Load Carriage Research Articles

Predicting Individualized Cardiovascular Responses To Loaded Military Exercise

Periodized endurance training requires exercise-specific knowledge of the cardiovascular demands of training to optimize long-term performance improvements. Tactical strength and conditioning communities lack resources for forecasting heart rate responses to common endurance exercises performed by dismounted warfighters such as military load carriage. PURPOSE: Develop an individualized model for predicting steady-state heart rate responses to walking with military backpack loads. METHODS: Thirty volunteers (3 women, 27 men; age, 25 ± 7 years old; height, 174 ± 7 cm; body mass, 77 ± 15 kg) carried backpacks loaded up to 66% body mass on a treadmill at walking speeds from 0.45 to 1.97 m·s-1. Heart rate responses were measured continuously using a chest-worn physiological status monitor (Equivital EQ02+ LifeMonitor (EQ02+); Equivital; Cambridge, UK) and averaged over the final minute of each trial. A new model was fit using a nonlinear mixed effects modeling approach that predicts a heart rate response to given walking speed and backpack load that is scaled to each individual’s resting and maximal heart rate. Model predictions were deemed statistically equivalent if the 90% confidence interval around the mean error was within equivalence limits set to ± 5% of the mean measured heart rate. RESULTS: The mean heart rate measured across volunteers and trials was 111.7 ± 25.1 bpm, setting the equivalence limit to ± 5.6 bpm. Model predictions were statistically equivalent to the measured heart rate data (90% Confidence Interval [-1.8, 2.4 bpm]). CONCLUSION: The model developed herein allows users to determine the pace and load to elicit a target heart rate for optimal training. Heart rate predictions can be used for designing individualized training intensity zones and benchmarks for ruck marching and hiking programs. Combining these cardiovascular estimates with existing metabolic and thermoregulatory models allows for more comprehensive planning of military exercises. The views expressed in this abstract are those of the authors and do not reflect the official policy of the Department of Army, Department of Defense, or the U.S. Government.

Anthropometrics And Body Composition Predict Performance During A Direct-fire Engagement Simulation.

Heavy load carriage is linked to lower performance in direct-fire engagements and higher physiological strain (higher O2 cost, lower cerebral blood flow); which have potential tactical consequences (impaired mobility, marksmanship, cognitive ability). However, performance may also deteriorate with other nonfunctional loads (i.e, excess body fat). PURPOSE: To determine the association between anthropometric and body composition measures and performance during a direct-fire engagement simulation. METHODS: Thirty three healthy male (n = 25) and female (n = 8) volunteers (age 25.7 ± 7.0 yr) underwent a direct-fire engagement simulation. Anthropometric and body composition measures were taken prior to the simulation using a stadiometer and bioelectrical impedance analysis. Marksmanship with cognitive workload and a fire and move drill (16 x 6 m sprints) were completed under combat load (25 kg) during the direct-fire engagement simulation. Marksmanship accuracy and reaction time were assessed as the number of target hits and the time between target callout and engagement, respectively. Cognitive performance was assessed as the number of correct arithmetic problems answered between target engagements. Susceptibility to enemy fire was modeled on sprint duration during the fire and move drill. Partial correlation and multiple linear regression were conducted to establish the relationship between anthropometric and body composition measures and performance outcomes, controlling for age and sex. RESULTS: Higher percent body fat and fat mass predicted greater susceptibility to enemy fire (r = 0.42, p = 0.03 and r = 0.38, p = 0.02, respectively), and worse cognitive performance (r = -0.49, p = 0.01 and r = -0.45, p = 0.01, respectively). Higher body mass index also predicted worse cognitive performance (r = -0.49, p = 0.01). Taller stature predicted worse marksmanship accuracy (r = -0.40, p = 0.02) and higher fat-free mass predicted slower marksmanship reaction times (r = 0.41, p = 0.02). CONCLUSIONS: Anthropometric and body composition measures were predictive of survivability (i.e., susceptibility to enemy fire) and lethality (i.e., marksmanship, cognitive performance) during the direct-fire engagement simulation. These data suggest anthropometrics and body composition modulate combat effectiveness.

The Load Carriage Index: Adjusting The Load Carried By Soldiers According To Body Composition

The Load Carriage Index: Adjusting The Load Carried By Soldiers According To Body Composition

Knee Joint Loading Distribution With Vest-borne Loads

Vest borne loads increase tibiofemoral joint (TFJ) contact forces, but the TFJ contact forces do not always increase proportionally to the increase in load (Lenton et al., 2018). It is unclear if and how increase in TFJ contact forces are attenuated during load carriage.PURPOSE: To determine the effects of load carriage on total, medial (MTFJ), and lateral (LTFJ) tibiofemoral joint contact forces, and to determine if increases in joint loads are attenuated via gait adaptations. METHODS: Twelve young, healthy adults (6 males [BMI = 22.19] and 6 females [BMI = 20.38]; 22 + 1.6 yrs), walked for 5 minutes per condition at 1.4 m·s-1 on an instrumented treadmill while carrying vest borne loads of 0%, 15%, and 30% body weight during 3D motion capture. Hip, knee, and ankle kinematic and kinetic data were used as inputs to an inverse-dynamics informed musculoskeletal model of axial TFJ contact force. Kinematic and TFJ contact force comparisons were made via repeated measures ANOVA. RESULTS: From 0% load to 15% and from 0% to 30%, total peak TFJ increased 14% and 32% (3.44 vs 3.92 vs 4.55 body weights (BW) p < 0.001); peak MTFJ increased 12% and 26.5% (2.42 vs 2.72 vs 3.05 BW, p < 0.001); peak LTFJ increased 13% and 38% (1.29 vs 1.46 vs 1.79 BW, p < 0.001), and leg stiffness decreased 10% and 28% (7.17 vs 6.46 vs 5.10 N/mm, p < 0.001), respectively. CONCLUSION: Young, healthy participants do not attenuate the increase in total and medial knee joint contact forces with increasing magnitude of load carriage. They respond to load by decreasing joint stiffness through small increases in dorsiflexion, knee flexion, and hip flexion, which does increase shock absorption and assists with energy transfer (Kinoshital, 1985). These minor increases in flexion coupled with increases in vertical ground reaction forces led to the approximately proportional relative percent increase in TFJ and MTFJ as compared to the increase in load. However, the increase in LTFJ from 0% load to 30% load was 8% greater indicating a disproportional increase in the lateral compartment, assuming that “disproportional” is greater or less than 5%. Further research should investigate if greater increases in load magnitude continue to lead to proportional increases in total TFJ and MTFJ, and disproportional increases LTFJ, especially in military populations who frequently carry heavy loads.

Biomechanical effects of the addition of a precision constraint on a collective load carriage task.

Team lifting is a complex and collective motor task comprising motor and cognitive components. The purpose of this research is to investigate how individual and collective performances are impacted during load transport combined with a cognitive task. Ten dyads performed a first condition in which they transported a load (CC), and a second one in which they transported the load while maintaining a ball on its top (PC). The recovery-rate, amplitude and period of the centre-of-mass (COM) trajectory were computed for the system (dyad + table = PACS). We analysed the forces and moments exerted at each joint of the upper limbs of the participants. We observed a decrease in the overall performance of the dyads during PC: (i) the velocity and amplitude of CoMPACS decreased by 1.7% and 5.8%, respectively, (ii) inter-participant variability of the Moment-Cost-Function and recovery rate decreased by 95%, and 19.2%, respectively during PC. Kinetic synergy analysis showed that the participants reorganized their coordination in the PC. We demonstrated that adding a precision task affects the economy of collective load carriage at the PACS level while the upper-limbs joint moments were better balanced across the paired participants for the PC.

Circulating and skeletal muscle microRNA profiles are more sensitive to sustained aerobic exercise than energy balance in males.

MicroRNAs (miRNAs) regulate molecular processes governing muscle metabolism. Physical activity and energy balance influence both muscle anabolism and substrate metabolism, but whether circulating and skeletal muscle miRNAs mediate those effects remains unknown. This study assessed the impact of sustained physical activity with participants in energy balance (BAL) or deficit (DEF) on circulating and skeletal muscle miRNAs. Using a randomized cross-over design, 10 recreational active healthy males (mean±SD, 22±5 years, 87±11kg) completed 72h of high aerobic exercise-induced energy expenditures in BAL (689±852kcal/day) or DEF (-2047±920kcal/day). Blood and muscle samples were collected under rested/fasted conditions before (PRE) and immediately after 120min load carriage exercise bout at the end (POST) of the 72h. Trials were separated by 7days. Circulating and skeletal muscle miRNAs were measured using microarray RT-qPCR. Independent of energy status, 36 circulating miRNAs decreased (P<0.05), while 10 miRNAs increased and three miRNAs decreased in skeletal muscle (P<0.05) at POST compared to PRE. Of these, miR-122-5p, miR-221-3p, miR-222-3p and miR-24-3p decreased in circulation and increased in skeletal muscle. Two circulating (miR-145-5p and miR-193a-5p) and four skeletal muscle (miR-21-5p, miR-372-3p, miR-34a-5p and miR-9-5p) miRNAs had time-by-treatment effects (P<0.05). These data suggest that changes in miRNA profiles are more sensitive to increased physical activity compared to energy status, and that changes in circulating miRNAs in response to high levels of daily aerobic exercise are not reflective of changes in skeletal muscle miRNAs. KEY POINTS: Circulating and skeletal muscle miRNA profiles are more sensitive to high levels of aerobic exercise-induced energy expenditure compared to energy status. Changes in circulating miRNA in response to high levels of daily sustained aerobic exercise are not reflective of changes in skeletal muscle miRNA.

Test-retest Reliability of Unilateral and Bilateral Carrying Protocol Based on Joule’s Functional Capacity Evaluation

Introduction: Load carriage is one of the most frequent manual material handlings in industrial settings. However, due to the biomechanical risk exposures, carrying could lead to work-related musculoskeletal disorders. Joule’s Functional Capacity Evaluation is an FCE system used widely in Malaysia in return-to-work programs to ensure work readiness and prevent re-injury. However, the literature regarding the test-retest reliability of the carrying protocols is minimal, leading to a questionable level of consistency. Therefore, this study aimed to investigate the test-retest reliability of the carrying protocols in Joule’s FCE. Methods: A cross-sectional study was conducted to evaluate test-retest reliability where the carrying protocol of Joule’s Functional Capacity Evaluation was used among healthy university students (N=30). The participants were asked to perform a retest of the carrying protocol after one week.Results: The ICC values for the carrying protocols were good for dominant unilateral carrying was (ICC: 0.82; 95% CI: -6.00 to 5.81), non-dominant carrying was (ICC: 0.74; 95% CI: -6.78 to 6.02) and bilateral carrying was (ICC: 0.85; 95% CI: -6.26 to 5.51). Bland and Altman’s plot indicated no visible distribution patterns of the differences without exceeding the 95% limits of agreement. The standard error of measurements (SEMs) was relatively small for all carrying protocols. Conclusion: The test-retest reliability of carrying protocols in Joule’s FCE was good. Future studies are needed to replicate this study in real patients to further verify the reliability for clinical settings.

Effect of long-distance load marching on physiological responses at desert environment

AIM: The present study was undertaken to examine the effect of long-distance load marching on the physiological responses, walking efficiency, and mobility of soldiers at sandy desert environment. METHODS: A total of nine physically fit soldiers (age, 30.00 [SE 0.9] years; height, 175.56 [SE 1.18] cm; and weight, 77.83 [SE 1.37] kg) volunteered for long-distance (6 km) load marching by self-selected speed when carrying 22 kg (28.27% of body weight [BW]) load and no load (NL). Heart rate (HR), respiratory frequency (RF), and core body temperature (CBT) were recorded. Relative workload (RWL) and Physiological Cost Index (PCI) were calculated to assess the work intensity and mobility. RESULTS: It was observed that HR (P = 0.01), RWL (P = 0.01), and PCI (P = 0.01) were significantly increased by 23.79, 39.71, and 77.73%, respectively, and mobility was significantly reduced (P = 0.01) by 18.56% during marching with 22 kg load as compared to NL. CONCLUSION: It may be that marching without external load at speed of 4.85 ± 0.54 km/h should not be continued for more than 2 h, whereas marching with load of 28.27% of BW at speed of 3.95 ± 0.55 km/h should be restricted to maximum 30 min. This combination of load, speed, and duration provides information about soldiers' routine load carriage tasks, which may help in optimizing the load carriage task to reduce the chances of cumulative carriage-related injuries and, therefore, may contribute to improved soldiers' operational readiness and mobility.

Physiological Demands and Characteristics of Movement During Simulated Combat.

Military tasks place considerable physiological demands on the soldier. It is therefore important to know the energy expenditure of soldiers while solving tasks in different environments. The purpose of this study was to describe the cardiorespiratory demands of certain movements and activities on ground combat soldiers during military field operations using body sensors and simulated combat. Movement characteristics and cardiorespiratory responses were assessed in 42 soldiers (three women) in the Swedish Army. The different posts assessed were commander, combat engineer, driver, and gunner. The military field exercises examined were urban operations and retrograde operations in rough terrain. Measurements included (1) body mass, (2) heart rate (HR) including maximal (HRmax), (3) velocity, (4) accelerations/decelerations, and (5) distance moved. Maximal aerobic capacity (V̇O2peak, mL·kg-1·min-1) was tested in a laboratory setting when wearing combat gear and body armor. There was a weak positive correlation (r = 0.41 and 0.28, both P < .05) between VO2peak and percentage of time over 40% and 50% of maximal aerobic capacity during simulated combat. No differences were found for the different posts in time spent over 40% or 50% of maximal aerobic capacity and 76% of their HRmax (P > .05). Wearing combat gear and additional load while solving tasks resulted in mean HR varying between 98 and 111 beats·min-1, corresponding with 50-57% of the soldiers HRmax. Studying all exercises, mean HR was 105 ± 11 beats min-1, 54 ± 5% of HRmax corresponding to light work intensity. Soldiers performed between 2.8 and 4.9 accelerations/min in the different exercises. A significant correlation between V̇O2peak (mL kg-1 min-1) and acceleration and m/min were found, implying that soldiers with good aerobic capacity were able to cope better with tasks requiring quick movements. Conducting military operations in urban terrain and retrograde operations in rough terrain strains ground combat soldiers' cardiorespiratory system, with work intensities close to 40% of maximal aerobic capacity in 15-33% of mission time. Tasks with external load carriage include change of direction, accelerations, bounds, and jumping over obstacles, and physical fitness tests should replicate this. Findings in this study also add objective data to the physiological demands of work performed by combat soldiers while conducting urban operations and retrograde operations in rough terrain. These findings could be used to develop a model for classifying work demands for ground combat forces.

Evaluating Firefighters' Joint Mobility and Muscular Activity during Load Carriage

Evaluating Firefighters' Joint Mobility and Muscular Activity during Load Carriage

Impact of Backpacks on Ergonomics: Biomechanical and Physiological Effects: A Narrative Review.

(1) Background: the effects of load carriage packs on human gait biomechanics, physiology and metabolism depend on the weight carried, the design of the pack and its interaction with the user. (2) Methods: An extensive search in the PubMed database was performed to find all the relevant articles using the following keywords: backpack, rucksack, backpack ergonomy and sports backpack; 60 articles were included. (3) Results and significance: Double pack (DP) and T-pack (TP) designs are recommended solutions for school children, compared with backpacks (BP). For soldiers and hikers, a backpack remains the best compromise. A hip belt is recommended for BPs as well as for the back of DPs. Shorter and stiffer shoulder straps combined with a higher and tighter load placement on the back provide the best combination in terms of balance, muscle activation and energy expenditure. It is, therefore, possible to determine guidelines for designing the optimal load carriage system, depending on the application. (4) Conclusions: based on the available evidence, DP and TP are advantageous in terms of posture. DP is better than conventional BPs in terms of balance and muscle activation, but has the disadvantage of limited visibility, thermal sensation and obstructed ventilation. In general, it is desirable not to exceed 40% of body mass (BM).

Application of the predicted biomechanics approach in assessing work-related musculoskeletal discomfort among female brickfield workers in West Bengal, India.

Manual brick manufacturing units in West Bengal, India are mostly unorganized sectors employing many migrant female workers in manual material handling tasks as brick moulders and brick carriers. The study estimated the biomechanical postural stress developed due to manual load handling, carriage and brick transportation. Body Part Discomfort Scale was used to assess the subjective pain felt by 18 adult female brick moulders and 12 brick carriers during work. Video recordings were taken during the actual field work and the images were analyzed for two-dimensional prediction kinetics and kinematics. Results show that the horizontal distance of the load from the body was 59.95±3.74 cm during the initial lifting of bricks by the brick carriers and so their biomechanical trunk angle inclination was significantly detrimental. The bending moment at the lumbosacral disc was much higher during the squatting posture while initial brick lifting. Moreover, the trunk and the neck pain of the brick carriers were caused by carrying 18% of body weight load. The brick carriers were the more vulnerable group in terms of work-related musculoskeletal disorders. Therefore, ergonomic interventions such as relay brick carrying and pole supported balanced brick carrying, may be implemented to reduce the prevalence of pain. This study is the first of its kind that validates the extent or the prevalence of work-related musculoskeletal disorders among the female brickfield workers through approaches of predicted biomechanics.

Physiological stress in flat and uphill walking with different backpack loads in professional mountain rescue crews

This study aimed to determine the interactive physiological effect of backpack load carriage and slope during walking in professional mountain rescuers. Sixteen mountain rescuers walked on a treadmill at 3.6 km/h for 5 min in each combination of three slopes (1%, 10%, 20%) and five backpack loads (0%, 10%, 20%, 30%, and 40% body weight). Relative heart rate (%HRmax), relative oxygen consumption (%VO2max), and rating of perceived exertion (RPE, Borg 1–10 scale) were compared across conditions using two-way ANOVA. Significant differences in %VO2max, %HRmax, and RPE across slopes and loads were found where burden increased directly with slope and load (main effect of slope, p < 0.001 for all; main effect of load, p < 0.001 for all). Additionally, significant slope by load interactions were found for all parameters, indicating an additive effect (p < 0.001 for all). Mountain rescuers should consider the physiological interaction between slope and load when determining safe occupational walking capacity.

Ability of Wearable Accelerometers-Based Measures to Assess the Stability of Working Postures.

With the rapid development and widespread application of wearable inertial sensors in the field of human motion capture, the low-cost and non-invasive accelerometer (ACC) based measures have been widely used for working postural stability assessment. This study systematically investigated the abilities of ACC-based measures to assess the stability of working postures in terms of the ability to detect the effects of work-related factors and the ability to classify stable and unstable working postures. Thirty young males participated in this study and performed twenty-four load-holding tasks (six working postures × two standing surfaces × two holding loads), and forty-three ACC-based measures were derived from the ACC data obtained by using a 17 inertial sensors-based motion capture system. ANOVAs, t-tests and machine learning (ML) methods were adopted to study the factors’ effects detection ability and the postural stability classification ability. The results show that almost all forty-three ACC-based measures could (p < 0.05) detect the main effects of Working Posture and Load Carriage, and their interaction effects. However, most of them failed in (p ≥ 0.05) detecting Standing Surface’s main or interaction effects. Five measures could detect both main and interaction effects of all the three factors, which are recommended for working postural stability assessment. The performance in postural stability classification based on ML was also good, and the feature set exerted a greater influence on the classification accuracy than sensor configuration (i.e., sensor placement locations). The results show that the pelvis and lower legs are recommended locations overall, in which the pelvis is the first choice. The findings of this study have proved that wearable ACC-based measures could assess the stability of working postures, including the work-related factors’ effects detection ability and stable-unstable working postures classification ability. However, researchers should pay more attention to the measure selection, sensors placement, feature selection and extraction in practical applications.

Cognitive performance of military men and women during prolonged load carriage

BackgroundThis study evaluated cognitive workload in soldiers undertaking a long duration march wearing different loads.MethodsMilitary participants (n=12 men and n=10 women) performed four 3-hour loaded marches (12.25 km at 4.9...

Mechanical Differences between Men and Women during Overground Load Carriage at Self-Selected Walking Speeds.

Few studies have directly compared physical responses to relative loading strategies between men and women during overground walking. This study aimed to compare gait mechanics of men and women during overground load carriage. A total of 30 participants (15 male, 15 female) completed three 10-min walking trials while carrying external loads of 0%, 20% and 40% of body mass at a self-selected walking speed. Lower-body motion and ground reaction forces were collected using a three-dimensional motion capture system and force plates, respectively. Female participants walked with a higher cadence (p = 0.002) and spent less absolute time in stance (p = 0.010) but had similar self-selected walking speed (p = 0.750), which was likely due to the female participants being shorter than the male participants. Except for ankle plantarflexion moments, there were no sex differences in spatiotemporal, kinematic, or kinetic variables (p > 0.05). Increasing loads resulted in significantly lower self-selected walking speed, greater stance time, and changes in all joint kinematics and kinetics across the gait cycle (p < 0.05). In conclusion, there were few differences between sexes in walking mechanics during overground load carriage. The changes identified in this study may inform training programs to increase load carriage performance.

Effects of anteriorly-loaded treadmill walking on dynamic gait stability in young adults

BackgroundAnteriorly-loaded walking is common in many occupations and may increase fall risk. Dynamic gait stability, defined by the Feasible Stability Region (FSR) theory, quantifies the kinematic relationship between the body’s center of mass (COM) and base of support (BOS). FSR-based dynamic gait stability has been used to evaluate the fall risk. Research questionHow does front load carriage affect dynamic gait stability, step length, and trunk angle among young adults during treadmill walking? MethodsIn this between-subject design study, 30 healthy young adults were evenly randomized into three load groups (0%, 10%, or 20% of body weight). Participants carried their assigned load while walking on a treadmill at a speed of 1.2 m/s. Body kinematics were collected during treadmill walking. Dynamic gait stability (the primary variable) was calculated for two gait events: touchdown and liftoff. Step length and trunk angle were measured as secondary variables. One-way analysis of variance was conducted to detect any group-related differences for all variables. Post-hoc analysis with Bonferroni correction was performed when main group differences were found. ResultsNo significant differences but medium to large effect sizes were found between groups for dynamic gait stability at touchdown (p = 0.194, η2 = 0.114) and liftoff (p = 0.122, η2 = 0.139). Trunk angle significantly increased (indicating backward lean) with the front load at touchdown (p < 0.001, η2 = 0.648) and liftoff (p < 0.001, η2 = 0.543). No significant between-group difference was found related to the step length (p = 0.344, η2 = 0.076). SignificanceCarrying a front load during walking significantly alters the trunk orientation and may change the COM-BOS kinematic relationship and, therefore, fall risk. The findings could inform the design of future studies focusing on the impact of anterior load carriage on fall risk during different locomotion.

Cardiorespiratory responses of load carriage in female and male soldiers

PurposeTo investigate the effect of sex and load carriage on cardiorespiratory responses to high intensity exercise in male and female soldiers. MethodsSoldiers (9 women, 9 men) performed a graded treadmill test until exhaustion with no load (NL) and combat-gear with body armor (CG). Cohen's d effect sizes, paired t-tests and ANOVA were used to study differences between conditions. A mixed linear regression model analyzed the relationship between heart rate (HR) and oxygen uptake (V̇O2) with load and between sexes. ResultsWearing CG resulted in, for both sexes, a decreased time to exhaustion (−11 min), lower V̇O2peak (L/min) ES = 0.56; VO2peak (mL//kg/min) ES = 2.44, both p < 0.001, a net decrease in minute ventilation (ES = 3.53) and no change in HRmax. No sex-difference were present except for absolute V̇O2peak. The VO2 and HR relationship showed a cardiorespiratory reduction wearing CG vs. NL. Added load was equal between sexes, although female soldiers' CG relative to body mass was higher (25%) than male soldiers’ (20%), p < 0.01. ConclusionWearing CG reduces soldiers’ cardiorespiratory capacity and exercise performance level, although the reduction cannot be explained solely based on the added load of CG, instead CG seems to restrict the capacity to fully ventilate. No sex differences were found in relative cardiorespiratory responses to wearing CG compared to NL.

Multiday load carriage decreases ability to mitigate ground reaction force through reduction of ankle torque production

The aim of this study was to examine the impact of backpack load carriage on lower limb strength and loading rate change in a cohort that match military recruit profiles. Twenty-six participants walked on a treadmill either carrying a military load carriage system (32 kg) or unloaded for 2 h on two consecutive days. Participants ground reaction forces and strength measures were assessed using a force platform and dynamometry, respectively. Testing included assessments before and after treadmill walking on days one and two, and 24 h following day 2. When assessed by mixed methods ANOVA (alpha: 0.05) statistically significant interaction effects were observed for loading peak (p = 0.031), loading rate (p = 0.035) and plantarflexor torque dynamometry variables at 60°s−1 (p = 0.011) and 120°s−1 (p = 0.024). Repeated measures correlation highlighted associations between plantarflexor torque at 60°s−1 and loading rate (r = −0.901, p < 0.001). Load carriage reduced lower limb torque which did not recover between days. Plantarflexor torque reductions were associated with increases in loading rate. Practitioners should consider that load bearers are more likely to experience lower limb injury during multi-day load carriage. Future work should develop protocols to reduce plantarflexor torque loss in order to reduce ground reaction force change.

Once daily calcium (1000mg) and vitamin D (1000IU) supplementation during military training prevents increases in biochemical markers of bone resorption but does not affect tibial microarchitecture in Army recruits.

Basic combat training (BCT) is a period of novel physical training including load carriage resulting in higher risk of stress fracture compared to any other time during military service. Prior trials reported a 20% reduction in stress fracture incidence with Ca and vitamin D (Ca+D) supplementation (2000mg Ca, 800IU vitamin D), and greater increases in tibia vBMD during BCT compared to placebo. The primary objective of this randomized, double-blind, placebo-controlled trial was to determine the efficacy of a lower dose of Ca (1000mg/d Ca, 1000IU vit D) on PTH, bone biomarkers and tibial microarchitecture during BCT. One hundred volunteers (50 males, 50 females; mean age 21.8±3.5 y) were block randomized by race and sex to receive a daily Ca+D fortified food bar or placebo. Anthropometrics, dietary intake, fasted blood draws and high resolution pQCT scans of the distal and mid-shaft tibia were obtained at the start of BCT and 8 wks later at the conclusion of training. As compliance was 98% in both treatment groups, an intent-to-treat analysis was used. At the distal tibia, total vBMD, Tb.vBMD, Tb.N, Th.Th and Tb.BV/TV increased (+1.07 to 2.12% for all, p<0.05) and Tb.Sp decreased (0.96 to 1.09%, p<0.05) in both treatment groups. At the mid-shaft, Ct.Pm increased (+0.18 to 0.21%, p=0.01) and Ct.vBMD decreased (-0.48 to -0.77%, p<0.001) in both groups. Ca+D prevented increases in CTX and TRAP, which were observed in the placebo group (group-by-time, p<0.05). Mean circulating 25OHD, BAP, P1NP and iCa increased and PTH decreased in both treatment groups (p<0.05). These results, in agreement with other studies, suggest that bone microarchitectural changes indicative of bone formation occur during BCT. While Ca+D supplementation at lower doses than those tested in previous studies prevented increases in biochemical markers of bone resorption in this study, there were no significant changes in bone tissue after 8 wks of Army BCT.