The influence of exercise load with and without different levels of blood flow restriction on acute changes in muscle thickness and lactate

The aim of this study was to compare exercise with and without different degrees of blood flow restriction (BFR) on acute changes in muscle thickness (MTH) and whole blood lactate (WBL). Forty participants were assigned to Experiment 1, 2 or 3. Each experiment completed protocols differing by pressure, load and/or volume. MTH and WBL were measured pre and postexercise. The acute changes in MTH appear be maximized at 30% one repetition maximum (1RM) with BFR, although the difference between 20% 1RM and 30% 1RM at the lateral site was small (0·1 versus 0·2 cm, P = 0·09). Increasing the exercise load from 20% to 30% 1RM with BFR produces clear changes in WBL (3·7 versus 5·5 mmol l^?1, P<0·001). The acute changes in MTH and WBL for 30% 1RM in combination with BFR were similar to that observed with 70% 1RM and 20 and 30% to failure, albeit at a lower exercise volume. These findings may have implications for designing future studies as it suggest that exercise load (to a point) may have a greater influence on acute changes in MTH and metabolic accumulation than the applied relative pressure.     

The effects of beta‐alanine supplementation on physical working capacity at heart rate threshold

Beta‐alanine (BA) supplementation has been shown to delay neuromuscular fatigue as a result of increased muscle carnosine concentrations. Carnosine has also been found in brain and cardiac tissue. The physical working capacity test at heart rate threshold (PWC_HRT) is a global estimate of the onset of fatigue during exercise, influenced by central and peripheral factors. The purpose of this study was to determine the effects of 28 days of BA supplementation on the PWC_HRT. Thirty subjects (mean ± SD; age: 21·0 ± 2·1 years; body mass: 72·7 ± 14·5 kg; height: 170·1 ± 7·9 cm) were randomly assigned to BA (n = 15) or placebo (PL, n = 15) groups. Testing included eight to nine total visits: an enrolment day, physical screening, peak oxygen consumption (V^·O_2peak) and two PWC_HRT assessments over 4 days. Significant differences existed between BA and PL for PWC_HRT (P = 0·001; mean?: BA? = +24·2 watts, PL? = +11·2 watts), but not for V^·O_2peak (P = 0·222), time to exhaustion (TTE; P = 0·562) or ventilatory threshold (VT; P = 0·134). Results suggest that BA may increase heart rate training threshold. These results, in combination with one previous study reporting a potential effect of BA on HR, suggest that future studies should evaluate both central and peripheral aspects of fatigue with BA intake.     

The exercise heart rate profile in master athletes compared to healthy controls

Endurance exercise protects the heart via effects on autonomic control of heart rate (HR); however, its effects on HR indices in healthy middle‐aged men are unclear. This study compared HR profiles, including resting HR, increase in HR during exercise and HR recovery after exercise, in middle‐aged athletes and controls. Fifty endurance‐trained athletes and 50 controls (all male; mean age, 48·7 ± 5·8 years) performed an incremental symptom‐limited exercise treadmill test. The electrocardiographic findings and HR profiles were evaluated. Maximal O₂ uptake (52·6 ± 7·0 versus 34·8 ± 4·5 ml kg^?1 min^?1; P<0·001) and the metabolic equivalent of task (15·4 ± 1·6 versus 12·2 ± 1·5; P<0·001) were significantly higher in athletes than in controls. Resting HR was significantly lower in athletes than in controls (62·8 ± 6·7 versus 74·0 ± 10·4 beats per minute (bpm), respectively; P<0·001). Athletes showed a greater increase in HR during exercise than controls (110·1 ± 11·0 versus 88·1 ± 15·4 bpm; P<0·001); however, there was no significant between‐group difference in HR recovery at 1 min after cessation of exercise (22·9 ± 5·6 versus 21·3 ± 6·7 bpm; P = 0·20). Additionally, athletes showed a lower incidence of premature ventricular contractions (PVCs) during exercise (0·0% versus 24·0%; P<0·001). Healthy middle‐aged men participating in regular endurance exercise showed more favourable exercise HR profiles and a lower incidence of PVCs during exercise than sedentary men. These results reflect the beneficial effect of endurance training on autonomic control of the heart.     

Changes in free radical generation and antioxidant capacity during ultramarathon foot race

Background Exhaustive exercise has been implicated in the generation of reactive oxygen species, resulting in oxidative stress. We studied the effect of a long‐distance, endurance exercise on oxidative stress parameters in athletes who participated in the ultramarathon race Spartathlon (246 km). Materials and methods This study included 18 runners (16 men and 2 women) aged 42·8 ± 1·4 years. Blood samples were obtained 24 h before (prerace), at the end (postrace) and 48 h after the end of the race (48 h postrace). We measured oxidative stress indices, including red cell glutathione, malonyldialdehyde and 8‐iso‐prostaglandin F_2a, as well as the total antioxidant capacity. Results 8‐Iso‐prostaglandin F_2a level increased significantly at the end of the race, compared to prerace levels (up to 914·7 ± 61·4 pg mL^?1 from 197·6 ± 8·4 pg mL^?1), and remained 2·5‐fold increased over the baseline 48 h after the race (532·0 ± 54·2 pg mL^?1, P < 0·000). The total antioxidant capacity of the athletes increased from a baseline of 289·6 ± 9·0 µmol L^?1 to 358·7 ± 11·0 µmol L^?1 immediately after the race and remained elevated 48 h later (350·6 ± 7·6 µmol L^?1) (P < 0·001). Conclusions Prolonged exercise induces a marked response of oxidative stress biomarkers, which in part is compensated by serum ability to scavenge free radicals. Whether these changes have long‐term negative effects in the organism needs further investigation.     

Acute hormonal responses following different velocities of eccentric exercise

The aim of this study was to compare the acute hormonal responses following two different eccentric exercise velocities. Seventeen healthy, untrained, young women were randomly placed into two groups to perform five sets of six maximal isokinetic eccentric actions at slow (30° s^?1) and fast (210° s^?1) velocities with 60‐s rest between sets. Growth hormone, cortisol, free and total testosterone were assessed by blood samples collected at baseline, immediately postexercise, 5, 15 and 30 min following eccentric exercise. Changes in hormonal responses over time were compared between groups, using a mixed model followed by a Tukey's post hoc test. The main findings of the present study were that the slow group showed higher growth hormone values immediately (5·08 ± 2·85 ng ml^?1, P = 0·011), 5 (5·54 ± 3·01 ng ml^?1, P = 0·004) and 15 min (4·30 ± 2·87 ng ml^?1, P = 0·021) posteccentric exercise compared with the fast group (1·39 ± 2·41 ng ml^?1, 1·34 ± 1·97 ng ml^?1 and 1·24 ± 1·87 ng ml^?1, respectively), and other hormonal responses were not different between groups (P>0·05). In conclusion, slow eccentric exercise velocity enhances more the growth hormone(GH) response than fast eccentric exercise velocity without cortisol and testosterone increases.     

Real‐time contrast‐enhanced ultrasound determination of microvascular blood volume in abdominal subcutaneous adipose tissue in man. Evidence for adipose tissue capillary recruitment

The adipose tissue metabolism is dependent on its blood perfusion. During lipid mobilization e.g. during exercise and during lipid deposition e.g. postprandial, adipose tissue blood flow is increased. This increase in blood flow may involve capillary recruitment in the tissue. We investigated the basic and postprandial microvascular volume in adipose tissue using real‐time contrast‐enhanced ultrasound (CEU) imaging in healthy normal weight subjects. In nine subjects, CEU was performed in abdominal subcutaneous adipose tissue and in the underlying skeletal muscle after a bolus injection of ultrasound contrast agent to establish the reproducibility of the technique. In nine subjects, the effect of an oral glucose load on blood flow and microvascular volume was measured in abdominal subcutaneous adipose tissue and forearm skeletal muscle. ¹³³Xe washout and venous occlusion strain‐gauge plethysmography was used to measure the adipose tissue and forearm blood flow, respectively. Ultrasound signal intensity of the first plateau phases was 27 ± dB in the abdominal subcutaneous adipose tissue and 18 ± 2dB (P<0·05) in the underlying skeletal muscle. The reproducibility of the measurements was good with a 4% coefficient of variation in both tissues. Blood flow and the change in signal intensity as a measure of the microvascular volume increased significantly and simultaneously in abdominal subcutaneous adipose tissue after glucose intake. The forearm blood flow and muscle signal intensity remained constant. It is concluded that the microvascular volume and changes in volume in abdominal subcutaneous adipose tissue can be assessed using CEU with good reproducibility. Postprandial capillary recruitment takes place in abdominal subcutaneous adipose tissue.     

The relationship between arterial stiffness and the lifestyle habits of female athletes after retiring from competitive sports: a prospective study

This study investigated the relationship between changes in arterial stiffness and the lifestyle habits of endurance athletes after retiring from competition. The subjects were 10 female university endurance athletes. We used formPWV/ABI^® as an index for arterial stiffness and measured brachial‐ankle pulse‐wave velocity (baPWV) directly before subjects retired (0Y) and at 2 years after retirement (2Y). Furthermore, to investigate the relationship between arterial stiffness and lifestyle habits 2 years later, Lifecorder ^® PLUS was used to measure physical activity levels, hours of sleep were surveyed using a questionnaire, and a food intake survey was conducted using Excel Eiyoukun Food Frequency Questionnaire Based on Food Group, FFQg Ver. 3.5. We found that baPWV increased significantly from 0Y to 2Y (P<0·05). Furthermore, negative correlations were observed between 2Y baPWV and step count as the physical activity index (r = ?0·653, P<0·05) and moderate physical activity (r = ?0·663, P<0·05). With regard to lifestyle habits that affected the amount of increase in baPWV from 0Y to 2Y (ΔbaPWV), negative correlations were noted between the step count (r = ?0·690, P<0·05) and total physical activity (r = ?0·657, P<0·05). However, no significant correlations were observed between 2Y baPWV and ΔbaPWV with food intake or hours of sleep. The results of this study suggested that physical activity was a lifestyle habit that inhibited an increase in arterial stiffness after retirement from competition and that having a high step count or engaging in physical activity for long periods of time in particular was useful in this regard.     

The impact of short duration,high intensity exercise on cardiac troponin release

The aim of this study was to assess the appearance of cardiac troponins (cTnI and/or cTnT) after a short bout (30 s) of ‘all‐out’ intense exercise and to determine the stability of any exercise‐related cTnI release in response to repeated bouts of high intensity exercise separated by 7 days recovery. Eighteen apparently healthy, physically active, male university students completed two all‐out 30 s cycle sprint, separated by 7 days. cTnI, blood lactate and catecholamine concentrations were measured before, immediately after and 24 h after each bout. Cycle performance, heart rate and blood pressure responses to exercise were also recorded. Cycle performance was modestly elevated in the second trial [6·5% increase in peak power output (PPO)]; there was no difference in the cardiovascular, lactate or catecholamine response to the two cycle trials. cTnI was not significantly elevated from baseline through recovery (Trial 1: 0·06 ± 0·04 ng ml^?1, 0·05 ± 0·04 ng ml^?1, 0·03 ± 0·02 ng ml^?1; Trial 2: 0·02 ± 0·04 ng ml^?1, 0·04 ± 0·03 ng ml^?1, 0·05 ± 0·06 ng ml^?1) in either trial. Very small within subject changes were not significantly correlated between the two trials (r = 0·06; P>0·05). Subsequently, short duration, high intensity exercise does not elicit a clinically relevant response in cTnI and any small alterations likely reflect the underlying biological variability of cTnI measurement within the participants.     

Metabolic and anti-inflammatory benefits of eccentric endurance exercise - a pilot study

Background Eccentric endurance exercise (e.g. hiking downwards) is less strenuous than concentric exercise (e.g. hiking upwards) but its potential to reduce cardiovascular risk is unknown. Materials and methods We randomly allocated 45 healthy sedentary individuals (16 men and 29 women, mean age 48 years) to one of two groups, one beginning with two months of hiking upwards, the other with two months of hiking downwards the same route, with a crossover for a further two months. For the opposite way, a cable car was used where compliance was recorded electronically. The difference in altitude was 540 metres; the distance was covered three to five times a week. Fasting and postprandial metabolic profiles were obtained at baseline and after the two month periods of eccentric and concentric exercise, respectively. Results Forty‐two of the 45 participants completed the study; the compliance rate was therefore 93%. Compared with baseline, eccentric exercise lowered total cholesterol (by 4·1%; P = 0·026), low‐density lipoprotein (LDL) cholesterol (by 8·4%, P = 0·001), Apolipoprotein B/Apolipoprotein A1 ratio (by 10·9%, P < 0·001), homeostasis model assessment of insulin resistance scores (by 26·2%, P = 0·017) and C‐reactive protein (by 30·0%; P = 0·007); the magnitude of these changes was comparable to that of concentric exercise. Eccentric exercise improved glucose tolerance (by 6·2%, P = 0·023), whereas concentric exercise improved triglyceride tolerance (by 14·9%, P = 0·022). Conclusions Eccentric endurance exercise is a promising new exercise modality with favourable metabolic and anti‐inflammatory effects and is well applicable to sedentary individuals.     

The washout rate of a subcutaneous 99mTc-HSA depot in lower extremity lymphoedema

Purpose: Lymphoscintigraphy is currently the leading diagnostic modality of lower extremity lymphoedema but has been criticized for being unreliable. Washout rate constants have been investigated and proven to be of diagnostic value in several studies of breast‐cancer‐related lymphoedema; however, the applicability in lower extremity lymphoedema needs further evaluation. The aim of the study was to verify if washout of ^99mTc‐Human Serum Albumin (^99mTc‐HSA) is a reliable diagnostic tool in lower extremity lymphoedema. Methods: Twenty healthy volunteers and eight patients (11 legs) with lymphoscintigraphy verified lower extremity lymphoedema participated in the study. A depot consisting of 0·1 ml 10 MBq/ml ^99mTc‐HSA was injected subcutaneously into the dorsum of each foot. The depot washout rate was measured using a portable scintillation detector system and time‐activity curves were generated. After 30 min of supine rest and 10 min of standardized ergometric exercise, measurements were recorded for 20 min. Following correction for physical decay of ^99mTc, the depot washout rate constant was calculated using linear regression analysis. Finally depot half‐life was calculated from the washout rate constant. Results: Median half‐life for healthy volunteers was 9·4 h (range 2·5–28·3 h). Median half‐life for lymphoedema patients was 10·7 h (range 1·5–35·1 h). No statistical significant difference could be detected between healthy volunteers and lymphoedema patients (P = 0·78). Conclusions: The washout rate of a subcutaneous ^99mTc‐HSA depot is not a reliable diagnostic tool in examination of lower extremity lymphoedema. Additional examinations revealed in vivo instability of the utilized ^99mTc‐HSA as the likely reason.     

The susceptibility of the knee extensors to eccentric exercise‐induced muscle damage is not affected by leg dominance but by exercise order

The aims of this study were first to compare the response of dominant and non‐dominant legs to eccentric exercise and second, to examine whether there is an effect of exercise order on the magnitude of symptoms associated with intense eccentric protocols. Eighteen young men performed three sets of 30 maximal eccentric isokinetic (60° s^?1) contractions of the knee extensors (range of motion, ROM: 0°–100°, 0 = full extension) using either dominant or non‐dominant leg. They repeated a similar eccentric bout using the contralateral leg 6 weeks later. The sequence of leg's use was allocated to create equally balanced groups. Four indirect markers of muscle damage including subjective pain intensity, maximal isometric strength, muscle stiffness and plasma creatine kinase (CK) activity were measured before and 24 h after exercise. All markers changed significantly following the eccentric bout performed either by dominant or non‐dominant legs, but no significant difference was observed between legs. Interestingly, the comparison between the first and second eccentric bouts revealed that muscle soreness (?42%, P<0·001), CK activity (?62%, P<0·05) and strength loss (?54%, P<0·01) were significantly lower after the second bout. This study suggests that leg dominance does not influence the magnitude of exercise‐induced muscle damage and supports for the first time the existence of a contralateral protection against exercise‐induced muscle damage in the lower limbs.     

Validity of Oxycon Mobile in measuring inspiratory capacity in healthy subjects

Introduction: Inspiratory capacity (IC) assessments have been performed mainly in laboratory settings, because of fixed measurement devices. Oxycon Mobile^® (OM) is the mobile and wireless version of Oxycon Pro^® (OP), a commonly used fixed measurement device. The purpose of this study was to examine IC agreement between OM and OP at rest and during steady‐state exercise. Also, the within‐ and between‐days variability of IC’s were determined. Methods: Thirty‐five healthy subjects were recruited. Twenty‐five subjects were included for determining validity of the OM and ten subjects for the variability study. For validation of OM, resting and exercise IC’s (IC_rest and IC_exercise respectively) were measured consecutively by OM and OP, in random order. Exercise consisted of cycle ergometry at 50% of subject’s predicted maximal exercise capacity. Results: The mean difference between OM and OP regarding IC_rest was ?0·05L, with limits of agreement of ?0·47 to 0·37L (or ?1·2% with limits of agreement of ?11·6 to 9·3%) (P>0·05). The mean difference of IC_exercise was ?0·06L, and the limits of agreement were ?0·48 to 0·35L (or ?1·4% with limits of agreement of ?11·8 to 9·0%) (P>0·05). No significant differences in IC’s within‐ or between‐days were found. Discussion: The limits of agreement of the IC measured by OM and OP were ±10%, which is recommended for interdevice reproducibility. We conclude that OM and OP can be used interchangeably for measuring IC at rest and during steady‐state exercise.     

Are early and late rate of force development differently influenced by fast‐velocity resistance training?

This study examined the effect of fast‐velocity concentric isokinetic resistance training (FV) on the rate of force development (RFD) at early (<100 ms) and late phases (>100 ms) of rising muscle force. Nine men participated in a 6‐week resistance training intervention for the lower body, and nine matched subjects participated as controls (CON). During concentric isokinetic (180°s^?1) knee extension training, subjects were instructed to do each contraction ‘as fast and forcefully as possible’. Maximal muscle strength (MVC) and RFD (0–10, 0–20, …, 0–250 ms from the onset of contraction) were measured during maximal voluntary isometric contraction of the knee extensors (KE). There were no significant changes in MVC of KE in both groups after intervention (FV = 314·2 ± 101·1 versus 338·7 ± 88·0 N?m, P>0·05; CON = 293·3 ± 94·8 versus 280·0 ± 72·2 N?m, P>0·05). The RFD increased 39–71% at time intervals up to 90 ms from the onset of the contraction (P < 0·05), whereas no change occurred at later time intervals. Similarly, relative RFD (i.e.%MVC?s^?1) (RFDr) increased 33–56% at time intervals up to 70 ms from the onset of the contraction (P<0·05). It can be concluded that a short period of resistance training performed with concentric fast‐velocity isokinetic muscle contractions is able to enhance RFD and RFDr obtained at the early phase of rising muscle force.     

Abnormal vascular reactivity at rest and exercise in obese boys

Background Obese children exhibit vascular disorders at rest depending on their pubertal status, degree of obesity, and level of insulin resistance. However, data regarding their vascular function during exercise remain scarce. The aims of the present study were to evaluate vascular morphology and function at rest, and lower limb blood flow during exercise, in prepubertal boys with mild‐to‐moderate obesity and in lean controls. Materials and methods Twelve moderately obese prepubertal boys [Body Mass Index (BMI: 23·9 ± 2·6 kg m^?2)] and thirteen controls (BMI:17·4 ± 1·8 kg m^?2), matched for age (mean age: 11·6 ± 0·6 years) were recruited. We measured carotid intima‐media thickness (IMT) and wall compliance and incremental elastic modulus, resting brachial flow‐mediated dilation (FMD) and nitrate‐dependent dilation (NDD), lower limb blood flow during local knee‐extensor incremental and maximal exercise, body fat content (DEXA), blood pressure, blood lipids, insulin and glucose. Results Compared to lean controls, obese boys had greater IMT (0·47 ± 0·06 vs. 0·42 ± 0·03 mm, P < 0·05) but lower FMD (4·6 ± 2·8 vs. 8·8 ± 3·2%, P < 0·01) in spite of similar maximal shear rate, without NDD differences. Lower limb blood flow (mL min^?1·100 g^?1) increased significantly from rest to maximal exercise in both groups, although obese children reached lower values than lean counterparts whatever the exercise intensity. Conclusions Mild‐to‐moderate obesity in prepubertal boys without insulin resistance is associated with impaired endothelial function and blunted muscle perfusion response to local dynamic exercise without alteration of vascular smooth muscle reactivity.     

Fatigue and rapid hamstring/quadriceps force capacity in professional soccer players

The aim of this study was to investigate the effect of fatigue induced by an exhaustive laboratory‐based soccer‐specific exercise on different hamstrings/quadriceps (H:Q) ratios of soccer players. Twenty‐two male professional soccer players (23·1 ± 3·4 year) performed maximal eccentric (ecc) and concentric (con) contractions for knee extensors (KE) and flexors (KF) at 60° s^?1 and 180° s^?1 to assess conventional (H_con:Q_con) and functional (H_ecc:Q_con) ratios. Additionally, they performed maximal voluntary isometric contraction for KE and KF, from which the maximal muscle strength, rate of force development (RFD) and RFD H:Q strength ratio (RFDH:Q) were extracted. Thereafter, subjects were performed an exhaustive laboratory‐based soccer‐specific exercise and a posttest similar to the pretest. There was significant reduction in H_con:Q_con (0·60 ± 0·06 versus 0·58 ± 0·06, P<0·05) and in H_ecc:Q_con (1·29 ± 0·2 versus 1·16 ± 0·2, P<0·01) after the soccer‐specific exercise. However, no significant difference between Pre and Post exercise conditions was found for RFDH:Q at 0–50 (0·53 ± 0·23 versus 0·57 ± 0·24, P>0·05) and 0–100 ms (0·53 ± 0·17 versus 0·55 ± 0·17, P>0·05). In conclusion, H:Q strength ratios based on peak force values are more affected by fatigue than RFDH:Q obtained during early contraction phase. Thus, fatigue induced by soccer‐specific intermittent protocol seems not reduce the potential for knee joint stabilization during the initial phase of voluntary muscle contraction.     

Acute resistance exercise using free weights on aortic wave reflection characteristics

Aortic wave reflection characteristics such as the augmentation index (AIx), wasted left ventricular pressure energy (ΔE_w) and aortic haemodynamics, such as aortic systolic blood pressure (ASBP), strongly predict cardiovascular events. The effects of acute resistance exercise (ARE) using free‐weight exercises on these characteristics are unknown. Therefore, we sought to determine the effects of acute free‐weight resistance exercise on aortic wave reflection characteristics and aortic haemodynamics in resistance‐trained individuals. Fifteen young, healthy resistance‐trained (9 ± 3 years) individuals performed two randomized sessions consisting of an acute bout of free‐weight resistance exercise (ARE) or a quiet control (CON). The ARE consisted of three sets of 10 repetitions at 75% one repetition maximum for squat, bench press and deadlift. In CON, the participants rested in the supine position for 30 min. Measurements were made at baseline before sessions and 10 min after sessions. A two‐way ANOVA was used to compare the effects of condition across time. There were no significant interactions for aortic or brachial blood pressures. Compared to rest, there were significant increases in augmentation pressure (rest: 5·7 ± 3·0 mmHg; recovery: 10·4 ± 5·7 mmHg, P = 0·002), AIx (rest: 116·8 ± 4·2%; recovery: 123·2 ± 8·4%, P = 0·002), AIx normalized at 75 bpm (rest: 5·2 ± 7·6%; recovery: 27·3 ± 13·2%, P<0·0001), ΔE_w (rest: 1215 ± 674 dynes s cm^?2; recovery: 2096 ± 1182 dynes s cm^?2, P = 0·008), and there was a significant decrease in transit time of the reflected wave (rest: 150·7 ± 5·8 ms; recovery 145·5 ± 5·6 ms, P<0·001) during recovery from ARE compared to CON. These data suggest that ARE using free‐weight exercises may have no effect on aortic and brachial blood pressure but may significantly alter aortic wave reflection characteristics.     

Effects of blood flow restriction duration on muscle activation and microvascular oxygenation during low‐volume isometric exercise

The purpose of the investigation was to observe how varying occlusion durations affected neuromuscular activation and microvascular oxygenation during low‐volume isometric knee extension exercise. Healthy, recreationally active males performed isometric knee extension at a variety of submaximal intensities under different blood flow restriction (BFR) occlusion durations. The occlusion pressure (130% SBP) was applied either 5 min prior to exercise (PO), immediately prior to exercise (IO) or not during exercise (CON). Surface electromyography (sEMG) and near‐infrared spectroscopy (NIRS) was used to record the neuromuscular activation and microvascular oxygenation of the knee extensors during exercise. No difference in sEMG was observed in the vastus lateralis or vastus medialis during any exercise condition or any submaximal intensity. PO elicited greater microvascular deoxygenation (deoxy‐[Hb + Mb]) compared to CON (P≤0·05) at all submaximal intensities and also compared to IO at 20% maximal voluntary contraction (MVC). IO resulted in a greater deoxy‐[Hb + Mb] response during low‐intensity exercise (20% and 40% MVC) compared to CON (P≤0·05). These findings suggest that applying BFR 5 min before exercise can enhance the exercise‐induced metabolic stress (i.e. deoxy‐[Hb + Mb]), measured via NIRS, during low‐intensity exercise (20% MVC) compared to applying BFR immediately prior to exercise. Furthermore, the increased metabolic stress observed during IO is attenuated during high‐intensity (60% MVC, 80% MVC) exercise when compared to CON conditions. Knowledge of the changes in exercise‐induced metabolic stress between the various occlusion durations may assist in developing efficient BFR exercise programmes.     

Acute physiological and perceptual responses to high‐load resistance exercise in hypoxia

This study assessed whether hypoxia during high‐load resistance exercise could enhance the acute physiological responses related to muscular development. Twelve trained men performed exercise in three conditions: normoxia (fraction of inspired oxygen [F_IO₂] = 21%), moderate‐level hypoxia (F_IO₂ = 16%) and high‐level hypoxia (F_IO₂ = 13%). Exercise comprised high‐load squats and deadlifts (5 × 5 using 80% of 1‐repetition maximum with 180‐s rest). Muscle oxygenation and activation were monitored during exercise. Metabolic stress was estimated via capillary blood sampling. Perceived fatigue and soreness were also quantified following exercise. While the hypoxic conditions appeared to affect muscle oxygenation, significant differences between conditions were only noted for maximal deoxyhaemoglobin in the deadlift (P = 0·009). Blood lactate concentration increased from 1·1 to 1·2 mmol l^?1 at baseline to 9·5–9·8 mmol l^?1 after squats and 10·4–10·5 mmol l^?1 after deadlifts (P≤0·001), although there were no between‐condition differences. Perceived fatigue and muscle soreness were significantly elevated immediately and at 24 h following exercise, respectively, by similar magnitudes in all conditions (P≤0·001). Muscle activation did not differ between conditions. While metabolic stress is thought to moderate muscle activation and subsequent muscular development during hypoxic resistance training, it is not augmented during traditional high‐load exercise. This may be explained by the low number of repetitions performed and the long interset rest periods employed during this training. These findings suggest that high‐load resistance training might not benefit from additional hypoxia as has been shown for low‐ and moderate‐load training.     

Measurement of cardiac output with non-invasive Aesculon impedance versus thermodilution

Background: This study compared the non‐invasive thoracic electrical bioimpedance Aesculon^® technique (TEB_Aesculon) with thermodilution (TD) to evaluate whether TEB_Aesculon may offer a reliable means for estimating cardiac output (CO) in humans. Material and method: Cardiac output was measured with TD and TEB_Aesculon in 33 patients, with a mean age ± SEM of 59 ± 2·7 years, that underwent right heart catheterization for clinical investigation of pulmonary hypertension or severe heart failure. Four to five CO measurements were performed with each technique simultaneously in 33 patients at rest, 11 during exercise and seven during NO inhalation. Result: Cardiac output correlated poorly between TEB_Aesculon and TD at rest (r = 0·46, P<0·001), during exercise (r = 0·35, P<0·013) and NO inhalation (r = 0·41, P<0·017). CO was higher for TEB_Aesculon than TD with 0·86 ± 0·14 l min^?1 at rest (P<0·001) and 2·95 ± 0·69 l min^?1 during exercise (P<0·003), but similar during NO inhalation, with a tendency (P<0·079) to be 0·44 ± 0·19 l min^?1 higher for TEB_Aesculon than TD. CO increased from rest to exercise for TEB_Aesculon and TD with 6·11 ± 0·6 l min^?1 (P<0·001) and 3·91 ± 0·36 l min^?1 (P<0·001), respectively; an increase that was higher (P<0·002) for TEB_Aesculon than TD. During NO inhalation, compared to rest, CO decreased for TEB_Aesculon with 0·62 ± 0·11 l min^?1 (P<0·002), but not significantly for TD with 0·21 ± 0·12 l min^?1 (P<0·11). Bland–Altman analysis showed a poor agreement between TEB_Aesculon and TD. Conclusion: TEB_Aesculon overestimated CO compared to TD with ～17% at rest and ～34% during exercise, but the techniques showed similar results during NO inhalation. CO, furthermore, correlated poorly between TEB_Aesculon and TD. TEB_Aesculon may at present not replace TD for reliable CO measurements in humans.     

Relationship between peak cardiac pumping capability and indices of cardio-respiratory fitness in healthy individuals

Cardiac power output (CPO) is a unique and direct measure of overall cardiac function (i.e. cardiac pumping capability) that integrates both flow‐ and pressure‐generating capacities of the heart. The present study assessed the relationship between peak exercise CPO and selected indices of cardio‐respiratory fitness. Thirty‐seven healthy adults (23 men and 14 women) performed an incremental exercise test to volitional fatigue using the Bruce protocol with gas exchange and ventilatory measurements. Following a 40‐min recovery, the subjects performed a constant maximum workload exercise test at or above 95% of maximal oxygen consumption. Cardiac output was measured using the exponential CO₂ rebreathing method. The CPO, expressed in W, was calculated as the product of the mean arterial blood pressure and cardiac output. At peak exercise, CPO was well correlated with cardiac output (r = 0·92, P<0·01), stroke volume (r = 0·90, P<0·01) and peak oxygen consumption (r = 0·77, P<0·01). The coefficient of correlation was moderate between CPO and anaerobic threshold (r = 0·47, P<0·01), oxygen pulse (r = 0·57, P<0·01), minute ventilation (r = 0·53, P<0·01) and carbon dioxide production (r = 0·56, P<0·01). Small but significant relationship was found between peak CPO and peak heart rate (r = 0·23, P<0·05). These findings suggest that only peak cardiac output and stroke volume truly reflect CPO. Other indices of cardio‐respiratory fitness such as oxygen consumption, anaerobic threshold, oxygen pulse, minute ventilation, carbon dioxide production and heart rate should not be used as surrogates for overall cardiac function and pumping capability of the heart.