Box-lifting Task Research Articles

A Novel Passive Shoulder Exoskeleton Using Link Chains and Magnetic Spring Joints.

Work-related musculoskeletal disorders represent a major occupational disability issue, and 53.4% of these disorders occur in the back or shoulders. Various types of passive shoulder exoskeletons have been introduced to support the weight of the upper arm and work tools during overhead work, thereby preventing injuries and improving the work environment. The general passive shoulder exoskeleton is constructed with rigid links and joints to implement shoulder rotation, but there exists a challenge to align with the flexible joint movements of the human shoulder. Also, a force-generating part using mechanical springs require additional mechanical components to generate torque similar to the shoulder joint, resulting in increased overall volume and inertia to the upper arm. In this study, we propose a new type of passive shoulder exoskeleton that uses magnetic spring joint and link chain. The redundant degrees of freedom in the link chains enables to follow the shoulder joint movement in the horizontal direction, and the magnetic spring joint generates torque without additional parts in a compact form. Conventional exoskeletons experience a loss in the assisting torque when the center of shoulder rotation changed during arm elevation. Our exoskeleton minimizes the torque loss by customizing the installation height and initial angle of the magnetic spring joint. The performances of the proposed exoskeleton were verified by an electromyographic evaluation of shoulder-related muscles in overhead work and box lifting task.

The effect of clinically elevated body mass index on physiological stress during manual lifting activities.

Individuals with a body mass index (BMI) classified as obesity constitute 27.7% of U.S. workers. These individuals are more likely to experience work-related injuries. However, ergonomists still design work tasks based on the general population and normal body weight. This is particularly true for manual lifting tasks and the calculation of recommended weight limits (RWL) as per National Institute of Occupational Safety & Health (NIOSH) guidelines. This study investigates the effects of BMI on indicators of physiological stress. It was hypothesized that, for clinically elevated BMI individuals, repeated manual lifting at RWL would produce physiological stress above safety limits. A repetitive box lifting task was designed to measure metabolic parameters: volume of carbon dioxide (VCO2) and oxygen (VO2), respiratory exchange ratio (RER), heart rate (HR), and energy expenditure rate (EER). A two-way ANOVA compared metabolic variables with BMI classification and gender, and linear regressions investigated BMI correlations. Results showed that BMI classification represented a significant effect for four parameters: VCO2 (p < 0.001), VO2 (p < 0.001), HR (p = 0.012), and EER (p < 0.001). In contrast, gender only had a significant effect on VO2 (p = 0.014) and EER (p = 0.017). Furthermore, significant positive relationships were found between BMI and VCO2 (R2 = 59.65%, p < 0.001), VO2 (R2 = 45.01%, p < 0.001), HR (R2 = 21.86%, p = 0.009), and EER (R2 = 50.83%, p < 0.001). Importantly, 80% of obese subjects exceeded the EER safety limit of 4.7 kcal/min indicated by NIOSH. Indicators of physiological stress are increased in clinically elevated BMI groups and appear capable of putting these individuals at increased risk for workplace injury.

Novel thoraco-lumbo-sacral corset design increases Biering-Sorensen back endurance and alters knee and ankle angles during a box lifting task

Research investigating lumbosacral corset designs and their effects are limited and conflicting. The objective was to compare thoraco-lumbo-sacral support corsets (polyester/nylon: TLSSC-poly and neoprene: TLSSC-neo) with a traditional model (TRAD) and Control. Twenty male, university-aged, healthy, recreationally active, participants performed Biering-Sorensen back endurance (BS) test and box lifting tasks (BL:30 repetitions using 20% body mass). Lower and upper erector spinae and hamstrings electromyography (EMG); trunk-hip, knee, and ankle kinematics as well as endurance time were monitored. With BL, the TLSSC-poly (121.4°±17.9) exhibited 1.9% (p = 0.01), 2.7% (p = 0.003), and 3.7% (p = 0.0003) greater knee flexion than TRAD (119.1°±17.5), TLSSC-neo (116.8°±17.4) and Control (120.1°±17.6) respectively. The TLSSC-poly (101.9°± 8.9) demonstrated significant 3.5% (p = 0.005), 2.2% (p = 0.002) and 1.4% (p = 0.01) greater dorsiflexion than TRAD (103.4°±8.7), TLSSC-neo (104.2°±9.8) and Control (105.7°±7.2) respectively. With BS, TLSSC-poly (137.4-s±31.2, 9.7%, p = 0.018) and TLSSC-neo (133.8-s±32.3, 9.2%, p = 0.006) exhibited significantly longer durations than Control (124.8-s±29.8). Relevance to industry: The TLSSC increased BS endurance and TLSSC-poly increased BL knee and ankle angles, possibly providing benefits for workers, with repeated actions over a full work day.

Factors affecting spine loading in a box lifting task: a digital human modelling study

This paper presents a digital human modelling (DHM) study of a box-lifting task considering human physical characteristics (i.e., gender and percentile) and task requirements (i.e., posture and force). Two response variables are considered: compression force on L4/L5 and the tension on right/left Latissimus Dorsi muscle. Multivariate analysis of variance (MANOVA) was used to analyse the data. Results showed that lower back compression force is positively correlated with Latissimus Dorsi muscle tension (r = 0.94). Moreover, the 95th percentile male in standing position experienced the highest compression force on the lower back; however, both males and females had similar muscle tension.

Factors Affecting Spine Loading in a Box Lifting Task: A Digital Human Modeling Study

This paper presents a digital human modelling (DHM) study of a box-lifting task considering human physical characteristics (i.e., gender and percentile) and task requirements (i.e., posture and force). Two response variables are considered: compression force on L4/L5 and the tension on right/left Latissimus Dorsi muscle. Multivariate analysis of variance (MANOVA) was used to analyse the data. Results showed that lower back compression force is positively correlated with Latissimus Dorsi muscle tension (r = 0.94). Moreover, the 95th percentile male in standing position experienced the highest compression force on the lower back; however, both males and females had similar muscle tension.

Sex differences in glenohumeral muscle activation and coactivation during a box lifting task

Manual material handling is associated with shoulder musculoskeletal disorders, especially for women. Sex differences in glenohumeral muscle activity may contribute to women’s higher injury risk by affecting shoulder load and stability. We assessed the effects of sex (25 women vs 26 men) and lifting load (6 kg vs 12 kg) on muscle activation during box lifting from hip to eye level. Surface and intramuscular electromyography were recorded from 10 glenohumeral muscles. Most muscles were more activated for the heavier box and for women. These effects were larger for ‘prime movers’ than for stabilisers and antagonists. Despite their apparently heterogeneous effects on muscle activity, sex and mass did not affect Muscle Focus, a metric of coactivation. This may be partly related to the limited sensitivity of the Muscle Focus. Nevertheless, sex differences in strength, more than in coactivation patterns, may contribute to the sex imbalance in the prevalence of musculoskeletal disorders. Practitioner summary: We studied sex differences in glenohumeral muscle activity in a lifting task to eye level. Women lifting a 6-kg box activated their muscles similarly to men lifting a 12-kg box, i.e. up to 48% of their maximum capacity. Interventions minimising shoulder load should be implemented, especially for women. Abbreviations: BB: biceps brachii; DeltA: anterior deltoid; DeltL: lateral deltoid; DeltP: posterior deltoid; DoF: degrees of freedom; ED: effect duration; EMG: electromyography; ES: effect size; Infra: infraspinatus; Lat: latissimus dorsi; MF: muscle focus; MMH: manual material handling; MVA: maximal voluntary activation; Pect: pectoralis major; Subscap: subscapularis; Supra: supraspinatus; TB: triceps brachii

Preliminary Analysis of StrongArm® Ergoskeleton on Knee and Hip Kinematics and User Comfort

This study was constructed to assess the influence of wearing semi-soft exoskeletons on hip and knee kinematics when engaging in a box lifting task. Six healthy college aged students (age: 21.7 ± 2.3; gender: 4 males, 2 females; height: 177.0 ± 3.4 cm; weight: 77.1 ± 17.9 kg; hand dominance: all right) completed box lifting tasks (at 10% and 20% of their body weight) while wearing no exoskeleton and two exoskeleton designs. Lifting a box at 20% body weight increased perceived exertion and was associated with poor hip and knee kinematics in some conditions. Wearing the StrongArm® V22 ERGOSKELETON without hand cables may diminish some of the poor kinematics associated with lifting objects.

Is rotating between static and dynamic work beneficial for our fatigue state?

Shoulder disorders comprise a large part of work-related musculoskeletal disorders. Risk factors, such as repetitiveness and monotony, may cause muscle fatigue and be attenuated by task rotation. We investigated rotation between a dynamic box-lifting task and a relatively static pick-and-place task and aimed to determine whether (1) a high rotation frequency leads to less fatigue development than a low rotation frequency, and (2) a self-selected rotation frequency leads to less fatigue development than imposed rotation frequencies. Ten participants performed four one-hour rotation schedules: two low frequency rotation schedules rotating at 30min, one high frequency rotation schedule rotating every sixth minute, and a self-selected rotation schedule. Borg, SOFI and electromyography of Trapezius and Deltoid subparts served as fatigue indicators. We found significant signs of fatigue for most schedules regarding the Borg and SOFI ratings and the M. Trapezius pars Descendens. Task rotation frequency had no significant effect on any of the outcome parameters, whereas the self-selected rotation schedule clearly resulted in less development of perceived fatigue than imposed schedules. In conclusion, we think that freedom of rotation has the greatest potential to attenuate potential development of musculoskeletal disorders and we require due caution with the use and interpretation of EMG indicators of fatigue.

A validation framework for predictive human models

A validation framework is introduced in this work to evaluate the motion of a predictive human model and provide feedback to the model developers for refinement in ergonomic applications. Two qualitative and two quantitative benchmark tests were designed and used to assess the strength and weakness of the model and to localise abnormalities in the predicted motion. Twelve subjects participated in a whole-body motion task, and another 12 subjects participated in the subjective evaluation of the predicted motion. The validation framework was able to highlight the weakness and limitations of a predicted human model with 55 degrees of freedom in a box-lifting task. The results have shown that the proposed framework was very effective in identifying the flaws in the model under investigation and in giving guides for improvement and acceptance.

Influence of Mild Dehydration From Occupational Work on Plasma Volume and Osmolality

High intensity exercise changes the volume and concentration of fluid compartments. The effects of mild dehydration are not well understood because previous studies have focused on either severe dehydration or water intoxication. Repetitive lifting is a task performed in military, industrial, and construction settings; such work often is performed under a time constraint without an adequate water supply. PURPOSE: The objective was to examine percent change of plasma volume (%ÄPV) and osmolality during and after a repetitive box lifting (RBL) task. METHODS: Ten healthy male subjects (mean ± SD; age 21±2 y; body mass (BM), 77.8±10.6 kg; height, 177±4 cm; and body fat, 10.7±8.8%) were randomly assigned to: trial F (ad libitum fluid given during exercise) and NF (no fluid) using a crossover design. The environmental conditions were the same for both trials (23°C, 50% relative humidity). A morning blood sample was taken from a Teflon catheter placed in a forearm vein. Subjects then ate a standard breakfast followed by a 2-hour rest/exercise period (30 min rest and 10 min RBL) performed 3 times (120 min total). RBL consisted of self-paced lifting of a 20.5 kg box from the floor to a 1.32 m platform. RESULTS: The exercise was intense, as evidenced by maximal plasma lactate concentration (17.1±2.4 mmol·L-1) and heart rate (190±7 bpm) with no differences between trials. Dehydration was 0.95±0.17%BM and rectal temperature rose to 38.3±0.3oC with no differences between trials. The change of posture from reclining (morning blood draw) to standing for the rest/exercise period altered %ÄPV -10.2±3.8% with no differences between trials. Return to a reclining posture 30 min after the protocol significantly changed %ÄPV +22.7±5.6 and +19.1±4.2%, for F and NF respectively (P<0.05). For both trials, %ÄPV was significantly reduced by 9.7% from rest to after RBL1 and then increased by 4.4% from before RBL1 to after RBL3. Plasma osmolality increased 5.5±1.1% after each RBL and then returned to pre-exercise values during rest for both trials. CONCLUSIONS: Mild dehydration did not change plasma osmolality and %ÄPV during exercise, but it decreased %ÄPV after strenuous occupational work.

METHODOLOGY AND EXPONENTIAL PROPERTIES OF CR-10 RATINGS

INTRODUCTION Perceived exertion is the subjective intensity of effort experienced during the performance of work. A variety of physiological, psychological and performance factors from both internal and external environments shape this perception. A majority of perceived exertion research uses one of several scales developed by Borg. Borg developed most of these scales based upon an adaptation of Stevens' law; which states that perceived intensities follow the form of a power function. When evaluating the stimulus-response relationship with the Borg CR-10 scale, the relation between perceived intensity and workload should be exponential. Furthermore, the exponent should be greater than one. However, some studies have reported exponents less than one. PURPOSE The purpose of this study was to use a standard occupational lifting task and the Borg CR-10 scale to depict the exponential relation between perceived intensity and work load. A secondary purpose was to provide a methodology that can be used to obtain exponents that are less than one, and to distinguish the difference in applications of these exponents. METHODS A total of 473 undergraduate students participated in this study. The subjects performed a box lifting task that consisted of eight. A dynamic lift profile was developed for each subject using their CR-10 ratings as the dependent variable and the weight of the box as the independent variable. Maximum functional lift capacity was estimated using the results of the dynamic lift profile analyses. Then, for each subject, one randomly selected weight load was used to estimate percent of maximum functional lift capacity. RESULTS An exponent greater than one resulted when the data were expressed in standard estimation format (M=2.28). The exponents were significantly different for males and females (p < 0.001). When expressed as a percentage of maximum functional lift capacity, an exponent less than one resulted (0.298). CONCLUSION When CR-10 ratings are expressed in actual estimation form, the resultant exponent should be greater than one. When CR-10 ratings are expressed as a percentage of maximum capacity, the resultant exponent should be less than one.

Reliability assessment of two militarily relevant occupational physical performance tests.

To determine the number of test sessions needed to stabilize performance on two military occupational physical tests and to assess their reliability, 10 male soldiers (22 +/- 3 yrs, 183 +/- 7 cm, 87 +/- 8 kg) performed both an indoor 6-station obstacle course (OC) and a repetitive box-lifting task (RBLT). The OC consisted of 46 cm-high hurdles, zigzag sprint, low crawl, horizontal pipe shimmy, 1.4 m wall traversal, and straight sprint. The RBLT required subjects to lift 20.5 kg boxes, continuously for 10 minutes, from the ground onto 1.3 m high platforms positioned 2.4 m apart. The OC mean +/- SD times (s), for sessions 1-4 respectively, were 37.4 +/- 2.2, 35.8 +/- 2.5, 34.7 +/- 2.1, and 34.5 +/- 1.7 seconds. The number of boxes lifted was 177 +/- 31, 194 +/- 28, 189 +/- 32, and 186 +/- 37 for the RBLT. Performance stabilized on the 3rd session for the OC (7% improvement over first trial, p < 0.05) and on the 2nd session for the RBLT (9% improvement over first trial, p < 0.05). The intraclass correlation coefficients were 0.92 and 0.94 for the OC and RBLT, respectively. This study demonstrates that both are reliable tests, but they do require administration of 1 single-trial session of RBLT and 2 two-trial sessions of OC before highly reliable performance data are obtained.

Canadian Journal of Applied Physiology: Northern Highlights

MALE SOLDIERS WERE TESTED with an indoor 6-station obstacle course (OC) and a repetitive boxlifting task (RBLT). Performance in the more-complex OC stabilized on the third dual-trial test session, whereas that in the more simple RBLT stabilized on the second single-trial test session. These can be reliable tests, but only after initial sessions have provided the participants with test familiarization. The same would apply to other occupational physical performance tasks or physical fitness tests in which performance depends considerably on skill. Pandorf, C.E., et al. Reliability assessment of two military relevant occupational physical performance tests. Can. J. Appl. Phys. 28(1):27–37. 2003.

PERFORMANCE RELIABILITY OF MILITARILY RELEVANT OCCUPATIONAL TASKS

Physical performance tests that simulate “real world” occupational tasks can be valuable for screening and assessing workers. Such tests must be reliable. However test performance improves with practice, especially for unfamiliar or complex tasks. To determine the amount of practice needed to stabilize performance on two military occupational physical tests and to assess reliability, ten male soldiers (22 ± 3 yrs, 183 ± 7 cm, 87 ± 8 kg) completed both an indoor 6-station obstacle course (OC) and a repetitive box-lifting task (RBL) in four separate sessions with at least 48 hours rest between sessions. The OC consisted of 46 cm-high hurdles, zigzag sprint, low crawl, horizontal pipe shimmy, 1.4 m wall traversal, and straight sprint. Two trials were performed on each of the four sessions, and the best time of the session was used for analysis. The RBL required subjects to lift a 20.5 kg box from the ground onto 1.3 m high platforms positioned 2.4 m apart, continuously for 10 minutes. One trial was performed in each session. Mean ± SD (different letters denote significant differences (p < 0.05): Performance stabilized on the 3rd session for the OC (8% overall improvement) and on the 2nd session for the RBL (8% overall improvement). After performance stabilized, the intraclass correlation coefficients were 0.92 and 0.94 for the OC and RBL respectively, demonstrating high test-retest reliability for both tests. The mean subject coefficient of variation was 5.1% on the box lift and 4.1% on the obstacle course. This study has demonstrated that both the OC and RBL are reliable tests, but do require 1 (i.e. RBL) or 2 (i.e. OC) practice sessions before highly reproducible results are obtained.Table

THE EFFECTS OF RESISTANCE TRAINING ON A HIGH INTENSITY MANUAL MATERIALS HANDLING TASK IN WOMEN

1806 Manual materials handling tasks in the workplace place high demands on strength and endurance. It is recognized that men possess advantages (i.e. because of greater size and strength) over women during such tasks, but the potential of training interventions for the improvement of women's occupational performance is largely unexplored. We evaluated the effects of two resistance training programs: (1) upper body training (UBT) and (2) total body training (TBT) on a repetitive box lifting task (RBLT) and a 1 repetition maximum (1RM) boxlift (BL). The RBLT consisted of the maximum # of boxes lifted from the floor to a height of 1.32 m within a 10 min period (subjects moved between two boxes 2.4 m apart between lifts). 37 women (24±4 yrs, 166±6 cm, 64±9 kg) underwent either UBT (n=17) or TBT (n=20) and trained 3 x/wk for 6 months (3 sets/exercise, reps were periodized from 8 to 12; rest periods varied between 45-90 secs). A 20-30 min aerobic component concluded each workout. Testing occurred pre (T1), mid-way (T2) and post (T3) training. An ANOVA with repeated measures indicated significant (p≤0.05) training effects for both the RBLT and 1RM BL (T1<T2<T3), but no group or interaction effects. Results (mean±SD) were: 1RM BL (TBG: T1=30±5, T2=35±5, T3=38±4; T1 to T2%Δ=≈17%, T1 to T3%Δ=≈27%; UBG: T1=31±6, T2=35±7, T3=38±6, T1 to T2%Δ=≈13%, T1 to T3%Δ=≈23%); RBLT (TBG: T1=89±24, T2=109±18, T3=118±16, T1 to T2%Δ=≈22%, T1 to T3%Δ=≈33%; UBG: T1=86±24, T2=108±26, T3=118±20, T1 to T2%Δ=≈26%, T1 to T3%Δ=≈37%). These data indicate that(1) adaptations in the upper body appear to account for a greater proportion than the lower body for the performance changes and (2) women can continue to exhibit performance improvements beyond 3 month of training.

Gender differences in performance of a selection test using the incremental lifting machine

The purpose of the study was twofold: (1) to examine any gender differences in the performance of a pre-employment selection test using the incremental lifting machine (ILM); and (2) to formulate recommendations regarding analyses of selection fairness in studies of pre-employment screening tests and devices. Data were collected in a series of studies designed to permit analyses of: (1) dynamic measures derived for a 1.8 m maximum ILM strength test; (2) relationships between ILM test scores and performance of a maximal box-lifting task using three different protocols; (3) the impact of anthropom trie measures on performance of both test and task; (4) prediction of actual task performance; and (5) accuracy of the ILM screening test for three different cut-off standards. Results revealed that females differed significantly from males in their performance of a 1.8 m maximum ILM strength test in terms of timing, displacement, velocity, acceleration, force and power. Maximum ILM scores attained by females were poorly correlated with maximum box-lifting scores, but they were significantly related to body weight. Also, regression analyses based on ILM scores and associated dynamic parameters accounted for twice as much variance in box-lifting scores for males than for females. Furthermore, the use of cut-off standards of 22.7 kg and 27.3 kg produced a percentage of false negative results for females (12% and 32% respectively), but not for males. Also, for the cut-off level of 27.3 kg, female selection rates were only 56% of the selection rates for males. Issues for future investigation are recommended.

Development of factor-score-based models to explain and predict maximal box-lifting performance.

The objectives of the study were threefold: (1) to develop factor-score-based models to predict maximum mass on a box-lifting task using multiple regressions; (2) to compare predictive and explanatory powers of factor-score-based models to models derived from data-level variables; and (3) to apply these findings to ergonomic research and practical problem-solving situations. Forty-eight volunteers (25 women and 23 men) completed a maximal box-lifting task and a maximal isoinertial lifting test on an Incremental Lifting Machine (ILM). Dynamic data collected during isoinertial testing were summarized into 32 lift parameters, and then subjected to principal components analyses using the 'FACTOR PROCEDURE' from the Statistical Analysis System (SAS). Factor scores were calculated for each participant on each of the four factors comprising the final solution, and multiple regression equations for men, women and combined data were generated using the 'GENERAL LINEAR MODELS' procedure from SAS. Results revealed that prediction of box-lifting performance was optimized when regression equations were developed using numerous data-level variables as predictors, i.e., all 32 lift parameters and ILM mass. In comparison, explanation was enhanced but predictive capabilities were reduced when linear models were formed using ILM mass and the factor scores derived from analyses of isoinertial lifting. The use of variables loading on the factors gave slightly increased predictive power than did the factor-score-based models. Similar trends in predictive and explanatory powers appeared when the data were analysed according to gender. Ergonomic applications of factor-score-based models were discussed with regard to ongoing research as well as to practical problem-solving situations. It was concluded that the advantages and usefulness of factor-score-based models warranted their inclusion in future investigations of lifting performance.

The effect of lifting protocol on comparisons with isoinertial lifting performance

The purpose of the study was threefold: (1) to determine if protocol constraints affected scores on a box-lifting task; (2) to identify any differences in impact of protocol changes on male and female scores; and (3) to determine if these protocol changes affected correlations between maximal box-lifting scores and maximal scores obtained on isoinertial lifting tests. Two hundred and sixty nine participants (143 males and 126 females) completed maximal isoinertial lifting tests to 1.50 m and 1.80 m using a constrained protocol on an Incremental Lifting Machine (ILM). Participants were divided into three samples for completion of a maximal box-lifting task, with each sample using one of the following task protocols: (1) set style; (2) free style; and (3) ergonomically redesigned. Statistical analyses using general linear models procedures revealed that changes in protocol constraints significantly affected scores on lifting tasks. Removal of protocol constraints resulted in greater percentage increases in task scores for females than for males. Furthermore, disparate patterns between genders in task-test correlations were observed. It was concluded that the ILM was unable to predict female lifting capabilities accurately using any of the three protocols.

The development of children's achievement-related expectancies and subjective uncertainty

Children between the ages of 3 and 6 years were asked to predict their success or failure in two different tasks: a box-lifting task and a task in which marbles had to be rolled through gates of different widths. Both tasks had five difficulty levels which were presented either simultancously or successively. Along with the verbal or nonverbal responses to questions about their chances of success, the time children needed to make the prediction (decision time), the number of eye movement during the decision time, and, in the box-lifting task, the time taken to approach the box were assessed. The results indicated that children from 3 years on make realistic assessments of their chances for success at the five different difficulty levels. The simultaneous presentation mode enables the children to make more realistic success predictions only in the marble-rolling task. For the box-lifting task, children seem to have a stabilized difficulty scale which allows sure predictions without the whole range of difficulty levels being physically presented.