Work-rest Cycles Research Articles

Assessment of physiological and fatigue endurance limit of dromedary camel in rotary mode of operation with optimal feeding ration

The studies was conducted on 3 dromedary camels (545–640 kg body weight; 8–10 years age) to assess their work performance and physiological endurance limit with optimum feeding ration in rotary mode of operation. The camels were offered gram straw (Cicer arietinum) as sole ration in all the treatments but in T2 and T3 camels were supplemented with concentrate mixture having 65 and 75% TDN, respectively. A loading car was used to apply and vary the load on the camels in rotary mode of operation. The camels were operated at a draught level of 14% of their body weight with work rest cycle of 2h (W)- 1h (R)- 2h (W)- 4h (R)- 2h (W)- 1h (R)-2h (W). The nutrient utilisation was significantly (P<0.05) higher in T1 followed by T2 and T3. The physiological responses of the camels viz. pulse rate, respiration rate and rectal temperature increased with duration of work where as speed of operation decreased with duration of work. The speed varied in range 2.97 to 2.75 km/h, 2.5 to 2.43 km/h and 2.26 to 2.2 km/h in I, II, III and IV session and the rate of decrease was 7.4, 3, 7.6 and 2.6%, respectively. Fatigue score was found to increase with duration of work which might be due to increase in the physiological response and appearance of physical symptoms with increase in duration of work. It was concluded from results that the physiological responses and fatigue score increased with duration of work where as, speed of operation decreased with duration of work in dromedary camels fed with optimal ration.

Cold Drink Attenuates Heat Strain during Work-rest Cycles

There is limited information on the ingestion of cold drinks after exercise. We investigated the thermoregulatory effects of ingesting drinks at 4°C (COLD) or 28°C (WARM) during work-rest cycles in the heat. On 2 separate occasions, 8 healthy males walked on the treadmill for 2 cycles (45 min work; 15 min rest) at 5.5 km/h with 7.5% gradient. Two aliquots of 400 mL of plain water at either 4°C or 28°C were consumed during each rest period. Rectal temperature (T re ), skin temperature (T sk ), heart rate and subjective ratings were measured. Mean decrease in T re at the end of the final work-rest cycle was greater after the ingestion of COLD drinks (0.5±0.2°C) than WARM drinks (0.3±0.2°C; P<0.05). Rate of decrease in T sk was greater after ingestion of COLD drinks during the first rest period (P<0.01). Mean heart rate was lower after ingesting COLD drinks (P<0.05). Ratings of thermal sensation were lower during the second rest phase after ingestion of COLD drinks (P<0.05). The ingestion of COLD drinks after exercise resulted in a lesser than expected reduction of T re . Nevertheless, the reduction in T re implies a potential for improved work tolerance during military and occupational settings in the heat.

The Effect of Air Permeability Characteristics of Protective Garments on the Induced Physiological Strain under Exercise-Heat Stress

The high values of thermal resistance (Rct) and/or vapor resistance (Ret) of chemical protective clothing (CPC) induce a considerable thermal stress. The present study compared the physiological strain induced by CPCs and evaluates the relative importance of the fabrics' Rct, Ret, and air permeability in determining heat strain. Twelve young (20-30 years) healthy, heat-acclimated male subjects were exposed fully encapsulated for 3h daily to an exercise-heat stress (35°C and 30% relative humidity, walking on a motor-driven treadmill at a pace of 5 km h(1) and a 4% inclination, in a work-rest cycle of 45 min work and 15 min rest). Two bipack CPCs (PC1 and PC2) were tested and the results were compared with those attained by two control suits-a standard cotton military BDU (CO1) and an impermeable material suit (CO2). The physiological burden imposed by the two bilayer garments was within the boundaries set by the control conditions. Overall, PC2 induced a lower strain, which was closer to CO1, whereas PC1 was closer to CO2. Air permeability of the PC2 cloth was almost three times higher than that of PC1, enabling a better heat dissipation and consequently a lower physiological strain. Furthermore, air permeability characteristic of the fabrics, which is associated with its construction and weave, significantly correlated with the physiological strain, whereas the correlation with Rct, Ret, and weight was poor. The results emphasize the importance of air permeability in reducing the physiological strain induced by CPCs.

Evaluation of Cardiopulmonary Stress of the China Clay Mine Workers

Background: Several risk factors are associated with cardiopulmonary stress of industrial workers. Most important factors are job strain, job demand, physical effort, work station environment etc. In India, study on occupational cardiopulmonary stress among china clay miners is scanty. Objectives: The present study was aimed to evaluate the cardiopulmonary stresses of the china clay mine workers. Methods: The investigation was carried out on male workers from different china clay mines in the Birbhum district, West Bengal. The cardiovascular stress was evaluated by noting pulse rate of the subjects both during rest and during performance of different types of mine tasks. The cardiovascular stress index (CSI) was evaluated in different mine task. The work rest cycle of different china clay mine tasks was analyzed by video-photographic method. Different pulmonary function parameters, viz, FVC, FEV1, FER and PEF were measured by a digital spirometer to assess the severity of Chronic Obstructive Pulmonary Disease (COPD). Results: The results showed that the working pulse rate and CSI vary with different mine task. It was highest in subjects carrying china clay by head mode. The magnitude of CSI was found to vary with the change of work time and the rest time among the workers. Pulmonary function parameters of china clay mine workers were significantly lower (P&lt;0.01) than other industrial workers. About 79% of total population was suffering from different grades of COPD. Among them, 12% were suffering from severe COPD and 60% from moderate COPD. The higher prevalence of COPD among china clay mine workers might be due to exposure of china clay dust in the work place. Conclusion: It was concluded that the china clay mine workers were suffering from high degree of physiological stress while performing different mine tasks.DOI: http://dx.doi.org/10.3126/ijosh.v2i2.6594 International Journal of Occupational Safety and Health, Vol 2. No 2 (2012) 27-33

Calculating Workplace WBGT from Meteorological Data: A Tool for Climate Change Assessment

The WBGT heat stress index has been well tested under a variety of climatic conditions and quantitative links have been established between WBGT and the work-rest cycles needed to prevent heat stress effects at the workplace. While there are more specific methods based on individual physiological measurements to determine heat strain in an individual worker, the WBGT index is used in international and national standards to specify workplace heat stress risks. In order to assess time trends of occupational heat exposure at population level, weather station records or climate modelling are the most widely available data sources. The prescribed method to measure WBGT requires special equipment which is not used at weather stations. We compared published methods to calculate outdoor and indoor WBGT from standard climate data, such as air temperature, dew point temperature, wind speed and solar radiation. Specific criteria for recommending a method were developed and original measurements were used to evaluate the different methods. We recommend the method of Liljegren et al. (2008) for calculating outdoor WBGT and the method by Bernard et al. (1999) for indoor WBGT when estimating climate change impacts on occupational heat stress at a population level.

The evaluation of heat stress through monitoring environmental factors and physiological responses in melting and casting industries workers

Aims: Evaluation of heat stress in workers exposed to hot/dry conditions of melting and casting industry is imperative for management of heat stress. This study aims to compare results of heat strain evaluation by monitoring environmental factors and physiological responses. Materials and Methods: This is a cross-sectional study that was conducted on 51 workers of a large melting and casting company in 2010. Wet Bulb Globe Temperature (WBGT) index, heart rate and ear canal temperature were measured by WBGT meter, heart rate monitor and personal heat stress monitor, respectively. Physical activity intensity was assessed based on the ratings of perceived exertion (RPE). Data were analyzed using descriptive statistics and Pearson correlation test. Results: WBGT index in 64.7% of workstations exceeded 30°C and in 41.2% was over 32°C. The value of WBGT index in 69% of work stations exceeded the threshold limit of the ACGIH standard. The physiological strain index (PSI) in 31% of worker was higher than 5, although its mean measured at 3.8 (1.8). Increase in the ear canal temperature in 64.7% of cases (33 persons) was over 1°C. Correlation between WBGT index with ear canal temperature and PSI index, adjusted body mass index and age, was 0.67 and 0.69 (P < 0.0001).Conclusion: In hot/dry conditions of melting and casting processes, despite moderate correlation between WBGT index with ear canal temperature and PSI index, work-rest cycles of WBGT index is not applicable for many of the workstations. Therefore, heat stress evaluation based on physiological variables probably has higher validity and is more appropriate.

Ambulatory Activity in Individuals With Multiple Sclerosis

Specific characteristics of physical activity limitations associated with multiple sclerosis (MS) remain unclear. Our purpose was to examine the impact of MS disability on physical activity behaviors involving ambulation. We also explored relationships among ambulatory activity parameters and clinical measures of gait, balance, and fatigue. Twenty-one adults with MS participated: 11 without ambulatory limitation (Expanded Disability Status Scale [EDSS] score ≤ 4.5) and 10 with ambulatory limitation (EDSS score > 4.5). Participants wore a step activity monitor for up to 7 days. Daily values were calculated for parameters indicative of (1) overall activity, (2) upper limits of activity output, and (3) activity work-rest cycles. Clinical measures included Multiple Sclerosis Walking Scale, Timed 25-Foot Walk, Timed Up and Go test, 6-Minute Walk, Dynamic Gait Index, Berg Balance Scale, Activities-specific Balance Confidence Scale, and Modified Fatigue Impact Scale. Statistical analyses were conducted using nonparametric tests. Participants without limitation were more active, demonstrated higher upper limits of activity output, and had longer activity bouts than participants with limitation (P < 0.05). Only 1 participant averaged more than 100 steps per minute over a 30-minute period. Of the ambulatory activity parameters, daily step count was most strongly related to gait and balance measures. Of the clinical measures, EDSS and Multiple Sclerosis Walking Scale scores were most strongly related to daily step count. Individuals with MS are not necessarily sedentary, but few may achieve recommended daily physical activity levels. Ambulatory activity characteristics revealed new insights into physical activity limitations in MS. The study findings suggest that disability status should direct physical activity interventions.

Prevention of Exercise-Related Death Unexplained by Preexisting Disease (EDU) Associated with Sickle Cell Trait (SCT) without Hemoglobin (Hb) Screening or Hb Specific Management

AbstractAbstract 945We previously reported EDU rates 37.5 fold higher among recruits with SCT than without Hb S in military entry basic training for 1977–1981(Kark JA et al. New Engl J Med 1987;317:781-87, revised). The National Collegiate Athletic Association now requires identification of SCT athletes to reduce this risk, based on a single institution opinion untested by controlled observation, that EDU's of college football players with SCT were due to explosive rhabdomyolysis from exertional sickling unrelated to muscle heat production. A mild syndrome of “exertional sickling” was postulated, consisting of myalgia with flaccid leg weakness, usually responding to O2 inhalation within 30 minutes. Their plan is for non-medical personnel to use SCT screening results to assign SCT athletes training runs at reduced intensity and to pull them out of exercise for myalgia more often than non-Hb S athletes, practices chosen for safety but detrimental to their sports career (Gatorade Sports Science Institute Sports Science Exchange 2006;19:1-4). The cited football EDU's with SCT were actually associated with multiple risk factors for exertional heat illness (EHI), e.g. competitive activity with incomplete acclimation to heat, sustained hot weather, high body mass index, poor fitness, and/or heat-retaining clothing. We conducted a prospective controlled trial to reduce EDU rates for all recruits by better prevention of heat retention during exercise. We compared changes in EDU rates from 1977–1981 versus 1982–2001 at test recruit centers providing our intervention to changes at control centers using prior practice (Kark JA et al. Blood 1997; 90: 447a). The intervention included adjustment of observed water intake, exercise intensity, and work-rest cycle based upon the current heat index on site, early clinical assessment with rectal temperature for recruits who failed to keep up or became symptomatic, and early aggressive medical management of EHI. We did not alter training practices, exercise performance standards, or treatment by Hb type. O2 was given only for signs of failure to adequately oxygenate arterial blood. EDU rates at test centers were reduced 22-fold for those with SCT (0 deaths/ 29,500 recruits vs 14/37,300, significant with P=0.0003) and 2-fold for those without Hb S (6 deaths/1.8 million vs 15/2.05 million, not significant with P= 0.1), but were not substantially reduced at control centers for recruits with SCT (4 deaths/13,500 recruits vs 14/37,300, RR= 0.8, P=0.7) or for recruits without Hb S (6 deaths/ 1 million recruits vs 15/2.1 million, RR=0.85, P=0.8). Despite not screening for SCT, recruits at Army test centers had a significant reduction of mortality with SCT (0 deaths/21,000 recruits vs 7/17,100, RR= 0.06, P=0.002) and without Hb S (4/1.1 million recruits vs 15/2.1 million, RR= 0.3, P=.048). Reducing heat retention with exercise may have eliminated excess EDU with SCT. Survival with SCT did not require prevention of ordinary exertional sickling by measures targeted to SCT. Our intervention appeared to reduce EDU's for people without Hb S by nearly 50%. We also studied all cases of recruit EHI at one basic training center using our intervention during 1979–1991. Rates of non-fatal EHI were 32 cases/5010 recruits with SCT versus 1,834 cases/263,000 recruits without Hb S, a relative risk that was not significant (RR=0.92, P=0.7). The incidence of symptomatic muscle injury, ataxia, falls, hypotension, tachycardia, elevated biochemical markers for EHI, and non-focal encephalopathy were not significantly different for SCT vs Non Hb S recruits. We did not identify a specific non-fatal syndrome associated with SCT. The predominant mechanism of EDU with SCT might involve initial severe EHI from heat retention, subsequently exacerbated by complications related to Hb S, rather than initiation of tissue damage by exertional sickling in the absence of EHI. Proof for any form of exercise might require similar descriptions of all EHI and EDU cases among at least 27,000 people with SCT and population controls during at least one hot season of heavy exercise. Prevention of this morbidity and mortality for SCT probably does not require genetic screening in the absence of effective specific remedies. It may be more effective to provide appropriate prevention and management of exertional heat illness, including isolated rhabdomyolysis, to all exercising people regardless of hemoglobin type. Disclosures:Labotka:HemaQuest Pharmaceuticals, Inc: Research Funding.

Dynamic analysis of combat vehicle accidents

AbstractTo the chagrin of well‐intentioned Army leaders, dozens of soldiers are killed each year as a result of combat vehicle accidents. The objective of this study is to look beyond the events and symptoms of accidents which normally indicate human error, and instead study the upper‐level organizational processes and problems that constitute the actual root causes of accidents. After a short review of the literature we report on our development of a system dynamics model. We then discuss the results of several simulations; these suggest that high‐level decisions that balance mission rate and operations tempo with troop availability, careful management of the work–rest cycle for deployed troops, and improvement of the processes for evaluating the lessons learned from accidents would lead to a reduction in Army combat vehicle accidents. Copyright © 2009 John Wiley &amp; Sons, Ltd.

A submaximal test to assess back muscle capacity: Evaluation of construct validity

A functional endurance test more specific to common occupational tasks is proposed for assessing back muscle capacity. The test involves static intermittent contractions (8-s work-rest cycles) using a predefined absolute load (90 Nm) across subjects. Since the test involved an absolute endurance task, it was hypothesized that performance would be influenced by both the strength and relative endurance of the subjects, thus demonstrating the construct validity of this new test. Fifteen males and 17 females were assessed on three different days to allow familiarization and to measure their Strength as well as their absolute and relative endurance. Absolute and relative endurance were defined as the time to reach exhaustion ( Tend abs and Tend rel , respectively) during a fatigue protocol including both an absolute (90 Nm) and a relative (40% of individual strength) load (extension moment at the L5/S1 joint). Strength and Tend rel each explained an almost equivalent portion of Tend abs (total variance explained: 61.5%), thus confirming the construct validity of the functional endurance test. This new test should better identify the back muscle impairments (weakness, fatigability) often observed in chronic low-back-pain patients.

Postural sway following prolonged exposure to an inclined surface

Fatal and non-fatal falls from elevation have been documented to be a significant issue. Historically, roofing work has been ranked among the highest in incidents of falls. Recent literature has indicated that exposure to inclined surfaces (roof) has a detrimental effect on postural stability. The purpose of this preliminary study was to determine if postural instability was found to increase following extended exposure to an inclined surface. Twenty-three participants were pre/post tested under four postural stability conditions while varying duration exposure (0.0–2.0 h) to an inclined surface. Dependent variable postural sway measures were calculated from center of pressure data derived from a portable force plate. The results indicate significant differences between pre and post-exposure measures. Specifically, the results imply that an individual is less stable directly after performing tasks on an inclined surface. These findings contribute to the literature and serve as a basis for further research into work rest cycles for those individuals who routinely work on inclined surfaces.

Effects of age, gender, and task parameters on fatigue development during intermittent isokinetic torso extensions

This study investigated the effects of age, gender, and task parameters on muscle fatigue during prolonged isokinetic torso exercises, and assessed the sensitivity of EMG-based measures to fatigue. Two groups of 24 participants (older: 55–65 years, younger: 18–25 years), with gender balanced within each group, performed repetitive intermittent torso extensions until exhaustion. Effort levels were set to 30% and 40% of individual maximum voluntary contraction (MVC) and work–rest cycles had durations of 30 and 60 s with a 50% duty cycle. Electromyographic (EMG) signals were obtained bilaterally from the paraspinal muscles. EMG-based fatigue measures, along with declines in MVC and changes in ratings of perceived discomfort, were used to evaluate fatigue progression. While the older group had 23% less initial strength than the younger counterpart, effects of age and gender on fatigue were marginal. However, significant interactive effects of age and gender with effort level were found. These findings overall suggest the importance of carefully considering individual factors and task parameters in designing jobs requiring repetitive torso efforts. In the dynamic torso efforts investigated, the sensitivity of EMG measures to fatigue was relatively low. Relevance to industry Manual material handling tasks such as lifting are often characterized by intermittent dynamic torso efforts. This paper provides evidence regarding age-related differences in torso capacity (strength, fatigue, and endurance), and the influences of effort level and cycle duration. These results can be used for task evaluation and design, and to address older workers in particular.

Hand immersion in cold water alleviating physiological strain and increasing tolerance to uncompensable heat stress

The current study examines the use of hand immersion in cold water to alleviate physiological strain caused by exercising in a hot climate while wearing NBC protective garments. Seventeen heat acclimated subjects wearing a semi-permeable NBC protective garment and a light bulletproof vest were exposed to a 125 min exercise-heat stress (35 degrees C, 50% RH; 5 km/h, 5% incline). The heat stress exposure routine included 5 min rest in the chamber followed by two 50:10 min work-rest cycles. During the control trial (CO), there was no intervention, whilst in the intervention condition the subjects immersed their hands and forearms in a 10 degrees C water bath (HI). The results demonstrated that hand immersion in cold water significantly reduced physiological strain. In the CO exposure during the first and second resting periods, the average rectal temperature (T (re)) practically did not decrease. With hand immersion, the mean (SD) T (re) decreased by 0.45 (0.05 degrees C) and 0.48 degrees C (0.06 degrees C) during the first and second rest periods respectively (P < 0.005). Significant decreases in skin temperature, sweat rate, heart rate, and heat storage was also noted in the HI vs. the CO trials. Tolerance time in the HI exposure were longer than in the CO exposure (only 12 subjects in the CO trial endured the entire heat exposure session, as opposed to all 17 subjects in the HI group). It is concluded that hand immersion in cold water for 10 min is an effective method for decreasing the physiological strain caused by exercising under heat stress while wearing NBC protective garments. The method is convenient, simple, and allows longer working periods in hot or contaminated areas with shorter resting periods.

An Experimental Model of Heat Storage in Working Firefighters

Objective. Develop experimental models to study uncompensable heat stress (UCHS) in working firefighters (FFs). Methods. FFs ingested core temperature (Tc) capsules prior to performing sequential tasks in 40°C andpersonal protective ensemble (PPE), or 18°C andno PPE. Both trials were conducted in an environmental chamber with FFs using self-contained breathing apparatus (SCBA). Results. FFs exercising in heat andPPE reproduced UCHS conditions. For every FF in both trials for whom the capsules worked, Tc was elevated, andTcmax occurred after completion of study protocol. Trials with PPE resulted in a mean maximum temperature of 38.94°C (± 0.37°C); Tcmax reached 40.4°C. Without PPE, maximum Tc averaged 37.79°C (± 0.07°C). Heat storage values ranged from 131 to 1205 kJ, averaging 578 kJ (± 151.47kJ) with PPE and210.83 kJ (± 21.77kJ) without PPE. Conclusions. An experimental model has been developed that simulates the initial phases of an interior fire attack to study the physiology of UCHS in FF. The hot environment andPPE increase maximum Tc andheat storage over that due to the exertion required to perform the tasks andmay decrease time to volitional fatigue. This model will permit controlled studies to optimize work-rest cycles, rehab conditions, andphysical conditioning of FFs.

Understanding Complexity: Dynamic Analysis of Combat Vehicle Accidents

Dozens of U.S. soldiers are killed each year as a result of both combat and motor vehicle accidents. The objective of this study is to look beyond the events and symptoms of accidents which normally indicate human error, and instead study the complex and poorly understood upper-level organizational processes and problems that may constitute the actual root causes of accidents - this is particularly challenging because the causes often involve nonlinear dynamic phenomena and have behaviors that are counter-intuitive to normal human thinking, these are often called wicked problems. After reviewing the available literature, a System Dynamics model was created to provide an analytical model of this multifaceted system that allows for extensive simulation. The results of these simulations suggest that high-level decisions that balance mission rate and operations tempo with troop availability, careful management of the work-rest cycle for deployed troops, and improvement of the processes for evaluating the lessons learned from accidents, will lead to a reduction in Army combat and motor vehicle accidents.

Reducing Combat Vehicle Accidents via Improved Organizational Processes

Despite extraordinary efforts by leaders at all levels throughout the U.S. Army, dozens of soldiers are killed each year as a result of both combat and motor vehicle accidents. The objective of this study is to look beyond the events and symptoms of accidents which normally indicate human error, and instead study the upper-level organizational processes and problems that may constitute the actual root causes of accidents. Critical to this process is identifying critical variables, establishing causality between variables, and quantifying variables that lead to both resilience against accidents and propensities for accidents. After reviewing the available literature we report on our development of a System Dynamics model, which is an analytical model of the system that allows for extensive simulation. The results of these simulations suggest that high-level decisions that balance mission rate and operations tempo with troop availability, careful management of the work-rest cycle for deployed troops, and improvement of the processes for evaluating the lessons learned from accidents, will lead to a reduction in Army combat and motor vehicle accidents.

Muscle fatigue and endurance during repetitive intermittent static efforts: development of prediction models

Localized muscle fatigue has received growing attention as a potential design variable and exposure metric in research towards prevention of musculoskeletal disorders in the workplace. While fatigue during sustained static work has been investigated extensively, effects during tasks comprising work–rest cycles are less clear. Work–rest models for static intermittent work have been presented in several reports, but the applicability is often limited to specific conditions. A study was conducted that facilitated a description of the relationships between static intermittent efforts and muscle endurance and fatigue. Exercises consisted of 1 h (maximum) of repetitive static arm abductions, involving a range of muscle contraction levels (10–30% maximum voluntary exertion), duty cycles (0.2–0.8) and cycle times (20–180 s). A between-subject central composite experimental design was used and 15 different exercise conditions were examined with six participants (three females and three males) for each. Along with endurance times, temporal changes related to fatigue were monitored using muscle strength, ratings of discomfort and electromyography (EMG) obtained from the middle-deltoid muscle during the contraction phase of the work cycles. The results of this study showed the influence of contraction level and duty cycle on the majority of fatigue measures used, while cycle time tended to affect EMG spectral measures. Using a response surface methodology, several fatigue prediction models and contour plots were developed that can be employed as an aid for design and evaluation of light repetitive static tasks. Good correspondence was generally found between discomfort rating and other measures of fatigue, suggesting the usefulness of this measure for rapid assessments of local fatigue in the workplace.

Optimal work–rest cycles for an isometric intermittent gripping task as a function of force, posture and grip span

The aim of this study was to investigate the maximum acceptable contraction frequencies (i.e. work–rest cycles) for an isometric-intermittent handgrip task as a function of grip span, applied force and shoulder posture using psychophysical and physiological approaches. Twelve healthy males served as subjects. The three grip spans investigated were the optimal, 2 cm narrower than the optimal, and 2 cm wider than the optimal. The grip force levels studied were 15% and 30% of maximum voluntary grip force and the two shoulder postures were 25° flexion and 30° abduction. The psychophysical results indicate that subjects work faster with the narrower grip span at 15% of maximum voluntary grip force level in comparison to working with the optimal and the wider spans. However, when the task required 30% of maximum grip force level, the subjects worked faster with the optimal grip span. These findings were supported by the results of electromyography, heart rate, blood pressure and perceived discomfort. The study suggests that grip span of a tool is an important factor to be considered in predicting optimal work–rest cycles for hand grip tasks, and the optimum setting of grip span of the hand-tool depends on the required task force level. That is, the optimality is relative rather than absolute. In addition, it appears that weaker subjects can work at a higher rate than stronger ones at the same relative force level.

Physiological Behaviour of Camel with Different Draught and Work-Rest Cycles in Field Operations

Camels of different age and body weights were selected randomly from a village in Bikaner District. The draught equivalent to 16, 18 and 20 % of body weight of camels were applied by using a multipurpose tool frame with tillage tools. Draught was varied by increasing/ decreasing the number of tynes and depth of operation. Physiological responses like pulse rate, respiration rate, body temperature and speed were recorded at all draught levels with three work rest cycles, namely WR,: 4h (W)- 5h (R)- 4h (W), WR2 : 3h (W)- 1h (R)- 2h (W)- 4h (R)-3h (W) and WR3 : 2h (W)- 1h (R) 2h (W)- 4h (R)- 2h (W)- 1h (R)- 2h (W). Maximum increase in physiological responses was observed with work rest cycle WR3 The increase in pulse rate, respiration rate and body temperature were 35 to 62 beats/min, 10 to 18 breaths/min and 37.5 to 39.2°C respectively with WR, while these were found minimum with WR3 in the range of 33 to 51 beats! min, 8 to 12 breaths/min and 37.3 to 38.4°C respectively. On the basis of physiological responses work rest cycles WR3 was found better as compared to other work rest cycles.

Impact of Stretch-Shortening Cycle Rest Interval on in Vivo Muscle Performance

Overuse and overtraining models have implicated both metabolic and mechanical disturbances as contributors to muscle damage and performance decrement but have produced equivocal results. The purpose of the present study was to investigate the impact of rest interval between sets of stretch-shortening cycles (SSC) on static and dynamic muscle performance Animals were randomly assigned to groups (N = 8 per group) of 10-s, 1-min, or 5-min rest between sets of isometric contractions (10-s, 1-min, or 5-min CON), or SSC (10-s, 1-min, or 5-min INJ). The dorsiflexor muscles were exposed in vivo to either seven sets of 10 SSC (500 degrees . s) or seven sets of isometric contractions. Performance was characterized by isometric exertions and positive, negative, and net work, at pretest, during the sets of SSC, and 48 h postexposure The isometric force at 48 h after the 10-s and 5-min INJ groups were statistically different from the 1-min group (P < 0.05), whereas there was no difference in the CON groups. Negative work of the INJ groups were statistically lower at 48 h than pretest values (P < 0.05), whereas there was no change in positive work. Of the real-time parameters, there was a difference in minimum force and positive work (P < 0.05) with treatment with the 10-s INJ group being most affected. SSC conducted at shorter work-rest cycles resulted in a more profound isometric force decrement 48 h postexposure, and in real-time changes in isometric prestretch force and positive work. These results indicate that short rest intervals between athletic or vocational tasks of heightened physical exertion (i.e., high intensity) may adversely affect performance and increase injury susceptibility.