Performance and perceived fatigability across the intensity spectrum: role of muscle mass during cycling.

The role of muscle mass in modulating performance and perceived fatigability across the entire intensity spectrum during cycling remains unexplored. We hypothesized that at task failure (Tlim), muscle contractile function would decline more following single- (SL) versus double-leg (DL) cycling within severe and extreme intensities, but not moderate and heavy intensities. After DL and SL ramp-incremental tests, on separate days, 11 recreationally active males (V̇o2max: 49.5 ± 7.7 mL·kg-1·min-1) completed SL and DL cycling until Tlim within each intensity domain. Power output for SL trials was set at 60% of the corresponding DL trial. Before and immediately after Tlim, participants performed an isometric maximal voluntary contraction (MVC) coupled with one superimposed and three resting femoral nerve stimulations [100 Hz; 10 Hz; single twitch (Qtw)] to measure performance fatigability. Perceived fatigue, leg pain, dyspnea, and effort were collected during trials. Tlim within each intensity domain was not different between SL and DL (all P > 0.05). MVC declined more for SL versus DL following heavy- (-42 ± 16% vs. -30 ± 18%; P = 0.011) and severe-intensity cycling (-41 ± 12% vs. -31 ± 15%; P = 0.036). Similarly, peak Qtw force declined more for SL following heavy- (-31 ± 12% vs. -22 ± 10%; P = 0.007) and severe-intensity cycling (-49 ± 13% vs. -40 ± 7%; P = 0.048). Except for heavy intensity, voluntary activation reductions were similar between modes. Similarly, except for dyspnea, which was lower for SL versus DL across all domains, ratings of fatigue, pain, and effort were similar at Tlim between exercise modes. Thus, the amount of muscle mass modulates the extent of contractile function impairment in an intensity-dependent manner.NEW & NOTEWORTHY We investigated the modulatory role of muscle mass on performance and perceived fatigability across the entire intensity spectrum. Despite similar time-to-task failure, single-leg cycling resulted in greater impairments in muscle contractile function within the heavy- and severe-intensity domains, but not the moderate- and extreme-intensity domains. Perceived fatigue, pain, and effort were similar between cycling modes. This indicates that the modulatory role of muscle mass on the extent of performance fatigability is intensity domain-dependent.

Effects of carbohydrate availability on cycling endurance at the maximal lactate steady state.

The impacts of carbohydrate (CHO) availability on time to task failure (TTF) and physiological responses to exercise at the maximal lactate steady state (MLSS) have not been studied. Ten participants (3 females, 7 males) completed this double-blinded, placebo-controlled study that involved a ramp incremental test, MLSS determination, and four TTF trials at MLSS, all performed on a cycle ergometer. With the use of a combination of nutritional (CHO, 7 g/kg, and placebo, PLA, 0 g/kg drinks) and exercise interventions [no exercise (REST) and glycogen-reducing exercise (EX)], the four conditions were expected to differ in preexercise CHO availability (RESTCHO > RESTPLA > EXCHO > EXPLA). TTF at MLSS was not improved by CHO loading, as RESTCHO (57.1 [16.6] min) and RESTPLA (57.1 [15.6] min) were not different (P = 1.00); however, TTF was ∼50% shorter in EX conditions compared with REST conditions on average (P < 0.05), with EXCHO (39.1 [9.2] min) ∼90% longer than EXPLA (20.6 [6.9] min; P < 0.001). There were effects of condition for all perceptual and cardiometabolic variables when compared at isotime (P < 0.05) and task failure (TF; P < 0.05), except for ventilation, perceptual responses, and neuromuscular function measures, which were not different at TF (P > 0.05). Blood lactate concentration was stable in all conditions for participants who completed 30 min of exercise. These findings indicate that TTF at MLSS is not enhanced by preexercise CHO supplementation, but recent intense exercise decreases TTF at MLSS even with CHO supplementation. Extreme fluctuations in diet and strenuous exercise that reduce CHO availability should be avoided before MLSS determination.NEW & NOTEWORTHY Carbohydrate (CHO) loading did not increase participants' ability to cycle at their maximal lactate steady state (MLSS); however, performing a glycogen depletion task the evening before cycling at MLSS reduced the time to task failure, even when paired with a high dose of CHO. These diet and exercise interventions influenced blood lactate concentration ([BLa]) but not the stability of [BLa]. Activities that reduce CHO availability should be avoided before MLSS determination.

Effects of acute simulated altitude on the maximal lactate steady state in humans.

We sought to determine the effects of acute simulated altitude on the maximal lactate steady state (MLSS) and physiological responses to cycling at and 10 W above the MLSS-associated power output (PO) (MLSSp and MLSSp+10, respectively). Eleven (4 female) participants (mean [SD]; 28 [4] years; V̇O2max: 54.3 [6.9] mL×kg-1×min-1) acclimatized to ~1100 m performed 30-min constant PO trials in simulated altitudes of 0 m (SL), 1111 m (MILD), and 2222 m (MOD). MLSSp, defined as the highest PO with stable (<1mM change) blood lactate concentration ([BLa]) between 10 and 30 min, was significantly lower in MOD (209 [54] W) compared to SL (230 [56] W; p<0.001) and MILD (225 [58] W; p=0.001), but MILD and SL were not different (p=0.12). V̇O2 and V̇CO2 decreased at higher simulated altitudes due to lower POs (p<0.05), but other end-exercise physiological responses (e.g., [BLa], ventilation (V̇E), heart rate (HR)) were not different between conditions at MLSSp or MLSSp+10 (p>0.05). At the same absolute intensity (MLSSp for MILD), [BLa], HR, and V̇E and all perceptual variables were exacerbated in MOD compared to SL and MILD (p<0.05). Maximum voluntary contraction, voluntary activation, and potentiated twitch forces were exacerbated at MLSSp+10 relative to MLSSp within conditions (p<0.05); however, condition did not affect performance fatiguability at the same relative or absolute intensity (p>0.05). As MLSSp decreased in hypoxia, adjustments in PO are needed to ensure the same relative intensity across altitudes, but common indices of exercise intensity may facilitate exercise prescription and monitoring in hypoxia.

Heavy-intensity priming exercise extends the V̇O2max plateau and increases peak power output during ramp-incremental exercise.

PURPOSE: To investigate whether a heavy-intensity priming exercise precisely prescribed within the heavy-intensity domain would lead to a greater peak-power output (POpeak) and a longer maximal oxygen uptake (V̇O2max) plateau. METHODS: Twelve recreationally active adults participated in this study. Two visits were required: (i) a step-ramp-step test (RI control), and (ii) a RI-test preceded by a priming exercise within the heavy-intensity domain (RI primed). A piece-wise equation was used to quantify the V̇O2 plateau duration (V̇O2plateau-time). The mean response time (MRT) was computed during the RI control condition. The delta (Δ) V̇O2-slope (S; mL·min-1·W-1) and V̇O2-Y-intercept (Y; mL·min-1) within the moderate-intensity domain between conditions (RI primed minus RI control) was also assessed using a novel graphical analysis. RESULTS: V̇O2plateau-time (P = 0.001; d = 1.27) and POpeak (P = 0.003; d = 1.08) were all greater in the RI Primed. MRT (P < 0.001; d = 2.45) was shorter in the RI primed compared to the RI control. A larger ΔV̇O2plateau-time was correlated with a larger ΔMRT between conditions (r = -0.79; P = 0.002). CONCLUSIONS: This study demonstrated that heavy-intensity priming exercise lengthened the V̇O2plateau-time and increased POpeak. The overall faster RI-V̇O2 responses seem to be responsible for the longer V̇O2plateau-time. Specifically, a shorter MRT, but not changes in RI-V̇O2-slopes, was associated to a longer V̇O2plateau-time following priming exercise.

Methodological considerations on near-infrared spectroscopy derived muscle oxidative capacity.

PURPOSE: Different strategies for near-infrared spectroscopy (NIRS)-derived muscle oxidative capacity assessment have been reported. This study compared and evaluated (I) approaches for averaging trials; (II) NIRS signals and blood volume correction equations; (III) the assessment of vastus lateralis (VL) and tibialis anterior (TA) muscles in two fitness levels groups. METHODS: Thirty-six participants [18 chronically trained (CT: 14 males, 4 females) and 18 untrained (UT: 10 males, 8 females)] participated in this study. Two trials of twenty transient arterial occlusions were performed for NIRS-derived muscle oxidative capacity assessment. Muscle oxygen consumption ( V ˙ O2m) was estimated from deoxygenated hemoglobin (HHb), corrected for blood volume changes following Ryan (HHbR) and Beever (HHbB) equations, and from oxygen saturation (StO2) in VL and TA. RESULTS: Superimposing or averaging V ˙ O2m or averaging the rate constants (k) from the two trials resulted in equivalent k values [two one-sided tests (TOST) procedure with 5% equivalence margin-P < 0.001]. Whereas HHbR (2.35 ± 0.61 min-1) and HHbB (2.34 ± 0.58 min-1) derived k were equivalent (P < 0.001), StO2 derived k (2.81 ± 0.92 min-1) was greater (P < 0.001) than both. k values were greater in CT vs UT in both muscles (VL: + 0.68 min-1, P = 0.002; TA: + 0.43 min-1, P = 0.01). CONCLUSION: Different approaches for averaging trials lead to similar k. HHb and StO2 signals provided different k, although different blood volume corrections did not impact k. Group differences in k were detected in both muscles.

The Effects of a 90-km Outdoor Cycling Ride on Performance Outcomes Derived From Ramp-Incremental and 3-Minute All-Out Tests.

ABSTRACT: Bitel, M, Keir, DA, Grossman, K, Barnes, M, Murias, JM, and Belfry, GR. The effects of a 90-km outdoor cycling ride on performance outcomes derived from ramp-incremental and 3-minute all-out tests. J Strength Cond Res 38(3): 540-548, 2024-The purpose of this study was to determine whether laboratory-derived exercise intensity and performance demarcations are altered after prolonged outdoor cycling. Male recreational cyclists ( n = 10; RIDE) performed an exhaustive ramp-incremental test (RAMP) and a 3-minute all-out test (3MT) on a cycle ergometer before and after a 90-km cycling ride. RAMP-derived maximal oxygen uptake (V̇O 2max ), gas exchange threshold (GET), respiratory compensation point (RCP), and associated power output (PO), as well as 3MT-derived critical power (CP) and work performed above CP, were compared before and after ∼3 hours of outdoor cycling. Six active men served as "no-exercise" healthy controls (CON), who, instead, rested for 3 hours between repeated RAMP and 3MT tests. During the 90-km ride, the duration within the moderate-intensity, heavy-intensity, and severe-intensity domains was 59 ± 24%, 40 ± 24%, and 1 ± 1%, respectively. Compared with pre-90 km, post-RAMP exhibited reductions in (a) V̇O 2max (4.04 ± 0.48 vs. 3.80 ± 0.38 L·min -1 ; p = 0.026) and associated PO (392 ± 30 W vs. 357 ± 26 W; p = 0.002); (b) the V̇O 2 and PO at RCP (3.49 ± 0.46 vs. 3.34 ± 0.43 L·min -1 ; p = 0.040 and 312 ± 40 W vs. 292 ± 24 W; p = 0.023); and (c) the PO (214 ± 32 W vs. 198 ± 25 W; p = 0.027), but not the V̇O 2 at GET (2.52 ± 0.44 vs. 2.44 ± 0.38 L·min -1 ; p = 0.388). Pre-90 km vs. post-90 km 3MT variables showed reduced W' (9.8 ± 3.4 vs. 6.8 ± 2.6 kJ; p = 0.002) and unchanged CP (304 ± 26 W and 297 ± 34 W; p = 0.275). In the CON group, there were no differences in V̇O 2max , GET, RCP, W', CP, or associated power outputs ( p > 0.05) pre-to-post 3 hours of rest. The preservation of critical power demonstrates that longer-duration maximal efforts may be sustained after long-duration cycle. However, shorter sprints and higher-intensity efforts eliciting V̇O 2max will exhibit decreased PO after 3 hours of a predominantly moderate-intensity cycle.

Combining Near-Infrared Spectroscopy and Heart Rate Variability Derived Thresholds to Estimate the Critical Intensity of Exercise.

ABSTRACT: Fleitas-Paniagua, PR, de Almeida Azevedo, R, Trpcic, M, Murias, JM, and Rogers, B. Combining near-infrared spectroscopy and heart rate variability derived thresholds to estimate the critical intensity of exercise. J Strength Cond Res 38(1): e16-e24, 2024-Critical intensity determination often requires costly tools and several testing sessions. Alternative approaches display relatively large individual variation. Therefore, simpler estimations with improved precision are needed. This study evaluated whether averaging the heart rate (HR) and oxygen uptake (V̇O 2 ) responses associated with the muscle deoxyhemoglobin concentration breakpoint ([HHb] BP ) and the heart rate variability (HRV) given by the detrended fluctuation analysis second threshold (HRVT2) during ramp incremental (RI) test improved the accuracy of identifying the HR and V̇O 2 at the respiratory compensation point (RCP). Ten female and 11 male recreationally trained subjects performed a 15 W·minute -1 RI test. Gas exchange, near-infrared spectroscopy (NIRS), and RR interval were recorded to assess the RCP, [HHb] BP , and HRVT2. Heart rate (mean ± SD : 158 ± 14, 156 ± 13, 160 ± 14 and, 158 ± 12 bpm) and V̇O 2 (3.08 ± 0.69, 2.98 ± 0.58, 3.06 ± 0.65, and 3.02 ± 0.60 L·minute -1 ) at the RCP, [HHb] BP , HRVT2, and HRVT2&[HHb] BP average (H&H Av ), respectively, were not significantly different ( p > 0.05). The linear relationship between H&H Av and RCP was higher compared with the relationship between [HHb] BP vs RCP and HRVT2 vs RCP for both HR ( r = 0.85; r = 0.73; r = 0.79, p > 0.05) and V̇O 2 ( r = 0.94; r = 0.93; r = 0.91, p > 0.05). Intraclass correlation between RCP, [HHb] BP , HRVT2, and H&H AV was 0.93 for V̇O 2 and 0.79 for HR. The [HHb] BP and the HRVT2 independently provided V̇O 2 and HR responses that strongly agreed with those at the RCP. Combining [HHb] BP and the HRVT2 resulted in estimations of the V̇O 2 and HR at the RCP that displayed smaller variability compared with each modality alone.

Neuromuscular and autonomic function is fully recovered within 24 h following a sprint interval training session.

BACKGROUND: Recovery is a key factor to promote adaptations and enhance performance. Sprint Interval Training (SIT) is known to be an effective approach to improve overall physical function and health. Although a 2-day rest period is given between SIT sessions, the time-course of recovery after SIT is unknown. PURPOSE: The aim of this study was to determine whether the neuromuscular and autonomic nervous systems would be impaired 24 and 48 h after an SIT session. METHODS: Twenty-five healthy subjects performed an 8 × 15 s all-out session on a braked cycle ergometer with 2 min of rest between repetitions. Isometric maximal voluntary contraction (iMVC) and evoked forces to electrical nerve stimulation during iMVC and at rest were used to assess muscle contractile properties and voluntary activation before (Pre), 1 (Post24h), and 2 (Post48h) days after the session. Two maximal 7 s sprints with two different loads were performed at those same time-points to evaluate the maximal theoretical force (F0), velocity (V0) and maximal power (Pmax) production during a dynamic exercise. Additionally, nocturnal heart rate variability (HRV) was assessed the previous and the three subsequent nights to the exercise bout. RESULTS: No significant impairments were observed for the iMVC or for the force evoked by electrical stimulation 1 day after the session. Similarly, F0, V0, and Pmax were unchanged at Post24h and Post48h. Furthermore, HRV did not reveal any temporal or frequential significant difference the nights following SIT compared to Pre. CONCLUSION: The results of this study show a full recovery of neuromuscular and autonomic functions a day after an all-out SIT session.

Sodium bicarbonate induces alkalosis, but improves high-intensity cycling performance only when participants expect a beneficial effect: a placebo and nocebo study.

The study aimed to investigate the effects of sodium bicarbonate (NaHCO3) intake with divergent verbal and visual information on constant load cycling time-to-task failure, conducted within the severe intensity domain. Fifteen recreational cyclists participated in a randomized double-blind, crossover study, ingesting NaHCO3 or placebo (i.e., dextrose), but with divergent information about its likely influence (i.e., likely to induce ergogenic, inert, or harmful effects). Performance was evaluated using constant load cycling time to task failure trial at 115% of peak power output estimated during a ramp incremental exercise test. Data on blood lactate, blood acid-base balance, muscle electrical activity (EMG) through electromyography signal, and the twitch interpolation technique to assess neuromuscular indices were collected. Despite reduced peak force in the isometric maximal voluntary contraction and post-effort peripheral fatigue in all conditions (P < 0.001), neither time to task failure, EMG nor, blood acid-base balance differed between conditions (P > 0.05). Evaluation of effect sizes of all conditions suggested that informing participants that the supplement would be likely to have a positive effect (NaHCO3/Ergogenic: 0.46; 0.15-0.74; Dextrose/Ergogenic: 0.45; 0.04-0.88) resulted in improved performance compared to control. Thus, NaHCO3 ingestion consistently induced alkalosis, indicating that the physiological conditions to improve performance were present. Despite this, NaHCO3 ingestion did not influence performance or indicators of neuromuscular fatigue. In contrast, effect size estimates indicate that participants performed better when informed that they were ingesting an ergogenic supplement. These findings suggest that the apparently ergogenic effect of NaHCO3 may be due, at least in part, to a placebo effect.

Can the heart rate response at the respiratory compensation point be used to retrieve the maximal metabolic steady state?

The metabolic rate (VO2) at the maximal metabolic steady state (MMSS) is generally not different from the VO2 at the respiratory compensation point (RCP). Based on this, it is often assumed that the heart rate (HR) at RCP would also be similar to that at MMSS. The study aims to compare the HR at RCP with that at MMSS. Seventeen individuals completed a ramp-incremental test, a series of severe-intensity trials to estimate critical power and two-to-three 30-min trials to confirm MMSS. The HR at RCP was retrieved by linear interpolation of the ramp-VO2/HR relationship and compared to the HR at MMSS recorded at 10, 15, 20, 25 and 30 min. The HR at RCP was 166 ± 12 bpm. The HR during MMSS at the timepoints of interest was 168 ± 8, 171 ± 8, 175 ± 9, 177 ± 9 and 178 ± 10 bpm. The HR at RCP was not different from the HR at MMSS at 10 min (P > 0.05) but lower at subsequent timepoints (P < 0.05) with this difference becoming progressively larger. For all timepoints, limits of agreement were large (~30 bpm). Given these differences and the variability at the individual level, the HR at RCP cannot be used to control the metabolic stimulus of endurance exercise.

An undergraduate laboratory to study exercise thresholds.

In exercise physiology, laboratory components help students connect theoretical concepts to their own exercise experiences and introduce them to data collection, analysis, and interpretation using classic techniques. Most courses include a lab protocol that involves exhaustive incremental exercise during which expired gas volumes and concentrations of oxygen and carbon dioxide are measured. During these protocols, there are characteristic alterations in gas exchange and ventilatory profiles that give rise to two exercise thresholds: the gas exchange threshold (GET) and the respiratory compensation point (RCP). The ability to explain why these thresholds occur and how they are identified is fundamental to learning in exercise physiology and requisite to the understanding of core concepts including exercise intensity, prescription, and performance. Proper identification of GET and RCP requires the assembly of eight data plots. In the past, the burden of time and expertise required to process and prepare data for interpretation has been a source of frustration. In addition, students often express a desire for more opportunities to practice/refine their skills. The objective of this article is to share a blended laboratory model that features the "Exercise Thresholds App," a free online resource that eliminates postprocessing of data and provides a bank of profiles on which end-users can practice threshold identification skills with immediate feedback. In addition to including prelaboratory and postlaboratory recommendations, we present student accounts of understanding, engagement, and satisfaction following completion of the laboratory experience and introduce a new quiz feature of the app to assist instructors with evaluating student learning.NEW & NOTEWORTHY We present a laboratory to study exercise thresholds from gas exchange and ventilatory measures that features the "Exercise Thresholds App," a free online resource that eliminates postprocessing of data and provides a bank of profiles on which end-users can practice threshold identification skills. In addition to including prelaboratory and postlaboratory recommendations, we present student accounts of understanding, engagement, and satisfaction and introduce a new quiz feature of the app to assist instructors with evaluating learning.

Beneficial Performance Effects of Training Load Intensification Can Be Abolished by Functional Overreaching: Lessons From a Water Polo Study in Female Athletes.

ABSTRACT: Brisola, GMP, Dutra, YM, Murias, JM, and Zagatto, AM. Beneficial performance effects of training load intensification can be abolished by functional overreaching: Lessons from a water polo study in female athletes. J Strength Cond Res 37(6): e391-e402, 2023-The purpose of this study was to compare the outcomes from 2 weeks of training load intensification strategy in female water polo players diagnosed with functional overreaching (F-OR) with no F-OR players (acute fatigue) on the performance outcomes and hormonal, immunological, and cardiac autonomic nervous system responses. Twenty-two female water polo players were allocated into control and intensification group during 7 weeks. The swimming performance, biochemical parameters, heart rate variability, profile of mood states, and upper respiratory tract infection symptoms were assessed twice before and twice after 2 weeks of intensification period. F-OR showed a worsening in total time of the repeated sprint ability (RSA) test compared with the control group and the acute fatigue group after intensification ( p ≤ 0.035). Furthermore, after the tapering period, the F-OR group maintained worse total time of the RSA test than the acute fatigue group ( p = 0.029). In addition, the acute fatigue group showed improvement in total time of the RSA test after intensification compared with the control group ( p < 0.001). No significant interactions were found for the other parameters. Therefore, periods of intensification without the F-OR development can promote higher gains in the total time of the RSA test after intensification and tapering period.

Easy Prediction of the Maximal Lactate Steady-State in Young and Older Men and Women.

Maximal Lactate steady-state (MLSS) demarcates sustainable from unsustainable exercise and is used for evaluation/monitoring of exercise capacity. Still, its determination is physically challenging and time-consuming. This investigation aimed at validating a simple, submaximal approach based on blood lactate accumulation ([Δlactate]) at the third minute of cycling in a large cohort of men and women of different ages. 68 healthy adults (40♂, 28♀, 43 ± 17 years (range 19-78), VO2max 45 ± 11 ml-1·kg-1·min-1 (25-68)) performed 3-5 constant power output (PO) trials with a target duration of 30 minutes to determine the PO corresponding to MLSS. During each trial, [Δlactate] was calculated as the difference between the third minute and baseline. A multiple linear regression was computed to estimate MLSS based on [Δlactate], subjects` gender, age and the trial PO. The estimated MLSS was compared to the measured value by paired t-test, correlation, and Bland-Altman analysis. The group mean value of estimated MLSS was 180 ± 51 W, not significantly different from (p = 0.98) and highly correlated with (R2 = 0.89) measured MLSS (180 ± 54 watts). The bias between values was 0.17 watts, and imprecision 18.2 watts. This simple, submaximal, time- and cost-efficient test accurately and precisely predicts MLSS across different samples of healthy individuals (adjusted R2 = 0.88) and offers a practical and valid alternative to the traditional MLSS determination.

Impairment in maximal lactate steady state after carbon monoxide inhalation is related to training status.

NEW FINDINGS: What is the central question of this study? What is the effect of an elevated carboxyhaemoglobin (COHb) concentration following carbon monoxide inhalation on the maximal lactate steady state (MLSS) in humans and is this effect dependent on aerobic fitness? What is the main finding and its importance? An elevated COHb concentration intensified physiological responses to exercise at the MLSS - including heart rate, ventilation and peripheral fatigue - in general and reduced the MLSS (i.e., destabilized the blood lactate concentration) in trained but not untrained males and females. ABSTRACT: This study investigated whether a lower effective [Hb], induced by carbon monoxide (CO) inhalation, reduces the peak oxygen uptake ( V ̇ O 2 peak ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}{\rm{peak}}}$ ) and the maximal lactate steady state (MLSS) and whether training status explains individual variation in these impairments. Healthy young participants completed two ramp incremental tests (n = 20, 10 female) and two trials at MLSS (n = 16, eight female) following CO rebreathe tests and sham procedures (SHAM) in random orders. All fitness variables were normalized to fat-free mass (FFM) to account for sex-related differences in body composition, and males and females were matched for aerobic fitness. The V ̇ O 2 peak ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}{\rm{peak}}}$ (mean (SD): -4.2 (3.7)%), peak power output (PPO) (-3.3 (2.2)%) and respiratory compensation point (RCP) (-6.3 (4.5)%) were reduced in CO compared with SHAM (P < 0.001 for all), but the gas exchange threshold (-3.3 (7.1)%) was not (P = 0.077). Decreases in V ̇ O 2 peak ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}{\rm{peak}}}$ (r = -0.45; P = 0.047) and PPO (r = -0.49; P = 0.029) in CO were correlated with baseline aerobic fitness. Compared to SHAM, physiological and perceptual indicators of exercise-related stress were exacerbated by CO while cycling at MLSS. Notably, the mean blood lactate concentration ([La]) increased (i.e., Δ[La] >1.0 mM) between 10 min (5.5 (1.4) mM) and 30 min (6.8 (1.3) mM; P = 0.026) in CO, with 9/16 participants classified as unstable. These unstable participants had a higher V ̇ O 2 peak ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}{\rm{peak}}}$ (66.2 (8.5) vs. 56.4 (8.8) ml kg FFM-1  min-1 , P = 0.042) and V ̇ O 2 ${\dot{V}}_{{{\rm{O}}}_{\rm{2}}}$ at MLSS (55.8 (7.0) vs. 44.3 (7.0) ml kg FFM-1  min-1 , P = 0.006) compared to the stable group. In conclusion, a reduced O2 -carrying capacity decreased maximal and submaximal exercise performance, with higher aerobic fitness associated with greater impairments in both.

Mild obesity does not affect the forearm muscle microvascular responses to hyperglycemia.

INTRODUCTION: Mild obesity has been associated with postprandial brachial artery vascular dysfunction. However, direct assessment of these effects within the forearm skeletal muscle microcirculation remains unclear. Thus, this study aimed to investigate the effects of mild obesity on the arm micro- and macrovascular responses to glucose ingestion. METHODS: This cross-sectional study combined NIRS assessments of forearm skeletal muscle (FDS) reactivity (reperfusion slope) with %FMD of conduit artery function (brachial artery) before (Pre), as well as 60 and 120 min after glucose ingestion in 10 lean (BMI 23.9 ± 1.8) and 10 obese (BMI 32.9 ± 1.9) individuals. RESULTS: Both groups showed a significant increase in the reperfusion slope at 60 and 120 min after glucose ingestion compared with the pre-glucose ingestion measurements. Obese individuals showed a significant (p < .05) reduction in %FMD at 60 min after glucose ingestion, while no significant changes in postprandial %FMD were observed in lean participants. CONCLUSION: Even though obese individuals showed impaired postprandial brachial artery function, the current findings suggest that mild obesity does not affect the forearm skeletal muscle responses to glucose ingestion.

Association between [Formula: see text]O2 kinetics and [Formula: see text]O2max in groups differing in fitness status.

PURPOSE: This study evaluated (i) the relationship between oxygen uptake ([Formula: see text]O2) kinetics and maximal [Formula: see text]O2 ([Formula: see text]O2max) within groups differing in fitness status, and (ii) the adjustment of [Formula: see text]O2 kinetics compared to that of central [cardiac output (Q̇), heart rate (HR)] and peripheral (deoxyhemoglobin over [Formula: see text]O2 ratio ([HHb]/[Formula: see text]O2)] O2 delivery, during step-transitions to moderate-intensity exercise. METHODS: Thirty-six young healthy male participants (18 untrained; 18 trained) performed a ramp-incremental test to exhaustion and 3 step-transitions to moderate-intensity exercise. Q̇ and HR kinetics were measured in 18 participants (9 untrained; 9 trained). RESULTS: No significant correlation between τ̇[Formula: see text]O2 and [Formula: see text]O2max was found in trained participants (r = 0.29; p > 0.05) whereas a significant negative correlation was found in untrained (r = - 0.58; p < 0.05) and all participants (r = - 0.82; p < 0.05). τQ̇ (18.8 ± 5.5 s) and τHR (20.1 ± 6.2 s) were significantly greater than τ[Formula: see text]O2 (13.9 ± 2.7 s) for trained (p < 0.05). No differences were found between τQ̇ (22.8 ± 8.45 s), τHR (21.2 ± 8.3 s) and τ[Formula: see text]O2 (28.9 ± 5.7 s) for untrained (p > 0.05). τQ̇ demonstrated a significant strong positive correlation with τHR in trained (r = 0.76; p < 0.05) but not untrained (r = 0.61; p > 0.05). A significant overshoot in the [HHb]/[Formula: see text]O2 ratio was found in the untrained groups (p < 0.05) but not in the trained groups (p > 0.05) CONCLUSION: The results indicated that when comparing participants of different fitness status (i) there is a point at which greater V̇O2max values are not accompanied by faster [Formula: see text]O2 kinetics; (ii) central delivery of O2 does not seem to limit the kinetics of [Formula: see text]O2; and (iii) O2 delivery within the active tissues might contribute to the slower [Formula: see text]O2 kinetics response in untrained participants.

Individual cardiovascular responsiveness to work-matched exercise within the moderate- and severe-intensity domains.

PURPOSE: We investigated the cardiovascular individual response to 6 weeks (3×/week) of work-matched within the severe-intensity domain (high-intensity interval training, HIIT) or moderate-intensity domain (moderate-intensity continuous training, MICT). In addition, we analyzed the cardiovascular factors at baseline underlying the response variability. METHODS: 42 healthy sedentary participants were randomly assigned to HIIT or MICT. We applied the region of practical equivalence-method for identifying the levels of responders to the maximal oxygen uptake (V̇O2max) response. For investigating the influence of cardiovascular markers, we trained a Bayesian machine learning model on cardiovascular markers. RESULTS: Despite that HIIT and MICT induced significant increases in V̇O2max, HIIT had greater improvements than MICT (p < 0.001). Greater variability was observed in MICT, with approximately 50% classified as "non-responder" and "undecided". 20 "responders", one "undecided" and no "non-responders" were observed in HIIT. The variability in the ∆V̇O2max was associated with initial cardiorespiratory fitness, arterial stiffness, and left-ventricular (LV) mass and LV end-diastolic diameter in HIIT; whereas, microvascular responsiveness and right-ventricular (RV) excursion velocity showed a significant association in MICT. CONCLUSION: Our findings highlight the critical influence of exercise-intensity domains and biological variability on the individual V̇O2max response. The incidence of "non-responders" in MICT was one third of the group; whereas, no "non-responders" were observed in HIIT. The incidence of "responders" was 11 out of 21 participants in MICT, and 20 out of 21 participants in HIIT. The response in HIIT showed associations with baseline fitness, arterial stiffness, and LV-morphology; whereas, it was associated with RV systolic function in MICT.

Effects of pre-induced fatigue vs. concurrent pain on exercise tolerance, neuromuscular performance and corticospinal responses of locomotor muscles.

KEY POINTS: Fatigue and muscle pain induced in a remote muscle group has been shown to alter neuromuscular performance in exercising muscles. Inhibitory neural feedback associated with activation of mechano- and metabo-sensitive muscle afferents has been implicated in this phenomenon. The present study aimed to quantify and compare the effects of pre-induced fatigue and concurrent rising pain (evoked by muscle ischaemia) on the contralateral leg exercise capacity, neuromuscular performance, and corticomotor excitability and inhibition of knee extensor muscles. Pre-induced fatigue in one leg had a greater detrimental effect than the concurrent rising pain on the contralateral limb cycling capacity. Furthermore, pre-induced fatigue, but not concurrent rising pain, reduced corticospinal inhibition recorded from tested contralateral muscles. Regardless of the origin or mechanisms modulating sensory afferents during single-leg cycling exercise (i.e. pre-induced fatigue vs. concurrent rising pain), the limit of exercise tolerance remained the same and exercise was terminated upon achievement of a sensory tolerance limit. ABSTRACT: Individuals often need to maintain voluntary contractions during high intensity exercise in the presence of fatigue and pain. This investigation examined the effects of pre-induced fatigue and concurrent rising pain (evoked by muscle ischaemia) in one leg on motor fatigability and corticospinal excitability/inhibition of the contralateral limb. Twelve healthy males undertook four experimental protocols including unilateral cycling to task failure at 80% of peak power output with: (i) the right-leg (RL); (ii) the left-leg (LL); (iii) RL immediately preceded by LL protocol (FAT-RL); and (iv) RL when blood flow was occluded in the contralateral (left) leg (PAIN-RL). Participants performed maximal and submaximal 5 s right-leg knee extensions during which transcranial magnetic and femoral nerve electrical stimuli were delivered to elicit motor-evoked and compound muscle action potentials, respectively. The pre-induced fatigue reduced the right leg cycling time-to-task failure (mean ± SD; 332 ± 137 s) to a greater extent than concurrent pain (460 ± 158 s), compared to RL (580 ± 226 s) (P < 0.001). The maximum voluntary contraction force declined less following FAT-RL (P < 0.019) and PAIN-RL (P < 0.032) compared to RL. Voluntary activation declined and the corticospinal excitability recorded from knee extensors increased similarly after the three conditions (P < 0.05). However, the pre-induced fatigue, but not concurrent pain, reduced corticospinal inhibition compared to RL (P < 0.05). These findings suggest that regardless of the origin and/or mechanisms modulating sensory afferent feedback during single-leg cycling (e.g. pre-induced fatigue vs. concurrent rising pain), the limit of exercise tolerance remains the same, suggesting that exercise will be terminated upon achievement of sensory tolerance limit.

Acute application of a transdermal nitroglycerin patch protects against prolonged forearm ischemia-induced microvascular dysfunction.

INTRODUCTION: Prolonged limb blood flow occlusion (ie, tourniquet application during limb surgery) causes transient microvascular dysfunction. We examined the ability of a local nitric oxide donor (transdermal nitroglycerin) administered during prolonged cuff forearm occlusion to protect against microvascular dysfunction and to alter brachial artery dilation. METHODS: Ten healthy men (28 ± 8 years) participated in the study. During the control visit, they completed three vascular occlusion tests in the right arm termed, PRE (5-min occlusion), POSTimmediate (20-min occlusion), and POST30min (5-min occlusion). During the nitroglycerin visit, subjects completed the same vascular occlusion tests, but with a nitroglycerin patch placed over the contralateral forearm during the 20-min occlusion test. Micro- and macrovascular function were assessed using the near-infrared spectroscopy-derived reperfusion upslope (reperfusion slope, %.s-1 ) and flow-mediated dilation (%FMD), respectively. RESULTS: The reperfusion slope (1.44 ± 0.72%.s-1 ) and the %FMD (15.0 ± 2.8%) of the POSTimmediate test of the nitroglycerin condition were significantly (P < .05) higher than the reperfusion slope (1.01 ± 0.37%.s-1 ) and %FMD (6.77 ± 1.8%) during the POSTimmediate test of the control visit. CONCLUSION: Transdermal nitroglycerin protects against ischemia-induced microvascular dysfunction and causes marked dilation of the brachial artery %FMD.

Evaluating the suitability of supra-POpeak verification trials after ramp-incremental exercise to confirm the attainment of maximum O2 uptake.

During exhaustive ramp-incremental cycling tests, the incidence of O2 uptake (V̇o2) plateaus is low. To verify the attainment of maximum V̇o2 (V̇o2max), it is recommended that a trial at a power output (PO) corresponding to 110% of the ramp-derived peak (POpeak) is performed. It remains unclear whether verification trials set at this PO can be tolerated for long enough to allow attainment of V̇o2max. Eleven recreationally trained individuals performed five ramp tests of varying slope (5, 10, 15, 25, and 30 W/min), each followed, in series, by two verification trials: the first at 110% POpeak of the 25 W/min ramp and the second at 110% POpeak attained in the preceding ramp test. Exercise duration of the first verification trial was on average 81 ± 15 s (CV = 9 ± 3%) versus 162 ± 32, 121 ± 24, 103 ± 15, and 73 ± 10 s for the second verification trials at 110% of POpeak of the 5, 10, 15, and 30 W/min ramp tests, respectively (P < 0.05). Compared with the highest V̇o2 recorded during ramp tests, V̇o2 from the subsequent verification trials was not different for the 5, 10, and 15 W/min ramp tests (P > 0.05) but was lower for the 25 and 30 W/min ramp tests (P < 0.05). Verification trials at 110% POpeak of rapidly incrementing ramp tests (i.e., 25 W/min) were not sustained for long enough to allow the attainment of V̇o2max. With commonly used rapidly incrementing ramp tests engendering exhaustion within 8-12 min, verification trials less than POpeak should be preferred as they can be sustained sufficiently long to allow the attainment of V̇o2max.