Slow component of VO2 kinetics: mechanistic bases and practical applications

Heavy-intensity priming exercise extends the V̇o2max plateau and increases peak-power output during ramp-incremental exercise

This study investigated whether a heavy-intensity priming exercise precisely prescribed within the heavy-intensity domain would lead to a greater peak-power output (POpeak) and a longer maximal oxygen uptake (V̇o2max) plateau. Twelve recreationally active adults participated in this study. Two visits were required: 1) a step-ramp-step test [ramp-incremental (RI) control], and 2) an RI test preceded by a priming exercise within the heavy-intensity domain (RI primed). A piecewise equation was used to quantify the V̇o2 plateau duration (V̇o2plateau-time). The mean response time (MRT) was computed during the RI control condition. The delta (Δ) V̇o2 slope (S; mL·min-1·W-1) and V̇o2-Y intercept (Y; mL·min-1) within the moderate-intensity domain between conditions (RI primed minus RI control) were also assessed using a novel graphical analysis. V̇o2plateau-time (P = 0.001; d = 1.27) and POpeak (P = 0.003; d = 1.08) were all greater in the RI primed. MRT (P < 0.001; d = 2.45) was shorter in the RI primed compared with the RI control. A larger ΔV̇o2plateau-time was correlated with a larger ΔMRT between conditions (r = -0.79; P = 0.002). This study demonstrated that heavy-intensity priming exercise lengthened the V̇o2plateau-time and increased POpeak. The overall faster RI-V̇o2 responses seem to be responsible for the longer V̇o2plateau-time. Specifically, a shorter MRT, but not changes in RI-V̇o2-slopes, was associated with a longer V̇o2plateau-time following priming exercise.NEW & NOTEWORTHY It remains unclear whether priming exercise extends the maximal oxygen uptake (V̇o2max) plateau and increases peak-power output (POpeak) during ramp-incremental (RI) tests. This study demonstrates that a priming exercise, precisely prescribed within the heavy-intensity domain, extends the plateau at V̇o2max and leads to a greater POpeak. Specifically, the extended V̇o2max plateau was associated with accelerated RI-V̇o2 responses.

The influence of race duration on oxygen demand, uptake and deficit in competitive cross-country skiers

PURPOSE

To measure oxygen demand, uptake, and deficits in competitive cross-country skiers during outdoor roller skiing at different competition durations, ranging from the endurance domain to the sprint domain.

METHODS

Ten competitive cross-country skiers (6 males; V ˙ O2max 78 ± 3 and 4 females; V ˙ O2max 62 ± 3 mL∙kg-1∙min-1) raced time trials consisting of 1, 2, and 4 laps in a 1.6 km racecourse in a randomized order with 35 min recovery in-between. Oxygen uptake was measured using a wearable metabolic system while oxygen demand was estimated from kinematic data (GPS and IMU) and an athlete-specific model of skiing economy. Skiing economy and V ˙ O2max was established on a separate test day using six submaximal constant-load trials at different speeds and inclines, and one maximal-effort trial on a roller-skiing treadmill.

RESULTS

Average oxygen demand was 112 ± 8%, 103 ± 7% and 98 ± 7% of V ˙ O2max during the 1 (3:37 ± 0:20 m:ss), 2 (7:36 ± 0:38 m:ss) and 4 (15:43 ± 1:26 m:ss) lap time trials, respectively, and appeared to follow an inverse relationship with time-trial duration. Average oxygen uptake was unaffected by race length (86 ± 5%, 86 ± 5%, and 86 ± 7% of V ˙ O2max, respectively). Accumulated oxygen deficit at the end of each time trial was 85 ± 13, 106 ± 32 and 158 ± 62 mL∙kg-1, while oxygen deficits per work bout was 23 ± 3, 18 ± 3 and 16 ± 3 mL∙kg-1 for the 1, 2, and 4-lap time trials, respectively.

CONCLUSION

Elite cross-country skiers adjust their pacing strategies from attaining relatively small oxygen deficits per work bout in the endurance domain, to larger deficits in the sprint domain. This indicates a shift in strategy from prioritizing stable work-economy and rate-of-recovery in the endurance domain, to maximizing power output in the sprint domain.

A Comparison of Methods to Identify the Mean Response Time of Ramp-Incremental Exercise for Exercise Prescription

Introduction: The oxygen uptake (V ˙ O2) vs power output relationship from ramp incremental exercise is used to prescribe aerobic exercise. As power output increases, there is a delay in V ˙ O2 that contributes to a misalignment of V ˙ O2 from power output; the mean response time (MRT). If the MRT is not considered in exercise prescription, ramp incremental-identified power outputs will elicit V ˙ O2 values that are higher than intended. We compared three methods of determining MRT (exponential modeling (MRTEXP), linear modeling (MRTLIN), and the steady-state method (MRTSS)) and evaluated their accuracy at predicting the V ˙ O2 associated with power outputs approximating 75% and 85% of gas exchange threshold and 15% of the difference between gas exchange threshold and maximal V ˙ O2 (Δ15). Methods: Ten males performed a 30-W∙min-1 ramp incremental and three 30-min constant power output cycle ergometer trials with intensities at 75% gas exchange threshold, 85% gas exchange threshold, and ∆15. At each intensity, the measured steady-state V ˙ O2 during each 30-min test was compared to the V ˙ O2 predicted after adjustment by each of the three MRTs. Results: For all three MRT methods, predicted V ˙ O2 was not different (p = 1.000) from the measured V ˙ O2 at 75%GET (MRTEXP, 31 mL, MRTLIN, -35 mL, MRTSS 11 mL), 85%gas exchange threshold (MRTEXP -14 mL, MRTLIN -80 mL, MRTSS -32 mL). At Δ15, predicted V ˙ O2 based on MRTEXP was not different (p = .767) from the measured V ˙ O2, but was different for MRTLIN (p < .001) and MRTSS (p = .03). Conclusion: Given that the intensity is below gas exchange threshold, all model predictions implemented from the current study matched the exercise prescription.

A verification phase adds little value to the determination of maximum oxygen uptake in well-trained adults

PURPOSE

The objective was to investigate if performing a sub-peak or supra-peak verification phase following a ramp test provides additional value for determining 'true' maximum oxygen uptake ( V ˙ O2).

METHODS

17 and 14 well-trained males and females, respectively, performed two ramp tests each followed by a verification phase. While the ramp tests were identical, the verification phase differed in power output, wherein the power output was either 95% or 105% of the peak power output from the ramp test. The recovery phase before the verification phase lasted until capillary blood lactate concentration was ≤ 4 mmol·L-1. If a V ˙ O2 plateau occurred during ramp test, the following verification phase was considered to provide no added value. If no V ˙ O2 plateau occurred and the highest V ˙ O2 ( V ˙ O2peak) during verification phase was < 97%, between 97 and 103%, or > 103% of V ˙ O2peak achieved during the ramp test, no value, potential value, and certain value were attributed to the verification phase, respectively.

RESULTS

Mean (standard deviation) V ˙ O2peak during both ramp tests was 64.5 (6.0) mL·kg-1·min-1 for males and 54.8 (6.2) mL·kg-1·min-1 for females. For the 95% verification phase, 20 tests showed either a V ˙ O2 plateau during ramp test or a verification V ˙ O2peak < 97%, indicating no value, 11 showed potential value, and 0 certain value. For the 105% verification phase, the values were 26, 5, and 0 tests, respectively.

CONCLUSION

In well-trained adults, a sub-peak verification phase might add little value in determining 'true' maximum V ˙ O2, while a supra-peak verification phase adds no value.

Energetics of sinusoidal exercise below and across critical power and the effects of fatigue

PURPOSE

Previous studies investigating sinusoidal exercise were not devoted to an analysis of its energetics and of the effects of fatigue. We aimed to determine the contribution of aerobic and anaerobic lactic metabolism to the energy balance and investigate the fatigue effects on the cardiorespiratory and metabolic responses to sinusoidal protocols, across and below critical power (CP).

METHODS

Eight males (26.6 ± 6.2 years; 75.6 ± 8.7 kg; maximum oxygen uptake 52.8 ± 7.9 ml·min-1·kg-1; CP 218 ± 13 W) underwent exhausting sinusoidal cycloergometric exercises, with sinusoid midpoint (MP) at CP (CPex) and 50 W below CP (CP-50ex). Sinusoid amplitude (AMP) and period were 50 W and 4 min, respectively. MP, AMP, and time-delay (tD) between mechanical and metabolic signals of expiratory ventilation (V ˙ E ), oxygen uptake (V ˙ O 2 ), and heart rate ( f H ) were assessed sinusoid-by-sinusoid. Blood lactate ([La-]) and rate of perceived exertion (RPE) were determined at each sinusoid.

RESULTS

V ˙ O 2 AMP was 304 ± 11 and 488 ± 36 ml·min-1 in CPex and CP-50ex, respectively. Asymmetries between rising and declining sinusoid phases occurred in CPex (36.1 ± 7.7 vs. 41.4 ± 9.7 s forV ˙ O 2 tD up and tD down, respectively; P < 0.01), with unchanged tDs.V ˙ O 2 MP and RPE increased progressively during CPex. [La-] increased by 2.1 mM in CPex but remained stable during CP-50ex. Anaerobic contribution was larger in CPex than CP-50ex.

CONCLUSION

The lower aerobic component during CPex than CP-50ex associated with lactate accumulation explained lowerV ˙ O 2 AMP in CPex. The asymmetries in CPex suggest progressive decline of muscle phosphocreatine concentration, leading to fatigue, as witnessed by RPE.

Ozone exposure limits cardiorespiratory function during maximal cycling exercise in endurance athletes

Ground-level ozone (O3) is a potent air pollutant well recognized to acutely induce adverse respiratory symptoms and impairments in pulmonary function. However, it is unclear how the hyperpnea of exercise may modulate these effects, and the subsequent consequences on exercise performance. We tested the hypothesis that pulmonary function and exercise capability would be diminished, and symptom development would be increased during peak real-world levels of O3 exposure compared with room air. Twenty aerobically trained participants [13 M, 7 F; maximal O2 uptake (V̇o2max), 64.1 ± 7.0 mL·kg-1·min-1] completed a three-visit double-blinded, randomized crossover trial. Following a screening visit, participants were exposed to 170 ppb O3 or room air (<10 ppb O3) on separate visits during exercise trials, consisting of a 25-min moderate-intensity warmup, 30-min heavy-intensity bout, and a subsequent time-to-exhaustion (TTE) performance test. No differences in O2 uptake or ventilation were observed during submaximal exercise between conditions. During the TTE test, we observed significantly lower end-exercise O2 uptake (-3.2 ± 4.3%, P = 0.004), minute ventilation (-3.2 ± 6.5%, P = 0.043), tidal volume (-3.6 ± 5.1%, P = 0.008), and a trend toward lower exercise duration in O3 compared with room air (-10.8 ± 26.5%, P = 0.092). As decreases in O2 uptake and alterations in respiratory pattern were also present at matched time segments between conditions, a limitation of oxygen transport seems likely during maximal exercise. A more comprehensive understanding of the direct mechanisms that limit oxygen transport during exercise in high-pollutant concentrations is key for mitigating performance changes.NEW & NOTEWORTHY We demonstrate that in highly trained endurance athletes, exposure to peak real-world levels of O3 air pollution (170 ppb) significantly diminishes O2 uptake along with corresponding changes in ventilation during maximal exercise. As no differences were observed during extended submaximal exercise, a combined effect of effective dose of pollution and exercise intensity on severity of responses seems likely.

Are incremental exercise relationships between rating of perceived exertion and oxygen uptake or heart rate reserve valid during steady-state exercises?

Background

Rating of perceived exertion (RPE) is considered a valid method for prescribing prolonged aerobic steady-state exercise (SSE) intensity due to its association with physiological indicators of exercise intensity, such as oxygen uptake (V̇O2) or heart rate (HR). However, these associations between psychological and physiological indicators of exercise intensity were found during graded exercise tests (GXT) but are currently used to prescribe SSE intensity even though the transferability and validity of the relationships found during GXT to SSE were not investigated. The present study aims to verify whether (a) RPE-HR or RPE-V̇O2 relations found during GXTs are valid during SSEs, and (b) the duration and intensity of SSE affect these relations.

Methods

Eight healthy and physically active males (age 22.6 ± 1.2 years) were enrolled. On the first visit, pre-exercise (during 20 min standing) and maximal (during a GXT) HR and V̇O2 values were measured. Then, on separate days, participants performed 4 SSEs on the treadmill by running at 60% and 80% of the HR reserve (HRR) for 15 and 45 min (random order). Individual linear regressions between GXTs' RPE (dependent variable) and HRR and V̇O2 reserve (V̇O2R) values (computed as the difference between maximal and pre-exercise values) were used to predict the RPE associated with %HRR (RPEHRR) and %V̇O2R (RPEV̇O2R) during the SSEs. For each relation (RPE-%HRR and RPE-%V̇O2R), a three-way factorial repeated measures ANOVA (α = 0.05) was used to assess if RPE (dependent variable) was affected by exercise modality (i.e., RPE recorded during SSE [RPESSE] or GXT-predicted), duration (i.e., 15 or 45 min), and intensity (i.e., 60% or 80% of HRR).

Results

The differences between RPESSE and GXT-predicted RPE, which were assessed by evaluating the effect of modality and its interactions with SSE intensity and duration, showed no significant differences between RPESSE and RPEHRR. However, when RPESSE was compared with RPEV̇O2R, although modality or its interactions with intensity were not significant, there was a significant (p = 0.020) interaction effect of modality and duration yielding a dissociation between changes of RPESSE and RPEV̇O2R over time. Indeed, RPESSE did not change significantly (p = 0.054) from SSE of 15 min (12.1 ± 2.0) to SSE of 45 min (13.5 ± 2.1), with a mean change of 1.4 ± 1.8, whereas RPEV̇O2R decreased significantly (p = 0.022) from SSE of 15 min (13.7 ± 3.2) to SSE of 45 min (12.4 ± 2.8), with a mean change of -1.3 ± 1.5.

Conclusion

The transferability of the individual relationships between RPE and physiological parameters found during GXT to SSE should not be assumed as shown by the results of this study. Therefore, future studies modelling how the exercise prescription method used (e.g., RPE, HR, or V̇O2) and SSE characteristics (e.g., exercise intensity, duration, or modality) affect the relationships between RPE and physiological parameters are warranted.

A Higher Kick Frequency Swimming Training Program Optimizes Swim-to-Cycle Transition in Triathlon

ABSTRACT

Ambrosini, L, Presta, V, Vitale, M, Menegatti, E, Guarnieri, A, Bianchi, V, De Munari, I, Condello, G, and Gobbi, G. A higher kick frequency swimming training program optimizes swim-to-cycle transition in triathlon. J Strength Cond Res 38(5): 976-984, 2024-The purpose of this study was to evaluate the effect of an 8-week swimming training program on biomechanical and physiological responses during a swim-to-cycle simulation. Fifteen triathletes were randomly allocated to 3 groups: a 6-beat-kick group (K6), a 4-beat-kick group (K4), and a control group (CG). Biomechanical and physiological parameters were evaluated during a 400-m swim and a 10-minute cycle segment before (Pretraining) and after (Posttraining) the program. A lower stroke frequency ( p = 0.004) and a higher stroke length ( p = 0.002) was found in K6 compared with CG at Posttraining. A reduction in the K6 emerged between Pretraining and Posttraining during cycling for heart rate ( p = 0.005), V̇O 2 ( p = 0.014), and energy expenditure ( p = 0.008). A positive association emerged between swim kick index and cycling cadence in the K6 group. The improvement in stroke frequency and length observed in the K6 group could be explained as an improvement in swimming technique. Similarly, the reduction in energy expenditure during cycling at Posttraining for the K6 group suggests an improvement in the working economy. Triathlon coaches and athletes should consider the inclusion of high swim kick into their training programs to enhance swim and cycling performance, which can ultimately lead to an improvement in the swim-to-cycle transition and the overall triathlon performance.

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.

Changes in running economy and attainable maximal oxygen consumption in response to prolonged running: The impact of training status

During prolonged running at moderate-to-high intensity, running economy (RE) deteriorates and attainable maximal oxygen consumption (VO2max) decreases. Whether these changes appear similarly in trained and untrained runners exercising at the same relative intensity is not clear. We recruited 10 trained runners (TR) and 10 active adults (AA), and compared RE and attainable VO2max before and after 1 h of running at 70% of VO2max. Submaximal VO2 increased more (p = 0.019) in AA (0.20 ± 0.13 L min-1) than in TR (0.07 ± 0.05 L min-1). Attainable VO2max decreased in AA (-0.21 ± 0.15 L min-1, p = 0.002), but remained unchanged in TR (-0.05 ± 0.10 L min-1, p = 0.18). Relative intensity (i.e., VO2/attainable VO2max), increased more (p = 0.001) in AA (8.3 ± 4.4%) than in TR (2.6 ± 1.9%). These results demonstrate that the ability to resist changes in RE and VO2max following prolonged running is superior in trained versus untrained runners, when exercising at the same relative intensity.

Metabolic and Perceptual Responses to Constant Heart Rate Exercise at Vigorous Intensities in Women

PURPOSE

This study quantified the metabolic demands (oxygen uptake (V̇O 2 )), power output adjustments, changes in the V̇O 2 /power output ratio, and perceptual responses (rating of perceived exertion (RPE)) during constant heart rate (HR) exercise performed within the vigorous intensity range (77%-95% HR peak ).

METHODS

Twelve women (mean ± SD age, 22 ± 4 yr) performed a graded exercise test to exhaustion to determine peak parameters, and three randomly ordered, constant HR trials to exhaustion or for 60 min at the lower (HR L = 77% HR peak ), middle (HR M = 86% HR peak ), and higher (HR H = 95% HR peak ) end of the vigorous intensity range. Time course of changes and patterns of responses were examined for V̇O 2 , power output, V̇O 2 /power output, and RPE for the composite and for each subject.

RESULTS

Across the HR L (time to exhaustion ( Tlim ) = 56.3 ± 9.9 min), HR M (51.8 ± 13.5 min), and HR H (27.2 ± 17.7 min) trials, V̇O 2 and power output decreased quadratically ( P < 0.05) relative to the initial value from 10% to 100% of Tlim , whereas the V̇O 2 /power output increased quadratically from 20% to 100% Tlim , and RPE increased linearly from 50% to 100% Tlim . The V̇O 2 and RPE, collapsed across time, for HR L (54.3% ± 3.3% V̇O 2peak , 11 ± 1.5 RPE) were lower than HR M (64.9% ± 4.5% V̇O 2peak , 14 ± 1.7 RPE), and both were lower than HR H (80.1% ± 4.1% V̇O 2peak , 17 ± 1.4 RPE). None of the 12 subjects at HR L , 6 at HR M , and 7 at HR H were within the vigorous V̇O 2 range.

CONCLUSIONS

The HR L was not sufficient to meet the desired metabolic intensity for vigorous exercise, whereas the middle to higher end of the range elicited a V̇O 2 within the prescribed range of only ~50%-60% of the subjects. This study indicated that exercise held constant at a percentage of HR peak cannot consistently be used to prescribe a desired metabolic stimulus.

Proof-of-concept model for instantaneous heart rate-drift correction during low and high exercise exertion

Introduction: This study aimed to model below and above anaerobic threshold exercise-induced heart rate (HR) drift, so that the corrected HR could better represent V ˙ O 2 kinetics during and after the exercise itself. Methods: Fifteen healthy subjects (age: 28 ± 5 years; V ˙ O 2 M a x : 50 ± 8 mL/kg/min; 5 females) underwent a maximal and a 30-min submaximal (80% of the anaerobic threshold) running exercises. A five-stage computational (i.e., delay block, new training impulse-calculation block, Sigmoid correction block, increase block, and decrease block) model was built to account for instantaneous HR, fitness, and age and to onset, increase, and decrease according to the exercise intensity and duration. Results: The area under the curve (AUC) of the hysteresis function, which described the differences in the maximal and submaximal exercise-induced V ˙ O 2 and HR kinetics, was significantly reduced for both maximal (26%) and submaximal (77%) exercises and consequent recoveries. Discussion: In conclusion, this model allowed HR drift instantaneous correction, which could be exploited in the future for more accurate V ˙ O 2 estimations.

The effect of advanced footwear technology on elite male marathon race speed

PURPOSE

The aim of this study was to explore the ergogenic effect of advanced footwear technology (AFT) upon world-class male marathon running speed.

METHOD

A retrospective analysis of 99 world-class male marathon runners' performances between 2012 and 2021 was undertaken, providing a sample size of 971 performances, split into two footwear groups: AFT (n = 299) and traditional (n = 672). Additionally, details regarding the year of the marathon performance and racecourse were extracted. A mixed model for repeated measures (MMRM) analysis were undertaken identifying athlete (Wald Z = 2.821; p = .005) and course (Wald Z = 4.111; p < 0.001) as significant contributors to the variance in marathon running speed and as such were included as random factors with footwear type set as a fixed factor.

RESULTS

World-class male marathon running speeds were significantly faster (p < 0.001) when running in AFT (5.441 m.s-1) when compared with traditional shoes (5.386 m.s-1) with a mean difference of 0.055 m.s-1 (95% CI 0.039-0.071 m.s-1), translating to an improvement in marathon speed of 1.0% or a 79 s improvement in marathon race time.

CONCLUSION

Our findings demonstrate an improvement in world-class male marathon running speed of 1% when running in AFT, a near identical degree of improvement to the male marathon world record ran in AFT. Whilst a 1% improvement in marathon running times associated with AFT is smaller than previously predicted utilizing laboratory-based models, this still reflects a significant degree of improvement at the elite level.

Running Critical Power and W´: Influence of the Environment, Timing and Time Trial Order

This study aimed to determine the influence of the testing environment (track vs. treadmill), time trial order (long-short vs. short-long), and timing (within-session vs. between-sessions) on the critical power (CP) and work over CP (W´), using the power metric in runners. Fifteen highly trained athletes performed three test sessions composed of two time trials of 9- and 3-min, separated by a 30-min rest period. One session was performed on a track, and two sessions on a treadmill, alternating the order of the time trials. The CP and W´ values determined on the track were significantly greater and lower than on the treadmill, respectively (p<0.001; CP≥89 W; W´≥3.7 kJ). Their degree of agreement was low (SEE CP>5%; W´>10%) and therefore was not interchangeable. There were no performance differences in the timing of the time trials (p=0.320). Lastly, performing the 9-min trial first resulted in a greater power output compared to when executed last (p<0.001; 4.9 W), although this resulted in similar CP and W´ values (Bias<5 and 10%, respectively). In conclusion, it is feasible to test CP and W´ in a single testing session, irrespective of the time trial order, although not interchangeably between track and treadmill.

Agreement between Ventilatory Thresholds and Bilaterally Measured Vastus Lateralis Muscle Oxygen Saturation Breakpoints in Trained Cyclists: Effects of Age and Performance

This study focused on comparing metabolic thresholds derived from local muscle oxygen saturation (SmO2) signals, obtained using near-infrared spectroscopy (NIRS), with global pulmonary ventilation rates measured at the mouth. It was conducted among various Age Groups within a well-trained cyclist population. Additionally, the study examined how cycling performance characteristics impact the discrepancies between ventilatory thresholds (VTs) and SmO2 breakpoints (BPs).

METHODS

Junior (n = 18) and Senior (n = 15) cyclists underwent incremental cycling tests to assess their aerobic performance and to determine aerobic (AeT) and anaerobic (AnT) threshold characteristics through pulmonary gas exchange and changes in linearity of the vastus lateralis (VL) muscle SmO2 signals. We compared the relative power (Pkg) at ventilatory thresholds (VTs) and breakpoints (BPs) for the nondominant (ND), dominant (DO), and bilaterally averaged (Avr) SmO2 during the agreement analysis. Additionally, a 30 s sprint test was performed to estimate anaerobic performance capabilities and to assess the cyclists' phenotype, defined as the ratio of P@VT2 to the highest 5 s sprint power.

RESULTS

The Pkg@BP for Avr SmO2 had higher agreement with VT values than ND and DO. Avr SmO2 Pkg@BP1 was lower (p < 0.05) than Pkg@VT1 (mean bias: 0.12 ± 0.29 W/kg; Limits of Agreement (LOA): -0.45 to 0.68 W/kg; R2 = 0.72) and mainly among Seniors (0.21 ± 0.22 W/kg; LOA: -0.22 to 0.63 W/kg); there was no difference (p > 0.05) between Avr Pkg@BP2 and Pkg@VT2 (0.03 ± 0.22 W/kg; LOA: -0.40 to 0.45 W/kg; R2 = 0.86). The bias between two methods correlated significantly with the phenotype (r = -0.385 and r = -0.515 for AeT and AnT, respectively).

CONCLUSIONS

Two breakpoints can be defined in the NIRS-captured SmO2 signal of VL, but the agreement between the two methods at the individual level was too low for interchangeable usage of those methods in the practical training process. Older cyclists generally exhibited earlier thresholds in muscle oxygenation signals compared to systemic responses, unlike younger cyclists who showed greater variability and no significant differences in this regard in bias values between the two threshold evaluation methods with no significant difference between methods. More sprinter-type cyclists tended to have systemic VT thresholds earlier than local NIRS-derived thresholds than athletes with relatively higher aerobic abilities.

Responses to Exercise at the Critical Heart Rate vs. the Power Output Associated With the Critical Heart Rate

ABSTRACT

Succi, PJ, Dinyer-McNeely, TK, Voskuil, CC, Abel, MG, Clasey, JL, and Bergstrom, HC. Responses to exercise at the critical heart rate vs. the power output associated with the critical heart rate. J Strength Cond Res 37(12): 2362-2372, 2023-This study examined the physiological (volume of oxygen consumption [V̇ o2 ], heart rate [HR], power output [PO], respiration rate [RR], muscle oxygen saturation [%SmO 2 ]), neuromuscular (electromyographic and mechanomyographic amplitude [EMG AMP and MMG AMP] and mean power frequency [EMG MPF and MMG MPF]), and perceptual (rating of perceived exertion [RPE]) responses during exercise anchored at the critical heart rate (CHR) vs. the PO associated with CHR (PCHR). Nine subjects (mean ± SD ; age = 26 ± 3 years) performed a graded exercise test and 4 constant PO trials to exhaustion at 85-100% of peak PO (PP) to derive CHR and PCHR on a cycle ergometer. Responses were recorded during trials at CHR (173 ± 9 b·min -1 , time to exhaustion [T Lim ] = 45.5 ± 20.2 minutes) and PCHR (198 ± 58 W, T Lim = 21.0 ± 17.8 minutes) and normalized to their respective values at PP in 10% intervals. There were significant ( p ≤ 0.05) mode (CHR vs. PCHR) × time (10%-100% T Lim ) interactions for all variables ( p < 0.001-0.036) except MMG AMP ( p > 0.05). Post hoc analyses indicated differences across time for CHR V̇ o2 (%change = -22 ± 16%), PCHR V̇ o2 (19 ± 5%), CHR RR (24 ± 23%), PCHR RR (45 ± 14%), CHR PO (-33 ± 11%), PCHR HR (22 ± 5%), CHR RPE (22 ± 14%), PCHR RPE (39 ± 6%), CHR %SmO 2 (41 ± 33%), PCHR %SmO 2 (-18 ± 40%), CHR EMG AMP (-13 ± 15%), PCHR EMG AMP (13 ± 13%), CHR EMG MPF (9 ± 8%), CHR MMG MPF (7 ± 11%), and PCHR MMG MPF (-3 ± 14%). The critical heart rate was more sustainable than PCHR but required adjustments in PO which traversed intensity domains and caused dissociations of the responses previously observed in exercise anchored to PO. These dissociations indicated the demands to exercise varied with anchoring scheme and provides an important consideration for practitioners prescribing endurance exercise.

Acute Oxygen Consumption Response to Fast Start High-Intensity Intermittent Exercise

The current investigation compared the acute oxygen consumption (VO2) response of two high-intensity interval exercises (HIIE), fast start (FSHIIE), and steady power (SPHIIE), which matched w prime (W') depletion. Eight cyclists completed an incremental max test and a three-minute all-out test (3MT) to determine maximal oxygen consumption (VO2max), critical power (CP), and W'. HIIE sessions consisted of 3 X 4 min intervals interspersed by 3 min of active recovery, with W' depleted by 60% (W'target) within each working interval. SPHIIE depleted the W'target consistently throughout the 3 min intervals, while FSHIIE depleted the W'target by 50% within the first minute, with the remaining 50% depleted evenly across the remainder of the interval. The paired samples t-test revealed no differences in the percentage of training time spent above 90% of VO2max (PT ≥ 90% VO2max) between SPHIIE and FSHIIE with an average of 25.20% and 26.07%, respectively. Pairwise comparisons indicated a difference between minute 1 peak VO2, minute 2, and minute 3, while no differences were present between minutes 2 and 3. The results suggest that when HIIE formats are matched based on W' expenditure, there are no differences in PT ≥ 90% VO2max or peak VO2 during each interval.

Critical power is a key threshold determining the magnitude of post-exercise hypotension in non-hypertensive young males

The effect of different exercise intensities on the magnitude of post-exercise hypotension has not been rigorously clarified with respect to the metabolic thresholds that partition discrete exercise intensity domains (i.e., critical power and the gas exchange threshold (GET)). We hypothesized that the magnitude of post-exercise hypotension would be greater following isocaloric exercise performed above versus below critical power. Twelve non-hypertensive men completed a ramp incremental exercise test to determine maximal oxygen uptake and the GET, followed by five exhaustive constant load trials to determine critical power and W' (work available above critical power). Subsequently, criterion trials were performed at four discrete intensities matched for total work performed (i.e., isocaloric) to determine the impact of exercise intensity on post-exercise hypotension: 10% above critical power (10% > CP), 10% below critical power (10% < CP), 10% above GET (10% > GET) and 10% below GET (10% < GET). The post-exercise decrease (i.e., the minimum post-exercise values) in mean arterial (10% > CP: -12.7 ± 8.3 vs. 10% < CP: v3.5 ± 2.9 mmHg), diastolic (10% > CP: -9.6 ± 9.8 vs. 10% < CP: -1.4 ± 5.0 mmHg) and systolic (10% > CP: -23.8 ± 7.0 vs. 10% < CP: -9.9 ± 4.3 mmHg) blood pressures were greater following exercise performed 10% > CP compared to all other trials (all P < 0.01). No effects of exercise intensity on the magnitude of post-exercise hypotension were observed during exercise performed below critical power (all P > 0.05). Critical power represents a threshold above which the magnitude of post-exercise hypotension is greatly augmented. NEW FINDINGS: What is the central questions of this study? What is the influence of exercise intensity on the magnitude of post-exercise hypotension with respect to metabolic thresholds? What is the main finding and its importance? The magnitude of post-exercise hypotension is greatly increased following exercise performed above critical power. However, below critical power, there was no clear effect of exercise intensity on the magnitude of post-exercise hypotension.

Prediction of Exercise Tolerance in the Severe and Extreme Intensity Domains by a Critical Power Model

This study aimed to assess the predictive capability of different critical power (CP) models on cycling exercise tolerance in the severe- and extreme-intensity domains. Nineteen cyclists (age: 23.0 ± 2.7 y) performed several time-to-exhaustion tests (Tlim) to determine CP, finite work above CP (W'), and the highest constant work rate at which maximal oxygen consumption was attained (IHIGH). Hyperbolic power-time, linear power-inverse of time, and work-time models with three predictive trials were used to determine CP and W'. Modeling with two predictive trials of the CP work-time model was also used to determine CP and W'. Actual exercise tolerance of IHIGH and intensity 5% above IHIGH (IHIGH+5%) were compared to those predicted by all CP models. Actual IHIGH (155 ± 30 s) and IHIGH+5% (120 ± 26 s) performances were not different from those predicted by all models with three predictive trials. Modeling with two predictive trials overestimated Tlim at IHIGH+5% (129 ± 33 s; p = 0.04). Bland-Altman plots of IHIGH+5% presented significant heteroscedasticity by all CP predictions, but not for IHIGH. Exercise tolerance in the severe and extreme domains can be predicted by CP derived from three predictive trials. However, this ability is impaired within the extreme domain.

Increased hip flexion gait as an exercise modality for individuals with obesity

PURPOSE

Exercise is a critical element for the management of body weight and improvement of quality of life of individuals with obesity. Due to its convenience and accessibility, running is a commonly used exercise modality to meet exercise guidelines. However, the weight-bearing component during high impacts of this exercise modality might limit the participation in exercise and reduce the effectiveness of running-based exercise interventions in individuals with obesity. The hip flexion feedback system (HFFS) assists participants in meeting specific exercise intensities by giving the participant specific increased hip flexion targets while walking on a treadmill. The resulting activity involves walking with increased hip flexion which removes the high impacts of running. The purpose of this study was to compare physiological and biomechanical parameters during an HFFS session and an independent treadmill walking/running session (IND).

METHODS

Heart rate, oxygen consumption (VO2), heart rate error, and tibia peak positive accelerations (PPA) were investigated for each condition at 40% and 60% of heart rate reserve exercise intensities.

RESULTS

VO2 was higher for IND despite no differences in heart rate. Tibia PPAs were reduced during the HFFS session. Heart rate error was reduced for HFFS during non-steady state exercise.

CONCLUSION

While demanding lower energy consumption compared to running, HFFS exercise results in lower tibia PPAs and more accurate monitoring of exercise intensity. HFFS might be a valid exercise alternative for individuals with obesity or individuals that require low-impact forces at the lower limbs.

Three weeks of mental training changes physiological outcomes during a time trial to exhaustion

Mental training (MT) can increase endurance performance. The purpose of this study was to examine the minimum dose of mental training needed to increase performance and elucidate the physiological mechanisms underlying this improvement. In a randomized between groups pre-test-post-test design, 33 participants visited the lab on 6 separate days. A VO2peak with ventilatory threshold (VT) was performed on day 1. The subsequent visits consisted of time trials to exhaustion (TTE) performed at 10% above VT. Between visit 3 and 6, the MT group (n = 16) watched a video for 10-15 min each day for 3 weeks, while the control group (CON; n = 17) did no mental training. Heart rate (HR), rate of perceived exertion (RPE), VAS scores for pain and fatigue, electromyography, and metabolic and neuromuscular data were collected and recorded during the time trials. The GRIT-S and CD-RISC 10 surveys were completed before study days 3 and 6. TTE increased significantly for MT beginning after 2 weeks (10.0 ± 13.1%) with no further change after 3 weeks (10.4 ± 13.2). TTE also significantly decreased during the last TTE for CON (-10.3 ± 12.7). VO2, ventilation, and frequency of breathing were significantly reduced in the latter stages of the TTE for MT. EMG was also significantly decreased for MT as compared for CON throughout the trial. Three weeks of mental training improves performance by reducing EMG, decreasing activation of the muscle and reducing metabolic factors during the latter stages of exercise.

Analysis of Individual V˙O2max Responses during a Cardiopulmonary Exercise Test and the Verification Phase in Physically Active Women

This study aimed to investigate the test-retest reliability, mean, and individual responses in the measurement of maximal oxygen consumption (V˙O2max) during a cardiopulmonary exercise test (CPET) and the verification phase during cycle ergometry in women. Nine women (22 ± 2 yrs, 166.0 ± 4.5 cm, 58.6 ± 7.7 kg) completed a CPET, passively rested for 5 min, and then completed a verification phase at 90% of peak power output to determine the highest V˙O2 from the CPET (V˙O2CPET) and verification phase (V˙O2verification) on 2 separate days. Analyses included a two-way repeated measures ANOVA, intraclass correlation coefficients (ICC2,1), standard errors of the measurement (SEM), minimal differences (MD), and coefficients of variation (CoV). There was no test (test 1 versus test 2) × method (CPET vs. verification phase) interaction (p = 0.896) and no main effect for method (p = 0.459). However, test 1 (39.2 mL·kg-1·min-1) was significantly higher than test 2 (38.3 mL·kg-1·min-1) (p = 0.043). The V˙O2CPET (ICC = 0.984; CoV = 1.98%; SEM = 0.77 mL·kg-1·min-1; MD = 2.14 mL·kg-1·min-1) and V˙O2verification (ICC = 0.964; CoV = 3.30%; SEM = 1.27 mL·kg-1·min-1; MD = 3.52 mL·kg-1·min-1) demonstrated "excellent" reliability. Two subjects demonstrated a test 1 V˙O2CPET that exceeded the test 2 V˙O2CPET, and one subject demonstrated a test 1 V˙O2verification that exceeded the test 2 V˙O2verification by more than the respective CPET and verification phase MD. One subject demonstrated a V˙O2CPET that exceeded the V˙O2verification, and one subject demonstrated a V˙O2verification that exceeded the V˙O2CPET by more than the MD. These results demonstrate the importance of examining the individual responses in the measurement of the V˙O2max and suggest that the MD may be a useful threshold to quantify real individual changes in V˙O2.

The fourth dimension: physiological resilience as an independent determinant of endurance exercise performance

Endurance exercise performance is known to be closely associated with the three physiological pillars of maximal O2 uptake (V ̇ O 2 max $\dot{V}_{{\rm O}_{2}{\rm max}}$ ), economy or efficiency during submaximal exercise, and the fractional utilisation ofV ̇ O 2 max $\dot{V}_{{\rm O}_{2}{\rm max}}$ (linked to metabolic/lactate threshold phenomena). However, while 'start line' values of these variables are collectively useful in predicting performance in endurance events such as the marathon, it is not widely appreciated that these variables are not static but are prone to significant deterioration as fatiguing endurance exercise proceeds. For example, the 'critical power' (CP), which is a composite of the highest achievable steady-state oxidative metabolic rate and efficiency (O2 cost per watt), may fall by an average of 10% following 2 h of heavy intensity cycle exercise. Even more striking is that the extent of this deterioration displays appreciable inter-individual variability, with changes in CP ranging from <1% to ∼32%. The mechanistic basis for such differences in fatigue resistance or 'physiological resilience' are not resolved. However, resilience may be important in explaining superlative endurance performance and it has implications for the physiological evaluation of athletes and the design of interventions to enhance performance. This article presents new information concerning the dynamic plasticity of the three 'traditional' physiological variables and argues that physiological resilience should be considered as an additional component, or fourth dimension, in models of endurance exercise performance.

Stroke volume response during prolonged exercise depends on left ventricular filling: evidence from a β-blockade study

Prolonged moderate-intensity exercise leads to a progressive upward drift in heart rate (HR) that may compromise stroke volume (SV). Alternatively, the HR drift may be related to abated SV due to impaired ventricular function. The aim of this study was to examine the effects of cardiovascular drift on left ventricular volumes and in turn SV. Thirteen healthy young males completed two 60-min cycling bouts on a semirecumbent cycle ergometer at 57% maximal oxygen consumption (V̇o2max) either under placebo condition (CON) or after ingesting a small dose of β1-blockers (BB). Measurements of HR, end-diastolic volume (EDV), and end-systolic volume were obtained by echocardiography and used to calculate SV. Other variables such as ear temperature, skin temperature, blood pressure, and blood volume were measured to assess potential changes in thermoregulatory needs and loading conditions. HR drift was successfully prevented when using BB from min 10 to min 60 (128 ± 9 to 126 ± 8 beats/min, P = 0.29) but not in CON (134 ± 10 to 148 ± 10 beats/min, P < 0.01). Conversely, during the same time, SV increased by 13% when using BB (103 ± 9 to 116 ± 7 mL, P < 0.01), whereas it was unchanged in CON (99 ± 7 to 101 ± 9 mL, P = 0.37). The SV behavior was mediated by a 4% increase in EDV in the BB condition (164 ± 18 to 170 ± 18 mL, P < 0.01), whereas no change was observed in the CON condition (162 ± 18 to 160 ± 18 mL, P = 0.23). In conclusion, blocking HR drift enhances EDV and SV during prolonged exercise. These findings suggest that SV behavior is tightly related to filling time and loading conditions of the left ventricle.

Aerobic adaptations following two iso-effort training programs: an intense continuous and a high-intensity interval

The intensity of the training stimulus and the effort exerted (regarded as an index of internal load) to complete an exercise session are driving forces for physiological processes and long-term training adaptations. This study compared the aerobic adaptations following two iso-effort, ratings of perceived exertion (RPE)-based training programs, an intense continuous (CON) and a high-intensity interval (INT). Young adults were assigned to a CON (n = 11) or an INT (n = 13) training group to perform 14 training sessions within 6 weeks. The INT group performed running bouts (9.3 ± 4.4 repetitions) at 90% of peak treadmill velocity (PTV) with bout duration equal to 1/4 of time to exhaustion at this speed (134.2 ± 27.9 s). The CONT group ran (1185.0 ± 487.6 s) at a speed corresponding to -2.5% of critical velocity (CV; 80.1% ± 3.0% of PTV). Training-sessions were executed until RPE attained 17 on the Borg scale. VO2max, PTV, CV, lactate threshold velocity (vLT), and running economy were assessed pre-, mid-, and post-training. Both CONT and INT methods increased (p < 0.05) VO2max (INT: 57.7 ± 8.1-61.41 ± 9.2; CONT: 58.1 ± 7.5-61.1 ± 6.3 mL kg-1 min-1), PTV (INT: 14.6 ± 1.8-15.7 ± 2.1; CONT: 15.0 ± 1.7-15.7 ± 1.8 km h-1), CV (INT: 11.8 ± 1.4-12.8 ± 1.8; CONT: 12.2 ± 1.6-12.9 ± 1.7 km h-1), and vLT (INT: 9.77 ± 1.1-10.8 ± 1.4; CONT: 10.4 ± 1.4-11.0 ± 1.8 km h-1) with no differences (p > 0.05) between them; running economy remained unchanged. The continuous training method, when matched for effort and executed at relatively high intensity at the upper boundaries of the heavy-intensity domain (∼80% of PTV), confers comparable aerobic adaptations to those attained after a high-intensity interval protocol following a short-term training period.

Oxygen Uptake and Bilaterally Measured Vastus Lateralis Muscle Oxygen Desaturation Kinetics in Well-Trained Endurance Cyclists

The aim of the present study was to compare and analyse the relationships between pulmonary oxygen uptake and vastus lateralis (VL) muscle oxygen desaturation kinetics measured bilaterally with Moxy NIRS sensors in trained endurance athletes. To this end, 18 trained athletes (age: 42.4 ± 7.2 years, height: 1.837 ± 0.053 m, body mass: 82.4 ± 5.7 kg) visited the laboratory on two consecutive days. On the first day, an incremental test was performed to determine the power values for the gas exchange threshold, the ventilatory threshold (VT), and V̇O_2max levels from pulmonary ventilation. On the second day, the athletes performed a constant work rate (CWR) test at the power corresponding to the VT. During the CWR test, the pulmonary ventilation characteristics, left and right VL muscle O₂ desaturation (DeSmO₂), and pedalling power were continuously recorded, and the average signal of both legs' DeSmO₂ was computed. Statistical significance was set at p ≤ 0.05. The relative response amplitudes of the primary and slow components of VL desaturation and pulmonary oxygen uptake kinetics did not differ, and the primary amplitude of muscle desaturation kinetics was strongly associated with the initial response rate of oxygen uptake. Compared with pulmonary O₂ kinetics, the primary response time of the muscle desaturation kinetics was shorter, and the slow component started earlier. There was good agreement between the time delays of the slow components describing global and local metabolic processes. Nevertheless, there was a low level of agreement between contralateral desaturation kinetic variables. The averaged DeSmO₂ signal of the two sides of the body represented the oxygen kinetics more precisely than the right- or left-leg signals separately.

How Priming Exercise Affects Oxygen Uptake Kinetics: From Underpinning Mechanisms to Endurance Performance

The observation that prior heavy or severe-intensity exercise speeds overall oxygen uptake ([Formula: see text]O₂) kinetics, termed the "priming effect", has garnered significant research attention and its underpinning mechanisms have been hotly debated. In the first part of this review, the evidence for and against (1) lactic acidosis, (2) increased muscle temperature, (3) O₂ delivery, (4) altered motor unit recruitment patterns and (5) enhanced intracellular O₂ utilisation in underpinning the priming effect is discussed. Lactic acidosis and increased muscle temperature are most likely not key determinants of the priming effect. Whilst priming increases muscle O₂ delivery, many studies have demonstrated that an increased muscle O₂ delivery is not a prerequisite for the priming effect. Motor unit recruitment patterns are altered by prior exercise, and these alterations are consistent with some of the observed changes in [Formula: see text]O₂ kinetics in humans. Enhancements in intracellular O₂ utilisation likely play a central role in mediating the priming effect, probably related to elevated mitochondrial calcium levels and parallel activation of mitochondrial enzymes at the onset of the second bout. In the latter portion of the review, the implications of priming on the parameters of the power-duration relationship are discussed. The effect of priming on subsequent endurance performance depends critically upon which phases of the [Formula: see text]O₂ response are altered. A reduced [Formula: see text]O₂ slow component or increased fundamental phase amplitude tend to increase the work performable above critical power (i.e. W´), whereas a reduction in the fundamental phase time constant following priming results in an increased critical power.

Carbohydrate intake before and during high intensity exercise with reduced muscle glycogen availability affects the speed of muscle reoxygenation and performance

Muscle glycogen state and carbohydrate (CHO) supplementation before and during exercise may impact responses to high-intensity interval training (HIIT). This study determined cardiorespiratory, substrate metabolism, muscle oxygenation, and performance when completing HIIT with or without CHO supplementation in a muscle glycogen depleted state. On two occasions, in a cross-over design, eight male cyclists performed a glycogen depletion protocol prior to HIIT during which either a 6% CHO drink (60 g.hr^-1) or placebo (%CHO, PLA) was consumed. HIIT consisted of 5 × 2 min at 80% peak power output (PPO), 3 × 10-min bouts of steady-state (SS) cycling (50, 55, 60% PPO), and a time-to-exhaustion (TTE) test. There was no difference in SS [Formula: see text], HR, substrate oxidation and gross efficiency (GE %) between CHO and PLA conditions. A faster rate of muscle reoxygenation (%. s^-1) existed in PLA after the 1st (Δ - 0.23 ± 0.22, d = 0.58, P < 0.05) and 3rd HIIT intervals (Δ - 0.34 ± 0.25, d = 1.02, P < 0.05). TTE was greater in CHO (7.1 ± 5.4 min) than PLA (2.5 ± 2.3 min, d = 0.98, P < 0.05). CHO consumption before and during exercise under reduced muscle glycogen conditions did not suppress fat oxidation, suggesting a strong regulatory role of muscle glycogen on substrate metabolism. However, CHO ingestion provided a performance benefit under intense exercise conditions commenced with reduced muscle glycogen. More research is needed to understand the significance of altered muscle oxygenation patterns during exercise.

Prescription of High-intensity Aerobic Interval Training Based on Oxygen Uptake Kinetics

Endurance training results in diverse adaptations that lead to increased performance and health benefits. A commonly measured training response is the analysis of oxygen uptake kinetics, representing the demand of a determined load (speed/work) on the cardiovascular, respiratory, and metabolic systems, providing useful information for the prescription of constant load or interval-type aerobic exercise. There is evidence that during high-intensity aerobic exercise some interventions prescribe brief interval times (<1-min), which may lead to a dissociation between the load prescribed and the oxygen uptake demanded, potentially affecting training outcomes. Therefore, this review explored the time to achieve a close association between the speed/work prescribed and the oxygen uptake demanded after the onset of high-intensity aerobic exercise. The evidence assessed revealed that at least 80% of the oxygen uptake amplitude is reached when phase II of oxygen uptake kinetics is completed (1 to 2 minutes after the onset of exercise, depending on the training status). We propose that the minimum work-time during high-intensity aerobic interval training sessions should be at least 1 minute for athletes and 2 minutes for non-athletes. This suggestion could be used by coaches, physical trainers, clinicians and sports or health scientists for the prescription of high-intensity aerobic interval training.

The effect of exercise hyperpnea on gross efficiency and anaerobic capacity estimates during a 3-min cycle time trial

This study aimed to analyze the effect of exercise-induced hyperpnea on gross efficiency (GE) and anaerobic capacity estimates during a self-paced 3-min supramaximal cycle time trial (TT). Fourteen highly trained male cyclists performed 7 × 4-min submaximal stages, a 6-min passive rest, a 3-min TT, a 5-min passive rest, and a 6-min submaximal stage. Three models were based on the 7 × 4-min linear regression extrapolation method, using 1) the conventional model (7-Y_LIN); 2) the same 7-Y_LIN model but correcting for the additional ventilatory cost (i.e., hyperpnea) (7-Y_LIN-V-cor); and 3) accounting for linearly declining GE during the TT (7-Y_LIN-D). The other three models were based on GE from the last submaximal stage, using the conventional model (GE_LAST) and the same modifications as described for 7+Y_LIN, i.e., 1) GE_LAST, 2) GE_LAST-V-cor, and 3) GE_LAST-D. The GE_LAST model generated 18% higher values of anaerobic capacity than the 7-Y_LIN model (P < 0.05). During the TT, the hyperpnea-corrected model (i.e., 7-Y_LIN-V-cor or GE_LAST-V-cor) generated, compared with the respective conventional model (i.e., 7-Y_LIN or GE_LAST), ∼0.7 percentage points lower GE and ∼11% higher anaerobic capacity (all, P < 0.05). The post-TT GE was 1.9 percentage points lower (P < 0.001) and the 7-Y_LIN-D or GE_LAST-D model generated, compared with the respective conventional model, a lower GE (∼1.0 percentage points) and ∼17% higher anaerobic capacity during the TT (all, P < 0.05). In conclusion, the correction for a declining GE due to hyperpnea during a supramaximal TT resulted in an increased required total metabolic rate and anaerobic energy expenditure compared with the conventional models.NEW & NOTEWORTHY This study demonstrates that GE declines during a 3-min supramaximal cycle TT, which is possibly related to the hyperpneic response during supramaximal exercise. The finding from this study also provides novel insight into how the increased ventilatory energy cost from exercise-induced hyperpnea contributes to decreased GE, increased required total metabolic rate, and increased anaerobic energy expenditure during supramaximal exercise. Therefore, conventional linear models for estimating anaerobic capacity are likely to generate underestimated values.

Myocardial inefficiency is an early indicator of exercise-induced myocardial fatigue

Background

The effect of prolonged, high-intensity endurance exercise on myocardial function is unclear. This study aimed to determine the left ventricular (LV) response to increased exercise duration and intensity using novel echocardiographic tools to assess myocardial work and fatigue.

Materials and methods

LV function was assessed by echocardiography before, immediately, and 24 h after a cardiopulmonary exercise test (CPET) and a 91-km mountain bike leisure race. Cardiac Troponin I (cTnI) was used to assess myocyte stress.

Results

59 healthy recreational athletes, 52 (43-59) years of age, 73% males, were included. The race was longer and of higher intensity generating higher cTnI levels compared with the CPET (p < 0.0001): Race/CPET: exercise duration: 230 (210, 245)/43 (40, 45) minutes, mean heart rate: 154 ± 10/132 ± 12 bpm, max cTnI: 77 (37, 128)/12 (7, 23) ng/L. Stroke volume and cardiac output were higher after the race than CPET (p < 0.005). The two exercises did not differ in post-exercise changes in LV ejection fraction (LVEF) or global longitudinal strain (GLS). There was an increase in global wasted work (p = 0.001) following the race and a persistent reduction in global constructive work 24 h after exercise (p = 0.003).

Conclusion

Increased exercise intensity and duration were associated with increased myocardial wasted work post-exercise, without alterations in LVEF and GLS from baseline values. These findings suggest that markers of myocardial inefficiency may precede reduction in global LV function as markers of myocardial fatigue.

Usefulness of V˙O2 Kinetics and Biomechanical Parameters as Predictors of Athlete's Performance in 800 m Running Race

Incremental tests to exhaustion have been usually employed as the “gold standard” to establish the fitness level of athletes. However, during real competition in many sport disciplines, exertion is not characterized by an increasing effort until failure. The purpose of this preliminary study was to add new evidence regarding the usability of parameters obtained from an on-field testing in 800 m running athletes. V˙O2 kinetics (mean, amplitude, phase time, and phase start time) and biomechanical parameters (velocity, stride frequency, and stride length) were analyzed in eight athletes during a maximal 800 m running race test. Our results showed that only the peak of blood lactate concentration after the 800 m test was correlated with the race time (p = 0.047). The race time was positively associated with both the phase duration and phase start time (all p-values < 0.05). Conversely, race time was negatively correlated with velocity, stride frequency, and amplitude (p-values < 0.05). Our results reveal that jointly studying the V˙O2 kinetics and biomechanical parameters during a maximal 800 m running race test is a useful tool to predict the athlete’s upcoming performance and improve the planning and control of the training process of 800 m running athletes.

The effect of severe intensity bouts on muscle oxygen saturation responses in trained cyclists

Near-infrared spectroscopy (NIRS) quantifies muscle oxygenation (SmO₂) during exercise. Muscle oxygenation response to self-paced, severe-intensity cycling remains unclear. Observing SmO₂ can provide cycling professionals with the ability to assess muscular response, helping optimize decision-making. We aimed to describe the effect of self-paced severe intensity bouts on SmO₂, measured noninvasively by a wearable NIRS sensor on the vastus lateralis (VL) muscle, and examine its reliability. We hypothesized a greater desaturation response with each bout, whereas, between trials, good reliability would be observed. Fourteen recreationally trained, and trained cyclists completed a ramp test to determine the power output (PO) at the respiratory compensation point (RCP). Athletes completed two subsequent visits of 50-minute sessions that included four severe-intensity bouts done at 5% above RCP PO. Muscle oxygenation in the VL was monitored using a wearable NIRS device. Measures included mean PO, heart-rate (HR), cadence, and SmO₂ at bout onset, during work (work SmO₂), and ΔSmO₂. The bouts were compared using a one-way repeated measures ANOVA. For significant differences, a Fisher's least square difference post-hoc analysis was used. A two-way repeated measures ANOVA was used using trial and bout as main factors. Intraclass correlations (ICC) were used to quantify relative reliability for mean work, and standard error of the measurement (SEM) was used to quantify absolute agreement of mean work SmO₂. Both PO and cadence showed no effect of bout or trial. Heart-rate at bout 2 (168 ± 8 bpm) and 4 (170 ± 7 bpm) were higher than bout 1 (160 ± 6 bpm). Onset SmO₂ (%) response significantly increased in the final two bouts of the session. Mean work SmO₂ increased across bouts, with the highest value displayed in bout 4 (36 ± 22%). ΔSmO₂ showed a smaller desaturation response during bout 4 (27 ± 10%) compared to bout 3 (31 ± 10%). Mean work SmO₂ ICC showed good reliability (ICC = 0.87), and SEM was 12% (CI 9-15%). We concluded that a non-invasive, affordable, wearable NIRS sensor demonstrated the heterogeneous muscle oxygenation response during severe intensity cycling bouts with good reliability in trained cyclists.

Respiratory Muscle Interval Training Improves Exercise Capacity in Obese Adolescents during a 3-Week In-Hospital Multidisciplinary Body Weight Reduction Program

The purpose of this study was to determine whether a novel approach of interval training targeted to the respiratory muscles (RMIT; normocapnic hyperpnea with resistance) in addition to a multidisciplinary in-hospital body weight reduction program (BWRP) was able to improve the integrative response to exercise in young patients with obesity. Nine male patients (17.9 ± 4.9 (x ± SD) years; 113.8 ± 16.3 kg) underwent 12 sessions of RMIT and eight age-and sex-matched patients underwent 12 sessions of a sham protocol (CTRL) during the same 3-week BWRP. Before and after the interventions the patients performed an incremental and a heavy-intensity constant work-rate (CWR>GET) cycling exercise to voluntary exhaustion. Body mass decreased by ~4.0 kg after both RMIT (p = 0.0001) and CTRL (p = 0.0002). Peak pulmonary O₂ uptake (V˙O₂) increased after RMIT (p = 0.02) and CTRL (p = 0.0007). During CWR>GET at ISO-time, V˙O₂ (p = 0.0007), pulmonary ventilation (p = 0.01), heart rate (p = 0.02), perceived respiratory discomfort (RPE_R; p = 0.03) and leg effort (p = 0.0003) decreased after RMIT; only RPE_R (p = 0.03) decreased after CTRL. Time to exhaustion increased after RMIT (p = 0.0003) but not after CTRL. In young patients with obesity, RMIT inserted in a 3-week BWRP reduced the cardiorespiratory burden, the metabolic cost, the perceived effort, and improved exercise tolerance during heavy-intensity cycling.

Application of V̇ o2 to the Critical Power Model to Derive the Critical V̇ o2

ABSTRACT

Succi, PJ, Dinyer, TK, Byrd, MT, Voskuil, CC, and Bergstrom, HC. Application of V̇ o2 to the critical power model to derive the critical V̇ o2 . J Strength Cond Res 36(12): 3374-3380, 2022-The purposes of this study were to (a) determine whether the critical power (CP) model could be applied to V̇ o2 to estimate the critical V̇ o2 (CV̇ o2 ) and (b) to compare the CV̇ o2 with the V̇ o2 at CP (V̇ o2 CP), the ventilatory threshold (VT), respiratory compensation point (RCP), and the CV̇ o2 without the V̇ o2 slow component (CV̇ o2 slow). Nine subjects performed a graded exercise test to exhaustion to determine V̇ o2 peak, VT, and RCP. The subjects performed 4 randomized, constant power output work bouts to exhaustion. The time to exhaustion (T Lim ), the total work (W Lim ), and the total volume of oxygen consumed with (TV̇ o2 ) and without the slow component (TV̇ o2 slow) were recorded during each trial. The linear regressions of the TV̇ o2 vs. T Lim , TV̇ o2 slow vs. T Lim , and W Lim vs. T Lim relationship were performed to derive the CV̇ o2 , CV̇ o2 slow, and CP, respectively. A 1-way repeated-measures analysis of variance ( p ≤ 0.05) with follow-up Sidak-Bonferroni corrected pairwise comparisons indicated that CV̇ o2 (42.49 ± 3.22 ml·kg -1 ·min -1 ) was greater than VT (30.80 ± 4.66 ml·kg -1 ·min -1 ; p < 0.001), RCP (36.74 ± 4.49 ml·kg -1 ·min -1 ; p = 0.001), V̇ o2 CP (36.76 ± 4.31 ml·kg -1 ·min -1 ; p < 0.001), and CV̇ o2 slow (38.26 ± 2.43 ml·kg -1 ·min -1 ; p < 0.001). However, CV̇ o2 slow was not different than V̇ o2 CP ( p = 0.140) or RCP ( p = 0.235). Thus, the CP model can be applied to V̇ o2 to derive the CV̇ o2 and theoretically is the highest metabolic steady state that can be maintained for an extended period without fatigue. Furthermore, the ability of the CV̇ o2 to quantify the metabolic cost of exercise and the inefficiency associated with the V̇ o2 slow component may provide a valuable tool for researchers and coaches to examine endurance exercise.

Deconstructing the Ergogenic Effects of Photobiomodulation: A Systematic Review and Meta-analysis of its Efficacy in Improving Mode-Specific Exercise Performance in Humans

BACKGROUND

Photobiomodulation therapy (PBMT) is defined as non-thermal electromagnetic irradiation through laser or light-emitting diode sources. In recent decades, PBMT has attracted attention as a potential preconditioning method. The current meta-analysis was conducted to assess the effectiveness of PBMT in improving mode-specific exercise performance in healthy young adults.

METHODS

A computerized literature search was conducted, ending on 15 May 2022. The databases searched were PubMed, Cochrane Central Register of Controlled Trials, Embase, SPORTDiscus, and the Physiotherapy Evidence Database. Inclusion/exclusion criteria limited articles to crossover, double-blind, placebo-controlled studies investigating the PBMT effects as a preconditioning method. The included trials were synthesized according to exercise mode (single-joint, cycling, running, and swimming). All results were combined using the standardized mean differences (SMDs) method and the 95% confidence intervals (CIs) were described.

RESULTS

A total of 37 individual studies, employing 78 exercise performance measurements in 586 participants, were included in the analyses. In single-joint exercises, PBMT improved muscle endurance performance (SMD 0.27, 95% CI 0.12-0.41; p < 0.01) but not muscle strength performance (p = 0.92). In cycling, PBMT improved time to exhaustion performance (SMD 0.35, 95% CI 0.10-0.59; p < 0.01) but had no effect on all-out sprint performance (p = 0.96). Similarly, PBMT had no effect on time to exhaustion (p = 0.10), time-trial (p = 0.61), or repeated-sprint (p = 0.37) performance in running and no effect on time-trial performance in swimming (p = 0.81).

CONCLUSION

PBMT improves muscle endurance performance in single-joint exercises and time to exhaustion performance in cycling but is not effective for muscle strength performance in single-joint exercises, running, or swimming performance metrics.

Physiological Responses and Performance During a 3-Minute Cycle Time Trial: Standard Paced Versus All-Out Paced

PURPOSE

To compare performance and physiological responses between a standard-paced 3-minute time trial (TTSP, ie, pacing based on normal intention) and a consistently all-out-paced 3-minute time trial (TTAOP).

METHODS

Sixteen well-trained male cyclists completed the TTSP and TTAOP, on separate days of testing, on a cycling ergometer with power output and respiratory variables measured. Time trials were preceded by 7 × 4-minute submaximal stages of increasing intensity with the linear relationship between power output and metabolic rate used to estimate the contribution from aerobic and anaerobic energy resources. The time course of anaerobic and aerobic contributions to power output was analyzed using statistical parametric mapping.

RESULTS

Mean power output was not different between the 2 pacing strategies (TTSP = 417 [43] W, TTAOP = 423 [41] W; P = 0.158). TTAOP resulted in higher peak power output (P < .001), mean ventilation rate (P < .001), mean heart rate (P = .044), peak accumulated anaerobically attributable work (P = .026), post-time-trial blood lactate concentration (P = .035), and rating of perceived exertion (P = .036). Statistical parametric mapping revealed a higher anaerobic contribution to power output during the first ∼30 seconds and a lower contribution between ∼90 and 170 seconds for TTAOP than TTSP. The aerobic contribution to power output was higher between ∼55 and 75 seconds for TTAOP.

CONCLUSIONS

Although there was no significant difference in performance (ie, mean power output) between the 2 pacing strategies, differences were found in the distribution of anaerobically and aerobically attributable power output. This implies that athletes can pace a 3-minute maximal effort very differently but achieve the same result.

Effects of Exercise Training Intensity and Duration on Skeletal Muscle Capillarization in Healthy Subjects: A Meta-analysis

PURPOSE

This study aimed to investigate the effect of intensity and duration of continuous and interval exercise training on capillarization in skeletal muscle of healthy adults.

METHODS

PubMed and Web of Science were searched from inception to June 2021. Eligibility criteria for studies were endurance exercise training >2 wk in healthy adults, and the capillary to fiber ratio (C:F) and/or capillary density (CD) reported. Meta-analyses were performed, and subsequent subgroup analyses were conducted by the characteristics of participants and training scheme.

RESULTS

Fifty-seven trials from 38 studies were included (10%/90%, athletic/sedentary). C:F was measured in 391 subjects from 47 trials, whereas CD was measured in 428 subjects from 50 trials. Exercise training increased C:F (mean difference, 0.33 (95% confidence interval, 0.30-0.37)) with low heterogeneity ( I2 = 45.08%) and CD (mean difference, 49.8 (36.9-62.6) capillaries per millimeter squared) with moderate heterogeneity ( I2 = 68.82%). Compared with low-intensity training (<50% of maximal oxygen consumption (V̇O 2max )), 21% higher relative change in C:F was observed after continuous moderate-intensity training (50%-80% of V̇O 2max ) and 54% higher change after interval training with high intensity (80%-100% of V̇O 2max ) in sedentary subjects. The magnitude of capillary growth was not dependent on training intervention duration. In already trained subjects, no additional increase in capillarization was observed with various types of training.

CONCLUSIONS

In sedentary subjects, continuous moderate-intensity training and interval training with high intensity lead to increases in capillarization, whereas low-intensity training has less effect. Within the time frame studied, no effect on capillarization was established regarding training duration in sedentary subjects. The meta-analysis highlights the need for further studies in athlete groups to discern if increased capillarization can be obtained, and if so, which combination is optimal (time vs intensity).

Prolonged mean response time in older adults with cardiovascular risk compared to healthy older adults

Background

During incremental exercise (Inc-Ex), the mean response time (MRT) of oxygen uptake (V̇O₂) represents the time delay before changes in muscle V̇O₂ reflect at the mouth level. MRT calculation by linear regression or monoexponential (τ’) fitting of V̇O₂ data are known to be highly variable, and a combination of incremental and constant load exercise (CL-Ex) is more reproducible.

Methods

We evaluated MRT in older adults using linear regression and combination methods. We recruited 20 healthy adults (male: 9, 69.4 ± 6.8 years) and 10 cardiovascular risk subjects (male: 8, 73.0 ± 8.8 years). On day 1, they performed Inc-Ex using a 10W/min ramp protocol, for determination of the ventilatory anaerobic threshold (VAT) using the V-slope method. On day 2, they performed Inc-Ex to VAT exercise intensity and CL-Ex for 25min total. The MRT was calculated from the CL-Ex V̇O₂ average and the time at equivalent V̇O₂ in the Inc-Ex. We also assessed the amount of physical activity using the International Physical Activity Questionnaire short form (IPAQ-SF).

Results

The MRT of healthy participants and those at cardiovascular risk were 49.2 ± 36.3 vs. 83.6 ± 45.4s (p = 0.033). Total physical activity in the IPAQ-SF was inversely correlated with MRT.

Conclusion

The MRT was significantly prolonged in cardiovascular risk participants compared to healthy participants, possibly related to the amount of daily physical activity. Individual MRT may be useful for adjustment of exercise intensity, but this should also be based on daily physical activity and individual condition during exercise.

Prolonged cycling reduces power output at the moderate-to-heavy intensity transition

Purpose

To determine the effect of prolonged exercise on moderate-to-heavy intensity transition power output and heart rate.

Methods

Fourteen endurance-trained cyclists and triathletes took part in the present investigation (13 males, 1 female, V·O₂peak 59.9 ± 6.8 mL^.kg^−1.min⁻¹). Following a characterisation trial, participants undertook a five-stage incremental step test to determine the power output and heart rate at the moderate-to-heavy intensity transition before and after two hours of cycling at 90% of the estimated power output at first ventilatory threshold (VT₁).

Results

Power output at the moderate-to-heavy intensity transition significantly decreased following acute prolonged exercise when determined using expired gases (VT₁, 217 ± 42 W vs. 196 ± 42 W, P < 0.0001) and blood lactate concentrations (LoglogLT, 212 ± 47 W vs. 190 ± 47 W, P = 0.004). This was attributable to loss of efficiency (VT₁, -8 ± 10 W; LoglogLT, − 7 ± 9 W) and rates of metabolic energy expenditure at the transition (VT₁, − 14 ± 11 W; LoglogLT, − 15 ± 22 W). The heart rate associated with the moderate-to-heavy intensity transition increased following acute prolonged exercise (VT_1, 142 ± 9 beats^.min⁻¹ vs. 151 ± 12 beats^.min⁻¹, P < 0.001; LoglogLT, 140 ± 13 beats^.min⁻¹ vs. 150 ± 15 beats^.min⁻¹, P = 0.006).

Conclusion

These results demonstrate the external work output at the moderate-to-heavy intensity transition decreases during prolonged exercise due to decreased efficiency and rates of metabolic energy expenditure, but the associated heart rate increases. Therefore, individual assessments of athlete ‘durability’ are warranted.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-022-05036-9.

A mathematical model for predicting cardiovascular responses at rest and during exercise in demanding environmental conditions

The present research describes the development and validation of a cardiovascular model (CVR Model) for use in conjunction with advanced thermophysiological models, where usually only a total cardiac output is estimated. The CVR Model detailed herein estimates cardio-dynamic parameters (changes in cardiac output, stroke volume, and heart rate), regional blood flow, and muscle oxygen extraction, in response to rest and physical workloads, across a range of ages and aerobic fitness levels, as well as during exposure to heat, dehydration, and altitude. The model development strategy was to first establish basic resting and exercise predictions for cardio-dynamic parameters in an "ideal" environment (cool, sea level, and hydrated person). This basic model was then advanced for increasing levels of altitude, heat strain, and dehydration, using meta-analysis and reaggregation of published data. Using the estimated altitude- and heat-induced changes in maximum oxygen extraction and maximum cardiac output, the decline in maximum oxygen consumption at high altitude and in the heat was also modeled. A validation of predicted cardiovascular strain using heart rate was conducted using a dataset of 101 heterogeneous individuals (1,371 data points) during rest and exercise in the heat and at altitude, demonstrating that the CVR Model performs well (R² = 0.82-0.84) in predicting cardiovascular strain, particularly at a group mean level (R² = 0.97). The development of the CVR Model is aimed at providing the Fiala thermal Physiology & Comfort (FPC) Model and other complex thermophysiological models with improved estimations of cardiac strain and exercise tolerance, across a range of individuals during acute exposure to environmental stressors.NEW & NOTEWORTHY The present research promotes the adaption of thermophysiological modeling to the estimation of cardiovascular strain in individuals exercising under acute environmental stress. Integration with advanced models of human thermoregulation opens doors for detailed numerical analysis of athletes' performance and physiology during exercise, occupational safety, and individual work tolerability. The research provides a simple-to-validate metric of cardiovascular function (heart rate), as well as a method to evaluate key principles influencing exercise- and thermoregulation in humans.

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 V˙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 V˙O2p kinetics in transplanted patients and suggest that the slower, V˙O2p kinetics is mainly caused by the impairment of peripherals exchanges likely due to the immunosuppressive medications and disuse.

Lactate Thresholds and the Simulation of Human Energy Metabolism: Contributions by the Cologne Sports Medicine Group in the 1970s and 1980s

Today, researchers, practitioners, and physicians measure the concentration of lactate during a graded exercise test to determine thresholds related to the maximal lactate steady state (maxLass) as a sensitive measure of endurance capacity. In the 1970s and 1980s, a group of Cologne-based researchers around Wildor Hollmann, Alois Mader, and Hermann Heck developed the methodology for systematic lactate testing and introduced a 4 mmol^.L⁻¹ lactate threshold. Later, they also developed the concept of the maxLass, and Mader designed a sophisticated mathematical model of human energy metabolism during exercise. Mader`s model simulates metabolic responses to exercise based on individual variables such as maximum oxygen uptake (V˙O_2max) and the maximal rate of lactate formation (ν_La.max). Mader’s model predicts that the ν_La.max reduces the power at the anaerobic threshold and endurance performance but that a high ν_La.max is required for events with high power outputs in elite athletes. Mader’s model also assumed before the millennium that the rate of fat oxidation is explained by the difference between glycolytic pyruvate synthesis and the actual rate of pyruvate oxidation which is consistent with current opinion. Mader’s model also simulated the V˙O_2max slow component in the mid-1980s. Unfortunately, several landmark studies by the Cologne group were only published in German, and as a result, contributions by the Cologne group are under-appreciated in the English-speaking world. This narrative review aims to introduce key contributions of the Cologne group to human metabolism research especially for readers who do not speak German.

Effects of Different Durations at Fixed Intensity Exercise on Internal Load and Recovery-A Feasibility Pilot Study on Duration as an Independent Variable for Exercise Prescription

Duration is a rarely investigated marker of exercise prescription. The aim of this study was to test the feasibility of the methodological approach, assessing effects of different duration constant-load exercise (CLE) on physiological responses (internal load) and recovery kinetics. Seven subjects performed an incremental exercise (IE) test, one maximal duration CLE at 77.6 ± 4.8% V˙O2max, and CLE's at 20%, 40%, and 70% of maximum duration. Heart rate (HR), blood lactate (La), and glucose (Glu) concentrations were measured. Before, 4, 24, and 48 h after CLE's, submaximal IE tests were performed. HR variability (HRV) was assessed in orthostatic tests (OT). Rating of perceived exertion (RPE) was obtained during all tests. CLE's were performed at 182 ± 27 W. HR_peak, La_peak, V˙Epeak, and RPE_peak were significantly higher in CLE's with longer duration. No significant differences were found between CLE's for recovery kinetics for HR, La, and Glu in the submaximal IE and for HRV or OT. Despite no significant differences, recovery kinetics were found as expected, indicating the feasibility of the applied methods. Maximum tests and recovery tests closer to CLE's termination are suggested to better display recovery kinetics. These findings are a first step to prescription of exercise by both intensity and duration on an individual basis.

Influence of current physical exercise on the relationship between aging and episodic memory and fluid intelligence

The present study examined the effects of current physical exercise and age on episodic memory and fluid intelligence, assessed with a free-recall task and the Culture Fair Intelligence Test (Cattell, 1963) respectively, while statistically controlling for other cognitive reserve factors (educational level, leisure activities, and vocabulary level). Two hundred and eight participants aged 20 to 85 participated in the study. Physical exercise level was indexed by weekly frequency over the last 12 months using self-reported measurement (from none to 4 times a week). Overall, results show a beneficial effect of physical exercise especially from a weekly practice of 2 times, and significant interaction between physical exercise and age on episodic memory and fluid intelligence capacities indicating a reduced effect of age in more physically active participants. These results reinforce the view that physical exercise is a strong and specific reserve factor that reduces decline in some cognitive functions during aging.

Determination of Critical Power Using Different Possible Approaches among Endurance Athletes: A Review

Critical power represents an important parameter of aerobic function and is the highest average effort that can be sustained for a period of time without fatigue. Critical power is determined mainly in the laboratory. Many different approaches have been applied in testing methods, and it is a difficult task to determine which testing protocol it the most suitable. This review aims to evaluate all possible tests on bicycle ergometers or bicycles used to estimate critical power and to compare them. A literature search was conducted in four databases (PubMed, Scopus, SPORTDiscus, and Web of Science) published from 2012 to 2022 and followed the PRISMA guidelines to process the review. Twenty-one articles met the eligibility criteria: records with trained or experienced endurance athletes (adults > 18), bicycle ergometer, a description of the testing protocol, and comparison of the tests. We found that the most widely used tests were the 3-min all-out tests set in a linear mode and the traditional protocol time to exhaustion. Some other alternatives could have been used but were not as regular. To summarize, the testing methods offered two main approaches in the laboratory (time to exhaustion test andthe 3-min all-out test with different protocols) and approach in the field, which is not yet completely standardized.

Oxygen uptake kinetics and ventilatory and metabolic parameters do not differ between moderate-intensity front crawl and breaststroke swimming

Pulmonary oxygen uptake ( V ̇ O 2 ) kinetics have been well studied during land-based exercise. However, less is known about V ̇ O 2 kinetics during swimming exercise and comparisons between strokes is non-existent. We aimed to characterize and compare the V ̇ O 2 kinetics, ventilatory,e and metabolic response to constant velocity moderate-intensity freely breathing front crawl (FC) and breaststroke (BR) swimming in a swimming flume. These two strokes reflect predominantly upper body versus lower body modes of swimming locomotion, respectively. Eight trained swimmers (4 females, 20 ± 1 years, 1.74 ± 0.06 m; 66.8 ± 6.3 kg) attended 5-6 laboratory-based swimming sessions. The first two trials determined FC and BR V ̇ O 2 max and the ventilatory threshold (VT), respectively, during progressive intensity swimming to the limit of tolerance. Subsequent trials involved counterbalanced FC and BR transitions from prone floating to constant velocity moderate-intensity swimming at 80% of the velocity at VT (vVT), separated by 30-min recovery. Breath-by-breath changes in pulmonary gas exchange and ventilation were measured continuously using a snorkel and aquatic metabolic cart system. The ventilatory and metabolic responses were similar (p > 0.05) between strokes during maximal velocity swimming, however, vVT and maximal velocity were slower (p < 0.05) during BR . During moderate-intensity swimming, V ̇ O 2 kinetics, ventilatory and metabolic parameters were similar (p > 0.05) between strokes. In conclusion, when breathing ad libitum, V ̇ O 2 kinetics during moderate-intensity constant velocity swimming, and ventilatory and metabolic responses during moderate-intensity and maximal velocity swimming, are similar between FC and BR strokes.