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 47,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

This study analyzes a new exercise training procedure, which includes interval exercise training on cycle ergometer (IntCT) (30-s work phases/60-s recovery phases) and on treadmill (60-s work and recovery phases each). Training was applied for 3 wk in 18 patients with severe chronic heart failure (CHF) ((mean +/- SEM) age 52 +/- 2 yr, ejection fraction 21 +/- 1%). Peak VO2 was increased from 12.2 +/- 0.7 to 14.6 +/- 0.7 ml-kg-1 min-1 owing to training (P < 0.001). A specific steep ramp test (work rate increments 25 W.10 s-1) was developed to derive exercise intensity for work phases in IntCT, which was 50% of the maximum work rate achieved. Steep ramp test was performed at the start of the study to determine the initial training work rate, then weekly to readjust it. Since the maximum work rate achieved from this test increased weekly (144 +/- 10 W -->172 +/- 10 W-->200 +/- 11 W; P < 0.001), the training work rate also increased (72 +/- 4 W-->86 +/- 6 W-->100 +/- 7 W; P < 0.001). Physical responses to IntCT were measured. There was no significant change in heart rate, blood pressure, and ratings of perceived exertion (RPE) using a Borg Scale between the first and the third week of training (heart rate 88 +/- 3 b.min-1; blood pressure 115 +/- 4/80 +/- 2 mm Hg; leg fatigue 12 +/- 1; dyspnea 10 +/- 1). Mean lactate concentration (1.70 +/- 0.09 mmol-1-1) indicated an overall aerobic range of training intensity. When compared with the commonly used intensity level of 75% peak VO2 from an ordinary ramp test (work rate increments 12.5 W.min-1), the performed training work rate was more than doubled (240%; P < 0.0001) while cardiac stress was lower (86%; P < 0.01). Values of norepinephrine and epinephrine as well as of RPE corresponded to those measured at 75% peak VO2. Interval exercise training is thus recommended for selected patients with CHF as it allows intense exercise stimuli on peripheral muscles with minimal cardiac strain. Using a steep ramp test, training work rate can be determined and readjusted weekly during initial training period.
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PMID:Interval training in patients with severe chronic heart failure: analysis and recommendations for exercise procedures. 913 68

The aim of this study was to examine whether ingesting water alone, or dextrose (7.5 g x 100 ml(-1)) with electrolytes, or fructose/corn solids (7.5 g x 100 ml(-1)) (400 ml every 20 min) would reduce the perceived exertion associated with 16 km (3 h) walking/running in the heat compared with that perceived during exercise with no fluid intake. Perceived exertion was assessed at 1-h intervals during exercise. Blood samples, required for analysis of blood glucose, plasma sodium, plasma osmolality and plasma volume, were obtained prior to exercise and at 1-h intervals during the exercise; further samples were obtained 1-h intervals for 3 h following the exercise. Drinking fluids at regular intervals reduced the level of perceived exertion. In the test during which no fluid was ingested, body mass decreased by 4.9 (0.4) kg [mean (SEM)], but decreased less with ingestion of either the dextrose/electrolytes or fructose/corn solids solutions, or water alone [1.3 (0.2) kg, 1.6 (0.3) kg and 2.0 (0.1) kg, respectively]. Plasma volume fell by 17% when taking no fluid, but fell less when ingesting fluids. Blood glucose fell significantly (P < 0.01) when taking no fluid and rose to 8.4 (1.3) mmol x l(-1) (P < 0.001) and 6.8 (1.1) mmol x l(-1) (P < 0.01) with ingestion of the dextrose/electrolytes or fructose/corn solids solutions, respectively. Urine output was greater with ingestion of water than with any of the other drinks. Six subjects experienced fatigue during exercise with no fluid and failed to complete the exercise. These results suggest that fatigue was caused by several interacting factors: a fall in blood glucose and plasma volume, dehydration, and neuroglycopenia. Taking fluids during exercise reduced the strain and the rating of perceived exertion; this was better achieved by ingesting a dextrose/electrolytes solution.
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PMID:Dehydration in soldiers during walking/running exercise in the heat and the effects of fluid ingestion during and after exercise. 940 63

A total of 80 freshly extracted human molars, free from caries, cracks & decalcifications, were used in this study. Conservative class I cavities were prepared in the occlusal surface. Two types of amalgam alloys were used, high copper (Dispersalloy) & conventional (Velvalloy). The prepared cavities were classified into 5 groups, 16 each carve (C), carve & polish (CP), precarve burnish (BC), past-carve (CB) & pre post carve burnish (BCB). The specimens were thermally stressed using the stress fatigue device. The marginal integrity of the amalgam enamel interface were evaluated using SEM, for the four marginal quantities: 1--excellent margin, 2--open margins, 3--enamel fracture, and 4--amalgam fracture. The results of this study revealed that higher copper amalgam demonstrated superior marginal integrity than the conventional one. The pre-post carve burnish group showed the highest percentage of excellent margin than the other groups.
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PMID:Effect of surface treatment on marginal integrity of amalgam restorations (in vitro study). 949 75

The aim of this study was to examine the isometric endurance response and the heart rate and blood pressure responses to isometric exercise in two muscle groups in ten young (age 23-29 years) and seven older (age 54-59 years) physically active men with similar estimated forearm and thigh muscle masses. Isometric contractions were held until fatigue using the finger flexor muscles (handgrip) and with the quadriceps muscle (one-legged knee extension) at 20%, 40%, and 60% of the maximal voluntary contraction (MVC). Heart rate and arterial pressure were related to the the individual's contraction times. The isometric endurance response was longer with handgrip than with one-legged knee extension, but no significant difference was observed between the age groups. The isometric endurance response averaged 542 (SEM 57), 153 (SEM 14), and 59 (SEM 5) s for the handgrip, and 276 (SEM 35), 94 (SEM 10) and 48 (SEM 5) s for the knee extension at the three MVC levels, respectively. Heart rate and blood pressure became higher during one-legged knee extension than during handgrip, and with increasing level of contraction. The older subjects had a lower heart rate and a higher blood pressure response than their younger counterparts, and the differences were more apparent at a higher force level. The results would indicate that increasing age is associated with an altered heart rate and blood pressure response to isometric exercise although it does not affect isometric endurance.
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PMID:Heart rate and blood pressure responses to isometric exercise in young and older men. 956 95

In surface electromyogram (EMG) and mechanomyogram (MMG) the electrical and mechanical activities of recruited motor units (MU) are summated. Muscle fatigue influences the electrical and mechanical properties of the active MU. The aim of this study was to evaluate fatigue-induced changes in the electrical and mechanical properties of MU after a short recovery period, using an analysis of force, surface EMG and MMG. In seven subjects the EMG and MMG were recorded from the biceps brachii muscle during sustained isometric effort at 80% of the maximal voluntary contraction (MVC), before (test 1) and 10 min after (test 2) a fatiguing exercise. From the time and frequency domain analysis of the signals, the root mean square (rms) and the mean frequency (f) of the power spectrum were calculated. The results were that the mean MVC was 412 (SEM 90) N and 304 (SEM 85) N in fresh and fatigued muscle, respectively; during tests 1 and 2 the mean EMG rms increased from 0.403 (SEM 0.07) mV to 0.566 (SEM 0.09) mV and from 0.476 (SEM 0.07) mV to 0.63 (SEM 0.09) mV, respectively; during test 1 the mean MMG rms decreased from 9.4 (SEM 0.8) mV to 5.7 (SEM 0.9) mV; in contrast, during test 2 constantly lower values were observed throughout contraction; during tests 1 and 2 the EMG f declined from 122 (SEM 7) Hz to 74 (SEM 7) Hz and from 106 (SEM 8) Hz to 60 (SEM 7) Hz, respectively; during test 1 the MMG f increased in the first 6 s from 19.3 (SEM 1.4) Hz to 23.9 (SEM 2.9) Hz, falling to 13.9 (SEM 1.3) Hz at the end of contraction; in contrast, during test 2 the MMG f declined continuously from 18.7 (SEM 1) Hz to 12.4 (SEM 0.8) Hz. The lower MVC after the fatiguing exercise and the changes in the EMG parameters confirmed that 10 min after the fatiguing exercise, the mechanical and electrical activities of MU were altered. In addition, the MMG results suggested that after a 10-min recovery, some highly fatigable MU might not be recruitable.
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PMID:Electromyogram and mechanomyogram changes in fresh and fatigued muscle during sustained contraction in men. 984 Apr 3

Among the potential hazards of laparoscopic surgery using electrocautery is the release of chemical by-products of incomplete tissue combustion into the pneumoperitoneum with subsequent transperitoneal absorption into the bloodstream and/or release into the operating room. The purpose of this study of patients undergoing laparoscopic cholecystectomy (LC) was twofold: (1) to assess the relationship between intraperitoneal concentration of carbon monoxide (CO) and blood levels of carboxyhemoglobin (COHb) and methemoglobin (MetHb), and (2) to assess the surgeon's inhalation of CO resulting from ambient smoke exposure. During LC with monopolar electrocautery, 21 patients were evaluated intraoperatively for intraperitoneal [CO] by sampling gas from a trocar, whereas arterial [COHb) and [MetHb] were determined perioperatively. The surgeon's venous blood was drawn pre- and postoperatively to assay [COHb] and [MetHb]. Patients completed visual analogue questionnaires 6 hours and 24 hours postoperatively to assess for adverse symptoms. Mean (+/- SEM) patient age and weight were 45 +/- 3 years and 84 +/- 4 kg, respectively. Mean duration of the operation was 69 +/- 5 minutes, and electrocautery was used for 3.0 +/- 0.3 minutes. Intraperitoneal [CO] rose to peak levels of 209 +/- 19 ppm at 50 minutes, whereas systemic [COHb] and [MetHb] were unchanged. The surgeon's systemic [COHb] and [MetHb] did not increase postoperatively. Nausea, abdominal pain, and fatigue scores decreased significantly between 6 and 24 hours postoperatively; however, there were no correlations between these symptoms and peak intraperitoneal [CO]. Although LC using electrocautery increases intraperitoneal [CO] to "hazardous" levels, systemic [COHb] and [MetHb] are not elevated by generation of intraperitoneal smoke. The surgeon's exposure to CO by the evacuation of smoke through laparoscopic ports is negligible. Production of smoke during LC using monopolar electrocautery, therefore, does not appear to pose a threat to either the patient or the surgeon.
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PMID:Production and systemic absorption of toxic byproducts of tissue combustion during laparoscopic cholecystectomy. 984 98

The effect of phosphate on the relaxation of isometrically contracting single skinned fibres from the semitendinosus muscle of the frog Rana temporaria has been investigated using laser pulse photolysis of the photolabile caged calcium-chelator diazo-2 to rapidly reduce the Ca2+ (<2 ms) within the fibre and produce >90% relaxation of force. Relaxation occurred in two phases - an initial linear shoulder which lasted approximately 20 ms followed by a double-exponential phase which gave two rate constants, k1 (43.4+/-1. 8 s-1, mean +/-SEM, n=14) and k2 (15.6+/-0.3 s-1, mean +/-SEM, n=14) at 12 degreesC. Increased phosphate concentrations did not affect the linear phase, but slowed the double-exponential phase following photolysis of diazo-2 in a dose-dependent fashion (k50= 0.9 mM for k1, 1.15 mM for k2). Reducing the concentration of contaminating phosphate (from 640 microM to 100 microM) led to an increase in the rate of the double-exponential phase (k1=67.1+/-4.4 s-1, k2=19.7+/-0. 6 s-1, mean +/-SEM, n=12). Time-resolved measurements of sarcomere length during relaxation, both in control fibres and in the presence of a raised phosphate concentration, reveal a <2% change throughout the whole relaxation transient, and less than 0.1% at the end of the linear phase. This finding implies that gross changes in sarcomere length do not contribute to the decay of the relaxation transient seen upon diazo-2 photolysis. Our results suggest that cross-bridges in states prior to phosphate release are already committed to force generation and must relax by releasing phosphate, rather than by a reversal of the force-generating step to a weakly bound, low-force phosphate-bound state. These findings also indicate that an increase in the phosphate concentration within muscle fibres plays an important part in the slowing of relaxation observed in skeletal muscle fatigue and that the relaxation transients observed upon diazo-2 photolysis represent a disengagement of the cross-bridges.
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PMID:The effect of phosphate on the relaxation of frog skeletal muscle. 991 95

It was shown that the amplitude of the soleus Mmax and Hmax responses decreases in the course of long-lasting H-reflex studies. The peak-to-peak amplitudes of the Mmax and Hmax responses in the soleus muscle (and the Mmax in the tibialis anterior muscle and small hand muscles) were measured repeatedly for 1-3 h in 20 subjects. 3-5 Mmax responses and 5-10 Hmax responses were elicited about every 3 min while the subject was at rest. Decreases in the soleus Mmax response of up to 50.5% (mean 20.5% SEM 2.2) and of the soleus Hmax of up to 49.7% (mean 19.1% SEM 3.7) in relation to the amplitudes measured at the beginning of the experiment were seen in 17 subjects. In 3 subjects no Mmax amplitude decrease was seen. The maximum decrease was reached between 10 and 100 min (mean 44.2 min SEM 4.3). An Mmax amplitude decrease was also seen in the tibialis anterior muscle and in two small hand muscles. In some subjects the decrease of the Mmax response seemed to be initiated by the infrequent supramaximal stimulations. The possible causes for this amplitude reduction, as well as the methodological consequences of these findings for H-reflex studies and fatigue studies, are briefly discussed.
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PMID:Amplitude of the maximum motor response (Mmax) in human muscles typically decreases during the course of an experiment. 992 49

This study investigated the effects of muscle glycogen availability on performance and selected physiological and metabolic responses during high-intensity intermittent exercise. Seven male subjects completed a regimen of exercise and dietary intake (48 h) to either lower and keep low (LOW-CHO) or lower and then increase (HIGH-CHO) muscle glycogen stores, on two separate occasions at least a week apart. On each occasion the subjects completed a short-term (<10 min) and prolonged (>30 min) intermittent exercise (IEX) protocol, 24 h apart, which consisted of 6-s bouts of high-intensity exercise performed at 30-s intervals on a cycle ergometer. Glycogen concentration (mean +/- SEM) in m. vastus lateralis before both IEx(short) and IEx(long) was significantly lower following LOW-CHO [180 (14), 181 (17) mmol kg (dw)(-1)] compared with HIGH-CHO [397 (35), 540 (25) mmol kg (dw)(-1)]. In both IEx(short) and IEx(long), significantly less work was performed following LOW-CHO compared with HIGH-CHO. In IEx(long), the number of exercise bouts that could be completed at a pre-determined target exercise intensity increased by 265% from 111 (14) following LOW-CHO to 294 (29) following HIGH-CHO (P < 0.05). At the point of fatigue in IEx(long), glycogen concentration was significantly lower with the LOW-CHO compared with HIGH-CHO [58 (25) vs. 181 (46) mmol kg (dw)(-1), respectively]. The plasma concentrations of adrenaline and nor-adrenaline (in IEx(short) and IEx(long)), and FFAand glycerol (in IEx(long)), increased several-fold above resting values with both experimental conditions. Oxygen uptake during the exercise periods in IEx(long), approached 70% of Vo2max. These results suggest that muscle glycogen availability can affect performance during both short-term and more prolonged high-intensity intermittent exercise and that with repeated exercise periods as short as 6 s, there can be a relatively high aerobic contribution.
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PMID:High-intensity exercise and muscle glycogen availability in humans. 1035 Feb 28

In this study we examined the time course of changes in the plasma concentration of oxypurines [hypoxanthine (Hx), xanthine and urate] during prolonged cycling to fatigue. Ten subjects with an estimated maximum oxygen uptake (VO2(max)) of 54 (range 47-67) ml x kg(-1) x min(-1) cycled at [mean (SEM)] 74 (2)% of VO2(max) until fatigue [79 (8) min]. Plasma levels of oxypurines increased during exercise, but the magnitude and the time course varied considerably between subjects. The plasma concentration of Hx ([Hx]) was 1.3 (0.3) micromol/l at rest and increased eight fold at fatigue. After 60 min of exercise plasma [Hx] was >10 micromol/l in four subjects, whereas in the remaining five subjects it was <5 micromol/l. The muscle contents of total adenine nucleotides (TAN = ATP+ADP+AMP) and inosine monophosphate (IMP) were measured before and after exercise in five subjects. Subjects with a high plasma [Hx] at fatigue also demonstrated a pronounced decrease in muscle TAN and increase in IMP. Plasma [Hx] after 60 min of exercise correlated significantly with plasma concentration of ammonia ([NH(3)], r = 0.90) and blood lactate (r = 0.66). Endurance, measured as time to fatigue, was inversely correlated to plasma [Hx] at 60 min (r = -0.68, P < 0.05) but not to either plasma [NH(3)] or blood lactate. It is concluded that during moderate-intensity exercise, plasma [Hx] increases, but to a variable extent between subjects. The present data suggest that plasma [Hx] is a marker of adenine nucleotide degradation and energetic stress during exercise. The potential use of plasma [Hx] to assess training status and to identify overtraining deserves further attention.
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PMID:Plasma hypoxanthine and ammonia in humans during prolonged exercise. 1050 75


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