Musculoskeletal injuries in military personnel-Descriptive epidemiology, risk factor identification, and prevention.

OBJECTIVES: To provide an overall perspective on musculoskeletal injury (MSI) epidemiology, risk factors, and preventive strategies in military personnel. DESIGN: Narrative review. METHODS: The thematic session on MSIs in military personnel at the 5th International Congress on Soldiers' Physical Performance (ICSPP) included eight presentations on the descriptive epidemiology, risk factor identification, and prevention of MSIs in military personnel. Additional topics presented were bone anabolism, machine learning analysis, and the effects of non-steroidal anti-inflammatory drugs (NSAIDs) on MSIs. This narrative review focuses on the thematic session topics and includes identification of gaps in existing literature, as well as areas for future study. RESULTS: MSIs cause significant morbidity among military personnel. Physical training and occupational tasks are leading causes of MSI limited duty days (LDDs) for the U.S. Army. Recent studies have shown that MSIs are associated with the use of NSAIDs. Bone MSIs are very common in training; new imaging technology such as high resolution peripheral quantitative computed tomography allows visualization of bone microarchitecture and has been used to assess new bone formation during military training. Physical activity monitoring and machine learning have important applications in monitoring and informing evidence-based solutions to prevent MSIs. CONCLUSIONS: Despite many years of research, MSIs continue to have a high incidence among military personnel. Areas for future research include quantifying exposure when determining MSI risk; understanding associations between health-related components of physical fitness and MSI occurrence; and application of innovative imaging, physical activity monitoring and data analysis techniques for MSI prevention and return to duty.

Assessing rectal temperature with a novel non-invasive sensor.

Athletes, soldiers, and workers who perform intense physical activities under extreme hot conditions might encounter increased physiological thermal strain. Consequently, the increase in body core temperature (Tc) might result in heat exhaustion and heatstroke. Thus, continuously following changes in Tc is of utmost importance. Recently, the Tcore sensor (Dräger, Germany), which employs a unique dual-sensor heat flux technology, became commercially available to measure Tc, in a hospital-controlled environment. This study aimed to evaluate the possibility of using the Tcore sensor to accurately monitor rectal temperature (Tre), reflecting Tc, under exercise-heat stress. Thirteen healthy young males completed the study protocol, consisting of 90 min of moderate exercise (walking on a treadmill - 5 km/h, 4% elevation) under controlled hot/dry and hot/wet climatic conditions (30 °C/60% rh, 34 °C/40% rh, and 40 °C/40% rh). Tcore sensors were placed on the forehead and the left wrist. Temperatures from both Tcore sensors were recorded continuously together with Tre using a rectal thermistor. The original algorithm used by the company to estimate Tre from the Tcore sensor was found to be inadequate under the study's conditions and new models for the forehead and the wrist measurements were developed. Nearly 150,000 measurement sets (after filtering) were used to build independent MATLAB software algorithms and test their reliability according to the cross-validation algorithm. Bland-Altman analysis was used to compare between the results obtained by the new models to Tre. The database consisted of a large Tre range (36.5-38.9 °C). The mean errors of the models were close to zero, and the mean absolute errors were 0.20 ± 0.16 °C and 0.27 ± 0.20 °C for the forehead and wrist, respectively. 95% of the measurements from the forehead model and 86% from the wrist model were within ±0.5 °C of Tre, and 78% (forehead) and 64% (wrist) were within ±0.3 °C. Root Mean Square Deviation (RMSD) values were 0.29 °C and 0.40 °C for the forehead and wrist models, respectively. The developed models show the feasibility to use the Tcore sensor for assessing Tre under exercise-heat conditions. Furthermore, the sensor was found to be adequate for use on the wrist as well, which might be more practical for use in field conditions.

The Cardiovascular Reserve Index-A Noninvasive Clinical Insight Into Heat Intolerance.

OBJECTIVE: To noninvasively explore the heat intolerance condition during exercise-heat stress by assessing cardiovascular (CV) performance. DESIGN: Prospective study of participants undergoing a standard heat-tolerance test (HTT). SETTING: Institutional study. PARTICIPANTS: Ninety-five young males: 16 heat-intolerant (HI) and 79 heat-tolerant (HT). INTERVENTIONS: Cardiovascular performance during an HTT was estimated by heart rate (HR) and blood pressure measurements. MAIN OUTCOME MEASURES: The sensitivity of the cardiovascular reserve index (CVRI) and the dynamic heart rate reserve (dHRR) index to predict heat intolerance was compared. RESULTS: A significant difference in the CV reserve during exercise-heat stress was exhibited between the HI and the HT groups. Starting at a similar level, the reduction in the CV reserve at HTT endpoint was much greater in the HI than the HT individuals (P < 0.0001), as depicted by both the CVRI and the dHRR. This result indicates a greater utilization of the CV reserve by HI individuals. The CVRI is likely to be better predictor of heat intolerance than the dHRR because the partial area under the curve in the high sensitivity (>90%) region of its receiver operating characteristic curve is higher (93.2 vs 76.8). CONCLUSIONS: More than being a predictor, the CVRI may provide a new clinical insight into heat intolerance because it noninvasively characterizes the efficiency of an individual's thermoregulatory mechanism and hints that an impaired CV reserve might underlie heat intolerance. The CVRI provides a noninvasive measurement of thermoregulation, which has been long awaited to enable on-field studies and dynamic monitoring of heat-exposed task forces.

Mild Physical Activity Does Not Improve Spatial Learning in a Virtual Environment.

It is well-established that physical exercise in humans improves cognitive functions, such as executive functions, pattern separation, and working memory. It is yet unknown, however, whether spatial learning, long known to be affected by exercise in rodents, is also affected in humans. In order to address this question, we recruited 20 healthy young male adults (18-30 years old) divided into exercise and control groups (n = 10 in each group). The exercise group performed three sessions per week of mild-intensity aerobic exercise for 12 weeks, while the control group was instructed not to engage in any physical activity. Both groups performed maximal oxygen uptake (VO2max) tests to assess their cardiovascular fitness at baseline and every 4 weeks through the 12 weeks of the training program. The effects of mild aerobic exercise were tested on performance in two different virtual reality (VR)-based spatial learning tasks: (1) virtual Morris water maze (VMWM) and (2) virtual Radial arm water maze (VRAWM). Subjects were tested in both tasks at baseline prior to the training program and at the end of 12 weeks training program. While the mild-intensity aerobic exercise did not affect subjects' VO2max parameters, mean time to anaerobic threshold increased for the exercise group compared with control. No effect was observed, however, on performance in the VMWM or VRAWM between the two groups. Based on these results, we suggest that mild-intensity aerobic exercise does not improve spatial learning and memory in young, healthy adults.

Cognitive and physical performance are well preserved following standard blood donation: A noninferiority, randomized clinical trial.

BACKGROUND: A walking blood bank (WBB) refers to the use of fellow combatants for battlefield blood donation. This requires pretesting combatants for infectious diseases and blood type. A fundamental prerequisite for this technique is that the donating soldier will suffer minimal physiological and mental impact. The purpose of the current study is to assess the effect of blood shedding on battlefield performance. METHODS: This is a double-blind randomized control trial. Forty Israel Defense Forces combatants volunteered for the study. Participants underwent baseline evaluation, including repeated measurement of vital signs, cognitive evaluation, physical evaluation, and a strenuous shooting test. Three weeks after the baseline evaluation, subjects were randomized to either blood donation or the control group. For blinding purposes, all subjects underwent venous catheterization for the duration of a blood donation. Repeated vital signs and function evaluation were then performed. RESULTS: Thirty-six patients were available for randomization. Baseline measurements were similar for both groups. Mean strenuous shooting score was 80.5 ± 9.5 for the control group and 82 ± 6.6 for the test group (p = 0.58). No clinically or statistically significant differences were found in tests designed to evaluate cognitive performance or physical functions. Vital signs taken multiple times were also similar between the test and control groups. CONCLUSIONS: Executive, cognitive, and physical functions were well preserved after blood donation. This study supports the hypothesis that a WBB does not decrease donor combat performance. The categorical prohibition of physical exercise following blood donation might need to be reconsidered in both military and civilian populations.

When Should a Heat-Tolerance Test Be Scheduled After Clinical Recovery From an Exertional Heat Illness?

OBJECTIVE: Researchers have produced a hypothesis of transient heat intolerance (HI) after exertional heat stroke (EHS). Based on this hypothesis, heat-tolerance testing (HTT) has been postponed until weeks 6 to 8 after EHS and other types of exertional heat illness (EHI). We compared the HTT results of participants after either EHS or other EHI who were tested earlier (≤6-week group) versus those who were tested later (>6-week group) to verify the hypothesis. DESIGN: Cohort study. SETTING: Data obtained from records of military athletes who experienced EHS or EHI. PATIENTS OR OTHER PARTICIPANTS: All participants who underwent HTT after EHI or EHS experienced between 2014 and 2018 and for whom complete data regarding the severity of the event (rectal temperature, neurologic symptoms, and laboratory results) and HTT results were available were included. Participants with suspected EHS and those with other EHIs were evaluated separately. MAIN OUTCOME MEASURE(S): The percentages of participants with HI and mean probability of heat tolerance were compared between those tested within 6 weeks of the event and those tested later. RESULTS: A total of 186 participants were included in this study (EHS: 12 in the <6-week group, 9 in the >6-week group; EHI: 94 in the <6-week group, 71 in the >6-week group). In the EHS group, the percentages with HI (33% versus 44%, P = .67) and mean probability of heat tolerance (0.82 versus 0.82, P = .98) did not differ. In the EHI group, participants who were tested after 6 weeks had a greater chance of being diagnosed with HI (38% versus 21.3%, P < .02). CONCLUSIONS: The HTT results were similar between participants with EHS who were tested early (<6 weeks) and those tested late (>6 weeks). Further investigation of heat-tolerance changes in larger cohorts of patients after EHS is required to verify the theory of transient HI.

Physiological Differences Between Heat Tolerant and Heat Intolerant Young Healthy Women.

Purpose: Heat intolerance (HI) is determined in the Israel Defense Force according to a heat tolerance test (HTT) before returning to duty after an exertional heat stroke (EHS) event. Recently, increased numbers of female combatants resulted in an increased number of EHS cases among women and a higher percentage of heat intolerance (HI) individuals. We aimed to evaluate the differences between tolerance to heat among women performing an HTT in relation to their menstrual cycle phase. Method: Thirty-three female participants were sorted into two groups: HI and heat tolerant (HT) according to two HTTs performed during both the luteal and follicular phases of the menstrual cycle or while consuming and during a break from consuming contraceptives. Results: HT women had an 18% higher maximal oxygen uptake (p < .005, 95% CI [2.6,9.8]) and 1.2% lower skin temperature in the HTT at the during and follicular phases (p < .01, 95% CI [0.12,0.77]) and 1.7% lower at the off and luteal phases (p < .001, 95% CI [0.34,0.92]). The mean sweat rate was 14% lower among the HI group only at the HTT at the during and follicular phases (p < .05, 95% CI (3,88)]). Conclusion: We found that HT can be predicted using aerobic capacity and core body temperature. Moreover, during the luteal phase, women presented altered thermoregulation that decreased the probability of being HT. This emphasizes the importance of considering the HT/HI criteria in the HTT for women, according to their aerobic ability and menstrual-cycle phase.

The relation between central variables, electromyography signals and peripheral microcirculation during intensive treadmill exercise.

BACKGROUND: Aerobic exercise under muscle fatigue can lead to muscular damage and injuries. Finding the correlations between central and peripheral microcirculation variables, as well as with electromyography signals of leg muscles during aerobic exercise, may contribute to early muscle fatigue identification. The goal of this study was to characterize the peripheral compensation following intensive exercise for assessment of muscle performance based on non-invasive techniques. METHODS: The experimental protocol included two days of measurements. Electrocardiography tests and anthropometric measurements of the volunteers (N = 14) were carried out. The maximal aerobic ability (first day), as well as electromyography and cutaneous hemodynamic variables (second day) were measured during treadmill run. A score-based Bayesian network machine-learning algorithm was used to predict ventilation values based on cutaneous hemodynamic measurements. FINDINGS: Transcutaneous oxygen tension can be used to identify anaerobic threshold for both trained and untrained subjects during treadmill running, while electromyography can be used to identify anaerobic threshold only of trained subjects. Predicted values of ventilation, based on the transcutaneous oxygen tension, showed high correlation with actual values. Prediction accuracy was better among trained subjects, compared to the untrained ones. INTERPRETATION: Transcutaneous oxygen tension could be used for prediction of maximal oxygen consumption during intense exercise and thus may provide improved assessment of premature fatigue during exercise.

Asthaxanthin Improves Aerobic Exercise Recovery Without Affecting Heat Tolerance in Humans.

Objectives: To examine the supplementation effects of the xanthophyll carotenoid Astaxanthin on physical performance and exertional heat strain in humans. Design: A randomized double blind placebo controlled trial. Methods: Twenty two male participants (Age: 23.14 ± 3.5 y, height: 175 ± 6 cm, body mass: 69.6 ± 8.7 kg, % body fat: 16.8 ± 3.8) received placebo (PLA, n = 10) or Astaxanthin (ATX, n = 12) 12 mg/day Per os (P.O), for 30 days, and were tested pre and post-supplementation with a maximal oxygen uptake (VO2 Max) test and the heat tolerance test (HTT) (2 h walk at 40°C, 40% relative humidity (RH), 5 kph, 2% incline). NIH database registration no. NCT02088242. Gas exchange, Heart rate (HR), Relative perceived exertion (RPE), and blood lactate were measured during the VO2 Max test. Heart rate (HR), rectal (Trec), and skin (Tskin) temperatures, RPE, and sweat rate (SR) were monitored in the HTT. Serum heat shock protein 72 (HSP72), Creatine phospho-kinase (CPK), C-reactive protein (CRP), and lipid profile were measured before and after the test. Results: The rise in blood lactate caused by the VO2 Max test was significantly diminished in the ATX group (9.4 ± 3.1 and 13.0 ± 3.1 mmole*l-1 in the ATX and PLA groups, respectively P < 0.02), as was the change in oxygen uptake during recovery (-2.02 ± 0.64 and 0.83 ± 0.79% of VO2 Max in the ATX and PLA group, respectively, p = 0.001). No significant differences were observed in the anaerobic threshold or VO2 Max. In the HTT, no significant physiological or biochemical differences were observed (HR <120 bpm, Trec rose by ~1°C to <38°C, no difference in SR). Conclusions: Astaxanthin supplementation improved exercise recovery. No benefit was observed for ATX over PLA in response to heat stress. Further examination of Astaxanthin in higher exertional heat strain is required.

Musculoskeletal Injuries Among Female Soldiers Working With Dogs.

INTRODUCTION: Female soldiers serving in the Israeli Defense Forces canine unit may be at increased risk of overuse injuries related to working with military dogs. We hypothesized that this particular type of occupational exposure may lead to an increased strain of the upper extremity due to such non-physiologic motions as pulling the dog's strap or resisting the sudden pulling by the dog, and may result in an increased rate of overuse injuries. MATERIALS AND METHODS: We compared incidence of overuse injuries in a retrospective cohort of female soldiers who served either in the military working dogs' unit (MWD), or in the light infantry battalions (Infantry) from 2005 to 2015. We compared injury incidence of both groups during two periods: 5 mo of basic training (neither worked with dogs) and 19 or more months of combat service. Incidence was calculated as number of diagnoses per person-months (rate ratios, RR); each diagnosis counted once per study subject. We used RR confidence intervals to compare incidence of injuries between groups. RESULTS: There were 3,443 person-months in the MWD group and 194,590 person-months in the Infantry group. There was no difference in injury incidence between groups during the initial period of basic training. During the second period, MWDs had higher incidence of upper limb (RR = 1.45, p = 0.048) and hip (RR = 3.6, p < 0.0001) injuries. The association between service with dogs and upper limb injuries remained significant (RR = 1.09, p = 0.005) after adjusting for confounding variables in the multivariate regression analysis. Other independent predictors of the upper limb overuse injuries included each additional month of service (RR = 1.003, p = 0.008), Eastern European origin compared with Israeli-born recruits (RR = 0.97, p = 0.03), increased body weight in increments of 10 kg (RR = 1.008, p = 0.03), anemia (RR = 1.02, p = 0.02) and fatigue (RR = 1.05, p ≤ 0.0001). CONCLUSIONS: We found that service in the MWD unit was associated with increased risk of upper limb injuries. Identification of the exact mechanism of injury and targeted interventions, as well as treatment of anemia and fatigue may lead to reduction of injuries in this unit.

Probability of Heat Intolerance: Standardized Interpretation of Heat-Tolerance Testing Results Versus Specialist Judgment.

CONTEXT: The heat-tolerance test (HTT) is a screening tool for secondary prevention of exertional heat illness by the Israel Defense Forces. To discern participant tolerance, recruits are exposed to intermediate environmental and exercise stresses, and their physiological responses, core temperature, and heart rate are monitored. When their physiological measures rise at a higher rate or exceed the upper levels of absolute values compared with other participants, heat intolerance (HI) is diagnosed. OBJECTIVE: To develop a mathematical model to interpret HTT results and provide a quantitative estimate of the probability of heat tolerance (PHT). DESIGN: Cross-sectional study. SETTING: Warrior Health Research Institute. PATIENTS OR OTHER PARTICIPANTS: The HTT results of 175 random individuals tested after an episode of exertional heat illness were classified qualitatively and then divided into training (n = 112) and testing (n = 63) datasets. All individuals were male soldiers (age range = 18-22 years) who had sustained an episode of definitive or suspected exertional heat stroke. MAIN OUTCOME MEASURE(S): Based on the decision algorithm used by the Israel Defense Forces for manual interpretation of the HTT, we designed a logistic regression model to predict the heat-tolerance state. The model used a time series of physiological measures (core temperature and heart rate) of individuals to predict the manually assigned diagnosis of HT or HI. It was initially fitted and then tested on 2 separate, random datasets. The model produced a single value, the PHT, and its predictive ability was demonstrated by prediction-density plots, receiver operating characteristic curve, contingency tables, and conventional screening test evaluation measures. RESULTS: According to prediction-density plots of the testing set, all HT patients had a PHT of 0.7 to 1. The receiver operating characteristic curve plot showed that PHT was an excellent predictor of the manual HT interpretations (area under the curve = 0.973). Using a cutoff probability of 0.5 for the diagnosis of HI, we found that PHT had sensitivity, specificity, and accuracy of 100%, 90%, and 92.06%, respectively. CONCLUSIONS: The PHT has the potential to be substituted for manual interpretation of the HTT and to serve in a variety of clinical and research applications.

Individualized estimation of human core body temperature using noninvasive measurements.

A rising core body temperature (Tc) during strenuous physical activity is a leading indicator of heat-injury risk. Hence, a system that can estimate Tc in real time and provide early warning of an impending temperature rise may enable proactive interventions to reduce the risk of heat injuries. However, real-time field assessment of Tc requires impractical invasive technologies. To address this problem, we developed a mathematical model that describes the relationships between Tc and noninvasive measurements of an individual's physical activity, heart rate, and skin temperature, and two environmental variables (ambient temperature and relative humidity). A Kalman filter adapts the model parameters to each individual and provides real-time personalized Tc estimates. Using data from three distinct studies, comprising 166 subjects who performed treadmill and cycle ergometer tasks under different experimental conditions, we assessed model performance via the root mean squared error (RMSE). The individualized model yielded an overall average RMSE of 0.33 (SD = 0.18)°C, allowing us to reach the same conclusions in each study as those obtained using the Tc measurements. Furthermore, for 22 unique subjects whose Tc exceeded 38.5°C, a potential lower Tc limit of clinical relevance, the average RMSE decreased to 0.25 (SD = 0.20)°C. Importantly, these results remained robust in the presence of simulated real-world operational conditions, yielding no more than 16% worse RMSEs when measurements were missing (40%) or laden with added noise. Hence, the individualized model provides a practical means to develop an early warning system for reducing heat-injury risk. NEW & NOTEWORTHY A model that uses an individual's noninvasive measurements and environmental variables can continually "learn" the individual's heat-stress response by automatically adapting the model parameters on the fly to provide real-time individualized core body temperature estimates. This individualized model can replace impractical invasive sensors, serving as a practical and effective surrogate for core temperature monitoring.

The validity of the heat tolerance test in prediction of recurrent exertional heat illness events.

OBJECTIVES: Heat-tolerance-testing (HTT) protocol is used as a screening test for secondary prevention of exertional heat illness (EHI) in the military. Subjects whose test results are positive (heat-intolerant, HI) are presumed to be at higher risk of repeated EHI events than heat-tolerant subjects (HT) and are therefore prevented from return to combat duty, but may return to unsupervised recreational activity. Our aim was to determine, whether HTT results predict the risk of repeated episodes of exertional heat illness (EHI). DESIGN: Retrospective cohort. METHODS: One-hundred-forty-five subjects (110 HT, 35 HI) who were diagnosed with an EHI event by a physician and underwent HTT during 2008-2015 were contacted and asked about recurrence of EHI. Incidence of recurrent events was reported as number of cases per 1000 person-years. Ratio of events among HI and HT individuals was presented as rate ratio (RR) and its 95% confidence interval. RESULTS: Of the 145 patients, six (4.1%) had experienced recurrent EHI events (10.63 per 1000PY): four HI subjects (11.4%, 26.6 per 1000PY) and two HT (1.8%, 4.8 per 1000PY) (RR=5.504, CI 95%=1.01-30, p=0.027). Only one of the six recurrent events was a heat stroke (HT individual), other five were heat exhaustions. Sensitivity, specificity and diagnostic accuracy of HTT were 66.7%, 77.7% and 77.2%, respectively. CONCLUSIONS: The risk of EHI recurrence is measurable and can be discussed with patients before they return to sports. A referral to HTT can be considered, as negative HTT result is associated with substantial and significant EHI risk reduction.

Past Methylphenidate Exposure and Stress Fractures in Combat Soldiers: A Case-Control Study.

BACKGROUND: Previous research has revealed decreased bone mineral density (BMD) among children and adolescents who receive methylphenidate (MP) treatment for attention deficit hyperactivity disorder (ADHD). These findings have major clinical implications given that the prevalence of medication-treated ADHD is on the rise worldwide. We decided to investigate the clinical effect of MP exposure on the incidence of stress fractures, for which a low BMD is a risk factor. HYPOTHESIS: Exposure to MP is a risk factor for stress fractures. STUDY DESIGN: Case-control study; Level of evidence, 3. METHODS: This is a case-control study of combat soldiers who served in the military for 3 years between 2005 and 2015. The case group included 2400 soldiers with at least 1 stress fracture diagnosed by a bone scan. The control group comprised 6187 combat soldiers without a diagnosis of a stress fracture. The use of MP was determined by an automated text search of medical records and manual sorting of the results. Other study variables included age; sex; weight; height; body mass index (BMI); place of birth; and characterization of fractures by location, side, and grade. Odds ratios of stress fractures, the attributable proportion among the exposed, and the population attributable fraction were calculated using standard contingency tables. Logistic regression was fitted after adjusting for covariates. RESULTS: The previous use of MP was associated with a higher risk of stress fractures (odds ratio, 1.15 [95% CI, 1.07-1.24]). The attributable proportion was 13.2%, and the population attributable fraction was 0.3%. Logistic regression demonstrated an increased risk of stress fractures associated with past MP use, preserved after adjusting for BMI, sex, and place of birth ( P = .005). Female sex, BMI ≤20 kg/m2, and 20 < BMI ≤25 kg/m2 were independent positive predictors of a stress fracture, while African origin was a negative predictor. Most participants who used MP had only 1 fracture (77.8%), while the majority of participants who did not use MP in the past had ≥2 coincident fractures (53.5%) ( P = .003). CONCLUSION: This study supports the hypothesis that an MP-associated reduction in BMD has a clinical effect in the form of an increased incidence of stress fractures. The high percentage of fractures attributed to MP use may serve as a basis for risk stratification, that is, the referral of patients with a history of MP use to BMD measurements.

Rhabdomyolysis After Crawling Military Training.

INTRODUCTION: Rhabdomyolysis is a syndrome characterized by muscle necrosis followed by release of intracellular muscle contents into the circulation. Exertional rhabdomyolysis (ER) occurs in response to nonfamiliar and/or excessive, prolonged, or repetitive exercises, with eccentric characteristics. In military populations, due to the type of intense, all out physical loads, ER is a significant threat, particularly when training under heat stress. However, many other etiologies exist, and clinical presentations vary greatly. This heterogeneity may result in difficulty in prevention, diagnosis, and return-to-duty decision. The purpose of this report is to point to a new potential risk factor to an extreme muscle breakdown and ER. CASES DESCRIPTION: In this article, we describe three cases of ER in army recruits after strenuous acts of crawling over hard surfaces during an intense military selection process. The soldiers' creatine phosphokinase levels were markedly raised (44,000, 123,500, and 176,599 IU/L), but none of them developed any significant medical complication. DISCUSSION: There are two major mechanisms leading to ER: the mechanical pathway which is associated with muscle tension, and the metabolic pathway which is associated with cellular energy depletion. During this military selection process, the intensity of the exercises, and cycles of work and rest are highly controlled, and so are the timings of meals and fluids consumption. Moreover, the soldiers were all at least moderately fit and had participated in strenuous exercise events before. According to years of experience with this military selection process, under similar conditions (exercise volumes and loads) we have experienced along the years minimal medical events. At the same time, and this was the unique part in these case, all patients suffered significantly from mechanical injuries caused by crawling on hard surface which were not a part of the planned selection program. Thus, we suggest that the significant muscle breakdown in the presented cases occurred mostly due to crush injury and was not solely a result of the metabolic strain. CONCLUSION: Thus, we suggest that the extreme creatine phosphokinase levels may be attributed to a synergistic interaction between low-energy trauma, caused by crawling on hard soil and stones, and exertion. We also emphasize the fact that proper physiological support such as proper hydration may assist in prevention of ER complication such as acute renal failure.

Measuring core body temperature with a non-invasive sensor.

In various occupations, workers may be exposed to extreme environmental conditions and physical activities. Under these conditions the ability to follow the workers' body temperature may protect them from overheating that may lead to heat related injuries. The "Dräger" Double Sensor (DS) is a novel device for assessing body-core temperature (Tc). The purpose of this study was to evaluate the accuracy of the DS in measuring Tc under heat stress. Seventeen male participants performed a three stage protocol: 30min rest in a thermal comfort environment (20-22°C, 50% relative humidity), followed by an exposure to a hot environment of 40°C, 40% relative humidity -30min at rest and 60min of exercise (walking on a treadmill at 5km/h and 2% elevation). Simultaneously temperatures measured by the DS (TDS) and by rectal temperature (Tre) (YSI-401 thermistor) were recorded and then compared. During the three stages of the study the average temperature obtained by the DS was within±0.3°C of rectal measurement. The correlation between TDS and Tre was significantly better during the heat exposures phases than during resting under comfort conditions. These preliminary results are promising for potential use of the DS by workers under field conditions and especially under environmental heat stress or when dressed in protective garments. For this goal, further investigations are required to validate the accuracy of the DS under various levels of heat stress, clothing and working levels.

Wheeled assistive device for load carriage - the effects on human gait and biomechanics.

Soldiers are often required to carry loads which impose biomechanical strain on the human body. This can adversely affect physical performances. Recently, wheel-based devices (WBD) were designed to reduce the load on the soldier. In the present study, a prototype of this newly developed WBD was evaluated. Thirteen volunteers performed three exercise protocols on a treadmill as follows: (1) no load; (2) carrying 40% of their bodyweight with a backpack or; (3) with the WBD. Data acquisition included: gait parameters, vertical ground reaction forces (VGRF) and contact pressure acting on the shoulder. Biomechanical analysis showed that the WBD decreased the contact pressure on the shoulder and the VGRF. However, greater gait variability, in terms of cycle-to-cycle gait line generation, was observed, which might point to a difficulty in maintaining stability while walking. The study suggests that WBD has a potential to reduce the biomechanical strain on the soldier while carrying heavy loads. Future potential adjustments for the development of a better WBD-based solution are suggested. Practitioner Summary: The present research observed the potential biomechanical advantages of using a wheel-based device designed to reduce the load on the soldier. It contributed to a lower mechanical force on the soldier's body, yet causing modulations in gait control. Future design adjustments should be made to optimise the platform.

Effect of cardiovascular and muscular endurance is not associated with stress fracture incidence in female military recruits: a 12-month follow up study.

BACKGROUND: Stress fracture (SF) is a common injury among military recruits, especially among women, during the army basic training (ABT). The purpose of this study was to evaluate the effects of health habits and physical activity before recruitment on the fitness level and the incidence of SF during the 4-month ABT. METHODS: We screened 226 female recruit volunteers (weight: 60.5±10 kg; height: 163±6 cm) from an integrated combat unit and 124 aged-matched female controls (weight: 57.0±8.3 kg, height 162±7 cm) from a non-combat unit. A self-report questionnaire on their habits pertaining to smoking, physical activity, and orthopedic injuries prior to recruitment were analyzed in relation to the incidences of SF during ABT. RESULTS: Aerobic fitness was similar between the two groups. The overall incidence of SFs was 10.2%. Physical training prior to recruitment had no significant effect on the incidence of SF during ABT (11.7% vs. 9.6% in those who trained and did not train before recruitment, respectively) (Odds ratio, OR)=1.24, p=0.236). Nearly 42% of the female recruits smoked regularly, and the incidence of SFs among smokers was 10.5% compared with 9.9% among the non-smokers (OR=1.07, p=0.188). The overall incidence of SFs 12 months after recruitment was 1.78%. The use of contraceptive medication did not affect the incidence of SF: 10.0% among prior-trained vs. 6.4% in non-prior trained (p>0.05) recruits. SFs were not correlated to these variables at the end of the ABT program and 16 months after recruitment. CONCLUSIONS: In the present female cohort, physical activity prior to recruitment had no protective effect against SF during or after ABT. The incidence of SFs during the 12-month period after ABT was negligible.