A comparison between intermittent and constant wheelchair propulsion strategies

The purpose of this study was to investigate the effect of different synchronous push strategies on physiological parameters and temporal timing characteristics. Eight novice male able-bodied participants completed four counter-balanced conditions: two push strategies (constant pushing) and intermittent pushing (INT) at two push frequencies (40 and 70 pushes/min) at 27 W. The ANOVA main effects for frequency indicated that regardless of push strategy, oxygen cost and mechanical efficiency increased with an increase in push frequency (p < 0.01). The INT40 strategy resulted in the lowest heart rate (115 ± 19 beats/min). With increased frequency the push angle was reduced (91° vs. 78° respectively) and the push was initiated at a more anterior position of the wheel (p < 0.05). The results suggest that regardless of push strategy, the over-riding factor that influences both the physiological and timing parameters measured was push frequency.     

Force, frequency and gripping alter upper extremity muscle activity during a cyclic push task

Factors, such as high repetition, high force and gripping play a role in the development of upper extremity work-related musculoskeletal disorders. The purpose of this study was to systematically examine the effects of push load and frequency on muscle activity with and without concurrent gripping. A total of 10 men and 10 women performed a cyclic bimanual pushing task. All combinations of three push loads (1 kg, 2 kg, 4 kg), three frequencies (4/min, 8/min, 16/min) and two grip conditions (no required grip and 30% of maximum grip force) were performed in randomised order. The muscle activity of the upper arm and shoulder complex reflected both frequency and load, often with significant interactions, thus may be better described by workload, the product of force and frequency. In the forearm, muscle activities were generally low but adding a submaximal grip superseded the effects of push load, with the activity reflecting frequency and grip. PRACTITIONER SUMMARY: Force and frequency are important risk factors for upper extremity disorders. We found that upper extremity muscle activity responds to workload (force × frequency) in a complex way which may be superseded if a grip is present. This electromyographic study provides physiological insights to muscular loading as basis for a variety of workplace disorders.     

Psychophysically determined forces of dynamic pushing for female industrial workers: Comparison of two apparatuses

Using psychophysics, the maximum acceptable forces for pushing have been previously developed using a magnetic particle brake (MPB) treadmill at the Liberty Mutual Research Institute for Safety. The objective of this study was to investigate the reproducibility of maximum acceptable initial and sustained forces while performing a pushing task at a frequency of 1 min⁻¹ both on a MPB treadmill and on a high-inertia pushcart. This is important because our pushing guidelines are used extensively as a ergonomic redesign strategy and we would like the information to be as applicable as possible to cart pushing. On two separate days, nineteen female industrial workers performed a 40-min MPB treadmill pushing task and a 2-hr pushcart task, in the context of a larger experiment. During pushing, the subjects were asked to select a workload they could sustain for 8 h without “straining themselves or without becoming unusually tired, weakened, overheated or out of breath.” The results demonstrated that maximum acceptable initial and sustained forces of pushing determined on the high inertia pushcart were 0.8% and 2.5% lower than the MPB treadmill. The results also show that the maximum acceptable sustained force of the MPB treadmill task was 0.5% higher than the maximum acceptable sustained force of Snook and Ciriello (1991). Overall, the findings confirm that the existing pushing data developed by the Liberty Mutual Research Institute for Safety still provides an accurate estimate of maximal acceptable forces for the selected combination of distance and frequency of push for female industrial workers.     

Spatial dependency of shoulder muscle demands in horizontal pushing and pulling

Pushing and pulling account for nearly half of all manual material handling tasks. The purpose of this investigation was to develop a 3-D spatial muscle activity map for the right upper extremity during pushing and pulling tasks. Nineteen males performed 140 ramped directional hand exertions (70 push; 70 pull) at locations along three axes aligned with the anatomical planes. Electromyography (EMG) of 14 sites on the right upper extremity was recorded. Two directional 3-way repeated measures ANOVAs assessed the influence of hand position on EMG. Hand position and exertion direction influenced total and individual muscle demand. During pulling exertions, all three hand location parameters influenced total muscle activity (p < 0.001) and similarly in pushing exertions (p < 0.002), though less pronounced than in pulling. Data were used to create equations to predict the muscle activity of untested hand locations for novel work design scenarios.     

Energy cost of pushing a wheelchair on various gradients in young men

This study investigated the effects of pushing a wheelchair on the energy cost of walking (C_w; defined as the ratio of the steady-state oxygen consumption to the walking speed) and economical speed (ES) on the level and ±5% gradients. Eight pairs were formed from twelve young men to minimize variation in body weight between pushing and assisted participants. The State Trait Anxiety Inventory (STAI) test was conducted to evaluate wheelchair occupants' anxiety before and after each trial. The C_w values were significantly higher when pushing a wheelchair on the uphill gradient at more than 45 m/min. ES was significantly lower when pushing a wheelchair on the level (−8.5%) and uphill gradient (−9.1%), but not on the downhill gradient (−0.3%). Individual ES was also estimated using the concept of “Froude number”, and “estimated” ES was significantly correlated with “measured” ES even when pushing a wheelchair on the downhill gradient. The STAI score was not significantly increased except at 105 m/min, regardless of gradient. These results indicated that the fastest walking speed without an enhancement in wheelchair occupants' anxiety corresponds to ES when pushing a wheelchair with a seated occupant on all gradients, at least in young fit men.     

Effectiveness of rest pauses and cooling in alleviation of heat stress during simulated fire-fighting activity

This study examined whether cooling a fire-fighter with a high velocity fan, during 10 min rest pauses between, and following, 10 min work periods, decreases heat stress during repetitive fire-fighting activity. Twelve professional fire-fighters (mean age 31.8 +/- 6.7 years) completed two, 40 min work/recovery trials in an environmental chamber at 40 degrees C and 70% relative humidity (RH). One trial was termed an enhanced recovery (ER) trial and the other was termed a normal recovery (NR) trial. In both conditions subjects wore full protective clothing and breathing apparatus during the work. In the ER trial a subject removed his protective coat and sat in front of a fan during each recovery period. In the NR trial a subject merely unbuckled his coat and was not cooled by a fan during either recovery period. The group mean metabolic cost (VO2), and the exercise and recovery heart rates were significantly lower (p < or = 0.05) during the ER trial than in the NR condition. Group mean rectal temperature increased by 1.5 degrees C in the NR trial but by only 0.8 degree C during the ER trial. The latter group's more effective cooling indicates the potential of fan cooling to reduce physiological strain and decrease the risk of heat exhaustion during repetitive fire-fighting activity. The results suggest that a fire-fighter's short 10 min exposure to heavy work in a hot environment of 40 degrees C and 70% RH produces minimal heat stress in a healthy fire-fighter. However, a period of fire-fighting exposure greater than 10 min without adequate rest and cooling may lead to a significant accumulation of heat stress and fatigue during further fire-fighting activity, irrespective of physical prowess.     

Strength of shoulder during one‐handed pushing in constrained conditions

This study hypothesizes that, by isolating the influences of contact surface friction, back foot support, and forward‐leaning body posture during pushing, the magnitude of recorded strength will be a closer estimate of physical capabilities of the shoulder. The shoulder strength of twelve participants during one‐handed pushing in constrained conditions in the coronal (frontal) plane, in a range from 5 to 30 degrees, was correlated with the anthropometric measures and two anatomical parameters of the shoulder joint. The data indicated that the acceptable loads at the handle for all the participants were lower than the recommended standards. Right arm length had the highest correlation coefficient with shoulder strength among anthropometric data, and the radius of the humerus bone among anatomical parameters. The findings from this study of one‐handed pushing will be used to help modify existing physical strength standards in an effort to reduce the high frequency of recorded shoulder injuries. © 2009 Wiley Periodicals, Inc.     

Intermittent microclimate cooling during exercise-heat stress in US army chemical protective clothing

The effectiveness of intermittent, microclimate cooling for men who worked in US Army chemical protective clothing (modified mission-oriented protective posture level 3; MOPP 3) was examined. The hypothesis was that intermittent cooling on a 2 min on-off schedule using a liquid cooling garment (LCG) covering 72% of the body surface area would reduce heat strain comparably to constant cooling. Four male subjects completed three experiments at 30 degrees C, 30% relative humidity wearing the LCG under the MOPP 3 during 80 min of treadmill walking at 224 +/- 5 W . m(-2). Water temperature to the LCG was held constant at 21 degrees C. The experiments were; 1) constant cooling (CC); 2) intermittent cooling at 2-min intervals (IC); 3) no cooling (NC). Core temperature increased (1.6 +/- 0.2 degrees C) in NC, which was greater than IC (0.5 +/- 0.2 degrees C) and CC (0.5 +/- 0.3 degrees C) ( p < 0.05). Mean skin temperature was higher during NC (36.1 +/- 0.4 degrees C) than IC (33.7 +/- 0.6 degrees C) and CC (32.6 +/- 0.6 degrees C) and mean skin temperature was higher during IC than CC ( p < 0.05). Mean heart rate during NC (139 +/- 9 b . min(-1)) was greater than IC (110 +/- 10 b . min(-1)) and CC (107 +/- 9 b . min(-1)) ( p < 0.05). Cooling by conduction (K) during NC (94 +/- 4 W . m(-2)) was lower than IC (142 +/- 7 W . m(-2)) and CC (146 +/- 4 W . m(-2)) ( p < 0.05). These findings suggest that IC provided a favourable skin to LCG gradient for heat dissipation by conduction and reduced heat strain comparable to CC during exercise-heat stress in chemical protective clothing.     

The natural angle between the hand and handle and the effect of handle orientation on wrist radial/ulnar deviation during maximal push exertions

The purpose of this experiment was to quantify the natural angle between the hand and a handle, and to investigate three design factors: handle rotation, handle tilt and between-handle width on the natural angle as well as resultant wrist radial/ulnar deviation (‘RUD’) for pushing tasks. Photographs taken of the right upper limb of 31 participants (14 women and 17 men) performing maximal seated push exertions on different handles were analysed. Natural hand/handle angle and RUD were assessed. It was found that all of the three design factors significantly affected natural handle angle and wrist RUD, but participant gender did not. The natural angle between the hand and the cylindrical handle was 65 ± 7°. Wrist deviation was reduced for handles that were rotated 0° (horizontal) and at the narrow width (31 cm). Handles that were tilted forward 15° reduced radial deviation consistently (12–13°) across handle conditions.

Practitioner summary: Manual materials handling (MMH) tasks involving pushing have been related to increased risk of musculoskeletal injury. This study shows that handle orientation influences hand and wrist posture during pushing, and suggests that the design of push handles on carts and other MMH aids can be improved by adjusting their orientation to fit the natural interface between the hand and handle.     

Exercise testing in children: an alternative approach

In recent years there has been a call for new methods of evaluating the cardiorespiratory responses of children to exercise that complement their everyday exercise patterns. One potential method would be to use a sub-maximal, intermittent, pseudo-random binary sequence (PRBS) exercise test protocol to measure oxygen uptake kinetics (VO2 kinetics). Ten children of mean (SD) age 10.8 (+/- 1.5) years completed a 20 - 50 W cycle ergometer protocol of 17-min duration. An estimate of alveolar oxygen uptake (VO2) was calculated on a breath-by-breath basis. The VO2 kinetic parameters were expressed in the frequency domain as amplitude ratio and phase delay using standard Fourier techniques. Analysis was restricted to the frequency range 2.2 to 8.9 mHz. The mean (SD) amplitude ratio responses decreased from 10.33 (+/- 0.73) to 7.42 (+/- 0.99) ml min(-1) W(-1) and the mean phase delay increased from -26.78 degrees (+/- 6.37 degrees) to -81.93 degrees (+/- 10.45 degrees) over the frequency range 2.2-8.9 mHz. Significant correlations (p < 0.05) were found between chronological age and amplitude ratio (r = 0.68 and 0.62), and chronological age and phase delay (r = -0.62 and -0.69) at the frequencies of 2.2 and 4.4 mHz, respectively. No significant correlations were found between VO2 kinetics and stature or VO2 kinetics and body mass. The observations demonstrated the use of the PRBS technique to measure VO2 kinetics in the frequency domain in children. This approach may be a useful addition to the tests that are used to quantify the oxygen uptake responses to exercise in children.     

Effects of wearing aircrew protective clothing on physiological and cognitive responses under various ambient conditions

Heat stress can be a significant problem for pilots wearing protective clothing during flights, because they provide extra insulation which prevents evaporative heat loss. Heat stress can influence human cognitive activity, which might be critical in the flying situation, requiring efficient and error-free performance. This study investigated the effect of wearing protective clothing under various ambient conditions on physiological and cognitive performance. On several occasions, eight subjects were exposed for 3 h to three different environmental conditions; 0 degrees C at 80% RH, 23 degrees C at 63% RH and 40 degrees C at 19% RH. The subjects were equipped with thermistors, dressed as they normally do for flights (including helmet, two layers of underwear and an uninsulated survival suit). During three separate exposures the subjects carried out two cognitive performance tests (Vigilance test and DG test). Performance was scored as correct, incorrect, missed reaction and reaction time. Skin temperature, deep body temperature, heart rate, oxygen consumption, temperature and humidity inside the clothing, sweat loss, subjective sensation of temperature and thermal comfort were measured. Rises in rectal temperature, skin temperature, heart rate and body water loss indicated a high level of heat stress in the 40 degrees C ambient temperature condition in comparison with 0 degrees C and 23 degrees C. Performance of the DG test was unaffected by ambient temperature. However, the number of incorrect reactions in the Vigilance test was significantly higher at 40 degrees C than at 23 degrees C (p = 0.006) or 0 degrees C (p = 0.03). The effect on Vigilance performance correlated with changes in deep-body temperature, and this is in accordance with earlier studies that have demonstrated that cognitive performance is virtually unaffected unless environmental conditions are sufficient to change deep body temperature.     

Gender differences in exerted forces and physiological load during pushing and pulling of wheeled cages by postal workers

The aim was to determine gender differences regarding exerted forces and physiological load during push/pull tasks simulating the daily working practice of postal workers. Eight female and four male workers handled four-wheeled cages under eight conditions corresponding to the cage weight (130, 250, 400, 550 kg) and the direction of force exertion (pushing, pulling). For each of the five dependent variables, average force, initial force, ending force, oxygen uptake and heart rate, two analyses of variance with repeated measurements were performed, i.e. with and without correction for the worker's body weight, body height and maximum capacity regarding the dependent variable. Exerted forces and physiological load were high for the cages weighing 400 and 550 kg. Gender differences were significant for all dependent variables (p = 0.030-0.000). When the personal factors were included in the model, male workers exerted significantly higher average forces and ending forces than their females, while differences regarding initial forces and physiological load were not significant. However, none of the personal factors were significantly related to any of the dependent variables. It is concluded that gender differences in exerted forces were not caused by differences in anthropometry and maximum capacity, but due to application of different work methods by women in order to balance work demands and work ability.     

Influence of environmental temperature on duathlon performance

The aim of this study was to evaluate the physiological, metabolic and performance responses to duathlon performance under a range of ambient temperatures. Ten male recreational athletes performed three self-paced duathlon time trials consisting of a 5 km run (R1), a 30 km cycle and a 5 km run (R2) at 10 degrees C, 20 degrees C and 30 degrees C and a relative humidity of 50%. Performance times, heart rate (HR), rating of perceived exertion (RPE), core temperature (Tc) and skin temperature (Tsk) were measured every kilometre. Carbohydrate and fat oxidation rates were calculated via expired gas analysis at the first and fourth kilometres during both running stages. Blood samples were taken before and after exercise for the determination of prolactin concentration.Overall performance was significantly faster at 10 degrees C (100.76+/-5.32 min) than at 30 degrees C (105.38 +/- 4.28 min). Significantly higher Tc was noted in the 30 degrees C trial than in the 10 degrees C trial, with concomitant elevations in prolactin after exercise (19.88 +/- 6.48 ng/ml at 30 degrees C; 13.10 +/- 8.75 ng/ml at 10 degrees C). The rates of carbohydrate oxidation did not differ between conditions, although fat oxidation rates were highest at 10 degrees C.Elevated ambient temperature has a negative effect on duathlon performance. This effect may be reflected in increased Tc and prolactin concentration.     

Forearm posture and grip effects during push and pull tasks

Direction of loading and performance of multiple tasks have been shown to elevate muscle activity in the upper extremity. The purpose of this study was to evaluate the effects of gripping on muscle activity and applied force during pushing and pulling tasks with three forearm postures. Twelve volunteers performed five hand-based tasks in supinated, neutral and pronated forearm postures with the elbow at 90° and upper arm vertical. All tasks were performed with the right (dominant) hand and included hand grip alone, push and pull with and without hand grip. Surface EMG from eight upper extremity muscles, hand grip force, tri-axial push and pull forces and wrist angles were recorded during the 10 s trials. The addition of a pull force to hand grip elevated activity in all forearm muscles (all p < 0.017). During all push with grip tasks, forearm extensor muscle activity tended to increase when compared with grip only while flexor activity tended to decrease. Forearm extensor muscle activity was higher with the forearm pronated compared with neutral and supinated postures during most isolated grip tasks and push or pull with grip tasks (all p < 0.017). When the grip dynamometer was rotated so that the push and pull forces could act to assist in creating grip force, forearm muscle activity generally decreased. These results provide strategies for reducing forearm muscle loading in the workplace.

Statement of Relevance: Tools and tasks designed to take advantage of coupling grip with push or pull actions may be beneficial in reducing stress and injury in the muscles of the forearm. These factors should be considered in assessing the workplace in terms of acute and cumulative loading.     

Maximum acceptable weights for asymmetric lifting of Chinese females

This study used the psychophysical approach to evaluate the effects of asymmetric lifting on the maximum acceptable weight of lift (MAWL) and the resulting heart rate, oxygen uptake and rating of perceived exertion (RPE). A randomized complete block factorial design was employed. Twelve female college students lifted weights at three different lifting frequencies (one-time maximum, 1 and 4 lifts/min) in the sagittal plane and at three different asymmetric angles (30 degrees, 60 degrees, and 90 degrees ) from the floor to a 68-cm height pallet. This lifting experiment was conducted for a 1-h work period using a free-style lifting technique. The MAWLs for asymmetric lifting were significantly lower than those for symmetric lifting in the sagittal plane. The MAWL decreased with the increase in the angle of asymmetry. However, the heart rate, oxygen uptake and RPE remained unchanged. Though the MAWL decreased significantly with lifting frequency, both the physiological costs (heart rate and oxygen uptake) and rating of perceived exertion increased with the increase in lift frequency. The most stressed body part was the arm. Lifting frequency had no significant effect on the percentage decrease in MAWL from the sagittal plane values. On average, decreases of 5%, 9% and 14% for MAWL at 30 degrees, 60 degrees and 90 degrees asymmetric lifting, respectively, were revealed. This result was in agreement with the findings of Chinese males studied by Wu [Int. J. Ind. Ergonom. 25 (2000) 675]. The percentage decrease in MAWL with twisting angle for the Chinese participants was somewhat lower than those for Occidental participants. In addition, even though there was an increase in heart rate and RPE with the increase in the symmetrical lift angle for Occidental participants, it was different from the Chinese participants. Lastly, the 1991 NIOSH equation asymmetry multiplier is more conservative in comparison with the results of the present study.     

Wheelchair pushing and turning: lumbar spine and shoulder loads and recommended limits

Abstract

The objective of this study was to determine how simulated manual wheelchair pushing influences biomechanical loading to the lumbar spine and shoulders. Sixty-two subjects performed simulated wheelchair pushing and turning in a laboratory. An electromyography-assisted biomechanical model was used to estimate spinal loads. Moments at the shoulder joint, external hand forces and net turning torque were also assessed. Multiple linear regression techniques were employed to develop biomechanically based wheelchair pushing guidelines relating resultant hand force or net torque to spinal load. Male subjects experienced significantly greater spinal loading (p < 0.01), and spine loads were also increased for wheelchair turning compared to straight wheelchair pushing (p < 0.001). Biomechanically determined maximum acceptable resultant hand forces were 17–18% lower than psychophysically determined limits. We conclude that manual wheelchair pushing and turning can pose biomechanical risk to the lumbar spine and shoulders. Psychophysically determined maximum acceptable push forces do not appear to be protective enough of this biomechanical risk.

Practitioner Summary: This laboratory study investigated biomechanical risk to the low back and shoulders during simulated wheelchair pushing. Manual wheelchair pushing posed biomechanical risk to the lumbar spine (in compression and A/P shear) and to the shoulders. Biomechanically determined wheelchair pushing thresholds are presented and are more protective than the closest psychophysically determined equivalents.     

Effects of handle orientation and between-handle distance on bi-manual isometric push strength

Hand-handle interface is seldom considered in contemporary upper limb biomechanical analyses of pushing and pulling strength. A laboratory study was designed to examine if handle rotation in the frontal plane (0°-horizontal, 45°, and 90°-vertical), anterior tilt (0°-parallel to the frontal plane, and 15°), and distance between two handles (31 and 48.6 cm) affect pushing strength and subjective rating of handle preference. A special testing station was constructed to elicit upper limb push exertions that involved minimal contribution of the torso and legs. Within the station, four load cells were used to measure the horizontal (forward pushing) and vertical components of the pushing forces. Thirty-one participants performed seated bi-manual pushing strength tests. Comparing to the reference handle configuration (horizontal, straight, and a 31-cm between-handle distance), the 45°-rotated and tilted handles with a 31-cm between-handle distance allowed 6.7% more pushing output, while the horizontal and tilted handles with a 31-cm between-handle distance resulted in 2.8% less. Subjective preference was correlated with normalized pushing strength (r=0.89). Tilted handles, at 45°-rotated and vertical positions received highest subjective ratings of preference among all handle configurations. Men exerted greater pushing strength with the 48.6-cm handle distance while women's capacity was greatest with the 31-cm distance. The results demonstrated that handle rotation and tilt angles affected pushing strength and should be taken into consideration when evaluating or designing pushing tasks.     

Influence of carrying heavy loads on soldiers' posture, movements and gait

Military personnel are required to carry heavy loads whilst marching; this load carriage represents a substantial component of training and combat. Studies in the literature mainly concentrate on physiological effects, with few biomechanical studies of military load carriage systems (LCS). This study examines changes in gait and posture caused by increasing load carriage in military LCS. The four conditions used during this study were control (including rifle, boots and helmet carriage, totalling 8 kg), webbing (weighing 8 kg), backpack (24 kg) and a light antitank weapon (LAW; 10 kg), resulting in an incremental increase in load carried from 8, 16, 40 to 50 kg. A total of 20 male soldiers were evaluated in the sagittal plane using a 3-D motion analysis system. Measurements of ankle, knee, femur, trunk and craniovertebral angles and spatiotemporal parameters were made during self-paced walking. Results showed spatiotemporal changes were unrelated to angular changes, perhaps a consequence of military training. Knee and femur ranges of motion (control, 21.1 degrees +/- 3.0 and 33.9 degrees +/- 7.1 respectively) increased (p < 0.05) with load (LAW, 25.5 degrees +/- 2.3 and 37.8 degrees +/- 1.5 respectively). The trunk flexed significantly further forward, confirming results from previous studies. In addition, the craniovertebral angle decreased (p < 0.001) indicating a more forward position of the head with load. It is concluded that the head functions in concert with the trunk to counterbalance load. The higher muscular tensions necessary to sustain these changes have been associated with injury, muscle strain and joint problems.     

Dynamic pushing on three frictional surfaces: maximum acceptable forces,cardiopulmonary and calf muscle metabolic responses in healthy men

Pushing is an important materials handling activity in many occupations; however, pushing-related physiological investigations are still in infancy. The purpose was to evaluate maximum acceptable forces and physiological responses while pushing on: treadmill (TREAD); plywood floor (PLY); and Teflon floor (TEF). Acceptable forces, cardiopulmonary and calf muscle oxygenation and blood volume responses were collected simultaneously while 12 men (age 39 ± 13 years; height 178 ± 6 cm; and body mass 91.5 ± 16 kg) pushed for 2 h on each surface at their psychophysical workload. Participants selected higher forces on the PLY, resulting in higher pulmonary oxygen uptake compared to that of TEF (by ～9%) and TREAD (by ～18%). Pushing on the TEF demonstrated 50–56% lower blood volume changes and 1.5–1.8 times more oxygenation-force ratio than that for other surfaces. It is concluded that, to avoid a potential slip, participants were conservative in selecting acceptable forces to push on the slippery TEF. Part of this compensatory strategy on the TEF resulted in less muscle activity and, therefore, less demand for oxygen delivery to the calf muscle than for other surfaces. The present findings of significant force- and physiological-related differences in treadmill vs. high inertia pushcart clearly demonstrate that pushing experiments are essential to evaluate functional abilities of the workers.     

Physiological responses of fire-fighter instructors during training exercises

Thirteen male instructors were monitored during a total of 44 live fire training exercises (ambient temperature 74+/-42 degrees C). Exposure time during the 'Hot Fire' (HF), 'Fire Behaviour' and 'Fire Attack' exercises was 33.0+/-7.9 min (n=30); 26.3+/-5.5 min (n=6); and 7.3+/-2.6 min (n=8) respectively. At the end of the exercises, mean core temperature (t(core)) was 38.5+/-0.9 degrees C (n=32), however eight instructors had a t(core) above 39 degrees C. The mean maximum temperature under the fire hood was 41.2+/-4.6 degrees C (n=40). Mean maximum heart rate (HR) was 138+/-26 bpm (n=34) however, in five exercises, HR exceeded 90% of the instructors' HR reserve. Mean fluid deficit was 0.62+/-0.6 l (n=30) at the end of the HF exercises, the maximum being 2.54 l. Four instructors doubted their ability to perform a rescue at the end of the exercise. The energy cost of performing simulated rescues of a 50 kg dummy in the cool was investigated in a pilot study. Mean HR during the rescues was 79+/-7% of the instructors' HR reserve and it was estimated that this could increase t(core) by 0.4 to 0.6 degrees C. The physiological responses to the fire-fighting exercises varied considerably and reflected the differences in work performed and external heat load. The results obtained from some individuals give cause for concern, and signs of heat strain were seen in at least two individuals.