Effect of load position on physiological and perceptual responses during load carriage with an internal frame backpack

The purpose of this study was to determine the effect of load position in an internal frame backpack on physiological and perceptual variables. Ten female participants walked on a level treadmill for 10?min carrying 25% of their body weight in a high, central, or low position. The variables measured included oxygen consumption (VO₂), heart rate (HR), respiratory exchange ratio (R), respiratory rate (RR), minute ventilation (VE), and rating of perceived exertion (RPE). VO₂, VE, and RPE were significantly lower in the high position (18.6?±?2.3?ml/kg/min, 31.7?±?5.0?l/min, 2.8?±?0.8, respectively) compared to the low position (22.2?±?3.0?ml/kg/min, 38.6?±?7.5?l/min, 3.7?±?1.0, respectively). HR, R, and RR did not change significantly as the load was moved from the high (129.8?±?16.8, 0.89?±?0.06, 30.3?±?4.2, respectively) to the low position (136.0?±?25.3, 0.92?±?0.04, 33.8?±?5.2, respectively). The results of this study suggest that load placement is an important factor in the physiological and perceptual responses to load carriage, and that packing heavy items high in the backpack may be the most energy efficient method of carrying a load on the back.     

Metabolic and cardiovascular responses to exercise with caffeine

The effect of caffeine on circulation and metabolism was studied during a discontinuous maximal oxygen uptake (VO₂ max) test on a bicycle ergometer. Eight male subjects were chosen for their minimal use of caffeine of which six normally did not ingest caffeinated beverages. Two caffeinated and two decaffeinated (control) trials were administered to each subject following double-blind and counterbalanced testing procedures. One hour before exercise, subjects ingested decaffeinated coffee with or without 350 mg of caffeine anhydrous added. Cardiac output (Q) was measured by a C0₂ rebreathing technique. Compared to control trials, caffeine increased the VO₂ max by an average of 140ml min?¹ (p <0-0·5)l. In addition, during caffeine trials, the average maximal heart rate (HR max) was elevated by 5 beats min^?1 (p<0·01). There were no other statistically significant changes in metabolic (VO₂ and R) and cardiovascular (Q, HR, SV and (a-v) 0₂ diff) variables during either submaximal or maximal exercise. Performance, as measured by total exercise time on the VO₂ max test, was not significantly different (p>0·05). It was concluded that caffeine has a small physiological but a statistically significant effect on VQ₂ max and HR max. During submaximal exercise, caffeine did not significantly effect the cardiovascular system.     

Optimization of load carriage at desert environment

The present study was undertaken to assess the effect of different magnitudes of load on physiological responses of soldiers in desert terrain and also to estimate an optimum load that can be carried comfortably at specific walking speed. Nine infantry male soldiers of SHAPE-I standard with age 25.22 ± 1.02 years, height 170.78 ± 0.95 cm and weight 66.56 ± 2.38 Kg volunteered in this study. All participants were marched at speed of 6.13 ± 0.40 Km h⁻¹ in desert terrain with 10.7 Kg (16.07% BW) and 21.4 Kg (32.15% BW) load and without load. Heart rate (HR), respiratory frequency (RF), oxygen consumption (VO₂), minute ventilation (VE), energy expenditure (EE) and relative work load (RWL) were recorded by using K4b² system. During carrying of 10.7 Kg load HR, VO₂, EE, RF, VE and RWL (%VO₂max) were increased 13.88, 18.20, 20.16, 7.86, 19.30 and 23.71% respectively in comparison to no load. Similarly, during 21.4 Kg load, physiological responses viz.; HR, VO₂, EE, RF, VE and RWL (%VO₂max) were increased 24.84, 36.98, 33.68, 21.24, 38.25 and 40.64% respectively in comparison to no load. The observation of this study stated that 6.27 Kg (9.42%BW, 50% RWL), 13.7 Kg (20.58%BW, 60%RWL) and 24.86 Kg (37.35%BW, 75% RWL) can be recommended for 8 h, 2 h and for 30 min respectively.Relevance to industryMost of the countries do not have their own database for load carriage in specific environmental conditions. Result of this study will be helpful to the similar kind of population working under specified conditions.     

Cardiac frequency throughout a working shift in coal miners

Despite the ever-increasing mechanization of industrial activities, coal mining still remains a physically demanding occupation as it is not always possible to extensively mechanize the extraction process. To estimate the physical effort necessary to sustain coal mining activities in a poorly-mechanized mine, cardiac frequency (?/_c) was measured throughout the working shift with a Sport-Tester PE3000 (Polar Electro OY. Finland) in a representative sample of 73 Asturian miners engaged in a full spectrum of underground work. The mean ± SD of the overall?/_c values measured in miners working at the coal face (Group 1, 33 subjects, mean age 32·7 years, age range 21–48 years R was 106·5 ± 18·2 beats min^?1. In other miners (Group 2, 40 subjects, mean age 34·6 years, age range 23–48 years) corresponding figures were 1031 ±177 beats-min_?1 (p<0·05). Subjects' average working shift?_c Lbeats. Min^?1) was not related to age, measured (treadmill) VO₂ max nor VO₂ max.kg body weight^?1, while average working-shift? _c (%? _c max) was weakly related to age (r = 0·396, p<0·05), VO₂ max (r equals; 0·295, p < 0·05) and VO₂max.kg body weight^?1 (r= 0·352, p<0·05). Working-shift peak? _c (beats · min^?1) was negatively related to age (r = 0·334, p < 0·05). Our study has provided the distribution of the overall ? _c values likely to be found in subjects working in these poorly-mechanized mines. However, average working-shift ? _c differs considerably from subject to subject and is largely unpredictable.     

Oxygen uptake and muscle activity limitations during stepping on a stair machine at three different climbing speeds

Abstract

This laboratory study examined human stair ascending capacity and constraining factors including legs’ local muscle fatigue (LMF) and cardiorespiratory capacity. Twenty-five healthy volunteers, with mean age 35.3 years, maximal oxygen uptake (VO_2max) of 46.7?mL·min^?1·kg^?1 and maximal heart rate (HR) of 190 bpm, ascended on a stair machine at 60 and 75% (3?min each) and 90% of VO_2max (5?min or until exhaustion). The VO₂, maximal heart rate (HR_max) and electromyography (EMG) of the leg muscles were measured. The average VO_2highest reached 43.9?mL·min^?1·kg^?1, and HR_highest peaked at 185 bpm at 90% of VO_2max step rate (SR). EMG amplitudes significantly increased at all three levels, p?<?.05, and median frequencies decreased mostly at 90% of VO_2max SR evidencing leg LMF. Muscle activity interpretation squares were developed and effectively used to observe changes over time, confirming LMF. The combined effects of LMF and cardiorespiratory constraints reduced ascending tolerance and constrained the duration to 4.32?min.

Practitioner Summary: To expedite ascending evacuation from high-rise buildings and deep underground structures, it is necessary to consider human physical load. This study investigated the limiting physiological factors and muscle activity rate changes (MARC) used in the muscle activity interpretation squares (MAIS) to evaluate leg local muscle fatigue (LMF). LMF and cardiorespiratory capacity significantly constrain human stair ascending capacities at high, constant step rates.     

Effects of activity-rest schedules on physiological strain and spinal load in hospital-based porters

Workers in physically demanding occupations require rest breaks to recover from physiological stress and biomechanical loading. Physiological stress can increase the risk of developing musculoskeletal disorders and repeated loading of the spine may increase the potential for incurring back pain. The aim of the study was to assess the impact of an altered activity-rest schedule on physiological and spinal loading in hospital-based porters. An existing 4-h activity-rest schedule was obtained from observations on eight male porters. This schedule formed the normal trial, which included two 5- and one 15-min breaks. An alternative 4-h schedule was proposed (experimental condition) that had two breaks each of 12.5 min. It was hypothesized that the experimental trial is more effective in promoting recovery from physiological strain and spinal shrinkage than the normal trial, due to the 5-min breaks being insufficient to allow physiological variables to return to resting levels or the intervertebral discs to reabsorb fluid. Ten males performed both test conditions and oxygen uptake VO₂, heart rate, minute ventilation VE, perceived exertion and spinal shrinkage were recorded. There were no significant differences in any of the measured variables between the two trials (p >0.05). Median heart rates were 78 (range 71–93) and 82 (71–90) beats.min ^{- 1} for the normal trial and the experimental trial respectively, indicating that the activity was of low intensity. The light intensity was corroborated by the oxygen uptakes (0.75, range 0.65-0.94 l.min ^{- 1}. Spinal shrinkage occurred to the same extent in the two trials (2.12±3.16 mm and 2.88±2.92 mm in the normal trial and the experimental trial respectively). Varying the length and positioning of the rest breaks did not significantly affect the physiological responses or magnitude of spinal shrinkage between the two trials. More physically demanding work than the porters' schedule should induce greater physiological fatigue and spinal shrinkage. The ratio between activity and rest breaks would then become more important.     

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°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°C (n?=?32), however eight instructors had a t_core above 39°C. The mean maximum temperature under the fire hood was 41.2?±?4.6°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°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.     

Increasing surfboard volume reduces energy expenditure during paddling

Abstract

The purpose of this study was to investigate how altering surfboard volume (BV) affects energy expenditure during paddling. Twenty surfers paddled in a swim flume on five surfboards in random order twice. All surfboards varied only in thickness and ranged in BV from 28.4 to 37.4 L. Measurements of heart rate (HR), oxygen consumption (VO₂), pitch angle, roll angle and paddling cadence were measured. VO₂ and HR significantly decreased on thicker boards [VO₂: r = ?0.984, p = 0.003; HR: r = ?0.972, p = 0.006]. There was also a significant decrease in pitch and roll angles on thicker boards [Pitch: r = ?0.995, p < 0.001; Roll: r = ?0.911, p = 0.031]. Results from this study suggest that increasing BV reduces the metabolic cost of paddling as a result of lower pitch and roll angles, thus providing mechanical evidence for increased paddling efficiency on surfboards with more volume.

Practioner Summary: This study investigated the impact of surfboard volume on energy expenditure during paddling. Results from this study suggest that increasing surfboard volume reduces the metabolic cost of paddling as a result of lower pitch and roll angles, thus providing mechanical evidence for increased paddling efficiency on surfboards with more volume.     

Metabolic,cardiovascular and spinal strain of a representative fuel replenishment task

The metabolic, cardiovascular and spinal strain of a representative fuel replenishment task for a tank crew were assessed using nine military subjects wearing coveralls in a comfortable ambient climate. The task involved lifting 5 gal jerry cans (weighing 23·4?kg) from the ground to a height representing a tank deck (1·676 m) at a rate of two lifts per minute for 15 min. Oxygen uptake ([Vdot]O₂), minute ventilation ([Vdot]E), heart rate (HR) and intra-abdominal pressure (IAP) were monitored continuously. After 15 min of lifting the mean [Vdot]O₂ was 0·821 min^?1 (S.D. 0·18). This was 27% of the predicted [Vdot]O₂ max. The mean [Vdot]E was 21·81 min^?1 (S.D.4·1) and the HR was 111·3 beats min^?1 (S.D. 17·8). The mean peak IAP was 105·6?mmHg, with 56% of the peak IAPs exceeding 90?Hg. The mean intrasubject coefficient of variation was 10·7% (range 7·2–24·2). In a separate series of 20 consecutive bimanual straight arm vertical lifts of 10?kg at 15 s intervals, the mean intrasubject COV% was 7·2% (range 3·2–11·2%). The replenishment task was considered acceptable in terms of the metabolic and cardiovascular strain. In terms of spinal strain, there may be an unacceptable risk of back injury if the task was normally undertaken as part of a soldier's full-time occupation over many years     

Cardiorespiratory and thermoregulatory response of working in fire-fighter protective clothing in a temperate environment

The cardiorespiratory and thermal responses of two intensities of treadmill exercise were compared for brief periods (12 min) in fire ensemble (FE) but without self contained breathing apparatus, and sports ensemble (SE), in a temperature environment. A further experiment explored the responses of subjects exercising in FE over a prolonged period (60 min). Eighteen male firefighters wearing either FE or SE walked on a level treadmill for 6 min at 5 km.h^-1 increasing to 7 km.h^-1 for 6 min. Following a recovery interval of 1 h, the exercise protocol was repeated in the second ensemble; the order of ensemble was balanced. Heart rate (HR), rectal temperature (T_re ), VO _2max and rating of perceived exertion (RPE) were monitored continuously under both ensembles. At 7 km.h^-1, VO ₂ was significantly higher (p<0.05) in FE (36.1 and 39.9 ml.kg^-1.min^-1) than in SE and represented 74% V _{O2 max}. There were no changes T _re. In experiment 2, following a rest interval of at least 36 h, eight subjects in FE walked on the treadmill at 6 km.h ^-1 (gradient 10%) for 60 min also in temperate conditions, where HR, T _re and R PE were recorded at 10-min intervals. During the 60-min exercise in FE, HR reached 161 beats.min ^-1 and T _re increased to 38.38°C. Despite considerable subject discomfort, T _re remained below dangerous levels (38.48°C). When R PE were compared with a physiological strain index (PSI) calculated from T _re and HR data over 60 min, there was no significant difference (p <0.05) with a correlation coefficient (r) of 0.98. The results suggest that R PE and PSI are closely related when exercise is sufficiently prolonged or intense to elevate T _re and HR in fire-fighters wearing FE in temperate conditions. If further investigation confirms this relationship for hot humid conditions in which fire-fighters operate, then with training, it may provide individuals with a valid measure of dangerous levels of perceived heat strain.     

The energy demands of portable gas analysis system carriage during walking and running

The aim of this study was to evaluate the carriage of a portable gas analyser during prolonged treadmill exercise at a variety of speeds. Ten male participants completed six trials at different speeds (4, 8 and 12 km h^? 1) for 40 min whilst wearing the analyser (P) or where the analyser was externally supported (L). Throughout each trial, respiratory gases, heart rate (HR), perceptions of effort and energy expenditure (EE) were measured. Significantly higher EE occurred during P12 (p = 0.01) than during L12 (855.3 ± 104.3; CI = 780.7–930.0 and 801.5 ± 82.2 kcal; CI = 742.7–860.3 kcal, respectively), but not at the other speeds; despite this, perceptions of effort and HR responses were unaffected. This additional EE is likely caused by alterations to posture which increase oxygen demand. The use of such systems is unlikely to affect low-intensity tasks, but researchers should use caution when interpreting data, particularly when exercise duration exceeds 30 min and laboratory-based analysers should be used where possible.     

Muscular,cardiorespiratory and thermal strain of mast and pole workers

This field study evaluated the level of muscular, cardiorespiratory and thermal strain of mast and pole workers. We measured the muscular strain using electromyography (EMG), expressed as a percentage in relation to maximal EMG activity (%MEMG). Oxygen consumption (VO₂) was indirectly estimated from HR measured during work and expressed as a percentage of maximum VO₂ (%VO₂max). Skin and deep body temperatures were measured to quantify thermal strain. The highest average muscular strain was found in the wrist flexor (24 ± 1.5%MEMG) and extensor (21 ± 1.0%MEMG) muscles, exceeding the recommendation of 14%MEMG. Average cardiorespiratory strain was 48 ± 3%VO₂max. Nearly half (40%) of the participants exceeded the recommended 50%VO₂max level. The core body temperature varied between 36.8°C and 37.6°C and mean skin temperature between 28.6°C and 33.4°C indicating possible occasional superficial cooling. Both muscular and cardiorespiratory strain may pose a risk of local and systemic overloading and thus reduced work efficiency. Thermal strain remained at a tolerable level.     

John G. Fox (1931-2004)

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°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°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°C) in NC, which was greater than IC (0.5 ± 0.2°C) and CC (0.5 ± 0.3°C) ( p < 0.05). Mean skin temperature was higher during NC (36.1 ± 0.4°C) than IC (33.7 ± 0.6°C) and CC (32.6 ± 0.6°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.     

Aerobic Capacity of Steel Workers in India

Abstract

Seventy-six workers, aged 21–43 y. drawn from three major steel plants—two located in the eastern and one in the central region of India (referred to as Group A, Group B and Group C respectively)—were studied on the bicycle ergometer to determine their aerobic capacity ([Vdot]_O2max), Both the direct and indirect methods were employed, the direct one being used only in the case of the workers in Group C. The mean [Vdot]_O2max of these workers was found to be 42·6 cm³ kg^?1 with a standard error of ± 0·71 cm³ kg^?1 min^?1. The highest values were observed among the workers in Group B (mean 47·0± 1·35 (S.E.)cm³kg^?1 min^?1) who are ethnically distinct and have a high level of customary activity, and the lowest among workers in Group C (mean: 39·0±0·74(S.E.) cm³kg^?1 min^?1).

As expected, the [Vdot]_O2max was found to be correlated positively with body weight, and negatively with age in a multiple regression analysis. Furthermore, the active Group B has values for [Vdot]_O2max that are significantly higher than those for the other Groups, a difference that is not attributable to weight or age.     

Energy expenditure and clearing snow: a comparison of shovel and snow pusher

In order to assess the energy demands of manual clearing of snow, nine men did snow clearing work for 15 min with a shovel and a snow pusher. The depth of the snowcover was 400–600 mm representing a very heavy snowfall. Heart rate (HR), oxygen consumption ([Vdot]O₂), pulmonary ventilation ( [Vdot]O_E), respiratory exchange ratio (R), and rating of perceived exertion (RPE) were determined during the work tasks. HR, [Vdot]O_E, R, and RPE were not significantly different between the shovel and snow pusher. HR averaged (± SD) 141 ± 20bmin_-1 with the shovel, and 142 ± 19 beats-min_-1 with the snow pusher. [Vdot]O₂was 2·1 ± 0·41 min_-1 (63 ± 12% [Vdot]O₂max) in shovelling and 2·6 ± 0·51 min_-1 (75 ± 14% [Vdot]O₂max) in snow pushing (p< 0·001). In conclusion manual clearing of snow in conditions representing heavy snowfalls was found to be strenuous physical work, not suitable for persons with cardiac risk factors, but which may serve as a mode of physical training in healthy adults.     

The genuine short GRB 090227B and the disguised by excess GRB 090510

GRB 090227B and GRB 090510, traditionally classified as short gamma-ray Bursts (GRBs), indeed originate from different systems. For GRB 090227B we inferred a total energy of the e ⁺ e ^? plasma \(E_{e^ + e^ - }^{tot} \) = (2.83 ± 0.15) × 10⁵³ erg, a baryon load of B = (4.1 ± 0.05) × 10^?5, and a CircumBurstMedium (CBM) average density 〈n _CBM〉 = (1.90 ± 0.20) × 10^?5 cm^?3. From these results we have assumed the progenitor of this burst to be a symmetric neutron stars (NSs) merger with masses m = 1.34 M_⊙, radii R = 12.24 km. GRB 090510, instead, has \(E_{e^ + e^ - }^{tot} \) = (1.10 ± 0.06) × 10⁵³ erg, B = (1.45 ± 0.28) × 10^?3, implying a Lorentz factor at transparency of Γ = (6.7 ± 1.7) × 10², which are characteristic of the long GRB class, and a very high CBM density, 〈n _CBM〉 = (1.85 ± 0.14) × 10³ cm^?3. The joint effect of the high values of Γ and of 〈n _CBM〉 compresses in time and “inflates” in intensity in an extended afterglow, making appear GRB 090510 as a short burst, which we here define as “disguised short GRB by excess” occurring an overdense region with 10³ cm^?3.     

A comparison of time to exhaustion at [vdot]O2;max in elite cyclists,kayak paddlers,swimmers and runners

Abstract

A recent study has shown the reproducibility of time to exhaustion (time limit: ttime) at the lowest velocity that elicits the maximal oxygen consumption (υ[vdot]O₂ max). The same study found an inverse relationship between this time to exhaustion at υ[vdot]O₂ max and υ[vdot]O₂ max among 38 élite long-distance runners (Billat et al. 1994b). The purpose of the present study was to compare the time to exhaustion at the power output (or velocity) at [vdot]O₂ max for different values of [vdot]O₂ max, depending on the type of exercise and not only on the aerobic capacity. The time of exhaustion at υ[vdot]O₂ max (tlim) has been measured among 41 élite (national level) sportsmen: 9 cyclists, 9 kayak paddlers, 9 swimmers and 14 runners using specific ergometers. Velocity or power at [vdot]O₂ max ( υ[vdot]O₂ max) was determined by continuous incremental testing. This protocol had steps of 2 min and increments of 50 W, 30 W, 0.05ms^? and 2km^? for cyclists, kayak paddlers, swimmers and runners, respectively. One week later, dim was determined under the same conditions. After a warm-up of 10 min at 60% of their υ[vdot]O₂ max, subjects were concluded (in less than 45 s) to their υ[vdot]O₂ max and then had to sustain it as long as possible until exhaustion. Mean values of υ[vdot]O₂ max and dim were respectively equal to 419±49 W (tlim = 222 ± 91 s), 239±56W ( tlim = 376 ± 134 s), l 46±009ms^?1 ( tlim = 287± 160s) and 22.4 ±0.8kmh^?1 ( tlim = 321 ±84s), for cyclists, kayak paddlers, swimmers and runners. Time to exhaustion at υ[vdot]O₂ max was only significantly different between cycling and kayaking (ANOVA test, p<0.05). Otherwise, υ[vdot]O₂max (expressed in ml min^?1 kg^?1) was significantly different between all sports except between cycling and running (p < 0.05). In this study, time to exhaustion at υ[vdot]O₂ max was also inversely related to υ[vdot]O₂ max for die entire group of elite sportsmen (r= ?0.320, p<0.05, n = 41). The inverse relationship between υ[vdot]O₂ max and dim at υ[vdot]O₂ max has to be explained, it seems that dim depends on υ[vdot]O₂ max regardless of the type of exercise undertaken.     

Tympanic temperature and heart rate changes in firefighters during treadmill runs performed with different fireproof jackets

Six well-trained firefighters performed six treadmill runs at 70% of the velocity at VO_2max (Maximal aerobic velocity MAV = 13.26±0.3 km h^-1). A recovery time of 1 week was allowed between trials. The first session was performed by subjects wearing only shorts (i.e. no fire jacket, J0). A similar protocol was applied subsequently to test the physiological eOEects associated with the wearing of one of five different fire jackets: one leather (J1) and four textile-type jackets: VTN^TM with membrane (J2), VTN^TM without membrane (J3), Vidal^TM with Kermel^® HTA (Haute Teneur en Aramide i.e. high density in Aramide) (J4); and Rolland^TM with Kermel^® HTA (J5). All sessions were performed in a randomized order and in laboratory conditions. Exercise with the fireproof jackets resulted in higher tympanic temperature (Tty), heart rate (HR) and body mass loss (BML) changes compared to J0 (p <0.001). The magnitudes of these changes depended on the type of the jacket. Exercise in the leather jacket (J1) resulted in the highest Tty and HR, which diOEered significantly from values in all other conditions (p<0.001). The exercise-induced increases in Tty wearing jackets J3 and J5 were also significantly (p<0.05) higher than those observed with jackets J2 and J4. In conclusion, textile jackets induced less HR and Tty stresses than the leather one. The magnitude of the physiological responses induced by textile jackets were correlated to jacket weight. J2 and J4 jackets were more effective in limiting hyperthermia and any potential detrimental effect on the exercise capacity.     

The effect of aerodynamic handlebars on oxygen consumption while cycling at a constant speed

Abstract

In this study, the oxygen consumption ([Vdot]O₂) of bicycling was measured at a fixed speed (40 km·h^?1on level terrain, with normal and aerodynamic handlebars using a Douglas bag collection system. Eleven elite (USCF category I or 2) men cyclists age 24 to 40 years (X¯=28·5, SD±4·6) performed four consecutive (two with each bar in alternating order) steady state rides at 40 km· h^?1over a 4 km flat course (same direction each trial). Expired gases were collected in a 1501 Douglas bag attached to a following vehicle during the last 45 s (approx. 0·5 km) of each trial. A repeated measures analysis of variance revealed a significant (p<0·02) handlebar effect. Specifically, [Vdot]O₂was 2% lower under the aerodynamic handlebar treatment (X¯=4·26, SD±0·36 1 min^?1when compared with that of the normal handlebar treatment (X¯=4·34, SD±0·35 1 min^?1The results of this study demonstrate that the reported aerodynamic advantage of the aerodynamic handlebars produces a small but significant reduction in the [Vdot]O₂of bicycling at 40 km·h^?1     

Ergonomics International

It was the purpose of this study to examine whether replacing long pants (P) with shorts (S) would reduce the heat stress of wearing firefighting protective clothing during exercise in a warm environment. Twenty-four Toronto Firefighters were allocated to one of four groups that performed heavy (H, 4.8?km·h^?1, 5% grade), moderate (M, 4.5?km·h^?1, 2.5% grade), light (L, 4.5?km·h^?1) or very light (VL, 2.5?km·h^?1) exercise while wearing their full protective ensemble and self-contained breathing apparatus. Participants performed a familiarization trial followed by two experimental trials at 35°C and 50% relative humidity wearing either P or S under their protective overpants. Replacing P with S had no impact on the rectal temperature (T_re) or heart rate response during heavy or moderate exercise where exposure times were less than 1?h (40.8?±?5.8 and 53.5?±?9.2?min for H and M, respectively while wearing P, and 43.5?±?5.3 and 54.2?±?8.4?min, respectively while wearing S). In contrast, as exposure times were extended during lighter exercise T_re was reduced by as much as 0.4°C after 80?min of exercise while wearing S. Exposure times were significantly increased from 65.8?±?9.6 and 83.5?±?11.6?min during?L and VL, respectively while wearing P to 73.3?±?8.4 and 97.0?±?12.5?min, respectively while wearing S. It was concluded that replacing P with S under the firefighting protective clothing reduced the heat stress associated with wearing the protective ensemble and extended exposure times approximately 10?–?15% during light exercise. However, during heavier exercise where exposure times were less than 1?h replacing P with S was of little benefit.