Human strength: terminology, measurement, and interpretation of data

Influence of Human Parameters on Labor Productivity in the Construction Industry

OBJECTIVE

The objective of this article is to investigate the influence of human parameters on qualitative assessment of labor productivity (LP) in the construction industry.

BACKGROUND

The theories involving workers have identified various parameters on physical efficiency, such as heart rate, relative heart rate, and calorie count, so as to improve the safety and social conditions of construction labor, thereby increasing LP. However, there is no direct emphasis on assessment of LP using human parameters related to physical strength.

METHOD

An exploratory study was conducted on 17 construction workers by observing their task-level LP in real time at a construction site. Human parameters, such as age, body mass index (BMI), handgrip strength, and upper body muscle strength of the laborers, were measured at the construction site. Performance levels of these workers were placed in three categories, and each worker was assigned a typical weightage to each category when correlated to physical strength.

RESULTS

Labor categories among the human parameters that included middle age, normal-range BMI, and strong muscular strength were shown as having higher LP than others. A quantitative parameter called the Human Parameter Index (HPI) was developed based on the performance categories developed for an individual worker. Human parameters revealed a significant relationship with respect to task-level LP.

CONCLUSION AND APPLICATION

The study determines the influence of human parameters on LP in construction. Introduction of human parameters in the construction industry will help in assessment of LP for various labor-intensive activities.

The Effects of Instruction, Verbal Encouragement, and Visual Feedback on Static Handgrip Strength

The objective of this study was to evaluate the effects of instruction, verbal encouragement, and real-time visual feedback on static handgrip strength. Sixteen subjects participated in this study and a computerized wrist dynamometer was used for the measurement of grip strength. The independent variables were five different instructions including the Caldwell Regimen, use of verbal encouragement and visual feedback. According to the results of ANOVA, there were significant differences in main effects. Therefore, the employment of verbal encouragement or visual feedback should be noted in any paper if used while measuring static strength. Since the comparison between peak forces showed that fast contraction and immediate release upon maximal contraction instruction had greater peak forces than all other instruction sets, it can be suggested for the standard of peak force measurement that the static strength should be reached within 1.5 seconds and immediately released when reaching the maximum force and the greatest force can be designated as the peak force.

Repeatability of Dynamic Strength Tests

The repeatability of dynamic strength tests was examined by calculating coefficients of variations (CV) for the forces exerted on lifting tests using the legs, torso and arms. Static strengths were also measured and compared to dynamic strengths. The CV for dynamic strengths, was in fact slightly lower than for static strengths, 9.79% vs. 10.6%. The correlations between the two types of strength measurements were large (r=.8l) and significant, indicating that along with good repeatability dynamic tests are an acceptable form of employee strength measurement.

Filling 'gaps' in strength data for design

Data on the physical strength capabilities of users are fundamental to the safe and usable design of products. It is recognised, however, that there are many 'gaps' in the ergonomics data available to designers. Whilst considerable research on human capabilities and limitations has already been carried out, few data exist which are directly applicable in the design process. This paper describes a two-stage research project which was undertaken to try to address some of these data 'gaps'. Potential needs for design-relevant data were identified in Stage 1 of the research and in Stage 2 new data were collected to meet some of those needs. Data were collected on children through to the older adult on a series of six strength measurements, all of which were intended to be directly applicable to design: (1) finger push strength, (2) pinch-pull strength, (3) hand grip strength, (4) wrist-twisting strength, (5) opening strength, and (6) push and pull strength. The methodology, findings and data from this research are presented and discussed.

Force exertion in awkward working postures--strength capability while twisting or working overhead

Isometric strength data have been collected for three of the awkward work situations often imposed by workplace constraints in industry, as found in jobs such as maintenance and repair. The effects of the task layout factors (location of the workpiece, reach distance and direction of force exertion) were investigated and the data has been tabulated to show the degree to which strength may be reduced in different situations. Strength measurements in the present study were found to be considerably higher than previous measurements, apparently due to differences in instructions on foot placement that were given to subjects, which indicates that even small constraints on posture within the workplace may have large effects on the ability to exert force.

Relationships among grip strength, work capacity, and recovery

The relationship between strength, fatigue, and work capacity is a central issue for occupational rehabilitation. Musculoskeletal impairments often are expressed functionally as a loss of strength. For work tasks that require strength, such impairments may have a detrimental effect on work capacity that is sufficient to be disabling. How important is strength as a component of work capacity? How do work capacity and strength affect recovery time from repetitive forceful upper extremity work ? A sample of 40 healthy subjects comprised of 20 males and 20 females was studied in a model that used the isotonic strength of each subject to set exercise levels for subsequent forceful repetitive gripping tasks. Resistance levels of 75%, 50%, and 25% of maximum were used for one-per-second repetitions until the subject could not maintain that pace. Isometric grip strength was measured after 1 minute of rest and after 5, 10, and 20 minutes. Results indicate that males and females do not differ in terms of their rate of recovery and that the best predictor of recovery time is the immediate measurement of strength loss following cessation of work activity.

Static strength and physical work capacity of agricultural labourers in the central plain of Thailand

An investigation was conducted to determine the static strength and physical work capacity of Thai agricultural labourers. Ten male and 10 female subjects, were randomly selected from the two provinces of the central plain of Thailand. The anthropometry of these labourers was determined by taking 42 body dimensions. During the static strength evaluation, back, arm, leg, shoulder, composite and hand grip strengths were measured. The physical work capacity was determined by using a bicycle ergometer. The oxygen consumption was determined by oxylog. It was observed that the composite strength was highest while grip strength was lowest for both male and female subjects. However, static strength of different body parts for all males was higher than that of similar body parts for females. Comparison of data obtained in this study was made with the data for subjects in other countries. The physical work capacity of female agricultural labourers participating in this study was found to be 69% that of male labourers.

Isometric strength in flexors, abductors, and external rotators of the shoulder

The aim of this study was to map the isometric shoulder muscle strength of 96 men and 90 women randomized from the population register of Stockholm citizens (reference groups), and of 83 male furniture removers and 89 female secretaries (aged 19-65 years, all four groups). Maximum isometric strength of the right-side shoulder flexors (90° joint angle), abductors, and external rotators (0°) was recorded with the subject sitting in a standardized position in an adjustable chair. Women had 43, 55, and 56% of the men's strength in the abductors, flexors, and external rotators respectively. Neither of the female test groups showed any change in maximum isometric strength with increasing age. Men from the reference group showed an age-related difference only in shoulder flexor strength, where the older men (45-65 years) had 89% of the younger men's (19-44 years) strength. The strength values of older furniture removers were 77-83% of the younger colleagues' values in all muscle groups tested. The muscular strength utilization ratio (MUR%) when holding the arm without external load at 90° shoulder flexion was 22-25 MUR% for the male groups and 34 MUR% for the female groups, which shows that the muscular load on the shoulder caused by the weight of the arm is of great importance.

Basic aspects of action tremors in the human M. brachioradialis

Since the first measurements of tremors it was obvious that the tremor signal originates from very complicated and continuously changing nervous and mechanical factors. However, the tremors originate in the beginning from the action tremors of the skeletal muscles. In this study the basic structure of the action tremors, regular 13-Hz oscillations, was revealed (measured by an accelerometer fixed on the distal end of the muscle belly of the m. brachioradialis). The mechanical oscillations measured with this technique had a linear relationship to the electrical oscillations of the EMG. Further, harmonic interference of isometric contraction with faradic contraction was observed. During simultaneous contraction of neighbouring muscles, completely synchronous but exactly out-of-phase oscillations were observed.

Determination of optimal location for parachute ripcord handle in a suspended position

A number of parachuting fatalities are attributed every year to the inability of the parachutist to pull the ripcord. The purpose of this study was to determine a location for the ripcord handle in parachutes, which would be most compatible with human capabilities. Eight different ripcord handle locations were selected for this investigation. Eighteen male and 18 female subjects participated in the study. The subjects were tested while being suspended 5 cm above floor level wearing a parachute harness. Maximum voluntary force exertions were measured with the subjects pulling the ripcord handle using their left, right and both hands at all locations. The results indicate that the thigh locations are superior in regard to pull forces for all hand applications (left, right, and both). Also, two-handed pulls yield the largest forces at all locations.

Arm lift strength in work space

This study was conducted to determine arm strength values for isometric and isokinetic efforts around the human trunk. Thirty-eight normal young adults (20 male and 18 female) performed a total of 19 tasks. These consisted of one self-selected optimum posture with upright stance and elbows bent at 90 degrees , designated as standard posture for isometric test. In addition, isometric testing was done sagittally symmetrical 30 degrees and 60 degrees lateral planes at half-, three-quarters- and full-reach distances at knuckle height. The isokinetic tests were done between knuckle height and shoulder height in postures identical to isometric tests. The sequence of these tasks was randomised. The peak strength in standard posture was invariably lower than the peak strength at half-reach in isometric condition in all three planes for both sexes with the exception of one condition among females (60 degrees lateral plane, half-reach isometric). Peak and average arm lift strengths of males were significantly higher than those of females (p < 0.01) and ranged between 44% and 71%. For both sexes isometric strength was significantly higher than isokinetic strength (p < 0.01). The peak and average strengths in the sagittal plane were invariably higher than those of asymmetric postures, with one exception among females. With increasing reach distance the strength declined significantly for all conditions among both genders (p < 0.01). The ANOVA showed that the gender, mode of lifting, postural symmetry and reach of lifting, in addition to affecting the peak and average strength individually (p < 0.01), had significant 2-way and 3-way interactions (p < 0.01). All strength values were inter-correlated (p < 0.01). The regressions predicting peak and average strengths from anthropometric characteristics and sagittal plane strengths accounted for 63% to 89% of all variance and were highly significant (p < 0.01).

The reliability and validity of two new tests of maximum lifting capacity

This study investigated the test-retest reliability and validity of the isokinetic and gravity/inertia modes of the Lido Lift (TM) and the Progressive Lifting Capacity II test (PLC II). Maximum lifting capacity tests were performed in the isokinetic and gravity/inertia modes on the Lido Lift and with the PLC II with 29 healthy male subjects. Pearson product-moment correlations were calculated to determine the test-retest reliabilities and to compare PLC II test values with isokinetic and gravity/inertia test values. The correlations for the isokinetic, gravity inertia, and the PLC II werer=.90, .82, and .91, respectively. The correlations between the isokinetic and gravity/inertia tests and the PLC II werer=.64 and .74 during the test andr=.72 and .81 during the retest. The results of this study support the reliability of both Lido Lift (TM) tests and of the PLC II, and the validity of the isokinetic and gravity/inertia tests when compared to the PLC II.

Isokinetic pull-up strength profiles of men and women in different working posture

This paper presents isokinetic (dynamic) strength profiles of males and females, engaged in infrequent force exertion, in 15 different working postures. The postures investigated ranged from kneeling to standing and involved both one-handed and two-handed exertions. The results indicated that both males and females exert maximum pull-up force with two hands in the stooped posture. Least force was exerted with the preferred hand at reach distance, in the sagittal plane (arm fully extended), in the sitting posture. As expected, large differences existed in the force exertion capability of males and females.

The age discrimination in employment act: a review of court decisions

Over 600 federal court cases filed between 1970 and 1986 were reviewed in an attempt to discover the major themes and issues. Over all personnel decisions the employer was consistently favored (65%). Performance evidence was central to all cases reviewed. Subjective appraisals were often presented by management and were not considered suspect by the courts. Evidence of management's concern over the age of the workforce (e.g., economic costs and stereotypic beliefs) was also probative. Statistical evidence was presented in a majority of cases. However, inaccurate data and inappropriate comparisons negated its value. Most cases involved a termination or reduction in workforce decision (54%), but the most controversial area involved BFOQ's. A three-part sequential inquiry was proposed that would attempt to clear up these issues. Recent legal refinements may ease the plaintiff's burden in establishing a prima facie case of discrimination. Current techniques from the fields of industrial gerontology and industrial psychology may help clarify inconsistencies in court decisions.

Human strengths and occupational safety

This paper presents a review of relatively recent North American literature concerning human strengths. It briefly covers basic strength definitions, measurement and prediction of strengths, and the role of strengths in employee screening and job matching procedures. In addition to discussing variations in strength with body posture and duration of exertion, a brief reflection on torque exertion capabilities of individuals with common hand tools is also included.

Reliability of repetitive dynamic strengths as a screening tool for manual lifting tasks

Recent studies have shown that maximal dynamic strengths (MDSs) of individuals are superior and more reliable predictors of their maximum safe lifting capacity compared to maximal static strengths. The evidence, however, is based on studies that have investigated only infrequent lifting activities, i.e. lifting only a few times a day and with complete recovery from fatigue between successive lifts. It remains to be seen if MDSs are also as highly correlated to lifting capacity for frequent lifting tasks i.e. tasks that do not allow complete recovery from fatigue between successive lifts. The study reported here was conducted to determine the degree of affinity between MDSs and lifting capacities of individuals for frequent and infrequent lifting tasks. In addition, the hypothesis that lifting capacity for frequent manual lifting tasks will be more highly correlated to dynamic strength values which take into account the effect of repetition related fatigue, instead of MDSs, was tested. The results overwhelmingly supported the hypothesis. We therefore concluded that repetitive dynamic strength (RDS) is a more accurate measure of an individual's lifting capacity for frequently performed tasks, than maximal static or dynamic strengths, and deserves recognition as a reliable pre-employment screening tool for frequently performed manual lifting tasks. The experimental evidence also indicated that manual lifting tasks performed once every minute or less frequently are strength oriented while those per formed three times a minute or more frequently are not.

Effort of preparation and age

In an experiment on 24 men and women who were selected for short simple RT (reaction time) and who ranged from 22 to 86 yr. of age, choice RT increased monotonically over 3.5 sec. of waiting time during which there was high momentary probability of stimulus occurrence. As use of a choice reaction minimized the possibility of a response set, the occurrence of a waiting decrement was regarded as support for Näätänen's 1971 proposal of short-term mental exhaustion, which was derived from a similar study but for simple RT. The effect of age on endurance was not clear. There appeared to be no greater waiting decrement with age up to about 65 yr., but the possibility of greater decrements beyond that age cannot be discounted. The existence of short-term exhaustion is consonant with Kahneman's (1973) view that effort is required for the generation of processing capacity. Kahneman and other investigators of mental effort have unanimously rejected the existence of any appreciable effort during preparation. However, Näätänen's evidence for short-term exhaustion apparently had not been considered. It is here suggested that short-term exhaustion usually is not incurred in information processing tasks as they are characterized by alternations of high and low demands for capacity, unlike the present high constant momentary probability of signal occurrence. It is further conjectured that such intermittent operation evolved as the optimum way of utilizing underlying resources that are subject to depletion.

Measuring muscle strength

A dynamometer that can be held in the hand and that was designed to measure muscle strength in a simple way in the range 2-5 of the MRC scale, was tested in order to establish to what extent differences in results can be attributed to the observer, the subject and replication. Observers learned the technique quickly and their results agreed with each other to a considerable extent. The subjects showed a small learning effect in three of the four muscles tested. Normal muscle strength was measured in one hundred 18-year-old men.

Evaluation of maximal and submaximal static muscle exertions

A model of the regulation of muscle strength exertion is proposed. Based on the model, methods are discussed to assess whether a subject exerts maximal or submaximal efforts. Results with 40 subjects indicate that a simple technique may be developed to judge if a subject is following instructions to exert a maximal contraction in a routine test of voluntary muscle strength.

Towards an objective assessment of the "maximal voluntary contraction" component in routine muscle strength measurements

Routine measurements of muscle strength capabilities commonly use external dynamometers against which the subject exerts maximal voluntary contractions of muscles in static (isometric) tests. These tests require active cooperation of the subject, i.e., full motivation to "give the best". At present, no practicable techniques exist that provide objective clues indicating that indeed a maximal effort is delivered, or if only a portion of the available strength is exerted. This paper describes experiments performed with 30 subjects which indicate that the rate of strength build-up in repeated exertions may provide objective criteria to judge whether or not a subject exerts full muscular strength in a routine test.

A dynamometer for biomechanical use

A dynamometer has been designed for measuring isometric forces in human body limb segments. The dynamometer constrains the chosen segment, and measures two orthogonal components of the force reaction between the segment and the dynamometer in a plane perpendicular to the long axis of the segment, plus the torque reaction parallel to the long axis of the segment. The testing and operating characteristics of the dynamometer are described, and it is concluded that in view of its versatility and accuracy, the dynamometer may be suitable both for research and for clinical use.

A Multifactor-Systems Theory of The Structure and Dynamics of Motor Functions

A theoretical analysis of the structure and dynamics of human motor functioning is presented from the perspective of a general theory of individuality. Within multifactor-systems theory, the structural units of the six systems of integrative personality (i.e., sensory, motor, cognitive, affect, style, and value) are hierarchical factor structures. Integrative functioning, both within and among systems, is described via the principles of general systems and information-processing theory. Our theoretical synthesis of the structure and dynamics of human motor functioning involves conceptualizing the hierarchy of motor factors as: (a) the basic dimensions of individual differences in the motor domain, (b) classes of decomposable motor programs that specify the spatio-temporal organization of behavior, and (c) decomposable classes of processing components entailed by motor programs. Some of the implications for understanding the role of affect in motor functioning and some research suggestions were presented.

Effect of acute infectious disease on isometric muscle strength

Isometric strength of different muscle groups was recorded in thiryty-nine patients suffering various acute infectious diseases, predominantly of viral or mycoplasma aetiology. Recordings were performed after subsidence of fever, and 1, and 4 months thereafter. A control group of twenty-two healthy men, confined to bed for the same period of time as the patients, were investigated at the same time intervals. In addition, control measurements were performed after 1 year in the patients, prior to bed rest in the control subjects. As a result of illness muscle strength was decreased significantly to 85.4-95.3% of that recorded at 4 months. In the control subjects strength did not change significantly, the corresponding percentages being 96.3-102.5. Thus, the present data indicate that these illnesses in themselves may bring about isometric muscle strength reduction.

Horizontal push and pull forces: exertable when standing in working positions on various surfaces

Push and pull forces are reported which can be exerted by one or several men while they assume common standing positions, either braced against sturdy supports or standing on slippery floors. Coefficients of friction between shoe and floor materials are listed.