Spatiotemporal Parameters are not Substantially Influenced by Load Carriage or Inclination During Treadmill and Overground Walking

Increased Metabolic Demand During Nighttime Walking in Hilly Forest Terrain While Wearing Night Vision Goggles

INTRODUCTION

Foot-borne soldiers sometimes carry out nighttime operations. It has previously been reported an elevated metabolic demand and impaired walking economy during outdoor walking on a gravel road in darkness wearing night vision goggles (NVG), compared with wearing a headlamp. The aim of the present study was to evaluate the effect of wearing NVG while walking in a hilly forest terrain and compare the results between experienced and inexperienced NVG users.

MATERIALS AND METHODS

At nighttime, two different groups, inexperienced (five men and six women) and experienced (nine men) NVG users, walked 1.1 km at a self-selected comfortable pace in a hilly forest. Part I was mainly uphill, and Part II was mainly downhill. Walks were performed wearing a headlamp (light), monocular NVG (mono), binocular NVG (bino), or mono with a 25 kg extra weight (backpack). Walking economy calculated from oxygen uptake in relation to body mass and covered distance (V̇O2 (mL/[kg · km])), heart rate, gait, and walking speed were measured.

RESULTS

In both groups, walking economy was deteriorated in all three conditions with limited vision (mono, bino, and backpack) compared to the light condition, both during Part I (mono/bino, experienced: +26/+25%, inexperienced: +34/+28%) and Part II (mono/bino, experienced: +44/+46%, inexperienced: +63/+49%). In the backpack condition, the relative change of walking economy was greater for the inexperienced group than the experienced group: Part I (experienced: +46%, inexperienced: +70%), Part II (experienced: +71%, inexperienced: +111%). Concurrently, the step length was shorter in all three conditions with limited vision during Part I (mono/bino/backpack, experienced: -7/-7/-15%, inexperienced: -12/-12/-19%) and Part II (mono/bino/backpack; experienced: -8/-8/-14%, inexperienced: -17/-15/-24%) than in the light condition. The experienced NVG users walked faster during all conditions, but there was no difference in heart rate between groups.

CONCLUSIONS

Despite that foveal vision using NVG is adequate, it appears that the mechanical efficiency during nighttime walking in hilly terrain was markedly lower while wearing NVG than with full vision, regardless of whether the soldier was an experienced or inexperienced NVG user. Moreover, the walking economy was even more affected when adding the 25-kg extra weight. It is probable that the deteriorated mechanical efficiency was partly due to the shorter step length in all three conditions with limited vision.

Physiological, perceptual, and biomechanical differences between treadmill and overground walking in healthy adults: A systematic review and meta-analysis

This systematic review and meta-analysis aims to compare physiological, perceptual and biomechanical outcomes between walking on a treadmill and overground surfaces. Five databases (CINAHL, EMBASE, MEDLINE, SPORTDiscus, Web of Science) were searched until September 2022. Included studies needed to be a crossover design comparing biomechanical, physiological, or perceptual measures between motorised-treadmill and overground walking in healthy adults (18-65 years) walking at the same speed (<5% difference). The quality of studies were assessed using a modified Downs and Black Quality Index. Meta-analyses were performed to determine standardised mean difference ± 95% confidence intervals for all main outcome measures. Fifty-five studies were included with 1,005 participants. Relative oxygen consumption (standardised mean difference [95% confidence interval] 0.38 [0.14,0.63]) and cadence (0.22 [0.06,0.38]) are higher during treadmill walking. Whereas stride length (-0.36 [-0.62,-0.11]) and step length (-0.52 [-0.98,-0.06]) are lower during treadmill walking. Most kinetic variables are different between surfaces. The oxygen consumption, spatiotemporal and kinetic differences on the treadmill may be an attempt to increase stability due to the lack of control, discomfort and familiarity on the treadmill. Treadmill construction including surface stiffness and motor power are likely additional constraints that need to be considered and require investigation. This research was supported by an Australian Government Research Training Program (RTP) scholarship. Protocol registration is CRD42020208002 (PROSPERO International Prospective Register of Systematic Reviews) in October 2020.

Can handling a weapon make soldiers more unstable?

Gait stability in soldiers can be affected by task constraints that may lead to injuries. This study determined the effects of weapon handling and speed on gait stability in seventeen soldiers walking on a treadmill with and without a replica weapon at self-selected (SS), 3.5 km·h-1, 5.5 km·h-1, and 6.5 km·h-1 while carrying a 23-kg load. Local dynamic stability was measured using accelerometry at the sacrum (LDESAC) and sternum (LDESTR). No significant weapon and speed interaction were found. A significant effect of speed for the LDESAC, and a significant effect of speed and weapon for the LDESTR were found. Per plane analyses showed that the weapon effect was consistent across all directions for the LDESTR but not for LDESAC. Weapon handling increased trunk but did not affect pelvis stability. Speed decreased stability when walking slower than SS and increased when faster. These findings can inform injury prevention strategies in the military. Practitioner summary: We determined the effects of two constraints in soldier's walking stability, weapon handling and speed, measured at the trunk and sacrum. No constraints interactions were found, however, lower stability when walking slow and greater stability with the weapon at the trunk can inform preventive strategies in military training.

Effect of load carriage on joint kinematics, vertical ground reaction force and muscle activity: Treadmill versus overground walking

BACKGROUND

Previous studies have investigated the effect of either different load or different surface conditions, such as overground or treadmill walking, on human biomechanics. However, studies combining these two aspects are scarce.

RESEARCH QUESTION

The purpose of this study was to quantify the difference in spatiotemporal parameters, lower extremity joint kinematics, vertical ground reaction forces (vGRF) and muscle activity between normal bodyweight (100 %BW) and 20 % increased bodyweight (120 %BW) during overground and treadmill walking.

METHODS

Ten healthy young adults walked overground at self-selected speed and on an instrumented treadmill set to the overground speed. Spatiotemporal parameters, 3-dimensional lower extremity kinematics, vGRF and muscle activity were measured and compared between conditions.

RESULTS

The stance phase was longer for 120 %BW than 100 %BW in both overground and treadmill walking. Further, the stance phase was longer and cadence higher in treadmill than overground walking for both load conditions. Knee flexion angles were more than 3° greater in the second half of swing in treadmill than in overground walking. The vGRF was higher for 120 %BW compared to 100 %BW on both surfaces (treadmill, first peak: +18.6 %BW; second peak: +13.5 %BW; overground, first peak: +22.2 %BW; second peak: +19.8 %BW). Differences between conditions greater than 20 % were observed in short periods during the gait cycle for vastus medialis, vastus lateralis and semitendinosus.

SIGNIFICANCE

Results regarding the effects of carrying additional load using a weight vest on joint kinematics during treadmill walking may be translated to overground walking but some changes in muscle activation can be expected.

Gait and neuromuscular dynamics during level and uphill walking carrying military loads

The neuromuscular system responds to perturbation and increasing locomotor task difficulty by altering the stability of neuromuscular output signals. The purpose of this study was to determine the effects of two different military load carriage systems on the dynamic stability of gait and muscle activation signals. 14 army office cadets (20 ± 1 years) performed 4-minute treadmill walking trials on level (0%) and uphill (10%) gradients while unloaded, and with 11 kg backpack and 11 kg webbing loads while the activity of 6 leg and trunk muscles and the motion of the centre of mass (COM) were recorded. Loaded and uphill walking decreased stability and increased magnitude of muscle activations compared to loaded and level gradient walking. Backpack loads increased the medio-lateral stability of COM and uphill walking decreased stability of vertical COM motion and increased stride time variability. However, there was no difference between the two load carriage systems for any variable. The reduced stability of muscle activations in loaded and uphill conditions indicates an impaired ability of the neuromuscular control systems to accommodate perturbations in these conditions which may have implications on the operational performance of military personnel. However, improved medio-lateral stability in backpack conditions may indicate that participants were able to compensate for the loads used in this study, despite the decreased vertical stability and increased stride time variability evident in uphill walking. This study did not find differences between load carriage systems however, specific load carriage system effects may be elicited by greater load carriage masses.Highlights Loaded and uphill walking decreased dynamic stability of muscle activationsLower activation stability indicates impaired neuromotor resistance to perturbationBackpack and webbing loads produced similar effects on muscle activations.

Military load carriage effects on the gait of military personnel: A systematic review

Carrying heavy loads results in biomechanical changes to gait and to an increased risk of injury in soldiers. The aim of this review is to examine the effects of military specific load carriage on the gait of soldiers. The Web of Science, PubMed and CINAHL databases were searched, a total of 1239 records were screened and 20 papers were included in the review. Participant, load and task characteristics and a summary of key findings were extracted. Due to heterogeneity in the reviewed studies, analysis was restricted to qualitative synthesis. There were limited effects on spatio-temporal variables but consistently reported increased trunk, hip and knee flexion and increased hip and knee extension moments. Muscle activation of lower limb and trunk muscles were also increased with loads. However, there were some conflicting findings for most parameters reviewed and apart from spatio-temporal parameters the findings of this review were in line with previous reviews of combined military and civilian populations.

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.

Effects of Load Carriage and Step Length Manipulation on Achilles Tendon and Knee Loads

INTRODUCTION

Longer steps with load carriage is common in shorter Soldiers when matching pace with taller Soldiers whereas shorter steps are hypothesized to reduce risk of injury with load carriage. The effects of load carriage with and without step length manipulation on loading patterns of three commonly injured structures were determined: Achilles tendon, patellofemoral joint (PFJ) and medial tibiofemoral joint (mTFJ).

MATERIALS AND METHODS

ROTC Cadets (n = 16; 20.1 years ± 2.5) walked with and without load carriage (20-kg). Cadets then altered preferred step lengths ±7.5% with load carriage. Achilles tendon, PFJ and mTFJ loads were estimated via musculoskeletal modeling.

RESULTS

Large increases in peak Achilles tendon load (p < 0.001, d = 1.93), Achilles tendon impulse per 1-km (p < 0.001, d = 0.91), peak mTFJ load (p < 0.001, d = 1.33), and mTFJ impulse per 1-km (p < 0.001, d = 1.49) were noted with load carriage while moderate increases were observed for the PFJ (peak: p < 0.001, d = 0.69; impulse per 1-km: p < 0.001, d = 0.69). Shortened steps with load carriage only reduced peak Achilles tendon load (p < 0.001, d = -0.44) but did not reduce Achilles impulse per km due to the resulting extra steps and also did not reduce peak or cumulative PFJ and mTFJ loads (p > 0.05). Longer steps with load carriage increased PFJ loads the most (p < 0.001, d = 0.68-0.75) with moderate increases in mTFJ forces (p < 0.001, d = 0.48-0.63) with no changes in Achilles tendon loads (p = 0.11-0.20).

CONCLUSION

A preferred step length is the safest strategy when walking with load carriage. Taking a shorter step is not an effective strategy to reduce loading on the Achilles tendon, PFJ, and mTFJ.

Gaze direction affects walking speed when using a self-paced treadmill with a virtual reality environment

BACKGROUND

In a previous study it was observed that participants increase their walking speed during a dual task while walking on a self-paced treadmill in a virtual reality (VR) environment (Gait Real time Analysis Interactive Lab (GRAIL)). This observation is in contrast with the limited resources hypothesis, which suggests walking speed of healthy persons to decrease when performing a cognitive dual task.

AIM

The aim of the present study was therefore to determine whether the cognitive demand of the task, an aroused feeling, discrepancy in optic flow or a change in gaze direction caused participants to walk faster in this computer assisted rehabilitation environment.

MATERIALS

The GRAIL included a self-paced treadmill, a motion-capture system and synchronized VR environments.

METHODS

Thirteen healthy young adults (mean age 21.6 ± 2.5) were included in this study. Participants walked on the self-paced treadmill while seven different intervention conditions (IC) were offered. Prior to each IC, a control condition (CC) was used to determine the natural self-selected walking speed. Walking speed during the last 30 s of each IC was compared with the walking speed during the last 30 s of the preceding CC.

RESULTS

Results show that the height on which a visual task was presented in the VR environment, influenced walking speed. Participants walked faster when gaze was directed above the focus of expansion.

SIGNIFICANCE

These findings contribute to a further understanding of the differences between walking in a real life environment or computer assisted rehabilitation environment. When analyzing gait on a self-paced treadmill in the future, one must be attentive where to place a visual stimulus in the VR environment.

Spatiotemporal and kinematic changes in gait while carrying an energy harvesting assault pack system

Soldiers are fielded with a variety of equipment including battery powered electronic devices. An energy harvesting assault pack (EHAP) was developed to provide a power source to recharge batteries and reduce the quantity and load of extra batteries carried into the field. Little is known about the biomechanical implications of carrying a suspended-load energy harvesting system compared to the military standard assault pack (AP). Therefore, the goal of this study was to determine the impact of pack type and load magnitude on spatiotemporal and kinematic parameters while walking at 1.34 m/s on an instrumented treadmill at decline, level, and incline grades. There was greater forward trunk lean while carrying the EHAP and the heavy load (decline: p < 0.001; level: p = 0.009; incline: p = 0.003). As load increased from light to heavy, double support stance time was longer (decline: p = 0.012; level: p < 0.001; incline: p < 0.001), strides were shorter (incline: p = 0.013), and knee flexion angle at heel strike was greater (decline: p = 0.033; level: p = 0.035; incline: p = 0.005). When carrying the EHAP, strides (decline: p = 0.007) and double support stance time (incline: p = 0.006) was longer, the knee was more flexed at heel strike (level: p = 0.014; incline: p < 0.001) and there was a smaller change in knee flexion during weight acceptance (decline: p = 0.0013; level: p = 0.007; incline: p = 0.0014). Carrying the EHAP elicits changes to gait biomechanics compared to carrying the standard AP. Understanding how load-suspension systems influence loaded gait biomechanics are warranted before transitioning these systems into military or recreational environments.

An evaluation of measurement systems estimating gait speed during a loaded military march over graded terrain

This study aimed to evaluate the accuracy of three measurement systems estimating gait speed during a loaded military march over graded terrain. Systems developed by the Swiss and Netherlands Armed Forces and a commercial wrist-based device were evaluated in comparison to a Global Positioning System. The first part of the paper focuses on the development of the Dutch system, where speed is estimated from a chest worn accelerometer and body measurements. For this validation study 36 subjects were walking or running 13 laps of 200 m at different speeds. Results showed that walking and running speed can be estimated with a R²_adj of 0.968 and 0.740, respectively. In the second part of this paper, data from 64 soldiers performing a 35 km march were used to evaluate the accuracy of three measurement systems in estimating speed. Data showed that estimating gait speed with a single accelerometer can be accurate for military activity, even without prior individual calibration measurements. However, predictions should be corrected for confounders such as body size and shoe type to be accurate. Both, downhill and uphill walking led to changes in gait characteristics and to an overestimation of speed by up to 10%. Correcting for slope or gradient using altimetry in future algorithms/experiments could improve the estimation of gait speed.

The effect of temperature, gradient, and load carriage on oxygen consumption, posture, and gait characteristics

PURPOSE

The purpose of this experiment was to evaluate the effect of load carriage in a range of temperatures to establish the interaction between cold exposure, the magnitude of change from unloaded to loaded walking and gradient.

METHODS

Eleven participants (19-27 years) provided written informed consent before performing six randomly ordered walking trials in six temperatures (20, 10, 5, 0, -5, and -10 °C). Trials involved two unloaded walking bouts before and after loaded walking (18.2 kg) at 4 km · h-1, on 0 and 10% gradients in 4 min bouts.

RESULTS

The change in absolute oxygen consumption (V̇O2) from the first unloaded bout to loaded walking was similar across all six temperatures. When repeating the second unloaded bout, V̇O2 at both -5 and -10 °C was greater compared to the first. At -10 °C, V̇O2 was increased from 1.60 ± 0.30 to 1.89 ± 0.51 L · min-1. Regardless of temperature, gradient had a greater effect on V̇O2 and heart rate (HR) than backpack load. HR was unaffected by temperature. Stride length (SL) decreased with decreasing temperature, but trunk forward lean was greater during cold exposure.

CONCLUSION

Decreased ambient temperature did not influence the magnitude of change in V̇O2 from unloaded to loaded walking. However, in cold temperatures, V̇O2 was significantly higher than in warm conditions. The increased V̇O2 in colder temperatures at the same exercise intensity is predicted to ultimately lead to earlier onset of fatigue and cessation of exercise. These results highlight the need to consider both appropriate clothing and fitness during cold exposure.