Sharp MA. Risk factors for musculoskeletal injuries for soldiers deployed to Afghanistan. Aviat Space Environ Med 83: 1060–1066, 2012.
28. Schonfeld BR, Doerr DF, Convertino VA. An occupational performance
test validation program for fire fighters at the Kennedy Space Center. J Occup Med 32: 638–643, 1990.
30. Sharp MA, Cohen BS, Boye MW, Foulis SA, Redmond JE, Larcom K, et al. U.S. Army Physical Demands Study: Identification and validation of the physically demanding tasks of combat arms occupations. J Sci Med Sport 20: S62–S67, 2017.
31. Sharp MA, Knapik JJ, Patton JF, Smutok MA, Hauret K, Canham-Chervak M, et al. Physical Fitness of Soldiers Entering and Leaving Basic Combat Training
. Technical Report T00-13. Natick, MA: U.S. Army Research Institute of Environmental Medicine, 2000. Available at: http://www.dtic.mil/get-tr-doc/pdf?AD=ADA374356
. Accessed December 13, 2017.
32. Shephard RU. Exercise and training
in women, part I: Influence of gender on exercise and training
responses. Can J Appl Physiol 25: 19–34, 2000.
33. Treloar AK, Billing DC. Effect of load carriage on performance of an explosive anaerobic military
task. Mil Med 176: 1027–1031, 2011.
34. von Heimburg ED, Rasmussen AK, Medbø JI. Physiological responses of fire fighters and performance predictors during a simulated rescue of hospital patients. Ergonomics 49: 111–126, 2006.