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At least 811 records · Page 45Linked to original sources
PubMed2004

Power output of the lower limb during variable inertial loading: a comparison between methods using single and repeated contractions.

The power-inertial load relationship of the lower limb muscles was studied during a single leg thrust using the Modified Nottingham Power Rig (mNPR) and during cycling exercise in nine young male subjects. The relationship between peak power and inertial load showed a parabolic-like relationship for mNPR exertions, with a peak [937 (SD 246) W] at 0.158 kg m(2), this being significantly (P <0.05) different from the power generated at both the lowest [723 (162) W] and highest [756 (206) W] inertial loads. In contrast, for cycling exercise power output did not differ significantly between inertial loads, except at the lowest inertia where power output was significantly ( P<0.05) less compared with all other inertial loads. Maximum peak power output during cycling was 1,620 (336) W, which was significantly (P <0.05) greater than that recorded on the mNPR. However, a close association was observed between the mean power generated by each method (r=0.84, P<0.05). The results suggest that during a single contraction a range of inertial loads is required to allow peak power to be expressed. Above a certain critical value, this is unnecessary during cycling movements where the load can be repeatedly accelerated.

Adaptation, Physiological↗
PubMed2004

Differences in the force/endurance relationship between young and older men.

The aim of the present study was to ascertain if in six young (23-35 years) and in six older (70-72 years) healthy men matched for comparable absolute and specific maximal force of the dominant elbow flexors, differences in isometric endurance, myoelectrical fatigability, and shortening velocity are still recognizable. To assess the specific force, the muscle cross sectional area (CSA) was determined from magnetic resonance imaging (MRI) scans. The performance of the elbow flexors was studied by assessing the isometric endurance times (ET) at different percentages of maximal isometric contraction (MVC), the average muscle fibre conduction velocity of action potentials (CV), and the median frequency (MDF) of the surface electromyogram (sEMG) of the biceps brachii. Finally, the torque-velocity curve was assessed by means of maximal isokinetic contractions at six fixed angular velocities. All data were expressed as the mean (SD). The results showed that: (1) the ET was longer in the older subjects at the highest levels of isometric contraction, independently from the absolute force; (2) the modifications of muscle fibre CV during isometric effort progressed less rapidly in the older than the younger groups, as did those of MDF; and (3) at the same angular velocity, the older subjects exerted less absolute force than the younger subjects. These results suggest an impairment of the neuromuscular system of older men, which is less powerful and less fatigable than that of young men.

Adult↗
PubMed2005

Aerobic exercise performance correlates with post-ischemic flow-mediated dilation of the brachial artery in young healthy men.

In older healthy men, aerobic exercise capacity is related to postischemic flow-mediated dilation of the brachial artery (FMD), but corresponding data in a younger population is not available. In addition, whether submaximal aerobic exercise performance also correlates with this kind of vasomotor reactivity is not known. Therefore, in 15 nonsmoking young healthy men [age 27 (5) years; body mass index: 24 (2) kg/m(2); mean (SD)] with different levels of ordinary physical activity, but not performing upper-extremity training, we measured FMD at 1 min after reactive hyperemia, and pulmonary oxygen uptake (VO(2)) at ventilatory anaerobic threshold (VO(2)AT) and at peak effort (peak VO(2)) during an incremental exercise on a treadmill. In our participants, FMD was 9.1 (3.4)%, VO(2)AT was 40.72 (5.92) ml/kg per min, and peak VO(2) was 52.95 (8.13) ml/kg per min. Using bivariate Pearson's correlation, and in separate multivariate regression analyses, VO(2)AT and peak VO(2) showed a significant and reasonably good correlation with FMD (r = 0.84, P < 0.001 and r = 0.77, P = 0.001, respectively), independent of age, body mass index and serum total cholesterol (beta = 0.77, P < 0.001, R(2) of the overall model = 0.79 and beta = 0.70, P < 0.005, R(2) of the overall model = 0.69, respectively). Our data provide evidence suggesting that in young healthy men a higher submaximal and maximal aerobic exercise performance is associated with a greater FMD of peripheral conduit arteries.

Aerobiosis↗
PubMed2005

Comparison between maximal power in the power-endurance relationship and maximal instantaneous power.

The purpose of this study was to analyze the relevance of introducing the maximal power (P(m)) into a critical-power model. The aims were to compare the P(m) with the instantaneous maximal power (P(max)) and to determine how the P(m) affected other model parameters: the critical power ( P(c)) and a constant amount of work performed over P(c)(W'). Twelve subjects [22.9 (1.6) years, 179 (7) cm, 74.1 (8.9) kg, 49.4 (3.6) ml/min/kg] completed one 15 W/min ramp test to assess their ventilatory threshold (VT), five or six constant-power to exhaustion tests with one to measure the maximal accumulated oxygen deficit (MAOD), and six 5-s all-out friction-loaded tests to measure P(max) at 75 rpm, which was the pedaling frequency during tests. The power and time to exhaustion values were fitted to a 2-parameter hyperbolic model (NLin-2), a 3-parameter hyperbolic model (NLin-3) and a 3-parameter exponential model (EXP). The P(m) values from NLin-3 [760 (702) W] and EXP [431 (106) W] were not significantly correlated with the P(max) at 75 rpm [876 (82) W]. The P(c) value estimated from NLin-3 [186 (47) W] was not significantly correlated with the power at VT [225 (32) W], contrary to other models ( P <0.001). The W' from NLin-2 [25.7 (5.7) kJ] was greater than the MAOD [14.3 (2.7) kJ, P < 0.001] with a significant correlation between them (R = 0.76, P <0.01). For NLin-3, computation of W (P > P c), the amount of work done over P(C), yielded results similar to the W' value from NLin-2: 27.8 (7.4) kJ, which correlated significantly with the MAOD (R = 0.72, P <0.01). In conclusion, the P(m) was not related to the maximal instantaneous power and did not improve the correlations between other model parameters and physiological variables.

Adult↗
PubMed2005

RPE-lactate dissociation during extended cycling.

This study examined the association of blood lactate concentration [La] and heart rate (HR) with ratings of perceived exertion (RPE) during 60 min of steady workload cycling. Physically active college-aged subjects (n = 14) completed an exhaustive cycling test to determine VO(2) (peak) and lactate threshold (2.5 mmol l(-1)). Subjects then cycled for 60 min at the power output associated with 2.5 mmol l(-1) [LA]. HR, [LA], RPE-overall, RPE-legs and RPE-chest were recorded at 5, 10, 20, 30, 40, 50 and 60 min. The 60-min trials were below maximal lactate steady state, with peak lactate concentration occurring at 20 min after which [LA] declined. The 20-min point was therefore considered pivotal, and data at other points were compared to this time point. Repeated measures ANOVA with simple contrasts (alpha = 0.05) showed (a) [LA] at 40, 50 and 60 min was significantly lower than at 20 min, (b) RPE-O and RPE-L were significantly greater at 30, 40, 50 and 60 min than at 20 min, (c) RPE-C was significantly greater at 40, 50 and 60 min than at 20 min, and (d) HR was significantly greater at 30, 40, 50 and 60 min than at 20 min. Significant (P < 0.05) positive correlations were found between HR and RPE-O (r = 0.43), RPE-L (r = 0.48) and RPE-C (r = 0.41) while correlations for [LA]-HR (r = 0.13) and [LA]-RPE (RPE-O: r = -0.11, RPE-L: r = 0.01, RPE-C: r = -0.06) were weak and non-significant. There is a dissociation of RPE and [LA] owing to RPE drift and lactate kinetics in longer duration sub-maximal exercise. Apparently, [LA] is not a strong RPE mediator during extended cycling.

Adult↗
PubMed2005

Body composition is related to increase in plasma adiponectin levels rather than training in young obese men.

We assessed the major factors regulating adiponectin levels and the influence of exercise training on adiponectin levels in young obese men (19.2 +/- 1.1 yrs, BMI: 31.1 +/- 4.2, %fat: 27.2 +/- 3.9%). Subjects were separated into three groups (aerobic exercise group [AE: n=7], aerobic and resistance exercise group [AE + RE: n = 7], control group [n = 7]). AE underwent an 8-week training program (three times per week, more than 30 min endurance exercise at ventilatory threshold (VT) intensity). AE + RE went through resistance exercise two or three times per week together with the above endurance exercise for 5 months. Prior to intervention (n = 21), adiponectin levels were significantly correlated with percentage of fat. Stepwise multiple regression analysis revealed that percent body fat was an independent predictor of basal adiponectin levels (r2 = 0.370; P<0.01). After intervention, fat mass, and VT were significantly improved in AE. AE + RE exhibited significant reduction in weight, BMI, percent body fat and fat mass, and had significantly increased VT, VO2max cycling power and torque. Insulin was not changed in both groups. The control group exhibited no significant change in any variables. Although adiponectin levels were unchanged in the three groups, a significant negative correlation between delta fat mass and delta adiponectin levels was observed (n = 21, r = -0.461, P<0.05). In addition, delta percent body fat was an independent predictor of delta adiponectin levels (r2 = 0.327, P<0.05). These findings indicate that for increasing the adiponectin level, improvement of the body composition of young obese men is more important than the way training is performed.

Adaptation, Physiological↗
PubMed2006

Post-resistance exercise hypotension, hemodynamics, and heart rate variability: influence of exercise intensity.

UNLABELLED: The occurrence of post-exercise hypotension after resistance exercise is controversial, and its mechanisms are unknown. To evaluate the effect of different resistance exercise intensities on post-exercise blood pressure (BP), and hemodynamic and autonomic mechanisms, 17 normotensives underwent three experimental sessions: control (C-40 min of rest), low- (E40%-40% of 1 repetition maximum, RM), and high-intensity (E80%-80% of 1 RM) resistance exercises. Before and after interventions, BP, heart rate (HR), and cardiac output (CO) were measured. Autonomic regulation was evaluated by normalized low- (LF(R-R)nu) and high-frequency (HF(R-R)nu) components of the R-R variability. In comparison with pre-exercise, systolic BP decreased similarly in the E40% and E80% (-6 +/- 1 and -8 +/- 1 mmHg, P < 0.05). Diastolic BP decreased in the E40%, increased in the C, and did not change in the E80%. CO decreased similarly in all the sessions (-0.4 +/- 0.2 l/min, P < 0.05), while systemic vascular resistance (SVR) increased in the C, did not change in the E40%, and increased in the E80%. Stroke volume decreased, while HR increased after both exercises, and these changes were greater in the E80% (-11 +/- 2 vs. -17 +/- 2 ml/beat, and +17 +/- 2 vs. +21 +/- 2 bpm, P < 0.05). LF(R-R)nu increased, while ln HF(R-R)nu decreased in both exercise sessions. IN CONCLUSION: Low- and high-intensity resistance exercises cause systolic post-exercise hypotension; however, only low-intensity exercise decreases diastolic BP. BP fall is due to CO decrease that is not compensated by SVR increase. BP fall is accompanied by HR increase due to an increase in sympathetic modulation to the heart.

Adult↗
PubMed2003

Carbohydrate supplementation improves moderate and high-intensity exercise in the heat.

The aim of the present study was to clarify the effect of carbohydrate (CHO) supplementation on moderate and high-intensity endurance exercise in the heat. Eight endurance-trained men [maximal oxygen uptake ( VO(2max)) 59.5+/-1.6 ml kg(-1) bw(-1), mean+/-SE] cycled to exhaustion twice at 60% VO(2max) and twice at 73% VO(2max) at an ambient temperature of 35 degrees C. Subjects ingested either a 6.4% maltodextrin solution (CHO) or an artificially flavoured and coloured placebo (PLA). Time to fatigue was significantly greater with CHO in both the 60% and 73% VO(2max) trials (14.5% and 13.5% improvement, respectively). Heart rate and oxygen uptake ( VO(2)) did not differ at any point between PLA and CHO. Hypoglycaemia was not seen in any condition but plasma glucose concentrations tended to be higher at both intensities when CHO was fed. CHO oxidation rates were similar at 60% VO(2max) between CHO and PLA. There were no differences between PLA and CHO in the rate of rise of rectal temperatures ( T(rec)) at either intensity but there was a trend for subjects to fatigue at a high temperature when taking CHO. Ratings of perceived exertion (RPE) tended to be lower throughout both CHO trials; this was significant at 80 min and at fatigue at 60% VO(2max). It is concluded that supplementation with CHO improves exercise performance in the heat at both moderate and high endurance intensities. In the absence of a clear metabolic explanation, a central effect involving an increased tolerance of rising deep body temperature merits further investigation.

Adult↗
PubMed2006

Effects of unmeasured heterogeneity in the linear transformation model for censored data.

We investigate the effect of unobserved heterogeneity in the context of the linear transformation model for censored survival data in the clinical trials setting. The unobserved heterogeneity is represented by a frailty term, with unknown distribution, in the linear transformation model. The bias of the estimate under the assumption of no unobserved heterogeneity when it truly is present is obtained. We also derive the asymptotic relative efficiency of the estimate of treatment effect under the incorrect assumption of no unobserved heterogeneity. Additionally we investigate the loss of power for clinical trials that are designed assuming the model without frailty when, in fact, the model with frailty is true. Numerical studies under a proportional odds model show that the loss of efficiency and the loss of power can be substantial when the heterogeneity, as embodied by a frailty, is ignored.

Clinical Trials as Topic↗
PubMed1996

Ultrasonographic assessment of the swelling of the human masseter muscle after static and dynamic activity.

Work-related fatigue, pain and disorders in skeletal muscles have been related to prolonged static and dynamic activity. Such contractions have been shown to impair blood flow and increase muscle thickness and fluid. In the present study the effect of static and dynamic activity was evaluated from changes in masseter thickness as a measure of oedema, simultaneously with assessment of perceived pain/discomfort and cardiovascular responses. As static activity, fourteen young healthy women bit at 15% maximal voluntary contraction on bite-force transducers in the molar regions until exhaustion or 20 min at maximum (median endurance time 7.1 min). For dynamic activity, the same individuals chewed gum unilaterally until exhaustion or 40 min at maximum (all endured 40 min) with a cycle time of 725 ms, an average load of 9.3% of maximal electromyographic activity (maxEMG) and a peak mean voltage of 54.3% of maxEMG. Muscle thickness was measured by ultrasonography at the mid-portion of the ipsilateral masseter. Immediately after exercise, muscle thickness was significantly increased, more after static (14.0%) than dynamic (8.6%), and returned to pre-exercise values after 20-min recovery. Visual analogue scales (VAS) revealed the concomitant occurrence of pain (static 11.9 VAS%; dynamic 5.9 VAS%), and discomfort (static 8.1 VAS%; dynamic 5.9 VAS%), and both sensations decreased to pre-exercise values after 20-min recovery. Systolic blood pressure increased significantly, more during static (12.5%) than dynamic activity (4.3%), whereas heart rate rose significantly only during dynamic exercise (13.3%). Hence, activity was associated with muscular swelling and pain, and, despite the relatively small size of the masticatory muscles, also with general cardiovascular responses.

Adult↗
PubMed1993

Inverse relationship between physical activity and plasma fibrinogen in postmenopausal women.

The relationship between habitual physical activity and plasma level of fibrinogen was investigated in a cohort of 180 postmenopausal women, aged 60-69 years. Plasma fibrinogen was determined from prediluted plasma by adding an appropriate amount of thrombin to the sample. The time until fibrin formation occurred was measured. Physical activity during the month and year preceding the examination was assessed using self-administered questionnaires. There was a statistically significant inverse relationship between physical activity and fibrinogen (beta = -0.20; P = 0.005). For further analyses of the association between physical activity and fibrinogen the subjects were classified into three categories according to their weekly physical activity frequency: 0 to 1, 2 to 3, and 4 or more during the preceding month. The mean (S.D. [95% CI]) levels of fibrinogen from lowest to highest categories were: 3.49 (1.10 [2.99, 3.99]), 3.31 (1.52 [2.82, 3.81]), and 3.20 (2.26 [2.73, 3.67]) g/l, respectively, when age, body mass index (BMI), smoking, alcohol intake, LDL-cholesterol and estrogen use were allowed for (P = 0.021). BMI was directly associated with fibrinogen (beta = 0.30; P < 0.001), especially in the physically least active women. Smoking was directly (beta = 0.19; P = 0.006) and estrogen use inversely (beta = -0.15; P = 0.037) related to plasma fibrinogen level. The present data suggest that in postmenopausal women a low level of physical activity is associated with a high level of plasma fibrinogen.

Aged↗
PubMed1986

Test-retest reliability of the Minnesota Leisure Time Physical Activity Questionnaire.

The test-retest reliability of the Minnesota Leisure Time Physical Activity Questionnaire was assessed by two administrations of the questionnaire at a five-week interval in 140 adults from a general population sample and at a two-week interval in 150 male participants in the Multiple Risk Factor Intervention Trial (MRFIT). In both study populations, there was a slight, nonsignificant drop in reported leisure time energy expenditure between the test and the retest. The largest test-retest differences in estimated energy expenditure were found among those reporting greater levels of energy expenditure. Nevertheless, in both study populations Spearman rank correlation coefficients between the test and retest were high--0.79 to 0.88 for total activity and ranging 0.69-0.86 among the light, moderate, and heavy intensity subcategories. The high reliability of the Minnesota Leisure Time Physical Activity Questionnaire corroborates its utility in epidemiologic research.

Adult↗
PubMed1988

A review of the social patterning and significance of measures of height, weight, blood pressure and respiratory function.

This paper reviews evidence about the social patterning and relationship to life chances of four measures of health, development or functioning; namely height, weight, blood pressure and respiratory function. It argues that these are useful supplements to more commonly used measures of 'health' such as mortality rates, morbidity rates, or self reports of health, and recommends the increased use of such direct physical measures in routine statistics and special health surveys.

Blood Pressure↗