Effect of load mass on posture, heart rate and subjective responses of recreational female hikers to prolonged load carriage

The comfort and functional performance of personal protective equipment for police officers: a systematic scoping review

This scoping review aimed to identify and summarise evidence on the comfort and functional performance of police officer personal protective equipment (PPE). The Arksey and O'Malley (2005) five-stage framework for scoping reviews was followed. PubMed, CINAHL, Scopus, and Web of Science were searched, and 35 articles were included in the review. The findings show that increased police PPE mass increases heart rate, metabolic energy expenditure, and perceived exertion in response to exercise. Unisex armour designs cause increased discomfort for females with larger bra sizes. PPE reduces joint-specific range of motion, with the design and location impairing movement more than mass. Jumping and sprinting performance is decreased with heavy PPE but unaffected by lighter protection, while agility is compromised with most forms of protection. Future research is needed on the fit and function of PPE for specialist police units, such as mounted police, along with further investigations on how fit can affect functional performance.

Metabolic power response to added mass on the lower extremities during running

BACKGROUND

Wearable exoskeletal devices can enhance locomotor performance, but their mass results in a metabolic penalty. Previous studies have quantified the metabolic cost of running with added mass on the feet, but less is known about the effects of adding mass to the thigh and shank segments.

AIM

To quantify the metabolic cost of running with additional leg mass.

METHODS

15 participants (7 F, 8 M) completed treadmill running trials (3 m/s) normally and with lead mass (300-1350 g) attached to either the thigh, shank, or foot, bilaterally. We measured metabolic power using expired gas analysis.

RESULTS

Per 1000 g of added mass per leg, gross metabolic power increased by approximately 16% (foot) and 11% (shank) for females which was slightly greater than the 11% and 8% increases for males, respectively. For thigh loading, metabolic power increased by just 4% per 1000 g in both sexes.

CONCLUSION

Adding mass more distally on the leg increases the metabolic cost of running to a greater extent. For the same absolute added mass on the foot or shank, metabolic power increases more in females.

Added mass increases Achilles tendon stress in female runners

CONTEXT

Achilles tendon (AT) injuries are common in female runners and military personnel where increased AT loading may be a contributing factor. Few studies have examined AT stress during running with added mass. The purpose was to examine the stress, strain, and force placed on the AT, kinematics and temporospatial variable in running with different amounts of added mass.

DESIGN

Repeated measure design METHODS: Twenty-three female runners with a rear-foot strike pattern were participants. AT stress, strain, and force were measured during running using a musculoskeletal model that used kinematic (180 Hz) and kinetic data (1800 Hz) as input. Ultrasound data were used to measure AT cross sectional area. A repeated measures multivariate analysis of variance (α = 0.05) was used on AT loading variables, kinematics and temporospatial variables.

RESULTS

Peak AT stress, strain, and force were greatest during the 9.0 kg added load running condition (p < .0001). There was a 4.3% and 8.8% increase in AT stress and strain during the 4.5 kg and 9.0 kg added load conditions, respectively, compared to baseline. Kinematics at the hip and knee changed with added load but not at the ankle. Small changes in temporospatial variables were seen.

CONCLUSION

Added load increased stress on the AT during running. There may be an increased risk for AT injury with added load. Individuals may consider slowly progressing training with added load to allow for increased AT loading.

Frequency of Knee Pain and Risk Factors and Its Impact on Functional Impairment: A Cross-Sectional Study from Saudi Arabia

BACKGROUND

Adolescents frequently self-report pain, according to epidemiological research. The knee is one of the sites wherein pain is most commonly reported. Musculoskeletal disorders play a significant role in the prolonged disability experienced by individuals, leading to substantial global personal, societal, and economic burdens. Patellofemoral pain (PFP) is a clinical knee pain commonly affecting adolescents. This study aimed to estimate the frequency of knee pain in Saudi adolescents.

METHODS

This cross-sectional survey was conducted from June to November 2022 and included 676 adolescents aged 10 to 18 years. The participants were questioned regarding their demographics, school habits, and the impact of these factors on back pain, musculoskeletal pain in the past 12 months, as well as quality-of-life scale and knee pain symptoms. The data were analyzed using descriptive statistics, with frequencies and percentages presented for categorical variables. Analysis of variance (ANOVA) was performed to compare means between groups, while the chi-squared test was used to compare categorical variables. Statistical significance was set at p < 0.05.

RESULTS

A total of 676 adolescents participated in the study, with 57.5% females and 42.5% males. Among the participants, 68.8% were aged between 15 and 18 years. The prevalence of knee pain was notably higher among females (26%) compared to males (19.2%). Age and BMI were identified as significant predictors of knee pain. A significant association was also found between BMI classification and knee stiffness (p-value = 0.008). Furthermore, a significant difference was observed between adolescents who engaged in physical activities during leisure time and those who experienced difficulty bending (p-value = 0.03).

CONCLUSIONS

Our study highlights a high prevalence of knee pain among Saudi adolescents, emphasizing the need for increased awareness about its risk factors. Preventive measures, including conservative approaches and lifestyle/activity modifications, can effectively mitigate adolescent knee pain.

Associations between Borg’s rating of perceived exertion and changes in urinary organic acid metabolites after outdoor weight-bearing hiking

BACKGROUND

Developing methods to monitor exercise load and evaluate body fatigue and muscle injury over time in hiking training remains a key problem to be solved. A widely used psycho-physical tool to assess the subjective perception of effort during exercise is Borg’s rating of perceived exertion (BRPE) scale. Data on the relationships and validity of the BRPE compared to objectively assessed metabolic criteria are still lacking, especially urinary organic acid concentrations.

AIM

To verify whether the BRPE scale could be used in the prescription of outdoor hiking with weight-bearing and reveal the relationship between the BRPE scale and urinary physiological measures.

METHODS

Eighty-nine healthy men (average age: 22 years) were enrolled in a 40 km (6 h) hiking training exercise with a 20 kg load. After training, the BRPE scale (6-20) was completed. All participants were divided into three groups according to the rating of the BRPE scale. Urine samples were collected before and after training. Urinary myoglobin levels were measured immediately using the fluorescent immunoassay method. The remaining urine was subpacked and frozen for the subsequent detection of urinary organic acids using gas chromatography and mass spectrometry.

RESULTS

The contents of organic acids and myoglobin in urine were significantly increased after participants hiked 40 km (6 h) with a 20 kg load. Only orthogonal partial least-squares discrimination analysis performed well in separating the group with a BRPE score of 6-12 from the group with a BRPE score of 13-20. Significant differences in the urine levels of several organic acids were observed between the two groups, and the heatmap also presented different metabolic profiles based on BRPE. According to the standard of a variable importance in the projection > 1, fold change > 1.5 and P < 0.05, 19 different metabolites of urinary organic acids were screened and enriched in pathways mainly including the citrate cycle (tricarboxylic acid cycle) and alanine, aspartate and glucose metabolism.

CONCLUSION

The BRPE scale identified significantly different urinary organic acid profiles between the higher and lower BRPE value groups, and, thus, could be used to monitor body fatigue in individuals participating in long-distance outdoor hiking with weight bearing.

Sex-Specific Physical Performance Adaptive Responses Are Elicited After 10 Weeks of Load Carriage Conditioning

INTRODUCTION

The purpose of this study was to identify and characterize sex-specific physical and psychophysical performance adaptations in response to a novel 10-week training program.

MATERIALS AND METHODS

Fifteen males and thirteen females completed a standardized load carriage task (5 km at 5.5 km.h-1, wearing a 23 kg torso-borne vest) before and after 10 weeks of resistance and load carriage training. Psychophysical responses (i.e., heart rate and ratings of perceived exertion) were measured throughout the load carriage task. Physical performance (i.e., countermovement and squat jumps, push-ups, sit-ups, and beep test) was measured at before, mid-way, and after the training program (weeks 0, 6, and 11, respectively).

RESULTS

Training elicited significant improvements in squat jump maximal force, push-ups, and beep test performance (P < .05). Males outperformed females in all performance measures, with interactions (time, sex) for push-ups, sit-ups, and beep test performance. After training, aerobic capacity improved by 5.4% (42.9 mL· kg-1· min-1 to 45.2 mL· kg-1· min-1) in males but did not improve in females. Psychophysical responses decreased for both sexes (P < .05) during the load carriage task post-training.

CONCLUSION

While 10 weeks of standardized training elicited positive adaptations in both physical and psychophysical performance, sex-specific differences were still evident. To lessen these differences, sex-specific training should be considered to optimize load carriage performance.

Dietary nitrate supplementation enhances heavy load carriage performance in military cadets

PURPOSE

To determine the effects of dietary nitrate (NO₃^-) supplementation on physiological responses, cognitive function, and performance during heavy load carriage in military cadets.

METHODS

Ten healthy males (81.0 ± 6.5 kg; 180.0 ± 4.5 cm; 56.2 ± 3.7 ml·kg·min^-1 VO_2max) consumed 140 mL·d^-1 of beetroot juice (BRJ; 12.8 mmol NO₃^-) or placebo (PL) for six d preceding an exercise trial, which consisted of 45 min of load carriage (55% body mass) at 4.83 km·h^-1 and 1.5% grade, followed by a 1.6-km time-trial (TT) at 4% grade. Gas exchange, heart rate, and perceptual responses were assessed during constant-load exercise and the TT. Cognitive function was assessed immediately prior to, during, and post-exercise via the psychomotor vigilance test (PVT).

RESULTS

Post-TT HR (188 ± 7.1 vs. 185 ± 7.4; d = 0.40; p = 0.03), mean tidal volume (2.15 ± 0.27 vs. 2.04 ± 0.23; p = 0.02; d = 0.47), and performance (770.9 ± 78.2 s vs. 809.8 ± 61.4 s; p = 0.03; d = 0.63) were increased during the TT with BRJ versus PL. There were no effects of BRJ on constant-load gas exchange or perceptual responses, and cognitive function was unchanged at all time points.

CONCLUSION

BRJ supplementation improves heavy load carriage performance in military cadets possibly as a result of attenuated respiratory muscle fatigue, rather than enhanced exercise economy.

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.

Oxygen Consumption and Blood Pressure Are Not Influenced by Use of a Backpack Hip Strap

INTRODUCTION

Several studies have explored the effect of backpack carriage on physiologic responses while walking, but few have focused specifically on the influence of the use of a hip strap on these responses. The aim of this study was to investigate the effect of a backpack hip strap on physiologic responses when walking at a moderate intensity while carrying a backpack with a standardized relative load of 30% of the wearer's body mass.

METHODS

Twenty-three healthy, active participants carrying backpacks walked on a treadmill at a speed and grade that elicited 40-50% of their heart rate reserve. Participants completed 2 counterbalanced 30-min trials, one with the hip strap in the strapped condition and one with the hip strap unfastened. Metabolic, heart rate, blood pressure, and muscle oxygen saturation (SmO₂) responses were recorded during both trials. For each variable, 5-min intervals were averaged at baseline, 5, 10, 15, 20, 25, and 30 min. A repeated measures ANOVA test was used to evaluate the differences between the conditions at each time point. Data reported are the values from the final 5-min interval (30 min) and are reported as mean±SD.

RESULTS

No differences were found between strapped and unstrapped trials for oxygen consumption (strapped 21.9±4.2 mL·kg^-1·min^-1; unstrapped 22.0±4.4 mL·kg^-1·min^-1, P=0.842), Δmean arterial pressure (strapped +5±17 Δmm Hg; unstrapped +12±14 Δmm Hg, P=0.128) or muscle oxygen saturation of the quadriceps (strapped 86±15%; unstrapped 90±12%, P=0.359) and calf (strapped 73±19%; unstrapped 81±12%, P=0.888).

CONCLUSIONS

These results suggest that wearing a hip strap does not influence physiologic responses up to 30 min of moderate intensity walking while carrying 30% of the wearer's mass.

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).

The assessment of a novel lower body resistance garment as a mechanism to increase the training stimulus during running: a randomised cross-over study

BACKGROUND

This study examined the physiological and perceived impact of wearing a novel lower body resistance garment during exercise and recovery.

METHODS

Using a randomised cross-over design, 15 recreationally-active males performed 2 × 10-min steady-state runs followed by a 10-min passive recovery with concomitant monitoring of oxygen consumption (V̇O2), heart rate (HR) and rating of perceived exertion (RPE; exercise portion only), wearing either the resistance garment (experimental) or running shorts (control).

RESULTS

During exercise, there was a trend for V̇O2 and RPE to be higher (4.5% and 7.7% respectively) in experimental than control (V̇O2: r = 0.24, p > 0.05; RPE: r = 0.32, p > 0.05) and for HR to be lower (- 0.4%, r = - 0.05, p > 0.05). During recovery, V̇O2 and HR tended to be lower (4.7% and 4.3% respectively) in experimental than control (V̇O2: r = - 0.32, p > 0.05; HR: r = - 0.27, p > 0.05).

CONCLUSIONS

Though effects were trivial to small, and not statistically significant, these findings provide proof of concept and suggest that this garment design may increase the training stimulus during running and aid post-exercise recovery.

Ergonomic problems in agricultural farms: Explainable relationship between awkward postures and body discomforts in Iranian leafy vegetable cultivation

BACKGROUND: Many agricultural activities excessively need human power and are associated with musculoskeletal disorders (MSDs). Leafy vegetable cultivation (LVC) is one of these. OBJECTIVE: The postural workload, body discomfort, and explainable linkage between these among Iranian wintry LVC workers were investigated. METHODS: Postures and body discomfort were evaluated using Ovako working posture analyzing system (OWAS) and a body map, respectively. The explainable body discomforts by working postures for each body region were descriptively discussed using some of the literature. RESULTS: Considering the maximum MSD risk value of 400%, irrigation and manual harvesting had the highest MSD risks with index risks of 313% and 305% respectively. Low back discomfort was the most common body discomfort in LVC which was reported for the operations of moldboard plowing, disking, manure application, chemical broadcasting, spraying, and manual harvesting. LVC operations seemed to rely heavily on the use of low back and shoulders. Bent and/or twist postures were the most common postures for the back. CONCLUSIONS: Almost all the body discomforts were explained by awkward postures shown by postural workload analysis. Therefore, the working posture analysis results may be reliable and utilized in future decisions around ergonomic interventions. Future studies may be conducted to investigate the simple and inexpensive ergonomic interventions to mitigate MSD risks.

Is skin pressure in load carriage over-evaluated?

Skin pressure is a biomechanical measure widely used in the assessment of load carriage systems. However, because of the complicated contour of human body, the stiffness of the pressure sensor array, and the large range of measurable pressures, there is much variability in previously reported results. In this paper, a simple mechanical model for load carriage was proposed, and the skin pressures beneath the shoulder and hip straps were predicted from the strap forces based on Laplace's law. The proposed model was used to analyze data from literature with an aim to check the reliability of existing pressure measurements. The static and dynamic pressures at five locations on eight subjects wearing a backpack with a 10 kg load, while standing and walking on a treadmill, were measured respectively using pressure sensors of the air pack type. The combination of literature data analysis and experimental testing proved that the existing measurement method of interface pressure in load carriage systems often leads to over-estimation and this might misguide the pressure criteria set for load carriage system usage and design. The proposed model will be useful for quick prediction of the interface pressure in load carriage systems.

Effect Vladimir Janda Balance Training on Postural Sway and Leg Muscle Strength

Background: The majority of people who work as tea plantation pickers are powerful. They carry heavy loads of tea on their backs while the roads are quite dangerous and sometimes cause problems. A balance training program has proven to reduce postural sway, increasing leg muscle strength and improving balance strategies. Objective:The aim of this study was to determine the effect of  Vladimir Janda balance training methods with an external load on postural sway and leg muscle strength of tea pickers. Methods: The study design used was quasi-experimental with a randomized control group pretest-posttest design. Subjects were tea pickers consisting of a productive age group of 15 people and 15 people as a control treatment group. The Vladimir Janda method balance exercises were conducted over five weeks consisting of 5 phases. Phase I-IV were carried out 5 times a week, while the V phase was done 3 times a week and each session lasted 15 minutes. Postural sway was measured with a posturometer. Leg muscle strength was measured by a back-leg dynamometer. The statistical tests used were Independent T-test and the Mann-Whitney test. Results:The statistical test for the control and treatment groups using the Mann-Whitney test showed p = 0.001, meaning no external load effects on postural sway. Independent t-test showed p = 0.000, meaning there are differences in the effect between the treatment and control groups after being given balance exercises to increase leg muscle strength. Logistic regression test results obtained the ROC value of 0.917, meaning the Vladimir Janda balance training can affect the postural sway and knee extensor muscle strength by 91.7%. Conclusion: The Vladimir Janda balance exercise method can reduce postural sway and increase the strength of knee extensor muscles and ankle flexor Dorsi muscles. External loads can affect the postural sway.

Treadmill load carriage overestimates energy expenditure of overground load carriage

This study compared physiological and biomechanical responses between treadmill and overground load carriage. Thirty adults completed six 10-minute walking trials across three loads (0, 20, and 40% body mass) and two surfaces (treadmill and overground). Relative oxygen consumption was significantly greater on the treadmill for 20% (1.54 ± 0.20 mL⋅kg^-1⋅min^-1) and 40% loads (1.08 ± 0.20 mL⋅kg^-1⋅min^-1). All other physiological and perceptual responses were significantly higher in the treadmill condition and with increases in load. Stance time was longer (0%: 0.05 s; 20%: 0.02 s, 40%: 0.05 s, p < 0.001) and cadence was lower (0%: 1 step·min^-1; 20%: 2 steps·min^-1; 40%: 3 steps·min^-1, p < 0.05) on the treadmill. Peak lower limb joint angles were similar between surfaces except for ankle plantar flexion, which was 8˚ greater on the treadmill. The physiological responses to treadmill-based load carriage are generally not transferable to overground load carriage and caution must be taken when conducting treadmill-based load carriage research to inform operational-based scenarios. Practitioner Summary: Literature is limited when comparing the physiological and biomechanical responses to treadmill and overground load carriage. Using a repeated measures design, it was shown that although walking kinematics are generally similar between surfaces, there was a greater physiological demand while carrying a load on a treadmill when compared with overground. Abbreviations: BM: body mass; e.g: for example; HR: heart rate; HR_max: heart rate maximum; Hz: hertz; kg: kilograms; km·h^-1: kilometres per hour; L⋅min^-1: litres per minute; m: metres; MD: mean difference; mL·kg^-1·min^-1: millilitres per kilogram per minute; mL⋅min^-1: millilitres per minute; η²p: partial-eta squared; OG: overground; RPE: rating of perceived exertion; s: seconds; SD: standard deviation; SE: standard error; steps·min^-1: steps per minute; TM: treadmill; V̇CO₂: volume of carbon dioxide; V̇E: ventilation; V̇O₂: volume of oxygen; V̇O_2max: maximum volume of oxygen; y: years.

Inspiratory muscle training at sea level improves the strength of inspiratory muscles during load carriage in cold-hypoxia

Inspiratory muscle training (IMT) and functional IMT (IMT_F: exercise-specific IMT activities) has been unsuccessful in reducing respiratory muscle fatigue following load carriage. IMT_F did not include load carriage specific exercises. Fifteen participants split into two groups (training and control) walked 6 km loaded (18.2 kg) at speeds representing ∼50%V̇O_2max in cold-hypoxia. The walk was completed at baseline; post 4 weeks IMT and 4 weeks IMT_F (five exercises engaging core muscles, three involved load). The training group completed IMT and IMT_F at a higher maximal inspiratory pressure (P_imax) than controls. Improvements in P_imax were greater in the training group post-IMT (20.4%, p  = .025) and post-IMT_F (29.1%, p  = .050) compared to controls. Respiratory muscle fatigue was unchanged (p  = .643). No other physiological or subjective measures were improved by IMT or IMT_F. Both IMT and IMT_F increased the strength of respiratory muscles pre-and-post a 6 km loaded walk in cold-hypoxia. Practitioner Summary: To explore the interaction between inspiratory muscle training (IMT), load carriage and environment, this study investigated 4 weeks IMT and 4 weeks functional IMT on respiratory muscle strength and fatigue. Functional IMT improved inspiratory muscle strength pre-and-post a loaded walk in cold-hypoxia but had no more effect than IMT alone. Abbreviations: ANOVA: analysis of variance; BF: breathing frequency; CON: control group; EELV: end-expiratory lung volume; EXP: experimental group; FEV₁: forced expiratory volume in one second; FiO₂: fraction of inspired oxygen; FVC: forced vital capacity; HR: heart rate; IMT: inspiratory muscle training; IMT_F: functional inspiratory muscle training; P_emax: maximal expiratory pressure; P_imax: maximal inspiratory pressure; RMF: respiratory muscle fatigue; RPE: rate of perceived exertion; RWU: respiratory muscle warm-up; SaO₂: arterial oxygen saturation; SpO₂: peripheral oxygen saturation; V̇E: minute ventilation; V̇O₂: rate of oxygen uptake.

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.

Measuring Effects of Two-Handed Side and Anterior Load Carriage on Thoracic-Pelvic Coordination Using Wearable Gyroscopes

Manual carrying of heavy weight poses a major risk for work-related low back injury. Body-worn inertial sensors present opportunities to study the effects of ambulatory work tasks such as load carriage in more realistic conditions. An immediate effect of load carriage is reflected in altered gait kinematics. To determine the effects of load carriage mode and magnitude on gait parameters using body-worn angular rate gyroscopes, two laboratory experiments (n = 9 and n = 10, respectively) were conducted. Participants performed walk trials at self-selected speeds while carrying hand loads in two modes (two-handed side vs. anterior) at four load levels (empty-handed, 4.5 kg, 9.1 kg, and 13.6 kg). Six measures of postural sway and three measures of thoracic-pelvic coordination were calculated from data recorded by four body-worn gyroscopes for 1517 gait cycles. Results demonstrated that, after adjusting for relative walking speed, thoracic-pelvic sway, and movement coordination particularly in the coronal and transverse planes, characterized by gyroscope-based kinematic gait parameters, are systematically altered by the mode of load carriage and load magnitude. Similar trends were obtained for an anthropometrically homogenous (Expt-1) and diverse (Expt-2) sample after adjusting for individual differences in relative walking speed. Measures of thoracic-pelvic coordination and sway showed trends of significant practical relevance and may provide sufficient information to typify alterations in gait across two-handed side vs. anterior load carriage of different load magnitudes. This study contributes to understanding the effects of manual load carriage on thoracic-pelvic movement and the potential application of body-worn gyroscopes to measuring these gait adaptations in naturalistic work settings.

Effects of Lifting Method, Safety Shoe Type, and Lifting Frequency on Maximum Acceptable Weight of Lift, Physiological Responses, and Safety Shoes Discomfort Rating

This study aimed to investigate the physical effects of precision lifting tasks on the maximal acceptable weight of a lift (i.e., psychophysiological lifting capacity where the workers adjust the lifting weight in order to work without any fatigue or strain at the end of the work while wearing common safety shoe types). Additionally, the physical difference between the precise and non-precise lifting conditions associated with wearing safety shoes were assessed by respiration responses and shoe discomfort ratings. To achieve the objective of the study, ten healthy male workers were selected by age (between 25 to 35 years old). Their anthropometric characteristics, including knuckle height, knee height, and body mass index (BMI), were measured. A three-way repeated measures design with three independent variables was used; the variables included-the (1) lifting method (precise and non-precise), (2) lifting frequency (1 and 4 lifts per min), and (3) safety shoe type (light-duty, medium-duty, and heavy-duty). The physiological response variables and one of the subjective factors of this study were-(1) respiration responses, and (2) shoe discomfort rating, respectively. The data were analyzed using the Mauchly's test of sphericity, Shapiro-Wilk normality test, and analysis of variance (ANOVA). The results showed that the use of heavy-duty safety shoes typically increased the shoe discomfort rating under precise lifting methods. Additionally, the lifting frequency was determined to be one of the main factors affecting respiratory responses and shoe discomfort rating. This study also found that respiration responses rose on four lifts per min as compared to 1 lift per min, regardless of the lifting method type. This study indicated that the replacement of some types of ordinary safety shoes used in some workplaces with those selected appropriately might significantly reduce the rating effort required to lift objects or tools. However, the benefits should be carefully evaluated before replacing the safety shoes.

How to Carry Loads Economically: Analysis Based on a Predictive Biped Model

Carrying heavy loads costs additional energy during walking and leads to fatigue of the user. Conventionally, the load is fixed on the body. Some recent studies showed energy cost reduction when the relative motion of the load with respect to the body was allowed. However, the influences of the load's relative motion on the user are still not fully understood. We employed an optimization-based biped model, which can generate human-like walking motion to study the load-carrier interaction. The relative motion can be achieved by a passive mechanism (such as springs) or a powered mechanism (such as actuators), and the relative motion can occur in the vertical or fore-aft directions. The connection between the load and body is added to the biped model in four scenarios (two types × two directions). The optimization results indicate that the stiffness values affect energy cost differently and the same stiffness value in different directions may have opposite effects. Powered relative motion in either direction can potentially reduce energy cost but the vertical relative motion can achieve a higher reduction than fore-aft relative motion. Surprisingly, powered relative motion only performs marginally better than the passive conditions at similar peak interaction force levels. This work provides insights into developing more economical load-carrying methods and the model presented may be applied to the design and control of wearable load-carrying devices.

Height adjustments on backpack-carrying systems and muscle activity

The aim of this study is to investigate the neuromuscular response of shoulder muscles at different attachment heights of a carrying system during arm movement. It was hypothesized that (1) different height adjustments lead to changes in muscle activity and (2) the shoulder horizontal provides a benchmark for the optimal attachment height of the shoulder belts. The musculus deltoideus was significantly relieved after the elevation of the shoulder belt for subjects with an initial attachment height of 2 cm below the shoulder. The musculus trapezius was relieved with the elevation above the shoulder. At a height of more than 2 cm above the shoulder, no further muscle unloading was achieved. These findings prove that a height adjustment can provide a systematic unloading or deloading of the shoulder musculature. Despite the fact that the magnitude and direction of changes in muscle activity lead to rather individual responses, the intra-individual responses are consistent. Therefore, support systems should provide the range of individual requirements.

Integrating a hip belt with body armour reduces the magnitude and changes the location of shoulder pressure and perceived discomfort in soldiers

Soldiers carry heavy loads that may cause general discomfort, shoulder pain and injury. This study assessed if new body armour designs that incorporated a hip belt reduced shoulder pressures and improved comfort. Twenty-one Australian soldiers completed treadmill walking trials wearing six different body armours with two different loads (15 and 30 kg). Contact pressures applied to the shoulders were measured using pressure pads, and qualitative assessment of comfort and usability were acquired from questionnaires administered after walking trials. Walking with hip belt compared to no hip belt armour resulted in decreased mean and maximum shoulder pressures (p < 0.005), and 30% fewer participants experiencing shoulder discomfort (p < 0.005) in best designs, although hip discomfort did increase. Laterally concentrated shoulder pressures were associated with 1.34-times greater likelihood of discomfort (p = 0.026). Results indicate body armour and backpack designs should integrate a hip belt and distribute load closer to shoulder midline to reduce load carriage discomfort and, potentially, injury risk. Practitioner Summary: Soldiers carry heavy loads that increase their risk of discomfort and injury. New body armour designs are thought to ease this burden by transferring the load to the hips. This study demonstrated that designs incorporating a hip belt reduced shoulder pressure and shoulder discomfort compared to the current armour design.

Physiological and Biomechanical Responses to Prolonged Heavy Load Carriage During Level Treadmill Walking in Females

Heavy load carriage has been identified as a main contributing factor to the high incidence of overuse injuries in soldiers. Peak vertical ground reaction force (VGRFMAX) and maximal vertical loading rates (VLRMAX) may increase during heavy prolonged load carriage with the development of muscular fatigue and reduced shock attenuation capabilities. The objectives of the current study were (1) to examine physiological and biomechanical changes that occur during a prolonged heavy load carriage task, and (2) to examine if this task induces neuromuscular fatigue and changes in muscle architecture. Eight inexperienced female participants walked on an instrumented treadmill carrying operational loads for 60 minutes at 5.4 km·h–1. Oxygen consumption (), heart rate, rating of perceived exertion (RPE), trunk lean angle, and ground reaction forces were recorded continuously during task. Maximal force and in-vivo muscle architecture were assessed pre- and posttask. Significant increases were observed for VGRFMAX, VLRMAX, trunk lean angle,, heart rate, and RPE during the task. Increased vastus lateralis fascicle length and decreased maximal force production were also observed posttask. Prolonged heavy load carriage, in an inexperienced population carrying operational loads, results in progressive increases in ground reaction force parameters that have been associated with overuse injury.

Validation of an instrumented dummy to assess mechanical aspects of discomfort during load carriage

Due to the increasing load in backpacks and other load carriage systems over the last decades, load carriage system designs have to be adapted accordingly to minimize discomfort and to reduce the risk of injury. As subject studies are labor-intensive and include further challenges such as intra-subject and inter-subject variability, we aimed to validate an instrumented dummy as an objective laboratory tool to assess the mechanical aspects of discomfort. The validation of the instrumented dummy was conducted by comparison with a recent subject study. The mechanical parameters that characterize the static and dynamic interaction between backpack and body during different backpack settings were compared. The second aim was to investigate whether high predictive power (coefficient of determination R²>0.5) in assessing the discomfort of load carriage systems could be reached using the instrumented dummy. Measurements were conducted under static conditions, simulating upright standing, and dynamic conditions, simulating level walking. Twelve different configurations of a typical load carriage system, a commercially available backpack with a hip belt, were assessed. The mechanical parameters were measured in the shoulder and the hip region of the dummy and consisted of average pressure, peak pressure, strap force and relative motion between the system and the body. The twelve configurations consisted of three different weights (15kg, 20kg, and 25kg), combined with four different hip belt tensions (30N, 60N, 90N, and 120N). Through the significant (p<0.05) correlation of the mechanical parameters measured on the dummy with the corresponding values of the subject study, the dummy was validated for all static measurements and for dynamic measurements in the hip region to accurately simulate the interaction between the human body and the load carriage system. Multiple linear regressions with the mechanical parameters measured on the dummy as independent variables and the corresponding subjective discomfort scores from the subject study as the dependent variable revealed a high predictive power of the instrumented dummy. The dummy can explain 75% or more of the variance in discomfort using average pressures as predictors and even 79% or more of the variance in discomfort using strap forces as predictors. Use of the dummy enables objective, fast, and iterative assessments of load carriage systems and therefore reduces the need for labor-intensive subject studies in order to decrease the mechanical aspects of discomfort during load carriage.

Knee pain in adolescents: prevalence, risk factors, and functional impairment

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Knee pain prevalence over the last 7 days was 22.6%.

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Knee functionality was investigated using the Knee injury and Osteoarthritis Outcome Score.

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More knee pain was found in older adolescents who do not have physical education at school.

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Functional impairment in girls and adolescents who are physically active in their leisure time.

Objective

To investigate knee pain prevalence, associated factors, and functional impairment among adolescents.

Method

This was a cross-sectional study conducted between May and June 2014 with a random sample of 619 adolescents aged between 10 and 17 years. Knee pain prevalence was investigated using the Nordic Questionnaire for Osteomuscular Symptoms and a number of independent variables (demographic data, nutritional status, form of carrying backpacks, and pain during and after walking) obtained by self-report questionnaires. Physical impairment of the knee was assessed using the Brazilian version of the Knee injury and Osteoarthritis Outcome Score questionnaire. Poisson regression analysis was used to estimate the ratios of crude and adjusted knee pain association with the investigated factors. ANOVA and Kruskal–Wallis tests were used to compare median functional impairment.

Results

Knee pain prevalence over the last 7 days was 22.6%. Factors having significant association with the outcome were: being between 12 and 14 years old (PR: 1.67; 95% CI: 1.07–2.58; p < 0.01), being between 15 and 17 years old (PR: 2.44; 95% CI: 1.51–3.94; p = 0.01), and not doing physical education at school (PR: 0.54; 95% CI: 0.35–0.82; p = 0.01). Total functional capacity among adolescents with pain was significantly lower among girls (68.7 points; PD ± 15.1) when compared with boys (74.3 points; PD ± 12.7) (p = 0.02). The mean value of disabling pain was lower (55.1 points; PD ± 12.3) among adolescents who were physically active in their leisure time compared to those who were insufficiently active (60.4 points; PD ± 12.4) (p = 0.02).

Conclusion

The results of this study show that knee pain among adolescents with no previous history should be investigated, particularly among older adolescents who do not have physical education at school, since it is highly prevalent and can result in functional impairment. Regarding functionality, more attention should be given to girls and adolescents who were physically active in their leisure time.

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.

Analyzing the potential benefits of using a backpack with non-flexible straps

BACKGROUND

Conventional backpack straps are flexible. Due to this flexibility, backpacks freely move on the human back. In this study, a new design of backpacks with non-flexible straps is proposed.

OBJECTIVE

The aim of the present research is to demonstrate the possible differences between normal gait and steps while participants carry two different backpacks.

METHODS

In this investigation, 9 healthy male college students were recruited with mean age, height and weight of 24.6 years, 179.6 cm and 76.41 kg, respectively. Each backpack was tested in two different steps. First, the participants were asked to walk on a treadmill, whose velocity was changed from 1.5 m/s to 2.5 m/s, for 15 minutes. Initial velocity was 1.5 m/s and the velocity increased 0.5 m/s in 5 minutes increments. In the next step, they walked for 15 minutes with constant velocity of 3 m/s. Head, neck, and trunk flexion or extension, lateral displacement, and velocity of the subjects during backpack carriage were compared with the obtained values during normal gait, when they walked without carrying a backpack. In addition, the level of discomfort (3 grades: Low, medium, severe) in the neck, shoulder, lumbar, upper and lower leg muscles were investigated by using a modified standardized questionnaire.

RESULTS

By wearing the modified design of backpack, trunk flexion decreased while there was no significant (p > 0.05) change in velocity and lateral displacement. According to the questionnaire reports, more than 80% of the participants believed that both backpack discomfort in the neck (anterior side) and upper and lower legs were low. More than 75% of the subjects believed that by using a modified backpack, discomfort decreased for muscles in the neck (posterior), shoulder (posterior) and lumbar muscles. About 60% of both backpack users reported low discomfort in anterior shoulder muscles.

CONCLUSION

Backpacks cause some bad effects on kinematics of gait. In this study, by testing modified backpacks, some improvements were seen, specifically in posture, which may be useful to reduce side effects of backpack carrying.

Sensory Enhancing Insoles Modify Gait during Inclined Treadmill Walking with Load

INTRODUCTION

Inclined walking while carrying a loaded backpack induces fatigue, which may destabilize gait and lead to injury. Stochastic resonance (SR) technology has been used to stabilize spatiotemporal gait characteristics of elderly individuals but has not been tested on healthy recreational athletes. Herein, we determined if sustained vigorous walking on an inclined surface while carrying a load destabilizes gait and if SR has a further effect.

METHODS

Participants were fitted with a backpack weighing 30% of their body weight and asked to walk at a constant self-selected pace while their feet were tracked using an optical motion capture system. Their shoes were fitted with SR insoles that were set at 90% of the participant's sensory threshold. The treadmill incline was increased every 5 min until volitional exhaustion after which the treadmill was returned to a level grade. SR stimulation was turned ON and OFF in a pairwise random fashion throughout the protocol. Spatiotemporal gait characteristics were calculated when SR was ON and OFF for the BASELINE period, the MAX perceived exertion period, and the POST period.

RESULTS

Vigorous activity increases variability in the rhythmic stepping (stride time and stride length) and balance control (double support time and stride width) mechanisms of gait. Overall, SR increased stride width variability by 9% before, during, and after a fatiguing exercise.

CONCLUSION

The increased stride time and stride length variability may compromise the stability of gait during and after vigorous walking. However, participants may compensate by increasing double support time and stride width variability to maintain their stability under these adverse conditions. Furthermore, applying SR resulted in an additional increase of stride width variability and may potentially improve balance before, during, and after adverse walking conditions.

The influence of gait cadence on the ground reaction forces and plantar pressures during load carriage of young adults

Biomechanical gait parameters--ground reaction forces (GRFs) and plantar pressures--during load carriage of young adults were compared at a low gait cadence and a high gait cadence. Differences between load carriage and normal walking during both gait cadences were also assessed. A force plate and an in-shoe plantar pressure system were used to assess 60 adults while they were walking either normally (unloaded condition) or wearing a backpack (loaded condition) at low (70 steps per minute) and high gait cadences (120 steps per minute). GRF and plantar pressure peaks were scaled to body weight (or body weight plus backpack weight). With medium to high effect sizes we found greater anterior-posterior and vertical GRFs and greater plantar pressure peaks in the rearfoot, forefoot and hallux when the participants walked carrying a backpack at high gait cadences compared to walking at low gait cadences. Differences between loaded and unloaded conditions in both gait cadences were also observed.

Lower limb kinematics and physiological responses to prolonged load carriage in untrained individuals

The aim of this study was to simultaneously assess the changes in physiology, and kinematic and spatiotemporal features of gait, during prolonged load carriage in individuals without load carriage experience. Eleven males, representative of new military recruits, walked for 120 min at 5.5 km h(- 1), 0% grade, on a motorised treadmill while carrying a 22 kg load. The load ( ≤ 30% body mass) was distributed over a weighted vest, combat webbing and replica model firearm, to reflect a patrol order load. Oxygen consumption and heart rate increased throughout the trial; however, apart from a minor increase in step length, there were no changes in the kinematic or spatiotemporal parameters, despite an increase in perceived exertion and discomfort. These data suggest that individuals with no experience in load carriage are able to maintain normal gait during 2 h of fixed speed walking, while carrying a patrol order load ≤ 30% body mass.

Metabolic rate of carrying added mass: a function of walking speed, carried mass and mass location

The effort of carrying additional mass at different body locations is important in ergonomics and in designing wearable robotics. We investigate the metabolic rate of carrying a load as a function of its mass, its location on the body and the subject's walking speed. Novel metabolic rate prediction equations for walking while carrying loads at the ankle, knees and back were developed based on experiments where subjects walked on a treadmill at 4, 5 or 6km/h bearing different amounts of added mass (up to 2kg per leg and 22kg for back). Compared to previously reported equations, ours are 7-69% more accurate. Results also show that relative cost for carrying a mass at a distal versus a proximal location changes with speed and mass. Contrary to mass carried on the back, mass attached to the leg cannot be modeled as an increase in body mass.

Influence of pressure-relief insoles developed for loaded gait (backpackers and obese people) on plantar pressure distribution and ground reaction forces

The aims of this study were to test the effects of two pressure relief insoles developed for backpackers and obese people on the ground reaction forces (GRF) and plantar pressure peaks during gait; and to compare the GRF and plantar pressures among normal-weight, backpackers, and obese participants. Based on GRF, plantar pressures, and finite element analysis two insoles were manufactured: flat cork-based insole with (i) corkgel in the rearfoot and forefoot (SLS1) and with (ii) poron foam in the great toe and lateral forefoot (SLS2). Gait data were recorded from 21 normal-weight/backpackers and 10 obese participants. The SLS1 did not influence the GRF, but it relieved the pressure peaks for both backpackers and obese participants. In SLS2 the load acceptance GRF peak was lower; however, it did not reduce the plantar pressure peaks. The GRF and plantar pressure gait pattern were different among the normal-weight, backpackers and obese participants.

Relationships of Borg's RPE 6-20 scale and heart rate in dynamic and static exercises among a sample of young Taiwanese men

The objective of this study was to assess the relationship between the scores collected from Borg's rating of perceived exertion (RPE) scale and the heart rates (HR) of young Taiwanese men. Three exercises types (dynamic, partially dynamic, and static) were performed by 12 participants (six were familiar with Borg's scale and 6 were unfamiliar) under nine test conditions of three load levels for each exercise. The effect of familiarity on the relationship between RPE and HR was also examined. The results showed that the familiarity of the participants regarding the Borg's scale did not affect the scores. The relationship between Borg's RPE 6-20 scale and the HR values during dynamic exercise was described by the regression equation HR = 8.88 x RPE + 38.2 (beats/min). The HR had lower correlations with RPE values when the participants performed both partially dynamic and static exercises. The findings may serve as a reference when using Borg's RPE scale to evaluate the physical exertion of young Taiwanese men.

Ground reaction forces and plantar pressure distribution during occasional loaded gait

This study compared the ground reaction forces (GRF) and plantar pressures between unloaded and occasional loaded gait. The GRF and plantar pressures of 60 participants were recorded during unloaded gait and occasional loaded gait (wearing a backpack that raised their body mass index to 30); this load criterion was adopted because is considered potentially harmful in permanent loaded gait (obese people). The results indicate an overall increase (absolute values) of GRF and plantar pressures during occasional loaded gait (p < 0.05); also, higher normalized (by total weight) values in the medial midfoot and toes, and lower values in the lateral rearfoot region were observed. During loaded gait the magnitude of the vertical GRF (impact and thrust maximum) decreased and the shear forces increased more than did the proportion of the load (normalized values). These data suggest a different pattern of GRF and plantar pressure distribution during occasional loaded compared to unloaded gait.

Ergonomics in developing hand operated maize dehusker-sheller for farm women

A hand operated maize dehusker-sheller to be operated by farm women was designed and developed to dehusk and shell the maize cobs using ergonomics (anthropometric, strength and physiological workload). Axial-flow maize dehusker-sheller with 540 mm cylinder length and 380 mm diameter required 3.03 N-m torque on cylinder shaft while operating at 5.6 m s(-1) peripheral speed and 100 kg h(-1) feed rate by feeding cob one by one. This torque was 30% of isometric torque obtained at front position of handle (greatest distance) with lowest crank length. The heart rate of subject while operating the maize dehusker-sheller at 54 rpm (5.6 m s(-1)) was 142 beats min(-1). The output of 60 kg h(-1) was obtained at the feed rate of 80 kg h(-1). Two subjects can operate the machine for an hour with a rest pause of 15 min by swapping the operation.

Does load position affect gait and subjective responses of females during load carriage?

Recreational hikers carry heavy loads while often walking long distances over uneven terrain. Previous studies have suggested that not only the load mass but also the position of the load may influence load carriage. The purpose of this study was to determine the effect of vertical load position on gait and subjective responses of female recreational hikers. Fifteen experienced female hikers walked for 2 km over a simulated hiking trail carrying 30% BW in three vertical load positions (high, medium and low). Lower limb and trunk kinematic, electromyography (EMG) and ground reaction force (GRF) data were collected together with heart rate (HR), ratings of perceived exertion (RPE) and discomfort measures. Although HR, RPE and discomfort measures were not able to discern statistical differences between load positions, the high load position was the most preferred by participants. The high load position also resulted in a more upright posture (p < 0.001), decreased gastrocnemius integrated EMG compared to the medium (p = 0.005) and low load positions (p = 0.02) and a higher first peak deceleration vertical GRF compared to the low load position (p = 0.011). However, the absolute differences were small and unlikely to be functionally relevant in load carriage studies. Based on the findings of this study, a high, medium or low load position cannot be preferentially recommended for healthy, experienced, female hikers carrying 30% BW.

Backpack load affects lower limb muscle activity patterns of female hikers during prolonged load carriage

This study investigated the effect of prolonged load carriage on lower limb muscle activity displayed by female recreational hikers. Electromyography (EMG) signals from vastus lateralis (VL), biceps femoris (BF), semitendinosus (ST), tibialis anterior (TA) and gastrocnemius (GM) were recorded for fifteen female hikers carrying four loads (0%, 20%, 30% and 40% body weight (BW)) over 8 km. Muscle burst duration, muscle burst onset relative to initial contact and integrated EMG signals (iEMG) were calculated to evaluate muscle activity, whereas the shift in mean power frequency (MPF) was used to evaluate muscle fatigue. Increased walking distance significantly decreased the MPF of TA; decreased the iEMG for VL, ST and GM; and shortened VL muscle burst duration. Furthermore, carrying 20-40% BW loads significantly increased VL and GM iEMG and increased BF muscle burst duration, whereas a 40% BW load caused a later VL muscle burst onset. The differences observed in muscle activity with increased load mass seem to be adjustments aimed at maintaining balance and attenuating the increased loads placed on the lower limbs during gait. Based on the changes in muscle activity, a backpack load limit of 30% BW may reduce the risk of lower limb injury for female hikers during prolonged walking.