Limit Exercise Performance Research Articles

Does a broad-spectrum cannabidiol supplement improve performance in a 10-min cycle ergometer performance-test?

Cannabidiol (CBD) is a non-intoxicating phytocannabinoid which has been proposed to possess anti-inflammatory and analgesic properties. Given the potential for perceptions of pain to limit exercise performance, the aim of the present study was to investigate if 3weeks of daily CBD supplementation (150mgday-1) improved performance in a 10-min performance-trial on a cycle ergometer. In a randomized, double-blind and placebo-controlled study, 22 healthy participants (n=11 male and n=11 female) completed two 10-min performance trials on a WattBike cycle ergometer interspersed with a 3-week supplementation period. Supplementation involved either 150mgday-1 oral CBD or 150mgday-1 of a visually identical placebo (PLA). During trials, ratings of perceived exertion (RPE [6-20]), heart rate (HR) and blood lactate (BLa) were collected every 2min. Mean power (W) was also taken throughout the exercise at each time point. All data were analyzed using two-way ANOVAs. There were no significant differences (P>0.05) between CBD or PLA groups for mean power (W) during the 10-min performance trial. There were also no significant differences (P>0.05) in any of the physiological or perceptual parameters (HR, BLa and RPE) between conditions. Three weeks supplementation of a broad-spectrum CBD supplement did not improve performance via any change in RPE during a 10-min time trial on a cycle ergometer, and as such, this evidence does not support the claim that broad-spectrum CBD supplements could be performance-enhancing in this exercise modality.

Left ventricular kinetic energy across heart failure subgroups and subclinical diastolic dysfunction

Abstract Background Diastolic dysfunction is a common finding in heart failure with preserved ejection fraction (HFpEF) and is considered a key mechanism for limiting exercise performance. Meanwhile, subclinical diastolic dysfunction (SDD) without heart failure is a growing concern and may be common in the general population [1,5[. The kinetic energy (KE) of intracardiac blood flow reflects the work spent on accelerating blood [3] and may provide a novel window into diastolic filling dynamics [2,4]. Our aim was therefore to quantify left ventricular KE in HFpEF patients and compare with healthy controls, subjects with SDD, and heart failure patients with moderately reduced (HFmrEF) or reduced ejection fraction (HFrEF). Methods We studied 12 healthy controls, 22 healthy subjects with 1–2 echocardiographic criteria of diastolic dysfunction (SDD), 16 HFpEF, 9 HFmrEF, and 16 HFrEF patients. All subjects underwent CMR imaging at 1.5T with acquisition of anatomical cines and 4D flow from a box covering the heart. The LV was delineated over the cardiac cycle and KE inside the segmentation calculated as 0.5 × m × v2, where v is the instantaneous velocity vector magnitude and m is blood mass. Group comparisons of peak and average values were performed using Kruskal-Wallis test with Dunn's uncorrected post hoc test. Significance was assigned at p<0.05. Median values are given. Results Groups were similar with regard to sex, blood pressure, and body surface area. HFpEF (median 72 years) and HFrEF patients (67 years) were significantly older than subjects with SDD (62 years, p=0.001). Examples of KE are shown in Fig. 1. Systolic peak and average KE did not differ between groups (p=0.81 and p=0.54 respectively, Fig. 2). Diastolic peak KE was higher in all groups of heart failure compared to controls (p<0.03 for all) and diastolic average KE was higher in HFmrEF and HFrEF compared to controls (p<0.02). The standard deviation for SDD was wider than in controls (1.6 mJ vs 0.8 mJ for systolic peaks, 2.7 mJ vs 1.1 mJ for diastolic peaks) and more closely resembled the HFpEF group (2.1 mJ in systole, 2.3 mJ in diastole). Conclusions Systolic kinetic energy expenditures are on average similar between controls, subjects with subclinical diastolic dysfunction, and heart failure patients, indicating that cardiac pumping involves approximately the same amount of systolic acceleration for a given afterload. Conversely, diastolic KE was found more dispersed both in heart failure and in asymptomatic individuals with subclinical diastolic dysfunction. Higher peak values of KE were seen in diastole for all types of heart failure including HFpEF, indicating more work is spent filling the ventricle. Measurements of KE in diastole could potentially be a new tool for assessment of heart failure, including early stages of disease development in some individuals with subclinical diastolic dysfunction. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): Swedish Heart Lung FoundationRegion of Scania, Sweden

Role of Cardiac AMP-Activated Protein Kinase in a Non-pathological Setting: Evidence From Cardiomyocyte-Specific, Inducible AMP-Activated Protein Kinase α1α2-Knockout Mice.

AMP-activated protein kinase (AMPK) is a key regulator of energy homeostasis under conditions of energy stress. Though heart is one of the most energy requiring organs and depends on a perfect match of energy supply with high and fluctuating energy demand to maintain its contractile performance, the role of AMPK in this organ is still not entirely clear, in particular in a non-pathological setting. In this work, we characterized cardiomyocyte-specific, inducible AMPKα1 and α2 knockout mice (KO), where KO was induced at the age of 8 weeks, and assessed their phenotype under physiological conditions. In the heart of KO mice, both AMPKα isoforms were strongly reduced and thus deleted in a large part of cardiomyocytes already 2 weeks after tamoxifen administration, persisting during the entire study period. AMPK KO had no effect on heart function at baseline, but alterations were observed under increased workload induced by dobutamine stress, consistent with lower endurance exercise capacity observed in AMPK KO mice. AMPKα deletion also induced a decrease in basal metabolic rate (oxygen uptake, energy expenditure) together with a trend to lower locomotor activity of AMPK KO mice 12 months after tamoxifen administration. Loss of AMPK resulted in multiple alterations of cardiac mitochondria: reduced respiration with complex I substrates as measured in isolated mitochondria, reduced activity of complexes I and IV, and a shift in mitochondrial cristae morphology from lamellar to mixed lamellar-tubular. A strong tendency to diminished ATP and glycogen level was observed in older animals, 1 year after tamoxifen administration. Our study suggests important roles of cardiac AMPK at increased cardiac workload, potentially limiting exercise performance. This is at least partially due to impaired mitochondrial function and bioenergetics which degrades with age.

Closure of outpatient cardiac rehabilitation during the first COVID-19 lockdown in Austria in spring 2020 resulted in deteriorating physical exercise capacity: a mixed-methods study

BackgroundGroup-based cardiac rehabilitation (CR) has inevitably been disrupted by COVID-19-related public health measures, increasing the risk of deterioration in modifiable risk factors for patients with cardiovascular disease (CVD).PurposeTo examine the impact of CR closure during the first COVID-19-related national lockdown in Austria in spring 2020 on patients' maintenance of physical activity, physical fitness levels, and cardiovascular risk profile; and to describe the patient experience of lack of group-based CR training due to COVID-19.MethodsThis mixed-methods study recruited patients from an outpatient CR centre in Austria during summer 2020. Eligibility criteria were regular attendance at weekly group-based exercise training at the centre until the COVID-19-related lockdown in March 2020; pre-lockdown completion of a maximal cycle ergometer test; no contraindications for maximal exercise testing; and no new complaints limiting exercise performance. Participants underwent post-lockdown quantitative assessment of physical fitness (maximal cycle ergometer testing, submaximal cycle ergometer training session at individual pre-lockdown settings) and cardiovascular risk status. These were compared with pre-lockdown data from medical records. Participants gave qualitative interviews about their experience of maintaining exercise during lockdown. Interviews were audio-recorded, transcribed, coded, and interpreted using framework analysis.ResultsTwenty-eight (57%) of 49 eligible patients were recruited, 1 withdrew, and 27 completed all study procedures. Two participants were excluded from analysis of physical fitness data, due to subsequent diagnosis of new complaints limiting exercise performance. Mean (SD) age was 69 (7.4) years. Six (22%) were female. Median (IQR) time since first CVD event was 8 (5.5, 9) years. In maximal ergometer testing, 14 (56%) had deteriorated, 10 (40%) were unchanged, and 1 (4%) had improved post-lockdown. At group level, power was significantly reduced (maximal ergometer testing, submaximal ergometer training), whereas CVD risk factors remained unchanged from pre- to post-lockdown (table 1). Qualitative analysis corroborated the negative impact of the closure of CR classes (table 2).ConclusionsThis patient cohort was heterogeneous with respect to physical activity levels and exercise capacity, yet overall motivated and experienced in exercise training, having regularly attended training sessions at the centre before the lockdown. Despite individually seeking out alternative exercise options during lockdown, group average exercise capacity deteriorated even in this motivated and exercise-conscious group. This highlights the importance of providing group-based opportunities for supervised high intensity training for patients who engage well in such a setting, and the detrimental impact of disruption to this type of CR service.Funding AcknowledgementType of funding sources: Public grant(s) – National budget only. Main funding source(s): Ludwig Boltzmann Gesellschaft COVID-19 Support Measure: Open Innovation in Science (OIS) Research Enrichment Fund

On the Influence of Group III/IV Muscle Afferent Feedback on Endurance Exercise Performance.

This review discusses evidence suggesting that group III/IV muscle afferents affect locomotor performance by influencing neuromuscular fatigue. These neurons regulate the hemodynamic and ventilatory response to exercise and, thus, assure appropriate locomotor muscle O2 delivery, which optimizes peripheral fatigue development and facilitates endurance performance. In terms of central fatigue, group III/IV muscle afferents inhibit motoneuronal output and thereby limit exercise performance.

The carotid bodies exercise control over active expiration but not peak performance during high-intensity treadmill running.

The carotid bodies exercise control over active expiration but not peak performance during high-intensity treadmill running.

The thermal limits of cardiorespiratory performance in anadromous Arctic char (Salvelinus alpinus): a field-based investigation using a remote mobile laboratory.

Despite immense concern over amplified warming in the Arctic, physiological research to address related conservation issues for valuable cold-adapted fish, such as the Arctic char (Salvelinus alpinus), is lacking. This crucial knowledge gap is largely attributable to the practical and logistical challenges of conducting sensitive physiological investigations in remote field settings. Here, we used an innovative, mobile aquatic-research laboratory to assess the effects of temperature on aerobic metabolism and maximum heart rate (fHmax) of upriver migrating Arctic char in the Kitikmeot region of Nunavut in the central Canadian Arctic. Absolute aerobic scope was unchanged at temperatures from 4 to 16°C, while fHmax increased with temperature (Q10 = 2.1), as expected. However, fHmax fell precipitously below 4°C and it began to plateau above ~ 16°C, reaching a maximum at ~ 19°C before declining and becoming arrhythmic at ~ 21°C. Furthermore, recovery from exhaustive exercise appeared to be critically impaired above 16°C. The broad thermal range (~4–16°C) for increasing fHmax and maintaining absolute aerobic scope matches river temperatures commonly encountered by migrating Arctic char in this region. Nevertheless, river temperatures can exceed 20°C during warm events and our results confirm that such temperatures would limit exercise performance and thus impair migration in this species. Thus, unless Arctic char can rapidly acclimatize or alter its migration timing or location, which are both open questions, these impairments would likely impact population persistence and reduce lifetime fitness. As such, future conservation efforts should work towards quantifying and accounting for the impacts of warming, variable river temperatures on migration and reproductive success.

GLUTATHIONE, INFLAMMATION, MITOCHONDRIAL FAT OXIDATION AND DIASTOLIC HEART FUNCTION IN OLD MICE

Impaired diastolic function is a risk factor for diastolic heart failure, may limit exercise performance, and is common in aging in both people and animals. This diastolic dysfunction seems to be associated with cardiac inflammation, fibrosis and impaired mitochondrial fatty acid metabolism. Old (24-28 m) mice fed a GlyNAC supplemented diet for 8 weeks were compared to those on control diet, and had dramatic improvement in all these parameters. For example, ATP generation from fatty acids with five-fold higher in the GlyNAC supplemented mice. In vitro studies compared NAC with GlyNAC and demonstrated the benefits only with supplementing both amino acids as compared to NAC alone. These data suggest that GlyNAC may have a role in improving cardiac function thus improving exercise tolerance and quality of life for older people.

Thermoregulatory burden of elite sailing athletes during exercise in the heat: A pilot study

ABSTRACTExercising in a hot and humid environment increases core body temperature, which may limit exercise performance. The risk of exercise-induced hyperthermia and associated performance decrement in Olympic sailing athletes is largely unknown. Therefore, this study aimed to compare thermoregulatory responses and performance indicators of elite sailors in a cool versus hot and humid environment. Seven elite athletes from four different Olympic sailing classes (Laser, RS:X, Finn, 470) performed cycling and/or rowing exercise in a cool (18°C) and hot (33°C) environment, while core body temperature (TC), skin temperature (TSK), exercise performance (covered distance), and rating of perceived exertion were measured continuously. TC increased significantly more in the hot environment (37.6 ± 0.2°C to 39.1 ± 0.1°C) compared to the cool environment (37.5 ± 0.1°C to 38.5 ± 0.2°C; p = 0.002), but the increase in TC between conditions differed substantially within individuals (range: 0.3°C – 0.9°C). Exercise performance decreased by 6.2 ± 2.9% in the hot environment (p = 0.013, range: 2.3%–9.5%), but more importantly, exercise performance was strongly inversely related to peak TC (R = −0.78, p = 0.039). Rating of perceived exertion (cool: 14.2 ± 0.6; hot: 13.9 ± 1.2) and increase in TSK (cool: 0.5 ± 1.0°C; hot: 0.9 ± 0.3°C) did not differ between conditions (p = 0.59 and p = 0.36, respectively). To conclude, a larger increase in TC and substantial exercise performance decrement were observed in the hot versus cool environment. As a further matter, large inter-individual differences were observed across athletes with an inverse relationship between TC and exercise performance, which stresses the importance of appropriate and personalized interventions to reduce thermoregulatory burden of elite sailors during exercise in the heat.

Exercise is Medicine for Concussion.

Sport-related concussion (SRC) is a physiological brain injury that produces cerebral and systemic effects, including exercise intolerance. Exercise intolerance after concussion is believed to be the result of autonomic nervous system (ANS) dysfunction. Ventilation is inappropriately low for the level of exercise intensity, raising arterial carbon dioxide (PaCO2) levels. Elevated PaCO2 increases cerebral blood flow (CBF) out of proportion to exercise intensity, which is associated with symptoms that limit exercise performance. Thus, elevated exercise PaCO2 may signal incomplete recovery from SRC. This article reviews recent observational and experimental data and presents the evidence that subthreshold aerobic exercise normalizes the cerebrovascular physiological dysfunction and is "medicine" for patients with concussion and persistent postconcussive symptoms (PPCS). It discusses the systematic evaluation of exercise tolerance after concussion using the Buffalo Concussion Treadmill Test (BCTT) and reviews the utility of the Buffalo Concussion Bike Test (BCBT), the data from which are used to establish an individualized heart rate "dose" of subthreshold exercise to safely speed recovery, which also may work in the acute recovery phase after SRC with the potential to reduce the incidence of PPCS. Evaluation and treatment approaches based on the physiology of concussion suggest that exercise is medicine for concussion, potentially adding a new dimension to concussion care to help safely speed recovery and prevent PPCS in some patients.

Influence of group III/IV muscle afferents on small muscle mass exercise performance: a bioenergetics perspective.

This investigation assessed the influence of group III/IV muscle afferents on small muscle mass exercise performance from a skeletal muscle bioenergetics perspective. Group III/IV muscle afferent feedback was attenuated with lumbar intrathecal fentanyl during intermittent isometric single-leg knee-extensor all-out exercise, while 31 P-MRS was used to assess skeletal muscle bioenergetics. Attenuation of group III/IV muscle afferent feedback improved exercise performance during the first minute of exercise, due to an increase in total ATP production with no change in the ATP cost of contraction. However, exercise performance was not altered during the remainder of the protocol, despite a sustained increase in total ATP production, due to an exacerbated ATP cost of contraction. These findings reveal that group III/IV muscle afferents directly limit exercise performance during small muscle mass exercise, but, due to their critical role in maintaining skeletal muscle contractile efficiency, with time, the benefit of attenuating the muscle afferents is negated. The direct influence of group III/IV muscle afferents on exercise performance remains equivocal. Therefore, all-out intermittent isometric single-leg knee-extensor exercise and phosphorous magnetic resonance spectroscopy (31 P-MRS) were utilized to provide a high time resolution assessment of exercise performance and skeletal muscle bioenergetics in control conditions (CTRL) and with the attenuation of group III/IV muscle afferent feedback via lumbar intrathecal fentanyl (FENT). In both conditions, seven recreationally active men performed 60 maximal voluntary quadriceps contractions (MVC; 3s contraction, 2s relaxation), while knee-extensor force and 31 P-MRS were assessed during each MVC. The cumulative integrated force was significantly greater (8±6%) in FENT than CTRL for the first minute of the all-out protocol, but was not significantly different for the second to fifth minutes. Total ATP production was significantly greater (16±21%) in FENT than CTRL throughout the all-out exercise protocol, due to a significantly greater anaerobic ATP production (11±13%) in FENT than CTRL with no significant difference in oxidative ATP production. The ATP cost of contraction was not significantly different between FENT and CTRL for the first minute of the all-out protocol, but was significantly greater (29±34%) in FENT than in CTRL for the second to fifth minutes. These findings reveal that group III/IV muscle afferents directly limit exercise performance during small muscle mass exercise, but, due to their critical role in maintaining skeletal muscle contractile efficiency, with time, the benefit from muscle afferent attenuation is negated.

Respiratory muscle strength is decreased after maximal incremental exercise in trained runners and cyclists

The respiratory muscle fatigue seems to be able to limit exercise performance and may influence the determination of maximal oxygen uptake (V̇O2max) or maximum aerobic work rate during maximal incremental test. The aim of this study was therefore to investigate whether maximal incremental exercise decreases respiratory muscle strength. We hypothesized that respiratory muscle strength (maximal pressure) will decrease after maximal incremental exercise to exhaustion. 36 runners and 23 cyclists completed a maximal incremental test on a treadmill or a cycle ergometer with continuous monitoring of expired gases. Maximal inspiratory (MIP) and expiratory (MEP) pressure measurements were taken at rest and post- exercise. At rest, the MIP and MEP were 140±25 and 172±27 in runners vs. 115±26 and 146±33 in cyclists (p<0.05 between groups, respectively). The rest values of MIP and MEP were correlated to the V̇O2peak in all athletes, r=0.34, p<0.01 and r=0.36, p<0.01, respectively. At exhaustion, the MIP and MEP decreased significantly post- test by 13±7% and 13±5% in runners vs. 17±11% and 15±10% in cyclists (p>0.05), respectively. Our results suggest that respiratory muscle strength is decreased following maximal incremental exercise in trained runners and cyclists.

Leg Blood Flow and Fatigability In People With Type 2 Diabetes

We have previously demonstrated that people with type 2 diabetes mellitus (T2D) have greater fatigability of the knee extensor muscles during a dynamic fatiguing contraction due to impairments within the skeletal muscle; however, the precise mechanism(s) are unknown. PURPOSE: To determine if impairments in leg blood flow are associated with greater fatigability of the knee extensor muscles during a dynamic fatiguing contraction in men and women with T2D. METHODS: 5 individuals with non-insulin dependent T2D (60 - 70 years; 3 women) with no signs of diabetic neuropathy were matched based on age, BMI and physical activity with four non-diabetic controls (CON) (60 - 68 years; 2 women). Physical activity was assessed over four days with a tri-axial accelerometer. To assess fatigability, participants performed a 6-minute single-limb dynamic fatiguing contractions with the knee extensors while seated at 90° of hip and knee flexion. 120 maximal voluntary concentric contractions (MVCCs) were performed with a load equivalent to 20% maximal voluntary isometric contraction torque through a 90° range of motion. Doppler ultrasonograpy was used to assess femoral artery diameter and pulse wave blood velocity before and immediately after the dynamic fatiguing contraction. RESULTS: The reduction in MVCC power was greater for T2D (40.5 ± 17.6%) compared with CON (31.3 ± 20.8%, P < 0.05) as assessed at the end of exercise. T2D and CON both demonstrated similar increases in leg blood flow after the dynamic fatiguing contraction (71.7 ± 41.1% vs. 69.0 ± 37.3%, respectively; p > 0.05). However, greater reductions in MVCC power (i.e. greater fatigability) was associated with lower blood flow following dynamic fatiguing contractions (p = 0.034, r = 0.633). CONCLUSIONS: Greater fatigability of the knee extensor muscles during dynamic fatiguing contractions was associated with lower blood flow. Impaired blood flow responses to exercise may limit exercise performance among T2D, and this work highlights the need for future studies that examine skeletal muscle perfusion during dynamic exercise in people with T2D. Supported by Marquette University Way Klingler Research Fellowship to SKH

Association of plasma 25-hydroxyvitamin D with physical performance in physically active children

Vitamin D is thought to regulate skeletal muscle function and boost physical performance. The aim of this study was to assess the relationship between vitamin D and physical performance in physically active children. This cross-sectional study included 125 children who practice football as a leisure activity. Plasma 25-hydroxyvitamin D (25-OHD) was assessed using a chemiluminescence immunoassay method. Vitamin D inadequacy was defined as 25-OHD < 20 ng/mL. Physical performance testing included measurements of muscle strength (maximal isometric contraction), jumping ability (vertical jump, standing broad jump, triple hop test), linear sprint (10 m and 20 m), and agility (9 × 4-m shuttle run). Plasma 25-OHD concentrations were positively correlated with muscle strength (r = 0.539; p < 0.001), vertical jump (r = 0.528; p < 0.001), and standing broad jump (r = 0.492; p < 0.001) but inversely correlated with sprint performance (r = -0.539; p < 0.001). In multivariate analysis models, plasma 25-OHD concentrations were associated with each physical performance parameter independently of age, maturity status, body mass index, fat mass, and protein and calcium intakes. In conclusion, a low plasma 25-OHD level was associated with decreased muscle strength, agility, and jumping and sprinting abilities in physically active children. Vitamin D inadequacy may limit exercise performance. Further research should verify whether correction of vitamin D deficiency enhances physical performance.

A Model of the Cardiorespiratory Response to Aerobic Exercise in Healthy and Heart Failure Conditions.

The physiological response to physical exercise is now recognized as an important tool which can aid the diagnosis and treatment of cardiovascular diseases. This is due to the fact that several mechanisms are needed to accommodate a higher cardiac output and a higher oxygen delivery to tissues. The aim of the present work is to provide a fully closed loop cardiorespiratory simulator reproducing the main physiological mechanisms which arise during aerobic exercise. The simulator also provides a representation of the impairments of these mechanisms in heart failure condition and their effect on limiting exercise capacity. The simulator consists of a cardiovascular model including the left and right heart, pulmonary and systemic circulations. This latter is split into exercising and non-exercising regions and is controlled by the baroreflex and metabolic mechanisms. In addition, the simulator includes a respiratory model reproducing the gas exchange in lungs and tissues, the ventilation control and the effects of its mechanics on the cardiovascular system. The simulator was tested and compared to the data in the literature at three different workloads whilst cycling (25, 49 and 73 watts). The results show that the simulator is able to reproduce the response to exercise in terms of: heart rate (from 67 to 134 bpm), cardiac output (from 5.3 to 10.2 l/min), leg blood flow (from 0.7 to 3.0 l/min), peripheral resistance (from 0.9 to 0.5 mmHg/(cm3/s)), central arteriovenous oxygen difference (from 4.5 to 10.8 ml/dl) and ventilation (6.1–25.5 l/min). The simulator was further adapted to reproduce the main impairments observed in heart failure condition, such as reduced sensitivity of baroreflex and metabolic controls, lower perfusion to the exercising regions (from 0.6 to 1.4 l/min) and hyperventilation (from 9.2 to 40.2 l/min). The simulator we developed is a useful tool for the description of the basic physiological mechanisms operating during exercise. It can reproduce how these mechanisms interact and how their impairments could limit exercise performance in heart failure condition. The simulator can thus be used in the future as a test bench for different therapeutic strategies aimed at improving exercise performance in cardiopathic subjects.

Fatigue and Exhaustion in Hypoxia: The Role of Cerebral Oxygenation.

Fan, Jui-Lin, and Bengt Kayser. Fatigue and exhaustion in hypoxia: the role of cerebral oxygenation. High Alt Med Biol. 17:72-84, 2016.-It is well established that ascent to high altitude is detrimental to one's aerobic capacity and exercise performance. However, despite more than a century of research on the effects of hypoxia on exercise performance, the underlying mechanisms remain incompletely understood. While the cessation of exercise, or the reduction of its intensity, at exhaustion, implies reduced motor recruitment by the central nervous system, the mechanisms leading up to this muscular derecruitment remain elusive. During exercise in normoxia and moderate hypoxia (∼1500-2500 m), peripheral fatigue and activation of muscle afferents probably play a major role in limiting exercise performance. Meanwhile, studies suggested that cerebral tissue deoxygenation may play a pivotal role in impairing aerobic capacity during exercise in more severe hypoxic conditions (∼4500-6000 m). However, recent studies using end-tidal CO2 clamping, to improve cerebral tissue oxygenation during exercise in hypoxia, failed to demonstrate an improvement in exercise performance. In light of these recent findings, which seem to contradict the hypothetical role of cerebral tissue deoxygenation as a performance limiting factor at high altitude, this short review aims to provide a critical reappraisal of the extant literature and ends exploring some potential avenues for further research in this field.

Engineering a solution to explore the cardiorespiratory limits to exercise performance: take a load off!

Engineering a solution to explore the cardiorespiratory limits to exercise performance: take a load off!

The 400- and 800-m Track Running Induces Inspiratory Muscle Fatigue in Trained Female Middle-Distance Runners.

Inspiratory muscle fatigue (IMF) may limit exercise performance. A few studies have reported that IMF occurs after short-duration swimming exercise, but whether short-duration running can induce IMF remains unclear. Intra-abdominal pressure is increased during running through diaphragmatic activation to stabilize the spine during movements of the upper limbs. This occurs along with the increased inspiratory muscle effort associated with increased respirations during exercise; thus, we hypothesized that short-duration running exercise would induce IMF. To test this hypothesis, we measured maximal inspiratory pressure (MIP) before and after 400- and 800-m track running sessions. Eight female middle-distance (400, 800 m) runners performed a 400- and 800-m running test. Maximal inspiratory pressure was measured before and after each test using a portable autospirometer. The mean MIPs were significantly lower after running than before running; values obtained were 107 ± 25 vs. 97 ± 27 cmH2O (p = 0.01, effect size [ES] = 0.65) and 108 ± 26 vs. 92 ± 27 cmH2O (p = 0.01, ES = 0.74) before vs. after the 400- and 800-m tests, respectively. The mean MIP after the 800-m test was significantly lower than after the 400-m test (p = 0.04, ES = 0.48). There was no correlation between IMF value and running time (r = 0.53 and r = -0.28 for either the 400- and 800-m tests, respectively; p > 0.05). In conclusion, IMF occurs after short-duration running exercise. Coaches could consider prescribing inspiratory muscle training or warm-up in an effort to reduce the inevitable IMF associated with maximal effort running.

The 400- And 800-m Track Running Induces Inspiratory Muscle Fatigue In Trained Female Middle-distance Runners

Inspiratory muscle fatigue (IMF) may limit exercise performance. A few studies have reported that IMF occurs after short-duration swimming exercise, but whether short-duration running can induce IMF remains unclear. Intra-abdominal pressure is increased during running through diaphragmatic activation to stabilize the spine during movements of the upper limbs. This occurs along with the increased inspiratory muscle effort associated with increased respirations during exercise; thus, we hypothesized that short-duration running exercise would induce IMF. PURPOSE: This study was designed to investigate short-duration running-induced IMF. To test this hypothesis we measured maximal inspiratory pressure (MIP) before and after 400-m and 800-m track running sessions. METHODS: Eight female middle-distance (400-m, 800-m) runners performed a 400-m and an 800-m running test on an outdoor 400-m tartan athletic track. All the participants were members of a collegiate athletic club and had participated in interscholastic and/or intercollegiate athletic competitions at least once. MIP was measured before whole-body warm-up, and within 2 min after completion of the 400-m and 800-m running tests, using a portable autospirometer. The percentage decrease in MIP from pre-warm up to post-test was considered to represent the IMF associated with each test. RESULTS: The mean MIPs were significantly lower after running than before running; values obtained were 107 ± 25 vs. 97 ± 27 cmH2O (P = 0.01, ES = 0.65) and 108 ± 26 vs. 92 ± 27 cmH2O (P = 0.01, ES = 0.74) before vs. after the 400-m and 800-m tests, respectively. The mean MIP after the 800-m test was significantly lower than after the 400-m test (P = 0.04, ES = 0.48). There was no correlation between IMF value and running time (r = 0.53 and r = –0.28 for either the 400-m and 800-m tests, respectively; P > 0.05). CONCLUSION: IMF occurs after short-duration running exercise. Coaches could consider prescribing inspiratory muscle training or warm-up in an effort to reduce the inevitable IMF associated with maximal effort running.

Thresholds in ventilation, cerebral and muscle oxygenation, and muscle activity during incremental cycling exercise

Introduction: Cycle time-trial performance is a function of the highest sustainable power output. The first (VT-1) and second (VT-2) ventilatory thresholds are practical tools for coaches and athletes to set training zones and exercise intensity. Specifically, VT-2 is closely linked to critical power, a primary determinant of endurance performance. The cascade of physiological events in the organs responsible for power production accompanying these respiratory thresholds remains contentious and yet to be fully characterized. Electromyographic (EMG) thresholds have been identified in leg muscles during incremental exercise while near infrared spectroscopy (NIRS) has revealed thresholds in both muscle deoxygenation and cerebral oxygenation towards the end of an incremental exercise test. However, the relative timing of the different muscle and brain oxygenation and muscle electrical activity responses to each other is unclear. Purpose: The aim of the present study was to examine the thresholds of cerebral and muscle oxygenation, along with muscle electrical activity during a ramp exercise test in relation to VT-1 and VT-2. Methods: Twenty-five recreational cyclists (mean±SD: age 37±8yrs, body mass 78±13kg, height 178±8cm, VO 2 max 53±8mL/kg/min) completed a ramp exercise test to exhaustion on an electromagnetically braked cycle-ergometer with a work rate increment of 25 W/min. Throughout the test, continuous measures of expired gas (breath-by-breath), prefrontal cortex and vastus lateralis (VL) oxygenation via NIRS, and EMG Root Mean Square activity for the VL, rectus femoris (RF), and biceps femoris (BF) muscles were recorded. Thresholds were defined by a double-linear model. Results: The results are summarized in Figure 1. VT-1 and VT-2 occurred at 57 ± 6% and 81 ± 6% of the exercise, respectively. There was a threshold in both cerebral deoxyhaemoglobin and oxyhaemoglobin (56±13% and 56±8% of exercise, respectively) which were not significantly different from VT-1 ( P >0.86, cohens d 0.8). Only one threshold could be identified for muscle parameters with a threshold in muscle oxyhaemoglobin (78±9% of exercise), attenuation in muscle deoxyhaemoglobin (80±8% of exercise), and increase in EMG activity of VL, RF and BF (89±5%, 82±14% and 85±9% of exercise, respectively). The thresholds in BF and VL EMG activity occurred after VT-2 ( P 0.6). Conclusion: The threshold in cerebral oxygenation parameters occurred at both VT-1 and VT-2. Conversely, the present investigation failed to support a role for VL muscle oxygenation and electrical activity at VT-1, but did display a threshold at or after VT-2. The changes in cerebral oxygenation and in BF and VL electrical activity occurred after VT-2, suggesting that the metabolic and ventilatory events characterizing this latter cardiorespiratory threshold may affect both cerebral and muscle oxygenation levels and subsequent muscle recruitment responses. These physiological mechanisms are important factors in describing key training concepts and performance capability; for instance critical power. Any marked rise in muscle recruitment above VT-2 or critical power will result in early onset of fatigue and limit exercise performance.