Physiological and psychophysical comparison between a lifting task with identical weight but different coupling factors

Revised NIOSH lifting equation: a critical evaluation

The revised NIOSH lifting equation (RNLE) aims to manage lifting-related lower back pain (LBP), by determining safe load limits. Many researchers have studied the multiplier development criteria, the universal applicability of the equation and its ability to identify an increased risk of LBP in lifting tasks. Although a number of strengths of the equation have been highlighted, many limitations have also been identified. The need for new multipliers, such as worker and environmental characteristics, was highlighted in order to make the equation more adaptable. The RNLE was designed to protect 75% of female workers and is therefore inherently conservative. Additionally, as all multipliers have values less than or equal to 1, the recommended weight limits (RWLs) can be further reduced. Thus, new multipliers may be defined, by combining two or more existing multipliers, to make the RWLs more realistic.

Cardiovascular and Psychophysical Response to Repetitive Lifting Tasks in Women

Background

Understanding the cardiovascular and psychophysical demands of repetitive lifting tasks is important in job design strategies. This study determined the cardiovascular (oxygen consumption (VO₂) and heart rate (HR) and psychophysical response to repetitive lifting tasks in women.

Methods

Ten female (age 27 ± 5 yrs) participants transferred 11.4, 15.9, and 20.5 kg weights back and forth from a rung 40.6 cm high to a rung 156.2 cm high. Rungs were 195.6 cm apart horizontally. Three, 10 minute bouts (1 = 11.4 kg; 2 = 15.9 kg; 3 = 20.5 kg) were performed at 6 lifts per minute. Cardiovascular and psychophysical (rating of perceived exertion, RPE) parameters were monitored throughout the bouts. VO₂max and HRmax were determined via a maximal treadmill test.

Results

VO₂, HR, and RPE were significantly different between each work bout (p < 0.01), with each outcome variable increasing as load increased. VO₂max and HRmax equaled 46.5 ± 7.5 mL·kg⁻¹·min⁻¹ and 191 ± 11 bpm, respectively. Work at 11.4 kg was performed at 38% VO₂max and 63% HRmax; at 15.9 kg at 41% VO₂max and 72% HRmax; and at 20.5 kg at 49% VO₂max and 81% HRmax. RPE at 11.4, 15.9, and 20.5 kgs were: 8.4 ± 1.6, 11.4 ± 1.9, and 15.0 ± 2.2.

Conclusion

During these repetitive lifting tasks, metabolic cost and perceived exertion increased with weight lifted; average work intensity ranged from 63 to 81% of HRmax and 38 to 49% of VO₂max. Results have important implications in relation to job pacing and design, and worksite health promotion strategies aimed at reducing work place injury.

Hand Grip Strength and Gender: Allometric Normalization in Older Adults and Implications for the NIOSH Lifting Equation

Background

Many countries are experiencing an aging workforce with women workers making up a growing proportion. Workplaces often require employees to complete lifting tasks that require the ability of the hand to grasp an implement (coupling). The National Institute for Occupational Safety and Health (NIOSH) has developed an equation for manual lifting tasks hoping to minimize the potential for a workplace back-injury related to a lifting task. The NIOSH lifting equation relies upon stress variables including a coupling factor. However, little is known regarding grip strength as related to the NIOSH lifting equation coupling factor. The purpose of this study was to investigate differences in grip strength due to gender in older adults.

Methods

The participant’s (68–88 years) maximal grip (MG) strength measures were collected for each hand with a hand grip dynamometer (kg). MG scores were converted to Newtons (N), normalized to body mass, and allometrically scaled. Measures of MG were than compared between genders with an independent t-test.

Results

The hand grip measures of MG (kg) [male: 30.3 ± 5.6, female: 10.6 ± 3.3], MG (kg) / body mass (kg) [male: 0.35 ± 0.06, female: 0.16 ± 0.04], MG (N) / (body mass (kg))^0.67 [male: 15.1 ± 2.5, female: 6.2 ± 1.7], and MG (N) / (body height (m))^1.84 [male: 103.6 ± 18.6, female: 42.6 ± 10.6] were all significantly lower (p < 0.0001) for women than men. Regardless of how grip strength was reported, there is a strong difference in grip strength between genders in this sample. The NIOSH lifting equation does not account for varying grip strength due to aging and gender differences.

Conclusions

It is recommended that grip strength variability be accounted for in the coupling factor of the NIOSH lifting equation.

Psychophysically determining the maximum acceptable weight of lift for polypropylene laminated bags

The objective of this study was to psychophysically determine the maximum acceptable weight of lift (MAWL) for polypropylene (PP) laminated bags. Twelve men were requested to decide their MAWLs under various task combinations involving 3 lifting ranges, 3 lifting frequencies, and 2 hand conditions. The results revealed that the MAWL was significantly affected by the frequency and range variables (all p<.001), whereas the hand condition did not influence the MAWL. The participants exhibited relatively low MAWL values compared with subjects in previous studies, especially in infrequent lifts. The results of multiple stepwise regression revealed that certain anthropometric data (e.g., chest circumference, wrist circumference, and acromial height) accounted for the percentage of variance for the determined MAWLs, ranging from 56.2% to 83.4%. These data can be obtained simply and quickly, and are considered the superior predictors for MAWL determination when handling PP laminated bags.

Evaluation of the Impact of the Revised National Institute for Occupational Safety and Health Lifting Equation

OBJECTIVE

The objective of this article is to evaluate the impact of the Revised National Institute for Occupational Safety and Health Lifting Equation (RNLE).

BACKGROUND

The RNLE has been used extensively as a risk assessment method for prevention of low back pain (LBP). However, the impact of the RNLE has not been documented.

METHODS

A systematic review of the literature on the RNLE was conducted. The review consisted of three parts: characterization of the RNLE publications, assessment of the impact of the RNLE, and evaluation of the influences of the RNLE on ergonomic standards. The literature for assessing the impact was categorized into four research areas: methodology, laboratory, field, and risk assessment studies using the Lifting Index (LI) or Composite LI (CLI), both of which are the products of the RNLE.

RESULTS

The impact of the RNLE has been both widespread and influential. We found 24 studies that examined the criteria used to define lifting capacity used by the RNLE, 28 studies that compared risk assessment methods for identifying LBP, 23 studies that found the RNLE useful in identifying the risk of LBP with different work populations, and 13 studies on the relationship between LI/CLI and LBP outcomes. We also found evidence on the adoption of the RNLE as an ergonomic standard for use by various local, state, and international entities.

CONCLUSION

The review found 13 studies that link LI/CLI to adverse LBP outcomes. These studies showed a positive relationship between LI/CLI metrics and the severity of LBP outcomes.