Heavy-intensity Exercise Research Articles

Differences in motivational dynamics between experienced cyclists and untrained participants during an incremental endurance exercise task

PurposeThe conflict between the desire to reduce effort during exercise and the performance goal of the exercise task contributes to explaining endurance exercise performance. However, whether the trajectories of these two motivational responses systematically differ across individuals with different characteristics is poorly understood. The present study examined whether changes in desire to reduce effort and performance goal value across moderate, heavy, and severe exercise intensity domains differed between cyclists and untrained, but active participants. MethodsFifty participants (14 cyclists and 36 untrained) completed an incremental step test on a cycle ergometer, in which work rate was increased by 25 W every 4 min until voluntary exhaustion. Desire to reduce effort, performance goal value, and blood lactate concentration (for determination of exercise intensity domains) were measured every 4 min and the data were analysed using multilevel modelling. ResultsDesire to reduce effort increased quicker for untrained participants in the moderate exercise intensity domain (b = 1.66, p < .001) and across the whole trial (b = 1.64, p < .001), compared to cyclists (b = .69, and b = 1.14, respectively, both p < .001). Untrained participants reported similar performance goal value at the beginning of the trial (b = 16.02, p < .001), compared to cyclists (b = 17.25, p < .001). Beyond moderate intensities, the performance goal value decreased significantly for the untrained participants (b = −.70, p < .001) but significantly increased for cyclists (b = .45, p = .01). This pattern was also observed when focusing solely on the severe intensity domain (cyclists: b = .90, p < .001; untrained: b = −.84, p < .001). ConclusionThere are distinct differences in the desire to reduce effort and performance goal value between cyclists and untrained athletes. Identifying these systematic differences enhances the credibility of the desire-goal conflict framework in explaining endurance performance and provides insight into the type and timing of interventions that might be successful in improving performance.

Effect of Intermittent Recovery Periods on the Magnitude of the VO2 Slow Component During Heavy Intensity Exercise

Effect of Intermittent Recovery Periods on the Magnitude of the VO2 Slow Component During Heavy Intensity Exercise

Upper- vs. Whole-Body Cooling During Exercise with Thermal Protective Clothing in the Heat.

INTRODUCTION: Firefighters operating in hot environments face challenges from protective garments that restrict heat dissipation, resulting in increased core temperature, thermal discomfort, and performance decline. Cooling vests represent a viable solution. The study aim was to compare effectiveness of the same amount of cooling power to the upper body (UB) or whole body (WB) in alleviating thermoregulatory and physiological stress, enhancing cognitive function, and reducing ratings of thermal discomfort and exertion, during 60 min of exercise in a hot environment (40°C, 40% relative humidity) while wearing firefighter turnout gear.METHODS: Eight healthy individuals (27.5 ± 3 y) participated in three conditions with either no cooling (Control) or active cooling with a liquid perfused shirt (UB cooling), or with a liquid perfused shirt and pants (WB cooling). In each trial, subjects performed three sets of 15 min of stepping (20 steps ⋅ min-1) and 5 min of rest.RESULTS: Both cooling strategies were beneficial compared to having no cooling at all. Subjects could only complete two exercise bouts during Control, but they completed all three bouts with active cooling. WB cooling provided an advantage over UB cooling for core and skin temperature, and thermal comfort and sensation. The advantage in minimizing the increase in core temperature was only evident during the third exercise bout.DISCUSSION: Active cooling is advantageous under these conditions. WB cooling provided some benefits vs UB cooling during heavy intensity exercise; however, it is uncertain whether these benefits would be observed during light-to-moderate exercise, which more likely reflects an actual firefighting scenario.Mansouri F, Talebian Nia M, Villar R, Cornish SM, Giesbrecht GG. Upper- vs. whole-body cooling during exercise with thermal protective clothing in the heat. Aerosp Med Hum Perform. 2024; 95(9):659-666.

Acute alcohol ingestion decreases the work done above the end-test power during a 3-min all-out cycling exercise.

Alcohol ingestion influences metabolism during a subsequent exercise session, as evidenced by increased blood lactate concentration during fixed-intensity exercise. Therefore, augmented blood concentrations of alcohol may interfere with the anaerobic metabolism during high-intensity, short-duration exercise bout, thereby leading to impaired athletic performance. This study investigated whether the acute ingestion of alcohol as ethanol modulates performance parameters derived from the power-duration relationship in a 3-min all-out cycling test that allows for identifying the power output related to heavy and severe exercise intensities. Twenty-four recreationally active cyclists (16 men and 8 women) ingested a beverage containing either 0.4g ethanol.kg-1 body mass (EtOH) or a placebo (PLA) solution. Thirty minutes following ingestion, they completed a 3-min all-out test to measure power output and determine the end-test power (EP) and the work done above EP (WEP). Alcohol ingestion decreased WEP by 16% (EtOH: 5.6 ± 2.5kJ vs. PLA: 6.7 ± 2.4kJ; P = .003) but did not change EP (EtOH: 211 ± 44W vs. PLA: 212 ± 44W; P = .671). The alcohol-mediated effect in WEP was not influenced when controlling for participants' sex or accuracy in identifying the beverage ingested. Our data indicate that alcohol ingestion impaired the anaerobic work capacity, as evidenced by the reduction in WEP during the 3-min all-out test. Moreover, the ability to exercise at an intensity above the heavy domain may be decreased after ingestion of a moderate alcohol dose.

Effect of catecholamines stimulation via hand cooling and the priming effect on the oxygen consumption kinetics

Introduction&#x0D; Priming effect has been shown to accelerate the oxygen consumption (V̇O2) kinetics. This phenomenon could be explained by muscle oxygen (O2) enhanced delivery, motor unit recruitment or intracellular O2 enhanced utilization (Goulding et al. 2023). Catecholamines such as epinephrine (E) and norepinephrine (NE) are known to impact the cardiovascular system as well as the respiratory system and metabolic effects (Zouhal et al. 2008). The aim of this study is two folds. Observing the effect of increased E and NE induced by cold-water hand immersion on V̇O2 kinetic during heavy intensity exercise bout (HCWR). Compare the effect of cold-water hand immersion and previous HCWR on V̇O2 kinetic to see if the sympathetic system could partially explain the priming effects.&#x0D; Methods&#x0D; Ten healthy active males (mean ± SD, age 23 ± 5 years, body mass 71 ± 6.5 kg) participated in this study. An incremental test was performed on ergometer to prescribe the intensity for the HCWR exercise (∆ 25%). Participants did an 8 min HCWR normal bout (NO), followed by 8 min rest and a second bout (SB) and hand cooling bout (HC) at heavy intensity in a randomized order. For the HC condition, participants put hands in cold water (0°C) for 2 min then directly did the HCWR. Blood samples has been taken at rest, before and directly after the HCWR.&#x0D; Results&#x0D; Just before exercise, all conditions were different, but HC E (1.095 ± 0.64 nmol/ml) increased by 347% while HC NE (6.98 ± 1.89 nmol/ml) matched values from SB NE (6.89 ± 2.22 nmol/ml). At the end of exercise, no significant difference has been found between NO E (1.44 ± 1.06) and HC E (1.54 ± 1.38 nmol/ml) while SB E (2.35 ± 1.55 nmol/ml) was significantly higher than both conditions but no differences have been found between HC (20.15 ± 8.76 nmol/ml) and SB (20.41 ± 9.74 nmol/ml) NE. V̇O2 kinetic has been sped up for both HC and SB by increasing the absolute primary prime amplitude of HC (33.88 ± 0.96 ml/min/kg),SB (34.60 ± 0.86ml/min/kg) compared to NO (32.75 ± 0.65 ml/min/kg) and reducing the prime amplitude of HC (3.22 ± 0.51 ml/min/kg), SB (2.90 ± 0.64 ml/min/kg) vs NO (3.87 ±0 .56 ml/min/kg) of the slow component of V̇O2.&#x0D; Discussion/Conclusion&#x0D; Catecholamines stimulation via hand cooling accelerated the V̇O2 kinetics enhancing the primary phase and reducing the slow component. This effect seemed to follow the priming effect but with less intensity. Increased O2 delivery appeared to be a common feature of both conditions, Motor neuron excitability due to increased NE was also a likely hypothesis, as both HC and SB had the same values just before exercise. Finally, intra-muscular enhancement illustrated by improved intracellular partial pressure kinetics and mitochondrial O2 utilization might explain the effects of catecholamines and part of the priming effect. Mitochondrial “warm-up” could be influenced by both catecholamines and priming effect resulting in a better production of adenosine triphosphate.&#x0D; References&#x0D; Goulding, R. P., Burnley, M., &amp; Wüst, R. C. I. (2023). How priming exercise affects oxygen uptake kinetics: From underpinning mechanisms to endurance performance. Sports Medicine, 53, 959-976. https://doi.org/10.1007/s40279-023-01832-1&#x0D; Zouhal, H., Jacob, C., Delamarche, P., &amp; Gratas-Delamarche, A. (2008). Catecholamines and the effects of exercise, training and gender. Sports Medicine 38, 401-423. https://doi.org/10.2165/00007256-200838050-00004

Calculation of a conversion factor for estimating the glycolytic contribution in exercise from post-exercise blood lactate concentration.

Purpose: Often, the glycolytic contribution in a bout of heavy or severe intensity exercise is estimated by multiplying the increase in blood lactate concentration above resting levels that is engendered by the exercise (in mM) by 3.3 (or 3) mL·kg-1 per mM. Our purpose was to verify the value of this conversion factor, using methods that were completely different from those of the original studies. Methods: Six women (mean ± SD), age, 23 ± 1year; VO2max, 46 ± 4mL·kg-1·min-1) and three men (23 ± 0years; 54 ± 8mL·kg-1·min-1) completed 6min of heavy intensity exercise in conditions of normoxia and hypoxia (FIO2, ∼12%). VO2 was measured throughout the exercise and 7min of recovery. The increase in glycolytic contribution was estimated as the reduction in aerobic contribution in hypoxia, after correction for the effects of hypoxia on the oxygen demand and on the contribution from phosphocreatine. The peak post-exercise blood lactate concentration was measured in fingerstick blood samples. Results: The ratio between the increase in estimated glycolytic contribution (in mL·kg-1) in hypoxia and the increase in peak blood lactate concentration (in mM) yielded an oxygen equivalent of 3.4 ± 0.4mL·kg-1 per mM (range, 2.6mL·kg-1 per mM to 4.0mL·kg-1 per mM) for cycle ergometer exercise. Conclusion: These results generally support the use of a common conversion factor to calculate the glycolytic contribution from post-exercise blood lactate concentrations. However, there is some inter-individual variability in the conversion factor.

No sex differences in oxygen uptake or extraction kinetics in the moderate or heavy exercise intensity domains.

The integrative response to exercise differs between sexes, with oxidative energy contribution purported as a potential mechanism. The present study investigated whether this difference was evident in the kinetics of oxygen uptake (V̇o2) and extraction (HHb + Mb) during exercise. Sixteen adults (8 males, 8 females, age: 27 ± 5 yr) completed three experimental visits. Incremental exercise testing was performed to obtain lactate threshold and V̇o2peak. Subsequent visits involved three 6-min cycling bouts at 80% of lactate threshold and one 30-min bout at a work rate of 30% between the lactate threshold and power at V̇o2peak. Pulmonary gas exchange and near-infrared spectroscopy of the vastus lateralis were used to continuously sample V̇o2 and HHb + Mb, respectively. The phase II V̇o2 kinetics were quantified using monoexponential curves during moderate and heavy exercise. Slow component amplitudes were also quantified for the heavy-intensity domain. Relative V̇o2peak values were not different between sexes (P = 0.111). Males achieved ∼30% greater power outputs (P = 0.002). In the moderate- and heavy-intensity domains, the relative amplitude of the phase II transition was not different between sexes for V̇o2 (∼24 and ∼40% V̇o2peak, P ≥ 0.179) and HHb + Mb (∼20 and ∼32% ischemia, P ≥ 0.193). Similarly, there were no sex differences in the time constants for V̇o2 (∼28 s, P ≥ 0.385) or HHb + Mb (∼10 s, P ≥ 0.274). In the heavy-intensity domain, neither V̇o2 (P ≥ 0.686) or HHb + Mb (P ≥ 0.432) slow component amplitudes were different between sexes. The oxidative response to moderate- and heavy-intensity exercises did not differ between males and females, suggesting similar dynamic responses of oxidative metabolism during intensity-matched exercise.NEW & NOTEWORTHY This study demonstrated no sex differences in the oxidative response to moderate- and heavy-intensity cycling exercise. The change in oxygen uptake and deoxyhemoglobin were modeled with monoexponential curve fitting, which revealed no differences in the rate of oxidative energy provision between sexes. This provides insight into previously reported sex differences in the integrative response to exercise.

Long-Term Alterations in Pulmonary V˙O2 and Muscle Deoxygenation On-Kinetics During Heavy-Intensity Exercise in Competitive Youth Cyclists: A Cohort Study.

The aim of this investigation was to assess alterations of pulmonary oxygen uptake (V˙O2) and muscle deoxygenation on-kinetics during heavy-intensity cycling in youth cyclists over a period of 15months. Eleven cyclists (initial age, 14.3 [1.6]y; peak V˙O2, 62.2 [4.5]mL·min-1·kg-1) visited the laboratory twice on 3 occasions within 15months. Participants performed an incremental ramp exercise test and a constant workrate test within the heavy-intensity domain during the first visitand second visit, respectively. Subsequently, parameter estimates of the V˙O2 and muscle deoxygenation on-kinetics were determined with mono-exponential models. The V˙O2 phase II time constant decreased from occasion 1 (34 [4]s) to occasion 2 (30 [4]s, P = .005) and 3 (28 [4]s, P = .010). However, no significant alteration was observed between occasions 2 and 3 (P = .565). The V˙O2 slow component amplitude either expressed in absolute values (ie,L·min-1) or relative to end exercise V˙O2 (ie,%) showed no significant changes throughout the study (P = .972 and .996). Furthermore, the muscle deoxygenation on-kinetic mean response time showed no significant changes throughout the study (18 [8], 18 [3], and 16 [5]s for occasions 1, 2, and 3, respectively; P = .279). These results indicate proportional enhancements of local muscle oxygen distribution and utilization, which both contributed to the speeding of the V˙O2 on-kinetics herein.

Wearable near-infrared spectroscopy: reliability and sensitivity among different endurance cycling exercise intensities.

The present study investigated the reliability and sensitivity of a wearable near-infrared spectroscopy (wNIRS) device in moderate and heavy exercise intensity domains. On three separate days, eleven males performed an incremental test to exhaustion, and in the following visits, four submaximal constant-load bouts (i.e., test and retest) were performed in the moderate-intensity domain (100 and 130 W) and heavy-intensity domain (160 and 190 W). The local tissue oxygen saturation index (SmO2) and pulmonary oxygen uptake (V̇O2) were measured continuously. The absolute SmO2 and V̇O2 values and the change (Δ) from the 3rd to 6th min of exercise were calculated. There was good reliability for SmO2 measurements, as indicated by the high intraclass correlation coefficient analysis (ICC ≥0.84 for all) and low coefficient of variation between the two trials (CV ≤4.1% for all). Steady-state responses were observed for SmO2 and V̇O2 from the 3rd to the 6th min in the two moderate-intensity bouts (P>0.05), whereas SmO2 decreased and V̇O2 increased from the 3rd to the 6th min in the two heavy-intensity bouts (P<0.05). Together, these findings suggested that the SmO2 measured with a wNIRS device is reliable and sensitive to track local metabolic changes provoked by slight increments in exercise intensity.

Stroke and physiological relationships during the incremental front crawl test: outcomes for planning and pacing aerobic training.

Purpose: This study aimed to evaluate the physiological responses associated with the stroke length (SL) and stroke rate (SR) changes as swimming velocity increases during an incremental step-test. Moreover, this study also aimed to verify if SL and SR relationships toward maximal oxygen uptake (V̇O2max), gas respiratory compensation point (RCP), exchange threshold (GET), and swimming cost can be applied to the management of endurance training and control aerobic pace. Methods: A total of 19 swimmers performed the incremental test until volitional exhaustion, with each stage being designed by percentages of the 400m (%v400) maximal front crawl velocity. V̇O2max, GET, RCP, and the respective swimming velocities (v) were examined. Also, the stroke parameters, SL, SR, the corresponding slopes (SLslope and SRslope), and the crossing point (Cp) between them were determined. Results: GET and RCP corresponded to 70.6% and 82.4% of V̇O2max (4185.3 ± 686.1mLmin-1), and V̇O2 at Cp, SLslope, and SRslope were observed at 129.7%, 75.3%, and 61.7% of V̇O2max, respectively. The swimming cost from the expected V̇O2 at vSLslope (0.85 ± 0.18kJm-1), vSRslope (0.77 ± 0.17kJm-1), and vCp (1.09 ± 0.19kJm-1) showed correlations with GET (r = 0.73, 0.57, and 0.59, respectively), but only the cost at vSLslope and vCp correlated to RCP (0.62 and 0.69) and V̇O2max (0.70 and 0.79). Conclusion: SL and SR exhibited a distinctive pattern for the V̇O2 response as swimming velocity increased. Furthermore, the influence of SL on GET, RCP, and V̇O2max suggests that SLslope serves as the metabolic reference of heavy exercise intensity, beyond which the stroke profile defines an exercise zone with high cost, which is recommended for an anaerobic threshold and aerobic power training. In turn, the observed difference between V̇O2 at SRslope and GET suggests that the range of velocities between SL and SR slopes ensures an economical pace, which might be recommended to develop long-term endurance. The results also highlighted that the swimming intensity paced at Cp would impose a high anaerobic demand, as it is located above the maximal aerobic velocity. Therefore, SLslope and SRslope are suitable indexes of submaximal to maximal aerobic paces, while Cp's meaning still requires further evidence.

Tramadol is a performance-enhancing drug in highly trained cyclists: a randomized controlled trial.

Tramadol is a potent narcotic analgesic reportedly used in multiple sports to reduce exertional pain and confer a performance advantage. This study sought to identify whether tramadol enhances performance in time trial cycling. Twenty-seven highly trained cyclists were screened for tramadol sensitivity and then attended the laboratory across three visits. Visit 1 identified maximal oxygen uptake, peak power output, and gas exchange threshold through a ramp incremental test. Participants returned to the laboratory on two further occasions to undertake cycling performance tests following the ingestion of either 100 mg of soluble tramadol or a taste-matched placebo control in a double-blind, randomized, and crossover design. In the performance tests, participants completed a 30 min non-exhaustive fixed intensity cycling task at a heavy exercise intensity (272 ± 42 W), immediately followed by a competitive self-paced 25-mile time trial (TT). Following removal of two outlier data sets, analysis was completed on n = 25. Participants completed the TT significantly faster (d = 0.54, P = 0.012) in the tramadol condition (3758 s ± 232 s) compared with the placebo condition (3808 s ± 248 s) and maintained a significantly higher mean power output (+9 W) throughout the TT (ηp2 = 0.262, P = 0.009). Tramadol reduced perception of effort during the fixed intensity trial (P = 0.026). The 1.3% faster time in the tramadol condition would be sufficient to change the outcomes of a race and is highly meaningful and pervasive in this cohort of highly trained cyclists. The data from this study suggests that tramadol is a performance-enhancing drug.NEW & NOTEWORTHY In the current study, when cycling with tramadol participants completed a time trial on average 50 s faster and at a 9 W higher power output than the placebo control. The study used both a fixed intensity and self-paced time trial exercise tasks to reflect the demands of a stage race. The outcomes from this study were used by the World Anti-Doping Agency to inform their addition of tramadol to the Prohibited List in 2024.

Acute stress imparts a transient benefit to task-switching that is not modulated following a single bout of exercise.

Cognitive flexibility represents a core component of executive function that promotes the ability to efficiently alternate-or "switch"-between different tasks. Literature suggests that acute stress negatively impacts cognitive flexibility, whereas a single bout of aerobic exercise supports a postexercise improvement in cognitive flexibility. Here, we examined whether a single bout of aerobic exercise attenuates a stress-induced decrement in task-switching. Forty participants (age range = 19-30) completed the Trier Social Stress Test (TSST) and were randomized into separate Exercise or Rest groups entailing 20-min sessions of heavy intensity exercise (80% of heart rate maximum via cycle ergometer) or rest, respectively. Stress induction was confirmed via state anxiety and heart rate. Task-switching was assessed prior to the TSST (i.e., pre-TSST), following the TSST (i.e., post-TSST), and following Exercise and Rest interventions (i.e., post-intervention) via pro- (i.e., saccade to veridical target location) and antisaccades (i.e., saccade mirror-symmetrical to target location) arranged in an AABB task-switching paradigm. The underlying principle of the AABB paradigm suggests that when prosaccades are preceded by antisaccades (i.e., task-switch trials), the reaction times are longer compared to their task-repeat counterparts (i.e., unidirectional prosaccade switch-cost). As expected, the pre-TSST assessment yielded a prosaccade switch cost. Notably, post-TSST physiological measures indicated a reliable stress response and at this assessment a null prosaccade switch-cost was observed. In turn, post-intervention assessments revealed a switch-cost independent of Exercise and Rest groups. Accordingly, the immediate effects of acute stress supported improved task-switching in young adults; however, these benefits were not modulated by a single bout of aerobic exercise.

Agreement between left and right middle cerebral artery blood velocity responses to incremental and constant work-rate exercise in healthy males and females

Objective. To quantify the agreement between left and right middle cerebral artery blood velocity (MCAv) responses to incremental and constant work-rate exercise in adults. Approach Seventeen healthy adults (23.8 ± 2.4 years, 9 females) completed a ramp incremental test to exhaustion on a cycle ergometer, three 6-minute transitions at a moderate-intensity, and three at a heavy-intensity, all on separate days. Bilateral MCAv was measured throughout using transcranial Doppler ultrasonography, with left and right MCAv data analysed separately. Data were analysed at baseline, gas exchange threshold, respiratory compensation point and exhaustion during ramp incremental exercise. MCAv responses to constant work-rate exercise were analysed using a mono-exponential model, to determine time- and amplitude-based kinetic response parameters. Main Results Left and right MCAv responses to incremental and constant work-rate exercise were significantly, strongly and positively correlated (r ≥ 0.61, P < 0.01). Coefficient of variation (left versus right) ranged from 7.3%–20.7%, 6.4%–26.2% and 5.9%–22.5% for ramp, moderate and heavy-intensity exercise, respectively. The relative change in MCAv from baseline was higher in the right compared to left MCAv during ramp, moderate and heavy-intensity exercise (all P < 0.05), but the effect sizes were small (d ≤ 0.4). Small mean left–right differences were present during ramp incremental exercise at all time-points (<6 cm s−1; <4%), and for all kinetic parameters during moderate and heavy-intensity exercise (<3 cm s−1, <3%, <4 s). Significance These findings demonstrate similarities between left and right MCAv responses to incremental and constant-work rate exercise in adults on a group-level, but also highlight individual variation in the agreement between left and right MCAv exercise responses.

Critical power: a paradigm-shift for benchmarking exercise testing and prescription.

Inherent in the work of Collins et al. (2022) is the notion that prescription of exercise intensity relative to CP (and also the gas exchange threshold, GET; see Lansley et al., 2011) will reduce the variability in physiological responses and exercise tolerance. And that is precisely the hypothesis tested by Meyler et al. (2023) in this issue of Experimental Physiology. Specifically, in healthy men and women who completed multiple exhausting cycling tests (graded exercise test, series of constant-power tests) to define GET, CP and W′, these parameters and also V ̇ O 2 max ${\dot V_{{{\rm{O}}_2}\max }}$ (i.e., at defined percentages of V ̇ O 2 max ${\dot V_{{{\rm{O}}_2}\max }}$ ) were utilized to anchor separate moderate- (MOD), heavy- and severe-intensity criterion exercise bouts. Subsequently, two series of MOD, HEAVY and SEVERE exercise bouts, the latter as high intensity 5 × 3 min intervals, were prescribed ‘traditionally’ (TRAD) based upon V ̇ O 2 max ${\dot V_{{{\rm{O}}_2}\max }}$ (i.e., 50%, 77% and 85%) or using the GET and CP parameters (THR; MOD: 30 min at 90% GET; HEAVY: 20 min at 50%∆ (midway between GET and CP); and SEVERE: at 110% CP). Primary results supported the hypothesis for HEAVY and SEVERE exercise with respect to reduced variability of work rates for THR versus TRAD. Crucially, whereas some subjects for HEAVY–TRAD exercised in the severe-intensity domain with the attendant V ̇ O 2 ${\dot V_{{{\rm{O}}_2}}}$ and [lactate] consequences – and 70% of them became exhausted for TRAD versus 0% for THR – this was not the case for HEAVY–THR. For the SEVERE trials neither peak nor mean V ̇ O 2 ${\dot V_{{{\rm{O}}_2}}}$ and heart rate variability were different between TRAD and THR, but peak and mean [lactate] variability were lower for THR, as was percentage W′ depletion. The scientific literature is, unfortunately, replete with examples of otherwise very well designed studies where the investigators have chosen to ‘normalize’ heavy exercise intensity by exercising their participants at either a fixed % V ̇ O 2 max ${\dot V_{{{\rm{O}}_2}\max }}$ , often 75% or 80%, or at 50%∆ between GET and V ̇ O 2 max ${\dot V_{{{\rm{O}}_2}\max }}$ . So doing has resulted in highly divergent physiological responses characteristic of some participants exercising in the heavy (i.e., stable V ̇ O 2 ${\dot V_{{{\rm{O}}_2}}}$ and [lactate] profiles, Tlim >> 30 min) and others in the severe (i.e., V ̇ O 2 max ${\dot V_{{{\rm{O}}_2}\max }}$ achieved, rising [lactate], exhaustion < 20 min) exercise domains. Meyler et al. (2023) demonstrate that prescribing exercise relative to CP can prevent this occurrence and, even for supra-CP exercise, reduce inter-subject response variability for key physiological indices. This rationale has also been presented, on a more theoretical level, for normalizing the assessment of exercise for therapeutic efficacy across patient populations, especially chronic obstructive pulmonary disease (Whipp & Ward, 2009). Although beyond the limits of the measurements in Meyler et al. (2023), it is also important to note that, by registering severe-intensity exercise bouts to CP and thereby lowering inter-subject variability for W′ depletion, it would be expected that greater homogeneity would be achieved across participants for intramyocyte perturbations (e.g., ∆[PCr], [Pi], [ADPfree], [H+], [glycogen]; Jones et al., 2008) in addition to, of course, improved ability to predict exercise tolerance. The implications and therefore putative impact of the findings of Meyler et al. (2023) are substantial and reach across the preserves of exercise science to better inform, prescribe and evaluate athletic training regimens, improve the assessment of the efficacy of therapeutic interventions and, of course, help resolve the mechanistic bases for exercise intolerance itself. Both authors have read and approved the final version of this manuscript and agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. All persons designated as authors qualify for authorship, and all those who qualify for authorship are listed. None declared. None.

The 'normal' adjustment of oxygen delivery to small muscle mass exercise is not optimized for muscle contractile function.

Oxygen delivery is viewed as tightly coupled to demand in exercise below critical power because increasing oxygen delivery does not increase . However, whether the 'normal' adjustment of oxygen delivery to small muscle mass exercise in the heavy intensity domain is optimal for excitation-contraction coupling is currently unknown. In 20 participants (10 female), a remote skeletal muscle (i.e. tibialis anterior) metaboreflex was (Hyperperfusion condition) or was not (Control condition) activated for 4min during both force of contraction (experimental model 1) and muscle activation-targeted (experimental model 2) rhythmic forearm handgrip exercise. Analysis was completed on the combined data from both experimental models. After 30s of remote skeletal muscle metaboreflex activation, mean arterial blood pressure, forearm blood flow and muscle oxygenation were increased and remained increased until metaboreflex discontinuation. While oxygen delivery was elevated, the muscle activation to force of contraction ratio was improved. Upon metaboreflex discontinuation, forearm oxygen delivery and the muscle activation and force of contraction ratio rapidly (within 30s) returned to control levels. These findings demonstrate that (a) the metaboreflex was effective at increasing forearm muscle oxygen delivery and oxygenation, (b) the muscle activation to force of contraction ratio was improved with increased oxygen delivery, and (c) in the heavy exercise intensity domain, the normal matching of oxygen delivery to metabolic demand is not optimal for muscle excitation-contraction coupling. These results suggest that the nature of vasoregulation in exercising muscle is such that it does not support optimal perfusion for excitation-contraction coupling. KEY POINTS: Oxygen delivery is viewed as tightly coupled to demand in exercise below critical power because increasing oxygen delivery does not increase the rate of oxygen uptake. Whether the 'normal' adjustment of oxygen delivery in small muscle mass exercise below critical power is optimal for excitation-contraction coupling is not known. Here we show in humans that increasing oxygen delivery above 'normal' improves excitation-contraction coupling. These results suggest that, in the heavy exercise intensity domain, the 'normal' matching of oxygen delivery to metabolic demand is not optimal for muscle excitation-contraction coupling. Therefore, the nature of vasoregulation in exercising muscle is such that it does not support optimal perfusion for excitation-contraction coupling.

Variability in exercise tolerance and physiological responses to exercise prescribed relative to physiological thresholds and to maximum oxygen uptake.

What is the central question of this study? Does prescribing exercise intensity using physiological thresholds create a more homogeneous exercise stimulusthanusing traditional intensity anchors? What is the main finding and its importance? Prescribing exercise using physiological thresholds, notably critical power, reduced the variability in exercise tolerance and acute metabolic responses. At higher intensities, approaching or exceeding the transition from heavy to severe intensity exercise, the imprecision of using fixed % as an intensity anchor becomes amplified. The objective of this study was to determine whether the variability in exercise tolerance and physiological responses is lower when exercise is prescribed relative to physiological thresholds (THR) compared to traditional intensity anchors (TRAD). Ten individuals completed a series of maximal exercise tests and a series of moderate (MOD), heavy (HVY) and severe intensity (HIIT) exercise bouts prescribed using THR intensity anchors (critical power and gas exchange threshold) and TRAD intensity anchors (maximum oxygen uptake; ). There were no differences in exercise tolerance or acute response variability between MODTHR and MODTRAD . All individuals completed HVYTHR but only 30% completed HVYTRAD . Compared to HVYTHR , where work rates were all below critical power, work rates in HVYTRAD exceeded critical power in 70% of individuals. There was, however, no difference in acute response variability between HVYTHR and HVYTRAD . All individuals completed HIITTHR but only 20% completed HIITTRAD . The variability in peak (F=0.274) and average (F=0.318) blood lactate responses was lower in HIITTHR compared to HIITTRAD . The variability in W' depletion (the finite work capacity above critical power) after the final interval bout was lower in HIITTHR compared to HIITTRAD (F=0.305). Using physiological thresholds to prescribe exercise intensity reduced the heterogeneity in exercise tolerance and physiological responses to exercise spanning the boundary between the heavy and severe intensity domains. To increase the precision of exercise intensity prescription, it is recommended that, where possible, physiological thresholds are used in place of .

Energy metabolism and muscle activation heterogeneity explain slow component and muscle fatigue of cycling at different intensities.

What is the central question of this study? What are the physiological mechanisms underlying muscle fatigue and the increase in the O2 cost per unit of work during high-intensity exercise? What is the main finding and its importance? Muscle fatigue happens before, and does not explain, the slow component ( ), but they share the same origin. Muscle activation heterogeneity is associated with muscle fatigue and . Knowing this may improve training prescriptions for healthy people leading to improved public health outcomes. This study aimed to explain the slow component ( ) and muscle fatigue during cycling at different intensities. The muscle fatigue of 16 participants was determined through maximal isokinetic effort lasting 3s during constant work rate bouts of moderate (MOD), heavy (HVY) and very heavy intensity (VHI) exercise. Breath-by-breath , near-infrared spectroscopy signals and EMG activity were analysed (thigh muscles). was higher during VHI exercise (∼70% vs. ∼28% of reserve in HVY). The deoxygenated haemoglobin final value during VHI exercise was higher than during HVY and MOD exercise (∼90% of HHb physiological normalization, vs. ∼82% HVY and ∼45% MOD). The muscle fatigue was greater after VHI exercise (∼22% vs. HVY ∼5%). There was no muscle fatigue after MOD exercise. The greatest magnitude of muscle fatigue occurred within 2min (VHI ∼17%; HVY ∼9%), after which it stabilized. No significant relationship between and muscle force production was observed. The τ of muscle was significantly related (R2 =0.47) with torque decrease for VHI. Type I and II muscle fibre recruitment mainly in the rectus femoris moderately explained the muscle fatigue (R2 =0.30 and 0.31, respectively) and the (R2 =0.39 and 0.27, respectively). The is also partially explained by blood lactate accumulation (R2 =0.42). In conclusion muscle fatigue and O2 cost seem to share the same physiological cause linked with a decrease in the muscle and a change in lactate accumulation. Muscle fatigue and are associated with muscle activation heterogeneity and metabolism of different muscles activated during cycling.

Cuffless Blood Pressure Estimation During Moderate- and Heavy-Intensity Exercise Using Wearable ECG and PPG.

To develop and evaluate an accurate method for cuffless blood pressure (BP) estimation during moderate- and heavy-intensity exercise. Twelve participants performed three cycling exercises: a ramp-incremental exercise to exhaustion, and moderate and heavy pseudorandom binary sequence exercises on an electronically braked cycle ergometer over the course of 21 minutes. Subject-specific and population-based nonlinear autoregressive models with exogenous inputs (NARX) were compared with feedforward artificial neural network (ANN) models and pulse arrival time (PAT) models. Population-based NARX models, (applying leave-one-subject-out cross-validation), performed better than the other models and showed good capability for estimating large changes in mean arterial pressure (MAP). The models were unable to track consistent decreases in BP during prolonged exercise caused by reduction in peripheral vascular resistance, since this information is apparently not encoded in the employed proxy physiological signals (electrocardiography and forehead PPG) used for BP estimation. Nevertheless, the population-based NARX model had an error standard deviation of 11.0 mmHg during the entire exercise window, which improved to 9.0 mmHg when the model was periodically calibrated every 7 minutes. Population-based NARX models can estimate BP during moderate- and heavy-intensity exercise but need periodic calibration to account for the change in vascular resistance during exertion. MAP can be continuously tracked during exercise using only wearable sensors, making monitoring exercise physiology more convenient and accessible.

The Effect of Endurance Training on Pulmonary V˙O2 Kinetics in Solid Organs Transplanted Recipients.

Background: We investigated the effects of single (SL-ET) and double leg (DL-ET) high-intensity interval training on O2 deficit (O2Def) and mean response time (MRT) during square-wave moderate-intensity exercise (DL-MOD), and on the amplitude of O2p slow component (SCamp), during heavy intensity exercise (DL-HVY), on 33 patients (heart transplant = 13, kidney transplanted = 11 and liver transplanted = 9). Methods: Patients performed DL incremental step exercise to exhaustion, two DL-MOD tests, and a DL-HVY trial before and after 24 sessions of SL-ET (n = 17) or DL-ET (n = 16). Results: After SL-ET, O2Def, MRT and SCamp decreased by 16.4% ± 13.7 (p = 0.008), by 15.6% ± 13.7 (p = 0.004) and by 35% ± 31 (p = 0.002), respectively. After DL-ET, they dropped by 24.9% ± 16.2 (p < 0.0001), by 25.9% ± 13.6 (p < 0.0001) and by 38% ± 52 (p = 0.0003), respectively. The magnitude of improvement of O2Def, MRT, and SCamp was not significantly different between SL-ET and DL-ET after training. Conclusions: We conclude that SL-ET is as effective as DL-ET if we aim to improve O2p kinetics in transplanted patients and suggest that the slower, O2p kinetics is mainly caused by the impairment of peripherals exchanges likely due to the immunosuppressive medications and disuse.

Power Output Manipulation from Below to Above the Gas Exchange Threshold Results in Exacerbated Performance Fatigability

Performance fatigability is substantially greater when exercising in the severe- versus heavy-intensity domain. However, the relevance of the boundary between moderate- and heavy-intensity exercise, the gas exchange threshold (GET), to performance fatigability is unclear. This study compared alterations in neuromuscular function during work-matched exercise above and below the GET. Seventeen male participants completed work-matched cycling for 90, 110, and 140 min at 110%, 90%, and 70% of the GET, respectively. Knee extensor isometric maximal voluntary contraction (MVC), high-frequency doublets (Db100), low- to high-frequency doublet ratio (Db10:100), and voluntary activation were measured at baseline, 25%, 50%, 75%, and 100% of task completion. During the initial baseline visit and after each constant work rate bout, ramp-incremental exercise was performed, and peak power output and oxygen uptake (V̇O 2peak ) were determined. After the 70% and 90% GET trials, similar reductions in MVC (-14% ± 6% and -14% ± 8%, respectively, P = 0.175) and Db100 (-7% ± 9% and -6% ± 9%, respectively, P = 0.431) were observed. However, for a given amount of work completed, reductions in MVC (-25% ± 15%, P = 0.008) and Db100 (-12% ± 8%, P = 0.029) were up to 2.6-fold greater during the 110% than the 90% GET trial. Peak power output and V̇O 2peak during ramp-incremental exercise were reduced by 7.0% ± 11.3% and 6.5% ± 9.3%, respectively, after the 110% GET trial relative to the baseline ramp ( P ≤ 0.015), with no changes after the moderate-intensity trials ( P ≥ 0.078). The lack of difference in fatigability between the trials at 70% and 90% GET, coupled with the greater fatigability at 110% relative to 90% GET, shows that exceeding the moderate- to heavy-intensity boundary has implications for performance fatigability, while also impairing maximal exercise performance capacity.