共查询到20条相似文献,搜索用时 93 毫秒
1.
E. Kellis V. Baltzopoulos 《European journal of applied physiology and occupational physiology》1997,76(3):253-259
The purpose of this study was to examine the effects of moment of antagonistic muscle on the resultant joint moment during
isokinetic eccentric and concentric efforts of the knee extensors. Ten males performed maximum eccentric and concentric knee
extension and flexion efforts on a Biodex dynamometer at 0.52 rad · s−1 (30° · s−1). Electromyographic (EMG) activity of vastus medialis and biceps femoris (hamstrings) was also recorded. The antagonistic
moment of the hamstrings was determined by recording the integrated EMG (iEMG)/moment relationship at different levels of
muscle effort. The iEMG/moment curves were fitted using second-degree polynomials. The polynomials were then used to predict
the antagonistic moment exerted by the hamstrings from the antagonist iEMG. The antagonistic moment had a maximum of 42.92
Nm and 28.97 Nm under concentric and eccentric conditions respectively; paired t-tests indicated that this was a significant difference (P < 0.05). These results indicate that the resultant joint moment of knee extensors is the result of both agonist and antagonist
muscle activation. The greater antagonist muscle activity under concentric activation conditions may be partly responsible
for the lower resultant joint concentric moment of knee extensors compared with the corresponding eccentric activation. The
antagonist moment significantly affects comparisons between the isokinetic moments and agonist EMG and in vitro force measurements
under different testing (muscle action and angular velocity) conditions.
Accepted: 25 February 1997 相似文献
2.
Prolonged intermittent high intensity exercise impairs neuromuscular performance of the knee flexors
T. H. Mercer N. P. Gleeson S. Claridge S. Clement 《European journal of applied physiology and occupational physiology》1998,77(6):560-562
This study investigated the effect of prolonged intermittent high intensity exercise upon the isokinetic leg strength and
electromechanical delay of the knee flexors. Seven male collegiate soccer players were exposed to: (i) a prolonged intermittent
high intensity exercise task (PIHIET) which required subjects to complete a single-leg pedalling task, with the preferred
limb, (75 rpm for all constant-load portions of the task) consisting of 48 × 1.8 minute cycles of exercise, and (ii) a control
task consisting of no exercise. Pre-, mid- and post-PIHIET gravity corrected indices of knee flexion angle-specific torque
(0.44 rad knee flexion (AST); 0 rad = full knee extension; [1.05 rad · s−1]) were made for both intervention and control limbs. Electromechanical delay (EMD) of the m. biceps femoris during supine
knee flexion movements was evaluated in the preferred leg on both intervention and control days. Repeated measures ANOVAs
revealed significant condition (intervention; control) by time (pre; mid; post) interactions for both knee flexor AST (F[2,12] = 4.8; p<0.03) and EMD (F[2,12] = 4.1; p<0.05). AST was observed to decrease by 16% and EMD increase by 30% pre to post intervention. These observations suggest an
impairment of neuromuscular control and the ability to maintain force generation in the knee flexors, near the extremes of
the range of motion during prolonged intermittent high-intensity exercise activities. Changes of this magnitude may pose a
threat to the integrity of the knee joint.
Accepted: 6 January 1998 相似文献
3.
Lundblad I Elert J Gerdle B 《European journal of applied physiology and occupational physiology》1998,79(1):7-16
The aim was to investigate whether output and electromyogram (EMG) variables obtained from an isokinetic endurance test of
the shoulder flexor muscles of 23 women with neck and shoulder problems in a car and truck industry correlated with improvement
or worsening of complaints 1 year later. Each subject performed 100 maximal isokinetic shoulder forward flexions at 60° · s−1. Surface EMG of the trapezius, deltoid, biceps brachii and infraspinatus muscles and mechanical output (peak torque) were
determined for each contraction. The EMG was used to determine mean frequency f
mean and the ratio between the signal amplitudes of the EMG of the passive relaxation and active flexion parts of each contraction
cycle (SAR). The subjects also rated the degree of fatigue they experienced throughout the test. The magnitude of the shift
in f
mean was correlated with whether improvement or worsening occurred for complaints in the neck and or shoulders; a significant
relationship (r
2 = 0.44; P = 0.001) existed between the total frequency shift of the four muscles and the variables measuring improvement in complaints.
In the multivariate predictions other f
mean variables and perception of fatigue were also of significance. The present study would indicate that a high degree of f
mean shift correlates with improvement in neck and shoulder complaints 1 year later. One possible reason could be that f
mean reflects the muscle morphology and/or a pathological situation for the type-1 muscle fibres.
Accepted: 27 May 1998 相似文献
4.
J. Hall I. A. Macdonald P. J. Maddison J. P. O''Hare 《European journal of applied physiology and occupational physiology》1998,77(3):278-284
This study compared the cardiorespiratory responses of eight healthy women (mean age 30.25 years) to submaximal exercise
on land (LTm) and water treadmills (WTm) in chest-deep water (Aquaciser). In addition, the effects of two different water
temperatures were examined (28 and 36°C). Each exercise test consisted of three consecutive 5-min bouts at 3.5, 4.5 and 5.5 km · h−1. Oxygen consumption (V˙O2) and heart rate (HR), measured using open-circuit spirometry and telemetry, respectively, increased linearly with increasing
speed both in water and on land. At 3.5 km · h−1
V˙O2 was similar across procedures [χ = 0.6 (0.05) l · min−1]. At 4.5 and 5.5 km · h−1
V˙O2 was significantly higher in water than on land, but there was no temperature effect (WTm: 0.9 and 1.4, respectively; LTm:
0.8 and 0.9 l · min−1, respectively). HR was significantly higher in WTm at 36°C compared to WTm at 28°C at all speeds, and compared to LTm at
4.5 and 5.5 km · h−1 (P ≤ 0.003). The HR-V˙O2 relationship showed that at a V˙O2 of 0.9 l · min−1, HR was higher in water at 36°C (115 beats · min−1) than either on land (100 beats · min−1) or in water at 28°C (99 beats · min−1). The Borg scale of perceived exertion showed that walking in water at 4.5 and 5.5 km · h−1 was significantly harder than on land (WTm: 11.4 and 14, respectively; LTm: 9.9 and 11, respectively; P ≤ 0.001). These cardiorespiratory changes occurred despite a slower cadence in water (the mean difference at all speeds was
27 steps/min). Thus, walking in chest-deep water yields higher energy costs than walking at similar speeds on land. This data
has implications for therapists working in hydrotherapy pools.
Accepted: 3 September 1997 相似文献
5.
H. Kanehisa M. Kondo S. Ikegawa T. Fukunaga 《European journal of applied physiology and occupational physiology》1998,77(4):352-359
The purpose of this study was to investigate the profiles of body composition and force generation capability in professional
Sumo wrestlers. The subjects were 23 professional Sumo wrestlers [mean age 22.0 (SEM 1.2) years] including those ranked in
the lower- (Jonokuchi, n = 10), middle- (Sandanme, n = 8) and higher-division (Makuuchi, n = 5), 22 weight-classified athletes [5 judo athletes, 5 wrestlers, and 12 weight lifters, mean age 20.7 (SEM 0.7) years],
and 21 untrained men [mean age 20.1 (SEM 0.2) years]. In the Sumo wrestlers, body mass ranged between 77.0 and 150.0 kg, body
mass index between 25.9 and 44.5 kg · m−2, relative fat mass (%FM) between 11.9 and 37.0%, and fat-free mass (FFM) between 59.1 and 107.6 kg. The Sumo wrestlers showed
significantly higher %FM and smaller elbow and knee extensor cross-sectional areas (CSA) than the weight-classified athletes
who weighed from 90.4 kg to 133.2 kg. Moreover, isokinetic forces in the flexion and extension of elbow and knee joints, respectively,
at three constant velocities of 1.05, 3.14 and 5.24 rad · s−1 were significantly lower in the Sumo wrestlers than in the weight-classified athletes and untrained subjects when expressed
per unit of body mass. However, the median value of FFM relative to body height in the higher-division Sumo wrestlers was
ranked high in the range of magnitude among those reported previously in the literature for heavyweight athletes. Moreover,
the results on the comparisons within the Sumo wrestlers showed that not only FFM but also force generation capability, expressed
both as an absolute term and as a value relative to both body mass and muscle CSA, might be factors contributing to the performance
of Sumo wrestlers.
Accepted: 18 August 1997 相似文献
6.
Leaf photosynthesis, plant growth and nitrogen allocation in rice under different irradiances 总被引:6,自引:0,他引:6
The photosynthetic rates and various components of photosynthesis including ribulose-1,5-bisphosphate carboxylase (Rubisco;
EC 4.1.1.39), chlorophyll (Chl), cytochrome (Cyt) f, and coupling factor 1 (CF1) contents, and sucrose-phosphate synthase (SPS; EC 2.4.1.14) activity were examined in young, fully expanded leaves of rice
(Oryza sativa L.) grown hydroponically under two irradiances, namely, 1000 and 350 μmol quanta · m−2 · s−1, at three N concentrations. The light-saturated rate of photosynthesis measured at 1800 μmol · m−2 · s−1 was almost the same for a given leaf N content irrespective of growth irradiance. Similarly, Rubisco content and SPS activity
were not different for the same leaf N content between irradiance treatments. In contrast, Chl content was significantly greater
in the plants grown at 350 μmol · m−2 · s−1, whereas Cyt f and CF1 contents tended to be slightly smaller. However, these changes were not substantial, as shown by the fact that the light-limited
rate of photosynthesis measured at 350 μmol · m−2 · s−1 was the same or only a little higher in the plants grown at 350 μmol · m−2 · s−1 and that CO2-saturated photosynthesis did not differ between irradiance treatments. These results indicate that growth-irradiance-dependent
changes in N partitioning in a leaf were far from optimal with respect to N-use efficiency of photosynthesis. In spite of
the difference in growth irradiance, the relative growth rate of the whole plant did not differ between the treatments because
there was an increase in the leaf area ratio in the low-irradiance-grown plants. This increase was associated with the preferential
N-investment in leaf blades and the extremely low accumulation of starch and sucrose in leaf blades and sheaths, allowing
a more efficient use of the fixed carbon. Thus, morphogenic responses at the whole-plant level may be more important for plants
as an adaptation strategy to light environments than a response of N partitioning at the level of a single leaf.
Received: 23 February 1997 / Accepted: 8 May 1997 相似文献
7.
Submerged aquatic higher plants maintain acropetal water transport to the young leaves in active growth to satisfy their
demand for nutrients and hormones derived from the roots. We here present the first measurements of hydraulic properties for
a submerged plant, the monocotyledon Sparganium emersum Rehman. The hydraulic conductance per unit length, Kh, was measured in leaf segments without the leaf tip and shown to be greater in old, fully developed leaves (1.5 · 10−10 · m4 · MPa−1 · s−1) than in young leaves (1.0 · 10−10 · m4 · MPa−1 · s−1). In leaves with intact leaf tips, however, Kh was significantly greater in the youngest leaves, which suggests that the leaf tip with the hydathode influences resistance
and thus flow. Microscopy confirmed that the hydathodal area, which is an apical opening, undergoes structural changes with
leaf age; a matrix of microorganisms develops in the older leaves and probably restricts water flow by clogging the hydathodes.
The leaf specific conductivity expressing transport capacity relative to the leaf area supplied, of S. emersum (0.1 · 10−8 to 9 · 10−8 · m2 MPa−1· s−1) was within the same range as for various species of terrestrial ferns, vines and trees. This finding does not support the
traditional concept of functionally reduced vascular transport in
Received: 15 July 1996 / Accepted: 30 November 1996 相似文献
8.
Carlo Capelli Dave R. Pendergast B. Termin 《European journal of applied physiology and occupational physiology》1998,78(5):385-393
The energy cost per unit of distance (C
s, kilojoules per metre) of the front-crawl, back, breast and butterfly strokes was assessed in 20 elite swimmers. At sub-maximal
speeds (v), C
s was measured dividing steady-state oxygen consumption (V˙O2) by the speed (v, metres per second). At supra-maximal v, C
s was calculated by dividing the total metabolic energy (E, kilojoules) spent in covering 45.7, 91.4 and 182.9 m by the distance. E was obtained as: E = E
an+V˙O2max
t
p−V˙O2max(1−e−(
t
p/)), where E
an was the amount of energy (kilojoules) derived from anaerobic sources, V˙O2max litres per second was the maximal oxygen uptake, α (=20.9 kJ · l O2
−1) was the energy equivalent of O2, τ (24 s) was the time constant assumed for the attainment of V˙O2max at muscle level at the onset of exercise, and t
p (seconds) was the performance time. The lactic acid component was assumed to increase exponentially with t
p to an asymptotic value of 0.418 kJ · kg−1 of body mass for t
p ≥ 120 s. The lactic acid component of E
an was obtained from the net increase of lactate concentration after exercise (Δ[La]b) assuming that, when Δ[La]b = 1 mmol · l−1 the net amount of metabolic energy released by lactate formation was 0.069 kJ · kg−1. Over the entire range of v, front crawl was the least costly stroke. For example at 1 m · s−1, C
s amounted, on average, to 0.70, 0.84, 0.82 and 0.124 kJ · m−1 in front crawl, backstroke, butterfly and breaststroke, respectively; at 1.5 m · s−1, C
s was 1.23, 1.47, 1.55 and 1.87 kJ · m−1 in the four strokes, respectively. The C
s was a continuous function of the speed in all of the four strokes. It increased exponentially in crawl and backstroke, whereas
in butterfly C
s attained a minimum at the two lowest v to increase exponentially at higher v. The C
s in breaststroke was a linear function of the v, probably because of the considerable amount of energy spent in this stroke for accelerating the body during the pushing
phase so as to compensate for the loss of v occurring in the non-propulsive phase.
Accepted: 14 April 1998 相似文献
9.
M. J. Tipton F. S. C. Golden C. Higenbottam I. B. Mekjavic C. M. Eglin 《European journal of applied physiology and occupational physiology》1998,78(3):253-257
The initial responses to cold-water immersion, evoked by stimulation of peripheral cold receptors, include tachycardia, a
reflex inspiratory gasp and uncontrollable hyperventilation. When immersed naked, the maximum responses are initiated in water
at 10°C, with smaller responses being observed following immersion in water at 15°C. Habituation of the initial responses
can be achieved following repeated immersions, but the specificity of this response with regard to water temperature is not
known. Thirteen healthy male volunteers were divided into a control (C) group (n = 5) and a habituation (H) group (n = 8). Each subject undertook two 3-min head-out immersions in water at 10°C wearing swimming trunks. These immersions took
place at a corresponding time of day with 4 days separating the two immersions. In the intervening period the C group were
not exposed to cold water, while the H group undertook another six, 3-min, head-out immersions in water at 15°C. Respiratory
rate (f
R), inspiratory minute volume (V˙
I) and heart rate (f
H) were measured continuously throughout each immersion. Following repeated immersions in water at 15°C, the f
R, V˙
I and f
H responses of the H group over the first 30 s of immersion were reduced (P < 0.01) from 33.3 breaths · min−1, 50.5 l · min−1 and 114 beats · min−1 respectively, to 19.8 breaths · min−1, 26.4 l · min−1 and 98 beats · min−1, respectively. In water at 10°C these responses were reduced (P < 0.01) from 47.3 breaths · min−1, 67.6 l · min−1 and 128 beats · min−1 to 24.0 breaths · min−1, 29.5 l · min−1 and 109 beats · min−1, respectively over a corresponding period of immersion. Similar reductions were observed during the last 2.5 min of immersions.
The initial responses of the C group were unchanged. It is concluded that habituation of the cold shock response can be achieved
by immersion in warmer water than that for which protection is required. This suggests that repeated submaximal stimulation
of the cutaneous cold receptors is sufficient to attenuate the responses to more maximal stimulation.
Accepted: 6 February 1998 相似文献
10.
Ronald Heus Alexander H. Wertheim George Havenith 《European journal of applied physiology and occupational physiology》1998,77(4):388-394
The assumption that working on board ship is more strenuous than comparable work ashore was investigated in this study. Various
physiological parameters (V˙O2, V˙CO2, V˙
E and HR) have been measured to determine the energy expenditure of subjects walking slowly on a moving platform (ship motion
simulator). Twelve subjects (eight men and four women) walked either freely on the floor or on a treadmill at a speed of 1 m · s−1. Platform motion was either in a heave, pitch or roll mode. These three conditions were compared with a control condition
in which the platform remained stationary. The results showed that during pitch and roll movements of the platform, the energy
expenditure for the same walking task was about 30% higher than under the stationary control condition (3.6 J · kg−1 · m−1 vs 2.5 J · kg−1 · m−1, P < 0.05) for both walking on a treadmill and free walking. The heart rate data supported the higher energy expenditure results
with an elevation of the heart rate (112 beats · min−1 vs 103 beats · min−1, P < 0.05). The heave condition did not differ significantly from the stationary control condition. Pitch and roll were not
significantly different from each other. During all experimental conditions free walking resulted in a higher energy cost
of walking than treadmill walking (3.5 J · kg−1 · m−1 vs 2.7 J · kg−1 · m−1, P < 0.05) at the same average speed. The results of this experiment were interpreted as indicating that the muscular effort,
needed for maintaining balance when walking on a pitching or rolling platform, resulted in a significantly higher work load
than similar walking on a stable or a heaving floor, independent of the mode of walking. These results explain in part the
increased fatigue observed when a task is performed on a moving platform.
Accepted: 3 October 1997 相似文献
11.
I. K. M. Brenner J. Zamecnik P. N. Shek R. J. Shephard 《European journal of applied physiology and occupational physiology》1997,76(5):445-454
To determine if heat exposure alters the hormonal responses to moderate, repeated exercise, 11 healthy male subjects [age = 27.1
(3.0) years; maximal oxygen consumption, V˙O2max = 47.6 (6.2) ml · kg · min−1; mean (SD)] were assigned to four different experimental conditions according to a randomized-block design. While in a thermoneutral
(23°C) or heated (40°C, 30% relative humidity) climatic chamber, subjects performed either cycle ergometer exercise (two 30-min
bouts at ≈50% V˙O2max, separated by a 45-min recovery interval, CEx and HEx conditions), or remained seated for 3 h (CS and HS conditions). Blood
samples were analyzed for various exercise stress hormones [epinephrine (E), norepinephrine (NE), dopamine, cortisol and human
growth hormone (hGH)]. Passive heating did not alter the concentrations of any of these hormones significantly. During both
environmental conditions, exercise induced significant (P < 0.001) elevations in plasma E, NE and hGH levels. At 23°C during bout 1: E = 393 (199) pmol · l−1 (CEx) vs 174 (85) pmol · l−1 (CS), NE = 4593 (2640) pmol · l−1 (CEx) vs 1548 (505) pmol · l−1 (CS), and hGH = 274 (340) pmol · l−1 (CEx)vs 64 (112) pmol · l−1 (CS). At 40°C, bout 1: E = 596 (346) pmol · l−1 (HEx) vs 323 (181) pmol · l−1 (HS), NE = 7789 (5129) pmol · l−1 (HEx) vs 1527 (605) pmol · l−1 (HS), and hGH = 453 (494) pmol · l−1 (HEx) vs 172 (355) pmol · l−1 (HS). However, concentrations of plasma cortisol were increased only in response to exercise in the heat [HEx = 364 (168)
nmol · l−1 vs HS = 295 (114) nmol · l−1). Compared to exercise at room temperature, plasma levels of E, NE and cortisol were all higher during exercise in the heat
(P < 0.001 in all cases). The repetition of exercise did not significantly alter the pattern of change in cortisol or hGH levels
in either environmental condition. However, repetition of exercise in the heat increased circulatory and psychological stress,
with significantly (P < 0.001) higher plasma concentrations of E and NE. These results indicate a differential response of the various stress hormones
to heat exposure and repeated moderate exercise.
Accepted: 16 April 1997 相似文献
12.
Well-trained subjects (n=6) were studied before and after losing a mean 3.0%–4.3% of body mass to determine whether muscle performance could be maintained
or even enhanced by dietary creatine supplementation. During a 5-day period of loss of mass the subjects were randomly assigned
to a creatine or placebo supplemented diet. All the subjects were measured before and after loss of mass on both supplements
for isokinetic peak torque (PT) and work at peak torque (W
PT) of knee extensors, also for intermittent high intensity working capacity of the same muscle group. The latter test consisted
of submaximal isokinetic knee extensions at an angular velocity of 1.57 rad · s−1 for 45 s at the rate of 30 contractions each min (submaximal work, W
s
max
) followed by 15-s maximal effort (maximal work, W
max
). Total duration of the test was 3 min. Haematocrit was measured and haemoglobin, ammonia, lactate, glucose and urea concentrations
were analysed in blood samples obtained at rest and after cessation of muscle performance tests. The results indicated that
creatine supplementation in comparison with placebo treatment during rapid body mass reduction may help to maintain muscle
PT and W
PT at high angular velocities, not influencing W
max
and the rate of fatigue development during W
max
, but affecting adversely W
s
max
. Within the limitations of the present study the reasons for the partially detrimental effect of creatine administration
remain obscure, but it is suggested that impaired creatine uptake in muscle during body mass loss as well as creatine induced
changes in muscle glucose and glycogen metabolism may be involved.
Accepted: 18 December 1997 相似文献
13.
The effects of light and elevated temperatures on the efficiency of energy conversion in PSII [?PSII = (Fm′−Fs)/Fm′], pigment composition and heat tolerance of shade-acclimated Alocasia macrorrhiza were investigated. Leaf discs were exposed for 3 h to high light (HL; 1600 μmol photons · m−2 · s−1) or low light (LL; 20 μmol photons · m−2 · s−1) and a series of constant temperatures ranging from 30 to 49 °C. All HL treatments led to rapid and severe decreases in ?PSII. During the 2-h recovery period (LL, 25 °C) following the HL treatments, fast and slow recovery phases could be distinguished.
Leaf discs that had experienced HL and 30 °C recovered completely while no recovery of ?PSII was seen after a 3-h exposure to HL and 45 °C. A 3-h exposure to 45 °C at LL led to a less severe decrease in ?PSII and complete recovery was accomplished after less than 1 h. Under LL conditions a temperature of 49 °C was necessary to cause
an irreversible decrease in ?PSII, followed by necrosis the next day. Streptomycin had no effect on the degree of reduction and recovery in ?PSII discs exposed to HL and 35–45 °C, but partially inhibited recovery in discs exposed to HL and 30 °C. Streptomycin led to
a more severe decrease in ?PSII at LL and 49 °C and completely inhibited recovery. Streptomycin had no effect on the conversion of the xanthophyll-cycle
pigments during the treatment or the recovery. The epoxidation state was roughly the same in all leaf discs after a 3-h HL
treatment (0.270–0.346) irrespective of the exposure temperature. The back-conversion of zeaxanthin into violaxanthin after
a 2-h recovery period was only seen in leaf discs that had been exposed to HL and 30 °C. The thermotolerance of shade A. macrorrhiza leaves of 49.0 ± 0.7 °C (determined by fluorescence) coincided with the temperature at which damage occurred in leaf discs
exposed to LL. However, under HL the critical temperature under which necrosis occurred was much lower (42 °C). The thermotolerance
of A. macrorrhiza shade leaves could be increased by a short exposure (<20 min) to slightly elevated temperatures.
Received: 11 June 1997 / Accepted: 9 September 1997 相似文献
14.
P. Pfeiffer B. M. Culik 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(2):143-148
We used a still-water swim channel in conjunction with open-flow oxygen and carbon dioxide respirometry to examine the energy
requirements of river-otters (Lutra lutra L.) swimming voluntarily underwater in Neumünster Zoo (Germany). While at rest on land (5 °C), river-otters had a respiratory
quotient of 0.77 and a resting metabolic rate of 4.1 W kg−1. This increased to an estimated 6.4 W kg−1 during rest in water (11–15 °C) and to 12.3 W kg−1 when the animals were feeding in the channel. River-otters swimming under water preferred a mean speed of 0.89 m s−1, and their energy requirements attained 11.6 W kg−1. Cost of transport, however, was minimal at 1.3 m s−1 and amounted to 0.95 J N−1 m−1.
Accepted: 3 November 1997 相似文献
15.
This study examined the thermoregulatory responses of men (group M) and women (group F) to uncompensable heat stress. In
total, 13 M [mean (SD) age 31.8 (4.7) years, mass 82.7 (12.5) kg, height␣1.79␣(0.06) m, surface area to mass ratio 2.46␣(0.18) m2 · kg−1 · 10−2, Dubois surface area 2.01 (0.16) m2, %body fatness 14.6 (3.9)%, V˙O2peak 49.0 (4.8) ml · kg−1 · min−1] and 17 F [23.2 (4.2) years, 62.4 (7.7) kg, 1.65 (0.07) m, 2.71 (0.14) m2 · kg−1 · 10−2, 1.68 (0.13) m2, 20.2 (4.8)%, 43.2 (6.6) ml · kg−1 · min−1, respectively] performed light intermittent exercise (repeated intervals of 15 min of walking at 4.0 km · h−1 followed by 15 min of seated rest) in the heat (40°C, 30% relative humidity) while wearing nuclear, biological, and chemical
protective clothing (0.29 m2 ·°C · W−1 or 1.88 clo, Woodcock vapour permeability coefficient 0.33 i
m). Group F consisted of eight non-users and nine users of oral contraceptives tested during the early follicular phase of
their menstrual cycle. Heart rates were higher for F throughout the session reaching 166.7 (15.9) beats · min−1 at 105 min (n = 13) compared with 145.1 (14.4) beats · min−1 for M. Sweat rates and evaporation rates from the clothing were lower and average skin temperature () was higher for F. The increase in rectal temperature (T
re) was significantly faster for the F, increasing 1.52 (0.29)°C after 105 min compared with an increase of 1.37 (0.29)°C for
M. Tolerance times were significantly longer for M [142.9 (24.5) min] than for F [119.3 (17.3) min]. Partitional calorimetric
estimates of heat storage (S) revealed that although the rate of S was similar between genders [42.1 (6.6) and 46.1 (9.7) W · m−2 for F and M, respectively], S expressed per unit of total mass was significantly lower for F [7.76 (1.44) kJ · kg−1] compared with M [9.45 (1.26) kJ · kg−1]. When subjects were matched for body fatness (n = 8 F and 8 M), tolerance times [124.5 (14.7) and 140.3 (27.4) min for F and M, respectively] and S [8.67 (1.44) and 9.39 (1.05) kJ · kg−1 for F and M, respectively] were not different between the genders. It was concluded that females are at a thermoregulatory
disadvantage compared with males when wearing protective clothing and exercising in a hot environment. This disadvantage can
be attributed to the lower specific heat of adipose versus non-adipose tissue and a higher percentage body fatness.
Accepted: 31 October 1997 相似文献
16.
Alfonso Gautieri Simone Vesentini Alberto Redaelli 《Journal of molecular modeling》2010,16(12):1845-1851
The normal diffusion regime of many small and medium-sized molecules occurs on a time scale that is too long to be studied
by atomistic simulations. Coarse-grained (CG) molecular simulations allow to investigate length and time scales that are orders
of magnitude larger compared to classical molecular dynamics simulations, hence providing a valuable approach to span time
and length scales where normal diffusion occurs. Here we develop a novel multi-scale method for the prediction of diffusivity
in polymer matrices which combines classical and CG molecular simulations. We applied an atomistic-based method in order to
parameterize the CG MARTINI force field, providing an extension for the study of diffusion behavior of penetrant molecules
in polymer matrices. As a case study, we found the parameters for benzene (as medium sized penetrant molecule whose diffusivity
cannot be determined through atomistic models) and Poly (vinyl alcohol) (PVA) as polymer matrix. We validated our extended
MARTINI force field determining the self diffusion coefficient of benzene (2.27·10−9 m2 s−1) and the diffusion coefficient of benzene in PVA (0.263·10−12 m2 s−1). The obtained diffusion coefficients are in remarkable agreement with experimental data (2.20·10−9 m2 s−1 and 0.25·10−12 m2 s−1, respectively). We believe that this method can extend the application range of computational modeling, providing modeling
tools to study the diffusion of larger molecules and complex polymeric materials. 相似文献
17.
H. Arabi H. Vandewalle P. Pitor J. de Lattre H. Monod 《European journal of applied physiology and occupational physiology》1997,76(2):122-127
The present experiment was designed to study the importance of strength and muscle mass as factors limiting maximal oxygen
uptake (V˙O2
max
) in wheelchair subjects. Thirteen paraplegic subjects [mean age 29.8 (8.7) years] were studied during continuous incremental
exercises until exhaustion on an arm-cranking ergometer (AC), a wheelchair ergometer (WE) and motor-driven treadmill (TM).
Lean arm volume (LAV) was estimated using an anthropometric method based upon the measurement of various circumferences of
the arm and forearm. Maximal strength (MVF) was measured while pushing on the rim of the wheelchair for three positions of
the hand on the rim (−30°, 0° and +30°). The results indicate that paraplegic subjects reached a similar V˙O2
max
[1.23 (0.34) l · min−1, 1.25 (0.38) l · min−1, 1.22 (0.18) l · min−1 for AC, TM and WE, respectively] and V˙O2
max
/body mass [19.7 (5.2) ml · min−1 · kg−1, 19.5 (6.14) ml · min−1 · kg−1, 19.18 (4.27) ml · min−1 · kg−1 for AC, TM and WE, respectively on the three ergometers. Maximal heart rate f
c
max
during the last minute of AC (173 (17) beats · min−1], TM [168 (14) beats · min−1], and WE [165 (16) beats · min−1], were correlated, but f
c
max
was significantly higher for AC than for TM (P<0.03). There were significant correlations between MVF and LAV (P<0.001) and between the MVF data obtained at different angles of the hand on the rim [311.9 (90.1) N, 313.2 (81.2) N, 257.1
(71) N, at −30°, 0° and +30°, respectively]. There was no correlation between V˙O2
max
and LAV or MVF. The relatively low values of f
c
max
suggest that V˙O2
max
was, at least in part, limited by local aerobic factors instead of central cardiovascular factors. On the other hand, the
lack of a significant correlation between V˙O2
max
and MVF or muscle mass was not in favour of muscle strength being the main factor limiting V˙O2
max
in our subjects.
Accepted: 31 January 1997 相似文献
18.
Light response characteristics of a morphologically diverse group of southern hemisphere conifers as measured by chlorophyll fluorescence 总被引:5,自引:0,他引:5
Unlike northern hemisphere conifer families, the southern family, Podocarpaceae, produces a great variety of foliage forms
ranging from functionally broad-, to needle-leaved. The production of broad photosynthetic surfaces in podocarps has been
linked qualitatively to low-light-environments, and we undertook to assess the validity of this assumption by measuring the
light response of a morphologically diverse group of podocarps. The light response, as apparent photochemical electron transport
rate (ETR), was measured by modulated fluorescence in ten species of this family and six associated species (including five
Cupressaceae and one functionally needle-leaved angiosperm) all grown under identical glasshouse conditions. In all species,
ETR was found to increase as light intensity increased, reaching a peak value (ETRmax) at saturating quantum flux (PPFDsat), and decreasing thereafter. ETRmax ranged from 217 μmol electrons · m−2 · s−1 at a PPFDsat of 1725 μmol photons · m−2 · s−1 in Actinostrobus acuminatus to an ETR of 60 μmol electrons · m−2 · s−1 at a PPFDsat of 745 μmol electrons · m−2 · s−1 in Podocarpus dispermis. Good correlations were observed between ETRmax and both PPFDsat and maximum assimilation rate measured by gas-exchange analysis. The effective quantum yield at light saturation remained
constant in all species with an average value of 0.278 ± 0.0035 determined for all 16 species. Differences in the shapes of
light response curves were related to differences in the response of non-photochemical quenching (q
n), with q
n saturating faster in species with low PPFDsat. Amongst the species of Podocarpaceae, the log of average shoot width was well correlated with PPFDsat, wider leaves saturating at lower light intensities. This suggests that broadly flattened shoots in the Podocarpaceae are
an adaptation to low light intensity.
Received: 15 April 1996 / Accepted: 30 September 1996 相似文献
19.
The effects of temperature on photosynthesis of a rosette plant growing at ground level, Acaena cylindrostachya R. et P., and an herb that grows 20–50 cm above ground level, Senecio formosus H.B.K., were studied along an altitudinal gradient in the Venezuelan Andes. These species were chosen in order to determine
– in the field and in the laboratory – how differences in leaf temperature, determined by plant form and microenvironmental
conditions, affect their photosynthetic capacity. CO2 assimilation rates (A) for both species decreased with increasing altitude. For Acaena leaves at 2900 m, A reached maximum values above 9 μmol m−2 s−1, nearly twice as high as maximum A found at 3550 m (5.2) or at 4200 m (3.9). For Senecio leaves, maximum rates of CO2 uptake were 7.5, 5.8 and 3.6 μmol m−2 s−1 for plants at 2900, 3550 and 4200 m, respectively. Net photosynthesis-leaf temperature relations showed differences in optimum
temperature for photosynthesis (A
o.t.) for both species along the altitudinal gradient. Acaena showed similar A
o.t. for the two lower altitudes, with 19.1°C at 2900 m and 19.6°C at 3550 m, while it increased to 21.7°C at 4200 m. Maximum
A for this species at each altitude was similar, between 5.5 and 6.0 μmol m−2 s−1. For the taller Senecio, A
o.t. was more closely related to air temperatures and decreased from 21.7°C at 2900 m, to 19.7°C at 3550 m and 15.5°C at 4200 m.
In this species, maximum A was lower with increasing altitude (from 6.0 at 2900 m to 3.5 μmol m−2 s−1 at 4200 m). High temperature compensation points for Acaena were similar at the three altitudes, c. 35°C, but varied in Senecio from 37°C at 2900 m, to 39°C at 3550 m and 28°C at 4200 m. Our results show how photosynthetic characteristics change along
the altitudinal gradient for two morphologically contrasting species influenced by soil or air temperatures.
Received: 5 July 1997 / Accepted: 25 October 1997 相似文献