Ran Yanovich

Effects of a 4-Month Recruit Training Program on Markers of Bone Metabolism

UNLABELLED Stress fracture susceptibility results from accelerated bone remodeling after onset of novel exercise and may be reflected in bone turnover changes. It is unknown if the bone turnover response to exercise is different between sexes. PURPOSE To assess disparity between sexes in bone metabolism markers during military recruit training and to evaluate relationships between bone turnover markers and factors that may affect bone metabolism. METHODS Volunteers were age-matched men (n = 58) and women (n = 199), 19 yr old, entering gender-integrated combat training. Blood was collected at 0, 2, and 4 months and anthropometric and fitness measures at 0 and 4 months. Serum was analyzed for biomarkers reflecting bone formation (bone alkaline phosphatase and procollagen I N-terminal peptide), bone resorption (C-telopeptide cross-links of type I collagen and tartrate-resistant acid phosphatase), endocrine regulation (parathyroid hormone, calcium, and 25(OH)D), and inflammation (interleukin 1B, interleukin 6, and tumor necrosis factor alpha). Data were analyzed using ANOVA, correlation, and regression analyses. RESULTS Bone turnover markers were higher in men (P < 0.01) and increased similarly for both sexes from 0 to 2 months (P < 0.01). Independent of gender, VO2max (R = 0.477) and serum calcium (R = 0.252) predicted bone formation activity (bone alkaline phosphatase) at baseline (P < 0.01). Serum calcium and parathyroid hormone decreased (2.0 and 6.4%, respectively) from 0 to 2 months (P < 0.001), returning to baseline at 4 months for both sexes. Men exhibited a decrease in 25(OH)D from 0 to 4 months (P = 0.007). Changes in endocrine regulators were significantly correlated with changes in bone turnover markers. Inflammatory markers did not differ between sexes and did not increase. CONCLUSION Military training increased bone formation and resorption markers in 2 months, suggesting rapid onset of strenuous exercise accelerates bone turnover similarly in men and women. Although bone turnover markers were higher in men than women, bone formation status may be related to aerobic fitness and serum calcium independent of gender and may be affected by small changes in endocrine regulators related to nutrition.

Sex Differences in Parameters of Bone Strength in New Recruits : Beyond Bone Density

BACKGROUND Stress fracture (SF) injuries in new recruits have long been attributed to low bone mineral density (BMD). Low areal BMD assessed using two-dimensional dual-energy x-ray absorptiometry imaging, however, reflects structural density and is affected by smaller measures of bone geometry. Recent studies support a relationship between bone size and SF and indicate that slender bones are more susceptible to damage under identical loading conditions. Peripheral quantitative computed tomography (pQCT) is a three-dimensional imaging tool that provides measures of tissue density and geometry parameters of the tibia, a common site of SF. PURPOSE To evaluate sex differences in parameters of volumetric BMD (vBMD), geometry, and strength of the tibia in new recruits using a novel pQCT image analysis procedure. METHODS pQCT images were obtained from 128 healthy men and women (20 male, 108 female, aged 18-21 yr) entering a 4-month gender-integrated combat training program in the Israeli Defense Forces. Tibial scans taken at sites 4% (trabecular bone), 38%, and 66% (cortical bone) from the distal end plate were analyzed using MATLAB to assess whole-bone and regional parameters. Measures included vBMD, geometry (diameter, area, cortical thickness, and canal radius), and strength (moments of inertia and bone strength and slenderness indices). RESULTS With the exception of normalized canal radius, which did not differ between sexes, all measures of bone geometry (P < 0.0001) and strength (P < 0.0001 to P = 0.07) were greater in men. Women exhibited 2.7% to 3.0% greater cortical vBMD than men, whereas trabecular vBMD was 8.4% lower in women (P < 0.001). These differences remained significant after adjusting for body size. CONCLUSION Sex differences in bone geometry and mineralization of the tibia may contribute to a decreased ability to withstand the demands imposed by novel, repetitive exercise in untrained individuals entering recruit training.

Dietary intake and stress fractures among elite male combat recruits

BackgroundAppropriate and sufficient dietary intake is one of the main requirements for maintaining fitness and health. Inadequate energy intake may have a negative impact on physical performance which may result in injuries among physically active populations. The purpose of this research was to evaluate a possible relationship between dietary intake and stress fracture occurrence among combat recruits during basic training (BT).MethodsData was collected from 74 combat recruits (18.2 ± 0.6 yrs) in the Israeli Defense Forces. Data analyses included changes in anthropometric measures, dietary intake, blood iron and calcium levels. Measurements were taken on entry to 4-month BT and at the end of BT. The occurrence of stress reaction injury was followed prospectively during the entire 6-month training period.ResultsTwelve recruits were diagnosed with stress fracture in the tibia or femur (SF group). Sixty two recruits completed BT without stress fractures (NSF). Calcium and vitamin D intakes reported on induction day were lower in the SF group compared to the NSF group-38.9% for calcium (589 ± 92 and 964 ± 373 mg·d-1, respectively, p < 0.001), and-25.1% for vitamin D (117.9 ± 34.3 and 157.4 ± 93.3 IU·d-1, respectively, p < 0.001). During BT calcium and vitamin D intake continued to be at the same low values for the SF group but decreased for the NSF group and no significant differences were found between these two groups.ConclusionsThe development of stress fractures in young recruits during combat BT was associated with dietary deficiency before induction and during BT of mainly vitamin D and calcium. For the purpose of intervention, the fact that the main deficiency is before induction will need special consideration.

Variation in tibial functionality and fracture susceptibility among healthy, young adults arises from the acquisition of biologically distinct sets of traits.

Physiological systems like bone respond to many genetic and environmental factors by adjusting traits in a highly coordinated, compensatory manner to establish organ‐level function. To be mechanically functional, a bone should be sufficiently stiff and strong to support physiological loads. Factors impairing this process are expected to compromise strength and increase fracture risk. We tested the hypotheses that individuals with reduced stiffness relative to body size will show an increased risk of fracturing and that reduced strength arises from the acquisition of biologically distinct sets of traits (ie, different combinations of morphological and tissue‐level mechanical properties). We assessed tibial functionality retrospectively for 336 young adult women and men engaged in military training, and calculated robustness (total area/bone length), cortical area (Ct.Ar), and tissue‐mineral density (TMD). These three traits explained 69% to 72% of the variation in tibial stiffness (p < 0.0001). Having reduced stiffness relative to body size (body weight × bone length) was associated with odds ratios of 1.5 (95% confidence interval [CI], 0.5–4.3) and 7.0 (95% CI, 2.0–25.1) for women and men, respectively, for developing a stress fracture based on radiography and scintigraphy. K‐means cluster analysis was used to segregate men and women into subgroups based on robustness, Ct.Ar, and TMD adjusted for body size. Stiffness varied 37% to 42% among the clusters (p < 0.0001, ANOVA). For men, 78% of stress fracture cases segregated to three clusters (p < 0.03, chi‐square). Clusters showing reduced function exhibited either slender tibias with the expected Ct.Ar and TMD relative to body size and robustness (ie, well‐adapted bones) or robust tibias with reduced residuals for Ct.Ar or TMD relative to body size and robustness (ie, poorly adapted bones). Thus, we show there are multiple biomechanical and thus biological pathways leading to reduced function and increased fracture risk. Our results have important implications for developing personalized preventative diagnostics and treatments.

Differences in physical fitness of male and female recruits in gender-integrated army basic training.

PURPOSE To evaluate gender differences in physical fitness before and after a 4-month gender-integrated basic training (BT) course and to determine whether this program effectively narrowed the differences between male and female soldiers in physical fitness parameters. METHODS One hundred and thirty-seven soldiers (109 females and 28 males) successfully completed a 4-month BT course in the Israeli Defense Forces (IDF). The subjects physical fitness was evaluated pre- and post-BT by three laboratory tests [the maximal aerobic capacity (VO2max), the Leonardo Ground Reaction Force Plate, and the Wingate Anaerobic Test (WAnT)] and by the IDF physical fitness test (IDF-PT). RESULTS Females significantly improved their scores in the IDF-PT and laboratory aerobic tests, whereas males significantly improved only in the IDF-PT. After BT, gender differences narrowed by approximately 4% in all tests except upper body strength. Although fitness improvement after BT was marginally higher in females than males, resulting in a slight narrowing of the gender differences, a significant gender gap in physical fitness still exists after BT. CONCLUSIONS There was only a small overlap in physical abilities at the beginning of BT, which indicated vast differences in physical fitness between the genders. As expected, integrated combat BT improved physical fitness. Although females demonstrated marginally higher improvement in aerobic capacity, basic physiological gender differences were still evident at the end of the training regimen.

Heat acclimation and performance in hypoxic conditions.

INTRODUCTION Hypoxia is known to reduce performance. Adaptation is limited and requires special conditions. Heat and hypoxia have been shown to share some adaptive mechanisms. The purpose of this study was to test the possibility that prior heat acclimation may preserve performance under hypoxia. METHODS Eight young healthy men participated in this study. They went through two cognitive tests: Visual Vigilance Task (VVT) and Four Choice Reaction Time (FCRT); through a Dynamic Posture Test (DPT); and through an exercise onset of blood lactate accumulation rate (OBLA) test under moderate hypoxia (O2 = 15.6%) before and after 12 d of heat acclimation. RESULTS Maximal heart rate and core temperature were lower during the last day of heat acclimation compared to baseline (103 +/- 14 compared to 115 +/- 13 bpm and 37.59 +/- 0.20 compared to 37.83 +/- 0.28 degrees C, respectively). OBLA was higher after heat acclimation under both normoxic and hypoxic conditions. Blood oxygen saturation during walking at a pace of 7 km/h in hypoxic conditions was higher after heat acclimation compared to baseline (88 +/- 2% and 86.5 +/- 2%, respectively). Average steps during DPT in hypoxic conditions increased from 4.083 +/- 0.044 to 4.75 +/- 0.326 after heat acclimation. The VVT results under hypoxia did not change after heat acclimation, but false positive results were lower. The FCRT test results improved after heat acclimation (475 +/- 30 ms compared to 500 +/- 24 ms). CONCLUSIONS Prior heat acclimation may reduce physiological strain and improve cognitive performance in moderate hypoxia. Further studies are required in order to evaluate the possibility of implementing this method as an operational preconditioning tool.

IGF-I, IGFBPs, and inflammatory cytokine responses during gender-integrated Israeli Army basic combat training.

Abstract Nindl, BC, Scofield, DE, Strohbach, CA, Centi, AJ, Evans, RK, Yanovich, R, Moran, DS. IGF-I, IGFBPs, and inflammatory cytokine responses during gender-integrated Israeli Army basic combat training. J Strength Cond Res 26(7): S73–S81, 2012—Insulin-like growth factor 1 (IGF-I) is a robust metabolic and anabolic biomarker that has been demonstrated to be reflective of military training–induced body composition changes and influenced by initial aerobic fitness level. Greater mechanistic insight into the IGF-I response to physical training can potentially be gleaned by also examining other regulatory factors that influence IGF-I biological activity (i.e., insulin-like growth factor–binding proteins [IGFBPs] and inflammatory cytokine responses). The purpose of this study was to assess the influence of sex and initial fitness level on the IGF-I and inflammatory cytokine response to gender-integrated Israeli Defense Forces (IDF) basic combat training (BCT). Recruits (29 men, 19.1 ± 1.3 years; 93 women, 18.8 ± 0.6 years) were recruited from a 4-month gender-integrated BCT of the IDF. Blood was drawn and assayed for total IGF-I, free IGF-I, IGFBPs 1-6, tumor necrosis factor alpha (TNF-&agr;), interleukin 6, and interleukin 1 beta. Body composition was determined via a 4-site skinfold (biceps, triceps, suprailiac, and subscapular) equation. Physical performance was assessed via a maximum volume of oxygen consumption (V[Combining Dot Above]O2max) test using a treadmill protocol. All measures were obtained pre- and posttraining. A 2-way (sex × time) analysis of variance was used to test for statistical differences (p ⩽ 0.05). Additionally, subjects were further partitioned (men and women separately) by tertiles of initial V[Combining Dot Above]O2max to assess the influence of initial fitness level on the IGF-I system and inflammatory cytokine responses to physical training. Pearson product moment correlational analysis was also used to examine relationships between percent changes in blood measures and physical performance and body composition changes. All data are presented as mean ± SE. Time effects were observed only for total IGF-I, IGFBP-2, TNF-&agr;, V[Combining Dot Above]O2max, fat-free mass, and fat mass. The only significant (p ⩽ 0.05) correlations observed for percent changes were in men between total IGF-I and V[Combining Dot Above]O2max (r = 0.49) and body mass (r = −0.42) During gender-integrated Israeli Army BCT, men and women generally respond in a similar fashion with regard to blood measures (IGF-I system and inflammatory cytokines) and V[Combining Dot Above]O2max. Initial fitness level only influenced the IGF-I response to training in women. Although the training-induced changes in total IGF-I (increase), IGFBP-2 (decrease), and TNF-&agr; (decrease) are all indicative of an enhanced circulating anabolic milieu, only total IGF-I for the men was correlated with body composition and fitness improvements.

Female recruits sustaining stress fractures during military basic training demonstrate differential concentrations of circulating IGF-I system components: A preliminary study

OBJECTIVE Stress fracture injuries sustained during military basic combat training (BT) are a significant problem and occur at a higher rate in female recruits than male recruits. Insulin-like growth factor-I (IGF-I) is an easily measured biomarker that is involved in bone formation and positively correlated with bone mineral density, especially in women. This study examined the response of the IGF-I system between female soldiers that sustained a stress fracture (SFX, n=13) during BT and female soldiers who did not (NSFX, n=49). DESIGN Female soldiers (n=62, 18.8 ± 0.6 yr) from 2 companies of a gender-integrated combat battalion in the Israeli Defense Forces participated in this study. Height, weight and blood draws were taken upon entry to BT (preBT) and after a four-month BT program (postBT). Stress fractures were diagnosed by bone scan. Serum was analyzed for total IGF-I, free IGF-I, IGF binding proteins (IGFBP)1-6, BAP, calcium, CTx, IL1β, IL6, PINP, PTH, TNFα, TRAP, and 25(OH)D. Statistical differences between SFX and NSFX groups and time points were assessed by RM ANOVA with Fisher post-hoc (p≤0.05). RESULTS The SFX group was significantly taller and had lower BMI than NSFX (p≤0.05). Serum concentrations of total IGF-I, bioavailable IGF-I, other bone biomarkers, and cytokines were not significantly different between SFX and NSFX preBT. Serum IGFBP-2 and IGFBP-5 were significantly higher in the SFX compared to the NSFX preBT (p≤0.05). In both groups, total IGF-I increased pre to postBT (p≤0.05). Additionally, a significant difference was observed in the bioavailable IGF-I response pre to postBT for both groups. The SFX group demonstrated a significant decrease in bioavailable IGF-I pre to postBT (preBT: 0.58 ± 0.58 ng/mL; postBT 0.39 ± 0.48; p≤0.05) whereas the NSFX group demonstrated a significant increase in bioavailable IGF-I pre to postBT (preBT: 0.53 ± 0.37 ng/mL; postBT: 0.63 ± 0.45; p≤0.05). CONCLUSIONS Our study demonstrated that serum IGF-I changes during basic training and that women sustaining stress fractures during BT significantly decreased bioavailable IGF-I, whereas their uninjured counter parts increased bioavailable IGF-I. These results suggest that stress fracture susceptibility may be related to differential IGF-I system concentrations and response to physical training.

Physical and psychological stressors linked with stress fractures in recruit training

This study aimed to measure ambulation in infantry army basic training, and to evaluate if covering more distance can explain stress fractures in a stressor–stress model. Forty‐four male combat recruits (18.7 ± 0.7 years) participated in a 6‐month rigorous high intensity combat training program. Baseline data included anthropometric measurements, VO2max, and psychological questionnaires. Actual distance covered was measured using a pedometer over an 11‐week training period. Psychological questionnaires were repeated after 2 months. Sixteen recruits were diagnosed with stress fractures by imaging (SFi = 36.4%). Statistical analysis included comparing measured variables between SFi and those without stress fractures (NSF). The recruits covered 796 ± 157 km, twofold the distance planned of 378 km (P < 0.001). The SFi group covered a distance 16.4% greater than that of the NSF group (866 ± 136 and 744 ± 161 km, respectively, P < 0.01), and also demonstrated greater psychological stress. These data reveal the importance of adherence to or enforcement of military training programs. In the light of these data, the Israeli Defense Forces program needs reappraisal. A stressor–stress response might explain the susceptibility of certain recruits for injury. Using advanced technology, monitoring ambulation may prevent stress fracture development by limiting subjects exceeding a certain level. Psychological profile may also play a role in predicting stress fracture development.

Anemia, Iron Deficiency, and Stress Fractures in Female Combatants During 16 Months

Yanovich, R, Merkel, D, Israeli, E, Evans, RK, Erlich, T, and Moran, DS. Anemia, iron deficiency, and stress fractures in female combatants during 16 months. J Strength Cond Res 25(12): 3412–3421, 2011—The purpose of this study is to evaluate the hematological profile of military recruits in different settings and training programs and to investigate the link between anemia and iron deficiency with stress fracture (SF) occurrence. We surveyed 3 groups of recruits for 16 months: 221 women (F) and 78 men (M) from 3 different platoons of a gender-integrated combat battalion and a control group (CF) of 121 female soldiers from a noncombat unit. Data were fully collected upon induction and at 4 and 16 months from 48F, 21M, and 31CF. Blood tests, anthropometry, physical aerobic fitness, and SF occurrence were evaluated. On induction day, 18.0 and 19.0% of F and CF were found to be anemic, and 61.4 and 50.9%, respectively, were found to have iron deficiency, whereas 7.7% of M were found to be anemic and 10.2% iron deficient. During the 4 months of army basic training (ABT), anemia and iron deficiency prevalence did not change significantly in any group. After 16-months, anemia prevalence decreased by 8% among F and CF and abated in M. Iron deficiency was prevalent in 50.0, 59.4, and 18.8% of F, CF, and M, respectively. Stress fractures were diagnosed in 14 F during ABT, and they had a significantly higher prevalence (p < 0.05) of anemia and iron deficiency anemia compared to F without SFs. The observed link between anemia and iron deficiency on recruitment day and SFs suggests the importance of screening female combat recruits for these deficiencies. To minimize the health impact of army service on female soldiers, preventative measures related to anemia and iron deficiency should be administered. Further research is needed for evaluating the influence of low iron in kosher meat as a possible explanation for the high prevalence of iron deficiency among young Israeli recruits.