Relationship between energy intake and expenditure during harvesting tasks

The objective of this study was to compare the energy demands of manual harvesting tasks with the associated energy intake of the workers’. Fifty eight workers (29 Chainsaw Operators and 29 Stackers) were assessed in South Africa prior to, and during a ‘normal’ working shift. Habitual dietary analyses showed that the workers were eating less than 56% of the recommended daily allowance and were thus arriving at work with reduced energy stores. Heart rate responses were measured continuously during work and energy expenditure was predicted from the heart rate/oxygen uptake relationship obtained at a post-work progressive step up test completed by each worker. The data indicated that the tasks placed ‘moderate-to-heavy’ demands on the workers resulting in a significant imbalance between the energy demands of the tasks and the associated energy intake of the workers. Energy deficits were in excess of 8 000 kJ and workers lost, on average, 2.8% body mass during work while felling and cross-cutting, and 3.6% during stacking

Consideration of the effect of nutritional status and disease patterns on the work output amongst Black South African workers involved in manual materials handling (MMH) tasks

The prevalence of malnutrition amongst low-income earning South Africans has been well documented and is reported to be particularly high amongst Black South African males. This, combined with poor living conditions associated with their poor socio-economic status, results in an increased prevalence of infectious diseases amongst this sector of the population. Additionally, Black South African males are most often employed by companies requiring them to carry out heavy manual materials handling tasks. It would appear that limited research has focused on the relationship between inadequate dietary intake combined with poor health status and the impact this may have on the performance of manual workers. Energy intake is in all probability considerably less than energy expenditure

A field investigation of physical workloads imposed on harvesters in South African forestry

The focus of this field investigation was an analysis of the work demands being placed on South African forestry workers, in particular Chainsaw Operators and Stackers. Working postures, physiological and perceptual responses were assessed on a sample of 58 workers (29 Chainsaw Operators and 29 Stackers) during a ‘normal’ working shift. Body mass was measured before and after work in order to determine dehydration levels. Polar heart rate monitors were fitted to six workers each day over a period of two weeks in order to record ‘working’ heart rates. Fluid and food intake was monitored and recorded during this initial data collection phase. The Rating of Perceived Exertion and Body Discomfort Scales were explained in Zulu, their native language, and workers were asked to rate their perceptions of effort at regular intervals during work, while areas and intensity of body discomfort was obtained on completion of work. After completing a work shift, a 30 minute ‘recovery’ period was given, thereafter a portable ergospirometer, the k4b², was attached to the worker who then participated in a progressive, submaximal step test for the purpose of establishing individual, and group, heart rate-oxygen uptake (HR/VO[subscript 2]) regressions for predicting oxygen uptake from ‘working’ heart rate responses. These procedures were repeated four weeks later following the introduction of a fluid and nutritional supplement during work which was delivered to the workers while they were executing their tasks. The results revealed awkward working postures with a predominance of trunk flexion during all the harvesting tasks; these postures, adopted for long periods during work, are very likely to lead to the development of musculoskeletal injuries. The mean working heart rates were 123.3 bt.min[superscript (-1)] and 117.6 bt.min[superscript (-1)] during chainsaw operations and stacking respectively. During the step test, the mean heart rate and oxygen uptake responses were 127.9 bt.min[superscript (-1)] and 22.9 mlO[subscript 2].kg[superscript (-1)].min[superscript (-1)] (Chainsaw Operators) and 116.9 bt.min[superscript (-1)] and 24.0 mlO[subscript 2].kg[superscript (-1)].min[superscript (-1)] (Stackers), revealing no significant difference between the ‘working’ heart rates and the heart rates recorded during the step test. Physiological responses were analyzed over the full work shift which was divided into four quarters. Heart rate and oxygen uptake were significantly higher during the last half of the Chainsaw Operators’ work shift compared to the first half. Heart rate increased from 120.7 bt.min[superscript (-1)] during the first quarter to 127.4 bt.min[superscript (-1)] during the last quarter of chainsaw operations. Likewise, oxygen uptake increased from 19.9 mlO[subscript 2].kg[superscript (-1)].min[superscript (-1)] to 22.9 mlO[subscript 2].kg[superscript (-1)].min[superscript (-1)] from the first to the last quarter of work. During stacking the heart rate (mean of 117.6 bt.min[superscript (-1)]) and oxygen uptake (mean of 24.6 ml.kg[superscript (-1)].min[superscript (-1)]) responses remained stable over the duration of the working shift. Workers lost, on average, 2.8% body mass during work while felling and cross-cutting and 3.6% during stacking. This reduced significantly to a loss of 0.4% body mass when re-tested following the introduction of water and food during the work period. Likewise, the energy deficit was significantly improved due to the introduction of a nutritional supplement. Pre-intervention the deficit was 8861.8 kJ (Chainsaw Operators) and 8804.2 kJ (Stackers) while in the post-intervention phase this deficit was reduced by approximately 50% for both groups of workers

Physiological and perceptual responses of SANDF personnel to varying combinations of marching speed and backpack load

The objective of the present study was to establish effective combinations of marching speed and backpack load in order to meet specific military requirements. Thirty infantrymen from the South African National Defence Force (SANDF) comprised the sample and experimental procedures were conducted in a laboratory setting using a Cybex Trotter treadmill. Sixteen conditions were set up which included combinations of four speeds (3.5, 4.5, 5.5, and 6.5 km.h⁻¹) and four backpack loads (20, 35, 50, and 65kg). Each subject was required to complete 8 of the sixteen conditions, each consisting of a six-minute treadmill march. Physiological data (heart rate, ventilation and metabolic responses), kinematic gait responses (step-rate and stride length) and perceptions of exertion (“Central” and “Local” RPE) were collected during the third and sixth minutes of the treadmill march and areas of body discomfort were identified post-march. Responses revealed five distinct categories of exertional strain. Three marches constituted “nominal” (below 40% VO₂max) and three “excessive” strain (above 75% VO₂ max). These represent combinations of extreme military demands and are highly unlikely to be utilised by the military. Three “tolerable” levels of required effort were recommended and these 10 combinations were further divided into three sub-categories. The “moderate” stress marches were identified as “ideal” for prolonged marches and had statistically similar responses of working heart rates (range of 118 bt.min⁻¹ to 127 bt.min⁻¹), energy expenditure (26 kJ.min⁻¹ and 27 kJ.min⁻¹) and ratings of perceived exertion (“Central” ratings of 10 and 11). Thus, marching at 5.5 km.h⁻¹with 20kg, 4.5 km.h⁻¹ with 35kg or 3.5 km.h⁻¹ with 50kg all require a similar energy cost. Four “heavy” category marches were identified for possible use when the duration of the march is reduced. During these marches responses were statistically similar with heart rates ranging from 127 bt.min⁻¹ to 137 bt.min⁻¹, energy expenditure from 32 kJ.min⁻¹ to 37 kJ.min⁻¹ and “Central” ratings of perceived exertion were 12 and 13. When short, high intensity marches are necessary, then combinations from the “very heavy” category may be utilised but with caution. During these marches, soldiers were taxed between 65% and 75% of VO2 max. The results of this study clearly demonstrate that the interplay between speed and load needs to be adjusted when determining “ideal” combinations for specific military demands. Essentially, if speed is of the essence then load must be reduced, and if heavy loads need to be transported then speed must be reduced

An indirect method to assess the energy expenditure of manual labourers in situ

The aim of ergonomics is to identify any incompatibility between worker capabilities and the demands of their job. It is therefore desirable that in a developing country such as South Africa we have some basic, yet valid and usable means of measuring worker responses to physically demanding manual tasks. Extensive ergonomic research has been conducted in the controlled environment of laboratories around the globe, but only a limited number of investigations have been conducted in the workplace. This is due to the impossibility of controlling the extraneous factors such as the environment and changing workloads while assessing worker responses, plus the impracticality of using hi-tech equipment under difficult conditions on unsophisticated workers. The likelihood of obtaining ‘natural’ responses thereby is low. The focus of this study was to establish a less invasive means of assessing the physiological responses (specifically energy expenditure) of manual labourers working in the field. Twenty-three forestry stackers were assessed. Heart-rate responses were recorded during a full shift, after which the workers participated in a submaximal incremental step test. Subjects were fitted with a gas analyser, and heart rate and oxygen consumption responses were measured throughout the 12-min test. These data were used to establish a regression equation based on the relationship between heart rate and oxygen consumption (r² = 0.49; r = 0.69). Using this equation (y=0.26x – 6.42), one can measure heart rate in the field and predict the energy cost of manual tasks

Enhancing military efficiency : a South African perspective

While extensive military research has been conducted in developed countries, very little work has been done on soldiers in industrially developing countries (IDCs). Although many aspects of marching are similar around the globe, the challenges facing soldiers in IDCs, and in particular South Africa, are unique. Since the 1990’s South Africa has seen a considerable shift in the morphological and cultural make-up of the South African National Defence Force (SANDF). The result is a mix of soldiers from a variety of ethnic backgrounds. Ethnic differences may ultimately impact performance particularly as research has postulated that Blacks and Whites may differ in body composition and body proportions. It is highly probable then that the universal recommendations of optimal marching speeds, load masses and gradients need to be modified to accommodate the diversity of soldiers which currently comprise the SANDF

Cardiac responses under diverse combinations of marching speed and backpack load

Thirty seasoned foot-soldiers were exposed to a total of 16 combinations of marching speed and backpack load, each soldier experiencing 8 of the combinations between 3.5km.h-1 with a 20kg load and 6.5km.h-1 with a 65kg load. Detailed physiological analyses were conducted, of which the heart rate responses are reported here. Steady state was achieved with all combinations under 5.5km.h-1 speed and 35kg load. Excessively elevated heart rates were elicited by all loads over 20kg at 6.5km.h-1 marching speed; by loads over 35kg at 5.5km.h-1 marching speed and by the 65kg load even at 4.5km.h-1 marching speed

Physical implications of prolonged sitting in a confined posture - a literature review

The main purpose of this review article was to highlight some of the physical consequences of sitting for prolonged periods in a confined setting. More specifically, the review relates this research to call centre work and where applicable comments on the limited literature relating specifically to ergonomics research within call centre settings. In particular the article explores the biomechanical stresses placed on the musculoskeletal system during prolonged sitting at a workstation, and the physiological consequences thereof. The paper then provides possible solutions to reduce the physical strain placed on these workers by looking at workstation design and work organisation emphasizing worker education and the promotion of worker well being

Strength and Sprint Time Changes in Response to Repeated Shuttles Between the Wickets During Batting in Cricket

Christie CJ, Sheppard B, Goble D, Pote L, and Noakes TD. Strength and sprint time changes in response to repeated shuttles between the wickets during batting in cricket. J Strength Cond Res XX(X): 000–000, 2018—No studies have investigated the impact of repeated sprints between the wickets on lower-limb strength and sprint performance. Therefore, the purpose of this study was to assess changes in knee extensor (EXT) and flexor (FLEX) strength after repeated sprints between the wickets and to relate these to changes in sprint times. Twenty batters completed 2 conditions: onewas high-volume running (HVR-twelve sprints per over) and the other, moderate-volume running (MVR-6 sprints per over) between the wickets (42 deliveries in both). Peak isokinetic torque was measured before and after each condition and sprint times were recorded. Eccentric and concentric peak torque decreased significantly (p , 0.05) at 1.05 rad˙s ̄1 for knee EXT in both conditions. There was an 18% (HVR) and 10% (MVR) decline in concentric and eccentric knee EXT peak torque. Peak FLEX torques were significantly (p , 0.05) reduced after HVR (16.7%) but not after the MVR condition (8%). There were similar declines in eccentric FLEX peak torque. Sprint times increased significantly (p , 0.05) during the HVR condition but not in the MVR condition; sprint times in the HVR condition were compromised as early as the third over. We conclude that a high volume of runs significantly reduces muscle function in the lower limbs, partly explaining the impairment in sprint performance. However, because batters slowed as early as the third over in the HVR condition, there may be some form of strategy used in anticipation of a higher overall workload. More middle wicket practices, focusing on repeat shuttle sprints while batting, should be included in the coaching program