The effect of exercise training on intrahepatic triglyceride and hepatic insulin sensitivity: a systematic review and meta-analysis.

This systematic review and meta-analysis determined the impact of structured exercise training, and the influence of associated weight loss, on intrahepatic triglyceride (IHTG) in individuals with non-alcoholic fatty liver disease (NAFLD). It also examined its effect on hepatic insulin sensitivity in individuals with or at increased risk of NAFLD. Analyses were restricted to studies using magnetic resonance spectroscopy or liver biopsy for the measurement of IHTG and isotope-labelled glucose tracer for assessment of hepatic insulin sensitivity. Pooling data from 17 studies (373 exercising participants), exercise training for one to 24 weeks (mode: 12 weeks) elicits an absolute reduction in IHTG of 3.31% (95% CI: -4.41 to -2.22%). Exercise reduces IHTG independent of significant weight change (-2.16 [-2.87 to -1.44]%), but benefits are substantially greater when weight loss occurs (-4.87 [-6.64 to -3.11]%). Furthermore, meta-regression identified a positive association between percentage weight loss and absolute reduction in IHTG (ß = 0.99 [0.62 to 1.36], P < 0.001). Pooling of six studies (94 participants) suggests that exercise training also improves basal hepatic insulin sensitivity (mean change in hepatic insulin sensitivity index: 0.13 [0.05 to 0.21] mg m-2  min-1 per µU mL-1 ), but available evidence is limited, and the impact of exercise on insulin-stimulated hepatic insulin sensitivity remains unclear.

Dynamic changes in dna methylation status in peripheral blood Mononuclear cells following an acute bout of exercise: Potential impact of exercise-induced elevations in interleukin-6 concentration.

The aim of the present study was to examine the relationship between interleukin (IL)-6 concentrations and DNA methylation in the peripheral blood mononuclear cells (PBMCs) of trained runners after a bout of prolonged, strenuous exercise. Eight healthy trained males completed a treadmill run at 60% vVO(2max) for 120 min followed by a 5-km time trial in a fasted condition. Whole blood samples were taken prior to, immediately before and 24 h following exercise. From these samples, PBMCs were isolated for analysis and plasma IL-6 concentrations were measured. The methylation status of DNA extracted from PBMCs was analysed using the Illumina 27k methylation beadchip platform. Global DNA methylation status was unaltered immediately and up to 24 hours following a bout of prolonged exercise in comparison to pre-exercise. Despite no change in global DNA methylation, plasma IL-6 concentrations were significantly related to the DNA methylation status of 11 genes. Our study demonstrates that the methylome is stable, while discovering a novel link between exercise-induced increases in circulating IL-6 and the DNA methylation status of 11 individual genes. Based on our preliminary findings, the mechanisms by which changes in plasma IL-6 concentrations and DNA methylation in response to exercise interact require further study.

Interleukin-6 in combination with the interleukin-6 receptor stimulates glucose uptake in resting human skeletal muscle independently of insulin action.

AIM: To examine if the physiological concentrations of both interleukin-6 (IL-6), in combination with IL-6 receptor (IL-6R), are able to stimulate glucose uptake in human skeletal muscle and to identify the associated signalling pathways. METHODS: Skeletal muscle tissue (~60 mg) obtained from healthy female volunteers via muscle biopsy was subjected to incubation in the absence or presence of insulin (60 µU/ml), recombinant human IL-6 (rhIL-6) (4 ng/ml) or a combination of rhIL-6 (4 ng/ml) and rhIL-6R (100 ng/ml) for 30 min, with glucose transport measured for each incubation. Western blot analysis was conducted on key signalling proteins, protein kinase B (PKB/Akt), adenosine monophosphate kinase (AMPK) and mammalian target of rapamycin (mTOR) to gain an early insight into any differing transport mechanisms. RESULTS: Human skeletal muscle exhibited increased glucose uptake with insulin (1.85-fold; p < 0.05) and stimulated phosphorylation of PKB/Akt and AMPK (0.98 ± 0.23 and 1.49 ± 0.13, respectively, phosphorylated: total; p < 0.05). IL-6/IL-6R increased phosphorylation of mTOR (fourfold, p < 0.05) compared to insulin, IL-6 alone and basal control. IL-6 did not stimulate glucose uptake but combined with IL-6R, induced 1.5-fold increase in glucose uptake (p < 0.05) and phosphorylation of AMPK (0.95 ± 0.19; phosphorylated: total, p < 0.05). CONCLUSIONS: IL-6 in combination with IL-6R and not IL-6 alone increased glucose uptake in human skeletal muscle. IL-6/IL-6R-mediated glucose uptake occurred independently of PKB/Akt phosphorylation, showing that IL-6/IL-6R-induced glucose uptake is dependent on a divergent pathway.

Type 2 diabetes mellitus and obesity in young adults: the extreme phenotype with early cardiovascular dysfunction.

AIM: A pilot study to phenotype young adults (< 40 years) with Type 2 diabetes mellitus. METHODS: Twenty people with Type 2 diabetes (aged 18-40 years), 10 lean and 10 obese control subjects underwent detailed assessment, including tagged cardiac magnetic resonance imaging, inflammatory proteins, lipids, vitamin D and maximal oxygen uptake. Outcomes were compared between the group with Type 2 diabetes and the control group. RESULTS: Mean (standard deviation) age, Type 2 diabetes duration and BMI in the group with Type 2 diabetes were 31.8 (6.6) years, 4.7 (4.0) years and 33.9 (5.8) kg/m(2) respectively. Compared with lean control subjects, those with Type 2 diabetes had more deleterious profiles of hyperlipidaemia, vitamin D deficiency, inflammation and maximal oxygen uptake relative to body mass. However, there was no difference between the group with Type 2 diabetes and the obese control group. The group with Type 2 diabetes had a higher left ventricular mass and a trend towards concentric remodelling compared with the lean control group (P = 0.002, P = 0.052) but not the obese control group (P > 0.05). Peak early diastolic strain rate was reduced in the group with Type 2 diabetes [1.51 (0.24)/s] compared with the lean control [1.97 (0.34)/s, P = 0.001] and obese control [1.78 (0.39)/s, P = 0.042] group. CONCLUSIONS: Young adults with Type 2 diabetes and those with obesity have similar adverse cardiovascular risk profiles, higher left ventricular mass and a trend towards left ventricular concentric remodelling. In addition, those with Type 2 diabetes demonstrate diastolic dysfunction, a known risk marker for future heart failure and mortality.

The effect of physical activity on mediators of inflammation.

Being physically active and undertaking exercise on a regular basis are critical lifestyle behaviours which protect against the development of numerous chronic metabolic conditions. One of the key mechanisms by which physical activity exerts favourable health effects appears to be due to its capacity to reduce chronic low-grade inflammation. Single bouts of exercise have a potent anti-inflammatory influence with recent advances describing important effects of acute exercise on inflammatory mediators produced within skeletal muscle (myokines), adipose tissue (adipokines) and leucocytes. The accumulated effects of physical activity or exercise training on systemic inflammation have been studied widely within epidemiological research; however, information from intervention trials is still emerging. Current data suggest that the most marked improvements in the inflammatory profile are conferred with exercise performed at higher intensities, with combined aerobic and resistance exercise training potentially providing the greatest benefit. The purpose of this review is to describe recent advances in our understanding surrounding the acute and chronic effects of physical activity on key mediators of inflammation. Within this, particular attention is given to the interleukin-6 system owing to its apparent centrality in mediating the anti-inflammatory effects of exercise.

Prevalence of diabetes and impaired glucose metabolism in younger 'at risk' UK adults: insights from the STAND programme of research.

AIMS: Rising rates of obesity have led to an increasing prevalence of Type 2 diabetes mellitus in young people. Uncertainty exists over the utility of screening younger adults for Type 2 diabetes, as existing data sets have focused on mature (> 40 years) cohorts. The aim of this study was to determine the prevalence of impaired glucose metabolism in higher risk younger adults. METHODS: Overweight (with an additional risk factor) or obese adults (18-40 years) were recruited for the Sedentary Time And Diabetes (STAND) randomized controlled trial. Measures included an oral glucose tolerance test, HbA1c , biochemical and anthropometric data. RESULTS: One hundred and ninety-three individuals (68% female; median age 33.8 years; median BMI 33.9 kg/m²) were recruited. Forty-three per cent had a first-degree family history of Type 2 diabetes. Previously undiagnosed Type 2 diabetes was present in 4.7% (n = 9). Of participants, 18.1% (n = 35) had impaired glucose metabolism: 4.7% (n = 9) HbA1c ≥ 48 mmol/mol (6.5%); 9.3% (n = 18) HbA1c 42-46 mmol/mol (6.0-6.4%); 3.1% (n = 6) Type 2 diabetes on oral glucose tolerance test; 6.2% (n = 12) isolated impaired glucose tolerance; 2.1% (n = 4) isolated impaired fasting glucose; 1% (n = 2) both impaired fasting glucose and impaired glucose tolerance. Of participants, 58.5% (n = 113) had dyslipidaemia, 28.0% (n = 54) had hypertension, 31.1% (n = 60) were vitamin D deficient and 7.3% (n = 14) had abnormal liver function. CONCLUSIONS: This study identified a high prevalence of Type 2 diabetes and impaired glucose regulation in overweight and obese younger adults. These findings require confirmation in a larger, representative, population.

Associations of objectively measured sedentary behaviour and physical activity with markers of cardiometabolic health.

AIMS/HYPOTHESIS: The study aimed to examine the associations between objectively measured sedentary time, breaks in sedentary time, moderate-to-vigorous physical activity (MVPA) and total physical activity with markers of cardiometabolic health in a population with known risk factors for type 2 diabetes mellitus. METHODS: This study reports data from two ongoing diabetes prevention programmes. Participants with known risk factors were recruited from primary care practices located within the East Midlands, UK, over the period 2010-2011. ActiGraph GT3X accelerometers (15 s epochs) were used to assess sedentary time (<25 counts per 15 s), MVPA (≥ 488 counts per 15 s) and total physical activity (total counts). A break was considered as any interruption in sedentary time (≥ 25 counts per 15 s). Linear regression examined the independent association of sedentary time, breaks in sedentary time, MVPA and total physical activity with markers of cardiometabolic health. RESULTS: The sample comprised 878 participants; 153 from Project STAND (Sedentary Time And Diabetes) (age 32.9 ± 5.6 years, 28.8% male) and 725 from Walking Away from Diabetes (age 63.7 ± 7.8 years, 64.8% male). Following adjustment for various covariates, including MVPA and BMI, there were detrimental linear associations of sedentary time with 2 h plasma glucose (standardised beta coefficient) (ß = 0.220, p < 0.001), triacylglycerol (ß = 0.206, p = 0.001) and HDL-cholesterol (ß = -0.123, p = 0.029). Breaks in sedentary time, total physical activity and MVPA were significantly inversely associated with measures of adiposity, but not with any other cardiometabolic variables after adjustment for sedentary time and BMI. CONCLUSIONS/INTERPRETATION: In adults at high risk of type 2 diabetes mellitus, time spent sedentary is strongly and adversely associated with cardiometabolic health and may be a more important indicator of poor health than MVPA.

Plasma IL-6, its soluble receptors and F2-isoprostanes at rest and during exercise in chronic fatigue syndrome.

The aim of the current study was to investigate the levels of interleukin-6 (IL-6), its soluble receptors (sIL-6R and sgp130) and F(2)-isoprostanes, at rest and during exercise, in patients with chronic fatigue syndrome (CFS). Six male CFS patients and six healthy controls performed an incremental exercise test to exhaustion and a submaximal exercise bout to exhaustion. Blood samples taken in the submaximal test at rest, immediately post-exercise and 24 h post-exercise were analyzed for IL-6, sIL-6R, sgp130 and F(2)-isoprostanes. A further 33 CFS and 33 healthy control participants gave a resting blood sample for IL-6 and sIL-6R measurement. During the incremental exercise test only power output at the lactate threshold was lower (P<0.05) in the CFS group. F(2)-isoprostanes were higher (P<0.05) in CFS patients at rest and this difference persisted immediately and 24 h post-exercise. The exercise study found no differences in IL-6, sIL-6R or sgp130 at any time point between groups. In the larger resting group, there were no differences in IL-6 and sIL-6R between CFS and control groups. This investigation has demonstrated that patients with CFS do not have altered plasma levels of IL-6, sIL-6R or sgp130 either at rest or following exercise. F(2)-isoprostanes, however, were consistently higher in CFS patients.

The response of circulating levels of the interleukin-6/interleukin-6 receptor complex to exercise in young men.

The formation of an interleukin-6/IL-6 receptor (IL-6/IL-6R) complex increases the biological activity and half-life of IL-6, with its response to exercise currently unknown. The aim of the present study was to determine the response of circulating levels of the IL-6/IL-6R complex to exercise. Nine healthy male participants performed 1h of cycling exercise at a workload required to elicit 90% lactate threshold. Venous blood samples were taken at rest, immediately post-exercise and after 1.5 h rest. Hemoglobin concentration and hematocrit were measured to estimate changes in plasma volume during exercise. The concentrations of IL-6, sIL-6R and the IL-6/IL-6R complex were measured via ELISA and corrected for changes in plasma volume. A single bout of acute exercise resulted in a 5-fold increase (P<0.05) in IL-6 and a 1.2-fold increase (P<0.05) in sIL-6R immediately after exercise. These returned to baseline at 1.5 h after the cessation of exercise. There was a 2.1-fold increase (P<0.05) in the levels of the IL-6/IL-6R complex post-exercise with levels remaining 1.8 times elevated (P<0.05) after 1.5 h rest. The present study has demonstrated, for the first time, that circulating levels of the IL-6/IL-6R complex are increased in response to acute exercise in young males.

Effect of moderate-intensity exercise session on preprandial and postprandial responses of circulating ghrelin and appetite.

Responses of plasma total ghrelin and appetite were investigated during preprandial and postprandial stages of recovery from a moderate-intensity cycling session. Healthy recreationally active men underwent one exercise and one control trial. In the exercise trial, subjects exercised for approximately 60 minutes, while in the control trial they rested quietly for the same duration. After the intervention, subjects rested for 120 minutes and then consumed a test meal. Measurements were obtained immediately and 120 minutes after the intervention and then during 180 minutes of the postprandial period. The post-intervention concentration of total ghrelin was lower (p<0.05) in the exercise than in the control trial. The modulating effect of exercise was related to the reduction in the postprandial rather than preprandial concentration. Post-intervention scores of appetite were not different between the two trials, but when preprandial and postprandial responses were considered separately, postprandial hunger and desire to eat was higher (p<0.05) in the exercise trial. In summary, during recovery from moderate-intensity exercise, total ghrelin does not respond in a compensatory manner to disturbances in energy balance. Thus, an exercise-induced increase in appetite during the later stages of recovery coinciding with the postprandial state cannot be explained by changes in the plasma concentration of total ghrelin.

Response of plasma IL-6 and its soluble receptors during submaximal exercise to fatigue in sedentary middle-aged men.

The pleiotropic cytokine interleukin-6 (IL-6) has been demonstrated to increase during exercise. Little is known regarding the response of the soluble IL-6 receptors (sIL-6R and sgp130) during such exercise. The aim of the current study was to investigate the response of plasma IL-6, sIL-6R and sgp130 during fatiguing submaximal exercise in humans. Twelve participants underwent an incremental exercise test to exhaustion and one week later performed a submaximal exercise bout (96 +/- 6% lactate threshold) to volitional exhaustion. Blood samples taken at rest and immediately post exercise were analyzed for IL-6, sIL-6R and sgp130. IL-6 increased (P < 0.01) by 8.4 +/- 8.9 pg ml(-1) (75.7%) during the exercise period. sIL-6R and sgp130 also increased (P < 0.05) by 2.7 +/- 3.9 ng ml(-1) (9.6%) and 37.7 +/- 55.6 ng ml(-1) (9.6%), respectively. The current study is the first investigation to demonstrate that alongside IL-6, acute exercise stress results in an increase in both sIL-6R and sgp130.

Fatigue and illness in athletes.

Adequate nutrition before, during, and after training and competition is a key element to maintaining health. During both sprint and endurance exercise, the availability of glycogen is fundamental to performance and any deficit will lead to early fatigue. In addition, strategies to offset the negative effects of the products of metabolism are presented. Although nutritional strategies can attenuate the immunosuppressive effects of exercise, there remains a period of susceptibility to infection after a hard exercise session and when this is repeated without sufficient recovery an athlete can enter a period of "overtraining" during which performance deteriorates. The aetiology and identification of this state is not clear and some current ideas are discussed. Finally, gastrointestinal problems during running can negate any training benefits and we propose some suggestions to reduce this problem.

Spontaneous activity responses to exercise in males and females.

OBJECTIVE: This study examines the impact of a short-term exercise programme, prescribed on the basis of current exercise recommendations, on energy balance in males and females to assess whether this type of exercise induces compensatory changes in spontaneous activity energy expenditure (SAEE) and energy intake (EI). DESIGN: Individuals were monitored for 16 days, 8 days of habitual physical activity (C) and 8 days when exercise was imposed (E). Total energy expenditure (TEE) was calculated from individual relationships of VO2 and VCO2 to heart rate (HR) records of HR and physical activity obtained during waking hours of the C and E periods and basal metabolic rate (BMR) measurements (Deltatrac System, Datex Instrumentation). Changes in nude body mass (BM) were estimated by using a digital scale (Sartorius AG, Gottigen, Germany). SETTING: Laboratory and free-living. SUBJECTS: Eight lean females (body fat: 17.5+/-4.5%) and eight males of similar percentage body fat participated in this study. All subjects were Caucasian and aged between 20 and 25 years. INTERVENTION: During the E period, a supervised exercise session was conducted every second day, each consisting of a total net energy expenditure of 2092 kJ+BMR at 90% lactate threshold. RESULTS: During the E period, TEE was higher than C in males and females (exercise: 95.2+/-13.9, 78.3+/-15.9 MJ; control: 82.4+/-10.4, 68.8+/-16.7 MJ, respectively; P<0.00; P=0.02). SAEE, calculated as TEE minus the energy expended during exercise, was not significantly different between C (males: 82.4+/-4.8 MJ; females: 68.8+/-7.6 MJ) and E (males: 86.8+/-6.3 MJ; females: 70.0+/-7.2 MJ) periods in either gender. Males showed no change in BM over the C (pre-intervention: 83.4+/-7.2 kg; post-intervention: 83.1+/-6.8 kg) or E (pre-intervention: 83.4+/-6.8 kg; post-intervention: 83.4+/-6.8 kg) periods. Females' BM over the C period did not alter (pre-intervention: 63.3+/-2.8 kg; post-intervention 63.7+/-3.1 kg); however, there was a significant decrease (P<0.00) in BM over the E period (pre-intervention: 63.0+/-2.7 kg; post-intervention: 62.4+/-2.7 kg). CONCLUSION: The exercise programme was achieved in males and females without any impact on SAEE. Therefore, differences between genders in relation to BM reduction can be explained by differences in the EI response to exercise.

Acute effects of dehydration on sweat composition in men during prolonged exercise in the heat.

AIM: To determine whether acute exercise-heat-induced dehydration affects sweat composition, eight males cycled for 2 h at 39.5 +/- 1.6% VO2peak on two separate occasions in a hot-humid environment (38.0 +/- 0.0 degrees C, 60.0 +/- 0.1% relative humidity). METHODS: During exercise, subjects ingested either no fluid (dehydration) or a 20 mmol L(-1) sodium chloride solution (euhydration). The volume of solution, calculated from whole-body sweat loss and determined in a familiarization trial, was ingested at 0 min and every 15 min thereafter. Venous blood was collected at 0, 60 and 120 min of exercise and sweat was aspirated from a patch located on the dominant forearm at 120 min. RESULTS: Following the 2-h cycling exercise, sweat [Na+] and [Cl-] was greater (P < 0.05) in the dehydration trial (Na+ 91.1 +/- 6.8 mmol L(-1); Cl- 73.3 +/- 3.5 mmol L(-1)) compared with the euhydration trial (Na+ 81.1 +/- 5.9 mmol L(-1); Cl- 68.5 +/- 3.3 mmol L(-1)). In addition, dehydration invoked a greater serum [Na+] (142.2 +/- 0.7 mmol L(-1); P < 0.05), [Cl-] (105.8 +/- 0.6 mmol L(-1); P < 0.05) and [K+] (5.27 +/- 0.2 mmol L(-1); P < 0.05) over the euhydration values for [Na+], [Cl-] and [K+], respectively (138.9 +/- 0.6, 102.9 +/- 0.5 and 4.88 +/- 0.1 mmol L(-1)). Plasma aldosterone was also significantly higher during exercise in the dehydration trial compared with the euhydration trial (53.8 +/- 3.8 vs. 40.0 +/- 4.3 ng dL(-1); P < 0.05). CONCLUSIONS: Acute exercise-heat stress without fluid replacement resulted in a greater sweat [Na+] and [Cl-] which was potentially related to greater extracellular fluid [Na+], plasma aldosterone or sympathetic nervous activity.

Effects of central sympathetic inhibition on heart rate variability during steady-state exercise in healthy humans.

The profound reduction in heart rate variability (HRV) that occurs during exercise is thought to be, at least in part, the result of sympathetic nervous system activation. Moxonidine is a centrally acting anti-sympathetic drug, which suppresses sympathetic nervous system outflow by stimulation of central imidazoline receptors located in the rostral ventro-lateral medulla. This study was designed to investigate the combined effects of central sympathetic inhibition with moxonidine and steady-dynamic exercise on HRV. Ten normal males participated in a double-blind cross-over study, taking either placebo or 0.4 mg of moxonidine. The subjects were studied at rest and during steady-state exercise. HRV was measured considering both time and frequency domain parameters. As a non-linear measure, the Poincaré scatter-plot was measured and analysed quantitatively. Ventilation and gas exchange were also measured during exercise. In addition, plasma catecholamines were measured at rest and during exercise. The only parameter changed, at rest, by moxonidine was the blood pressure which was reduced. During exercise, moxonidine reduced plasma noradrenaline (NA), compared with the placebo (P<0.01). The only change observed in HRV during exercise was a significant reduction of the continuous long-term standard deviation (SD2) of the Poincaré scatter-plot of the R-R interval (P<0.05). However, the potential and prognostic significance of this result needs to be further assessed.

Effect of induced metabolic alkalosis on sweat composition in men.

To determine whether induced metabolic alkalosis affects sweat composition, 10 males cycled for 90 min at 62.5 +/- 1.3% peak oxygen uptake, on two separate occasions. Subjects ingested either empty capsules (placebo) or capsules containing NaHCO3- (0.3 g kg-1 body mass; six equal doses) over a 2-h period, which commenced 3 h prior to exercise. Arterialized-venous blood samples were drawn prior to and after 15, 30, 60 and 90 min of exercise. Sweat was aspirated at the end of exercise from a patch located on the right scapula region. NaHCO3- ingestion elevated blood pH, [HCO3-] and serum [Na+], whereas serum [Cl-] and [K+] were reduced, both at rest and during exercise (P < 0.05). Sweat pH was greater in the NaHCO3- trial (6.24 +/- 0.18 vs. 6.38 +/- 0.18; P < 0.05), whereas sweat [Na+] (49.5 +/- 4.8 vs. 50.2 +/- 4.3 mEq L-1), [Cl-] (37.5 +/- 5.1 vs. 39.3 +/- 4.2 mEq L-1) and [K+] (4.66 +/- 0.19 vs. 4.64 +/- 0.34 mEq L-1) did not differ between trials (P > 0.05). Sweat [HCO3-] (2.49 +/- 0.58 vs. 3.73 +/- 1.10 mEq L-1) and [lactate] (8.92 +/- 0.79 vs. 10.51 +/- 0.32 mmol L-1) tended to be greater after NaHCO3- ingestion, although significance was not reached (P=0.07 and P=0.08, respectively). These data indicate that induced metabolic alkalosis can modify sweat composition, although it is unclear whether the secretory coil, reabsorptive duct, or both are responsible for this alteration.

Low dosage monophasic oral contraceptive use and intermittent exercise performance and metabolism in humans.

Nine untrained women using low dosage monophasic oral contraceptives (OC) performed an intermittent treadmill test on two different occasions within one pill-cycle to determine the effect of OC on performance and some commonly used metabolic markers. The first test was performed after 5-8 days of resuming the OC agents after menstrual bleeding while the other test was performed after 19-21 days. Performance time on the final exhausting run of six intermittent high intensity 20 s runs was no different between trials [mean days 5-8: 22.3 (SEM 1.2) s vs days 19-21: 22.7 (SEM 1.1) s]. There was no difference in heart rate [peak heart rate days 5-8: 183 (SEM 3) beats.min-1 vs days 19-21: 186 (SEM 2) beats.min-1], oxygen consumption during any run [run 5 of days 5-8: 1,392 (SEM 51) ml.min-1 vs run 5 of days 19-21: 1,494 (SEM 3) ml.min-1] or in any of the metabolic variables measured at any time in venous blood [peak blood lactate concentration days 5-8: 8.4 (SEM 0.3) mmol.l-1 vs days 19-21: 8.1 (SEM 0.5) mmol.l-1; peak blood glycerol concentration days 5-8: 0.39 (SEM 0.02) mmol.l-1 vs days 19-21: 0.38 (SEM 0.02) mmol.l-1; resting free fatty acids concentration days 5-8: 0.25 (SEM 0.05) mmol.l-1 vs days 19-21: 0.29 (SEM 0.07) mmol.l-1; peak blood glucose concentration days 5-8: 6.7 (SEM 0.5) mmol.l-1 vs days 19-21: 6.6 (SEM 0.2) mmol.l-1; peak capillary blood ammonia concentration days 5-8: 139 (SEM 18.3) mumol.l-1 vs days 19-21: 170 (SEM 18.0) mumol.l-1]. These results suggest neither intermittent high intensity exercise performance nor energy metabolism change between days 5-8 and days 19-21 of a low dosage monophasic OC pill during one pill-cycle.

Electromyogram changes during sustained contraction after resistance training in women in their 3rd and 8th decades.

The present study aimed at investigating the neuromuscular adaptations to 6 weeks of resistance training in women in their third (6 experimental, 8 controls) and eighth decades (8 experimental, 8 controls). The surface electromyogram (sEMG) was measured from the biceps brachii muscle during constant-force isometric contractions lasting 12 s at 80% of maximal voluntary contraction (MVC). All the signals were analysed adopting in the time domain the root mean square (RMS) as a measure of amplitude and in the frequency domain the median frequency (MDF) of the power spectrum. Quantitative analysis was performed from the 3rd to the 6th second, to describe the early phase of the contraction ("Early"), starting from point at which 80% of the MVC was reached, and from the 9th to the 12th second, to describe the last part of the constant-force sustained contraction ("Late"). After training, the MVC increased by 22.4% in the young (P < 0.0001) and by 13.4% in the older (P < 0.05) women. The "Early" RMS increased by 60.4% with respect to the pre-training condition in the young (P < 0.01) but not in the older women. In contrast, the "Late" RMS increased by 46.7% in the older (P < 0.05) but not in the young women. The MDF remained unchanged in both groups. These results indicate that young and older women showed different training-induced adaptation of the motor unit (MU) activation pattern, in order to keep a constant level of force during a sustained isometric contraction at 80% of MVC.

Effects of moderate dietary manipulation on intermittent exercise performance and metabolism in women.

The aim of the current study was to examine the effect of a moderate alteration in pre-exercise diet composition on the performance of, and metabolic response to, intermittent treadmill exercise in a group of normally menstruating females. Eight recreationally active women performed two intermittent, incremental exercise trials, one preceded by 2 days of a high [61 (1)%] carbohydrate (CHO) diet and the other by 2 days of a low [31 (1)%] CHO diet. Oxygen uptake (VO2) was measured during, and blood samples were obtained immediately after, each bout for the determination of blood lactate, glucose, glycerol, plasma free fatty acids and plasma ammonia. Performance, as assessed by time to exhaustion in the final bout, was found to be similar whether preceded by a high- or low-CHO diet [median (range): 28.0 (18-54) s, 29 (18-54) s, respectively]. No significant between trial differences were found in VO2, heart rate, or any of the blood metabolites. The results of the current, study indicate that moderate alterations of pre-exercise diet do not affect intermittent, high-intensity exercise performance in women, despite some evidence of an alteration in the pattern of the metabolic response to exercise.

Variations in regional sweat composition in normal human males.

This project aimed to quantify the regional distribution of sweat composition over the skin surface and to determine whether sweat constituent concentrations collected from regional sites can estimate whole-body concentrations. Ten males cycled for 90 min in a 20 degrees C (50% relative humidity) environment at 45% peak aerobic power. Sweat was collected from eleven skin regions and the whole body, using a wash-down technique. Strong relationships were evident between the regional and whole-body sweat [Na+] and [Cl-], such that the thigh and calf exhibited greater correlation coefficients than area-weighted means derived from four and eight skin regions. Therefore, in this particular protocol the whole-body sweat [Na+] and [Cl-] could be predicted from regional sweat collections. Relationships between sweat constituents were evident for sweat [Na+] and pH, and sweat [K+] and [lactate] when data were pooled between skin regions and subjects. To our knowledge this is the first investigation to report a positive relationship between sweat [K+] and [lactate]. The exact mechanism responsible for the positive relationship between sweat [K+] and [lactate] is uncertain although it is speculated to occur at the secretory coil.