Females and males use different hip and knee mechanics in response to symmetric military-relevant loads

Effects of a passive upper-body exoskeleton on whole-body kinematics, leg muscle activity, and discomfort during a carrying task

OBJECTIVE

To compare whole-body kinematics, leg muscle activity, and discomfort while performing a 10-min carrying task with and without a passive upper-body exoskeleton (CarrySuitⓇ), for both males and females.

BACKGROUND

Diverse commercial passive exoskeletons have appeared on the market claiming to assist lifting or carrying task. However, evidence of their impact on kinematics, muscle activity, and discomfort while performing these tasks are necessary to determine their benefits and/or limitations.

METHOD

Sixteen females and fourteen males carried a 15kg load with and without a passive exoskeleton during 10-min over a round trip route, in two non-consecutive days. Whole-body kinematics and leg muscle activity were evaluated for each condition. In addition, leg discomfort ratings were quantified before and immediately after the task.

RESULTS

The gastrocnemius and vastus lateralis muscle activity remained constant over the task with the exoskeleton. Without the exoskeleton a small decrease of gastrocnemius median activation was observed regardless of sex, and a small increase in static vastus lateralis activation was observed only for females. Several differences in sagittal, frontal, and transverse movements' ranges of motion were found between conditions and over the task. With the exoskeleton, ROM in the sagittal plane increased over time for the right ankle and pelvis for both sexes, and knees for males only. Thorax ROMs in the three planes were higher for females only when using the exoskeleton. Leg discomfort was lower with the exoskeleton than without.

CONCLUSION

The results revealed a positive impact on range of motion, leg muscle activity, and discomfort of the tested exoskeleton.

Sex- and age-related differences in kinetics and tibial accelerations during military-relevant movement tasks in U.S. Army trainees

Lower extremity injuries are prevalent in military trainees, especially in female and older trainees. Modifiable factors that lead to higher injury risk in these subgroups are not clear. The purpose of this study was to identify whether external loading variables during military-relevant tasks differ by age and sex in U.S. Army trainees. Data was collected on 915 trainees in the first week of Basic Combat Training. Participants performed running and ruck marching (walking with 18.1 kg pack) on a treadmill, as well as double-/single-leg drop landings. Variables included: vertical force loading rates, vertical stiffness, first peak vertical forces, peak vertical and resultant tibial accelerations. Comparisons were made between sexes and age groups (young, ≤19 years; middle, 20-24 years; older, ≥25 years). Significant main effects of sex were found, with females showing higher vertical loading rates during ruck marching, and peak tibial accelerations during running and ruck marching (p ≤ 0.03). Males showed higher vertical stiffness during running and peak vertical tibial accelerations during drop landings (p < 0.01). A main effect of age was found for vertical loading rates during running (p = 0.03), however no significant pairwise differences were found between age groups. These findings suggest that higher external loading may contribute to higher overall injury rates in female trainees. Further, higher stiffness during running may contribute to specific injuries, such as Achilles Tendinopathy, that are more prevalent in males. The lack of differences between age groups suggests that other factors contribute more to higher injury rates in older trainees.

Load carriage changes tibiofemoral arthrokinematics during ambulatory tasks in recruit-aged women

The introduction of women into U.S. military ground close combat roles requires research into sex-specific effects of military training and operational activities. Knee osteoarthritis is prevalent among military service members; its progression has been linked to occupational tasks such as load carriage. Analyzing tibiofemoral arthrokinematics during load carriage is important to understand potentially injurious motion and osteoarthritis progression. The study purpose was to identify effects of load carriage on knee arthrokinematics during walking and running in recruit-aged women. Twelve healthy recruit-aged women walked and ran while unloaded (bodyweight [BW]) and carrying additional + 25%BW and + 45%BW. Using dynamic biplane radiography and subject-specific bone models, tibiofemoral arthrokinematics, subchondral joint space and center of closest contact location between subchondral bone surfaces were analyzed over 0-30% stance (separate one-way repeated measures analysis of variance, load by locomotion). While walking, medial compartment contact location was 5% (~ 1.6 mm) more medial for BW than + 45%BW at foot strike (p = 0.03). While running, medial compartment contact location was 4% (~ 1.3 mm) more lateral during BW than + 25%BW at 30% stance (p = 0.04). Internal rotation was greater at + 45%BW compared to + 25%BW (p < 0.01) at 30% stance. Carried load affects tibiofemoral arthrokinematics in recruit-aged women. Prolonged load carriage could increase the risk of degenerative joint injury in physically active women.

Hip Range of Motion During Passive and 1-Leg Exercises Is Greater in Women: A Meta-analysis and Systematic Review

PURPOSE

To summarize sex-related differences in hip range of motion (ROM), including flexion, extension, abduction, adduction, internal rotation, and external rotation.

METHODS

We performed a systematic search of 3 databases (PubMed, CINAHL [Cumulative Index to Nursing and Allied Health Literature], and Embase). The search terms were as follows: hip, pelvis, range of motion, kinematic, men, and women. Included studies reported sex-specific data on hip ROM in healthy, uninjured adults. To generate hip ROM mean differences, a DerSimonian-Laird random-effects model was used. Effect sizes were pooled for each exercise. Subgroup analyses compared hip ROM by physical activity group: passive ROM, 1-leg hop or jump, 2-leg hop or jump, 2-leg drop or landing, 1-leg squat, 2-leg squat, walking, and jogging/running. Positive effect sizes represent greater ROM in women.

RESULTS

Thirty-eight studies with 3,234 total subjects were included; of these subjects, 1,639 were women (50.1%). The mean age was 25.3 years. An effect difference was considered statistically significant if P < .05 and clinically significant if the mean difference was greater than 4.0°. Women showed statistically and clinically significantly greater hip flexion in passive ROM (mean difference, 6.4°) and during the 1-leg hop or jump exercise (mean difference, 6.5°). Women also showed statistically and clinically significantly greater hip adduction during the 1-leg hop or jump (mean difference, 4.5°) and 1-leg squat (mean difference, 4.4°) exercises, as well as statistically and clinically significantly greater hip internal rotation in passive ROM (mean difference, 8.2°). In contrast, men showed statistically and clinically significantly greater flexion during the 2-leg hop or jump exercise (mean difference, -9.1°). No clinically significant differences in extension, abduction, or external rotation were found between women and men.

CONCLUSIONS

On average, women showed statistically and clinically significantly greater flexion, adduction, and internal rotation during passive and 1-leg exercises whereas men showed statistically and clinically significantly greater flexion during the 2-leg hop or jump exercise.

LEVEL OF EVIDENCE

Level IV, meta-analysis and systematic review of Level II-IV studies.

A systematic review of the physiological and biomechanical differences between males and females in response to load carriage during walking activities

The purpose of this review was to systematically assess literature on differences between males and females in the physiological and biomechanical responses to load carriage during walking. PubMed, CINAHL, Scopus, Web of Science and the Cochrane library were searched. A total of 4637 records were identified and screened. Thirty-three papers were included in the review. Participant characteristics, load carriage conditions, study protocol, outcome measures and main findings were extracted and qualitatively synthesised. Absolute oxygen uptake and minute ventilation were consistently greater in males but there were limited sex-specific differences when these were expressed relative to physical characteristics. There is limited evidence of sex-specific differences in spatio-temporal variables, ground reaction forces (normalised to body mass) or sagittal plane joint angles with load. However, differences have been found in hip and pelvic motions in the frontal and horizontal planes, which might partly explain an economical advantage for females proposed by some authors.

Musculoskeletal disorders risk assessment methods: a scoping review from a sex perspective

The evidence points to differences in the impact of musculoskeletal disorders (MSD) in males and females due to different exposure to risk factors and inherent characteristics. To identify risks associated with MSDs, ergonomic assessment is carried out by applying various methods. The aim of this scoping review was to determine to what extent ergonomic assessment methods consider sex-related factors and if they were found to do so, to determine the extent of this consideration. A total of 31 papers on 32 ergonomic assessment methods were analysed in the review. Of these 32 methods, only 6 considered sex as an assessment parameter or when interpreting the results. The results revealed that the limited consideration given to the sex factor in ergonomic methods, together with the different impacts of MSDs and their consequences according to a person's sex, supports the importance of including sex factors in ergonomic assessment methods. Practitioner summary: This scoping review determined to what extent ergonomic assessment methods consider sex-related factors and if they do so, to establish the extent of such consideration. Of the 32 methods analysed, only 6 considered a person's sex. The results revealed that only a limited consideration is given to the sex factor in ergonomic methods.

The association between tibial torsion, knee flexion excursion and foot progression during gait in people with knee osteoarthritis: a cross-sectional study

BACKGROUND

Lower limb malalignment is associated with gait kinematics, but there is limited information on the relationship between gait kinematics and tibial torsion in individuals with knee osteoarthritis (OA). This study aimed to investigate possible associations between tibial torsion and early stance kinematics during gait in people with mild and moderate medial knee OA.

METHODS

Forty-seven participants (age: 62.1 ± 6.0 years; female/male: 37/10) diagnosed with medial knee OA were recruited from a regional hospital. Thirty of them had mild and seventeen had moderate knee OA. Lower limb alignment including tibial torsion and valgus/varus alignment were assessed by an EOS biplaner X-ray system with participants in weight-bearing position. Lower limb kinematics during gait was captured using the Vicon motion analysis system. The associations were estimated by partial Pearson correlation coefficient test.

RESULTS

Our results indicated that external tibial torsion was related to early stance knee flexion excursion in participants with moderate knee OA (r = -0.58, p = 0.048), but not in participants with mild knee OA (r = 0.34, p = 0.102). External tibial torsion was associated with external foot progression angle (r = 0.48, p = 0.001), and knee varus/valgus alignment was associated with knee flexion excursion (r = -0.39, p = 0.010) in all participants.

CONCLUSIONS

Both horizontal and frontal lower limb alignments were associated with knee flexion excursion at early stance of gait cycle in participants with medial knee OA. The distal rotational profile of lower limb would likely affect knee motion in sagittal plane. It implies that people with moderate knee OA could possibly benefit from correction of rotational alignment of lower limb.

Comparison of In-service Reduced vs. Full Torso Coverage Armor for Females

INTRODUCTION

Body armor and torso-borne equipment are critical to the survivability and operational effectiveness of a soldier. Historically, in-service designs have been predominantly designed for males or unisex, which may be disadvantageous for females who are shaped differently and, on average, smaller in stature and mass than their male counterparts. This study assesses the biomechanical and performance impact of two Canadian in-service armors and fighting load conditions on females.

MATERIALS AND METHODS

Four tasks (i.e., range of motion, treadmill march [×2], and a wall obstacle) were performed in a Baseline condition and two in-service torso-borne equipment conditions; the full torso coverage (FTC) condition has full upper torso soft armor with the fighting load carried in a separate vest, while the reduced coverage (RC) has a plate carrier with fighting load integrated into the armor carrier, bulk positioned higher, and less torso coverage. Both used identical combat loads and front and back armor plates. Trunk range of motion, march lower limb kinematics, march shoulder and hip skin pressures, perceived discomfort after the march, and time to traverse a wall obstacle were captured. Data were collected to assess the biomechanics and usability of the systems for eight females, representative of military recruits. Linear mixed-effects models were created, and analysis of variances (ANOVAs) were then performed on all the outcome measures (P < .05). Tukey's post-hoc procedures were performed when appropriate (P < .05).

RESULTS

There were significant differences between the RC and FTC for the sit and reach test (P < .001), lateral bend test (P < .001), and wall traverse time (P < .01). In all cases, the RC outperformed FTC. There were no differences between the two in-service conditions with respect to hip, knee, and ankle flexion/extension. The RC average skin pressure was higher than the FTC at the left and right shoulders by 103% and 79%, respectively, and peak skin pressure at the left shoulder by 75%. Both in-service conditions showed decrements in performance from Baseline for sit and reach (P < .001), lateral bend (P < .001), and peak hip and knee flexion (P < .01) with the FTC showing decreases in trunk rotation (P < .001) and wall traverse time (P < .01).

CONCLUSIONS

Improved outcomes for the RC can be attributed to design differences. The lower placement of bulk in FTC may act as a physical barrier during range of motion tasks and the wall obstacle. The presence of shoulder caps on FTC provides another physical barrier that likely impedes full movement through the arms and shoulders. While the narrower shoulder straps of the RC remove the barrier, it causes more concentrated skin pressures on the shoulder that can lead to injury. The results suggest that the RC offers a potential for increased operational effectiveness in females (and potentially for males) compared to the FTC system. Shoulder pressure, an important predictor of discomfort and injury, is the only measure for which FTC outperformed the RC. Future torso-borne equipment designs targeting this outcome measure could help increase the effectiveness of the RC and other similar systems that reduce torso coverage, though survivability implications must also be considered.

Transcriptomic response of bioengineered human cartilage to parabolic flight microgravity is sex-dependent

Spaceflight and simulated spaceflight microgravity induced osteoarthritic-like alterations at the transcriptomic and proteomic levels in the articular and meniscal cartilages of rodents. But little is known about the effect of spaceflight or simulated spaceflight microgravity on the transcriptome of tissue-engineered cartilage developed from human cells. In this study, we investigate the effect of simulated spaceflight microgravity facilitated by parabolic flights on tissue-engineered cartilage developed from in vitro chondrogenesis of human bone marrow mesenchymal stem cells obtained from age-matched female and male donors. The successful induction of cartilage-like tissue was confirmed by the expression of well-demonstrated chondrogenic markers. Our bulk transcriptome data via RNA sequencing demonstrated that parabolic flight altered mostly fundamental biological processes, and the modulation of the transcriptome profile showed sex-dependent differences. The secretome profile analysis revealed that two genes (WNT7B and WNT9A) from the Wnt-signaling pathway, which is implicated in osteoarthritis development, were only up-regulated for female donors. The results of this study showed that the engineered cartilage tissues responded to microgravity in a sex-dependent manner, and the reported data offers a strong foundation to further explore the underlying mechanisms.

Putting your best weighted foot forward: Reviewing lower extremity injuries by sex in weighted military marching

LAY SUMMARY

International marching events, such as the Nijmegen Marches, have a prominent place in Canadian military history, and participation continues today. In the Dutch military, the load carriage requirements previously differed by sex, with men carrying 10 kilograms during the march and women carrying no weight. The Canadian delegation requires both male and female participants to carry 10 kilograms. This article examines the effect of this policy on possible injuries using a Gender-based Analysis Plus lens. Weight carriage should focus on anthropometric factors, not sex, which will allow for appropriate and equal increased stresses (weight) for march participants while minimizing injuries.

Load Carriage and Physical Exertion Influence Soldier Emotional Responses

INTRODUCTION

Regular aerobic exercise benefits psychological health, enhancing mood in clinical and nonclinical populations. However, single bouts of exercise exert both positive and negative effects on emotion. Exercise reliably increases emotional arousal. Its effects on emotional valence are thought to depend on an interplay between cognitive and interoceptive factors that change as a function of exercise intensity, as studied in clinical, healthy, and athlete populations. However, special populations, such as military, first responders, and endurance athletes, have unique physical exertion requirements that can coincide with additional cognitive, physical, and environmental stressors not typical of the general population. Load carriage is one such activity. The present study examined emotional valence and arousal during sustained, heavy load carriage akin to military training and operations.

METHODS

Thirteen (one woman) active duty soldiers completed a V̇O2max test, a 2-h loaded (up to 50% body mass) and unloaded (empty rucksack) treadmill foot march (3 mph/4% incline) on separate days, during which they rated their exertion and emotional valence and arousal every 40 min. They also completed measures of positive and negative affect and anxiety before and every 20 min after the foot march.

RESULTS

Two hours of loaded foot march led to elevated perceived exertion and less positive, more negative and anxious feelings. Higher rated exertion and more negative emotion were associated with higher percent HRmax and V̇O2peak at multiple time points.

CONCLUSIONS

These results support affect exertion models such as the Dual Mode Theory, whereby physical exertion becomes less pleasant with increasing intensity, and provide insights into how affective responses applied contexts may help predict time to fatigue or failure.

Biomechanical and physiological effects of female soldier load carriage: A scoping review

Loads carried by military populations can affect those of smaller stature, such as the average female, due to the higher percentage of body weight the loads represent. Despite this, most load carriage research is performed on males. Peer reviewed articles were collected from four databases to summarize available research on biomechanical and physiological effects of load carriage on females in the military. Extraction and thematic analysis were performed on 18 articles. 39% looked at biomechanical differences between loads in females, 61% looked at how the same load affected males and females, 44% looked at sex-by-load interaction effects, and 72% discussed impacts of load on females. The research revealed that military load carriage affects the biomechanics and physiology differently in females and to a greater extent than in males. Several gaps in available literature were found. Very few studies used military participants, military equipment, and/or employed occupationally relevant data collection methodologies.

6DOF knee kinematic alterations due to increased load levels

Whether load carriage leads to six-degrees-of-freedom (6DOF) knee kinematic alterations remains unclear. Exploring this mechanism may reveal meaningful knee kinematic information that can be used to improve load carriage conditions, the design of protective devices, and the knowledge of the effects of load carriage on knees. We recruited 44 subjects to explore kinematic alterations from an unloaded state to 60% bodyweight (BW) load carriage. A three-dimensional gait analysis system was used to collect the knee kinematic data. One-way repeated analysis of variance (ANOVA) was used to explore the effects of load levels on knee kinematics. The effects of increasing load levels on knee kinematics were smooth with decreased or increased trends. We found that knees significantly exhibited increased lateral tibial translation (up to 1.2 mm), knee flexion angle (up to 1.4°), internal tibial rotation (up to 1.3°), and tibial proximal translation (up to 1.0 mm) when they went from an unloaded state to 60%BW load carriage during the stance phase (p < 0.05). Significant small knee adduction/abduction angle and posterior tibial translation alterations (<1°/mm) were also identified (p < 0.05). Load carriage can cause significant 6DOF knee kinematic alterations. The results showed that knee kinematic environments are challenging during increased load. Our results contain kinematic information that could be helpful for knee-protection-related activities, such as target muscle training to reduce abnormal knee kinematics and knee brace design.

Can increased load carriage affect lower limbs kinematics during military gait?

The aim of this study was to investigate if increased load carriage, in male military personnel, can affect the lower limbs kinematics. Twelve male military volunteers from the Portuguese Army were recruited and evaluated in an unloaded and loaded gait condition. Linear kinematics and lower limbs joint angle at heel strike, midstance and toe off were calculated. The stance, swing and double support times were found to be different between load conditions (p < 0.05). There was an interaction between load and limb (p < 0.05) for joint angles, during midstance, with limbs performing different movements in the frontal plane during loaded gait. Load increase had a different effect on the right knee, with a reduction in the abduction (valgus). This study may be beneficial in offering suggestion to improve the performance of gait with load and in an attempt to help prevent possible injuries. Practitioner summary: Increased load can affect lower limbs of male soldiers at the pelvic, hip and knee angles on the frontal plane, which can alter the joint force distribution. While these alterations may indicate protective mechanics, load management procedures should be implemented along with gait monitoring to avoid negative effects in performance.

Considerations for Sex-Cognizant Research in Exercise Biology and Medicine

As the fields of kinesiology, exercise science, and human movement developed, the majority of the research focused on male physiology and extrapolated findings to females. In the medical sphere, basing practice on data developed in only males resulted in the removal of drugs from the market in the late 1990s due to severe side effects (some life-threatening) in females that were not observed in males. In response to substantial evidence demonstrating exercise-induced health benefits, exercise is often promoted as a key modality in disease prevention, management, and rehabilitation. However, much like the early days of drug development, a historical literature knowledge base of predominantly male studies may leave the exercise field vulnerable to overlooking potentially key biological differences in males and females that may be important to consider in prescribing exercise (e.g., how exercise responses may differ between sexes and whether there are optimal approaches to consider for females that differ from conventional approaches that are based on male physiology). Thus, this review will discuss anatomical, physiological, and skeletal muscle molecular differences that may contribute to sex differences in exercise responses, as well as clinical considerations based on this knowledge in athletic and general populations over the continuum of age. Finally, this review summarizes the current gaps in knowledge, highlights the areas ripe for future research, and considerations for sex-cognizant research in exercise fields.

The effects of incremental changes in rucksack load on lower extremity joint Kinetic patterns during ruck marching

Injuries are often attributed to ruck marching. Therefore, it is important to examine how load carriage influences gait mechanics. The purpose of this study was to examine how subtle changes in rucksack load influence joint torque patterns during marching. Fourteen Army ROTC cadets marched with light, moderate, and heavy rucksack loads. Kinetic and kinematic data were recorded via an instrumented treadmill and motion capture system and principal component analysis was used to analyse the joint torque waveforms. Cadets exhibited moderate-large increases in knee extension torques during early stance (effect sizes ≥0.45) and small-moderate increases in ankle plantarflexion torques during push off (effect sizes ≥0.23) with each incremental increase in rucksack load. The lighter load also resulted in lower hip extension torques during early stance and flexion torques during late stance, vs. the moderate and heavier loads (effect sizes ≥0.23). It appears that subtle changes in rucksack load influence marching mechanics. Practitioner Summary: The purpose of this study was to examine how relatively subtle changes in rucksack load influence marching mechanics. Army ROTC cadets marched with relatively light, moderate, and heavy rucksack loads. Our results indicate that even subtle changes in rucksack load influence joint torque patterns of the hip, knee, and ankle. Abbreviations: ROTC: reserve officer training corps; RoF: rating-of-fatigue; PC: principal component; ICC: intraclass correlation coefficient; ES: effect size.

Loaded forced-marching shifts mechanical contributions proximally and disrupts stride-to-stride joint work modulation in recruit aged women

BACKGROUND

Military personnel in combat roles often perform gait tasks with additional load, which can affect the contributions of joint mechanical work (positive and negative). Furthermore, different locomotion patterns can also affect joint specific work contributions. While mean behavior of joint work is important to understanding gait, changes in joint kinetic modulation, or the regulation/control of stride-to-stride joint work variability is necessary to elucidate locomotor system function. Suboptimal modulation exhibited as a stochastic time-series (large fluctuation followed by an opposite smaller fluctuation) could potentially affect locomotion efficiency and portend injury risk. It remains unclear how the locomotor system responds to a combination of load perturbations and varying locomotion patterns.

RESEARCH QUESTION

What are the interactive effects of load magnitude and locomotion pattern on joint positive/negative work and joint work modulation in healthy, active, recruit-aged women?

METHODS

Eleven healthy, active, recruit-aged (18-33 years) women ran and forced-marched (walking at a velocity an individual would typically jog) in bodyweight (BW), an additional 25 % of BW (+25 %BW) and an additional 45 % of BW (+45 %BW) conditions at a velocity above their gait transition velocity. Joint work was calculated as the time integral of joint power. Joint work modulation was assessed with detrended fluctuation analysis (DFA) on consecutive joint work time-series.

RESULTS

Joint work contributions shifted proximally for forced-marching demonstrated by lesser (p < .001) positive/negative ankle work but greater (p = .001) positive hip work contributions compared to running. Running exhibited optimal positive ankle work modulation compared to forced-marching (p = .040). Knee and ankle negative joint work modulation was adversely impacted compared to the hip during forced-marching (p < .001).

SIGNIFICANCE

Employing forced-marching gait while under loads of 25 and 45 % of BW reduces the ability of the plantar-flexors and knee extensors to optimally contribute to energy absorption and propulsion in recruit-aged women, potentially reducing metabolic efficiency and increasing injury risk.

Increases in Load Carriage Magnitude and Forced Marching Change Lower-Extremity Coordination in Physically Active, Recruit-Aged Women

The objective was to examine the interactive effects of load magnitude and locomotion pattern on lower-extremity joint angles and intralimb coordination in recruit-aged women. Twelve women walked, ran, and forced marched at body weight and with loads of +25%, and +45% of body weight on an instrumented treadmill with infrared cameras. Joint angles were assessed in the sagittal plane. Intralimb coordination of the thigh-shank and shank-foot couple was assessed with continuous relative phase. Mean absolute relative phase (entire stride) and deviation phase (stance phase) were calculated from continuous relative phase. At heel strike, forced marching exhibited greater (P < .001) hip flexion, knee extension, and ankle plantar flexion compared with running. At mid-stance, knee flexion (P = .007) and ankle dorsiflexion (P = .04) increased with increased load magnitude for all locomotion patterns. Forced marching (P = .009) demonstrated a "stiff-legged" locomotion pattern compared with running, evidenced by the more in-phase mean absolute relative phase values. Running (P = .03) and walking (P = .003) had greater deviation phase than forced marching. Deviation phase increased for running (P = .03) and walking (P < .001) with increased load magnitude but not for forced marching. With loads of >25% of body weight, forced marching may increase risk of injury due to inhibited energy attenuation up the kinetic chain and lack of variability to disperse force across different supportive structures.

Spatiotemporal and Kinematic Comparisons Between Anthropometrically Paired Male and Female Soldiers While Walking With Heavy Loads

INTRODUCTION

Limited work comparing the effect of heavier carried loads (greater than 30 kg) between men and women has attributed observed differences to sex with the possibility that anthropometric differences may have contributed to those discrepancies. With the recent decision permitting women to enter Combat Arms roles, knowledge of sex-based differences in gait response to load carriage is more operationally relevant, as military loads are absolute and not relative to body weight. The purpose of this study was to describe differences in gait parameters at light to heavy loads between anthropometrically similar male and female soldiers.

MATERIALS AND METHODS

Eight female and 8 male soldiers, frequency-matched (1-to-1) on height (±0.54 cm) and mass (±0.52 kg), walked at 1.34 m∙s-1 for 10-min bouts on a level treadmill while unloaded (BM) and then carrying randomized vest-borne loads of 15, 35, and 55 kg. Spatiotemporal and kinematic data were collected for 30 s after 5 min. Two-way repeated measures analyses of variance were conducted to compare the gait parameter variables between sexes at each load.

RESULTS

As load increased, overall, the percent double support increased, step frequency increased, stride length decreased, hip and ankle range of motion (ROM) increased, and vertical center of mass (COM) displacement increased. Sex-based significant differences were observed in knee ROM and mediolateral COM displacement. Among the male participants, knee ROM increased significantly for all loads greater than BM. For mediolateral COM displacement, male remained constant as load increased, whereas female values decreased between BM and 35 kg.

CONCLUSIONS

Spatiotemporal and kinematic differences in gait parameters were primarily because of increases in load magnitude. The observed sex-related differences with increasing loads suggest that women may require a more stable gait to support the additional load carried.

Analysis of 3-D Kinematics Using H-Gait System during Walking on a Lower Body Positive Pressure Treadmill

Recently, treadmills equipped with a lower-body positive-pressure (LBPP) device have been developed to provide precise body weight support (BWS) during walking. Since lower limbs are covered in a waist-high chamber of an LBPP treadmill, a conventional motion analysis using an optical method is impossible to evaluate gait kinematics on LBPP. We have developed a wearable-sensor-based three-dimensional motion analysis system, H-Gait. The purpose of the present study was to investigate the effects of BWS by a LBPP treadmill on gait kinematics using an H-Gait system. Twenty-five healthy subjects walked at 2.5 km/h on a LBPP treadmill under the following three conditions: (1) 0%BWS, (2) 25%BWS and (3) 50%BWS conditions. Acceleration and angular velocity from seven wearable sensors were used to analyze lower limb kinematics during walking. BWS significantly decreased peak angles of hip adduction, knee adduction and ankle dorsiflexion. In particular, the peak knee adduction angle at the 50%BWS significantly decreased compared to at the 25%BWS (p = 0.012) or 0%BWS (p < 0.001). The present study showed that H-Gait system can detect the changes in gait kinematics in response to BWS by a LBPP treadmill and provided a useful clinical application of the H-Gait system to walking exercises.

Lower Limb Biomechanical Responses During a Standardized Load Carriage Task are Sex Specific

INTRODUCTION

The purpose of this study was to investigate sex-specific lower limb biomechanical adaptations during a standardized load carriage task in response to a targeted physical training program.

MATERIALS AND METHODS

Twenty-five healthy civilians (males [n = 13] and females [n = 12]) completed a load carriage task (5 km at 5.5 km·h-1, wearing a 23 kg vest) before and after a 10-week lower-body-focused training program. Kinematics and ground reaction force data were collected during the task and were used to estimate lower limb joint kinematics and kinetics (i.e., moments and powers). Direct statistical comparisons were not conducted due to different data collection protocols between sexes. A two-way repeated measures ANOVA tested for significant interactions between, and main effects of training and distance marched for male and female data, respectively.

RESULTS

Primary kinematic and kinetic changes were observed at the knee and ankle joints for males and at the hip and knee joints for females. Knee joint moments increased for both sexes over the 5 km distance marched (P > .05), with males demonstrating significant reductions in peak knee joint extension after training. Hip adduction, internal rotation, and knee internal rotation angles significantly increased after the 5 km load carriage task for females but not males.

CONCLUSION

Differences in adaptive gait strategies between sexes indicate that physical training needs to be tailored to sex-specific requirements to meet standardized load carriage task demands. The findings highlighted previously unfound sex-specific responses that could inform military training and facilitate the integration of female soldiers into physically demanding military roles.

Effects of body size and load carriage on lower-extremity biomechanical responses in healthy women

BACKGROUND

Musculoskeletal injuries, such as stress fractures, are the single most important medical impediment to military readiness in the U.S. Army. While multiple studies have established race- and sex-based risks associated with a stress fracture, the role of certain physical characteristics, such as body size, on stress-fracture risk is less conclusive.

METHODS

In this study, we investigated the effects of body size and load carriage on lower-extremity joint mechanics, tibial strain, and tibial stress-fracture risk in women. Using individualized musculoskeletal-finite-element-models of 21 women of short, medium, and tall statures (n = 7 in each group), we computed the joint mechanics and tibial strains while running on a treadmill at 3.0 m/s without and with a load of 11.3 or 22.7 kg. We also estimated the stress-fracture risk using a probabilistic model of bone damage, repair, and adaptation.

RESULTS

Under all load conditions, the peak plantarflexion moment for tall women was higher than those in short women (p < 0.05). However, regardless of the load condition, we did not observe differences in the strains and the stress-fracture risk between the stature groups. When compared to the no-load condition, a 22.7-kg load increased the peak hip extension and flexion moments for all stature groups (p < 0.05). However, when compared to the no-load condition, the 22.7-kg load increased the strains and the stress-fracture risk in short and medium women (p < 0.05), but not in tall women.

CONCLUSION

These results show that women of different statures adjust their gait mechanisms differently when running with external load. This study can educate the development of new strategies to help reduce the risk of musculoskeletal injuries in women while running with external load.

Effects of prolonged walking with body borne load on knee adduction biomechanics

BACKGROUND

Soldiers that suffer a service-related knee musculoskeletal injury routinely develop joint osteoarthritis. Knee osteoarthritis is a substantial and costly problem among soldiers, yet it is unknown how body borne load and duration of walking impact knee adduction biomechanics linked to progression and severity of osteoarthritis.

RESEARCH QUESTION

This study determined the adaptations in magnitude and variability of knee adduction joint angle (KAA) and moment (KAM) during prolonged walking with body borne load.

METHODS

Thirteen recreationally active participants had knee biomechanics quantified while walking over-ground for 60-min at 1.3 m/s with three body borne loads (0, 15, and 30 kg). Magnitude and variability of KAA and KAM measures were quantified and submitted to a RM ANOVA to test the main effect and interactions between load (0, 15 and 30 kg) and time (0, 15, 30, 45 and 60 min).

RESULTS

Body borne load increased peak KAM (p < 0.001), whereas time increased peak and range of KAA (both: p < 0.001). Specifically, peak KAM increased with each addition of body borne load (all: p < 0.025), and peak and range of KAA increased after 30 min of walking (both: p < 0.040). Neither body borne load, nor time had a significant effect on KAA or KAM variability (both: p > 0.05).

SIGNIFICANCE

Prolonged walking with heavy body borne load increased knee adduction biomechanics related to osteoarthritis. Adding heavy body borne load increased in peak KAM whereas duration of walking increased KAA, knee biomechanics that may increase loading of the medial knee joint compartment and risk of OA at the joint.

Are female soldiers satisfied with the fit and function of body armour?

Design and development of contemporary military body armour has traditionally focused primarily on male soldiers. As the anthropometric body dimensions of male and female soldiers differ, we aimed to determine whether current body armour was meeting fit and functional requirements of female soldiers. One-hundred and forty-seven female Australian Defence Force soldiers completed a 59-item questionnaire regarding the fit and function of current body armour. Most (68%) participants reported wearing ill-fitting body armour, which was associated with increased total musculoskeletal pain and discomfort, as well as pain at the shoulders, abdomen, and hips. Body armour that was too large was more likely to interfere with task performance when it was integrated with a combat belt, as well as when female soldiers performed operationally representative tasks. Modifying body armour design and sizing to cater to the anthropometric dimensions of female soldiers is recommended.

Load Magnitude and Locomotion Pattern Alter Locomotor System Function in Healthy Young Adult Women

Introduction

During cyclical steady state ambulation, such as walking, variability in stride intervals can indicate the state of the system. In order to define locomotor system function, observed variability in motor patterns, stride regulation and gait complexity must be assessed in the presence of a perturbation. Common perturbations, especially for military populations, are load carriage and an imposed locomotion pattern known as forced marching (FM). We examined the interactive effects of load magnitude and locomotion pattern on motor variability, stride regulation and gait complexity during bipedal ambulation in recruit-aged females.

Methods

Eleven healthy physically active females (18–30 years) completed 1-min trials of running and FM at three load conditions: no additional weight/bodyweight (BW), an additional 25% of BW (BW + 25%), and an additional 45% of BW (BW + 45%). A goal equivalent manifold (GEM) approach was used to assess motor variability yielding relative variability (RV; ratio of “good” to “bad” variability) and detrended fluctuation analysis (DFA) to determine gait complexity on stride length (SL) and stride time (ST) parameters. DFA was also used on GEM outcomes to calculate stride regulation.

Results

There was a main effect of load (p = 0.01) on RV; as load increased, RV decreased. There was a main effect of locomotion (p = 0.01), with FM exhibiting greater RV than running. Strides were regulated more tightly and corrected quicker at BW + 45% compared (p < 0.05) to BW. Stride regulation was greater for FM compared to running. There was a main effect of load for gait complexity (p = 0.002); as load increased gait complexity decreased, likewise FM had less (p = 0.02) gait complexity than running.

Discussion

This study is the first to employ a GEM approach and a complexity analysis to gait tasks under load carriage. Reduction in “good” variability as load increases potentially exposes anatomical structures to repetitive site-specific loading. Furthermore, load carriage magnitudes of BW + 45% potentially destabilize the system making individuals less adaptable to additional perturbations. This is further evidenced by the decrease in gait complexity, which all participants demonstrated values similarly observed in neurologically impaired populations during the BW + 45% load condition.

Effects of Backpack Loads on Leg Muscle Activation during Slope Walking

Hikers and soldiers usually walk up and down slopes with a load carriage, causing injuries of the musculoskeletal system, especially during a prolonged load journey. The slope walking has been reported to lead to higher leg extensor muscle activities and joint moments. However, most of the studies investigated muscle activities or joint moments during slope walking without load carriage or only investigated the joint moment changes and muscle activities with load carriages during level walking. Whether the muscle activation such as the signal amplitude is influenced by the mixed factor of loads and grades and whether the influence of the degrees of loads and grades on different muscles are equal have not yet been investigated. To explore the effects of backpack loads on leg muscle activation during slope walking, ten young male participants walked at 1.11 m/s on a treadmill with different backpack loads (load masses: 0, 10, 20, and 30 kg) during slope walking (grade: 0, 3, 5, and 10°). Leg muscles, including the gluteus maximus (GM), rectus femoris (RF), hamstrings (HA), anterior tibialis (AT), and medial gastrocnemius (GA), were recorded during walking. The hip, knee, and ankle extensor muscle activations increased during the slope walking, and the hip muscles increased most among hip, knee, and ankle muscles (GM and HA increased by 46% to 207% and 110% to 226%, respectively, during walking steeper than 10° across all load masses (GM: p = 1.32 × 10−8 and HA: p = 2.33 × 10−16)). Muscle activation increased pronouncedly with loads, and the knee extensor muscles increased greater than the hip and ankle muscles (RF increased by 104% to 172% with a load mass greater than 30 kg across all grades (RF: p = 8.86 × 10−7)). The results in our study imply that the hip and knee muscles play an important role during slope walking with loads. The hip and knee extension movements during slope walking should be considerably assisted to lower the muscle activations, which will be useful for designing assistant devices, such as exoskeleton robots, to enhance hikers’ and soldiers’ walking abilities.

Load carriage magnitude and locomotion strategy alter knee total joint moment during bipedal ambulatory tasks in recruit-aged women

Knee osteoarthritis (OA) is prevalent among female soldiers, resulting in limited duty and long term adverse ambulatory effects. A proposed mechanism to the development of knee OA is the assiduous execution of load carriage tasks. Soldiers are often required to maintain a walking gait with load at velocities beyond their gait transition velocity (GTV) known as forced marching. The primary aim of this investigation is to determine the interactive effects of load magnitude and locomotion pattern on relative knee total joint moment (KTJM) in healthy recruit-aged women. The secondary aims are to determine knee total joint moment limb differences and to determine the interactive effect of load magnitude and locomotion pattern on the percent contributions of each plane of motion moment. Individuals were tasked with running and forced marching at 10% above their GTV at body weight (BW) and with an additional 25% and 45% of their BW. KTJM was analyzed at two specific gait events of heel-strike and mid-stance. At heel-strike, forced marching exhibited greater KTJM compared to run for all load conditions but running had greater KTJM than forced marching at mid-stance. The forced marching pattern exhibited larger KTJM for the dominant limb at both gait events compared to running. Lastly, at mid-stance the knee adduction moment percent (KAM%) contribution was greater for forced marching compared to running. The forced marching pattern demonstrates joint kinetics that may be more deleterious with prolonged exposure. Likewise, forced marching induced KAM% similar to those already suffering from knee OA.