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.

Evaluation of the "Step-Ramp-Step" Protocol: Accurate Aerobic Exercise Prescription with Different Steps and Ramp Slopes

PURPOSE

To assess whether: i) a lower amplitude constant-load MOD is appropriate to determine the mean response time (MRT); ii) the method accurately corrects the dissociation in the V̇O 2 -PO relationship during ramp compared with constant-load exercise when using different ramp slopes.

METHODS

Eighteen participants (7 females) performed three SRS tests including: i) step-transitions into MOD from 20 to 50 W (MOD 50 ) and 80 W (MOD 80 ); and ii) slopes of 15, 30, and 45 W·min -1 . The V̇O 2 and PO at the gas exchange threshold (GET) and the corrected respiratory compensation point (RCP CORR ) were determined. Two to three 30-min constant-load trials evaluated the V̇O 2 and PO at the maximal metabolic steady state (MMSS).

RESULTS

There were no differences in V̇O 2 at GET (1.97 ± 0.36, 1.99 ± 0.36, 1.95 ± 0.30 L·min -1 ), and RCP (2.81 ± 0.57, 2.86 ± 0.59, 2.84 ± 0.59) between 15, 30, and 45 W·min -1 ramps, respectively ( P > 0.05). The MRT in seconds was not affected by the amplitude of the MOD or the slope of the ramp (range 19 ± 10 s to 23 ± 20 s; P > 0.05). The mean PO at GET was not significantly affected by the amplitude of the MOD or the slope of the ramp (range 130 ± 30 W to 137 ± 30 W; P > 0.05). The PO at RCP CORR was similar for all conditions ((range 186 ± 43 W to 193 ± 47 W; P > 0.05).

CONCLUSIONS

The SRS protocol accounts for the V̇O 2 MRT when using smaller amplitude steps, and for the V̇O 2 slow component when using different ramp slopes, allowing for accurate partitioning of the exercise intensity domains in a single test.

A Ramp versus Step Transition to Constant Work Rate Exercise Decreases Steady-State Oxygen Uptake

PURPOSE

This study aimed to investigate whether a ramp-to-constant WR (rCWR) transition compared with a square-wave-to-constant WR (CWR) transition within the heavy-intensity domain can reduce metabolic instability and decrease the oxygen cost of exercise.

METHODS

Fourteen individuals performed (i) a ramp-incremental test to task failure, (ii) a 21-min CWR within the heavy-intensity domain, and (iii) an rCWR to the same WR. Oxygen uptake (V̇O 2 ), lactate concentration ([La - ]), and muscle oxygen saturation (SmO 2 ) were measured. V̇O 2 and V̇O 2 gain (V̇O 2 -G) during the first 10-min steady-state V̇O 2 were analyzed. [La - ] before, at, and after steady-state V̇O 2 and SmO 2 during the entire 21-min steady-state exercise were also examined.

RESULTS

V̇O 2 and V̇O 2 -G during rCWR (2.49 ± 0.58 L·min -1 and 10.7 ± 0.2 mL·min -1 ·W -1 , respectively) were lower ( P < 0.001) than CWR (2.57 ± 0.60 L·min -1 and 11.3 ± 0.2 mL·min -1 ·W -1 , respectively). [La - ] before and at steady-state V̇O 2 during the rCWR condition (1.94 ± 0.60 and 3.52 ± 1.19 mM, respectively) was lower than the CWR condition (3.05 ± 0.82 and 4.15 ± 1.25 mM, respectively) ( P < 0.001). [La - ] dynamics after steady-state V̇O 2 were unstable for the rCWR ( P = 0.011). SmO 2 was unstable within the CWR condition from minutes 4 to 13 ( P < 0.05).

CONCLUSIONS

The metabolic disruption caused by the initial minutes of square-wave exercise transitions is a primary contributor to metabolic instability, leading to an increased V̇O 2 -G compared with the rCWR condition approach. The reduced early reliance on anaerobic energy sources during the rCWR condition may be responsible for the lower V̇O 2 -G.

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.

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.

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.

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 ([Formula: see text]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 [Formula: see text]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.

Heart Rate Variability Thresholds: Agreement with Established Approaches and Reproducibility in Trained Females and Males

PURPOSE

To determine in trained females and males: i) the agreement between the gas exchange threshold (GET), lactate threshold 1 (LT1) and heart rate variability threshold 1 (HRVT1), as well as between the respiratory compensation point (RCP), lactate threshold 2 (LT2) and heart rate variability threshold 2 (HRVT2) and ii) the reproducibility of HRVT1 and HRVT2 during two-min incremental step protocols.

METHODS

Fifty-seven trained participants (24 females) completed a 2 min step incremental test to task failure. Nineteen participants (8 females) completed a second test to evaluate reproducibility. Gas exchange and ventilatory responses, blood lactate concentration, and RR time series were recorded to assess the oxygen consumption (V̇O2) and heart rate (HR) associated with the GET, RCP, LT1, LT2, HRVT1 and HRVT2.

RESULTS

V̇O2-GET vs V̇O2-HRVT1 and HR-GET vs HR-HRVT1 were statistically different for females (29.5 ± 4.0 vs 34.6 ± 6.1 mL·kg-1·min-1; 154 ± 11 vs 166 ± 12 bpm) and for males (33.9 ± 4.2 vs 42.7 ± 4.6 mL·kg-1·min-1; 145 ± 11 vs 165 ± 9 bpm) (p < 0.001). V̇O2 and HR at HRVT1 were greater than at LT1 (p < 0.05). V̇O2-RCP vs V̇O2-HRVT2 and HR-RCP vs HR-HRVT2 were not statistically different for females (40.1 ± 4.7 vs 39.5 ± 6.7 mL·kg-1·min-1; 177 ± 9 vs 176 ± 9 bpm) and males (48.4 ± 5.4 vs 47.8 ± 4.8 mL·kg-1·min-1; 176 ± 8 vs 175 ± 9 bpm) (p > 0.05). V̇O2 and HR responses at LT2 were similar to HRVT2 (p > 0.05). Intraclass correlation (ICC) for V̇O2-HRVT1, HR-HRVT1, V̇O2-HRVT2, and HR-HRVT2 indicated good reproducibility when comparing the two different timepoints to standard methods.

CONCLUSIONS

Whereas HRVT2 is a valid and reproducible estimate of the RCP/LT2, current approaches for HRVT1 estimation did not show good agreement with outcomes at GET and LT1.

Heavy-, Severe-, and Extreme-, but not Moderate-Intensity Exercise Increase V̇o2max and Thresholds after 6 Weeks of Training

INTRODUCTION

This study assessed the effect of individualized, domain-based exercise intensity prescription on changes in maximal oxygen uptake (V̇O2max) and submaximal thresholds.

METHODS

Eighty-four young healthy participants (42 Females, 42 Males) were randomly assigned to six age, sex, and V̇O2max-matched groups (14 participants each). Groups performed continuous cycling in the 1) moderate (MOD)-, 2) lower heavy (HVY1)-, and 3) upper heavy-intensity (HVY2)- domain; interval cycling, in the form of 4) high-intensity interval training (HIIT) in the severe-intensity domain, or 5) sprint-interval training (SIT) in the extreme-intensity domain; or no exercise for, 6) control (CON). All training groups except SIT, were work-matched. Training participants completed three sessions per week for six weeks with physiological evaluations performed at PRE, MID and POST intervention.

RESULTS

Compared to the change in V̇O2max (∆V̇O2max) in CON (0.1 ± 1.2 mL·kg-1·min-1), all training groups except MOD (1.8 ± 2.7 mL·kg-1·min-1), demonstrated a significant increase (p < 0.05). HIIT produced the highest increase (6.2 ± 2.8 mL·kg-1·min-1) followed by HVY2 (5.4 ± 2.3 mL·kg-1·min-1), SIT (4.7 ± 2.3 mL·kg-1·min-1), and HVY1 (3.3 ± 2.4 mL·kg-1·min-1), respectively. The Δ PO at the estimated lactate threshold (θLT) was similar across HVY1, HVY2, HIIT and SIT which were all greater than CON (p < 0.05). The Δ V̇O2 and Δ PO at θLT for MOD was not different from CON (p > 0.05). HIIT produced the highest Δ PO at maximal metabolic steady state, which was greater than CON, MOD, and SIT (p < 0.05).

CONCLUSIONS

This study demonstrated that i) exercise intensity is a key component determining changes in V̇O2max and submaximal thresholds and ii) exercise intensity domain-based prescription allows for a homogenous metabolic stimulus across individuals.

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.

Within- and between-day reliability and repeatability of neuromuscular function assessment in females and males

The study evaluated the reliability and repeatability of the force and surface electromyography activity (EMG) outcomes obtained through voluntary and electrically evoked contractions of knee extensors in females (n = 18) and males (n = 20) and compared these data between sexes. Maximal isometric voluntary contractions (iMVCs) of knee extensors associated with electrical stimulation of the femoral nerve were performed over 4 days (48-h interval), with the first day involving familiarization procedures, the second involving three trials (1-h interval), and the third and fourth involving just one trial. The intraclass correlation coefficient (ICC), coefficient of variation (CV), and repeatability of outcomes from within- and between-day trials were determined for each sex. Females presented lower maximal voluntary force during iMVC (iMVCForce) and associated vastus lateralis EMG activity (root mean square, RMSVL), force evoked by potentiated doublet high-frequency (Db100Force) and single stimuli (Qtw), and M-wave amplitude than males (P ≤ 0.01, partial eta squared ≥0.94). Voluntary activation (VA) and RMSVL/M-wave amplitude did not differ between sexes. iMVCForce, VA, Db100Force, Qtw, and M-wave amplitude were the most reliable outcomes in within-day trials, with similar results between sexes (ICC > 0.62; CV < 6.4%; repeatability: 12.2%-22.6%). When investigating between-day trials, the iMVCForce, VA, Db100Force, and Qtw were the most reliable (ICC > 0.66; CV < 7.5%; repeatability: 13.2%-33.45%) with similar results between sexes. In conclusion, females presented lower iMVCForce and evoked response than males. Although reliability and repeatability statistics vary between trials, data (e.g., from EMG or force signal), and sexes, most of the outcomes obtained through this technique are reliable in females and males.NEW & NOTEWORTHY Although reliability and repeatability of knee extensors vary according to the type of neuromuscular function outcome (e.g., from force or EMG responses), the trial intervals (i.e., hours or days), and the sex of the participant, most force and EMG outcomes obtained through these neuromuscular assessment protocols present ICC > 0.75, very good CV (<10%), and repeatability <25% in within- and between-day trials in both sexes.

A Single Test Protocol to Establish the Full Spectrum of Exercise Intensity Prescription

PURPOSE

We aimed to test the extended capabilities of the SRS protocol by validating its capacity to predict the power outputs for targeted metabolic rates (V̇O 2 ) and time-to-task failure ( Tlim ) within the heavy- and severe-intensity domain, respectively.

METHODS

Fourteen young individuals completed (i) an SRS protocol from which the power outputs at GET and RCP (RCP CORR ), and the work accruable above RCP CORR , defined as W ' RAMP , were derived; (ii) one heavy-intensity bout at a power output predicted to elicit a targeted V̇O 2 equidistant from GET and RCP; and (iii) four severe-intensity trials at power outputs predicted to elicit targeted Tlim at minutes 2.5, 5, 10, and 13. These severe-intensity trials were also used to compute the constant-load-derived critical power and W ´ ( W ' CONSTANT ).

RESULTS

Targeted (2.41 ± 0.52 L·min -1 ) and measured (2.43 ± 0.52 L·min -1 ) V̇O 2 at the identified heavy-intensity power output (162 ± 43 W) were not different ( P = 0.71) and substantially concordant (CCC = 0.95). Likewise, targeted and measured Tlim for the four identified severe-intensity power outputs were not different ( P > 0.05), and the aggregated coefficient of variation was 10.7% ± 8.9%. The derived power outputs at RCP CORR (192 ± 53 W) and critical power (193 ± 53 W) were not different ( P = 0.65) and highly concordant (CCC = 0.99). There were also no differences between W ' RAMP and W ' CONSTANT ( P = 0.51).

CONCLUSIONS

The SRS protocol can accurately predict power outputs to elicit discrete metabolic rates and exercise durations, thus providing, with time efficiency, a high precision for the control of the metabolic stimulus during exercise.

Sex-related differences in profiles of muscle oxygen saturation of different muscles in trained cyclists during graded cycling exercise

Although in recent years near-infrared spectroscopy has been used in many sports to monitor muscle oxygen saturation (SmO2), there is a lack of knowledge about the sex differences in SmO2 during exercise in different muscles. Our study aimed to examine SmO2 differences in muscles between female and male cyclists, during a graded cycling test and at the first and second lactate thresholds. Twenty-five trained cyclists and triathletes (15 males: 23 ± 7 yr, 1.78 ± 0.05 m, 70.2 ± 5.3 kg, and 10 females: 22 ± 5 yr, 1.64 ± 0.06 m, 58 ± 8 kg) performed a graded cycling test on the cycle ergometer. Power output and SmO2 in five muscles (dominant vastus lateralis, tibialis anterior, gastrocnemius medial, biceps femoris, and triceps brachii) were measured. Our mixed regression models showed that the interaction between power output and sex was significant for all the muscles analyzed (P < 0.001), indicating a greater decrease in SmO2 for males as power output increased. Moreover, the statistical parametric mapping analyses showed for females higher SmO2 in the middle of the test in biceps femoris (P = 0.03), gastrocnemius medial (P = 0.02), and tibialis anterior (P = 0.04). Finally, the males presented a lower SmO2 in all muscles where the second lactate threshold occurred, with greater evidence than in the first lactate threshold. In conclusion, females have higher SmO2 in all muscles, and these differences are more noticeable during the graded cycling test, such that males seem to have a greater reliance on oxygen extraction than females for a given relative intensity of exercise.NEW & NOTEWORTHY This study investigated the profiles of muscle oxygen saturation (SmO2) during incremental exercise in females and males. Females presented higher overall SmO2 than males during moderate and heavy intensity domain exercise in all muscles including muscles that are not mainly involved in pedaling (triceps brachii), from those that are stabilizers (medial gastrocnemius, tibialis anterior, and biceps femoris), to those that are related to power output production (vastus lateralis).

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.

Effect of ramp slope on intensity thresholds based on correlation properties of heart rate variability during cycling

An index of heart rate variability (HRV), detrended fluctuation analysis (DFA a1) has gathered interest as a surrogate marker of exercise intensity boundaries. The aim of this report was to examine heart rate variability threshold (HRVT) behavior across different ramp incremental (RI) slopes. Seventeen participants completed a series of three RI (15, 30, and 45 W · min-1 slopes) with monitoring of gas exchange parameters, heart rate (HR) and HRV. HRVT1 was defined as the V̇O2 or HR at which DFA a1 reached 0.75 and the HRVT2 at which these values reached 0.5. HRVTs were compared by Pearson's r, Bland-Altman analysis, ICC3,1 , ANOVA, and paired t-testing. An excellent degree of reliability was seen across all three ramps, with an ICC3,1 of 0.93 and 0.88 for the HRVT1 V̇O2 and HR, respectively, and 0.90 and 0.92 for the HRVT2 V̇O2 and HR, respectively. Correlations between HRVT1/2 of the individual ramps were high with r values 0.84-0.95 for both HR and V̇O2 . Bland-Altman differences ranged between -1.4 and 1.2 mL · kg-1  · min-1 and -2 and +2 bpm. Paired t-testing showed no mean differences between any HRVT1/2 ramp comparisons. Cycling ramp slope does not appear to affect either HRVT1 or HRVT2 in terms of HR or V̇O2 .

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 are 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 8 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 post-processing of data and provides a bank of profiles on which end-users can practice threshold identification skills with immediate feedback. In addition to including pre-laboratory and post-laboratory 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.

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.

Different ramp-incremental slopes elicit similar V̇O2max and fatigability profiles in females and males despite differences in peak power output

PURPOSE

to investigate the effects of different ramp incremental (RI) slopes on fatigability and its recovery in females and males.

METHODS

Ten females and 11 males performed RI tests with distinct slopes, in separated and randomized sessions, 15 (RI₁₅), 30 (RI₃₀), and 45 (RI₄₅) W·min^-1. Performance fatigability was assessed by femoral nerve electrical stimuli evoked during and after isometric maximal voluntary contraction (IMVC) of knee extensors at baseline and after task failure at min 0.5,1.5, 2.5, 5 and 10. Maximal oxygen uptake (V̇O₂max) and peak power output (POpeak) were also measured.

RESULTS

There were significant and similar declines from pre to post RI test in RI₁₅, RI₃₀ and RI₄₅ for IMVC (-23%; -25%; -25%, respectively; p<0.05) and potentiated single twitch (-46%; -47%; -49%; p<0.05) whereas, voluntary activation did not change (-1%; -1%; 0%; p>0.05). There were no RI condition effects, nor time × condition interaction for IMVC, potentiated single twitch and voluntary activation (all p > 0.05). V̇O₂maxwas not different amongst RI₁₅, RI₃₀ and RI₄₅ conditions (3.30, 3.29, 3.26 L·min^-1, respectively; p=0.717), but POpeak was (272, 304, 337 W, respectively; p<0.001). Overall, performance fatigability profiles were similar between sexes after the RI tests and during recovery. Additionally, during recovery, high-frequency doublets and single twitch recovered faster after RI₃₀ and RI₄₅ compared to RI₁₅, regardless of sex (all p>0.05 for sex-differences).

CONCLUSION

RI tests of different slopes that elicited similar V̇O₂max but different POpeakdid not affect the profile of performance fatigability at task failure in females and males.

An evaluation of the role of the exercise training dose for changes in exercise capacity following a standard cardiac rehabilitation program

BACKGROUND

To retrospectively characterize and compare the dose of exercise training (ET) within a large cohort of patients demonstrating different levels of improvement in exercise capacity following a cardiac rehabilitation (CR) program.

METHODS

A total of 2310 patients who completed a 12-week, center-based, guidelines-informed CR program between January 2018 and December 2019 were included in the analysis. Peak metabolic equivalents (MET_peak) were determined pre- and post-CR during which total duration (ET time) and intensity [percent of heart rate peak (%HR_peak)] of supervised ET were also obtained. Training responsiveness was quantified on the basis of changes in MET_peak from pre- to post-CR. A cluster analysis was performed to identity clusters demonstrating discrete levels of responsiveness (i.e., negative, low, moderate, high, and very-high). These were compared for several baseline and ET-derived variables which were also included in a multivariable linear regression model.

RESULTS

At pre-CR, baseline MET_peak was progressively lower with greater training responsiveness (F_(4,2305) = 44.2, P < 0.01, η²_p = 0.71). Likewise, average training duration (F_(4,2305) = 10.7 P < 0.01, η²_p = 0.02) and %HR_peak (F_(4,2305) = 25.1 P < 0.01, η²_p = 0.042) quantified during onsite ET sessions were progressively greater with greater training responsiveness. The multivariable linear regression model confirmed that baseline MET_peak, training duration and intensity during ET, BMI, and age (P < 0.001) were significant predictors of MET_peak post-CR.

CONCLUSIONS

Along with baseline MET_peak, delta BMI, and age, the dose of ET (i.e., training duration and intensity) predicts MET_peak at the conclusion of CR. A re-evaluation of current approaches for exercise intensity prescription is recommended to extend the benefits of completing CR to all patients.

A "Step-Ramp-Step" Protocol to Identify Running Speed and Power Associated with the Maximal Metabolic Steady State

PURPOSE

A previously established Step-Ramp-Step (SRS) exercise protocol was able to accurately predict the work rate associated with the maximal metabolic steady state (MMSS) in cyclists. The purpose of this study was to determine whether a modified SRS protocol could predict the running speed and power associated with the MMSS.

METHODS

Fifteen (8 male; 7 female) runners (V̇O 2max 54.5 [6.5] mL·kg -1 ·min -1 ) were recruited for this investigation composed of four to five visits. In the first visit, runners performed a moderate intensity step (MOD), an incremental exercise test, and a heavy intensity step (HVY), on a motorized treadmill. This SRS protocol was used to predict the running speed and power associated with the MMSS (i.e., the SRS-MMSS), where running power was assessed by a wearable device (Stryd) attached to each runner's shoe. Subsequent visits were used to confirm the maximal lactate steady state (MLSS) as a proxy measure of the MMSS (i.e., the MLSS-MMSS) and to validate the SRS-MMSS speed and power estimates.

RESULTS

The estimated SRS-MMSS running speed (7.2 [0.6] mph) was significantly lower than confirmed running speed at MLSS-MMSS (7.5 [0.8] mph; bias = 3.6%, P = 0.005); however, the estimated SRS-MMSS running power (241 [35] W) was not different than the MLSS-MMSS confirmed running power (240 [37] W; bias = -0.6%; P = 0.435). V̇O 2 at SRS-MMSS (3.22 [0.49] L·min -1 ) was not different than respiratory compensation point (3.26 [0.58] L·min -1 ; P = 0.430). Similarly, V̇O 2 at MLSS-MMSS (3.30 [0.54] L·min -1 ) was not different than respiratory compensation point ( P = 0.438).

CONCLUSIONS

The SRS protocol allows MMSS, as measured by MLSS, to be accurately determined using running power (Stryd), but not speed, in a single laboratory visit.

Changes in Cost of Locomotion Are Higher after Endurance Cycling Than Running When Matched for Intensity and Duration

INTRODUCTION

Cost of locomotion (C L ) has been shown to increase after endurance running and cycling bouts. The main purpose of this study was to compare, in the same participants, the effect of both modalities on C L when matched for relative intensity and duration.

METHODS

Seventeen recreational athletes performed two incremental tests in running and cycling to determine the first ventilatory threshold then two 3-h bouts of exercise at 105% of threshold, with gas exchange measurements taken for 10 min at the start, middle and end of the 3 h to calculate C L . Neuromuscular fatigue during isometric knee extensor contractions and force-velocity profile on a cycle ergometer were assessed before and immediately after the 3-h trials.

RESULTS

C L significantly increased at mid (+3.7%, P = 0.006) and end (+7.4%, P < 0.001) of exercise for cycling compared with start, whereas it did not change with time for running. Cardio-respiratory and metabolic variables changed similarly for cycling and running, therefore not explaining the time-course differences in C L between modalities. Changes in C L during cycling correlated significantly with loss of maximal force extrapolated from the force-velocity profile ( r = 0.637, P = 0.006) and changes in cadence ( r = 0.784, P < 0.001).

CONCLUSIONS

The type of locomotion influences the effects of exercise on energy cost because 3 h of exercise at the same relative intensity caused a significant increase of cycling C L , and no changes in running C L . The changes in C L in cycling are likely due, at least in part, to fatigue in the locomotor muscles.

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), VO_2max 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.

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 XX(X): 000-000, 2022-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.

Time Course of Performance Fatigability during Exercise below, at, and above the Critical Intensity in Females and Males

PURPOSE

This study aimed to investigate the time course and amplitude of performance fatigability during cycling at intensities around the maximal lactate steady state (MLSS) until task failure (TTF).

METHODS

Ten females and 11 males were evaluated in eight visits: 1) ramp incremental test; 2-3) 30-min constant power output (PO) cycling for MLSS determination; and 4-8) cycling to TTF at PO relative to the MLSS of (i) -15%, (ii) -10 W, (iii) at MLSS, and (iv) +10 W, and (v) +15%. Performance fatigability was characterized by femoral nerve electrical stimulation of knee extensors at baseline; minutes 5, 10, 20, and 30; and TTF. Oxygen uptake, blood lactate concentration, muscle oxygen saturation, and perceived exertion were evaluated.

RESULTS

Approximately 75% of the total performance fatigability occurred within 5 min of exercise, independently of exercise intensity, followed by a further change at minute 30. Contractile function declined more in males than females (all P < 0.05). At task failure, exercise duration declined from MLSS -15% to MLSS +15% (all P < 0.05), accompanied by a greater rate of decline after MLSS +15% and MLSS +10 compared with MLSS, MLSS -10 , and MLSS -15% for voluntary activation (-0.005 and -0.003 vs -0.002, -0.001 and -0.001%·min -1 , respectively) and contractile function (potentiated single twitch force, -0.013 and -0.009 vs -0.006, -0.004 and -0.004%·min -1 , respectively).

CONCLUSIONS

Whereas the time course of performance fatigability responses was similar regardless of exercise intensity and sex, the total amplitude and rate of change were affected by the distinct metabolic disturbances around the MLSS, leading to different performance fatigability etiologies at task failure.

Physiological responses to ramp-incremental cycling tests performed at three simulated altitudes: A randomized crossover trial

Hypoxia negatively impacts aerobic exercise, but exercise testing in hypoxia has not been studied comprehensively. To determine the effects of simulated altitude on the gas exchange threshold (GET), respiratory compensation point (RCP), and maximal oxygen uptake (V̇O2max), 24 participants (mean [SD]; 26 [4] years; 171.6 [9.7] cm; 69.2 [11.9] kg) acclimatized to mild altitude (~1100 m) performed three cycling ramp-incremental exercise tests (with verification stages performed at 110 % of peak power output (PPO)) in simulated altitudes of 0m (SL), 1111m (MILD), and 2222m (MOD), in a randomized order. There were significant effects of condition (i.e., fraction of inspired oxygen [(FIO2]) for GET (p=0.001), RCP (p<0.001), V̇O2max (p<0.001), and PPO (p<0.001). The V̇O2 corresponding to GET and RCP (mL·kg-1·min-1) in MOD (24.1 [4.3]; 37.3 [5.1]) were significantly lower (p<0.05) compared to SL (27.1 [4.4]; 41.8 [6.6]) and MILD (26.8 [5.7]; 40.7 [7.3]) but similar (p>0.05) between SL and MILD. For each increase in simulated altitude, V̇O2max (SL: 51.3 [7.4]; MILD: 50.0 [7.6]; MOD: 47.3 [7.1] mL·kg-1·min-1) and PPO (SL: 332 [80]; MILD: 327 [78]; SL: 316 [76] W) decreased significantly (p<0.05 for all comparisons). V̇O2max values from the verification stage were lower than those measured during the ramp-incremental test (p=0.017). Overall, a mild simulated altitude had a significant effect on V̇O2max and PPO but not GET and RCP, moderate altitude decreased all four variables, and the inclusion of a verification stage had little effect on the determination of V̇O2max in a group of young healthy adults regardless of the FIO2.

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 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 all participants 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 (V̇O₂ 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 [8 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 V̇O₂ peak (mean [SD]: -4.2 [3.7]%), peak power output (-3.3 [2.2]%), and respiratory compensation point (-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 V̇O₂ peak (r = -0.45; P = 0.047) and peak power output (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 V̇O₂ peak (66.2 [8.5] vs. 56.4 [8.8] mL·kg FFM^-1 ·min^-1 , P = 0.042) and V̇O₂ at MLSS (55.8 vs. 44.3 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. This article is protected by copyright. All rights reserved.

A single dose of dietary nitrate supplementation protects against endothelial ischemia-reperfusion injury in early postmenopausal women

The onset of menopause and accompanying changes to ovarian hormones often precedes endothelial dysfunction in women. In particular, accelerated impairments in macrovascular and microvascular function coincide with the loss of estrogen, as does impaired endothelial responses to ischemia-reperfusion (IR) injury. In healthy, early postmenopausal women (n = 12; 3.9 ± 1.5 years since menopause) we tested the hypothesis that acute dietary nitrate (NO3-) supplementation would improve endothelial function and attenuate the magnitude of endothelial dysfunction following whole-arm IR in comparison with placebo. In this randomized, double-blind, placebo-controlled, crossover study we tested participants before and after NO3--rich (BRnitrate) and NO3--depleted (BRplacebo) beetroot juice (BR) consumption, as well as following IR injury, and 15 min after IR to assess recovery. Analyses with repeated-measures general linear models revealed a condition × time interaction for brachial artery flow-mediated dilation (FMD; P = 0.04), and no interaction effect was found for the near-infrared spectroscopy-derived reperfusion slope (P = 0.86). Follow-up analysis showed a significant decline in FMD following IR injury with BRplacebo in comparison with all other timepoints (all, P < 0.05), while this decline was not present with BRnitrate (all, P > 0.05). Our findings demonstrate that a single dose of dietary NO3- minimizes IR-induced macrovascular endothelial dysfunction in healthy, early postmenopausal women, but does not improve resting macrovascular and microvascular function. Trial registration number: NCT03644472. Novelty: In healthy, early postmenopausal women, a single dose of NO3--rich BR can protect against IR-induced endothelial dysfunction. This protection may be due to nitric oxide bioactivity during IR rather than improved endothelial function prior to the IR protocol per se.

Neuromuscular and perceptual mechanisms of fatigue accompanying task failure in response to moderate-, heavy-, severe-, and extreme-intensity cycling

A comprehensive characterization of neuromuscular and perceptual mechanisms of fatigue at task failure following exercise across the entire intensity spectrum is lacking. This study evaluated the extent of peripheral and central fatigue, and corresponding perceptual attributes, at task failure following cycling within the moderate-(MOD), heavy-(HVY), severe-(SVR), and extreme-(EXT) intensity domains. After a ramp-incremental test, eleven young males performed four constant-power output trials to the limit of tolerance (T_lim) at four distinct domain-specific workloads. These trials were preceded and followed by 5-s knee-extension maximal voluntary contractions (MVC) and femoral nerve electrical stimuli to quantify peripheral and central fatigue. Additionally, perceptual measures including ratings of global fatigue, legs pain, dyspnea and perceived effort (RPE) were also collected. At T_lim, reductions in MVC were independent of intensity (P>0.05). However, peripheral fatigue was greater following EXT and SVR and progressively, but distinctively, lower following HVY and MOD (P<0.05). Central fatigue was similar after SVR, HVY, and MOD, but absent after EXT (P<0.05). At T_lim, subjective ratings of global fatigue were progressively higher with lower exercise intensities, while ratings of legs pain and dyspnea were progressively higher with higher exercise intensities. On the other hand, RPE was maximal following HVY, SVR, and EXT, but not MOD. The findings demonstrate that at T_lim the extent of peripheral fatigue is highly domain-specific whereas the extent of central fatigue is not. Sensations such as fatigue, pain, and dyspnea may integrate with mechanisms of sense of effort to determine task failure in a manner specific to each intensity domain.

The effects of pain induced by blood flow occlusion in one leg on exercise tolerance and corticospinal excitability and inhibition of the contralateral leg in males

Experiencing pain in one leg can alter exercise tolerance and neuromuscular fatigue (NMF) responses in the contralateral leg; however, the corticospinal modulations to non-local experimental pain induced by blood flow occlusion remain unknown. In three randomized visits, thirteen male participants performed 25% of isometric maximal voluntary contraction (25%IMVC) to task failure with one leg preceded by (i) 6-min rest (CON), (ii) cycling at 80% of peak power output until task failure with the contralateral leg (CYCL) or (iii) CYCL followed by blood flow occlusion (OCCL) during 25%IMVC. NMF assessments (IMVC, voluntary activation [VA] and potentiated twitch [Qtw]) were performed at baseline and task failure. During the 25%IMVC, transcranial magnetic stimulations were performed to obtain motor evoked potential (MEP), silent period (SP), and short intracortical inhibition (SICI). 25%IMVC was shortest in OCCL (105±50s) and shorter in CYCL (154±68s) than CON (219±105s) (P<0.05). IMVC declined less after OCCL (-24±19%) and CYCL (-27±18%) then CON (-35±11%) (P<0.05). Qtw declined less in OCCL (-40±25%) compared to CYCL (-50±22%) and CON (-50±21%) (P<0.05). VA was similar amongst conditions. MEP and SP increased and SICI decreased throughout the task while SP was longer for OCCL compared to CYC condition (P<0.05). The results suggest that pain in one leg diminishes contralateral limb exercise tolerance and NMF development and modulate corticospinal inhibition in males. Novelty: Pain in one leg diminished MVC and twitch force decline in the contralateral limb Experimental pain induced by blood flow occlusion may modulation corticospinal inhibition of the neural circuitries innervating the contralateral exercise limb.

Comparing muscle VO2 from near-infrared spectroscopy desaturation rate to pulmonary VO2 during cycling below, at and above the maximal lactate steady state

Muscle oxygen uptake (V̇O_2m) evaluated from changes in the near-infrared spectroscopy oxygen desaturation slope during a 5-s arterial blood flow occlusion has been proposed as an estimation of the actual V̇O_2m. However, its correspondence with pulmonary oxygen uptake (V̇O_2p) during exercise remains unknown.

PURPOSE

to investigate the V̇O_2m and V̇O_2p relationship in females and males in response to prolonged constant-load cycling exercise at different intensities.

METHODS

Eighteen participants (8 females) visited the laboratory on six occasions: 1) ramp incremental test; 2-3) 30-min constant power output (constant-PO) exercise bout to determine the maximal lactate steady state (MLSS); 4-6) constant-PO exercise bouts to task failure at (i) 15% below MLSS (MLSS_-15%); (ii) MLSS; (iii) 15% above MLSS (MLSS_+15%). V̇O_2m was estimated at baseline, at min 5, 10, 20, 30, and at task failure. V̇O_2p was continuously recorded during the constant-PO bouts.

RESULTS

V̇O_2pand V̇O_2m significantly increased from min 5 to min 30 in MLSS condition (all p < 0.05) and from min 5 to min 10 in MLSS_+15% condition (all p < 0.05). V̇O_2pand V̇O_2m were correlated (r² adj range of 0.70-0.98, all p < 0.001) amongst exercise intensities in both females and males. Additionally, both variables were also correlated when expressed as percent (r² adj range of 0.52-0.77, all p < 0.001).

CONCLUSION

V̇O_2p and V̇O_2m responses were similar when exercising below, at, and above the MLSS independently of sex. Most importantly, V̇O_2p andV̇O_2m were correlated regardless the exercise intensity and sex of the participants.

The effects of exercise intensity and duration on the relationship between the slow component of V̇O2 and peripheral fatigue

AIM

If the development of the oxygen uptake slow component (V̇O_2SC ) and muscle fatigue are related, these variables should remain coupled in a time- and intensity-dependent manner.

METHODS

16 participants (7 females) visited the laboratory on 7 separate occasions: (1) three 6-minutes moderate-intensity cycling exercise bouts proceeded by a ramp incremental test; (2-3) 30-minutes constant power output (PO) exercise bout to determine the maximal lactate steady state (MLSS); (4-7) constant-PO exercise bouts to task failure (TTF), pseudorandomized order, at (i) 15% below the PO at MLSS; (ii) 10 W below MLSS; (iii) MLSS; (iv) 10 W above MLSS (first intensity and randomized order thereafter). Neuromuscular fatigue was characterized by isometric maximal voluntary contractions and femoral nerve electrical stimulation of knee extensors to measure peripheral fatigue at baseline, at min 5, 10, 20, 30 and TTF. Pulmonary oxygen uptake (V̇O₂ ) was continuously recorded during the constant-PO bouts and V̇O_2SC was characterized based on each individual V̇O₂ kinetics during moderate transitions.

RESULTS

The development of V̇O_2SC and peripheral fatigue were correlated across time (r² adj range of 0.64-0.80) and amongst each exercise intensity (r² adj range of 0.26-0.30) (all P < .001). Also, TTF was correlated with V̇O_2SC and neuromuscular fatigue parameters (r² adj range of 0.52-0.82, all P < .001).

CONCLUSION

The V̇O_2SC and peripheral fatigue development are correlated throughout the exercise in a time- and intensity-dependent manner, suggesting that the V̇O_2SC may depend on muscle fatigue even if the mechanisms of reduced contractile function are different amongst intensities.

The Effect of Breathing Patterns Common to Competitive Swimming on Gas Exchange and Muscle Deoxygenation During Heavy-Intensity Fartlek Exercise

During competitive freestyle swimming, the change of direction requires a turn followed by ∼15 m of underwater kicking at various intensities that require a ∼5 s breath-hold (BH). Upon surfacing, breathing must be regulated, as head rotation is necessary to facilitate the breath while completing the length of the pool (∼25 s). This study compared the respiratory and muscle deoxygenation responses of regulated breathing vs. free breathing, during these 25–5 s cycles. It was hypothesized that with the addition of a BH and sprint during heavy-intensity (HVY) exercise, oxygen uptake (VO₂) and oxygen saturation (S_atO₂) would decrease, and muscle deoxygenation ([HHb]) and total hemoglobin ([Hb_tot]) would increase. Ten healthy male participants (24 ± 3 years) performed 4–6 min trials of HVY cycling in the following conditions: (1) continuous free breathing (CONLD); (2) continuous with 5 s BH every 25 s (CONLD-BH); (3) Fartlek (FLK), a 5 s sprint followed by 25 s of HVY; and (4) a combined Fartlek and BH (FLK-BH). Continuous collection of VO₂ and S_atO₂, [Hb_tot], and [HHb] via breath-by-breath gas analysis and near-infrared spectroscopy (normalized to baseline) was performed. Breathing frequency and tidal volumes were matched between CONLD and CONLD-BH and between FLK and FLK-BH. As a result, VO₂ was unchanged between CONLD (2.12 ± 0.35 L/min) and CONLD-BH (2.15 ± 0.42 L/min; p = 0.116) and between FLK (2.24 ± 0.40 L/min) and FLK-BH (2.20 ± 0.45 L/min; p = 0.861). S_atO₂ was higher in CONLD (63 ± 1.9%) than CONLD-BH (59 ± 3.3%; p < 0.001), but was unchanged between FLK (61 ± 2.2%) and FLK-BH (62 ± 3.1%; p = 0.462). Δ[Hb_tot] is higher in CONLD (3.3 ± 1.6 μM) than CONLD-BH (-2.5 ± 1.2 μM; Δ177%; p < 0.001), but was unchanged between FLK (2.0 ± 1.6 μM) and FLK-BH (0.82 ± 1.4 μM; p = 0.979). Δ[HHb] was higher in CONLD (7.3 ± 1.8μM) than CONLD-BH (7.0 ± 2.0μM; Δ4%; p = 0.011) and lower in FLK (6.7 ± 1.8μM) compared to FLK-BH (8.7 ± 2.4 μM; p < 0.001). It is suggested that the unchanged VO₂ between CONLD and CONLD-BH was supported by increased deoxygenation as reflected by decreased Δ[Hb_tot] and blunted Δ[HHb], via apneic-driven redistribution of blood flow away from working muscles, which was reflected by the decreased S_atO₂. However, the preserved VO₂ during FLK-BH vs. FLK has been underpinned by an increase in [HHb].

Methodological Reconciliation of CP and MLSS and Their Agreement with the Maximal Metabolic Steady State

The critical power (CP) and maximal lactate steady state (MLSS) are operational surrogates of the maximal metabolic steady state (MMSS). However, their concordance and their agreement with MMSS remains variable likely due to methodological factors.

PURPOSE

To compare the concordance between CP and MLSS estimated by various models and criteria and their agreement with MMSS.

METHODS

After a ramp-test, ten recreationally active males performed four-to-five severe-intensity constant-power output (PO) trials to estimate CP, and three-to-four constant-PO trials to determine MLSS and identify MMSS. CP was computed using the 3-parameter hyperbolic (CP3-hyp), 2-parameter hyperbolic (CP2-hyp), linear (CPlin), and inverse of time (CP1/Tlim) models. In addition, the model with lowest combined parameter error identified the "best-fit" CP (CPbest-fit). MLSS was determined as an increase in blood lactate concentration ≤ 1 mM during constant-PO cycling from the 5th (MLSS10-30), 10th (MLSS10-30), 15th (MLSS15-30), 20th (MLSS20-30), or 25th (MLSS25-30) to 30th minute. MMSS was identified as the greatest PO associated with the highest submaximal steady state V[Combining Dot Above]O2 (MV[Combining Dot Above]O2ss).

RESULTS

Concordance between the various CP and MLSS estimates was greatest when MLSS was identified as MLSS15-30, MLSS20-30, and MLSS25-30. The PO at MV[Combining Dot Above]O2ss was 243 ± 43 W. Of the various CP models and MLSS criteria, CP2-hyp (244 ± 46 W) and CPlin (248 ± 46 W) and MLSS15-30 and MLSS20-30 (both 245 ± 46 W), respectively displayed, on average, the greatest agreement with MV[Combining Dot Above]O2ss. Nevertheless, all CP models and MLSS criteria demonstrated some degree of inaccuracies with respect to MV[Combining Dot Above]O2ss.

CONCLUSIONS

Differences between CP and MLSS can be reconciled with optimal methods of determination. When estimating MMSS, from CP the error margin of the model-estimate should be considered. For MLSS, MLSS15-30 and MLSS20-30 demonstrated the highest degree of accuracy.

Identification of Non-Invasive Exercise Thresholds: Methods, Strategies, and an Online App

During incremental exercise, two thresholds may be identified from standard gas exchange and ventilatory measurements. The first signifies the onset of blood lactate accumulation (the lactate threshold, LT) and the second the onset of metabolic acidosis (the respiratory compensation point, RCP). The ability to explain why these thresholds occur and how they are identified, non-invasively, from pulmonary gas exchange and ventilatory variables is fundamental to the field of exercise physiology and requisite to the understanding of core concepts including exercise intensity, assessment, prescription, and performance. This review is intended as a unique and comprehensive theoretical and practical resource for instructors, clinicians, researchers, lab technicians, and students at both undergraduate and graduate levels to facilitate the teaching, comprehension, and proper non-invasive identification of exercise thresholds. Specific objectives are to: (1) explain the underlying physiology that produces the LT and RCP; (2) introduce the classic non-invasive measurements by which these thresholds are identified by connecting variable profiles to underlying physiological behaviour; (3) discuss common issues that can obscure threshold detection and strategies to identify and mitigate these challenges; and (4) introduce an online resource to facilitate learning and standard practices. Specific examples of exercise gas exchange and ventilatory data are provided throughout to illustrate these concepts and a novel online application tool designed specifically to identify the estimated LT (θ_LT) and RCP is introduced. This application is a unique platform for learners to practice skills on real exercise data and for anyone to analyze incremental exercise data for the purpose of identifying θ_LT and RCP.

What Is Moderate to Vigorous Exercise Intensity?

A variety of health benefits associated with physical activity depends upon the frequency, intensity, duration, and type of exercise. Intensity of exercise is the most elusive of these elements and yet has important implications for the health benefits and particularly cardiovascular outcomes elicited by regular physical activity. Authorities recommend that we obtain 150min of moderate to vigorous intensity physical activity (MVPA) each week. The current descriptions of moderate to vigorous intensity are not sufficient, and we wish to enhance understanding of MVPA by recognition of important boundaries that define these intensities. There are two key thresholds identified in incremental tests: ventilatory and lactate thresholds 1 and 2, which reflect boundaries related to individualized disturbance to homeostasis that are appropriate for prescribing exercise. VT2 and LT2 correspond with critical power/speed and respiratory compensation point. Moderate intensity physical activity approaches VT1 and LT1 and vigorous intensity physical activity is between the two thresholds (1 and 2). The common practice of prescribing exercise at a fixed metabolic rate (# of METs) or percentage of maximal heart rate or of maximal oxygen uptake (V̇O₂max) does not acknowledge the individual variability of these metabolic boundaries. As training adaptations occur, these boundaries will change in absolute and relative terms. Reassessment is necessary to maintain regular exercise in the moderate to vigorous intensity domains. Future research should consider using these metabolic boundaries for exercise prescription, so we will gain a better understanding of the specific physical activity induced health benefits.

Fitness Level- and Sex-related Differences in Macro- and Microvascular Responses during Reactive Hyperemia

PURPOSE

Reactive hyperemia (RH) is widely used for the investigation of macrovascular (Flow-Mediated Dilation, FMD) and microvascular (Near Infrared Spectroscopy-Vascular Occlusion Test, NIRS-VOT) function. Mixed results have been reported on fitness level- and sex-related differences in FMD outcomes, and little is known about microvascular differences in untrained and chronically trained males and females.

METHODS

Fifteen chronically trained (CT: 8 MALES, 7 FEMALES) and sixteen untrained (UT: 8 MALES, 8 FEMALES) individuals participated in this study. Aerobic fitness (V[Combining Dot Above]O2max) was assessed during a cycling incremental exercise test to volitional exhaustion. FMD and NIRS-VOT were performed simultaneously on the lower limb investigating superficial femoral artery and vastus lateralis muscle, respectively.

RESULTS

%FMD was not different between groups (CT MALES, 4.62 ± 1.42; CT FEMALES, 4.15 ± 2.23; UT MALES, 5.10 ± 2.53; CT FEMALES, 3.20 ± 1.67). Peak blood flow showed greater values in CT vs UT (p ≤ 0.0001) and MALES vs FEMALES (p = 0.032). RH blood flow AUC was greater in CT vs UT (p = 0.001). At the microvascular level, desaturation and reperfusion rates were faster in CT vs UT (p = 0.018 and p = 0.013) and MALES vs FEMALES (p = 0.011 and p = 0.005). V[Combining Dot Above]O2max was significantly correlated with reperfusion rate (p = 0.0005) but not with %FMD.

CONCLUSION

Whereas NIRS-VOT outcomes identified fitness- and sex-related differences in vascular responses, %FMD did not. However, when reactive hyperemia-related outcomes from the FMD analysis were considered, fitness- and/or sex-related differences were detected. These data highlight the importance of integrating FMD and NIRS-VOT outcomes for a more comprehensive evaluation of vascular function.

Responders and non-responders to aerobic exercise training: beyond the evaluation of V˙O2max

The evaluation of the maximal oxygen uptake ( V ˙ O 2 max ) following exercise training is the classical assessment of training effectiveness. Research has lacked in investigating whether individuals that do not respond to the training intervention ( V ˙ O 2 max ), also do not improve in other health-related parameters. We aimed to investigate the cardiovascular and metabolic adaptations (i.e., performance, body composition, blood pressure, vascular function, fasting blood markers, and resting cardiac function and morphology) to exercise training among participants who showed different levels of V ˙ O 2 max responsiveness. Healthy sedentary participants engaged in a 6-week exercise training program, three times a week. Our results showed that responders had a greater increase in peak power output, second lactate threshold, and microvascular responsiveness, whereas non-responders had a greater increase in cycling efficiency. No statistical differences were observed in body composition, blood pressure, fasting blood parameters, and resting cardiac adaptations. In conclusion, our study showed, for the first time, that in addition to the differences in the V ˙ O 2 max , a greater increase in microvascular responsiveness in responders compared to non-responders was observed. Additionally, responders and non-responders did not show differences in the adaptations on metabolic parameters. There is an increasing need for personalized training prescription, depending on the target clinical outcome.

Hypoxia equally reduces the respiratory compensation point and the NIRS-derived [HHb] breakpoint during a ramp-incremental test in young active males

This study investigated the effect of reduced inspired fraction of O₂ (FiO₂) in the correspondence between the respiratory compensation point (RCP) and the breakpoint in the near‐infrared spectroscopy‐derived deoxygenated hemoglobin signal ([HHb]_bp) during a ramp‐incremental (RI) test to exhaustion. Eleven young males performed, on two separated occasions, a RI test either in normoxia (NORM, FiO₂ = 20.9%) or hypoxia (HYPO, FiO₂ = 16%). Oxygen uptake ( V˙O₂), and [HHb] signal from the vastus lateralis muscle were continuously measured. Peak V˙O₂ (2.98 ± 0.36 vs. 3.39 ± 0.26 L min⁻¹) and PO (282 ± 29 vs. 310 ± 19 W) were lower in HYPO compared to NORM condition, respectively. The V˙O₂ and PO associated with RCP and [HHb]_bp were lower in HYPO (2.35 ± 0.24 and 2.34 ± 0.26 L min⁻¹; 198 ± 37 and 197 ± 30 W, respectively) when compared to NORM (2.75 ± 0.26 and 2.75 ± 0.28 L min⁻¹; 244 ± 29 and 241 ± 28 W, respectively) (p < .05). Within the same condition, the V˙O₂ and PO associated with RCP and [HHb]_bp were not different (p > .05). Bland–Altman plots mean average errors between RCP and [HHb]_bp were not different from zero in HYPO (0.01 L min⁻¹ and 1.1 W) and NORM (0.00 L min⁻¹ and 3.6 W) conditions. The intra‐individual changes between thresholds associated with V˙O₂ and PO in HYPO from NORM were strongly correlated (r = .626 and 0.752, p < .05). Therefore, breathing a lower FiO₂ during a RI test resulted in proportional reduction in the RCP and the [HHb]_bp in terms of V˙O₂ and PO, which further supports the notion that these physiological responses may arise from similar metabolic changes reflecting a common phenomenon.

Slight power output manipulations around the maximal lactate steady state have a similar impact on fatigue in females and males

Neuromuscular fatigue (NMF) and exercise performance are affected by exercise intensity and sex differences. However, whether slight changes in power output (PO) below and above the maximal lactate steady state (MLSS) impact NMF and subsequent performance (time to task failure, TTF) is unknown. This study compared NMF and TTF in females and males in response to exercise performed at MLSS, 10 W below (MLSS_-10) and above (MLSS₊₁₀). Twenty participants (9 females) performed three 30-min constant-PO exercise bouts followed (1-min delay) by a TTF at 80% of the peak-PO. NMF was characterized by isometric maximal voluntary contractions (IMVC) and femoral nerve electrical stimulation of knee extensors [e.g., peak torque of potentiated high-frequency (Db100) and single twitch (TwPt)] before and immediately after the constant-PO and TTF bouts. IMVC declined less after MLSS_-10 (-18 ± 10%) compared to MLSS (-26 ± 14%) and MLSS₊₁₀ (-31 ± 11%; all P < 0.05), and the Db100 decline was greater after MLSS₊₁₀ (-24 ± 14%) compared to the other intensities (MLSS_-10: -15 ± 9%; MLSS: -18 ± 11%; all P < 0.05). Females showed smaller reductions, relative to baseline, in IMVC and TwPt compared to males after constant-PO bouts (all P < 0.05), this difference being not dependent on intensity. TTF was negatively impacted by increasing the PO in the constant-PO (P < 0.001), with no differences in end-exercise NMF (P > 0.05). Slight manipulations in PO around MLSS elicited great changes in the reduction of maximal voluntary force and impairments in contractile function. Although NMF was lower in females compared to males, the changes in PO around the MLSS impacted both sexes similarly.NEW & NOTEWORTHY It is unknown whether minimum changes in power output (PO) below and above the maximal lactate steady state (MLSS) affect neuromuscular fatigue (NMF) development in females and males. The present data showed that a decrease or increase of 10 W in PO in relation to MLSS elicited lower and greater impairments in contractile function, respectively. Even though females had less of an overall decline in NMF than males, similar exercise intensity-dependent response occurred independently of sex.

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 (V̇O_2max) 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 V̇O_2max, 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 ∆V̇O_2max 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 V̇O_2max 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.

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]O_2max) 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]O_2max 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 V̇O_2max 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.

Prior exercise impairs subsequent performance in an intensity- and duration-dependent manner

Prior constant-load exercise performed for 30-min at or above maximal lactate steady state (MLSS_p) significantly impairs subsequent time-to-task failure (TTF) compared with TTF performed without prior exercise. We tested the hypothesis that TTF would decrease in relation to the intensity and the duration of prior exercise compared with a baseline TTF trial. Eleven individuals (6 males, 5 females, aged 28 ± 8 yrs) completed the following tests on a cycle ergometer (randomly assigned after MLSS_p was determined): (i) a ramp-incremental test; (ii) a baseline TTF trial performed at 80% of peak power (TTF_b); (iii) five 30-min constant-PO rides at 5% below lactate threshold (LT_-5%), halfway between LT and MLSS_p (Delta₅₀), 5% below MLSS_p (MLSS_-5%), MLSS_p, and 5% above MLSS_p (MLSS_+5%); and (iv) 15- and 45-min rides at MLSS_p (MLSS₁₅ and MLSS₄₅, respectively). Each condition was immediately followed by a TTF trial at 80% of peak power. Compared with TTF_b (330 ± 52 s), there was 8.0 ± 24.1, 23.6 ± 20.2, 41.0 ± 14.8, 52.2 ± 18.9, and 75.4 ± 7.4% reduction in TTF following LT_-5%, Delta₅₀, MLSS_-5%, MLSS_p, and MLSS_+5%, respectively. Following MLSS₁₅ and MLSS₄₅ there were 29.0 ± 20.1 and 69.4 ± 19.6% reductions in TTF, respectively (P < 0.05). It is concluded that TTF is reduced following prior exercise of varying duration at MLSS_p and at submaximal intensities below MLSS. Novelty: Prior constant-PO exercise, performed at intensities below MLSS_p, reduces subsequent TTF performance. Subsequent TTF performance is reduced in a linear fashion following an increase in the duration of constant-PO exercise at MLSS_p.

Dynamic Changes of Performance Fatigability and Muscular O2 Saturation in a 4-km Cycling Time Trial

PURPOSE

The current study characterized the performance fatigability etiology, immediately after exercise cessation, and its relation to the dynamic changes in muscle O2 saturation (SmO2) at different TT phases.

METHODS

Twelve males performed three separated TT of different distances, in a crossover counterbalanced design, until the end of the fast-start (FS, 827 ± 135 m), even-pace (EP, 3590 ± 66 m), or end-spurt (ES, 4000 m) TT phases. Performance fatigability was characterized by using isometric maximal voluntary contractions (IMVC), whereas the maximal voluntary activation (VA) and contractile function of knee extensors (e.g., peak torque of potentiated twitches [TwPt]) were evaluated using electrically evoked contractions performed before and immediately after each exercise bouts. SmO2, power output (PO), and EMG were also recorded.

RESULTS

Immediately after the FS phase, there were lower values for IMVC (-23%), VA (-8%), and TwPt (-43%) (all P < 0.001), but no further changes were measured after EP (IMVC, -28%; VA, -8%; TwPt, -38%). After the ES phase, IMVC (-34%) and TwPt (-59%) further decreased compared with the previous phases (P < 0.05). There were lower SmO2 and higher EMG/PO values during FS and ES compared with EP phase.

CONCLUSION

FS and EP phases had similar performance fatigability etiology, but ES showed further impairments in contractile function. This later finding might be due to the abrupt changes in SmO2 and EMG/PO because of the high exercise intensity during the ES, which elicited maximal decline in contractile function at the finish line.

A "Step-Ramp-Step" Protocol to Identify the Maximal Metabolic Steady State

The oxygen uptake (V[Combining Dot Above]O2) at the respiratory compensation point (RCP) closely identifies with the maximal metabolic steady state. However, the power output (PO) at RCP cannot be determined from contemporary ramp-incremental exercise protocols.

PURPOSE

This study aimed to test the efficacy of a "step-ramp-step" (SRS) cycling protocol for estimating the PO at RCP and the validity of RCP as a maximal metabolic steady-state surrogate.

METHODS

Ten heathy volunteers (5 women; age: 30 ± 7 yr; V[Combining Dot Above]O2max: 54 ± 6 mL·kg·min) performed in the following series: a moderate step transition to 100 W (MOD), ramp (30 W·min), and after 30 min of recovery, step transition to ~50% POpeak (HVY). Ventilatory and gas exchange data from the ramp were used to identify the V[Combining Dot Above]O2 at lactate threshold (LT) and RCP. The PO at LT was determined by the linear regression of the V[Combining Dot Above]O2 versus PO relationship after adjusting ramp data by the difference between the ramp PO at the steady-state V[Combining Dot Above]O2 from MOD and 100 W. Linear regression between the V[Combining Dot Above]O2-PO values associated with LT and HVY provided, by extrapolation, the PO at RCP. Participants then performed 30-min constant-power tests at the SRS-estimated RCP and 5% above this PO.

RESULTS

All participants completed 30 min of constant-power exercise at the SRS-estimated RCP achieving steady-state V[Combining Dot Above]O2 of 3176 ± 595 mL·min that was not different (P = 0.80) from the ramp-identified RCP (3095 ± 570 mL·min) and highly consistent within participants (bias = -26 mL·min, r = 0.97, coefficient of variation = 2.3% ± 2.8%). At 5% above the SRS-estimated RCP, four participants could not complete 30 min and all, but two exhibited non-steady-state responses in blood lactate and V[Combining Dot Above]O2.

CONCLUSIONS

In healthy individuals cycling at their preferred cadence, the SRS protocol and the RCP are capable of accurately predicting the PO associated with maximal metabolic steady state.