Incremental Cycle Exercise Test Research Articles

The time course of irisin release after an acute exercise: relevant implications for health and future experimental designs.

This study aimed to analyze the acute impact of exercise on serum irisin levels in 22 young (YA, 24.6 ± 3.5 yrs) and in 12 middle-aged male adults (MA, 54.6 ± 5.7 yrs) 15 min and 24 h after an incremental cycling exercise test to exhaustion. ELISA assay was used for serum irisin detection. Circulating irisin increased significantly from baseline (9.0 ± 2.0 ng/ml) to 15 min post-exercise (10.2 ± 2.0 ng/ml, P < 0.001), but the greatest increment was detected after 24 h (13.5 ± 2.5 ng/ml, P < 0.001) reaching more than 50% of the basal release. Levels were significantly higher in YA (9.7 ± 1.7 to 11.1 ± 1.8 to 14.5 ± 2.2 ng/ml) than MA (7.6 ± 1.6 to 8.7 ± 1.5 to 11.8± 2.2 ng/ml) for all measured time-points (P < 0.05). Nevertheless, MA showed a comparable increase in serum irisin levels when compared to YA. These findings highlight the importance of acute physical exercise as a countermeasure against age-related deterioration of skeletal muscle mass and function in both YA and MA.

Facial electromyography during exercise using soft electrode array: A feasibility study.

The use of wearable sensors for real-time monitoring of exercise-related measures has been extensively studied in recent years (e.g., performance enhancement, optimizing athlete's training, and preventing injuries). Surface electromyography (sEMG), which measures muscle activity, is a widely researched technology in exercise monitoring. However, due to their cumbersome nature, traditional sEMG electrodes are limited. In particular, facial EMG (fEMG) studies in physical training have been limited, with some scarce evidence suggesting that fEMG may be used to monitor exercise-related measurements. Altogether, sEMG recordings from facial muscles in the context of exercise have been examined relatively inadequately. In this feasibility study, we assessed the ability of a new wearable sEMG technology to measure facial muscle activity during exercise. Six young, healthy, and recreationally active participants (5 females), performed an incremental cycling exercise test until exhaustion, while facial sEMG and vastus lateralis (VL) EMG were measured. Facial sEMG signals from both natural expressions and voluntary smiles were successfully recorded. Stable recordings and high-resolution facial muscle activity mapping were achieved during different exercise intensities until exhaustion. Strong correlations were found between VL and multiple facial muscles' activity during voluntary smiles during exercise, with statistically significant coefficients ranging from 0.80 to 0.95 (p<0.05). This study demonstrates the feasibility of monitoring facial muscle activity during exercise, with potential implications for sports medicine and exercise physiology, particularly in monitoring exercise intensity and fatigue.

The modified Medical Research Council scale misclassifies exertional breathlessness among people referred for exercise testing.

Exertional breathlessness is a major symptom in cardiorespiratory disease and is often assessed using the modified Medical Research Council (mMRC) questionnaire. The mMRC might underestimate exertional breathlessness in people with impaired exercise capacity who have reduced their physical activity to avoid the symptom. We aimed to evaluate the ability of mMRC to detect abnormally high exertional breathlessness or abnormally low exercise capacity during incremental cycle exercise testing (IET). A secondary analysis of data from a randomised controlled trial of outpatients aged 18 years or older referred for IET was carried out. Participants completed the mMRC before IET. Abnormally high exertional breathlessness was defined as a breathlessness (Borg 0-10) intensity response more than the upper limit of normal. Abnormally low exercise capacity was defined using published reference equations. The sensitivity, specificity, accuracy and discriminative ability of each mMRC rating to detect each outcomewas calculated. 92 participants were included; the mean age was 59 years, 61% were male, and 64% and 15% had mMRC 1 and ≥2, respectively. An mMRC ≥2 had the highest accuracy (71%) to detect abnormally high exertional breathlessness, with a specificity of 93% but a sensitivity of only 28%, failing to identify 72% of people with abnormally high exertional breathlessness. The accuracy, specificity and sensitivity for abnormally low exercise capacity was 64%, 88% and 19%, respectively. Among people referred for clinical exercise testing, the mMRC dyspnoea scale misclassified exertional breathlessness and exercise capacity assessed using cycle IET, with substantial underdetection. A mMRC dyspnoea rating of 0-1 does not preclude the presence of abnormally high exertional breathlessness or abnormally low exercise capacity.

Normative Reference Equations for Breathlessness Intensity during Incremental Cardiopulmonary Cycle Exercise Testing.

Rationale: Cardiopulmonary exercise testing (CPET) is the gold standard to evaluate exertional breathlessness, a common and disabling symptom. However, the interpretation of breathlessness responses to CPET is limited by a scarcity of normative data. Objectives: We aimed to develop normative reference equations for breathlessness intensity (Borg 0-10 category ratio) response in men and women aged ⩾40 years during CPET, in relation to power output (watts), oxygen uptake, and minute ventilation. Methods: Analysis of ostensibly healthy people aged ⩾40 years undergoing symptom-limited incremental cycle CPET (10 W/min) in the CanCOLD (Canadian Cohort Obstructive Lung Disease) study. Participants had smoking histories <5 pack-years and normal lung function and exercise capacity. The probability of each Borg 0-10 category ratio breathlessness intensity rating by power output, oxygen uptake, and minute ventilation (as an absolute or a relative value [percentage of predicted maximum]) was predicted using ordinal multinomial logistic regression. Model performance was evaluated by fit, calibration, and discrimination (C statistic) and externally validated in an independent sample (n = 86) of healthy Canadian adults. Results: We included 156 participants (43% women) from CanCOLD; the mean age was 65 (range, 42-91) years, and the mean body mass index was 26.3 (standard deviation, 3.8) kg/m2. Reference equations were developed for women and men separately, accounting for age and/or body mass. Model performance was high across all equations, including in the validation sample (C statistic for men = 0.81-0.92, C statistic for women = 0.81-0.96). Conclusions: Normative reference equations are provided to compare exertional breathlessness intensity ratings among individuals or groups and to identify and quantify abnormal breathlessness responses (scores greater than the upper limit of normal) during CPET.

The Effect of Skeletal Muscle Oxygenation on Hemodynamics, Cerebral Oxygenation and Activation, and Exercise Performance during Incremental Exercise to Exhaustion in Male Cyclists.

This study aimed to elucidate whether muscle blood flow restriction during maximal exercise is associated with alterations in hemodynamics, cerebral oxygenation, cerebral activation, and deterioration of exercise performance in male participants. Thirteen healthy males, cyclists (age 33 ± 2 yrs., body mass: 78.6 ± 2.5 kg, and body mass index: 25.57 ± 0.91 kg·m-1), performed a maximal incremental exercise test on a bicycle ergometer in two experimental conditions: (a) with muscle blood flow restriction through the application of thigh cuffs inflated at 120 mmHg (with cuffs, WC) and (b) without restriction (no cuffs, NC). Exercise performance significantly deteriorated with muscle blood flow restriction, as evidenced by the reductions in V˙O2max (-17 ± 2%, p < 0.001), peak power output (-28 ± 2%, p < 0.001), and time to exhaustion (-28 ± 2%, p < 0.001). Muscle oxygenated hemoglobin (Δ[O2Hb]) during exercise declined more in the NC condition (p < 0.01); however, at exhaustion, the magnitude of muscle oxygenation and muscle deoxygenation were similar between conditions (p > 0.05). At maximal effort, lower cerebral deoxygenated hemoglobin (Δ[HHb]) and cerebral total hemoglobin (Δ[THb]) were observed in WC (p < 0.001), accompanied by a lower cardiac output, heart rate, and stroke volume vs. the NC condition (p < 0.01), whereas systolic blood pressure, rating of perceived exertion, and cerebral activation (as assessed by electroencephalography (EEG) activity) were similar (p > 0.05) between conditions at task failure, despite marked differences in exercise duration, maximal aerobic power output, and V˙O2max. In conclusion, in trained cyclists, muscle blood flow restriction during an incremental cycling exercise test significantly limited exercise performance. Exercise intolerance with muscle blood flow restriction was mainly associated with attenuated cardiac responses, despite cerebral activation reaching similar maximal levels as without muscle blood flow restriction.

Cardiovascular Hemodynamic Response to Peak Exercise in Individuals with Multiple Sclerosis

Multiple sclerosis (MS) is a chronic, progressive neurological condition that results in physical disability brought about, in part, by decreased aerobic capacity. Physical disability and aerobic deconditioning may increase risks of cardiovascular morbidity and mortality. The reduction in aerobic capacity may be associated with low maximal heart rate and/or low cardiac output. Yet it is unclear if the cardiovascular hemodynamic response to peak exercise differs between individuals with and without MS who have similar aerobic capacities. Purpose: To compare the cardiovascular hemodynamic response to peak exercise between individuals with and without MS, with similar aerobic capacities. We hypothesized individuals with similar aerobic capacities would also exhibit similar hemodynamic responses, regardless of disease condition. Methods: Individuals with MS (n=14 (2 males), 38 ± 8 yrs, 24.6 ± 4.5 kg/m 2 ) and without MS (n=14 (1 male), 33 ± 9 yrs, 28.8 ± 13.8 kg/m 2 ) underwent maximal incremental cycle exercise test to assess maximal aerobic capacity (VO 2 peak). Heart rate (HR) was measured continuously via Polar Heart Rate Monitor. Ascending aortic blood flow velocity images (VTI) via continuous wave Doppler echocardiography, and brachial blood pressure (BP) via brachial sphygmomanometry were obtained every other minute of the exercise test. Stroke volume (SV) was calculated from VTI and the area of the aorta, cardiac output (Q) was calculated as SV × HR, and Mean arterial pressure (MAP) was calculated from BP. Maximal arteriovenous oxygen difference (avO2diff) was calculated as VO 2 peak ⁄ Q. Results: There was no significant difference in VO 2 peak between groups (MS: 30.8 ml/kg·min -1 vs CON: 28.2 ml/kg·min -1 , p=0.65). Both groups (MS and CON) had significant time (rest to peak) differences in SV (rest: MS = 74.6 ± 32.5 mL, CON = 65.7 ± 23.1 mL, peak: MS = 114.4 ± 42.4 mL, CON = 84.2 ± 33.3 mL; p&lt;0.001), HR (rest: MS = 65 ± 15 bpm, CON = 61 ± 10 bpm, peak: MS = 167 ± 13 bpm, CON = 175 ± 11 bpm; p&lt;0.001), Q (rest: MS = 4.7 ± 2.2 L/m, CON = 4.0 ± 1.3 L/m, peak: MS = 12.3 ± 5.0 L/min, CON = 12.3 ± 5.1 L/min; p&lt;0.001), and MAP (rest: MS = 84 ± 10 mmHg, CON = 83 ± 13 mmHg, peak: MS = 102 ± 7 mmHg, CON = 104 ± 17 mmHg, p &lt;0.001). There was also a significant group by time interaction in HR (p = 0.04), but no group by time interactions in SV, Q, or MAP. Finally, there was not significant difference in avO 2 diff between groups (MS: 2.3 ± 1.2 mL/100 mL vs CON: 2.7 ± 1.5 mL/100 mL). Conclusion: Our findings suggest that individuals with MS exhibit different cardiac hemodynamics to achieve maximal aerobic capacity than those without MS. Individuals with MS reached maximal Q via a slightly higher, although statistically non-significant, stroke volume but a lower HR. This suggests that people with MS may rely on different mechanisms for achieving VO2peak compared to controls, but future research is needed to elucidate this hemodynamic pattern. Department of Defense office of the Congressionally Directed Medical Research Program on Multiple Sclerosis This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Perception of exercise-induced dyspnea after experimentally induced breathing discomfort.

The perception of dyspnea is influenced by both physiological and psychological factors. We sought to determine whether exertional dyspnea perception could be experimentally manipulated through prior exposure to heightened dyspnea while exercising. We hypothesized that dyspnea perception during exercise would be lower following an induced dyspnea task (IDT). Sixteen healthy participants (eight females, eight males) completed two days of exercise testing. Day 1 involved an incremental cycle exercise test starting at 40 W for females and 60 W for males, increasing by 20 W each minute until volitional exhaustion. Following the maximal exercise test on Day 1, participants completed IDT, involving 5 min of exercise at 70% of peak work rate with 500 mL dead space and external resistance (i.e., 6.8 ± 2.3 cm·H2O·s-1·L-1 inspiration, 3.8 ± 0.7 cm·H2O·s-1·L-1 expiration). Day 2 consisted of an incremental exercise test identical to Day 1. At maximal exercise, there were no differences in oxygen uptake (V̇O2; 44.7 ± 7.7vs. 46.5 ± 6.3 mL·kg-1·min-1), minute ventilation (120 ± 35vs. 127 ± 38 L·min-1), dyspnea (6.5 [4, 8.5] vs. 6 [4.25, 8.75]), or leg discomfort (6 [5, 8.75] vs. 7 [5, 9]) between days (all p > 0.05). At 60%-80% of peak V̇O2 (V̇O2peak), dyspnea was significantly lower on Day 2 (-0.75 [-1.375, 0] for 60% and -0.5 [0, -2] for 80%, p < 0.05) despite no differences in relevant physiological variables. The onset of perceived dyspnea occurred at a significantly higher exercise intensity on Day 2 than on Day 1 (42% ± 19%vs. 51% ± 17% V̇O2peak, respectively; p < 0.05). Except for 40% V̇O2peak (p = 0.05), RPE-L was not different at any intensities nor was the onset of perceived leg discomfort different between days (38% ± 14%vs. 43% ± 10% V̇O2peak, respectively; p = 0.10). Exposure to heightened dyspnea alters exercise-induced dyspnea perception during subsequent submaximal exercise bouts.

The Validity of Ultra-Short-Term Heart Rate Variability during Cycling Exercise.

Ultra-short-term heart rate variability (HRV) has been validated in the resting state, but its validity during exercise is unclear. This study aimed to examine the validity in ultra-short-term HRV during exercise considering the different exercise intensities. HRVs of twenty-nine healthy adults were measured during incremental cycle exercise tests. HRV parameters (Time-, frequency-domain and non-linear) corresponding to each of the 20% (low), 50% (moderate), and 80% (high) peak oxygen uptakes were compared between the different time segments of HRV analysis (180 s (sec) segment vs. 30, 60, 90, and 120-sec segments). Overall, the differences (bias) between ultra-short-term HRVs increased as the time segment became shorter. In moderate- and high-intensity exercises, the differences in ultra-short-term HRV were more significant than in low intensity exercise. Thus, we discovered that the validity of ultra-short-term HRV differed with the duration of the time segment and exercise intensities. However, the ultra-short-term HRV is feasible in the cycling exercise, and we determined some optimal time duration for HRV analysis for across exercise intensities during the incremental cycling exercise.

Reference equations for breathlessness during incremental cycle exercise testing.

Exertional breathlessness is commonly assessed using incremental exercise testing (IET), but reference equations for breathlessness responses are lacking. We aimed to develop reference equations for breathlessness intensity during IET. A retrospective, consecutive cohort study of adults undergoing IET was carried out in Sweden. Exclusion criteria included cardiac or respiratory disease, death or any of the aforementioned diagnoses within 1 year of the IET, morbid obesity, abnormally low exercise capacity, submaximal exertion or an abnormal exercise test. Probabilities for breathlessness intensity ratings (Borg CR10) during IET in relation to power output (%predWmax), age, sex, height and body mass were analysed using marginal ordinal logistic regression. Reference equations for males and females were derived to predict the upper limit of normal (ULN) and the probability of different Borg CR10 intensity ratings. 2581 participants (43% female) aged 18-90 years were included. Mean breathlessness intensity was similar between sexes at peak exertion (6.7±1.5 versus 6.4±1.5 Borg CR10 units) and throughout exercise in relation to %predWmax. Final reference equations included age, height and %predWmax for males, whereas height was not included for females. The models showed a close fit to observed breathlessness intensity ratings across %predWmax values. Models using absolute W did not show superior fit. Scripts are provided for calculating the probability for different breathlessness intensity ratings and the ULN by %predWmax throughout IET. We present the first reference equations for interpreting breathlessness intensity during incremental cycle exercise testing in males and females aged 18-90 years.

Metabolomic, oxidative, and inflammatory responses to acute exercise in chronic obstructive pulmonary disease

BackgroundThere is currently a need to identify metabolomic responses to acute exercise in chronic obstructive pulmonary disease (COPD). ObjectiveWe investigated the metabolomic, oxidative, and inflammatory responses to constant (CE) and intermittent (IE) work rate exercises in COPD. MethodsSixteen males with COPD performed a symptom-limited incremental cycle exercise test (ICE). Metabolomic, oxidative, and inflammatory responses to CE and IE (based on the performance of ICE) were analyzed in the plasma. ResultsFructose-6-phosphate, 3-phosphoglyceric acid, l-carnitine, and acylcarnitines levels were significantly decreased, whereas alpha-ketoglutaric, malic, 2-hydroxybutyric, and 3-hydroxybutyric acids were increased, after CE and IE (p<0.05). Increases in citric, isocitric, and lactic acids, as well as decreases in pyruvic and oxalic acids, were only present with IE (p<0.05). Isoleucine was decreased after both exercises (p<0.05). We observed an increase in inosine-5′-diphosphate, uric acid, ascorbic acid, and pantothenic acid, as well as a decrease in 5-hydroxymethyluridine, threonic acid, and dehydroascorbic acid, after IE (p<0.05). Catalase, reduced glutathione, and total antioxidant status difference values for both exercises were similar (p>0.05). The change in glutathione peroxidase (GPx) with CE was more significant than that with IE (p = 0.004). The superoxide dismutase change was greater with IE than with CE (p = 0.015). There were no significant changes in inflammatory markers after exercise (p>0.05). ConclusionCE and IE cause isoleucine, l-carnitine, and acylcarnitine levels to decrease, whereas ketone bodies were increased, thus indicating the energy metabolism shift from carbohydrates to amino acid utilization and lipid metabolism in COPD. Compared with CE, IE produces significant changes in more metabolomics in terms of carbohydrates, lipids, amino acids, nucleotides, and vitamins. Acute CE and IE alter circulating GPx levels in COPD.

Five Days of Tart Cherry Supplementation Improves Exercise Performance in Normobaric Hypoxia.

Previous studies have shown tart cherry (TC) to improve exercise performance in normoxia. The effect of TC on hypoxic exercise performance is unknown. This study investigated the effects of 5 days of tart cherry (TC) or placebo (PL) supplementation on hypoxic exercise performance. Thirteen healthy participants completed an incremental cycle exercise test to exhaustion (TTE) under two conditions: (i) hypoxia (13% O2) with PL and (ii) hypoxia with TC (200 mg anthocyanin per day for 4 days and 100 mg on day 5). Pulmonary gas exchange variables, peripheral arterial oxygen saturation (SpO2), deoxygenated hemoglobin (HHb), and tissue oxygen saturation (StO2) assessed by near-infrared spectroscopy in the vastus lateralis muscle were measured at rest and during exercise. Urinary 8-hydro-2' deoxyguanosine (8-OHdG) excretion was evaluated pre-exercise and 1 and 5 h post-exercise. The TTE after TC (940 ± 84 s, mean ± standard deviation) was longer than after PL (912 ± 63 s, p &lt; 0.05). During submaximal hypoxic exercise, HHb was lower and StO2 and SpO2 were higher after TC than PL. Moreover, a significant interaction (supplements × time) in urinary 8-OHdG excretion was found (p &lt; 0.05), whereby 1 h post-exercise increases in urinary 8-OHdG excretion tended to be attenuated after TC. These findings indicate that short-term dietary TC supplementation improved hypoxic exercise tolerance, perhaps due to lower HHb and higher StO2 in the working muscles during submaximal exercise.

Effect of 3 and 6 mg/kg of caffeine on fat oxidation during exercise in healthy active females.

The aim of this study was to investigate the effect of 3 and 6 mg of caffeine per kg of body mass (mg/kg) on whole-body substrate oxidation during an incremental cycling exercise test in healthy active women. Using a double-blind placebo-controlled counterbalanced experimental design, 14 subjects performed three identical exercise trials after the ingestion of 3 or 6 mg/kg of caffeine or placebo. The exercise trials consisted of an incremental test on a cycle ergometer with 3-min stages at workloads from 30 to 70% of maximal oxygen uptake (VO2max). Substrate oxidation rates were measured by indirect calorimetry. During exercise, there was a significant effect of substance (F = 5.221; p = 0.016) on fat oxidation rate. In comparison to the placebo, 3 mg/kg of caffeine increased fat oxidation rates at 30 to 60% of VO2max (all p < 0.050) and 6 mg/kg at 30 to 50% of VO2max (all p < 0.050). There was also a significant effect of substance (F = 5.221; p = 0.016) on carbohydrate oxidation rate (F = 9.632; p < 0.001). In comparison to placebo, both caffeine doses decreased carbohydrate oxidation rates at 40 to 60% VO2max (all p < 0.050). The maximal rate of fat oxidation with placebo was 0.24 ± 0.03 g/min, which increased with 3 mg/kg to 0.29 ± 0.04 g/min (p = 0.032) and to 0.29 ± 0.03 with 6 mg/kg of caffeine (p = 0.042). Acute intake of caffeine improves the utilization of fat as a fuel during submaximal aerobic exercise in healthy active women with an effect of similar magnitude after the intake of 3 and 6 mg of caffeine per kg of body mass. Thus, the use of 3 mg/kg of caffeine would be more recommended than 6 mg/kg for women seeking increased fat utilization during submaximal exercise.

The effect of proportional assist ventilation on the electrical activity of the human diaphragm during exercise.

What is the central question of this study? What is the effect of lowering the normally occurring work of breathing on the electrical activity and pressure generated by the diaphragm during submaximal exercise in healthy humans? What is the main finding and its importance? Ventilatory assist during exercise elicits a proportional lowering of both the work performed by the diaphragm and diaphragm electrical activity. These findings have implications for exercise training studies using proportional assist ventilation to reduce diaphragm work in patients with cardiopulmonary disease. We hypothesized that when a proportional assist ventilator (PAV) is applied in order to reduce the pressure generated by the diaphragm, there would be a corresponding reduction in electrical activity of the diaphragm. Healthy participants (five male and four female) completed an incremental cycle exercise test to exhaustion in order to calculate workloads for subsequent trials. On the experimental day, participants performed submaximal cycling, and three levels of assisted ventilation were applied (low, medium and high). Ventilatory parameters, pulmonary pressures and EMG of the diaphragm (EMGdi ) were obtained. To compare the PAV conditions with spontaneous breathing intervals, ANOVA procedures were used, and significant effects were evaluated with a Tukey-Kramer test. Significance was set at P<0.05. The work of breathing was not different between the lowest level of unloading and spontaneous breathing (P=0.151) but was significantly lower during medium (25%, P=0.02) and high (36%, P<0.001) levels of PAV. The pressure-time product of the diaphragm (PTPdi ) was lower across PAV unloading conditions (P<0.05). The EMGdi was significantly lower in medium and high PAV conditions (P=0.035 and P<0.001, respectively). The mean reductions of EMGdi with PAV unloading were 14, 22 and 39%, respectively. The change in EMGdi for a given lowering of PTPdi with the PAV was significantly correlated (r=0.61, P=0.01). Ventilatory assist during exercise elicits a reduction in the electrical activity of the diaphragm, and there is a proportional lowering of the work of breathing. Our findings have implications for exercise training studies using assisted ventilation to reduce diaphragm work in patients with cardiopulmonary disease.

The mediating role of inhibitory control in the relationship between prefrontal cortex hemodynamics and exercise performance in adults with overweight or obesity

Physical inactivity has been suggested to impair physical performance, cognitive functions and facilitate weight gain. One hypothesis is that long periods of physical inactivity could impair oxygen delivery to the prefrontal cortex (PFC), impairing one's cognitive ability to inhibit unhealthy automated behaviors and, therefore, reduce exercise tolerance. The present study sought to further understand the relationship among PFC hemodynamics, inhibitory control, and exercise tolerance in individuals with low physical fitness levels who are overweight or obese. Thirty-four participants were asked to perform a series of inhibitory control tests (i.e., Stroop task) in one testing session and complete an incremental cycling exercise test with hemodynamic fluctuations of the PFC measured with functional near-infrared spectroscopy in another session. Our results indicate that exercise performance varied with PFC oxygenation. We also found that inhibitory control played a key role mediating the relationship between PFC oxygenation and exercise performance, suggesting that the cognitive ability to inhibit automated responses has an impact on exercise behavior in adults with overweight and obesity.

Cortisol response under low intensity exercise during cognitive-behavioral therapy is associated with therapeutic outcome in panic disorder-an exploratory study.

Patients with Panic Disorder (PD) show an abnormal stress-induced functioning of the Hypothalamic-Pituitary-adrenal (HPA)-axis. Different protocols for stress induction are of rather low relevance for the psychotherapeutic treatment. In practice, interoceptive exposure is often realized as Low Intensity Exercise (LIE), as compared to an incremental cycle exercise test to exhaustion. Currently, it is not known, whether LIE displays an effective interoceptive stressor 1.) leading to a significant anxiety induction; 2.) a comparable HPA- and Sympathetic-Adreno-Medullar (SAM)-axis response in both patients and healthy controls; 3.) stress responses under LIE are associated with treatment outcomes. N = 20 patients with PD and n = 20 healthy controls were exposed to ten minutes of LIE on an exercise bike. LIE was applied as part of the interoceptive exposure, during an intensive Cognitive-Behavioral Therapy (CBT) in a day clinic. Heart rate was monitored and salivary cortisol samples collected. Before and after the LIE, state anxiety/ arousal were assessed. In order to evaluate psychopathology, the Panic and Agoraphobia Scale, Mobility Inventory, Agoraphobic Cognitions Questionnaire and Body Sensations Questionnaire were applied, before (T1) and after five weeks (T2) of an intensive CBT. LIE led to a significant and similar heart rate increase in both groups. Cortisol decreased over time in both groups, especially in male patients. A higher psychopathology before, and after CBT, was associated with a significantly lower cortisol response under LIE. In the present study, LIE led to a divergent stress response: while there was a significant heart rate increase, cortisol decreased over time, particularly in male patients. A lower reactivity of the HPA-axis seems to be associated with a lower treatment outcome, which may affect extinction based learning. The findings suggest, that interoceptive stimuli should be designed carefully in order to be potent stressors.

Effect of caffeine intake on fat oxidation rate during exercise: is there a dose-response effect?

The effect of caffeine to enhance fat utilisation as fuel for submaximal aerobic exercise is well established. However, it is unknown whether this effect is dose dependent. The aim of this study was to investigate the effect of 3 and 6mg of caffeine per kg of body mass (mg/kg) on whole-body substrate oxidation during an incremental cycling exercise test. In a double-blind, randomised, and counterbalanced experiment, 18 recreationally active males (maximal oxygen uptake [VO2max] = 56.7 ± 8.2mL/kg/min) performed three experimental trials after ingesting either 3mg/kg of caffeine, 6mg/kg of caffeine or a placebo (cellulose). The trials consisted of an incremental exercise test on a cycle ergometer with 3-min stages at workloads from 30 to 80% of VO2max. Energy expenditure, fat oxidation rate, and carbohydrate oxidation rate were continuously measured by indirect calorimetry. During exercise, there was significant effect of substance (F = 7.969; P = 0.004) on fat oxidation rate. In comparison to the placebo, the rate of fat oxidation was higher with 3mg/kg of caffeine at 30, 40, 50 and 70% of VO2max [all P < 0.050, effect sizes (ES) from 0.38 to 0.50] and with 6mg/kg of caffeine at 30, 40, 50, 60 and 70% of VO2max (all P < 0.050, ES from 0.28 to 0.76). Both 3mg/kg (0.40 ± 0.21g/min, P = 0.021, ES = 0.57) and 6mg/kg of caffeine (0.40 ± 0.17g/min P = 0.001, ES = 0.60) increased the maximal rate of fat oxidation during exercise over the placebo (0.31 ± 0.15g/min). None of the caffeine doses produced any significant effect on energy expenditure or heart rate during exercise, while both caffeine doses reduced perceived fatigue at 80% of VO2max (all P < 0.050, ES from 0.71 to 1.48). The effect of caffeine to enhance fat oxidation during submaximal aerobic exercise is of similar magnitude with 3 and 6mg of caffeine per kg of body mass. Thus, a dose of 3mg of caffeine per kg of body mass would be sufficient to enhance fat utilisation as fuel during submaximal exercise.

Predictors of Expiratory Flow Limitation during Exercise in Healthy Males and Females

It is unclear whether the frequency and mechanisms of expiratory flow limitation (EFL) during exercise differ between males and females. This study aimed to determine which factors predispose individuals to EFL during exercise and whether these factors differ based on sex. We hypothesized that i) EFL frequency would be similar in males and females and ii) in females, EFL would be associated with indices of low ventilatory capacity, whereas in males, EFL would be associated with indices of high ventilatory demand. Data from n = 126 healthy adults (20-45 y, n = 60 males, n = 66 females) with a wide range of cardiorespiratory fitness (81%-182% predicted maximal oxygen uptake) were included in the study. Participants performed spirometry and an incremental cycle exercise test to exhaustion. Standard cardiorespiratory variables were assessed throughout exercise. The tidal flow-volume overlap method was used to assess EFL based on a minimum threshold of 5% overlap between the tidal and the maximum expiratory flow-volume curves. Predictors of EFL during exercise were determined via multiple logistical regression using anthropometric, pulmonary function, and peak exercise data. During exercise, EFL occurred in 49% of participants and was similar between the sexes (females = 45%, males = 53%; P = 0.48). In males, low forced expired flow between 25% and 75% of forced vital capacity and high slope ratio as well as low end-expiratory lung volume, high breathing frequency, and high relative tidal volume at peak exercise were associated with EFL ( P < 0.001; Nagelkerke R2 = 0.73). In females, high slope ratio, high breathing frequency, and tidal volume at peak exercise were associated with EFL ( P < 0.001; Nagelkerke R2 = 0.61). Despite sex differences in respiratory system morphology, the frequency and the predictors of EFL during exercise do not substantially differ between the sexes.

Disturbance of desire-goal motivational dynamics during different exercise intensity domains.

PurposeThe desire‐goal motivational conflict helps explain endurance performance; however, the physiological concomitants are unknown. The present study examined disturbances in desire to reduce effort and performance goal value across moderate, heavy, and severe exercise intensity domains, demarcated by the first (LT1) and second (LT2) lactate thresholds. In addition, the within‐person relationships among blood lactate concentration, heart rate, and desire‐goal conflict were examined.MethodsThirty participants (53% female, Mage = 21.03 years; SD = 2.06 years) completed an incremental cycling exercise test, in which work rate was increased by 25 watts every four minutes, until voluntary exhaustion or sufficient data from the severe intensity domain had been collected. Desire to reduce effort, performance goal value, blood lactate concentration (for determination of LT1 and LT2), and heart rate were measured at the end of each stage and analyzed using multilevel models.ResultsThe desire to reduce effort increased over the exercise test with additional shifts and accelerations after each lactate threshold. The performance goal did not show general declines, nor did it shift at LT1. However, the performance goal value shifted at LT2, and the rate of change increased at both thresholds. Within‐person variation in blood lactate concentration positively correlated with the desire to reduce effort and negatively correlated with the performance goal. Within‐person variation in heart rate correlated with desire to reduce effort but not the performance goal.ConclusionTransitioning through both lactate thresholds is important phases for motivation during progressive exercise, particularly for the desire to reduce effort. Within‐person variation in blood lactate concentration is more influential for motivation, compared with heart rate.

Effect of protocol on peak power output in continuous incremental cycle exercise tests.

Peak power output ([Formula: see text]peak) in an incremental exercise test (EXT) is considered an important predictor of performance for cyclists. However, [Formula: see text]peak is protocol dependent. The purpose of this study was to model the effect of EXT design on [Formula: see text]peak. An adapted version of a previously developed mathematical model was used. For the purpose of validity testing, we compared predicted [Formula: see text]peak differences (predicted Δ[Formula: see text]peak) with actual Δ[Formula: see text]peak found in sports science literature. The model quantified Δ[Formula: see text]peak between 36 EXT designs with stage durations in the range 1-5min and increments in the range 10-50W. Predicted Δ[Formula: see text]peak and actual Δ[Formula: see text]peak across a wide range of performance levels of cyclists were in good agreement. Depending on the specific combination of increment and stage duration, [Formula: see text]peak may be widely different or equivalent. A minimum difference in increment (5W) or in stage duration (1min) already results in significantly different [Formula: see text]peak. In EXTs having the same ratio between increment and stage duration, [Formula: see text]peak in the EXT with the shortest stage duration or the greatest increment is significantly higher. Tests combining 15W, 25W or 40W increments with 2, 3 and 4min stage durations, respectively, are 'special' in that their [Formula: see text]peak approximates the power output associated with maximal oxygen uptake ([Formula: see text]). The modeling results allow comparison of [Formula: see text]peak between widely different EXT designs. Absolute performance level does not affect Δ[Formula: see text]peak. [Formula: see text]peak15/2, [Formula: see text]peak25/3 and [Formula: see text]peak40/4 constitute a practical physiologic reference for performance diagnostics and exercise intensity prescription.

Impacts of different intensities of exercise on inflammation and hypoxia markers in low altitude

BackgroundThis study aims to determine and compare the effects of exercise modalities with different intensities on the secretion of key inflammation and hypoxia markers in amateur athletes.MethodsTwenty-three athletes with a mean age of 20.1 years, living at low altitude (1850 m) participated in this study. The participants' maximal oxygen consumption values (VO2 max) were determined with an incremental cycle exercise test as 54.15 ± 6.14 mL kg min−1. Athletes performed four protocols: at rest, 50% VO2 max, 75% VO2 max and 100% VO2 max (until exhaustion) with one-week intervals. 50% VO2 max, 75% VO2 max sessions were performed continuously for 30 min on a bicycle ergometer and 100% VO2 max session was performed by cycling until exhaustion. Blood samples were obtained at rest and immediately after each exercise session. Serum tumor necrosis factor alpha (TNF-α), C-reactive protein (CRP), interleukin-10 (IL-10), and hypoxia inducible factor-1 alpha (HIF-1α) levels were measured.ResultsThere were significant differences in serum TNF-α levels in 75% VO2 max and 100% VO2 max sessions (489.03 ± 368.37 and 472.70 ± 365.21 ng/L, respectively) compared to rest conditions (331.65 ± 293.52 ng/L). Serum CRP levels of 50% VO2 max and 75% VO2 max sessions (1.19 ± 0.50; 1.07 ± 0.52 mg/L) were significantly higher than the rest condition (0.74 ± 0.35 mg/L). There were significant differences in serum IL-10 levels of rest condition and 50% VO2 max; 50% VO2 max, and 100% VO2 max sessions (328.09 ± 128.87; 446.36 ± 142.84; 347.44 ± 135.69; 324.88 ± 168.06 pg/mL). Serum HIF-1α levels were significantly higher in 75% VO2 max session compared to rest (1.26 ± 0.16; 1.08 ± 0.19 ng/mL) (P < 0.05 for all comparisons).ConclusionsBoth inflammatory and anti-inflammatory pathway is induced on different exercise intensities. Exercise protocols performed until exhaustion may lead to activation of inflammatory pathways and hypoxia-induced damage.