Absolute Exercise Intensity Research Articles

Exogenous Glucose Oxidation During Exercise Is Positively Related to Body Size.

There is little evidence that body size alters exogenous glucose oxidation rates during exercise. This study assessed whether larger people oxidize more exogenous glucose during exercise than smaller people. Fifteen cyclists were allocated into two groups based on body mass (SMALL, <70kg body mass, n = 9, two females) or (LARGE, >70kg body mass, n = 6) matched for lactate threshold (SMALL: 2.3 ± 0.4W/kg, LARGE: 2.3 ± 0.3W/kg). SMALL completed 120min of cycling at 95% of lactate threshold1. LARGE completed two trials in a random order, one at 95% of lactate threshold1 (thereby exercising at the same relative intensity [RELATIVE]) and one at an absolute intensity matched to SMALL (ABSOLUTE). In all trials, cyclists ingested 90 g/hr of 13C-enriched glucose. Total exogenous glucose oxidation was (mean ± SD) 33 ± 8 g/hr in SMALL versus 45 ± 13 g/hr in LARGE-RELATIVE (mean difference: 13 g/hr, 95% confidence interval [2, 24] g/hr, p = .03). Large positive correlations were observed for measures of exogenous carbohydrate oxidation versus body size (body mass, height, and body surface area; e.g.,body surface area vs. peak exogenous glucose oxidation, r = .85, 95% confidence interval [.51, .95], p < .01). When larger athletes reduced the intensity from RELATIVE to ABSOLUTE, total exogenous glucose oxidation was 39 ± 7 g/hr (p = .43 vs. LARGE-RELATIVE). In conclusion, the capacity for exogenous glucose oxidation is, on average, higher in larger athletes than smaller athletes during exercise. The extent to which this is due to higher absolute exercise intensity requires further research, but body size may be a consideration in tailoring sports nutrition guidelines for carbohydrate intake during exercise.

Blood Pressure Responses to Postexercise Circulatory Occlusion Are Attenuated After Exercise-Induced Muscle Weakness.

Exercise blood pressure (BP) responses are thought to be determined by relative exercise intensity (percent maximal voluntary contraction (MVC) strength). However, cross-sectional studies report that during a static contraction, higher absolute force is associated with greater BP responses to relative intensity exercise and subsequent muscle metaboreflex activation with postexercise circulatory occlusion (PECO). We hypothesized that a bout of unaccustomed eccentric exercise would reduce knee extensor MVC and subsequently attenuate BP responses to PECO. Continuous BP, heart rate, muscle oxygenation, and knee extensor electromyography were recorded in 21 young healthy individuals (female, n = 10) during 2 min of 20% MVC static knee extension exercise and 2 min of PECO, performed before and 24 h after 300 maximal knee extensor eccentric contractions to cause exercise-induced muscle weakness. As a control, 14 participants repeated the eccentric exercise 4 wks later to test whether BP responses were altered when exercise-induced muscle weakness was attenuated via the protective effects of the repeated bout effect. Eccentric exercise reduced MVC in all participants (144 ± 43 vs 110 ± 34 N·m, P < 0.0001). BP responses to matched relative intensity static exercise (lower absolute force) were unchanged after eccentric exercise ( P > 0.99) but were attenuated during PECO (systolic BP: 18 ± 10 vs 12 ± 9 mm Hg, P = 0.02). Exercise-induced muscle weakness modulated the deoxygenated hemoglobin response to static exercise (64% ± 22% vs 46% ± 22%, P = 0.04). When repeated after 4 wks, exercise-induced weakness after eccentric exercise was attenuated (-21.6% ± 14.3% vs -9.3 ± 9.7, P = 0.0002) and BP responses to PECO were not different from control values (all, P > 0.96). BP responses to muscle metaboreflex activation, but not exercise, are attenuated by exercise-induced muscle weakness, indicating a contribution of absolute exercise intensity on muscle metaboreflex activation.

Intracellular Oxidative Stress Induced by Physical Exercise in Adults: Systematic Review and Meta-Analysis.

A physical exercise program is one of the commonly used methods for improving an individual’s antioxidative capacity. However, an inappropriate physical exercise program would induce extra oxidative stress (OS), and the relationship between the details of a physical exercise protocol and the severity of intracellular OS is still unclear. A systematic review and meta-analysis of randomized controlled trials were conducted by searching PubMed, Medline, and Web of Science with the eligibility criteria: (1) participants over 18 years old; (2) physical exercise interventions; (3) 8-hydroxydeoxyguanosine, F2-isoprostanes, and protein carbonyls (PCs) as outcome measures; (4) published in English and peer-reviewed. 12 studies were included, and the data of 8 in them were pooled together. The agreement between authors reached a kappa value of 0.73. The results of the meta-analysis showed that: (1) the level of OS did not depend on the absolute intensity of physical exercise but on both the intensity and the volume of exercise; (2) high-intensity aerobic exercise (HIAE) and a combined protocol of HIAE and resistance training had the highest potential to induce large OS in unhealthy people; (3) the OS induced by moderate-to-high intensity aerobic exercise was significantly larger than that induced by ordinary life activities in healthy adults; (4) high-intensity interval training and moderate-intensity aerobic exercise had the lowest and sub-lowest probabilities to induce high intracellular OS for unhealthy adults. activities induce OS in various tissues in the human body, and the severity of OS depends on many factors of physical exercises as well as the health condition of an individual. A high-intensity and high-volume physical exercise program has the largest possibility of inducing severe OS, while a moderate-intensity aerobic exercise program and a high-intensity interval training program with a relatively low volume might be beneficial to the redox balance for unhealthy individuals. In conclusion, continuous aerobic exercise under moderate-intensity or high-intensity interval training could be recommended to enhance the body’s capacity for maintaining redox balance, especially for unhealthy individuals. The PROSPERO Registration Number is CRD42022349687.

Cerebrovascular Dynamics During Light Exercise

Cerebral blood flow (CBF) dynamic response to moderate‐intensity exercise has a time delay (TD) of ~ 40s. This is dramatically longer compared to other physiological responses to exercise (e.g. skeletal muscle blood flow &lt;10 s) and CBF response to other stimuli (e.g. hypercapnia, thigh cuff occlusion, ~ 10‐20 s). A possible explanation is that a rest‐to‐exercise transition induces a brief hypotensive response due to intensity dependent rapid vasodilation of the periphery (exercise‐onset hypotension, EoH).PurposeTo determine if the magnitude and timing of EoH, effectively reduces CBF at exercise onset causing the longer observed TD. To test this, we modelled CBF kinetic response to light‐intensity exercise to mitigate the magnitude of EoH and determine if components of the CBF response were quickened in young healthy adults.Methods26 young healthy adults (13 Women, 23.8 ± 4 yrs; 23.9 ± 2.9 kg/m2) completed a rest (2min seated quietly, BL) to exercise (3 minutes at 50W, EX) transition on a recumbent cycle ergometer. Middle cerebral artery velocity (MCAv; transcranial doppler) and mean arterial pressure (MAP; finger photoplethysmography) were measured on a heartbeat‐by‐heartbeat basis. End‐tidal CO2 (EtCO2) was measured using breath‐by‐breath capnography. Cerebral vascular conductance index (CVCi) was calculated as (CVCi = MCAv/MAP *100 mmHg). Change in MCAv data (ΔMCAv = MCAvEX‐MCAvBL) were averaged into 2 s bins and fit to a monoexponential model (ΔMCAv(t)= Amp(1‐e‐(t‐TD)/ τ)). Time delay (TD), tau (τ), and mean response time (MRT = TD + τ) were obtained from the model. Several subjects (N=11) exhibited little to no TD (TD &lt; 1 s), these subjects (FAST) were separated out and compared to individuals with longer TDs (TD ≥ 3 s; SLOW). Comparisons were made using an independent t‐test.ResultsAll data is mean±SD. In total, subjects exhibited a TD of 15.4 ± 18.2 s, τ of 79.8 ± 139.7, and MRT of 95.3 ± 134.9 s. This coincided with a ΔMAPNADIR (‐14.5 ± 8.2 mmHg), ΔMCAvNADIR (‐5.7 ± 5.8 cm/s) which occurred at similar times (14.0 ± 17.2 vs. 18.6 ± 14.4 s; p=0.30 MAPNADIR vs. MCAvNADIR), and ΔCVCiMAX (25.3 ± 34.0 cm/s/100mmHg). When data were split, the FAST group experienced a faster TD compared to SLOW (0.01 ± 0.01 vs. 26.8 ± 16.4 s; p&lt;0.001). ΔMCAvNADIR although different (‐1.0 ± 4.0 vs. ‐9.1 ± 4.2 cm/s; p&lt;0.001, FAST vs. SLOW), occurred at similar times (20.5 ± 17.3 vs. 17.3 ± 12.5 s; p=0.59, FAST vs. SLOW). ΔMAPNADIR (‐14.4 ± 10.4 vs. ‐14.6 ± 6.5 mmHg; p=0.97) and CVCiMAX (22.1 ± 25.4 vs. 27.6 ± 39.9 cm/s/100mmHg; p=0.56 FAST vs. SLOW) were not different between groups. There were no other differences between groups regrading demographic, EtCO2, or other kinetic variables.DiscussionOur data indicates EoH is related to the initial drop in CBF and TD during light‐exercise is faster (15.9 s) when compared to previous research during moderate‐intensity exercise (~40 s). However, our data identifies fast responders who have minimal TD and MCAvNADIR responses without differing EoH at the same absolute exercise intensity. Therefore, these data reveal monoexponential CBF models ignore initial perturbances to CBF and disregard potentially important cerebrovascular mechanisms occurring prior to model predicted blood flow increases.

The short-term development of performance and aerobic endurance following prolonged low-intensity ski trekking in Svalbard: A case study

Abstract The purpose of this case study was to examine the short-term development of performance and aerobic endurance following prolonged low-intensity ski trekking (LIST) in an Arctic region. Two male recreational athletes (aged 24 and 26 years) with high aerobic fitness performed LIST 7 ± 2 h·day−1 for 23 consecutive days, while hauling sledges (∼80 kg initially) with supplies from the north to the south of Svalbard (∼640 km). Time to exhaustion, maximal oxygen uptake (V̇O2max), lactate threshold (LT) and work economy were evaluated at pre- and post-trek. The results showed that the absolute and relative exercise intensity during LIST were ∼3.9 km·h−1 and ∼60% of maximal heart rate, respectively. Time to exhaustion during a ∼4–6 min ramp walking test, and a &gt;45 min stepwise walking test, while pulling 12.5 kg weights (simulation of ski trekking with loaded sledge), increased by 11–17% and 3–9%, respectively, following LIST. Body mass and V̇O2max relative to body mass (ml·kg−1·min−1) decreased by 5–8% and increased by 3–8%, respectively. Furthermore, the workload associated with LT and LT percentage of V̇O2max increased by 39–69% and 12–13%, respectively. No notable change in work economy was observed. The mean pace during LIST (∼3.9 km·h−1) corresponded to the treadmill walking speed (4 km·h−1) with the lowest oxygen cost (mL·kg−1·m−1) in both participants. It can be concluded that short-term prolonged LIST can improve ski trek-simulated performance and fractional utilisation of V̇O2max in recreational athletes with high aerobic fitness. Moreover, highly aerobically fit ski trekkers appear to instinctively choose the most energy-efficient pace during LIST.

Monitoring Physical Activity Intensity During Pregnancy.

For apparently healthy pregnant women, regular physical activity is recommended. The American College of Obstetricians and Gynecologists (ACOG) created recommendations for physical activity and exercise during pregnancy in 1985. At that time, pregnant women were advised to not exceed a heart rate of 140 beats per minute with physical activity. The heart rate recommendation was subsequently removed with the recommendations published in 1994, 2002, and 2015. In 2020, the ACOG updated its recommendations on physical activity for pregnant and postpartum women. The recommendation included exercising at a "fairly light to somewhat hard" perceived intensity and at less than 60-80% of age-predicted maximum heart rate, usually not exceeding a heart rate of 140 beats per minute. Women often seek advice from healthcare providers on physical activity during pregnancy, yet providers report concern about giving appropriate physical activity guidance. This paper summarizes the key scientific literature on monitoring absolute and relative exercise intensity in relation to the current ACOG recommendations, providing background on intensity-related concepts used in the recommendation. This paper also provides practical guidance to assist healthcare providers in relaying this information to pregnant women.

Exercise temperature regulation following a 35-day horizontal bedrest.

What is the central question of this study? Does a 35-day horizontal bedrest impair thermoeffector responses during whole-body submaximal exercise performed in temperate conditions? What is the main finding and its importance? Cardiovascular and muscular deconditioning ensuing from prolonged recumbency seems to augment, at least to a degree, exercise-induced increase in body core temperature, most likely due to an impairment in non-evaporative heat loss. The response is a function of the absolute exercise intensity imposed. We examined the effects of a 35-day horizontal bedrest on thermoregulation during whole-body exercise. Fifteen healthy men were randomly assigned to either a bedrest (BR; n=10) or a control (CON; n=5) group. Prior to bedrest, both groups performed 40-min constant-load upright cycling at 30% of their peak workload (Wpeak ; PRE). One and 2days after bedrest, the BR group performed, in a randomised counterbalanced order, two 40-min trials at 30% of (i) the pre-bedrest Wpeak (i.e., at a fixed absolute intensity; POST-A) and (ii) the post-bedrest Wpeak (i.e., at a fixed relative intensity; POST-R). The CON group conducted only the POST-A trial, at the same time intervals. During the trials, rectal (Trec ) and skin ( sk ) temperatures, and the forehead sweating rate (SwR) were monitored. In the CON group, no differences were observed between the trials. Bedrest potentiated moderately the Trec elevation during the latter part of POST-A (∼0.10°C; P≤0.05), but not of POST-R (∼0.04°C; P=0.11). In both post-bedrest trials, sk was attenuated by ∼1.5-2.0°C throughout (P<0.01), whereas the forehead SwR was not modulated. Trec and sk were similar in POST-A and POST-R, yet the forehead SwR was more dependent on the relative workload imposed (P=0.04). The present findings therefore suggest that the cardiovascular and muscular deconditioning ensuing from a 35-day bedrest may aggravate the exercise-induced increase in body core temperature when working at a given absolute intensity, most likely due to an impairment in non-evaporative heat loss.

Real-Time Estimation of Aerobic Threshold and Exercise Intensity Distribution Using Fractal Correlation Properties of Heart Rate Variability: A Single-Case Field Application in a Former Olympic Triathlete.

A non-linear heart rate variability (HRV) index based on fractal correlation properties called alpha1 of Detrended Fluctuation Analysis (DFA-alpha1), has been shown to change with endurance exercise intensity. Its unique advantage is that it provides information about current absolute exercise intensity without prior lactate or gas exchange testing. Therefore, real-time assessment of this metric during field conditions using a wearable monitoring device could directly provide a valuable exercise intensity distribution without prior laboratory testing for different applied field settings in endurance sports. Until of late no mobile based product could display DFA-alpha1 in real-time using off the shelf consumer products. Recently an app designed for iOS and Android devices, HRV Logger, was updated to assess DFA-alpha1 in real-time. This brief research report illustrates the potential merits of real-time monitoring of this metric for the purposes of aerobic threshold (AT) estimation and exercise intensity demarcation between low (zone 1) and moderate (zone 2) in a former Olympic triathlete. In a single-case feasibility study, three practically relevant scenarios were successfully evaluated in cycling, (1) estimation of a HRV threshold (HRVT) as an adequate proxy for AT using Kubios HRV software via a typical cycling stage test, (2) estimation of the HRVT during real-time monitoring using a cycling 6 min stage test, (3) a simulated 1 h training ride with enforcement of low intensity boundaries and real-time HRVT confirmation. This single-case field evaluation illustrates the potential of an easy-to-use and low cost real-time estimation of the aerobic threshold and exercise intensity distribution using fractal correlation properties of HRV. Furthermore, this approach may enhance the translation of science into endurance sports practice for future real-world settings.

Identifying sex differences in neuromuscular fatigue: the challenge of normalizing exercise intensity and interpreting the results between populations.

Identifying sex differences in neuromuscular fatigue: the challenge of normalizing exercise intensity and interpreting the results between populations.

Exercício aeróbio, de resistência ou combinado: que tipo mais contribui para melhorar a função endotelial? Resenha da metanálise de Ashor et al.

Introdução: Como parte da Edição Especial de 2020 I, a Revista de Educação Física / Journal of Physical Education (REF/JPE) está trazendo aspectos científicos da prática de atividade física relacionados à pandemia de CoViD-19.&#x0D; Objetivo: Apresentar e indicar aos leitores da REF/JPE, a leitura do estudo de revisão, com metanálise, de Ashor et al., publicado em um periódico internacional. Baseado em estudos de ensaio clínico randomizados, os efeitos do exercício aeróbio, de resistência e combinado de ambos sobre a função endotelial foram comparados. A literatura recente indica que a CoViD-19 envolve o endotélio no processo, nesse sentido, avaliar qual o tipo de exercício melhora sua função é de alta relevância.&#x0D; Conclusão: Todas as modalidades de exercício (aeróbio, resistidos e combinados) aumentaram a função endotelial significativamente em comparação com os grupos controle. Os maiores efeitos foram observados com os exercícios aeróbicos, seguidos pelos exercícios combinados e resistidos. Em exercícios aeróbios, houve uma relação dose-resposta significativa entre a intensidade tanto absoluta quanto relativa do exercício aeróbio e a função endotelial. Em exercícios resistidos a correlação positiva foi encontrada na frequência e não na intensidade. Os resultados foram discutidos pelos autores, recomenda-se a leitura.

Investigation of the Relationship Between Peak Vertical Accelerations and Aerobic Exercise Intensity During Graded Walking and Running in Postmenopausal Women

How exercise intensity targets, calibrated according to oxygen consumption, relate to vertical impacts during weight-bearing exercise is currently unknown. The authors investigated the relationship between vertical peaks (VPs) and metabolic equivalents (METs) of oxygen consumption in 82 women during walking and running. The magnitude of VPs, measured using a hip-worn triaxial accelerometer, was derived from recommended aerobic exercise intensity targets. VPs were 0.63 ± 0.18g at the lower recommended absolute exercise intensity target (3 METs) but >1.5g at the upper end of moderate-intensity activities (1.90 ± 1.13g at 6 METs). Multilevel linear regression analyses identified speed and type of locomotion as the strongest independent predictors of VPs, explaining 54% and 11% of variance, respectively. The authors conclude that, in contrast to lower intensities, exercising close to or above the 6-MET threshold generates VPs of osteogenic potential, suggesting this could provide simultaneous benefits to decrease all-cause mortality and osteoporosis risk.

Carbohydrate Hydrogel Products Do Not Improve Performance or Gastrointestinal Distress During Moderate-Intensity Endurance Exercise.

The benefits of ingesting exogenous carbohydrate (CHO) during prolonged exercise performance are well established. A recent food technology innovation has seen sodium alginate and pectin included in solutions of multiple transportable CHO, to encapsulate them at pH levels found in the stomach. Marketing claims include enhanced gastric emptying and delivery of CHO to the muscle with less gastrointestinal distress, leading to better sports performance. Emerging literature around such claims was identified by searching electronic databases; inclusion criteria were randomized controlled trials investigating metabolic and/or exercise performance parameters during endurance exercise >1hr, with CHO hydrogels versus traditional CHO fluids and/or noncaloric hydrogels. Limitations associated with the heterogeneity of exercise protocols and control comparisons are noted. To date, improvements in exercise performance/capacity have not been clearly demonstrated with ingestion of CHO hydrogels above traditional CHO fluids. Studies utilizing isotopic tracers demonstrate similar rates of exogenous CHO oxidation, and subjective ratings of gastrointestinal distress do not appear to be different. Overall, data do not support any metabolic or performance advantages to exogenous CHO delivery in hydrogel form over traditional CHO preparations; although, one study demonstrates a possible glycogen sparing effect. The authors note that the current literature has largely failed to investigate the conditions under which maximal CHO availability is needed; high-performance athletes undertaking prolonged events at high relative and absolute exercise intensities. Although investigations are needed to better target the testimonials provided about CHO hydrogels, current evidence suggests that they are similar in outcome and a benefit to traditional CHO sources.

Exogenous glucose oxidation during endurance exercise in hypoxia.

PurposeEndurance exercise in hypoxia promotes carbohydrate (CHO) metabolism. However, detailed CHO metabolism remains unclear. The purpose of this study was to evaluate the effects of endurance exercise in moderate hypoxia on exogenous glucose oxidation at the same energy expenditure or relative exercise intensity.MethodsNine active healthy males completed three trials on different days, consisting of 30 min of running at each exercise intensity: (a) exercise at 65% of normoxic maximal oxygen uptake in normoxia [NOR, fraction of inspired oxygen (FiO2) = 20.9%, 10.6 ± 0.3 km/h], (b) exercise at the same relative exercise intensity with NOR in hypoxia (HYPR, FiO2 = 14.5%, 9.4 ± 0.3 km/h), and (c) exercise at the same absolute exercise intensity with NOR in hypoxia (HYPA, FiO2 = 14.5%, 10.6 ± 0.3 km/h). The subjects consumed 113C‐labeled glucose immediately before exercise, and expired gas samples were collected during exercise to determine 13C‐excretion (calculated by 13CO2/12CO2).ResultsThe exercise‐induced increase in blood lactate was significantly augmented in the HYPA than in the NOR and HYPR (p = .001). HYPA involved a significantly higher respiratory exchange ratio (RER) during exercise compared with the other two trials (p < .0001). In contrast, exogenous glucose oxidation (13C‐excretion) during exercise was significantly lower in the HYPA than in the NOR (p = .03). No significant differences were observed in blood lactate elevation, RER, or exogenous glucose oxidation between NOR and HYPR.ConclusionEndurance exercise in moderate hypoxia caused a greater exercise‐induced blood lactate elevation and RER compared with the running exercise at same absolute exercise intensity in normoxia. However, exogenous glucose oxidation (13C‐excretion) during exercise was attenuated compared with the same exercise in normoxia.

Sex Differences In Microvascular Function In Pre-pubertal Children

There is little research examining the effect of sex on skin blood flow (SkBF) in adults, and less in children. Sex-related differences in SkBF may help explain known thermoregulatory differences between males and females. PURPOSE: To determine whether there are sex-related differences in the SkBF response to exercise, local heating, and acetylcholine (ACh). Additionally, the role of nitric oxide (NO) was examined. METHODS: Laser-Doppler flowmetry was used to assess forearm SkBF. Responses to exercise (30 min cycling, 60%V˙O2max), local heating (44°C), and ACh iontophoresis were assessed in 15 pre-pubertal boys (age=10±1y, VO2max=1.66±0.25 l/min) and 10 girls (age=10±1y, VO2max=1.58±0.35 l/min), with and without NO synthase inhibition, using L-NAME iontophoresis. Three-way (group, time, treatment) repeated measures ANOVA was used to examine sex-related differences in the SkBF response during exercise and in the SkBF-ACh dose response. A two-way (group, treatment) repeated measures ANOVA was used to examine local heathing-induced increase in SkBF. RESULTS: Exercise-induced SkBF was greater in boys compared with girls (654±355 and 316±182% of baseline, respectively, p=<.0001). L-NAME blunted the SkBF response more in boys than in girls (group-by-treatment interaction, p=.004). Local heating-induced SkBF was not significantly different between boys and girls (1705±739% and 1488±600%, respectively, p=.35), with no effect of L-NAME. The maximal ACh-induced SkBF was similar in boys and girls (650±420% and 612±411%, respectively). L-NAME similarly blunted the SkBF response in boys and girls (group-by-treatment interaction, p=.52). CONCLUSION: These findings demonstrate that while maximal SkBF and the vasodilatory response to ACh stimulation are similar in boys and girls, boys display a greater increase in SkBF during exercise of similar intensity. Further, the role of NO in the SkBF response appears greater in boys than girls only during exercise. Since absolute and relative exercise intensity was similar in the two groups, it is suggested that sex-related factors (e.g., hormones) may interact with the exercise response or with other vasodilators, resulting in different SkBF response.

Fat Oxidation Kinetics Is Related to Muscle Deoxygenation Kinetics During Exercise

PurposeThe present study aimed to determine whether whole-body fat oxidation and muscle deoxygenation kinetics parameters during exercise were related in individuals with different aerobic fitness levels.MethodsEleven cyclists [peak oxygen uptake (): 64.9 ± 3.9 mL⋅kg–1⋅min–1] and 11 active individuals (: 49.1 ± 7.4 mL⋅kg–1⋅min–1) performed a maximal incremental cycling test to determine and a submaximal incremental cycling test to assess whole-body fat oxidation using indirect calorimetry and muscle deoxygenation kinetics of the vastus lateralis (VL) using near-infrared spectroscopy (NIRS). A sinusoidal (SIN) model was used to characterize fat oxidation kinetics and to determine the intensity (Fatmax) eliciting maximal fat oxidation (MFO). The muscle deoxygenation response was fitted with a double linear model. The slope of the first parts of the kinetics (a1) and the breakpoint ([HHb]BP) were determined.ResultsMFO (p = 0.01) and absolute fat oxidation rates between 20 and 65% were higher in cyclists than in active participants (p < 0.05), while Fatmax occurred at a higher absolute exercise intensity (p = 0.01). a1 was lower in cyclists (p = 0.02) and [HHb]BP occurred at a higher absolute intensity (p < 0.001) than in active individuals. was strongly correlated with MFO, Fatmax, and [HHb]BP (r = 0.65–0.88, p ≤ 0.001). MFO and Fatmax were both correlated with [HHb]BP (r = 0.66, p = 0.01 and r = 0.68, p < 0.001, respectively) and tended to be negatively correlated with a1 (r = -0.41, p = 0.06 for both).ConclusionThis study showed that whole-body fat oxidation and muscle deoxygenation kinetics were both related to aerobic fitness and that a relationship between the two kinetics exists. Individuals with greater aerobic fitness may have a delayed reliance on glycolytic metabolism at higher exercise intensities because of a longer maintained balance between O2 delivery and consumption supporting higher fat oxidation rates.

Inflammation and the Cardiovascular Responses to Exercise in Patients with Peripheral Artery Disease

BackgroundPatients with peripheral artery disease (PAD) demonstrate an exaggerated exercise pressor response (EPR). Heightened inflammation critically contributes to this exaggerated EPR in animal models of PAD, however, this relationship remains largely unexplored in humans. Therefore, we tested the hypotheses that the blood pressure response to exercise would be exaggerated in patients with PAD compared to controls; and that markers of inflammation would be positively related to this response.MethodsEight patients with PAD (ABI: 0.67±0.11) and eight healthy controls (HC; ABI: 1.16±0.07) matched for age, sex, physical activity, and physical characteristics completed plantar flexion exercise at both absolute (2.7 W) and relative (40% max; PAD: 2.1±0.2 vs HC: 4.3±0.4 W, p&lt;0.001) intensities. Popliteal artery blood flow (Flow) was measured via Doppler ultrasound and systemic mean arterial pressure (MAP) via Finapres. Resting systemic and intramuscular markers of inflammation and oxidative stress were quantified from plasma and muscle biopsies.ResultsThe exercise‐induced ΔMAP was greater for PAD at both the absolute (PAD: 20±3 vs HC: 9±2 mmHg, p&lt;0.01) and relative (PAD: 23±5 vs HC: 11±2 mmHg, p=0.02) exercise intensities. The ΔFlow was lower for PAD compared to HC during both absolute (PAD: 251±53 vs HC: 545±66 ml/min, p&lt;0.01) and relative intensities (PAD: 242±61 vs HC: 595±89 ml/min, p&lt;0.01). Inflammatory markers including plasma tumor necrosis factor alpha (TNFα: ↑134%), interleukin‐6 (IL6: ↑92%), and intramuscular IL6 (↑77%) were elevated in PAD compared to HC (p&lt;0.05). Additionally, markers of oxidative stress including intramuscular protein carbonyls (PC: ↑57%) and 4‐hydroxynonenal (HNE: ↑80%) were elevated in PAD (p&lt;0.05). TNFα, plasma IL6, and PC were positively correlated with ΔMAP (r: 0.57–0.82, all p&lt;0.05) while plasma and intramuscular IL6, PC, and HNE were negatively correlated with ΔFlow (r: 0.64–0.78, all p&lt;0.05).ConclusionsThe present findings indicate an association between markers of inflammation with the cardiovascular responses to exercise in humans with PAD. Specifically, heightened inflammation and oxidative stress appear to contribute to the exaggeration the exercise pressor reflex and attenuated blood flow response during lower limb exercise in PAD. Therapeutically, targeting systemic and local inflammation may be a viable option to improve the blood pressure and blood flow responses to exercise in patients with PAD.

The training induced increase in whole-body peak fat oxidation rate may be attenuated with aging

An attenuated ability to appropriately oxidize fat (metabolic inflexibility) has been associated with the development of obesity and type 2 diabetes. Previous studies have found that regular exercise training increases the body’s ability to oxidize fat during exercise, but also shown that fat oxidation at the same relative and absolute exercise intensity is lower in old compared with young adults. Based on these studies we investigated the effect of training status on the whole-body peak fat oxidation rate (PFO) during exercise in young and middle-aged trained and untrained men. We hypothesized that aging was associated with decreased PFO, but regular exercise training could counteract this decline. 36 healthy non-overweight young and middle-aged men were recruited into a four groups: young (27 [24–30] yrs, (Mean [95% CI])) untrained (⩒O2peak: 47 [44–49] ml/min/kg), young (28 [26–30] yrs) trained (⩒O2peak: 64 [62–67] ml/min/kg), middle-aged (55 [53–57] yrs) untrained (⩒O2peak: 37 [32–42] ml/min/kg) and middle-aged (54 [51–57] yrs) trained (⩒O2peak: 55 [51–58] ml/min/kg). PFO was measured by indirect calorimetry while subjects performed a validated incremental exercise protocol on a cycle ergometer. Whole-body peak fat oxidation rate was higher in the young trained compared to young untrained subjects (0.70 [0.65–0.75] vs.0.45 [0.36–0.54] g/min, post-hoc: p < 0.001); however, this training effect was attenuated in middle-aged trained and untrained subjects (0.44 [0.38–0.50] vs. 0.41 [0.35–0.47] g/min, post-hoc: p = 0.83, respectively). In summary, these findings suggest that the training induced effects on whole-body fat oxidation found in young men may be attenuated in middle-aged men.

It's well and truly time to stop stating that AMPK regulates glucose uptake and fat oxidation during exercise.

None for Perspective.

Cardiopulmonary function during supramaximal exercise in hypoxia, normoxia and hyperoxia in Thoroughbred horses.

ABSTRACTSupramaximal exercise while inspiring different O2 gases may induce different responses in cardiopulmonary function at the same relative and/or absolute exercise intensity. The purpose of this study was to compare the effects of supramaximal exercise in hypoxia, normoxia and hyperoxia on cardiopulmonary function in Thoroughbred horses. Using a crossover design, five well-trained horses were made to run up a 6% grade on a treadmill at supramaximal speeds sustainable for approximately 110 sec (approximately 115% V̇O2max) while breathing normoxic gas (NO, 21% O2) or hypoxic gas (LO, 15.3% O2) in random order. Horses also ran at the same speed, incline and run time as in NO while breathing hyperoxic gas (HONO, 28.8% O2) and as in LO while breathing normoxic gas (NOLO). Runs were on different days, and cardiopulmonary variables were analyzed with repeated-measures ANOVA and the Holm-Šidák method for pairwise comparisons. Supramaximal speeds differed significantly between NO and LO (14.0 ± 0.5 [SD] m/sec vs. 12.6 ± 0.5 m/sec), but run times to exhaustion did not (112 ± 17 sec vs. 103 ± 14 sec). The V̇O2max in NO was higher than that in LO (165 ± 11 vs. 120 ± 15 ml (min× kg)), as was the arterial oxygen tension (66 ± 5 vs. 45 ± 2 Torr). Oxygen consumption was increased in HONO and NOLO compared with the values in NO and LO, respectively. Supramaximal exercise in hypoxia induces more severe hypoxemia and decreases V̇O2max compared with normoxia at the same relative intensity. Conversely, supramaximal exercise in hyperoxia alleviates hypoxemia and increases V̇O2 compared with normoxia at the same absolute intensity.

Forty high-intensity interval training sessions blunt exercise-induced changes in the nuclear protein content of PGC-1α and p53 in human skeletal muscle.

Exercise-induced increases in peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) and p53 protein content in the nucleus mediate the initial phase of exercise-induced mitochondrial biogenesis. Here, we investigated whether exercise-induced increases in these and other markers of mitochondrial biogenesis were altered after 40 sessions of twice-daily high-volume, high-intensity interval training (HVT) in human skeletal muscle. Vastus lateralis muscle biopsies were collected from 10 healthy recreationally active participants before, immediately postexercise, and 3 h after a session of high-intensity interval exercise (HIIE) performed at the same absolute exercise intensity before and after HVT (pre-HVT and post-HVT, respectively). The protein content of common markers of exercise-induced mitochondrial biogenesis was assessed in nuclear- and cytosolic-enriched fractions by immunoblotting; mRNA contents of key transcription factors and mitochondrial genes were assessed by qPCR. Despite exercise-induced increases in PGC-1α, p53, and plant homeodomain finger-containing protein 20 (PHF20) protein content, the phosphorylation of p53 and acetyl-CoA carboxylase (p-p53 Ser15 and p-ACC Ser79, respectively), and PGC-1α mRNA Pre-HVT, no significant changes were observed post-HVT. Forty sessions of twice-daily high-intensity interval training blunted all of the measured exercise-induced molecular events associated with mitochondrial biogenesis that were observed pre-HVT. Future studies should determine whether this loss relates to the decrease in relative exercise intensity, habituation to the same exercise stimulus, or a combination of both.