The relationship between maximal lifting capacity and maximum acceptable lift in strength-based soldiering tasks

Psychophysical assessments, such as the maximum acceptable lift, have been used to establish worker capability and set safe load limits for manual handling tasks in occupational settings. However, in military settings, in which task demand is set and capable workers must be selected, subjective measurements are inadequate, and maximal capacity testing must be used to assess lifting capability. The aim of this study was to establish and compare the relationship between maximal lifting capacity and a self-determined tolerable lifting limit, maximum acceptable lift, across a range of military-relevant lifting tasks. Seventy male soldiers (age 23.7 ± 6.1 years) from the Australian Army performed 7 strength-based lifting tasks to determine their maximum lifting capacity and maximum acceptable lift. Comparisons were performed to identify maximum acceptable lift relative to maximum lifting capacity for each individual task. Linear regression was used to identify the relationship across all tasks when the data were pooled. Strong correlations existed between all 7 lifting tasks (rrange = 0.87-0.96, p < 0.05). No differences were found in maximum acceptable lift relative to maximum lifting capacity across all tasks (p = 0.46). When data were pooled, maximum acceptable lift was equal to 84 ± 8% of the maximum lifting capacity. This study is the first to illustrate the strong and consistent relationship between maximum lifting capacity and maximum acceptable lift for multiple single lifting tasks. The relationship developed between these indices may be used to help assess self-selected manual handling capability through occupationally relevant maximal performance tests.     

Biomechanical analysis of manual lifting tasks

This paper presents the findings of a study conducted to determine peak forces generated in the human spine while the individual is engaged in lifting maximum acceptable weight. Calculations of forces and moments, acting on each body segment, were based on film data collected on four individuals for twelve variations of the manual lifting task. The variations were defined by: box-size (three different boxes were used), presence or absence of handles, and symmetry and asymmetry of the lifting task (sagittal and nonsagittal lifting). In general, lower loads were accepted for lift when lifting asymmetrically or when lifting boxes without handles or when lifting bigger boxes. However, peak forces (compressive and shear forces in the spine and ground reaction forces) for these situations were not always lower than those generated when handling either compact boxes or boxes with handles or when lifting boxes symmetrically in the sagittal plane. On the basis of these results, it was concluded that lifting loads asymmetrically or in boxes without handles or in bulky boxes is relatively much more stressful than lifting the same load symmetrically or in boxes with handles or in compact boxes.     

Relationship between moments at the L5/S1 level, hip and knee joint when lifting

A study was performed to determine the influence of load magnitude on the self selected technique of lifting. Specifically, it was hypothesized that with heavier weights a tendency would occur to lift more with the back and less with the legs. Flexion-extension moments at the L5/S1 level, hip and knee joints were calculated for subjects when lifting boxes weighing from 50 to 250 N. Lifts were performed using a freestyle technique at normal speed. The moment profiles (moment plotted vs time) were analyzed kinematically and as a function of the weight lifted. The kinematics of the lift changed as the weight increased. The moment at the L5/S1 level increased with increasing weight, however, the corresponding knee moment decreased. Thus, an inverse relationship was found between the moment at the L5/S1 level and the knee joint moment. An increase in weight lifted was also associated with an increase in the angular velocity at the knee while lifting. Apparently with heavier weights there is a tendency to extend the knees earlier during the lift than with lighter weights, confirming our hypothesis. This explains the reduced knee moment. Our findings lead to the hypothesis that quadriceps muscle strength limits the subjects' ability to lift with their knees flexed.     

Self-selected resistance training intensity in novice weightlifters

The purpose of this study was to determine the intensity of self-selected weightlifting exercise in untrained men and women. Thirteen men (age = 19.5 +/- 1.9, height = 70.0 +/- 2.4 in., weight = 174 +/- 20.1 lb, % fat = 14.3 +/- 6.7) and 17 women (age =18.7 +/- 1.0, height = 64.9 +/- 2.3 in., weight = 135.4 +/- 22.8 lb, % fat= 23.4 +/- 4.7) who were novice lifters completed seated bench press, leg extension, seated back row, military press, and biceps curl. Following self-selection trials, subjects' 1 repetition maximum (1RM) was assessed for each lift. Results showed that for both genders, self-selected loads were all below 60% 1RM. All lift intensities were similar for men and women (range = 42-57% 1RM). Repetitions completed and rating of perceived exertion responses were not different between gender. Results show that subjects do not select a lifting intensity sufficient to induce hypertrophic responses and subsequent strength increases.     

Lifting Capacity of Horned Passalus Beetles During Passive and Stressed States

Many beetle species engage in territorial behaviors or male-male contests involving lifting or flipping their opponents, although this type of strength has never been empirically quantified. This study examined the lifting capacity of a medium-sized (1–2 g) saprolytic beetle native to the United States (horned passalus beetle, Odontotaenius disjunctus), and strength was measured during passive and stressed states. Twenty beetles were individually placed in a ‘push-up’ position with a force sensor on their backs and allowed to lift continuously for 2 min without manipulation, and then for another 2 min with a mild stress stimulus applied (tapping the elytra with a probe). The unmanipulated peak force readings during the first half were surprisingly high (up to 5 N, or 500 g), based on prior experiments examining the pulling strength of this species (indicating they can pull up to 100 g), but in nearly all beetles their peak lifting power in the stressed state increased by an average of 87 %. There was a positive relationship between strength measurements in both passive and stressed states. This appears to be the first empirical demonstration of the lifting capacity of a beetle, and these results also have considerable implications for the study of physical performance in beetles and other animals, especially in cases where maximum exertion data are of interest.     

The effects of competition and the presence of an audience on weight lifting performance

The purpose of this investigation was to examine the effects of the presence of an audience and competition on maximal weight lifting performance. Thirty-two recreationally trained participants (15 men, 17 women; 21 +/- 2.5 years) performed a 1 repetition maximum (1 RM) bench press during 3 different situations (coaction, competitive coaction, and audience condition). Subjects also completed the Activation-Deactivation Adjective Checklist Short Form following the 3 trials to measure arousal state during each of the 3 trials. Significant differences (p < 0.05) were found between competitive coaction and coaction trials as well as between audience and coaction trials. Both men and women demonstrated the highest performance in front of an audience (105 +/- 48 kg) followed by competition (103 +/- 46 kg) and then the coaction trial (93 +/- 43 kg). No significant difference in arousal was measured between trials. The data suggest that performing a maximal lift in the presence of an audience or in competition facilitates performance and support the self-presentation and self-awareness theories. Social facilitation effects should be controlled in research settings and may aid the performance of weight lifting activities during events or competition.     

Lifting patients in bed with and without a drawsheet: a comparative ergonomics study

Two techniques for lifting a patient in bed, namely with and without the use of a drawsheet, have been compared from an ergonomics point of view. Forty-two nurses of a Thai university hospital were studied before and after using each method by measuring back strengths and by using a questionnaire for feelings of fatigue and for musculoskeletal fatigue and pain. Decreases in back strength 10 minutes after and immediately after lifting with each method were found to be significant (90% confidence). The decrease 10 minutes after lifting was found to be significantly smaller with a drawsheet than without one (98% confidence). Immediately after lifting there was less difference between the two methods, which indicates that the use of a drawsheet reduced the recovery time and the decrease in back strength. Increases in feelings of fatigue from lifting with each method were also found to be significant (90% confidence), and the results indicate that the increase was lower with a drawsheet than without one. Musculoskeletal fatigue and pain immediately after lifting were more common without a drawsheet than with one. In conclusion, the lifting technique with a drawsheet is ergonomically superior and should be used by nursing personnel.     

Dynamically and statically determined low back moments during lifting

Assessment of the effects of lifting on the low back has most frequently been done with the aid of static models. Many lifting movements appear to have substantial inertial components. It was of interest, therefore, to determine the size of the difference between statically and dynamically calculated lumbar moments during a demanding but not unusual manual lift observed in a metal fabrication industry.

The results of several trials by four young men showed that the dynamic model resulted in peak L4 L5 moments 19% higher on average, with a maximum difference of 52%, than those determined from the static model. The technique adopted in the lift could minimize the difference. When the inertial forces of the load itself and the load weight were incorporated into an otherwise static model (quasi-dynamic) then the resulting L4/L5 moments exceeded those of the fully dynamic model by 25%.

In many industrial tasks static analyses may severely underestimate the demands of dynamic lifts. These results show that a reasonably inexpensive approach in lifting task analysis is to measure the dynamic forces of the load on the hands and to use these in an otherwise static model. This results in a conservative assessment of the injury risk of lifts at least of the type reported in this study.     

The effect of an on-body personal lift assist device (PLAD) on fatigue during a repetitive lifting task

Occupations demanding frequent and heavy lifting are associated with an increased risk of injury. A personal lift assist device (PLAD) was designed to assist human muscles through the use of elastic elements. This study was designed to determine if the PLAD could reduce the level of general and local back muscle fatigue during a cyclical lifting task. Electromyography of two erector spinae sites (T9 and L3) was recorded during a 45-min lifting session at six lifts/lowers per minute in which male participants (n = 10) lifted a box scaled to represent 20% of their maximum back extensor strength. The PLAD device reduced the severity of muscular fatigue at both muscle sites. RMS amplitude increased minimally (22% and 26%) compared to the no-PLAD condition (104% and 88%). Minimal median frequency decreases (0.33% and 0.41%) were observed in the PLAD condition compared to drops of 12% and 20% in the no-PLAD condition. The PLAD had an additional benefit of minimizing pre–post changes in muscular strength and endurance. The PLAD also resulted in a significantly lower rate of perceived exertion across the lifting session. It was concluded that the PLAD was effective at decreasing the level of back muscular fatigue.     

A Quasi-Steady Lifting Line Theory for Insect-Like Hovering Flight

A novel lifting line formulation is presented for the quasi-steady aerodynamic evaluation of insect-like wings in hovering flight. The approach allows accurate estimation of aerodynamic forces from geometry and kinematic information alone and provides for the first time quantitative information on the relative contribution of induced and profile drag associated with lift production for insect-like wings in hover. The main adaptation to the existing lifting line theory is the use of an equivalent angle of attack, which enables capture of the steady non-linear aerodynamics at high angles of attack. A simple methodology to include non-ideal induced effects due to wake periodicity and effective actuator disc area within the lifting line theory is included in the model. Low Reynolds number effects as well as the edge velocity correction required to account for different wing planform shapes are incorporated through appropriate modification of the wing section lift curve slope. The model has been successfully validated against measurements from revolving wing experiments and high order computational fluid dynamics simulations. Model predicted mean lift to weight ratio results have an average error of 4% compared to values from computational fluid dynamics for eight different insect cases. Application of an unmodified linear lifting line approach leads on average to a 60% overestimation in the mean lift force required for weight support, with most of the discrepancy due to use of linear aerodynamics. It is shown that on average for the eight insects considered, the induced drag contributes 22% of the total drag based on the mean cycle values and 29% of the total drag based on the mid half-stroke values.     

Underestimation of object mass in lifting does not increase the load on the low back.

Sudden, unexpected loading on the low back is associated with a high incidence of low back pain. Experiments in which sudden loading was applied during standing revealed increased compression forces on the spine and increased trunk angle, which may cause injury to the spine and hence explain this association. During a more dynamic daily activity, i.e. lifting, this could not be demonstrated, which may be due to experimental constraints. We therefore reinvestigated the loading of the low back when subjects were lifting an unexpectedly heavy object. Ten males lifted boxes, weighing 1.6 or 6.6 kg, at a self-selected lifting velocity. In some trials the mass of these boxes was unexpectedly increased by 10 kg. The ground reaction forces, body movements and trunk muscle activity were measured and from these, the L5/S1 torques and compression forces were estimated. Underestimation of the mass did not lead to an increase in low back loading. This finding was independent of the mass the subjects were expecting to lift. In conclusion, no evidence was found to support inference regarding causality of the association between sudden loading and low back pain during whole body lifting movements.     

A preliminary investigation of the biomechanical and perceptual influence of chain resistance on the performance of the snatch

The purpose of this study was to determine whether the addition of chains to a barbell during the performance of the snatch would invoke differences in execution compared with lifting a conventional barbell without chains. Additionally, subjects were asked whether they perceived that the addition of chains had effects on their performance, and, if so, what those effects were. Four male and 3 female competitive weightlifters who regularly used chains as part of their training programs participated in the study. They were compared lifting 80% of 1 repetition maximum (1RM) using conventional barbells with 80% of 1RM, 5% of which was accounted for by chains. The same procedure was used with 85% of 1RM. Variables examined included maximum vertical displacement of the bar, maximum bar velocity, rate of force production of the bar, and vertical ground reaction forces for the first pull, unweighting, and second pull phases of the lift. Results indicated that there were no statistically significant differences between the chain vs. no-chain conditions at either 80% or 85% of 1RM. In contrast, 100% of the subjects stated that they perceived that the addition of chains made them work harder during the snatch. They suggested that the chains forced them to pull harder throughout the lift and that oscillation of the chains required their shoulders, abdominals, and back to work harder to stabilize the bar in the catch phase. Although statistical results indicate that chains have no influence on the snatch technique, chains may have a psychological impact and possibly invoke a physiological training response by increasing strength of muscles required to stabilize the bar during the catch phase if used over time.     

Fatigue effects on bar kinematics during the bench press

The bench press is one of the most popular weight training exercises. Although most training regimens incorporate multiple repetition sets, there are few data describing how the kinematics of a lift change during a set to failure. To examine these changes, recreational lifters (10 men and 8 women) were recruited. The maximum weight each subject could bench press (1RM) was determined. Subjects then performed as many repetitions as possible at 75% of the 1RM load. Three-dimensional kinematic data were recorded and analyzed for all lifts. Statistical analysis revealed that differences between maximal and submaximal lifts and the kinematics of a submaximal lift change as a subject approaches failure in a set. The time to lift the bar more than doubled from the first to the last repetition, causing a decrease in both mean and peak upward velocity. Furthermore, the peak upward velocity occurred much earlier in the lift phase in these later repetitions. The path the bar followed also changed, with subjects keeping the bar more directly over the shoulder during the lift. In general, most of the kinematic variables analyzed became more similar to those of the maximal lift as the subjects progressed through the set, but there was considerable variation between subjects as to which repetition was most like the maximal lift. This study shows that there are definite changes in the lifting kinematics in recreational lifters during a set to failure and suggests it may be particularly important for coaches and less-skilled lifters to focus on developing the proper bar path, rather than reaching momentary muscular failure, in the early part of a training program.     

Kinetic comparison of free weight and machine power cleans

The purpose of this investigation was to compare the kinetic characteristics of the power clean exercise using either free weight or machine resistance. After familiarization, 14 resistance trained men (mean +/- SD; age = 24.9 +/- 6.2 years) participated in two testing sessions. During the initial testing session, one-repetition maximum performance (1RM) was assessed in either the free weight or machine power clean from the midthigh. This was followed by kinetic assessment of either the free weight or the machine power clean at 85% of 1RM. One week after the initial testing session, 1RM performance, as well as the subsequent kinetic evaluation, were performed for the alternate exercise modality. All performance measures were obtained using a computer-interfaced FiTROdyne dynamometer (Fitronic; Bratislava, Slovakia). Maximum strength (1RM) and average power were significantly greater for the free weight condition, whereas peak velocity and average velocity were greater for the machine condition (p < 0.05). Although peak power was not different between modalities, force at peak power (free weights = 1445 +/- 266 N, machine = 1231 +/- 194 N) and velocity at peak power (free weights = 1.77 +/- 0.28 m x s(-1), machine = 2.20 +/- 0.24 m x s(-1)) were different (p < 0.05). It seems that mechanical limitations of the machine modality (i.e., lift trajectory) result in different load capacities that produce different kinetic characteristics for these two lifting modalities.     

History of Intentional and Unintentional Weight Loss in a Population-Based Sample of Women Aged 55 to 69 Years

FRENCH, SIMONE A, ROBERT W JEFFERY, AARON R FOLSOM, DAVID F WILLIAMSON AND TIM BYERS. History of intentional and unintentional weight loss in a population-based sample of women aged 55 to 69 years. Obes Res. 1995;3:163–170. Although both overweight and body weight fluctuation are related to chronic disease risk, little is known about the history of and reasons for body weight change in the general population. This paper reports the incidence of intentional and unintentional weight loss episodes during adulthood in a population-based sample of 26, 261 women aged 55 to 69 years. Intentional weight loss episodes of each of four amounts (5–9, 10–19, 20–49, 50+ lbs.) and unintentional weight loss episodes of 20 or more lbs. were recalled for each of three age periods (18–39, 40–54, 55+ years). At least one intentional weight loss episode of 5 or more lbs. was reported by 69% of women, 46% reported at least one intentional weight loss episode of 10 or more lbs, and 25% reported at least one intentional weight loss episode 20 or more lbs. At least one unintentional weight loss episode of 20 or more lbs. was reported by 29% of the women. Reasons for weight losses of 20 or more lbs. were also recalled. Women who had intentionally lost 20 or more lbs. were more likely to report weight losses due to low-calorie diets, exercise and weight loss groups, while women who had unintentionally lost 20 or more lbs. were more likely to report weight losses due to depression or stress. These findings question the common assumption that weight losses in adult women are primarily intentional and emphasize the need to distinguish the reasons for weight loss in studies examining the relationship between body weight changes and health outcomes.     

Body contouring

LEARNING OBJECTIVES: After studying this article, the participant should be able to: 1. List patient selection factors for body lift surgery. 2. Describe operative approaches for brachioplasty, upper body lift, abdominoplasty, lower body lift, and thigh lift. 3. Identify complications and pitfalls related to body lifting and describe how to avoid them. SUMMARY: The author discusses the preoperative assessment, surgical treatment plan, postoperative management, outcomes, and possible complications for a comprehensive spectrum of body-contouring surgical procedures. Preoperative planning includes medical history and physical examination, along with an open discussion with the patient. Surgical procedures for brachioplasty, upper back lift, abdominoplasty, lower back lift, gluteal augmentation and thigh lift are discussed. Postoperative management pearls are shared, as well as pitfalls to be avoided.     

High-precision satellite positioning system as a new tool to study the biomechanics of human locomotion

New Global Positioning System (GPS) receivers allow now to measure a location on earth at high frequency (5 Hz) with a centimetric precision using phase differential positioning method. We studied whether such technique was accurate enough to retrieve basic parameters of human locomotion. Eight subjects walked on an athletics track at four different imposed step frequencies (70–130 steps/min) plus a run at free pace. Differential carrier phase localization between a fixed base station and the mobile antenna mounted on the walking person was calculated. In parallel, a triaxial accelerometer, attached to the low back, recorded body accelerations. The different parameters were averaged for 150 consecutive steps of each run for each subject (total of 6000 steps analyzed). We observed a perfect correlation between average step duration measured by accelerometer and by GPS (r=0.9998, N=40). Two important parameters for the calculation of the external work of walking were also analyzed, namely the vertical lift of the trunk and the velocity variation per step. For an average walking speed of 4.0 km/h, average vertical lift and velocity variation were, respectively, 4.8 cm and 0.60 km/h. The average intra-individual step-to-step variability at a constant speed, which includes GPS errors and the biological gait style variation, were found to be 24.5% (coefficient of variation) for vertical lift and 44.5% for velocity variation. It is concluded that GPS technique can provide useful biomechanical parameters for the analysis of an unlimited number of strides in an unconstrained free-living environment.     

Validation of an optical encoder during free weight resistance movements and analysis of bench press sticking point power during fatigue

During the concentric movement of the bench press, there is an initial high-power push after chest contact, immediately followed by a characteristic area of low power, the so-called "sticking region." During high-intensity lifting, a decline in power can result in a failed lift attempt. The purpose of this study was to determine the validity of an optical encoder to measure power and then employ this device to determine power changes during the initial acceleration and sticking region during fatiguing repeated bench press training. Twelve subjects performed a free weight bench press, a Smith Machine back squat, and a Smith Machine 40-kg bench press throw for power validation measures. All barbell movements were simultaneously monitored using cinematography and an optical encoder. Eccentric and concentric mean and peak power were calculated using time and position data derived from each method. Validity of power measures between the video (criterion) and optical encoder scores were evaluated by standard error of the estimate (SEE) and coefficient of variation (CV). Seven subjects then performed 4 sets of 6 free weight bench press repetitions progressively increasing from 85 to 95% of their 6 repetition maximum, with each repetition continually monitored by an optical encoder. The SEE for power ranged from 3.6 to 14.4 W (CV, 1.0-3.0%; correlation, 0.97-1.00). During the free weight bench press training, peak power declined by approximately 55% (p < 0.01) during the initial acceleration phase of the final 2 repetitions of the final set. Although decreases in power of the sticking point were significant (p < 0.01), as early as repetition 5 (-40%) they reached critically low levels in the final 2 repetitions (>-95%). In conclusion, the optical encoder provided valid measures of kinetics during free weight resistance training movements. The decline in power during the initial acceleration phase appears a factor in a failed lift attempt at the sticking point.     

The role of proprioceptive information in programming of anticipatory postural components of voluntary movements

Anticipatory components of the EMG activity of the postural muscles during a voluntary movement were analyzed to find out how the CNS regulates these components in response to changes in the movement parameters and what information is used for programming these components. The fast lift of an arm in an erect posture was used as a model. The parameters of the movement were modified by varying weights held in the hand (0.5, 1.0, and 1.5 kg) and the preliminary information on these weights: lifting the hand holding a weight and lifting an unknown weight from a support in the absence of information on its value or after receiving verbal information on it. Our experiments showed that the program of maintaining an erect posture while performing a fast voluntary lift of the arm involves anticipatory adjustments of postural muscles (the soleus muscle, biceps muscle of the thigh, and sacrospinal muscle) using information on the parameters of the movement to be performed. For all these muscles, the anticipation time did not depend on either experimental conditions or the velocity of lifting the arm. The duration of the activity and its amount had different dependences on the lifted weight. The parameters of inhibition of the soleus muscle did not depend on the lifted weight, the activity of the biceps muscle of the thigh was mainly regulated by varying its amplitude, and the regulation of the sacrospinal muscle involved both amplitude and duration changes. It was shown that the adjustment of anticipatory movement components can be only based on proprioceptive rather than verbal (conscious) information.