Psychophysical and physiological responses to lifting symmetrical and asymmetrical loads symmetrically and asymmetrically

Eighteen adult males (mean age 22·6 years, weight 78·6kg and height 176·6cm) participated in a study designed to investigate the effects of symmetrical and asymmetrical lifting on the maximum acceptable weight of lift and the resulting physiological cost. Each subject performed sixty different lifting tasks involving two lifting heights, three lifting frequencies and five containers. For each lifting task, the load was lifted either symmetrically (sagittal lifting) or asymmetrically (turning 90^° while continuing to lift). The heart rate and oxygen uptake of the individuals at the maximum acceptable weight of lift were measured. At the end of the experiment, subjects also verbally indicated their preference for symmetrical and asymmetrical lifting. When lifting asymmetrically, subjects accepted approximately 8·5% less weight. There was, however, no difference in the physiological costs when lifting symmetrically or asymmetrically. Lifting asymmetrical loads also resulted in lower maximum acceptable weights. No difference in either oxygen uptake or heart rate was observed when the centre of gravity of the load was offset by 10·16 or 20·32 cm from the mid-sagittal plane in the frontal plane towards the preferred hand. All subjects indicated, verbally, that asymmetrical lifting tasks were physically more difficult to perform.     

An electromyographic analysis of seated and standing lifting tasks

The objective of this project was to compare the muscular effort exerted during manual lifting tasks performed in standing versus seated posture. Six male undergraduate and graduate students performed 12 different static and dynamic lifts in both sitting and standing positions. During each effort electromyographic (EMG) data were collected on four muscles groups (low back, upper back, shoulder, and abdominals). Four contractions were designed to elicit maximum muscular effort in the four groups being monitored. The remaining data were then expressed as a percentage of maximum EMG. Each subject performed the following: maximum static lift when sitting; maximum static lift when standing; sitting, static lift with 15·9 kg; standing, static lift with 15·9 kg; dynamic sit-forward lift with 15·9 kg, dynamic stand-forward lift with 15·9 kg, dynamic sit-twist with 15·9 kg, dynamic stand-vertical lift with 15·9 kg. Each of the lifts was performed with a wooden tray with slotted handles. Root mean square (RMS) values of the EMG data were calculated for three second periods. EMG activity in the low back, upper back, and shoulder was greater during sitting lifting than during standing lifting. The sit-twist lift resulted in the highest EMG in the abdominal muscles. Dynamic lifts resulted in more muscle activity than did static lifts. From these data it was concluded that sitting-lifting results in greater stress in the low back, upper back, and shoulders than does lifting while standing.     

The psychophysical lifting capacities of Chinese subjects

The psychophysical lifting capacity (MAWL) of twelve subjects was determined in this study. The subjects were all young Chinese males who performed lifting tasks in three lifting ranges (floor to knuckle, floor to shoulder, and knuckle to shoulder) and four lifting frequencies (one-time maximum, 1 lift/min, 4 lifts/min, and 6 lifts/min). The oxygen uptake (1/min) and heart rate (beats/min) were recorded while subjects were lifting. Upon completion of each lifting task, the subjects were required to rate their perceived exertion levels. The statistical analyses results indicated the following. Chinese subjects have smaller body size and MAWLs compared with past studies using the US population. The MAWLs decreased with an increase in lifting frequencies. The decrements of MAWL due to lifting frequencies were in agreement with the results of past studies. However, there were larger decreases due to lifting ranges. The MAWLs of the floor to knuckle height lift were the largest, followed by the MAWLs of the floor to shoulder height lift, and the MAWLs of the knuckle to shoulder height lift. The measured physiological responses were considered similar to those obtained in past studies. Subjects' perceived stress levels increased with the lifting frequency and the upper extremities received the most stress for the total range of lifting tasks. The comparisons of the Chinese MAWLs with the NIOSH lifting guidelines for limits (AL and MPL) indicated that the vertical discounting factor in the guidelines should be modified before the NIOSH limits can be applied to non-Western populations.     

An electromyographic analysis of seated and standing lifting tasks.

The objective of this project was to compare the muscular effort exerted during manual lifting tasks performed in standing versus seated posture. Six male undergraduate and graduate students performed 12 different static and dynamic lifts in both sitting and standing positions. During each effort electromyographic (EMG) data were collected on four muscles groups (low back, upper back, shoulder, and abdominals). Four contractions were designed to elicit maximum muscular effort in the four groups being monitored. The remaining data were then expressed as a percentage of maximum EMG. Each subject performed the following: maximum static lift when sitting; maximum static lift when standing; sitting, static lift with 15.9 kg; standing, static lift with 15.9 kg; dynamic sit-forward lift with 15.9 kg, dynamic stand-forward lift with 15.9 kg, dynamic sit-twist with 15.9 kg, dynamic stand-vertical lift with 15.9 kg. Each of the lifts was performed with a wooden tray with slotted handles. Root mean square (RMS) values of the EMG data were calculated for three second periods. EMG activity in the low back, upper back, and shoulder was greater during sitting lifting than during standing lifting. The sit-twist lift resulted in the highest EMG in the abdominal muscles. Dynamic lifts resulted in more muscle activity than did static lifts. From these data it was concluded that sitting-lifting results in greater stress in the low back, upper back, and shoulders than does lifting while standing.     

Maximum acceptable lifting loads during seated and standing work positions

The psychophysical method was used to determine the maximal acceptable load that eight males (age 22-30 years) would lift in each of four different positions: (1) seated, two-handed, symmetrical lift from a table, to a position 38 cm forward of the edge, (2) a seated lift from a position at the subject's side, on to a table in front of the subject involving a 90 degree twist of the torso, (3) standing, two-handed, symmetrical lift from the table, to a position 38 cm forward of the edge, and (4) standing, vertical lift from 86 above the floor. Subsequent to a training period, subjects lifted a tray with slotted handles at the rate of 1 or 4 lifts/min. Each subject chose the weight of the tray which was acceptable to him by adding or removing flat pieces of lead over a 45 min period. The weight of the tray, heart rate, and the perceived exertion were measured at 15, 30 and 45 min. Oxygen consumption was measured during the last 5 min of the 45 min experiment. Statistical analysis revealed a significant frequency and position effect. An increase in frequency from 1 to 4 lifts/min resulted in a decrease of 1.6 to 2.1 kg in the maximum acceptable weight for the various tasks. On average, the maximum acceptable weight of lift for standing positions was 16% greater than for sitting positions. Oxygen consumption and heart rate were significantly higher for 4 lifts/min than for 1 lift/min; however, the rating of perceived exertion did not differ for any factor.     

Maximum weights of lift acceptable to male and female industrial workers for extended work shifts

Abstract

This paper reports the development of maximum acceptable weight of lift databases for male and female industrial workers for 12-hour work periods. Using a psychophysical methodology, 37 males and 37 females, experienced in manual lifting, performed various lifting tasks involving four frequencies, three box sizes, and three height levels. The maximum acceptable weight of lift was significantly influenced by the frequency of lift, height of lift, and box size. Box size effects were, however, less profound than frequency, and height effects. The maximum weight, acceptable for 12 hours of lifting, elicited an average heart rate of 90 and 101 beats min ^?1 for males and females, respectively. Males selected weights that, on average, resulted in metabolic energy expenditure rates of 23% of their aerobic capacity for 12 hours of lifting. Females required metabolic energy expenditure rates equivalent to 24% of their aerobic capacity for lifting acceptable levels of weight for 12 hours.     

Manual handling performance: the effects of menstrual cycle phase

Physiological and subjective responses to physical performance have been shown to interrelate with fluctuations in the female hormonal environment throughout the menstrual cycle. The aim of this study was to examine whether these fluctuations affect the strenuous performance required in manual handling. Seventeen eumenorrheic females performed lifting tasks in five phases of their menstrual cycle. These tasks were maximal isometric lifting strength (MILS) and an endurance lift at 45% MILS (t), at both knee and waist height; and the selection of a maximal acceptable load (MAL) to lift six times per min, for 10 min, in both the sagittal and asymmetric planes. Heart rate response (HR) and rating of perceived exertion (RPE) were recorded throughout each of the lifting tasks. MILS, t and the chosen MAL were unaffected by menstrual phase over both heights and planes of lift (p>0.05). HR to the isometric endurance lift was greater following ovulation than prior to ovulation by ? 7 beats.min^?1 (p> 0.05). This was true when the data were analysed at 50, 80 and 100% of the time to volitional fatigue, and by an area under the curve procedure. HR to the dynamic lifting tasks was also elevated by ? 7 beats.min^?1 following ovulation. This difference was non-significant due to the low power of the analysis. Re-analysis of the data by re-sampling 1000 matched comparisons produced significant phase variations (p> 0.05). The RPE for all of the lifting tasks was independent of menstrual phase (p> 0.05). The impact of the eumenorrheic menstrual cycle on lifting capability was negligible in the present study. However, the results of this study indicate that all further investigations utilizing HR data to produce recommendations for health and safety in manual handling tasks must control for menstrual cycle phase in female populations.     

Effects of frequency and load to lift on endurance time

The purpose of the present study was to determine endurance time for manual lifting tasks which were performed over a wide range of loads (5, 10, 15, and 20 kg) and frequencies (4, 6, 8, and 10 times/min) for a lift from floor to table height. Endurance time was defined in this study as the maximum length of time during which an individual was capable of lifting a given load at a given frequency continuously. The upper limit of endurance time was set to 8 h. Eleven male subjects participated in this study, and the lifting technique utilized with the straight back-bent knees method. The results showed that endurance time was significantly reduced with an increase in frequency or load of lift. The lightest frequency-load combination (4 times/min; 5 kg) was maintained by most of the subjects for 8 h. Conversely, the average endurance time for the heaviest frequency-load combination (10 times/min; 20 kg) was about 27 minutes.     

Acceptable weights and physiological costs of performing combined manual handling tasks in restricted postures

Eight healthy, male underground coal miners (mean age=36·9 yrs±4·5 SD) participated in a study examining psychophysical acceptable weights and physiological costs of performing combined lifting and lowering tasks in restricted headroom conditions. Independent variables included posture (stooping or kneeling on two knees), task symmetry (symmetric or asymmetric), and vertical lift distance (35 cm or 60cm). All tasks were 10min in duration and were performed under a 1·22 m ceiling to restrict the subject's posture. Subjects were required to raise and lower a lifting box every 10 s, and asked to adjust the box weight to the maximum amount they could handle without undue strain or fatigue. During the final 5 min of each test, data were collected to determine the energy expenditure requirements of the task. Results of this study demonstrated that psychophysical lifting capacity averaged 11·3% lower when kneeling as compared to stooping. Subjects selected 3·5% more weight in asymmetric tasks, and lifted 5·0% less weight to the 60 cm shelf compared to the 35 cm shelf. Heart rate was not significantly affected by posture, but was increased an average of 4 beats/min in asymmetric conditions, and by 3·5 beats/min while lifting/lowering to/from the high shelf. Oxygen uptake was increased by 9% when stooped, by 10% when lifting/lowering asymmetrically, and by 8·2% when performing the task to the high shelf. Results of this study indicate that, wherever possible, materials that must be lifted manually in low-seam coal mines be designed in accordance with the decreased lifting capacity exhibited in the kneeling posture.     

Manual handling performance: the effects of menstrual cycle phase

Physiological and subjective responses to physical performance have been shown to interrelate with fluctuations in the female hormonal environment throughout the menstrual cycle. The aim of this study was to examine whether these fluctuations affect the strenuous performance required in manual handling. Seventeen eumenorrheic females performed lifting tasks in five phases of their menstrual cycle. These tasks were maximal isometric lifting strength (MILS) and an endurance lift at 45% MILS (t), at both knee and waist height; and the selection of a maximal acceptable load (MAL) to lift six times per min, for 10 min, in both the sagittal and asymmetric planes. Heart rate response (HR) and rating of perceived exertion (RPE) were recorded throughout each of the lifting tasks. MILS, t and the chosen MAL were unaffected by menstrual phase over both heights and planes of lift (p > 0.05). HR to the isometric endurance lift was greater following ovulation than prior to ovulation by approximately 7 beats.min-1 (p < 0.05). This was true when the data were analysed at 50, 80 and 100% of the time to volitional fatigue, and by an area under the curve procedure. HR to the dynamic lifting tasks was also elevated by approximately 7 beats.min-1 following ovulation. This difference was non-significant due to the low power of the analysis. Re-analysis of the data by re-sampling 1000 matched comparisons produced significant phase variations (p < 0.05). The RPE for all of the lifting tasks was independent of menstrual phase (p > 0.05). The impact of the eumenorrheic menstrual cycle on lifting capability was negligible in the present study. However, the results of this study indicate that all further investigations utilizing HR data to produce recommendations for health and safety in manual handling tasks must control for menstrual cycle phase in female populations.     

Maximal and sub-maximal functional lifting performance at different platform heights

Introducing valid physical employment tests requires identifying and developing a small number of practical tests that provide broad coverage of physical performance across the full range of job tasks. This study investigated discrete lifting performance across various platform heights reflective of common military lifting tasks. Sixteen Australian Army personnel performed a discrete lifting assessment to maximal lifting capacity (MLC) and maximal acceptable weight of lift (MAWL) at four platform heights between 1.30 and 1.70 m. There were strong correlations between platform height and normalised lifting performance for MLC (R² = 0.76 ± 0.18, p < 0.05) and MAWL (R² = 0.73 ± 0.21, p < 0.05). The developed relationship allowed prediction of lifting capacity at one platform height based on lifting capacity at any of the three other heights, with a standard error of < 4.5 kg and < 2.0 kg for MLC and MAWL, respectively.     

Tolerability to prolonged lifting tasks assessed by subjective perception and physiological responses

Prolonged physical exertion is regulated subjectively by the perception of effort. This preliminary study was conducted to validate the use of subjective perceptions of effort in assessing objectively tolerable workloads for prolonged lifting tasks. Eight healthy male subjects underwent incremental and 30-minute endurance lifting tests. Cardiorespiratory parameters were monitored with an oxygen uptake analyser and mechanical parameters were calculated using a lift dynamometer. Ratings of perceived exertion were given on Borg's 10-point scale. Physiological responses to repetitive lifting were matched with subjective perceptions. The relationship between the perception of exertion and the duration of the endurance tests was described by power functions; Y=aXⁿ in which 0 > n >1. A single-variable statistical regression for power functions was performed to obtain the individual ‘iso-perception’ curves as functions of the mechanical work exerted. It was found that the ‘iso-perception’ curve corresponding to a ‘moderate’ perception of effort may represent the individual ‘tolerance threshold’ for prolonged lifting tasks, since physiological responses at this intensity of effort did not change significantly and the respiratory exchange ratio was less than one. The individually tolerable power over lime for lifting tasks has been estimated.     

The effects of container size, frequency and extended horizontal reach on maximum acceptable weights of lifting for female industrial workers

In the development of our present manual materials handling (MMH) guidelines (Snook, S.H., Ciriello, V.M., 1991. The design of manual tasks: revised tables of maximum acceptable weights and forces. Ergonomics 34, 1197-1213), the assumption was made that the effects of frequency on maximum acceptable weights (MAWs) of lifting with a large box (hand distance, 38 cm from chest) were similar to that of lifting with a small box (hand distance, 17 cm from chest). The first purpose of the present experiment was to investigate this assumption with female industrial workers. The second purpose was to study the effects of extended horizontal reach lifting (hand distance, 44.6 cm from chest) on MAWs as a confirmation of the results of a previous studies on this variable with males (Ciriello, V.M., Snook, S.H., Hughes, G.J., 1993. Further studies of psychophysically determined maximum acceptable weights and forces. Hum. Factors 35(1), 175-186; Ciriello, V.M., 2003. The effects of box size, frequency, and extended horizontal reach on maximum acceptable weights of lifting. Int. J. Ind. Ergon. 32, 115-120). Lastly, we studied the effects of high frequency (20 lifts/min) on MAWs of lifting. Ten female industrial workers performed 15 variations of lifting using our psychophysical methodology whereby the subjects were asked to select a workload they could sustain for 8h without "straining themselves or without becoming unusually tired weakened, overheated or out of breath". The results confirmed that MAWs of lifting with the large box was significantly effected by frequency. The frequency factor pattern in this study was similar to the frequency pattern from a previous study using the small box (Ciriello, V.M., Snook, S.H., 1983. A study of size distance height, and frequency effects on manual handling tasks. Hum. Factors 25(5), 473-483) for all fast frequencies down to one lift every 2 min with deviations of 7%, 15%, and 13% for the one lift every 5 and 30 min tasks and the one lift in 8h task, respectively. The effects of lifting with an extended horizontal reach decreased MAW 22% and 18% for the mid and center lift and the effects of the 20 lifts/min frequency resulted in a MAW that was 47% of a 1 lift/min MAW. Incorporating these results in future guidelines should improve the design of MMH tasks for female workers.     

The load on the back in different handling operations

The study consisted of two parts. In part one the load on the back and muscle fatigue in bimanual symmetrical lifting from floor to table were studied in a lifting experiment of 1 hour' s duration. The following weights and lifting frequencies were used. 10% of max. lifting capacity (MLC) 6 and 15 times per min, 25% MLC 5 and 10 times per min and 50% MLC 3 and 6 times per min. The EMG mean amplitude from the back muscles (L3) showed that even light burdens (10 kg) cause considerable back-toads equivalent to 40–50% MVC. When lifting 50 kg burdens short lasting backloads near the MVC were present. Mean amplitudes and mean spectral frequencies of the EMG were in general increasing, respectively decreasing, as the lifting experiment progressed. Such changes in the EMG are normally interpreted as muscle fatigue caused by changes in the concentration of the chemical substances from the muscle. The EMG changes are most pronounced when lifting 50% MLC (6 times per min) and 10% MLC (15 times per min) and are to a higher extent dependent on the lifting frequency than on the weight or on the mechanical work performed on the burden. Further the RPE values from the back show the same pattern as the EMG. The V˙O₂ and HR, however, do not seem to discriminate as clearly between the different lifting tasks. In part two of the study the load on the back is studied by EMG during a number of manual handling operations applied when handling logs in the forest, i.e. frontal carrying, frontal carrying with a hook, frontal carrying with a pair of tongs, shoulder carrying and dragging with a pair of tongs. Three types of logs were used 1 m (30 kg), 3 m (30 kg), and 3 m (50 kg). All experiments were performed in the forest on two 5×3 m horizontal tracks standardized for the experiment, an easy and a difficult one. It was found that: normal manual handling operations in forestry work cause average backloads in young trained workers varying from 25% to 50% MVC, i.e. equivalent to 1400–2800 N extensor muscle tension of the back, assuming a 5 cm muscle lever arm. Backload levels equivalent to 75–100% MVC are present from a few per cent to 25% of the handling time in all the tasks studied. Asymmetrical loading of the back muscles is frequently seen most markedly in the lifting phases of the handling operations. Conclusion: the dragging method exposes the back to the smallest load on level smooth surface. Under difficult surface conditions, however, frontal carrying with hook and shoulder carrying seem to cause the smallest strain on the back. The backload measures obtained when lifting logs are considerably larger than the measures when lifting boxes of the same weight. Therefore, backload measures obtained in laboratory studies must be used with care when applied in actual working environments     

The effects of load knowledge on stresses at the lower back during lifting

This study investigated the effects of load uncertainty on the lifting characteristics of 40 male volunteers during the initial portion of a lift. Twenty subjects were experienced weightlifters while another 20 were subjects who had never lifted weights nor held a job that required them to on a regular basis. The subjects each lifted a container 20 × 45 × 40 cm, with handles, from floor to waist height 12 times with loads of 68, 10·2 or 13·6 kg. The loads were lifted under conditions of either havingor not having verbal and visual knowledge of the load magnitude prior to the lift. The subjects were allowed to perform the lift in a manner of their choosing. A 2 (groups) × 3 (loads) × 2 (load knowledge) ANOVA was performed on the data. Maximim force (F_max) value analysis revealed group and technique differences. The experienced lifters had lower stress levels at L4/L5 and utilized two technique strategies that were dependent upon the load knowledge condition, whereas the non-lifters used the same strategy for all lifts. Maximum moment values (M_max were significantly higher for the inexperienced lifters under all conditions, indicating a greater dependence on the low back musculature for initiating the lifting of a load.     

The effects of horizontal load speed and lifting frequency on lifting technique and biomechanics

Lifting loads that have a horizontal velocity (e.g. lifting from a conveyor) is often seen in industry and it was hypothesised that the inertial characteristics of these loads may influence lifting technique and low back stress. Seventeen male participants were asked to perform lifting tasks under conditions of four horizontal load speeds (0 m/s, 0.7 m/s, 1.3 m/s and 2.4 m/s) and two lifting frequencies (10 and 20 lifts/min) while trunk motions and trunk muscle activation levels were monitored. Results revealed that increasing horizontal load speed from 0 m/s to 2.4 m/s resulted in an increase in peak sagittal angle (73° vs. 81°) but lower levels of peak sagittal plane angular acceleration (480°/s² vs. 4°/s²) and peak transverse plane angular acceleration (200°/s per s vs. 140°/s per s) and a consistent increase in trunk muscle co-activation. Participants used the inertia of the load to reduce the peak dynamics of the lifting motion at a cost of increased trunk flexion and higher muscle activity.

Statement of Relevance: Conveyors are ubiquitous in industry and understanding the effects of horizontal load speed on the lifting motions performed by workers lifting items from these conveyors may provide some insight into low back injury risk posed by these tasks.     

Effect of safety shoes type,lifting frequency,and ambient temperature on subject's MAWL and physiological responses

ObjectiveThe purpose of this paper is to evaluate the lifting capabilities of individuals while wearing safety shoes in a hot environment and to investigate the behavior of the physiological responses induced by the lifting process associated with those variables.MethodsIn order to achieve the objectives of this research, two sequential studies were conducted. The first part was an acclimatization and training program followed by a psychophysical experiment. Seven male workers participated in this experiment from the university. A three-way repeated measures design, with three independent variables and seven response variables, was utilized in this study. The independent variables studied in the psychophysical experiment were: 1) environmental temperature (20 and 30 °C WBGT), 2) lifting frequency (1 and 5 lifts/min), and 3) safety shoes (light-duty, medium-duty and heavy-duty). The response variables for this experiment were: 1) maximum acceptable weight of lift (MAWL), 2) heart rate, 3) aural-canal temperature, 4) muscle electromyography (EMG) of four muscle groups (biceps brachii, anterior deltoid, trapezius, and erector spinae), 5) rating of perceived exertion, 6) rating of thermal sensation and7) safety shoes discomfort rating.ResultsThe psychophysical experiment results showed that the weights selected by participants at higher levels of the independent variables were significantly less than those selected at lower levels of the independent variables. Some of the interaction effects were also significant.ConclusionThis study found evidence that – in addition to lifting frequency, which is well reported in the literature – heat stress increases the workload intensity in manual lifting tasks influencing the psychophysical selection of MAWL and the physiological responses of the human body represented in aural-canal temperature, heart rate and muscular activities. The study findings demonstrated the necessity of accounting for work environmental temperature and type of worn safety shoes, which is a safety requirement by most employers, when calculating the recommended weight limits.Practitioner summaryMost of the manual materials handling studies had investigated worker's capacity to perform lifting tasks in different environmental conditions not considering the effect of wearing safety shoes. This research fills the gap by presenting safety guidelines regarding lifting tasks in a hot environment while wearing safety shoes.     

Disturbance and recovery of trunk mechanical and neuromuscular behaviours following repetitive lifting: influences of flexion angle and lift rate on creep-induced effects

Repetitive lifting is associated with an increased risk of occupational low back disorders, yet potential adverse effects of such exposure on trunk mechanical and neuromuscular behaviours were not well described. Here, 12 participants, gender balanced, completed 40 min of repetitive lifting in all combinations of three flexion angles (33, 66, and 100% of each participant's full flexion angle) and two lift rates (2 and 4 lifts/min). Trunk behaviours were obtained pre- and post-exposure and during recovery using sudden perturbations. Intrinsic trunk stiffness and reflexive responses were compromised after lifting exposures, with larger decreases in stiffness and reflexive force caused by larger flexion angles, which also delayed reflexive responses.Consistent effects of lift rate were not found. Except for reflex delay no measures returned to pre-exposure values after 20 min of recovery. Simultaneous changes in both trunk stiffness and neuromuscular behaviours may impose an increased risk of trunk instability and low back injury.

Practitioner summary An elevated risk of low back disorders is attributed to repetitive lifting. Here, the effects of flexion angle and lift rate on trunk mechanical and neuromuscular behaviours were investigated. Increasing flexion angle had adverse effects on these outcomes, although lift rate had inconsistent effects and recovery time was more than 20 min.     

Isoinertial tests to predict lifting performance

Previous research has found isoinertial strength testing to be superior to isometric and isokinetic strength testing for prediction of task performance. The purpose of this study was to investigate tests on an isoinertial lifting machine (ILM) and their ability to predict performance on actual lifting tasks. Sixteen male subjects performed two lifting tasks: maximum box lift to truck-bed height of 1.35 m; and 'speed lifts' of 60 concrete blocks (each 22.7 kg) to the same height. These performance tests were compared to three ILM tests: a maximal lift to 1.83 m, a second maximal lift to 1.52 m, and an endurance test that entailed 60 timed ILM lifts of 22.7 kg to 1.83 m. Pearson product-moment correlations between ILM tests and performance tasks varied from r = 0.55 to 0.71. Therefore, the isoinertial test protocols employed in this study were able to account for only 30% to 50% of the variance in the performance of maximal lifting and endurance tasks. In was concluded that prediction of maximal lifting ability or endurance ability using an ILM might be enhanced by closer approximation of specific task variables, or by inclusion of dynamic parameters to measure technique.     

Effect of hypoxia,safety shoe type,and lifting frequency on cardiovascular and ventilation responses

ObjectiveThere is limited work on the physiological demands of lifting activities at different altitudes and different lifting frequencies when wearing different types of shoes. This study aimed to examine the heart rate variability (HRV) and ventilation responses of individuals in normobaric hypoxia (ambient oxygen of 15%, 18%, and 21%) while doing lifting tasks and wearing three types of different safety shoes (“light, medium, and heavy-duty”) at two different lifting frequencies (“1 lift/min and 4 lifts/min”).MethodsUsing an experimental study design, two sessions were conducted by ten male university students that included an acclimatization and training session followed by experimental lifting. The study used a four-way repeated measures design (4 independent and twenty-one responses, i.e., twelve HRV and nine ventilation responses).ResultsThe findings highlighted substantial low HRV and ventilation parameters for the light workload stress in the form of higher ambient oxygen content and lowered lifting frequency while wearing light safety shoe type. It also presented an increase in the physical demand, followed by increased lifting frequency and replication with increased mean heart rate and decreased mean RR, very low frequency (VLF) power, low frequency (LF) power, and low frequency to a high-frequency ratio (LF/HF).ConclusionOur findings suggest that if a safe lifting load limit is applied for workers in the industrial environment, the risk of musculoskeletal disorders will be mainly decreased, and the rate of production will be better with ambient oxygen content and appropriate safety shoes. This research would safeguard industrial workers' physical capacities and future health risks.