Journal Title (Medline/Pubmed accepted abbreviation): Appl. Physiol. Nutr. Metab.
Page numbers: 967-975
doi (if applicable): 10.1139/H11-124
Summary of background and research design:
Background: Military training is extremely intense and involves many physical stressors, including energy deficit. The lack of sufficient calories can lead to a decrease in physical performance (ex. vertical jump) which has obvious detriments if the soldiers are deployed shortly after military training.
Hypothesis: A daily mixed supplement will help soldiers retain body mass (fat and fat-free) as well as strength during arduous military training. Also, this supplement will help maintain normal levels of insulin-like growth factor (IGF-1), testosterone, and cortisol.
Subjects: Thirty healthy British soldiers, age about 25 ± 3 y
Experimental design: randomized, parallel groups
Treatments: Those in the supplement group (SUP) received an additional 5.1 MJ/day (1219 kcal) during weeks 0-6 and 3.6 MJ/day (860 kcal) during weeks 6-8. Those that were not in SUP were in the control group (CON).
Protocol: The training was 8 wks long, during which the soldiers consumed ~14.0 MJ/day (3346 kcal) during weeks 0-6 and 17.7 MJ/day (4230 kcal) during weeks 6-8. Prior to the study, body composition was evaluated, physical performance tests were conducted including maximal dynamic lift strength (power clean) and vertical jump height, and a fasting blood sample was collected. The same assessments were conducted after the 8 wk training period.
Summary of research findings:
- Without the supplement, the soldiers' routines put them at a daily energy deficit of about 2.2 MJ (526 kcal). The soldiers, on average, consumed 66% of the 5.1 MJ/day supplement and it reduced the magnitude of the energy deficit to 0.7 MJ per day (P < 0.001).
- Body mass decreased significantly in both groups during the 8 wks. However, the losses in CON were greater than the losses in SUP (P < 0.001). CON lost 22.8% fat whereas SUP lost 8.2% fat.
- Maximal dynamic lift strength, vertical just height, and explosive power output all decreased significantly in CON but were retained in SUP.
- Circulating IGF-1 decreased significantly in both groups after training. IGF-BP2 (an IGF binding protein) did not change in either group. IGF-BP3 decreased significantly in CON but did not change in SUP.
- Testosterone levels decreased more for CON than SUP, but this difference was not statistically significant. Cortisol levels did not change.
- There was a modest correlation between changes in IGF-1 and changes in body mass (r = 0.52, P = 0.003). No other correlations were noted.
Key practice applications:
Among British soldiers in an arduous training routine, a smaller energy deficit (351 kcal) was associated with better strength retention and physical performance compared with a larger energy deficit (526 kcal). The soldiers in this study, especially those in CON, were experiencing a phenomenon called "overreaching", which is characterized by decreased efficiency of the nervous system, repeated microtrauma to the muscle which leads to soreness, fatigue, and loss of motivation. Circulating levels of IGF-BP3 may be a useful biomarker for identifying over-worked athletes.
The military training protocol is designed to stress the soldiers maximally, to best prepare them to perform in the harshest conditions. It would be interesting to evaluate how the soldiers would perform 1) if both groups were provided adequate nutrition for a few weeks and then underwent the performance tests, and 2) if, after a few weeks of adequate nutrition, the soldiers underwent stressful conditions and then repeated the performance tests.