The Value of Strength as a Predictor of Musculoskeletal Injury in Canadian Armed Forces Basic Infantry Candidates.

INTRODUCTION: Musculoskeletal injuries (MSKI) impact military organizations by threatening their operational readiness, warranting investigation into relevant factors to inform risk reduction strategies. While several self-reported and physical performance measures have been associated with MSKI among military personnel, few have been validated and none have been reported in Canadian basic infantry candidates. The purpose of this study was to investigate associations between self-reported and physical performance measures and MSKI, and determine their validity as predictors of MSKI, in Canadian basic infantry candidates. METHODS: This was a planned secondary analysis of a study tracking MSKI at a basic infantry training facility in Ontario, Canada approved by Defence Research & Development Canada. Before the basic infantry training, consenting candidates completed a baseline testing session including self-reported questionnaires, measures of anthropometry, and physical performance previously associated with MSKI (ankle dorsiflexion test, Y-Balance Test, Isometric Mid-Thigh Pull, and the Fitness for Operational Requirements of CAF Employment (FORCE) evaluation). All MSKI reported by candidates were diagnosed by licensed healthcare providers. From a total sample of 129 candidates, 76% (n = 98) were used to determine any associations between baseline testing variables and MSKI and to develop a predictive model (Development Sample), while 24% (n = 33) were used to offer preliminary validation of the same predictive model (Validation Sample). The binary logistic regression and independent sample t-testing determined independent associations with MSKI in the Development Sample. All continuous variables and dichotomous variables previously associated with MSKI risk (Smoker Yes/No, previous history of MSKI, and physical inactivity) were entered into a backward stepwise logistic regression analysis to assess the predictive association with MSKI incidence in the Development Sample. The regression model was then applied to the Validation Sample. RESULTS: A total of 35 MSKI were diagnosed by Health Services Centre staff. The majority of the MSKI were acute (63%), sustained to the hip, knee, and ankle (74%). The most common diagnoses were strains and sprains (71%). Uninjured participants performed significantly better on the Relative Isometric Mid-Thigh Pull, FORCE 20 mR, FORCE ILS, and FORCE Estimated VO2peak compared to injured participants. Logistic regression analysis showed that the only variable with significant independent association with diagnosed MSKI incidence was self-reported previous history of MSKI. However, the backward stepwise logistic regression analysis retained self-reported previous history of MSKI, FORCE SBD, FORCE Estimated VO2peak, and Isometric Mid-Thigh Pull Peak Force as predictors of MKSI. The logistic regression model including these variables could predict MSKI with an accuracy of 79% in the Development Sample and 67% in the Validation Sample. CONCLUSION: This study provides preliminary support for the value of measures of absolute muscular strength and cardiorespiratory fitness as predictors of MSKI in Canadian basic infantry candidates. Given the associations between physical performance measures and MSKI, and their necessity during occupational tasks, it is recommended that Canadian basic infantry training facilities integrate resistance training with external loads to best prepare their candidates to meet their occupational demands and potentially minimize MSKI. Further investigations to confirm the predictive capacity of these variables in a larger sample across additional facilities are warranted.

Physiological Demands of Basic Fire Management Tasks in Members of the Canadian Armed Forces: A Pilot Study.

INTRODUCTION: Members of the Canadian Armed Forces (CAF) are required to meet the minimum standards of the Fitness for Operational Requirements of CAF Employment (FORCE) job-based simulation test (JBST) and must possess the capacity to perform other common essential tasks. One of those tasks is to perform basic fire management tasks during fire emergencies to mitigate damage and reduce the risk of injuries and/or death until professional firefighters arrive at the scene. To date however, the physiological demands of common firefighting tasks have mostly been performed on professional firefighters, thus rendering the transferability of the demands to the general military population unclear. This pilot study aimed to quantify, for the first time, the physiological demands of basic fire management tasks in the military, to determine if they are reflected in the FORCE JBST minimum standard. We hypothesized that the physiological demands of basic fire management tasks within the CAF are below the physiological demands of the FORCE JBST minimum standard, and as such, be lower than the demands of professional firefighting. MATERIALS AND METHODS: To achieve this, 21 CAF members (8 females; 13 males; mean [SD] age: 33 [10] years; height: 174.5 [10.5] cm; weight: 85.4 [22.1] kg, estimated maximal oxygen uptake [$\dot V$O2peak]: 44.4 (7.4) mL kg-1 min-1) participated in a realistic, but physically demanding, JBST developed by CAF professional firefighting subject matter experts. The actions included lifting, carrying, and manipulating a 13-kg powder fire extinguisher and connecting, coupling, and dragging a 38-mm fire hose over 30 m. The rate of oxygen uptake ($\dot V$O2), heart rate, and percentage of heart rate reserve were measured continuously during two task simulation trials, which were interspersed by a recovery period. Rating of perceived exertion (6-no exertion; 20-maximal exertion) was measured upon completion of both task simulations. Peak $\dot V$O2 ($\dot V$O2peak) was estimated based on the results of the FORCE JBST. RESULTS: The mean (SD) duration of both task simulation trials was 3:39 (0:19) min:s, whereas the rest period in between both trials was 62 (19) minutes. The mean O2 was 21.1 (4.7) mL kg-1 min-1 across trials, which represented 52.1 (12.2) %$\dot V$O2peak and ∼81% of the FORCE JBST. This was paralleled by a mean heart rate of 136 (18) beats min-1, mean percentage of heart rate reserve of 61.2 (10.8), and mean rating of perceived exertion of 11 ± 2. Other physical components of the JBST consisted of lifting, carrying, and manipulating a 13-kg load for ∼59 seconds, which represents 65% of the load of the FORCE JBST. The external resistance of the fire hose drag portion increased up to 316 N, translating to a total of 6205 N over 30 m, which represents 96% of the drag force measured during the FORCE JBST. CONCLUSIONS: Our findings demonstrate that the physiological demands of basic fire management tasks in the CAF are of moderate intensity, which are reflected in the CAF physical fitness standard. As such, CAF members who achieve the minimum standard on the FORCE JBST are deemed capable of physically performing basic fire management tasks during fire emergencies.

Assessment of Training Load, Sleep, Injuries, and Operational Physical Performance During Basic Military Qualification.

INTRODUCTION: Optimizing training load (TL) and sleep is essential to maximize physical performance and prevent musculoskeletal injuries (MSKIs) for Canadian forces recruits during the 10-week basic military qualification (BMQ) course. The purpose of this study was to assess the TL, sleep duration, the occurrence of MSKIs during the BMQ, and the operation fitness performance during the BMQ. MATERIALS AND METHODS: Forty Canadian recruits, eight females and 32 males, (age 24 ± 5 years; height 176.4 ± 10.4 cm), were monitored with an accelerometer (GENEActiv) on their wrist between weeks 1 and 9 to evaluate the TL and sleep duration. During weeks 2 and 10, the recruits completed an operational fitness evaluation. Injury surveillance was performed over 10 weeks. RESULTS: TL intensity was significantly different (P = 0.0001) from week to week. The weekly average total time of moderate and vigorous physical activity was 189.7 ± 48.1 min and 44.7 ± 15.2 min, respectively. The average sleep duration was 5.4 ± 0.4 h per night and decreased to 4.2 h ± 0.4 during field exercises. A significant difference in sleep duration was observed between recruits with and without a MSKI. The recruits accumulated a total of 95 days under medical restrictions with an average of 3.8 consecutive days. The VO2peak estimated from the Fitness for Operational Requirements of Canadian Armed Forces Employment job-based simulation test significantly improved from weeks 2 to 10 (pre, 47.1 ± 6.3; post: 50.2 ± 5.8; P = 0.001). CONCLUSIONS: TL is of high magnitude and varies from week to week. The reported mean sleep duration per week may perhaps negatively impact the occurrence of MSKI. No significant improvement was detected in operational fitness by the end of the BMQ.

The feasibility of implementing an evidence-based physical training program during a Canadian Armed Forces basic infantry course.

OBJECTIVES: Determine the feasibility of implementing an evidence-based training program compared to a control during a basic infantry training course, and compare their effectiveness on measures of injuries and associated burdens. DESIGN: Prospective, cohort, feasibility study. METHODS: Infantry candidates awaiting course between 01-April-2019 and 31-March-2020 were invited to participate while those releasing from the military, awaiting occupational transfer or having >5 medical employment limitation days were excluded. Consenting participants were allocated to an infantry course prospectively scheduled to host either the evidence-based program or a control. The evidence-based program adapted modified physical training strategies from previous studies reporting reduced injuries in recruits and was supervised by certified fitness professionals, while the control was at the discretion of infantry instructors. RESULTS: With the exception of intervention duration which was limited due to operational factors, all feasibility outcomes were met including a recruitment rate of 171/203=84.2% and an intervention adherence of 126/144=87.5%. Stakeholders reported that the evidence-based program implementation was feasible, posing a manageable demand on resources without compromising operations. Evidence-based program participants reported 68% fewer overuse musculoskeletal injuries, 296 fewer medical employment limitation days and 11 fewer attritions than control participants. CONCLUSIONS: An evidence-based training program is feasible to implement on a basic infantry training course, and results in fewer musculoskeletal injuries, medical employment limitation days and attrition. Given these results, this program should be generalizable for a full experimental trial, and may be scaled for intermediate/advanced infantry and/or other combat occupation courses to promote an evolution towards evidence-based training.

Association Between Musculoskeletal Injuries and the Canadian Armed Forces Physical Employment Standard Proxy in Canadian Military Recruits.

INTRODUCTION: Musculoskeletal injuries (MSKIs) and recruitment are major challenges faced by modern military forces. The Canadian Armed Forces uses a physical employment standard (PES) proxy to determine occupational fitness and job suitability. It is unknown whether the performance on the PES proxy can be also used as predictor of MSKIs. The purpose of this study was to investigate for relationships between age, sex, body composition, aerobic fitness, performance on the Canadian Armed Forces PES proxy (FORCE evaluation), and risk of sustaining a MSKI requiring intervention in the Training Rehabilitation Program (MSKI-TRP1) during Canadian Basic Military Qualification. MATERIALS AND METHODS: This was a retrospective analysis of MSKIs in recruits introduced in the Training Rehabilitation Program (TRP1) in 2016 and 2017. A two-tailed t-test and a multivariate stepwise logistic regression were completed to investigate the interrelationships of sex, age, FORCE performance (20 m rushes, sandbag lift, intermittent loaded shuttles, sandbag drag) and health-related characteristics (waist circumference, predicted peak oxygen consumption [$\dot{V}$O2peak]), and odds for sustaining a MSKI-TRP. RESULTS: The MSKI-TRP1 intervention rate observed was 4.3%. Rehabilitation duration was an average (SD) of 87 (76) days; nearly 80% of MSKI-TRP were lower body injuries. MSKI-TRP recruits were older, had a lower score on FORCE, and had a larger mean waist circumference and lower $\dot{V}$O2peak than non-TRP1 recruits (all P < 0.01). Recruits with performance lower than 1 SD below mean on the 20 m rushes, intermittent loaded shuttle, or sandbag drag were 2.69 (1.89-3.83), 2.74 (1.91-3.95), and 2.26 (1.52-3.37) times more likely to sustain a MSKI-TRP1, respectively (all P < 0.01). Recruits with $\dot{V}$O2peak lower than 1 SD below mean were also 2.19 (1.30-3.70) times more likely to sustain a MSKI-TRP. Neither sex, age, nor waist circumference impacted the risk of MSKI-TRP1 when controlling for FORCE performance. CONCLUSIONS: The Canadian Armed Forces PES proxy performance can be used to assess the odds of sustaining a MSKI-TRP1 in Canadian military recruit training.

The Effect of Acute Continuous Hypoxia on Triglyceride Levels in Constantly Fed Healthy Men.

INTRODUCTION: Elevated plasma triglyceride (TG) concentrations are an important contributor to deleterious metabolic alterations. Evidence in animals suggest that acute exposure to an environment with reduced oxygen inhibits plasma TG clearance and causes important rise in plasma TG, especially in the postprandial state. The objective of this study was to characterize the effects of an acute exposure to normobaric hypoxia on prandial TG levels in 2 distinct lipoprotein subtypes in healthy humans: chylomicrons which are secreted by the intestine and carry dietary lipids, and denser TG carriers (mainly VLDL), which are secreted by the liver and carry endogenous lipids. Plasma lipolytic activity was also assessed. It was hypothesized that hypoxia would reduce prandial plasma lipolytic activity and raise prandial TG levels in both lipoprotein subtypes. METHODS: Using a randomized crossover design, 9 healthy young men were studied for 6 h in a constantly fed state while being exposed to either normobaric hypoxia (FiO2 = 0.12) and normoxic conditions on two different days. Prandial glucose, TG, non-esterified fatty acid (NEFA), and post-heparin plasma lipolytic activity were measured during each session. RESULTS: Six hours of exposure to hypoxia marginally increase prandial glycemia (+5%, p = 0.06) while increasing insulinemia by 40% (p = 0.04). Hypoxia induced a 30% rise in prandial NEFA levels and tended to slightly increased total prandial TG levels by 15% (p = 0.11). No difference was observed in TG concentrations and metabolism of chylomicrons between conditions. However, TG in the VLDL containing fraction decreased significantly overtime under normoxia but not under hypoxia (time × condition interaction, p = 0.02). No difference was observed in post-heparin plasmatic lipolytic activity between conditions. CONCLUSION: Acute hypoxia in healthy men tends to increase prandial VLDL-TG levels. These results lend support to the increased blood lipid levels reported in animals exposed acutely to lower partial pressures of oxygen.

Factors Affecting Performance on an Army Urban Operation Casualty Evacuation for Male and Female Soldiers.

INTRODUCTION: This study was conducted to determine what physical and physiological characteristics contribute to the performance of an urban operation casualty evacuation (UO) and its predictive test, FORCE combat (FC) and describe the metabolic demand of the UO in female soldiers. METHODS: Seventeen military members (9 M and 8 F) completed a loaded walking maximal aerobic test, the UO and FC. Heart rate reserve (HRR) and completion time were used as efficiency/performance measures. Oxygen consumption (VO2) was directly measured for UO on five female participants with a portable indirect calorimetry system, and analyzed using descriptive statistics. Stepwise multiple regression analysis was used to determine the contribution of the non-modifiable (age, sex, height) and modifiable characteristics (lean body mass to dead mass ratio (LBM:DM), VO2max corrected for load (L.VO2max), peak force (PF) measured on an isometric mid-thigh pull (IMTP) and medicine ball chest throw distance (Dist) on to the performance of each exercise. RESULTS: LBM:DM and PF were the only factors included in the stepwise regression model for UO, predicting 70% of UO performance (p < 0.01). For FC, L.VO2max only was included in the stepwise regression model predicting 54% of FC performance (p < 0.01). Sex, age and height were not included in the regression model. The average metabolic cost of UO was 21.4 mL of O2*kg-1*min-1 in female soldiers while wearing PPE. CONCLUSION: This study showed that modifiable factors such as body composition, PF on IMTP and L.VO2max are key contributors to performance on UO and FC performance.

No effect of acute normobaric hypoxia on plasma triglyceride levels in fasting healthy men.

Circulating fatty acids are a major systemic energy source in the fasting state as well as a determinant of hepatic triglycerides (TG)-rich very-low-density lipoprotein production. Upon acute hypoxia, sympathetic arousal induces adipose tissue lipolysis, resulting in an increase in circulating nonesterified fatty acids (NEFA). Animal studies suggest that TG clearance may also be strongly reduced under hypoxia, though this effect has been shown to be dependent on temperature. Whether the hypoxia-induced rise in blood fatty acid concentrations affects fasting TG levels in humans under thermoneutral conditions remains unknown. TG, NEFA, and glycerol levels were measured in fasted healthy young men (n = 10) exposed for 6 h to either normoxia (ambient air) or acute hypoxia (fraction of inspired oxygen = 0.12) in a randomized, crossover design. Participants were casually clothed and rested in front of a fan in an environmental chamber maintained at 28 °C during each trial. Under hypoxia, a significantly greater increase in NEFA occurred (condition × time interaction, p = 0.049) and glycerol levels tended to be higher (condition × time, p = 0.104), suggesting an increase in adipose tissue lipolysis. However, plasma TG levels did not change over time and did not differ between the normoxia and hypoxia conditions. In conclusion, acute exposure to normobaric hypoxia under thermoneutral condition in healthy men during fasting state increased lipolysis without affecting circulating TG.

Effects of acute hypoxia on human adipose tissue lipoprotein lipase activity and lipolysis.

BACKGROUND: Adipose tissue regulates postprandial lipid metabolism by storing dietary fat through lipoprotein lipase-mediated hydrolysis of exogenous triglycerides, and by inhibiting delivery of endogenous non-esterified fatty acid to nonadipose tissues. Animal studies show that acute hypoxia, a model of obstructive sleep apnea, reduces adipose tissue lipoprotein lipase activity and increases non-esterified fatty acid release, adversely affecting postprandial lipemia. These observations remain to be tested in humans. METHODS: We used differentiated human preadipocytes exposed to acute hypoxia as well as adipose tissue biopsies obtained from 10 healthy men exposed for 6 h to either normoxia or intermittent hypoxia following an isocaloric high-fat meal. RESULTS: In differentiated preadipocytes, acute hypoxia induced a 6-fold reduction in lipoprotein lipase activity. In humans, the rise in postprandial triglyceride levels did not differ between normoxia and intermittent hypoxia. Non-esterified fatty acid levels were higher during intermittent hypoxia session. Intermittent hypoxia did not affect subcutaneous abdominal adipose tissue lipoprotein lipase activity. No differences were observed in lipolytic responses of isolated subcutaneous abdominal adipocytes between normoxia and intermittent hypoxia sessions. CONCLUSIONS: Acute hypoxia strongly inhibits lipoprotein lipase activity in differentiated human preadipocytes. Acute intermittent hypoxia increases circulating plasma non-esterified fatty acid in young healthy men, but does not seem to affect postprandial triglyceride levels, nor subcutaneous abdominal adipose tissue lipoprotein lipase activity and adipocyte lipolysis.