Human muscle net K(+) release during exercise is unaffected by elevated anaerobic metabolism, but reduced after prolonged acclimatization to 4,100 m

[EN] It was investigated whether skeletal muscle K(+) release is linked to the degree of anaerobic energy production. Six subjects performed an incremental bicycle exercise test in normoxic and hypoxic conditions prior to and after 2 and 8 wk of acclimatization to 4,100 m. The highest workload completed by all subjects in all trials was 260 W. With acute hypoxic exposure prior to acclimatization, venous plasma [K(+)] was lower (P < 0.05) in normoxia (4.9 +/- 0.1 mM) than hypoxia (5.2 +/- 0.2 mM) at 260 W, but similar at exhaustion, which occurred at 400 +/- 9 W and 307 +/- 7 W (P < 0.05), respectively. At the same absolute exercise intensity, leg net K(+) release was unaffected by hypoxic exposure independent of acclimatization. After 8 wk of acclimatization, no difference existed in venous plasma [K(+)] between the normoxic and hypoxic trial, either at submaximal intensities or at exhaustion (360 +/- 14 W vs. 313 +/- 8 W; P < 0.05). At the same absolute exercise intensity, leg net K(+) release was less (P < 0.001) than prior to acclimatization and reached negative values in both hypoxic and normoxic conditions after acclimatization. Moreover, the reduction in plasma volume during exercise relative to rest was less (P < 0.01) in normoxic than hypoxic conditions, irrespective of the degree of acclimatization (at 260 W prior to acclimatization: -4.9 +/- 0.8% in normoxia and -10.0 +/- 0.4% in hypoxia). It is concluded that leg net K(+) release is unrelated to anaerobic energy production and that acclimatization reduces leg net K(+) release during exercise.

Effects of recovery mode on performance, O2 uptake, and O2 deficit during high-intensity intermittent exercise

[EN] The aim of this study was to determine the influence of activity performed during the recovery period on the aerobic and anaerobic energy yield, as well as on performance, during high-intensity intermittent exercise (HIT). Ten physical education students participated in the study. First they underwent an incremental exercise test to assess their maximal power output (Wmax) and VO2max. On subsequent days they performed three different HITs. Each HIT consisted of four cycling bouts until exhaustion at 110% Wmax. Recovery periods of 5 min were allowed between bouts. HITs differed in the kind of activity performed during the recovery periods: pedaling at 20% VO2max (HITA), stretching exercises, or lying supine. Performance was 3-4% and aerobic energy yield was 6-8% (both p < 0.05) higher during the HITA than during the other two kinds of HIT. The greater contribution of aerobic metabolism to the energy yield during the high-intensity exercise bouts with active recovery was due to faster VO2 kinetics (p< 0.01) and a higher VO2peak during the exercise bouts preceded by active recovery (p < 0.05). In contrast, the anaerobic energy yield (oxygen deficit and peak blood lactate concentrations) was similar in all HITs. Therefore, this study shows that active recovery facilitates performance by increasing aerobic contribution to the whole energy yield turnover during high-intensity intermittent exercise.

Ruolo del test da sforzo cardiopolmonare nei pazienti affetti da cardiomiopatia ipertrofica in età pediatrica

Background Decreased exercise capacity, and reduction in peak oxygen uptake are present in most patients affected by hypertrophic cardiomyopathy (HCM) . In addition an abnormal blood pressure response during a maximal exercise test was seen to be associated with high risk for sudden cardiac death in adult patients affected by HCM. Therefore exercise test (CPET) has become an important part of the evaluation of the HCM patients, but data on its role in patients with HCM in the pediatric age are quite limited. Methods and results Between 2004 and 2010, using CPET and echocardiography, we studied 68 children (mean age 13.9 ± 2 years) with HCM. The exercise test was completed by all the patients without adverse complications. The mean value of achieved VO2 max was 31.4 ± 8.3 mL/Kg/min which corresponded to 77.5 ± 16.9 % of predicted range. 51 patients (75%) reached a subnormal value of VO2max. On univariate analysis the achieved VO2 as percentage of predicted and the peak exercise systolic blood pressure (BP) Z score were inversely associated with max left ventricle (LV) wall thickness, with E/Ea ratio, and directly related with Ea and Sa wave velocities No association was found with the LV outflow tract gradient. During a mean follow up of 2.16 ± 1.7 years 9 patients reached the defined clinical end point of death, transplantation, implanted cardioverter defibrillator (ICD) shock, ICD implantation for secondary prevention or myectomy. Patients with peak VO2 < 52% or with peak systolic BP Z score < -5.8 had lower event free survival at follow up. Conclusions Exercise capacity is decreased in patients with HCM in pediatric age and global ventricular function seems being the most important determinant of exercise capacity in these patients. CPET seems to play an important role in prognostic stratification of children affected by HCM.

Mannitol dry powder challenge in comparison with exercise testing in children

Rationale Mannitol dry powder (MDP) challenge is an indirect bronchial provocation test, which is well studied in adults but not established for children. Objective We compared feasibility, validity, and clinical significance of MDP challenge with exercise testing in children in a clinical setting. Methods Children aged 6–16 years, referred to two respiratory outpatient clinics for possible asthma diagnosis, underwent standardized exercise testing followed within a week by an MDP challenge (Aridol™, Pharmaxis, Australia). Agreement between the two challenge tests using Cohen's kappa and receiving operating characteristic (ROC) curves was compared. Results One hundred eleven children performed both challenge tests. Twelve children were excluded due to exhaustion or insufficient cooperation (11 at the exercise test, 1 at the MDP challenge), leaving 99 children (mean ± SD age 11.5 ± 2.7 years) for analysis. MDP tests were well accepted, with minor side effects and a shorter duration than exercise tests. The MDP challenge was positive in 29 children (29%), the exercise test in 21 (21%). Both tests were concordant in 83 children (84%), with moderate agreement (κ = 0.58, 95% CI 0.39–0.76). Positive and negative predictive values of the MDP challenge for exercise-induced bronchoconstriction were 68% and 89%. The overall ability of MDP challenge to separate children with or without positive exercise tests was good (area under the ROC curve 0.83). Conclusions MDP challenge test is feasible in children and is a suitable alternative for bronchial challenge testing in childhood. Pediatr. Pulmonol. 2011; 46:842–848. © 2011 Wiley-Liss, Inc.

The effect of increased lipid intake on hormonal responses during aerobic exercise in endurance-trained men

In view of the growing health problem associated with obesity, clarification of the regulation of energy homeostasis is important. Peripheral signals, such as ghrelin and leptin, have been shown to influence energy homeostasis. Nutrients and physical exercise, in turn, influence hormone levels. Data on the hormonal response to physical exercise (standardized negative energy balance) after high-fat (HF) or low-fat (LF) diet with identical carbohydrate intake are currently not available. The aim of the study was to investigate whether a short-term dietary intervention with HF and LF affects ghrelin and leptin levels and their modulators, GH, insulin and cortisol, before and during aerobic exercise. Eleven healthy, endurance-trained male athletes (W(max) 365 +/- 29 W) were investigated twice in a randomized crossover design following two types of diet: 1. LF - 0.5 g fat/kg body weight (BW) per day for 2.5 days; 2. HF - 0.5 g fat/kg BW per day for 1 day followed by 3.5 g fat/kg BW per day for 1.5 days. After a standardized carbohydrate snack in the morning, metabolites and hormones (GH, ghrelin, leptin, insulin and cortisol) were measured before and at regular intervals throughout a 3-h aerobic exercise test on a cycloergometer at 50% of W(max). Diet did not significantly affect GH and cortisol concentrations during exercise but resulted in a significant increase in ghrelin and decrease in leptin concentrations after LF compared with HF diet (area under the curve (AUC) ghrelin LF vs HF: P < 0.03; AUC leptin LF vs HF: P < 0.02, Wilcoxon rank test). These data suggest that acute negative energy balance induced by exercise elicits a hormonal response with opposite changes of ghrelin and leptin. In addition, the hormonal response is modulated by the preceding intake of fat.

Methodological approach to the first and second lactate threshold in incremental cardiopulmonary exercise testing

Determination of an 'anaerobic threshold' plays an important role in the appreciation of an incremental cardiopulmonary exercise test and describes prominent changes of blood lactate accumulation with increasing workload. Two lactate thresholds are discerned during cardiopulmonary exercise testing and used for physical fitness estimation or training prescription. A multitude of different terms are, however, found in the literature describing the two thresholds. Furthermore, the term 'anaerobic threshold' is synonymously used for both, the 'first' and the 'second' lactate threshold, bearing a great potential of confusion. The aim of this review is therefore to order terms, present threshold concepts, and describe methods for lactate threshold determination using a three-phase model with reference to the historical and physiological background to facilitate the practical application of the term 'anaerobic threshold'.

Influence of exertional oscillatory ventilation on exercise performance in heart failure

BACKGROUND: Exertional oscillatory ventilation (EOV) in heart failure may potentiate the negative effects of low cardiac output and high ventilation on exercise performance. We hypothesized that the presence of EOV might, per se, influence exercise capacity as evaluated by maximal cardiopulmonary exercise test. METHODS AND RESULTS: We identified 78 severe chronic heart failure patient pairs with and without EOV. Patients were matched for sex, age and peak oxygen consumption (VO2). Patients with EOV showed, for the same peak VO2, a lower workload (WL) at peak (DeltaWatts=5.8+/-23.0, P=0.027), a less efficient ventilation (higher VE/VCO2 slope: 38.0+/-8.3 vs. 32.8+/-6.3, P<0.001), lower peak exercise tidal volume (1.49+/-0.36 L vs. 1.61+/-0.46 L, P=0.015) and higher peak respiratory rate (34+/-7/min vs. 31+/-6/min, P=0.002). In 33 patients, EOV disappeared during exercise, whereas in 45 patients EOV persisted. Fifty percent of EOV disappearing patients had an increase in the VO2/WL relationship after EOV regression, consistent with a more efficient oxygen delivery to muscles. No cardiopulmonary exercise test parameter was associated with the different behaviour of VO2/WL. CONCLUSION: The presence of EOV negatively influences exercise performance of chronic heart failure patients likely because of an increased cost of breathing. EOV disappearance during exercise is associated with a more efficient oxygen delivery in several cases.

Exercise capacity and biventricular function in adult patients with repaired tetralogy of Fallot

BACKGROUND: Adult patients with repaired tetralogy of Fallot (rTOF) often have diminished exercise capacity. The primary objective of this study was to examine whether abnormalities of biventricular function play a role in exercise limitation in patients with rTOF. METHODS: This was a retrospective review of 99 adult patients with rTOF. Right ventricular (RV) and left ventricular (LV) function were assessed echocardiographically using the myocardial performance index (MPI). Maximal oxygen consumption (VO(2) Max) was measured during a level 1 cardiopulmonary exercise test. RESULTS: The mean age of the cohort was 34 +/- 11 years (50% females). Although most of the patients reported good functional capacity, the peak Vo(2)max was decreased at 22 +/- 6 mL/kg per minute (66% +/- 13% predicted Vo(2)max for age and sex). The mean RV and LV MPI were 0.30 +/- 0.07 and 0.42 +/- 0.09, respectively. In the multivariate model, higher RV MPI (P = .04) and LV MPI (P = .005) values, representing impaired ventricular function, were associated with diminished Vo(2)max. There was a significant correlation between the RV and LV MPI (r = 0.54, P = .001). CONCLUSIONS: Impairment of RV and LV function, as measured by MPI, is associated with diminished exercise capacity in patients with repaired tetralogy of Fallot. Furthermore, there is a linear relationship between the RV and LV function suggesting that ventricular interactions are contributing to the limited exercise capacity in this group of patients. Strategies aimed at preserving biventricular function or improving adverse ventricular interactions could help to improve functional capacity in these patients.

Electrocardiographic changes during stress test in a patient with "Brugada syndrome".

We report a 28 year old man with the Brugada syndrome characterised by an electrocardiographic pattern of a right bundle branch block and an ST segment elevation in the right precordial leads as well as syncope. During an exercise test, we observed a normalization of the ST segment in V2+ while in the postexercise phase, the ST segment elevation in the right leads was established. This is the first case reported of the Brugada syndrome in Mexico, with spontaneous changes on the EKG masked during exercise and apparent during postexercise phase.

Exercise capacity, physical activity patterns and outcomes six years after cardiac rehabilitation in patients with heart failure.

OBJECTIVE To determine the short- and long-term effects of an intensive, concentrated rehabilitation programme in patients with chronic heart failure. DESIGN Randomized controlled trial, with one-month and six-year evaluations. SETTING Residential rehabilitation centre in Switzerland. SUBJECTS Fifty patients with chronic heart failure, randomized to exercise or control groups. INTERVENTIONS A rehabilitation programme lasting one month, including educational sessions, a low-fat diet, and 2 hours of individually prescribed exercise daily. MAIN MEASURES Exercise test responses, health outcomes and physical activity patterns. RESULTS Peak Vo(2) increased 21.4% in the exercise group during the rehabilitation programme (P<0.05), whereas peak Vo(2) did not change among controls. After the six-year follow-up period, peak Vo(2) was only slightly higher than that at baseline in the trained group (7%, NS), while peak Vo(2) among controls was unchanged. During long-term follow-up, 9 and 12 patients died in the exercise and control groups, respectively (P = 0.63). At six years, physical activity patterns tended to be higher in the exercise group; the mean energy expenditure values over the last year were 2,704 +/- 1,970 and 2,085 +/- 1,522 kcal/week during recreational activities for the exercise and control groups, respectively. However, both groups were more active compared to energy expenditure prior to their cardiac event (P<0.001). CONCLUSIONS Six years after participation in a residential rehabilitation programme, patients with chronic heart failure had slightly better outcomes than control subjects, maintained exercise capacity and engaged in activities that exceed the minimal amount recommended by guidelines for cardiovascular health.

Feasibility of cardiopulmonary exercise testing and training using a robotics-assisted tilt table in dependent-ambulatory stroke patients

BACKGROUND: We evaluated the feasibility of an augmented robotics-assisted tilt table (RATT) for incremental cardiopulmonary exercise testing (CPET) and exercise training in dependent-ambulatory stroke patients. METHODS: Stroke patients (Functional Ambulation Category ≤ 3) underwent familiarization, an incremental exercise test (IET) and a constant load test (CLT) on separate days. A RATT equipped with force sensors in the thigh cuffs, a work rate estimation algorithm and real-time visual feedback to guide the exercise work rate was used. Feasibility assessment considered technical feasibility, patient tolerability, and cardiopulmonary responsiveness. RESULTS: Eight patients (4 female) aged 58.3 ± 9.2 years (mean ± SD) were recruited and all completed the study. For IETs, peak oxygen uptake (V'O2peak), peak heart rate (HRpeak) and peak work rate (WRpeak) were 11.9 ± 4.0 ml/kg/min (45 % of predicted V'O2max), 117 ± 32 beats/min (72 % of predicted HRmax) and 22.5 ± 13.0 W, respectively. Peak ratings of perceived exertion (RPE) were on the range "hard" to "very hard". All 8 patients reached their limit of functional capacity in terms of either their cardiopulmonary or neuromuscular performance. A ventilatory threshold (VT) was identified in 7 patients and a respiratory compensation point (RCP) in 6 patients: mean V'O2 at VT and RCP was 8.9 and 10.7 ml/kg/min, respectively, which represent 75 % (VT) and 85 % (RCP) of mean V'O2peak. Incremental CPET provided sufficient information to satisfy the responsiveness criteria and identification of key outcomes in all 8 patients. For CLTs, mean steady-state V'O2 was 6.9 ml/kg/min (49 % of V'O2 reserve), mean HR was 90 beats/min (56 % of HRmax), RPEs were > 2, and all patients maintained the active work rate for 10 min: these values meet recommended intensity levels for bouts of training. CONCLUSIONS: The augmented RATT is deemed feasible for incremental cardiopulmonary exercise testing and exercise training in dependent-ambulatory stroke patients: the approach was found to be technically implementable, acceptable to the patients, and it showed substantial cardiopulmonary responsiveness. This work has clinical implications for patients with severe disability who otherwise are not able to be tested.

Effects of Estrogen on Muscle Damage in Response to an Acute Resistance Exercise Protocol

Creatine Kinase (CK) is used as a measure of exercise-induced muscle membrane damage. During acute eccentric (muscle lengthening) exercise, muscle sarcolemma, sarcoplasmic reticulum, and Z-lines are damaged, thus causing muscle proteins and enzymes to leak into the interstitial fluid. Strenuous eccentric exercise produces an elevation of oxygen free radicals, which further increases muscle damage. Muscle soreness and fatigue can be attributed to this membrane damage. Estradiol, however, may preserve membrane stability post-exercise (Brancaccio, Maffulli, & Limongelli, 2007; Carter, Dobridge, & Hackney, 2001; Tiidus, 2001). Because estradiol has a similar structure to Vitamin E, which is known to have antioxidant properties, and both are known to affect membrane structure, researchers have proposed that estrogen acts as an antioxidant to provide a protective effect on the post-exercise muscle of women (Sandoval & Matt, 2002). As a result, it has been postulated that muscles in women incur less damage in response to an acute strenuous exercise as compared to men. PURPOSE: To determine if circulating estrogen concentrations are related to muscle damage, as measured by creatine kinase activity and to determine gender differences in creatine kinase as a marker of muscle damage in response to an acute heavy resistance exercise protocol. METHODS: 7 healthy, resistance-trained, eumenhorrheic women (23±3 y, 169±9.1 cm, 66.4±10.5 kg) and 8 healthy, resistance-trained men (25±5 y, 178±6.7 cm, 82.3±9.33 kg) volunteered to participate in the study. Subjects performed an Acute Resistance Exercise Test (ARET) consisting of 6 sets of 5 repetitions Smith machine squats at 90% of their previously determined 1-RM. Blood samples were taken pre-, mid-, post-, 1 hour post-, 6 hours post-, and 24 hours post-exercise. Samples were stored at -80ºC until analyzed. Serum creatine kinase was measured using an assay kit from Genzyme (Framingham, MA). Serum estradiol was measured by an ELISA from GenWay (San Diego, CA). Estradiol b-receptor presence on granulocytes was measured via flow cytometry using primary antibodies from Abcam (Cambridge, MA) and PeCy7 antibodies (secondary) from Santa Cruz (Santa Cruz, CA). RESULTS: No significant correlations between estrogen and CK response were found after an acute resistant exercise protocol. Moreover, no significant change in estradiol receptors were expressed on granulocytes after exercise. Creatine Kinase response, however, differed significantly between genders. Men had higher resting CK concentrations throughout all time points. Creatine Kinase response increased significantly after exercise in both men and women (p=0.008, F=9.798). Men had a significantly higher CK response at 24 hours post exercise than women. A significant condition/sex/time interaction was exhibited in CK response (p=0.02, F=4.547). Perceived general soreness presented a significant condition, sex interaction (p=0.01, F=9.532). DISCUSSION: Although no estradiol and CK response correlations were found in response to exercise, a significant difference in creatine kinase activity was present between men and women. This discrepancy of our results and findings in the literature may be due to the high variability between subjects in creatine kinase activity as well as estrogen concentrations. The lack of significance in change of estradiol receptor expression on granulocytes in response to exercise may be due to intracellular estradiol receptor staining and non-specific gating for granulocytes rather than additional staining for neutrophil markers. Because neutrophils are the initial cells present in the inflammatory response after strenuous exercise, staining for estrogen receptors on this cell type may allow for a better understanding of the effect of estrogen and its hypothesized protective effect against muscle damage. Furthermore, the mechanism of action may include estradiol receptor expression on the muscle fiber itself may play a role in the protective effects of estradiol rather than or in addition to expression on neutrophils. We have shown here that gender differences occur in CK activity as a marker of muscle damage in response to strenuous eccentric exercise, but may not be the result of estradiol concentration or estradiol receptor expression on granulocytes. Other variables should be examined in order to determine the mechanism involved in the difference in creatine kinase as a marker of muscle damage between men and women after heavy resistance exercise.

Maximal exercise hemodynamics and risk of mortality in apparently healthy men and women

The use of exercise electrocardiography (ECG) to detect latent coronary heart disease (CHD) is discouraged in apparently healthy populations because of low sensitivity. These recommendations however, are based on the efficacy of evaluation of ischemia (ST segment changes) with little regard for other measures of cardiac function that are available during exertion. The purpose of this investigation was to determine the association of maximal exercise hemodynamic responses with risk of mortality due to all-causes, cardiovascular disease (CVD), and coronary heart disease (CHD) in apparently healthy individuals. Study participants were 20,387 men (mean age = 42.2 years) and 6,234 women (mean age = 41.9 years) patients of a preventive medicine center in Dallas, TX examined between 1971 and 1989. During an average of 8.1 years of follow-up, there were 348 deaths in men and 66 deaths in women. In men, age-adjusted all-cause death rates (per 10,000 person years) across quartiles of maximal systolic blood pressure (SBP) (low to high) were: 18.2, 16.2, 23.8, and 24.6 (p for trend $<$0.001). Corresponding rates for maximal heart rate were: 28.9, 15.9, 18.4, and 15.1 (p trend $<$0.001). After adjustment for confounding variables including age, resting systolic pressure, serum cholesterol and glucose, body mass index, smoking status, physical fitness and family history of CVD, risks (and 95% confidence interval (CI)) of all-cause mortality for quartiles of maximal SBP, relative to the lowest quartile, were: 0.96 (0.70-1.33), 1.36 (1.01-1.85), and 1.37 (0.98-1.92) for quartiles 2-4 respectively. Similar risks for maximal heart rate were: 0.61 (0.44-0.85), 0.69 (0.51-0.93), and 0.60 (0.41-0.87). No associations were noted between maximal exercise rate-pressure product mortality. Similar results were seen for risk of CVD and CHD death. In women, similar trends in age-adjusted all-cause and CVD death rates across maximal SBP and heart rate categories were observed. Sensitivity of the exercise test in predicting mortality was enhanced when ECG results were evaluated together with maximal exercise SBP or heart rate with a concomitant decrease in specificity. Positive predictive values were not improved. The efficacy of the exercise test in predicting mortality in apparently healthy men and women was not enhanced by using maximal exercise hemodynamic responses. These results suggest that an exaggerated systolic blood pressure or an attenuated heart rate response to maximal exercise are risk factors for mortality in apparently healthy individuals. ^

STRUCTURAL AND FUNCTIONAL CORRELATES OF EXERCISE VENTILATORY INEFFICIENCY IN CHRONIC OBSTRUCTIVE PULMONARY DISEASE PATIENTS WITH MILD-TO-MODERATE SPIROMETRIC ABNORMALITIES

Background: Individuals with chronic obstructive pulmonary disease (COPD) have higher than normal ventilatory equivalents for carbon dioxide (VE/VCO2) during exercise. There is growing evidence that emphysema on thoracic computed tomography (CT) scans is associated with poor exercise capacity in COPD patients with only mild-to-moderate airflow obstruction. We hypothesized that emphysema is an underlying cause of microvascular dysfunction and ventilatory inefficiency, which in turn contributes to reduced exercise capacity. We expected ventilatory inefficiency to be associated with a) the extent of emphysema; b) lower diffusing capacity for carbon monoxide; c) a reduced pulmonary blood flow response to exercise; and d) reduced exercise capacity. Methods: In a cross-sectional study, 19 subjects with mild-to-moderate COPD (mean ± SD FEV1= 82 ± 13% predicted, 12 GOLD grade 1) and 26 age-, sex-, and activity-matched controls underwent a ramp-incremental symptom-limited exercise test on a cycle ergometer. Ventilatory inefficiency was assessed by the minimum VE/VCO2 value (nadir). A subset of subjects also completed repeated constant work rate exercise bouts with non-invasive measurements of pulmonary blood flow. Emphysema was quantified as the percentage of attenuation areas below -950 Housefield Units on CT scans. An electronic scoresheet was used to keep track of emphysema sub-types. Results: COPD subjects typically had centrilobular emphysema (76.8 ± 10.1% of total emphysema) in the upper lobes (upper/lower lobe ratio= 0.82 ± 0.04). They had lower peak oxygen uptake (VO2), higher VE/VCO2 nadir and greater dyspnea scores than controls (p<0.05). Lower peak O2 and worse dyspnea were found in COPD subjects with VE/VCO2 nadirs ≥ 30. COPD subjects had blunted increases in pulmonary blood flow from rest to iso-VO2 exercise (p<0.05). Higher VE/VCO2 nadir in COPD subjects correlated with emphysema severity (r= 0.63), which in turn correlated with reduced lung diffusing capacity (r= -0.72) and blunted changes in pulmonary blood flow from rest to exercise (r= -0.69) (p<0.01). Conclusions: Ventilation “wasted” in emphysematous areas is associated with reduced exercise ventilatory efficiency in mild-to-moderate COPD. Exercise ventilatory inefficiency links structure (emphysema) and function (gas transfer) to a key clinical outcome (reduced exercise capacity) in COPD patients with modest spirometric abnormalities.

Locomotor Muscle Fatigue Does Not Alter Oxygen Uptake Kinetics during High-Intensity Exercise

The V˙O2 slow component (V˙O2sc) that develops during high-intensity aerobic exercise is thought to be strongly associated with locomotor muscle fatigue. We sought to experimentally test this hypothesis by pre-fatiguing the locomotor muscles used during subsequent high-intensity cycling exercise. Over two separate visits, eight healthy male participants were asked to either perform a non-metabolically stressful 100 intermittent drop-jumps protocol (pre-fatigue condition) or rest for 33 min (control condition) according to a random and counterbalanced order. Locomotor muscle fatigue was quantified with 6-s maximal sprints at a fixed pedaling cadence of 90 rev·min−1. Oxygen kinetics and other responses (heart rate, capillary blood lactate concentration and rating of perceived exertion, RPE) were measured during two subsequent bouts of 6 min cycling exercise at 50% of the delta between the lactate threshold and V˙O2max determined during a preliminary incremental exercise test. All tests were performed on the same cycle ergometer. Despite significant locomotor muscle fatigue (P = 0.03), the V˙O2sc was not significantly different between the pre-fatigue (464 ± 301 mL·min−1) and the control (556 ± 223 mL·min−1) condition (P = 0.50). Blood lactate response was not significantly different between conditions (P = 0.48) but RPE was significantly higher following the pre-fatiguing exercise protocol compared with the control condition (P < 0.01) suggesting higher muscle recruitment. These results demonstrate experimentally that locomotor muscle fatigue does not significantly alter the V˙O2 kinetic response to high intensity aerobic exercise, and challenge the hypothesis that the V˙O2sc is strongly associated with locomotor muscle fatigue.