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1.
A. X. Bigard D. Merino F. Lienhard B. Serrurier C. Y. Guezennec 《European journal of applied physiology and occupational physiology》1997,75(5):380-387
The aim of this study was to quantify the degenerative and regenerative changes in rat soleus muscle resulting from 3-week
hindlimb suspension at 45° tilt (HS group, n = 8) and 4-week normal cage recovery (HS-R group, n = 7). Degenerative changes were quantified by microscope examination of muscle cross sections, and the myosin heavy chain
(MHC) composition of soleus muscles was studied by sodium dodecyl sulphate polyacrylamide gel electrophoresis. At the end
of 3-week hindlimb suspension, histological signs of muscle degenerative changes were detected in soleus muscles. There was
a significant variability in the percentage of fibres referred to as degenerating (%dg) in individual animals in the HS group
[%dg = 8.41 (SEM 0.5)%, range 4.66%–14.08%]. Moreover, %dg varied significantly along the length of the soleus muscle. The
percentage of fibres with internal nuclei was less than %dg in HS-soleus muscles [4.12 (SEM 0.3)%, range 1.24%–8.86%]. In
4-week recovery rats, the greater part of the fibres that were not referred to as normal, retained central nuclei [15.8 (SEM
2.2)%, range 6.2%–21.1%]. A significant increase in the slow isoform of MHC was recorded in the HS-R rats, compared to muscles
from age-matched rats (P < 0.01). These results would suggest that a cycle of myofibre degeneration-regeneration occurred during HS and passive recovery,
and that the increased accumulation of slow MHC observed in soleus muscles after recovery from HS could be related to the
prevalence of newly formed fibres.
Accepted: 14 October 1996 相似文献
2.
Ole Rintek Madsen Ulrik Birk Lauridsen Andreas Hartkopp Ole Helmer S?rensen 《European journal of applied physiology and occupational physiology》1997,75(3):239-245
Dual energy x-ray absorptiometry (DEXA) offers the possibility of assessing regional soft tissue composition, i.e. lean mass (LM) and fat
mass : LM may be considered a measure of muscle mass. We examined age-related differences in LM, percentage fat (%fat) and
muscle strength in 100 healthy non-athletic women aged 18–87 years. Relationships between muscle strength and leg LM in 20
elite female weight lifters and in 18 inactive women with previous hip fractures were also studied. The LM and %fat of the
whole body, trunk, arms and legs were derived from a whole body DEXA scan. Isokinetic knee extensor strength (KES) and flexor
strength (KFS) at 30° · s–1 were assessed using an isokinetic dynamometer. The women aged 71–87 years had 35% lower KES and KFS than the women aged 18–40
years (P < 0.0001). Differences in LM were less pronounced. The LM of the legs, for instance, was 15% lower in the old than in the
young women (P < 0.0001). In a multiple regression analysis with age, body mass, height and leg LM or KES as independent variables and KES
or leg LM as the dependent variable, age was the most important predictor of KES (r
partial = −0.74, P < 0.0001). The same applied to KFS. Body mass, not age, was the most important predictor of leg LM (r
partial = 0.65, P < 0.0001) and of LM at all other measurement sites. The LM measured at different regions decreased equally with increasing
age. The KES:leg LM ratio was negatively correlated with age (r = −0.70, P < 0.0001). The weight lifters had significantly higher KES:leg LM ratios than age-matched controls (+12%, P < 0.0001) and vice versa for the women with previous hip fractures (–36%, P < 0.0001). In conclusion, from our study it would seem that in healthy nonathletic women, age is a more important determinant
of muscle strength than is LM as measured by DEXA. Muscle strengthening exercises and inactivity seem to have a considerably
stronger influence on muscle strength than on LM.
Accepted: 27 August 1996 相似文献
3.
Brendan J. Humphries Peter J. Abernethy Kirsten D. Blake Robert U. Newton 《European journal of applied physiology and occupational physiology》1997,75(6):532-536
The relative content of myosin heavy chain (MHC) isoforms IIb, IIa and I in human skeletal muscle taken from the m. vastus
lateralis of 30 healthy male subjects was analysed using mini-gel electrophoresis. Repeated electrophoretic gels utilizing
the same methods were produced for all subjects and the determination of MHC protein bands was performed using a digital scanner
and National Institutes of Health (NIH) Image software and laser densitometry. A comparison between the NIH Image processing
technique and laser densitometry revealed differences of 6.47%, 6.35% and 6.84% between these measurement techniques for MHC-IIb,
-IIa and -I isoforms, respectively. The percentage technical error of measurement (TEM%) between electrophoretic gels was
shown to be 19.1%, 17.8% and 14.2%, with regard to percentage of occurrence of MHC-IIb, -IIa and -I isoforms respectively.
The variation in electrophoretic gel analyses was shown to be 5.7%, 7.3% and 5.5%, with regard to the percentage of MHC-IIb,
-IIa and -I isoforms respectively. Intra-class correlations comparing NIH Image and laser densitometry produced r values in the range 0.38–0.63. Comparisons between and within gel analyses produced r values in the range 0.59–0.94 and 0.93–0.98, respectively. Analyses of variance revealed no significant differences (P < 0.05) between analysis techniques, between␣gels or within gels for the measurement of MHC-IIb, -IIa and -I isoforms. The inter-gel
error between fibre subgroups was moderate for the two type-II MHC populations and less for type-I MHC; the intra-individual
error in the measuring technique used for classifying the MHC-IIb, -IIa and -I protein bands was small. The results obtained
in this investigation showed consistent trends which may reflect a false classification of the type-II MHC populations for
the inter-gel and intra-individual analyses. The NIH Image software and digitizing process was shown to be a valid and reliable
method for distinguishing between MHC protein bands of human skeletal tissue as separated by mini-gel electrophoretic techniques.
Accepted: 6 January 1997 相似文献
4.
Tatiana Aminoff Juhani Smolander O. Korhonen Veikko Louhevaara 《European journal of applied physiology and occupational physiology》1997,75(4):363-368
Ten young (aged 23–30 years) and nine older (aged 54–59 years) healthy men with a similar size of limb muscle mass performed
arm crank and leg cycle exercise for 30 min at relative exercise intensities of 50% and 75% of maximal oxygen uptake for the
corresponding muscle group. In the tests, heart rate, blood pressure, gas exchange variables, rating of perceived exertion
and blood lactate concentration were measured. The limb muscle mass was determined by anthropometric measurements. At the
75% target exercise level, four of the older men and two of the young men could not complete the arm-cranking test, and one
of the older men and two of the young men could not complete the leg-cycle test. During arm-cranking the absolute exercise
intensity was similar for the young and older men because of similar maximal values during arm-cranking. But during leg-cycling
the absolute excercise intensity was higher for the young men than for the older men due to the difference in corresponding
maximal values. During arm-cranking there were no significant differences in the physiological responses between the age groups
except that a higher ventilatory response was noted among the older compared to the young men. During leg-cycling the heart
rate values were higher among the young compared to the older men. But, when the heart rate values were expressed as a percentage
of maximal heart rate in the corresponding maximal tests, no significant differences between the age groups were found. The
results indicated that 30-min of arm or leg exercise at the same relative submaximal excercise intensity produces a similar
degree of physiological strain in healthy older compared to young men. During arm-cranking, the young and the older men exercised
at the same external intensity, indicating a similar ability to perform prolonged excercise using smaller muscle groups expressed
both in absolute and relative terms.
Accepted: 7 October 1996 相似文献
5.
Michael S. Conley Michael H. Stone Michael Nimmons G. A. Dudley 《European journal of applied physiology and occupational physiology》1997,75(5):443-448
This study examined hypertrophy after head extension resistance training to assess which muscles of the complicated cervical
neuromuscular system were used in this activity. We also determined if conventional resistance exercises, which are likely
to evoke isometric action of the neck, induce generalized hypertrophy of the cervical muscle. Twenty-two active college students
were studied. [mean (SE) age, weight and height: 21 (1) years, 71 (4) kg and 173 (3) cm, respectively]. Subjects were assigned
to one of three groups: RESX (head extension exercise and other resistance exercises), RES (resistance exercises without specific
neck exercise), or CON (no training). Groups RESX (n = 8) and RES (n = 6) trained 3 days/week for 12 weeks with large-muscle mass exercises (squat, deadlift, push press, bent row and mid-thigh
pull). Group RESX also performed three sets of ten repetitions of a head extension exercise 3 days/week with a load equal
to the 3 × 10 repetition maximum (RM). Group CON (n = 8) was a control group. The cross-sectional area (CSA) of nine individual muscles or muscle groups was determined by magnetic
resonance imaging (MRI) of the cervical region. The CSA data were averaged over four contiguous transaxial slices in which
all muscles of interest were visible. The 3 × 10 RM for the head extension exercise increased for RESX after training [from
17.9 (1.0) to 23.9 (1.4) kg, P < 0.05] but not for RES [from 17.6 (1.4) to 17.7 (1.9)␣kg] or CON [from 10.1 (2.2) to 10.3 (2.1) kg]. RESX showed an increase
in total neck muscle CSA after training [from 19.5 (3.0) to 22.0 (3.6) cm2, P < 0.05], but RES and CON did not [from 19.6 (2.9) to 19.7 (2.9)␣cm2 and 17.0 (2.5) to 17.0 (2.4) cm2, respectively]. This hypertrophy for RESX was due mainly to increases in CSA of 23.9 (3.2), 24.0 (5.8), and 24.9 (5.3)% for
the splenius capitis, and semispinalis capitis and cervicis muscles, respectively. The lack of generalized neck muscle hypertrophy
in RES was not due to insufficient training. For example, the CSA of their quadriceps femoris muscle group, as assessed by
MRI, increased by 7 (1)% after this short-term training (P < 0.05). The results suggest that: (1) the splenius capitis, and semispinalis capitis and cervicis muscles are mainly responsible
for head extension; (2) short-term resistance training does not provide a sufficient stimulus to evoke neck muscle hypertrophy
unless specific neck exercises are performed; and (3) the postural role of head extensors provides modest loading in bipeds.
Accepted: 15 October 1996 相似文献
6.
Sieve-tube exudate protein (STEP) from Ricinus communis L. seedlings consists of a characteristic set of more than 100 different polypeptides, against which a complex antiserum
was raised. This antiserum cross-reacted with dominant protein species (molecular weights 10–30 kDa) present in the sieve-tube
exudate and, to a lesser extent, with proteins in tissue extracts of Ricinus and a wide range of other plant species. For further elucidation of the nature of individual STEPs in the sieve tubes the
anti-STEP serum was used to screen a cDNA expression library constructed from Ricinus cotyledon mRNA. Two clones that differed in the 3′ untranslated region encoded a protein of 11 kDa which showed striking
homology to bacterial and eucaryotic glutaredoxin sequences. Glutaredoxin activity was confirmed for the recombinant protein
after overexpression in Escherichia coli and characterised in detail in sieve-tube exudate. Michaelis Menten constants (K
m) for reduced glutathione and cysteine were 2 mM and 50 μM, respectively. Besides l-cysteine, dehydroascorbate and protein disulphides were also reduced by the activity present in the sieve-tube exudate. Glutathione,
which is the obligate donor of reduced thiols for glutaredoxin, was present in sieve-tube sap in millimolar concentrations
(up to 3 mM) with a ratio of total to oxidised glutathione of 3:1. It is suggested that glutaredoxin and glutathione in sieve
tubes prevent oxidative damage and may be involved in redox regulation of sieve-tube proteins.
Received: 13 December 1996 / Accepted: 28 December 1996 相似文献
7.
Using an exclosure experiment in the willow stage of primary succession on the floodplain of the Tanana River, we tested
the hypothesis that browsing can reduce mycorrhizal infection. We measured the effects winter browsing by moose (Alcesalces) and snowshoe hare (Lepusamericanus) had on mycorrhizal infection and fine root biomass of willow (Salix spp.) and balsam poplar (Populusbalsamifera). We found that protection from winter browsing increased ectomycorrhizal infection by 10% in the top 5 cm of the soil profile,
by 23% at 5–10 cm, and by 42% at the 10–15 cm depth. Mammal browsing in taiga forests is now recognized as a major cause of
the shift from palatable deciduous species such as willow and balsam poplar to less palatable species such as alder and spruce.
We suggest that browsing-induced reduction in ectomycorrhizal infection of salicaceous species plays a central role in this
shift in plant community composition.
Received: 26 March 1996 / Accepted: 26 September 1996 相似文献
8.
Phlorotannins versus other factors affecting epiphyte abundance on the kelp Ecklonia radiata 总被引:3,自引:0,他引:3
We examined factors affecting the abundance and distribution of epiphytes (fouling) on the sublittoral kelp Ecklonia radiata. We first assessed the importance of phlorotannins as chemical defences against epiphytes by (a) correlating epiphyte loads
on different parts of the thallus with the phlorotannin content of those tissues, and (b) experimentally testing the effects
of variation in phlorotannin concentration against the settlement and growth of gametes of Ulva lactuca, a common epiphyte in the system. Tissue phlorotannin content was, at best, only weakly related to epiphyte loads, with r
2 values typically <0.10. Inhibition of Ulva gametes only occurred at concentrations >10 mg l−1, which is 5 orders of magnitude greater than levels of phlorotannins in the water column around beds of E. radiata, and 1–3 orders of magnitude greater than estimated levels in the boundary layer at the surface of the plant. We concluded
that phlorotannins have a negligible impact on patterns of epiphytism on E. radiata, and proceeded to investigate other factors influencing the distribution and abundance of epiphytes. In our samples the relative
age of different parts of the thallus was strongly correlated with epiphyte abundance, with epiphyte densities greatest on
the oldest tissue and least on the youngest. Distal parts of the thalli also had greater epiphyte loads than basal parts.
Field experiments in which kelp tissue was suspended at two heights in an E. radiata forest for varying lengths of time confirmed the importance of the length of time that the tissue was in the water, and its
height in the water column, to the development of an epiphyte community. Comparison of epiphyte loads on tissue from primary
(smooth) and secondary (rough) laminae in these experiments indicated that surface rugosity also affected fouling. Macroherbivores
were rare on E. radiata, and abundances of mesofauna and epiphytes were positively related, suggesting that grazers were not important determinants
of patterns of epiphyte abundance. Although phlorotannins have been previously suggested to play an important role as defences
against epiphytes, we suggest that water-soluble compounds such as phlorotannins are less likely to be effective defences
against epiphytes than non-polar metabolites, which can adhere to the surface of the producing organism. 相似文献
9.
P. J. Ponganis G. L. Kooyman L. M. Winter L. N. Starke 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):9-16
California sea lions, Zalophus californianus, were trained to elicit maximum voluntary breath holds during stationary underwater targeting, submerged swimming, and trained
diving. Lowest heart rate during rest periods was 57 bpm. The heart rate profiles in all three protocols were dominated by
a bradycardia of 20–50 bpm, and demonstrated that otariid diving heart rates were at or below resting heart rate. Venous blood
samples were collected after submerged swimming periods of 1–3 min. Plasma lactate began to increase only after 2.3-min submersions.
This rise in lactate and our inability to train sea lions to dive or swim submerged for periods longer than 3 min lead us
to conclude that an aerobic limit had been reached. Due to the similarity of heart rate responses and swimming velocities
recorded during submerged swimming and trained diving, this 2.3-min limit should approximate the aerobic dive limit in these
40-kg sea lions. Total body O2 stores, based on measurements of blood and muscle O2 stores in these animals, and prior lung O2 store analyses, were 37–43 ml O2 kg−1. The aerobic dive limit, calculated with these O2 stores and prior measurements of at-sea metabolic rates of sea lions, is 1.8–2 min, similar to that measured by the change
in post-submersion lactate concentration.
Accepted: 7 July 1996 相似文献
10.
Jaak Jürim?e Peter J. Abernethy B. M. Quigley Kirsten Blake Michael T. McEniery 《European journal of applied physiology and occupational physiology》1997,75(4):357-362
The purpose of this investigation was to compare the myosin heavy chain (MHC) isoform expression of the triceps brachii muscle
and isoinertial, isometric and isokinetic strength indices in competitive bodybuilders (CB, n = 5), recreational resistance trainers (RT, n = 5), endurance-trained rowers (ER, n = 5) and control (C, n = 5) subjects. Muscle tissue samples were analysed for MHC isoform content using 6% sodium dodecyl sulphate-polyacrylamide
gel electrophoresis. The CB possessed significantly smaller (P < 0.05) percentage of MHC type IIb proteins [12.92 (SD 7.08)%] than RT [30.08 (SD 6.58)%] ER [31.20 (SD 2.74)%] and C [38.22
(SD 2.95)%] groups (i.e. CB < RT ≈ ER < C). While the content of MHC type IIa isoforms did not differ significantly between
the two resistance-trained groups [CB = 55.76 (SD 5.38)%; RT = 45.72 (SD 7.8)%], CB presented significantly more type IIa
MHC isoforms than ER [42.84 (SD 2.98)%] and C [34.72 (SD 1.57)%] subjects (i.e. CB ≈ RT > ER ≈ C). The MHC type I protein
content did not differ significantly among RT [24.20 (SD 4.89)%] ER [25.38 (SD 1.67)%] and C [27.06 (SD 1.81)%] groups. The
CB [31.32 (SD 2.67)%] presented significantly more type I MHC isoforms only in comparison with RT. However, when changes in
the percentage of MHC type I isoforms were converted to effect sizes (ES), it appeared that low statistical power rather than
the absence of an effect accounted for the nonsignificant differences between CB and other groups (i.e. CB > RT ≈ ER ≈ C).
Significant differences existed in isoinertial strength among the trained athletes (i.e. CB > RT > ER ≈ C), while isometric
and isokinetic strength were not significantly different among any of the trained groups. However, the ES transformation of
data demonstrated that large differences existed between resistance-trained groups and ER for isometric and isokinetic strength
(i.e. CB ≈ RT > ER ≈ C). A statistically significant negative correlation (P < 0.001) was found between MHC type IIb isoforms and isoinertial strength index (r = − 0.68). The MHC type IIa proteins were positively related to all the strength measures considered (r = 0.51 – 0.61; P < 0.001). These data demonstrated different patterns of MHC isoform expression among the different groups of athletes and
it is suggested that these differences on occasion may affect the expression of strength.
Accepted: 24 September 1996 相似文献
11.
T. J. Vasankari U. M. Kujala H. Rusko S. Sarna M. Ahotupa 《European journal of applied physiology and occupational physiology》1997,75(5):396-399
We investigated the effect of training and racing at moderate altitude (MA) on oxidative stress by assessment of serum diene
conjugation (DC) and serum antioxidant potential (TRAP). Nine male top level skiers were studied during a national race (20–30
km) at sea level (SL). Thereafter, the athletes trained for 2 weeks at MA, after which they participated in a 20–30 km race
at MA. Venous blood samples were taken before and after the race. The DC, indicating early events of lipid peroxi dation,
did not change during the race at SL (16 850 vs 15 900 ΔAbsorbance · l−1) or at MA (19 870 vs. 20 630 ΔAbs · l−1). At MA serum DC was higher than at SL both before (25%) and after (30%) the race, the postrace difference being statistically
significant (P < 0.05). The TRAP increased during the race at MA (from 1387 to 1943 μmol · 1−1, P = 0.016), but not at SL (1713 vs 1582 μmol · l−1). These observations would suggest that the level of oxidative stress might be greater during living, training and racing
at MA (higher DC levels). Increased TRAP during the race at MA may indicate that the physiological adaptation to extreme acute
oxidative stress was altered. The physiological significance of this observation remains to be investigated.
Accepted: 18 October 1996 相似文献
12.
M. D. Baustian S. Q. Wang K. W. Beyenbach 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1997,167(1):61-70
Plasma and urine of toadfish (Opsanus tau) in sea water and 10% sea water were analyzed to assess responses of an aglomerular fish to hypoosmotic challenge. Following
transfer to 10% sea water, plasma osmotic pressure decreased slowly from 318 to 241 mmol · kg H2O−1, over a period of 10–15 days. Urine osmotic pressure decreased in parallel from 299 to 207 mmol · kg H2O−1, leaving urine/plasma ratios of osmotic pressure essentially unchanged. In contrast, the volume and composition of urine
changed rapidly following transfer to 10% sea water. Urine flow rate increased 110% from 3.0 to 6.3 μl · 100g−1 · h−1 and Na+ excretion increased 346%, while excretion of Mg2− and SO4
2− decreased 81% and 90%, respectively. Excretion rates for Cl− were low in seawater toadfish and decreased further in 10% sea water. An unknown sulfur-containing anion, present in the
urine of seawater toadfish, contributed significantly to the composition and ionic balance in urine of toadfish in 10% sea
water. These results suggest that the inability to produce strongly dilute urine obliges toadfish to lose salt in order to
excrete water, in hypoosmotic media. The decrease in plasma osmotic pressure may be both a strategy to reduce osmotic and
ionic gradients in dilute media and a consequence of the kidney's inability to excrete water without salt.
Accepted: 22 August 1996 相似文献
13.
Carmel M. McEniery David G. Jenkins Christopher Barnett 《European journal of applied physiology and occupational physiology》1997,75(5):462-466
The present study investigated the relationship between plasma potassium ion concentration ([K+]) and skeletal muscle torque during three different 15-min recovery periods after fatigue induced by four 30-s sprints. Four
males and one female completed the multiple sprint exercise on three separate days; recovery was passive, i.e. no cycling
exercise (PRec), active cycling at 30% peak oxygen consumption O2peak (30% Rec) and active cycling at 60% O2peak (60% Rec). Plasma [K+] was measured from blood sampled from an antecubital vein of subjects at rest and at 0, 3, 5, 10 and 15 min into each recovery.
Isokinetic leg strength was measured at rest and at 1, 6, 11 and 16 min during each recovery. Following the exhaustive sprints,
[K+] increased significantly from an average mean (SEM) resting value of 3.81 (0.07) mmol · l−1 to 4.48 (0.19) mmol · l−1 (P < 0.01). In all recovery conditions, plasma [K+] returned to resting levels within 3 min following the fourth sprint. However, in the two active recovery conditions plasma
[K+] increased over the remainder of the recovery periods to 4.36 (0.12) mmol · l−1 in the 30% Rec condition and 4.62 (0.12) mmol · l−1 in the 60% Rec condition, the latter being significantly higher than the former (P < 0.01). The maximum torque measured following the sprints decreased significantly, on average, to 61.1 (8.36)% of peak levels
(P < 0.01). After 15 min of recovery, maximum torque was highest in the 30% Rec condition at 92.13 (3.06)% of peak levels (P < 0.01), compared to 85.23 (3.64)% and 85.71 (0.82)% for the PRec and 60% Rec conditions, respectively. In contrast to the
significant differences in plasma [K+] across all three recovery conditions, muscle torque recovery was significantly different in only the 30% Rec condition.
In summary, recovery of peak levels of muscle torque following fatiguing exercise does not appear to follow changes in plasma
[K+].
Accepted: 18 October 1996 相似文献
14.
We investigated how infection by the mermithid nematode Gasteromermis sp. affected predation on its nymphal mayfly host, Baetisbicaudatus, by two invertebrate predators – the stonefly nymphs of Kogotusmodestus and the caddisfly larvae of Rhyacophilahyalinata. Predation trials and behavioral observations were conducted in stream-side, flow-through experimental chambers. When parasitized
and unparasitized prey were offered in equal numbers, K. modestus consumed significantly more parasitized than unparasitized nymphs. R. hyalinata consumed equal numbers of both prey types. Behavioral observations of foraging K.␣modestus on parasitized and unparasitized prey suggested that the increased consumption of parasitized nymphs was due to differences
in the behavior of infected mayflies in response to the predator. Specifically, parasitized nymphs drifted less often to escape
an approaching predator (non-contact encounters) compared to unparasitized nymphs, which increased the number of contact encounters
and attacks that occurred between K.␣modestus and parasitized prey. Because all hosts are castrated, these behavioral alterations affect only the fitness of the parasite,
which is killed along with its host by invertebrate predation. We present a number of hypotheses to explain why the parasite
causes increased predation on its host. These include the large size of the parasite affecting the sensory abilities of the
host, the larger energetic costs of escape behavior for parasitized individuals, and natural selection from fish predation
against drifting behavior by parasitized individuals.
Received: 27 May 1996 / Accepted: 30 September 1996 相似文献
15.
H. J. Bogaard H. H. Woltjer B. M. Dekker A. R. J. van Keimpema P. E. Postmus P. M. J. M. de Vries 《European journal of applied physiology and occupational physiology》1997,75(5):435-442
Whereas with advancing age, peak heart rate (HR) and cardiac index (CI) are clearly reduced, peak stroke index (SI) may decrease,
remain constant or even increase. The aim of this study was to describe the patterns of HR, SI, CI, arteriovenous difference
in oxygen concentration (C
a-vO2), mean arterial pressure (MAP), systemic vascular resistance index (SVRI), stroke work index (SWI) and mean systolic ejection
rate index (MSERI) in two age groups (A: 20–30 years, n = 20; B: 50–60 years n = 20. After determination of pulmonary function, an incremental bicycle exercise test was performed, with standard gas-exchange
measurements and SI assessment using electrical impedance cardiography. The following age-related changes were found: similar
submaximal HR response to exercise in both groups and a higher peak HR in A than in B[185 (SD 9) vs 167 (SD 14) beats · min−1, P < 0.0005]; increase in SI with exercise up to 60–90 W and subsequent stabilization in both groups. As SI decreased towards
the end of exercise in B, a higher peak SI was found in A [57.5 (SD 14.0) vs 43.6 (SD 7.7) ml · m−2, P < 0.0005]; similar submaximal CI response to exercise, higher peak CI in A [10.6 (SD 2.5) vs 7.2 (SD 1.3) l · min−1 · m−2, P < 0.0005]; no differences in C
a-vO2 during exercise; higher MAP at all levels of exercise in B; higher SVRI at all levels of exercise in B; lower SWI in B after
recovery; higher MSERI at all levels of exercise in A. The decrease in SI with advancing age would seem to be related to a
decrease in myocardial contractility, which can no longer be compensated for by an increase in preload (as during submaximal
exercise). Increases in systemic blood pressure may also compromise ventricular function but would seem to be of minor importance.
Accepted: 24 September 1996 相似文献
16.
Masashi Shibata Mitsuko Shimura Shiori Shibata Tomoko Wakamura Toshio Moritani 《European journal of applied physiology and occupational physiology》1997,75(3):206-211
The purpose of this study was to determine the walking speed which has the greatest influence on neural relaxation in healthy
elderly women as determined by electromyogram (EMG) and electroencephalogram (EEG) analyses. Seven elderly female volunteers
[mean age 68.5 (SD 3.95) years] served as subjects for this study. The EMG signals were recorded from the gastrocnemius (MG),
soleus (SL) and tibialis anterior (TA) muscles while walking on a treadmill, starting at 40␣m · min−1 and increasing 6 m · min−1 incrementally for 10␣min. The turning point of muscle activities (by integrated EMG, iEMGtp) was determined as the walking speed at the point at which the mean rate of change of iEMG (MG + SL + TA) abruptly increased.
After the determination of iEMGtp, the treadmill was set at three constant speeds, one corresponding to the speed for the iEMGtp and two others 20% higher or lower than that for the iEMGtp. The subjects then walked for 20 min at each of these speeds on 3 separate days and their EEG power spectrum data were obtained
for frequencies from the 8 to 13 Hz (α-wave component, AWC). The mean of iEMGtp for our subjects was at a mean walking speed of 64.7 (SD 7.9) m · min−1. Considering the subjects' age and height, iEMGtp was somewhat faster than their expected self-paced normal walking speed. There were no differences between the mean AWC values
of the subjects prior to exercising at each of the three speeds. The mean AWC values after exercise were significantly (P < 0.01) greater than before. The extent of the increase in AWC at iEMGtp was greater than those at slower speeds. Our data would suggest that walking exercise at the speed which corresponds with
EMG evidence of iEMGtp may induce the most significant relaxing effects in elderly women.
Accepted: 11 September 1996 相似文献
17.
A. D. Taylor R. Bronks P. Smith B. Humphries 《European journal of applied physiology and occupational physiology》1997,75(2):151-159
Integrated electromyography (iEMG) of the m. vastus lateralis was analysed during cycle ergometry in male subjects (n = 8). Two work trials were conducted, one under normoxia (N), the other under environmental normobaric hypoxia (EH in which
the oxygen fraction in inspired gas = 0.116), each trial lasting 10 min. The absolute power output (180 W) was the same for
both trials and was equivalent to 77 (4)% of maximum heart rate in trial N. Maximal voluntary isometric contractions were
performed after each trial to assess changes in force, muscle fibre conduction velocity (MFCV), electromechanical delay (EMD),
median frequency of EMG (MF) and maximal iEMG (iEMGmax). Biopy samples of muscle were obtained from the m. vastus medialis before testing. Myosin heavy chain (MHC) differences
were determined through sodium dodecyl-polyacrylamide gel electrophoresis followed by densitometric analysis. No differences
in submaximal iEMG were observed between EH and N trials during the first minute of work. At the end of both work trials iEMG
was significantly elevated compared with starting values, however the iEMG recorded in EH exceeded N values by 15%. At the
end of the EH trials the following were observed: a decrease in isometric force, MFCV and MF with an increase in EMD and the
iEMGmax/force ratio. The iEMGmax was unchanged. No differences in any of these variables were observed after the N trial. Mean (SD) lactate concentrations
following EH and N trials were 9.2 (4.4) mmol · 1−1 and 3.5 (1.1) mmol · 1−1, respectively. Results indicate that an increased motor unit recruitment and rate coding was needed in EH to maintain the
required power output. The increased motor unit recruitment and rate coding were associated with myoelectric evidence of “peripheral”
muscle fatigue. Subjects with higher compositions of type II MHC accumulated more lactate and displayed greater reductions
in MF and MFCV during fatigue.
Accepted: 16 June 1996 相似文献
18.
G. M. H?gg J. Robert M. Ojok 《European journal of applied physiology and occupational physiology》1997,75(3):263-267
As an alternative to a conventional endurance electromyogram (EMG) test for assessment of muscle capacity in the upper trapezius
muscle (isotonic test, IT), an isoelectric test (IE) has been investigated. Nine subjects performed the two endurance tests.
The tests were performed with a straight horizontal arm in the plane of the scapula. In IE, EMG amplitude was fed back to
the subject and the subject was instructed to maintain a constant EMG activity equal to the level with the arm unsupported.
Subjective ratings of local fatigue were obtained during the experiments. The EMG recordings from both tests were analysed
for the root mean square value as well as according to the mean power frequency (MPF) technique. All the subjects endured
maximal 15 min IE while in IT the median endurance was 11.9 min. Average subjective ratings of perceived fatigue increased
more in IT compared to IE. The average normalised MPF curve from IT increased while that from IE was unaffected. There was
a significant difference between the MPF results at 6 and 8 min. It is noteworthy that the MPF was higher in IT in spite of
a higher accumulated biomechanical load. It was concluded from these studies that the interpretation of decreased MPF as an
indicator of increased local muscle fatigue is doubtful at low contraction levels. It is suggested that an IE is a more appropriate
method for the functional evaluation of low threshold motor units of the upper trapezius muscle in research into occupational
disorders.
Accepted: 15 October 1996 相似文献
19.
P. E. Mozdziak Q. Truong A. Macius E. Schultz 《European journal of applied physiology and occupational physiology》1998,78(2):136-140
Exposure of juvenile skeletal muscle to a weightless environment reduces growth and satellite cell mitotic activity. However,
the effect of a weightless environment on the satellite cell population during muscle repair remains unknown. Muscle injury
was induced in rat soleus muscles using the myotoxic snake venom, notexin. Rats were placed into hindlimb-suspended or weightbearing
groups for 10 days following injury. Cellular proliferation during regeneration was evaluated using 5-bromo-2′-deoxyuridine
(BrdU) immunohistochemistry and image analysis. Hindlimb suspension reduced (P<0.05) regenerated muscle mass, regenerated myofiber diameter, uninjured muscle mass, and uninjured myofiber diameter compared
to weightbearing rats. Hindlimb suspension reduced (P<0.05) BrdU labeling in uninjured soleus muscles compared to weightbearing muscles. However, hindlimb suspension did not abolish
muscle regeneration because myofibers formed in the injured soleus muscles of hindlimb-suspended rats, and BrdU labeling was
equivalent (P>0.10) on myofiber segments isolated from the soleus muscles of hindlimb-suspended and weightbearing rats following injury.
Thus, hindlimb suspension (weightlessness) does not suppress satellite cell mitotic activity in regenerating muscles before
myofiber formation, but reduces growth of the newly formed myofibers.
Accepted: 11 December 1997 相似文献
20.
A. K. Tryba H. B. Hartman 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1997,180(3):215-221
Receptors monitoring muscle force innervate the opener muscle apodeme in the walking legs of the blue crab, Callinectes sapidus. Biocytin backfills reveal 9–15 bipolar neurons with somata as large as 60 μm positioned at the distal end of the apodeme.
Sensory endings insert into the apodeme and are in series with the opener muscle. The axons of these neurons form the opener
apodeme sensory nerve that merges with the most distal branch of the opener motor nerve. Recordings reveal that the receptors
are not spontaneously active nor do they respond to passive muscle stretch. Isometric muscle contraction evoked by stimulating
the opener excitor motor neuron is the adequate stimulus for receptor firing. Most significant is the finding that during
contraction, over a wide range of forces, the firing rate of individual receptors closely parallels the rate of change of
isometric force. The peak instantaneous frequency typically occurs at the force derivative maximum, but not at maximum force
development. Thus, receptors of the opener apodeme sensory nerve more closely monitor changes in isometric force rather than
the total force achieved.
Accepted: 20 September 1996 相似文献