Critical power as a measure of physical work capacity and anaerobic threshold

The influence of sex, hemoglobin mass, and skeletal muscle characteristics on cycling critical power

Critical power (CP) represents an important threshold for exercise performance and fatiguability. We sought to determine the extent to which sex, hemoglobin mass (Hbmass), and skeletal muscle characteristics influence CP. Before CP determination (i.e., 3-5 constant work rate trials to task failure), Hbmass and skeletal muscle oxidative capacity (τ) were measured and vastus lateralis (VL) muscle biopsy samples were collected from 12 females and 12 males matched for aerobic fitness relative to fat-free mass (FFM) [means (SD); V̇o2max: 59.2 (7.7) vs. 59.5 (7.1) mL·kg·FFM-1·min-1, respectively]. Males had a significantly greater CP than females in absolute units [225 (28) vs. 170 (43) W; P = 0.001] but not relative to body mass [3.0 (0.6) vs. 2.7 (0.6) W·kg·BM-1; P = 0.267] or FFM [3.6 (0.7) vs. 3.7 (0.8) W·kg·FFM-1; P = 0.622]. Males had significantly greater W' (P ≤ 0.030) and greater Hbmass (P ≤ 0.016) than females, regardless of the normalization approach; however, there were no differences in mitochondrial protein content (P = 0.375), τ (P = 0.603), or MHC I proportionality (P = 0.574) between males and females. Whether it was expressed in absolute or relative units, CP was positively correlated with Hbmass (0.444 ≤ r ≤ 0.695; P < 0.05), mitochondrial protein content (0.413 ≤ r ≤ 0.708; P < 0.05), and MHC I proportionality (0.506 ≤ r ≤ 0.585; P < 0.05), and negatively correlated with τ when expressed in relative units only (-0.588 ≤ r ≤ -0.527; P < 0.05). Overall, CP was independent of sex, but variability in CP was related to Hbmass and skeletal muscle characteristics. The extent to which manipulations in these physiological parameters influence CP warrants further investigation to better understand the factors underpinning CP.NEW & NOTEWORTHY In males and females matched for aerobic fitness [maximal oxygen uptake normalized to fat-free mass (FFM)], absolute critical power (CP) was greater in males, but relative CP (per kilogram body mass or FFM) was similar between sexes. CP correlated with hemoglobin mass, mitochondrial protein content, myosin heavy chain type I proportion, and skeletal muscle oxidative capacity. These findings demonstrate the importance of matching sexes for aerobic fitness, but further experiments are needed to determine causality.

Skeletal muscle mitochondrial correlates of critical power and W' in healthy active individuals

The asymptote (critical power; CP) and curvature constant (W') of the hyperbolic power-duration relationship can predict performance within the severe-intensity exercise domain. However, the extent to which these parameters relate to skeletal muscle mitochondrial content and respiratory function is not known. Fifteen males (peak O2 uptake, 52.2 ± 8.7 mL kg-1 min-1; peak work rate, 366 ± 40 W; and gas exchange threshold, 162 ± 41 W) performed three to five constant-load tests to task failure for the determination of CP (246 ± 44 W) and W' (18.6 ± 4.1 kJ). Skeletal muscle biopsies were obtained from the vastus lateralis to determine citrate synthase (CS) activity, as a marker of mitochondrial content, and the ADP-stimulated respiration (P) and maximal electron transfer (E) through mitochondrial complexes (C) I-IV. The CP was positively correlated with CS activity (absolute CP, r = 0.881, P < 0.001; relative CP, r = 0.751, P = 0.001). The W' was not correlated with CS activity (P > 0.05). Relative CP was positively correlated with mass-corrected CI + IIE (r = 0.659, P = 0.038), with absolute CP being inversely correlated with CS activity-corrected CIVE (r = -0.701, P = 0.024). Relative W' was positively correlated with CS activity-corrected CI + IIP (r = 0.713, P = 0.021) and the phosphorylation control ratio (r = 0.661, P = 0.038). There were no further correlations between CP or W' and mitochondrial respiratory variables. These findings support the assertion that skeletal muscle mitochondrial oxidative capacity is positively associated with CP and that this relationship is strongly determined by mitochondrial content.

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.

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

INTRODUCTION

Alcohol ingestion influences metabolism during a subsequent exercise session, as evidenced by increased blood lactate concentration during fixed-intensity exercise. Therefore, augmented blood concentrations of alcohol may interfere with the anaerobic metabolism during high-intensity, short-duration exercise bout, thereby leading to impaired athletic performance.

OBJECTIVE

This study investigated whether the acute ingestion of alcohol as ethanol modulates performance parameters derived from the power-duration relationship in a 3-min all-out cycling test that allows for identifying the power output related to heavy and severe exercise intensities.

METHODS

Twenty-four recreationally active cyclists (16 men and 8 women) ingested a beverage containing either 0.4 g ethanol.kg-1 body mass (EtOH) or a placebo (PLA) solution. Thirty minutes following ingestion, they completed a 3-min all-out test to measure power output and determine the end-test power (EP) and the work done above EP (WEP).

RESULTS

Alcohol ingestion decreased WEP by 16% (EtOH: 5.6 ± 2.5 kJ vs. PLA: 6.7 ± 2.4 kJ; P = .003) but did not change EP (EtOH: 211 ± 44 W vs. PLA: 212 ± 44 W; P = .671). The alcohol-mediated effect in WEP was not influenced when controlling for participants' sex or accuracy in identifying the beverage ingested.

CONCLUSION

Our data indicate that alcohol ingestion impaired the anaerobic work capacity, as evidenced by the reduction in WEP during the 3-min all-out test. Moreover, the ability to exercise at an intensity above the heavy domain may be decreased after ingestion of a moderate alcohol dose.

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.

Can We Predict Long-Duration Running Power Output? Validity of the Critical Power, Power Law, and Logarithmic Models

ABSTRACT

Ruiz-Alias, SA, Ñancupil-Andrade, AA, Pérez-Castilla, A, and García-Pinillos, F. Can we predict long-duration running power output? Validity of the critical power, power law, and logarithmic models. J Strength Cond Res 38(2): 306-310, 2024-Predicting long-distance running performance has always been a challenge for athletes and practitioners. To ease this task, different empirical models have been proposed to model the drop of the running work rate with the increase of time. Therefore, this study aims to determine the validity of different models (i.e., CP, power law, and Peronnet) to predict long-duration running power output (i.e., 30 and 60 minutes). In a 4-week training period, 15 highly trained athletes performed 7-time trials (i.e., 3, 4, 5, 10, 20, 30, and 60 minutes) in a randomized order. Then, their power-duration curves (PDCs) were defined through the work-time critical power model (CP work ), power-1/time (CP 1/time ), 2-parameter hyperbolic (CP 2hyp ), 3-parameter hyperbolic (CP 3hyp ), the undisclosed Stryd (CP stryd ), and Golden Cheetah (CP cheetah ) proprietary models, and the power law and Peronnet models using the 3 to 20 minutes time trials. These ones were extrapolated to the 30- and 60-minute power output and compared with the actual performance. The CP 2hyp , CP 3hyp , CP stryd , and CP cheetah provided valid 30- and 60-minute power output estimations (≤2.6%). The CP work and CP 1/time presented a large predicting error for 30 minutes (≥4.4%), which increased for 60 minutes (≥8.1%). The power law and Peronnet models progressively increased their predicting error at the longest duration (30 minutes: ≤-1.6%; 60 minutes: ≤-6.6%), which was conditioned by the endurance capability of the athletes. Therefore, athletes and practitioners are encouraged to applicate the aforementioned valid models to their PDC to estimate the 30-minute and 60-minute power output.

A dynamic model of the bi-exponential reconstitution and expenditure of W' in trained cyclists

ABSTRACTThe aim of this study was to investigate the effects of different recovery power outputs on the reconstitution of W' and to develop a dynamic bi-exponential model of W' during depletion and reconstitution. Ten trained cyclists (mass 71.7 ± 8.4 kg; V̇O2max 60.0 ± 6.3 ml·kg-1·min-1) completed three incremental ramps (20 W·min-1) to the limit of tolerance on each of six occasions with recovery durations of 30 and 240 s. Recovery power outputs varied between 50 W (LOW); 60% of critical power (CP) (MOD) and 85% of CP (HVY). W' reconstitution was measured following each recovery and fitted to a bi-exponential model. Amplitude and time constant (τ) parameters were then determined via regression analysis accounting for relative intensity and duration to produce a dynamic model of W'. W' reconstitution slowed disproportionately as recovery power output increased (p < 0.001) and increased with recovery duration (p < 0.001). The amplitudes of each recovery component were strongly correlated to W' reconstitution after 240 s at HVY (r = 0.95), whilst τ parameters were found to be related to the fractional difference between recovery power and CP. The predictive capacity of the resultant model was assessed against experimental data with no differences found between predicted and experimental values of W' reconstitution (p > 0.05). The dynamic bi-exponential model of W' accounting for varying recovery intensities closely described W' kinetics in trained cyclists facilitating real-time decisions about pacing and tactics during competition. The model can be customised for individuals from known CP and W' and a single additional test session.HighlightsA dynamic bi-exponential model of W' accounting for both varying power output and duration.Individual customisation of the model can be achieved with a single specific test session.W' reconstitution slows disproportionally with increasing intensity after repeated bouts.

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.

The influence of skeletal muscle mitochondria and sex on critical torque and performance fatiguability in humans

Critical torque (CT) represents the highest oxidative steady state for intermittent knee extensor exercise, but the extent to which it is influenced by skeletal muscle mitochondria and sex is unclear. Vastus lateralis muscle biopsy samples were collected from 12 females and 12 males -matched for relative maximal oxygen uptake normalized to fat-free mass (FFM) (F: 57.3 (7.5) ml (kg FFM)-1  min-1 ; M: 56.8 (7.6) ml (kg FFM)-1  min-1 ; P = 0.856) - prior to CT determination and performance fatiguability trials. Males had a lower proportion of myosin heavy chain (MHC) I isoform (40.6 (18.4)%) compared to females (59.5 (18.9)%; P = 0.021), but MHC IIa and IIx isoform distributions and protein markers of mitochondrial content were not different between sexes (P > 0.05). When normalized to maximum voluntary contraction (MVC), the relative CT (F: 42.9 (8.3)%; M: 37.9 (9.0)%; P = 0.172) and curvature constant, W' (F: 26.6 (11.0) N m s (N m)-1 ; M: 26.4 (6.5) N m s (N m)-1 ; P = 0.962) were not significantly different between sexes. All protein biomarkers of skeletal muscle mitochondrial content, as well as the proportion of MHC I isoform, positively correlated with relative CT (0.48 < r < 0.70; P < 0.05), and the proportion of MHC IIx isoform correlated positively with relative W' (r = 0.57; P = 0.007). Indices of performance fatiguability were not different between males and females for MVC- and CT-controlled trials (P > 0.05). Greater mitochondrial protein abundance was associated with attenuated declines in potentiated twitch torque for exercise at 60% MVC (P < 0.05); however, the influence of mitochondrial protein abundance on performance fatiguability was reduced when exercise was prescribed relative to CT. Whether these findings translate to whole-body exercise requires additional research. KEY POINTS: The quadriceps critical torque represents the highest intensity of intermittent knee extensor exercise for which an oxidative steady state is attainable, but its relationship with skeletal muscle mitochondrial protein abundance is unknown. Matching males and females for maximal oxygen uptake relative to fat-free mass facilitates investigations of sex differences in exercise physiology, but studies that have compared critical torque and performance fatiguability during intermittent knee extensor exercise have not ensured equal aerobic fitness between sexes. Skeletal muscle mitochondrial protein abundance was correlated with critical torque and fatigue resistance for exercise prescribed relative to maximum voluntary contraction but not for exercise performed relative to the critical torque. Differences between sexes in critical torque, skeletal muscle mitochondrial protein abundance and performance fatiguability were not statistically significant. Our results suggest that skeletal muscle mitochondrial protein abundance may contribute to fatigue resistance by influencing the critical intensity of 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.

Running Critical Power: A Comparison Of Different Theoretical Models

This study aimed (i) to compare the critical power (CP) and work capacity over CP (W´) values reported by the different CP models available in current analysis software packages (Golden Cheetah and Stryd platform), (ii) to locate the CP values in the power-duration curve (PDC), and (iii) to determine the influence of the CP model used on the W´ balance. Fifteen trained athletes performed four time trials (i. e., 3, 5, 10, 20 minutes) to define their PDC through different CP models: work-time (CPwork), power-1/time (CP1/time), Morton hyperbolic (CPhyp), Stryd platform (CPstryd), and Bioenergetic Golden Cheetah (CPCheetah). Three additional time trials were performed: two to locate the CP values in the PDC (30 and 60 minutes), and one to test the validity of the W' balance model (4 minutes). Significant differences (p<0.001) were reported between models for the estimated parameters (CP, W´). CPcheetah was associated with the power output developed between 10 to 20 minutes, CP1/time, CPstryd CPwork and CPhyp. The W´ reported by the three-parameter CP models overestimated the actual 4 minutes time to exhaustion, with CPwork (0.48 [- 0.19 to 1.16] minutes); and CP1/time (0.40 [- 0.13 to 0.94] minutes) being the only valid models (p≥0.240).

Competitive Cross-Country Skiers Have Longer Time to Exhaustion Than Recreational Cross-Country Skiers During Intermittent Work Intervals Normalized to Their Maximal Aerobic Power

PURPOSE

To investigate differences in time to exhaustion (TTE), O2 uptake (V˙O2), and accumulated O2 deficit (O2def) between competitive and recreational cross-country (XC) skiers during an intermittent-interval protocol standardized for maximal aerobic power (MAP).

METHODS

Twelve competitive (maximal V˙O2 [V˙O2max]=76.5±3.8 mL·kg-1·min-1) and 10 recreational (V˙O2max=63.5±6.3 mL·kg-1·min-1) male XC skiers participated. All tests were performed on a rollerski treadmill in the V2 ski-skating technique. To quantify MAP and maximal accumulated oxygen deficit (MAOD), the skiers performed a steady-state submaximal test followed by a 1000-m time trial. After a 60-minute break, TTE, V˙O2, and accumulated O2def were measured during an intermittent-interval protocol (40-s work and 20-s recovery), which was individually tailored to 120% and 60% of each subject's MAP.

RESULTS

During the 1000-m time trial, the competitive skiers had 21% (95% CI, 12%-30%) shorter finish time and 24% (95% CI, 14%-34%) higher MAP (all P < .01) than the recreational skiers. No difference was observed in relative exercise intensity (average power/MAP; P = .28), MAOD (P = .18), or fractional utilization of V˙O2max. During the intermittent-interval protocol, the competitive skiers had 34% (95% CI, 3%-65%) longer TTE (P = .03) and accumulated 61% (95% CI, 27%-95%) more O2def (P = .001) than the recreational skiers during work phases.

CONCLUSIONS

Competitive XC skiers have longer TTE and accumulate more O2def than recreational XC skiers during an intermittent-interval protocol at similar intensity relative to MAP. This implies that performance in intermittent endurance sports is related to the ability to repeatedly recharge fractions of MAOD.

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.

Can we predict long-duration running power output? A matter of selecting the appropriate predicting trials and empirical model

When facing a long-distance race, athletes and practitioners could develop an efficient pacing strategy and training paces if an accurate performance estimate of the target distance is achieved. Therefore, this study aims to determine the validity of different empirical models (i.e. critical power [CP], Power law and Peronnet) to predict long-duration power output (i.e. 60 min) when using two or three time trial configurations. In a 5-week training period, fifteen highly trained athletes performed nine-time trials (i.e. 1, 2, 3, 4, 5, 10, 20, 30, and 60 min) in a randomized order. Their power-duration curves were defined through the work-time (CPwork), power-1/time (CP1/time), two-parameter hyperbolic (CP2hyp), three-parameter hyperbolic (CP3hyp) CP models using different two- and three-time trial configurations. The undisclosed proprietary CP models of the Stryd (CPstryd) and Golden Cheetah training software (CPcheetah) were also computed as well as the non-asymptotic Power law and Peronnet models. These were extrapolated to the 60-min power output and compared to the actual performance. The shortest valid configuration (95% confidence interval < 12 W) for CPwork and CP1/time was 3-30 min (Bias: 8.3 [4.9 to 11.7] W), for CPstryd was 10-30 min (Bias: 4.2 [- 1.0 to 9.4] W), for CP2hyp, CP3hyp and CPcheetah was 3-5-30 min (Bias < 5.7 W), for Power law was 1-3-10 min (- 1.0 [- 11.9 to 9.9] W), and for Peronnet was 4-20 min (- 3.0 [- 10.2 to 4.3] W). All the empirical models provided valid estimates when the two or three predicting trial configurations selected attended each model fitting needs.

Acute effects of fatigue on internal and external load variables determining cyclists' power profile

The aim of the present study was to determine whether fatigue affects internal and external load variables determining power profile in cyclists. Ten cyclists performed outdoor power profile tests (lasting 1-, 5 and 20-min) on two consecutive days, subject either to a fatigued condition or not. Fatigue was induced by undertaking an effort (10-min at 95% of average power output obtained in a 20-min effort followed by 1-min maximum effort) until the power output decreased by 20% compared to the 1-min power output. Fatigued condition decreased power output (p < 0.05, 1-min: 9.0 ± 3.8%; 5-min: 5.9 ± 2.5%; 20-min: 4.1 ± 1.9%) and cadence in all test durations, without differences in torque. Lactate decreased in longer efforts when a fatigue protocol had previously been conducted (e.g., 20-min: 8.6 ± 3.0 vs. 10.9 ± 2.7, p < 0.05). Regression models (r² ≥ 0.95, p < 0.001) indicated that a lower variation in load variables of 20-min in fatigued condition compared with the non-fatigued state resulted in a lower decrease in critical power after the fatigue protocol. The results suggest that fatigued condition on power was more evident in shorter efforts and seemed to rely more on a decrease in cadence than on torque.

Critical Power and Respiratory Compensation Point Are Not Equivalent in Patients with COPD

INTRODUCTION

Several studies report that pulmonary oxygen uptake (V̇O 2 ) at the respiratory compensation point (RCP) is equivalent to the V̇O 2 at critical power (CP), suggesting that the variables can be used interchangeably to demarcate the threshold between heavy and severe intensity domains. However, if RCP is a valid surrogate for CP, their values should correspond even when assessed in patients with chronic obstructive pulmonary disease (COPD) in whom the "normal" mechanisms linking CP and RCP are impeded. The aim of this study was to compare V̇O 2 at CP with V̇O 2 at RCP in patients with COPD.

METHODS

Twenty-two COPD patients (14 male/8 female; forced expiratory volume in 1 s, 46% ± 17% pred) performed ramp-incremental cycle ergometry to intolerance (5-10 W·min -1 ) for the determination of gas exchange threshold (GET) and RCP. CP was calculated from the asymptote of the hyperbolic power-duration relationship from 3-5 constant-power exercise tests to intolerance. CP was validated with a 20-min constant-power ride.

RESULTS

GET was identified in 20 of 22 patients at a V̇O 2 of 0.93 ± 0.18 L·min -1 (75% ± 13% V̇O 2peak ), whereas RCP was identified in just 3 of 22 patients at a V̇O 2 of 1.40 ± 0.39 L·min -1 (85% ± 2% V̇O 2peak ). All patients completed constant-power trials with no difference in peak physiological responses relative to ramp-incremental exercise ( P > 0.05). CP was 46 ± 22 W, which elicited a V̇O 2 of 1.04 ± 0.29 L·min -1 (90% ± 9% V̇O 2peak ) during the validation ride. The difference in V̇O 2 at 15 and 20 min of the validation ride was 0.00 ± 0.04 L, which was not different from a hypothesized mean of 0 ( P = 0.856), thereby indicating a V̇O 2 steady state.

CONCLUSIONS

In COPD patients, who present with cardiopulmonary and/or respiratory-mechanical dysfunction, CP can be determined in the absence of RCP. Accordingly, CP and RCP are not equivalent in this group.

Sex Differences in the Speed-Duration Relationship of Elite Runners across the Lifespan

PURPOSE

To determine if the speed-duration relationship is altered with age and sex of elite Master's runners.

METHODS

The world's top 10 performances for men and women in three events (800, 1500, and 5000 m) across six age groups (18-34 yr, 40-49 yr, 50-59 yr, 60-69 yr, 70-79 yr, and 80-89 yr) were analyzed from public data to establish theoretical models of the speed-duration relationship. Critical speed (CS) and the curvature constant ( D ') were estimated by fitting the average speeds and performance times with a two-parameter hyperbolic model.

RESULTS

Critical speed expressed relative to the 18- to 34-yr-olds, declined with age (92.2% [40-49] to 55.2% [80-89]; P < 0.001), and absolute CS was higher in men than women within each age group ( P < 0.001). The percent difference in CS between the men and women progressively increased across age groups (10.8% [18-34] to 15.5% [80-89]). D ' was lower in women than men in the 60-69 yr, 70-79 yr, and 80-89 yr age groups ( P < 0.001), but did not differ in the 18-34 yr, 40-49 yr, or 50-59 yr age groups.

CONCLUSIONS

Critical speed progressively decreased with age, likely due to age-related decrements in several physiological systems that cause reduced aerobic capacity. The mechanism for the larger sex difference in CS in the older age groups is unknown but may indicate physiological differences that occur with aging and/or historical sociological factors that have reduced participation opportunities of older female runners resulting in a more limited talent pool.

Invited review: The speed-duration relationship across the animal kingdom

The parameters of the hyperbolic speed-duration relationship (the asymptote critical speed, CS, and the curvature constant, D') provide estimates of the maximal steady state speed (CS) and the distance an animal can run, swim, or fly at speeds above CS before it is forced to slow down or stop (D'). The speed-duration relationship has been directly studied in humans, horses, mice and rats. The technical difficulties with treadmill running in dogs and the relatively short greyhound race durations means that, perhaps surprisingly, it has not been assessed in dogs. The endurance capabilities of lizards, crabs and salamanders has also been measured, and the speed-duration relationship can be calculated from these data. These analyses show that 1) raising environmental temperature from 25 °C to 40 °C in lizards can double the CS with no change in D'; 2) that lungless salamanders have an extremely low critical speed due, most likely, to O₂ diffusion limitations associated with cutaneous respiration; and 3) the painted ghost crab possesses the highest endurance parameter ratio (D'/CS) yet recorded (470 s), allowing it to maintain high speeds for extended periods. Although the speed-duration relationship has not been measured in fish, the sustainable swimming speed has been quantified in a range of species and is conceptually similar to the maximal steady state in humans. The high aerobic power of birds and low metabolic cost of transport during flight permits the extreme feats of endurance observed in bird migrations. However, the parameters of the avian speed-duration relationship have not been quantified.

Capacidad física de trabajo y composición corporal

Introducción: la capacidad física de trabajo (CFT) se describe como el conjunto de tareas utilizadas para llevar a cabo las actividades de la vida diaria comparada con individuos sanos; incluye fuerzas de agarre y de abdomen, equilibrio, flexibilidad, velocidad de marcha y capacidad aeróbica.  Por eso la CFT y el índice de masa muscular esquelético (IMME) tienen relación entre sí y son susceptibles de mejorar si se realiza entrenamiento físico. Objetivo: determinar si un programa de entrenamiento supervisado y controlado una vez a la semana durante seis meses es efectivo para cambiar la CFT y el IMME en sujetos mayores de 18 años. Métodos: estudio observacional, analítico, de cohorte retrospectiva, de 565 pacientes que asistieron a un programa de entrenamiento supervisado y controlado una vez a la semana durante seis meses.  Resultados: hay mejoría de la media de la CFT en -8.59 puntos al finalizar la intervención (P=0.000) y aumento del IMME en -0.06 puntos (P=0.002). Conclusiones: este estudio sugiere que una intervención de una hora guiada y supervisada una vez a la semana durante seis meses brinda beneficios en variables de la CFT con mejoría del IMME, que se explica por cambios en la microestructura muscular (mejoría en la capacidad de realizar un trabajo por unidad de masa muscular).

Interaction of Factors Determining Critical Power

The physiological determinants of high-intensity exercise tolerance are important for both elite human performance and morbidity, mortality and disease in clinical settings. The asymptote of the hyperbolic relation between external power and time to task failure, critical power, represents the threshold intensity above which systemic and intramuscular metabolic homeostasis can no longer be maintained. After ~ 60 years of research into the phenomenon of critical power, a clear understanding of its physiological determinants has emerged. The purpose of the present review is to critically examine this contemporary evidence in order to explain the physiological underpinnings of critical power. Evidence demonstrating that alterations in convective and diffusive oxygen delivery can impact upon critical power is first addressed. Subsequently, evidence is considered that shows that rates of muscle oxygen utilisation, inferred via the kinetics of pulmonary oxygen consumption, can influence critical power. The data reveal a clear picture that alterations in the rates of flux along every step of the oxygen transport and utilisation pathways influence critical power. It is also clear that critical power is influenced by motor unit recruitment patterns. On this basis, it is proposed that convective and diffusive oxygen delivery act in concert with muscle oxygen utilisation rates to determine the intracellular metabolic milieu and state of fatigue within the myocytes. This interacts with exercising muscle mass and motor unit recruitment patterns to ultimately determine critical power.

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.

Effect of varying recovery intensities on power outputs during severe intensity intervals in trained cyclists during the Covid-19 pandemic

Purpose

The study aimed to investigate the effects of different recovery intensities on the power outputs of repeated severe intensity intervals and the implications for W' reconstitution in trained cyclists.

Methods

Eighteen trained cyclists (FTP 258.0 ± 42.7 W; weekly training 8.6 ± 1.7 h∙week-1) familiar with interval training, use of the Zwift® platform throughout the Covid-19 pandemic, and previously established FTP (95% of mean power output from a 20-min test), performed 5 × 3-min severe intensity efforts interspersed with 2-min recoveries. Recovery intensities were: 50 W (LOW), 50% of functional threshold power (MOD), and self-selected power output (SELF).

Results

Whilst power outputs declined as the session progressed, mean power outputs during the severe intervals across the conditions were not different to each other (LOW 300.1 ± 48.1 W; MOD: 296.9 ± 50.4 W; SELF: 298.8 ± 53.3 W) despite the different recovery conditions. Mean power outputs of the self-selected recovery periods were 121.7 ± 26.2 W. However, intensity varied during the self-selected recovery periods, with values in the last 15 s being greater than the first 15 s (p < 0.001) and decreasing throughout the session (128.7 ± 25.4 W to 113.9 ± 29.3 W).

Conclusion

Reducing recovery intensities below 50% of FTP failed to enhance subsequent severe intensity intervals, suggesting that a lower limit for optimal W' reconstitution had been reached. As self-selected recoveries were seen to adapt to maintain the severe intensity power output as the session progressed, adopting such a strategy might be preferential for interval training sessions.

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.

Neuromuscular recovery from severe- and extreme-intensity exercise in men and women

Maximal voluntary contraction force (MVC), potentiated twitch force (Q_pot), and voluntary activation (%VA) recover to baseline within 90 s following extreme-intensity exercise. However, methodological limitations mask important recovery kinetics. We hypothesized reductions in MVC, Q_pot, and %VA at task failure following extreme-intensity exercise would be less than following severe-intensity exercise, and Q_pot and MVC following extreme-intensity exercise would show significant recovery within 120 s but remain depressed following severe-intensity exercise. Twelve subjects (6 men) completed 2 severe-intensity (40, 50% MVC) and 2 extreme-intensity (70, 80% MVC) isometric knee-extension exercise bouts to task failure (T_lim). Neuromuscular function was measured at baseline, T_lim, and through 150 s of recovery. Each intensity significantly reduced MVC and Q_pot compared with baseline. MVC was greater at T_lim (p < 0.01) and at 150 s of recovery (p = 0.004) following exercise at 80% MVC compared with severe-intensity exercise. Partial recovery of MVC and Q_pot were detected within 150 s following T_lim for each exercise intensity; Q_pot recovered to baseline values within 150 s of recovery following exercise at 80% MVC. No differences in %VA were detected pre- to post-exercise or across recovery for any intensity. Although further analysis showed sex-specific differences in MVC and Q_pot, future studies should closely examine sex-dependent responses to extreme-intensity exercise. It is clear, however, that these data reinforce that mechanisms limiting exercise tolerance during extreme-intensity exercise recover quickly. Novelty: Severe- and extreme-intensity exercise cause independent responses in fatigue accumulation and the subsequent recovery time courses. Recovery of MVC and Q_pot occurs much faster following extreme-intensity exercise in both men and women.

A critical review of critical power

The elegant concept of a hyperbolic relationship between power, velocity, or torque and time to exhaustion has rightfully captivated the imagination and inspired extensive research for over half a century. Theoretically, the relationship's asymptote along the time axis (critical power, velocity, or torque) indicates the exercise intensity that could be maintained for extended durations, or the "heavy-severe exercise boundary". Much more than a critical mass of the extensive accumulated evidence, however, has persistently shown the determined intensity of critical power and its variants as being too high to maintain for extended periods. The extensive scientific research devoted to the topic has almost exclusively centered around its relationships with various endurance parameters and performances, as well as the identification of procedural problems and how to mitigate them. The prevalent underlying premise has been that the observed discrepancies are mainly due to experimental 'noise' and procedural inconsistencies. Consequently, little or no effort has been directed at other perspectives such as trying to elucidate physiological reasons that possibly underly and account for those discrepancies. This review, therefore, will attempt to offer a new such perspective and point out the discrepancies' likely root causes.

Relationship between neuromuscular fatigue, muscle activation and the work done above the critical power during severe intensity exercise

NEW FINDINGS

What is the central question of this study? Does the work done above critical power (W') or muscle activation determine the degree of peripheral fatigue induced by cycling time-trials performed in the severe intensity domain? What is the main finding and its importance? We found that peripheral fatigue increased when power output and muscle activation increased whereas W' did not change between the time-trials. Therefore, no relationship was found between W' and exercise-induced peripheral fatigue such as previously postulated in the literature. In contrast, we found a significant association between EMG amplitude during exercise and exercise-induced reduction in the potentiated quadriceps twitch, suggesting that muscle activation plays a key role in determining peripheral fatigue during severe intensity exercise.

ABSTRACT

In order to determine the relationship between peripheral fatigue, muscle activation and the total work done above critical power (W'), ten men and four women performed, on separated days, self-paced cycling time-trials of 3, 6, 10, and 15 min. Exercise-induced quadriceps fatigue was quantified using pre- to post-exercise (15 s through 15 min recovery) changes in maximal voluntary contraction peak force (MVC), voluntary activation (VA) and potentiated twitch force (QT). VA was measured using the interpolated twitch technique, and QT was evoked by electrical stimulations of the femoral nerve. Quadriceps muscle activation was determined using the root mean square of surface electromyography of vastus lateralis (VL_RMS ), vastus medialis (VM_RMS ) and rectus femoris (RF_RMS ). Critical power and W' were calculated from the power/duration relationship from the four time-trials. Mean power output and mean VL_RMS , VM_RMS and RF_RMS were greater during shorter compared to longer exercises (P<0.05) whereas no significant between-trials change in W' was found. The magnitude of exercise-induced reductions in QT increased with the increase in power output (P<0.001) and were associated with mean VL_RMS and VM_RMS (P<0.001, r² >0.369) but not W' (P>0.150, r² <0.044). Reduction in VA tended (P = 0.067) to be more pronounced with the lengthening in time-trial duration while no significant between-trials change in MVC were found. Our data suggest that peripheral fatigue is not related to the amount of work done above the critical power but rather to the level of muscle activation during exercise the severe intensity domain. This article is protected by copyright. All rights reserved.

Bi-exponential modelling of [Formula: see text] reconstitution kinetics in trained cyclists

PURPOSE

The aim of this study was to investigate the individual [Formula: see text] reconstitution kinetics of trained cyclists following repeated bouts of incremental ramp exercise, and to determine an optimal mathematical model to describe [Formula: see text] reconstitution.

METHODS

Ten trained cyclists (age 41 ± 10 years; mass 73.4 ± 9.9 kg; [Formula: see text] 58.6 ± 7.1 mL kg min^-1) completed three incremental ramps (20 W min^-1) to the limit of tolerance with varying recovery durations (15-360 s) on 5-9 occasions. [Formula: see text] reconstitution was measured following the first and second recovery periods against which mono-exponential and bi-exponential models were compared with adjusted R² and bias-corrected Akaike information criterion (AICc).

RESULTS

A bi-exponential model outperformed the mono-exponential model of [Formula: see text] reconstitution (AICc 30.2 versus 72.2), fitting group mean data well (adjR² = 0.999) for the first recovery when optimised with parameters of fast component (FC) amplitude = 50.67%; slow component (SC) amplitude = 49.33%; time constant (τ)_FC = 21.5 s; τ_SC = 388 s. Following the second recovery, W' reconstitution reduced by 9.1 ± 7.3%, at 180 s and 8.2 ± 9.8% at 240 s resulting in an increase in the modelled τ_SC to 716 s with τ_FC unchanged. Individual bi-exponential models also fit well (adjR² = 0.978 ± 0.017) with large individual parameter variations (FC amplitude 47.7 ± 17.8%; first recovery: (τ)_FC = 22.0 ± 11.8 s; (τ)_SC = 377 ± 100 s; second recovery: (τ)_FC = 16.3.0 ± 6.6 s; (τ)_SC = 549 ± 226 s).

CONCLUSIONS

W' reconstitution kinetics were best described by a bi-exponential model consisting of distinct fast and slow phases. The amplitudes of the FC and SC remained unchanged with repeated bouts, with a slowing of W' reconstitution confined to an increase in the time constant of the slow component.

Acute Effects of Aerobic Exercise on Muscle Strength and Power in Trained Male Individuals: A Systematic Review with Meta-analysis

BACKGROUND

Concurrent training can be an effective and time-efficient method to improve both muscle strength and aerobic capacity. A major challenge with concurrent training is how to adequately combine and sequence strength exercise and aerobic exercise to avoid interference effects. This is particularly relevant for athletes.

OBJECTIVE

We aimed to examine the acute effects of aerobic exercise on subsequent measures of muscle strength and power in trained male individuals.

DESIGN

We performed a systematic review with meta-analysis.

DATA SOURCES

Systematic literature searches in the electronic databases PubMed, Web of Science, and Google Scholar were conducted up to July 2021.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies were included that applied a within-group repeated-measures design and examined the acute effects of aerobic exercise (i.e., running, cycling exercise) on subsequent measures of lower limb muscle strength (e.g., maximal isometric force of the knee extensors) and/or proxies of lower limb muscle power (e.g., countermovement jump height) in trained individuals.

RESULTS

Fifteen studies met the inclusion criteria. Aerobic exercise resulted in moderate declines in muscle strength (standardized mean difference [SMD] = 0.79; p = 0.003). Low-intensity aerobic exercise did not moderate effects on muscle strength (SMD = 0.65; p = 0.157) while moderate-to-high intensity aerobic exercise resulted in moderate declines in muscle strength (SMD = 0.65; p = 0.020). However, the difference between subgroups was not statistically significant (p = 0.979). Regarding aerobic exercise duration, large declines in muscle strength were found after > 30 min (SMD = 1.02; p = 0.049) while ≤ 30 min of aerobic exercise induced moderate declines in muscle strength (SMD = 0.59; p = 0.013). The subgroup difference was not statistically significant (p = 0.204). Cycling exercise resulted in significantly larger decrements in muscle strength (SMD = 0.79; p = 0.002) compared with running (SMD = 0.28; p = 0.035). The difference between subgroups was statistically significant (p < 0.0001). For muscle power, aerobic exercise did not result in any statistically significant changes (SMD = 0.04; p = 0.846).

CONCLUSIONS

Aerobic exercise induced moderate declines in measures of muscle strength with no statistically significant effects on proxies of muscle power in trained male individuals. It appears that higher compared with lower intensity as well as longer compared with shorter aerobic exercise duration exacerbate acute declines in muscle strength. Our results provide evidence for acute interference effects when aerobic exercies is performed before strength exercises. These findings may help practitioners to better prescribe single training sessions, particularly if environmental and/or infrastructural reasons (e.g., availability of training facilities) do not allow the application of strength training before aerobic exercise.

Effects of surgical masks on the responses to constant work-rate cycling performed at different intensity domains

We aimed at examining the impact of wearing surgical face masks on exercise performance. Thirty-two healthy adults (16 males and 16 females) completed a graded exercise test to measure peak oxygen uptake (VO_2peak ) and the ventilatory threshold (VT). Then, on separate days, all participants performed resting and standardized protocols (moderate intensity: 25% infra-VT; severe intensity: 25% supra-VT) on two different conditions (with and without a surgical mask). The use of masks reduced both VO₂ and minute ventilation during moderate and severe exercise (p < 0.0001), and this effect was particularly pronounced during severe exercise. Time to exhaustion was also shortened by ~10% on the face mask condition (p = 0.014). In contrast, neither heart rate nor the respiratory exchange ratio was affected by masking. The submaximal VO₂ was similar between the two epochs of analysis obtained during moderate cycling (i.e. 3-6 min vs. 7-10 min) and this occurred similarly between conditions. In conclusion, the impact of the surgical masks on exercise capacity is particularly pronounced during severe exercise performed at constant work rate. Ultimately, this may implicate a considerable impairment of structured or even unstructured strenuous physical activity. Clinical Trials registration number: NCT04963049.

The impact of elevated body core temperature on critical power as determined by a 3-min all-out test

The parameters of the power-duration relationship (critical power and W′) estimated by a 3-min all-out test were not altered by elevated body core temperature as compared with a thermoneutral condition.

Power profiling and the power-duration relationship in cycling: a narrative review

Emerging trends in technological innovations, data analysis and practical applications have facilitated the measurement of cycling power output in the field, leading to improvements in training prescription, performance testing and race analysis. This review aimed to critically reflect on power profiling strategies in association with the power-duration relationship in cycling, to provide an updated view for applied researchers and practitioners. The authors elaborate on measuring power output followed by an outline of the methodological approaches to power profiling. Moreover, the deriving a power-duration relationship section presents existing concepts of power-duration models alongside exercise intensity domains. Combining laboratory and field testing discusses how traditional laboratory and field testing can be combined to inform and individualize the power profiling approach. Deriving the parameters of power-duration modelling suggests how these measures can be obtained from laboratory and field testing, including criteria for ensuring a high ecological validity (e.g. rider specialization, race demands). It is recommended that field testing should always be conducted in accordance with pre-established guidelines from the existing literature (e.g. set number of prediction trials, inter-trial recovery, road gradient and data analysis). It is also recommended to avoid single effort prediction trials, such as functional threshold power. Power-duration parameter estimates can be derived from the 2 parameter linear or non-linear critical power model: P(t) = W′/t + CP (W′—work capacity above CP; t—time). Structured field testing should be included to obtain an accurate fingerprint of a cyclist’s power profile.

Over 55 years of critical power: Fact or artifact?

This report aims to generate an evidence-based debate of the Critical Power (CP), or its analogous Critical Speed (CS), concept. Race times of top Spanish runners were utilized to calculate CS based on three (1500-m to 5000-m; CS_1.5-5km ) and four (1500-m to 10000-m; CS_1.5-10km ) distance performances. Male running world records from 1000 to 5000-m (CS_1-5km ), 1000 to 10,000-m (CS_1-10km ), 1000-m to half marathon (CS_{1km-half marathon} ), and 1000-m to marathon (CS_1km-marathon ) distance races were also utilized for CS calculations. CS_1.5-5km (19.62 km h^-1 ) and CS_1.5-10km (18.68 km h^-1 ) were different (p < 0.01), but both approached the average race speed of the longest distance chosen in the model, and were remarkably homogeneous among subjects (97% ±1% and 98% ±1%, respectively). Similar results were obtained using the world records. CS values progressively declined, until reaching a CS_1km-marathon value of 20.77 km h^-1 (10% lower than CS_1-5km ). Each CS value approached the average speed of the longest distance chosen in the model (96.4%-99.8%). A power function better fitted the speed-time relationship compared with the standardized hyperbolic function. However, the horizontal asymptote of a power function is zero. This better approaches the classical definition of CP: the power output that can be maintained almost indefinitely without exhaustion. Beyond any sophisticated mathematical calculation, CS corresponds to 95%-99% of the average speed of the longest distance chosen as an exercise trial. CP could be considered a mathematical artifact rather than an important endurance performance marker. In such a case, the consideration of CP as a physiological "gold-standard" should be reevaluated.

Validity and Reliability of Hydraulic-Analogy Bioenergetic Models in Sprint Roller Skiing

Purpose: To develop a method for individual parameter estimation of four hydraulic-analogy bioenergetic models and to assess the validity and reliability of these models' prediction of aerobic and anaerobic metabolic utilization during sprint roller-skiing. Methods: Eleven elite cross-country skiers performed two treadmill roller-skiing time trials on a course consisting of three flat sections interspersed by two uphill sections. Aerobic and anaerobic metabolic rate contributions, external power output, and gross efficiency were determined. Two versions each (fixed or free maximal aerobic metabolic rate) of a two-tank hydraulic-analogy bioenergetic model (2TM-fixed and 2TM-free) and a more complex three-tank model (3TM-fixed and 3TM-free) were programmed into MATLAB. The aerobic metabolic rate (MR _ae ) and the accumulated anaerobic energy expenditure (E _an,acc ) from the first time trial (STT1) together with a gray-box model in MATLAB, were used to estimate the bioenergetic model parameters. Validity was assessed by simulation of each bioenergetic model using the estimated parameters from STT1 and the total metabolic rate (MR _tot ) in the second time trial (STT2). Results: The validity and reliability of the parameter estimation method based on STT1 revealed valid and reliable overall results for all the four models vs. measurement data with the 2TM-free model being the most valid. Mean differences in model-vs.-measured MR _ae ranged between -0.005 and 0.016 kW with typical errors between 0.002 and 0.009 kW. Mean differences in E _an,acc at STT termination ranged between -4.3 and 0.5 kJ and typical errors were between 0.6 and 2.1 kJ. The root mean square error (RMSE) for 2TM-free on the instantaneous STT1 data was 0.05 kW for MR _ae and 0.61 kJ for E _an,acc , which was lower than the other three models (all P < 0.05). Compared to the results in STT1, the validity and reliability of each individually adapted bioenergetic model was worse during STT2 with models underpredicting MR _ae and overpredicting E _an,acc vs. measurement data (all P < 0.05). Moreover, the 2TM-free had the lowest RMSEs during STT2. Conclusion: The 2TM-free provided the highest validity and reliability in MR _ae and E _an,acc for both the parameter estimation in STT1 and the model validity and reliability evaluation in the succeeding STT2.

Steady-state [Formula: see text] above MLSS: evidence that critical speed better represents maximal metabolic steady state in well-trained runners

The metabolic boundary separating the heavy-intensity and severe-intensity exercise domains is of scientific and practical interest but there is controversy concerning whether the maximal lactate steady state (MLSS) or critical power (synonymous with critical speed, CS) better represents this boundary. We measured the running speeds at MLSS and CS and investigated their ability to discriminate speeds at which \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{2}$$\end{document}V˙O2 was stable over time from speeds at which a steady-state \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{2}$$\end{document}V˙O2 could not be established. Ten well-trained male distance runners completed 9–12 constant-speed treadmill tests, including 3–5 runs of up to 30-min duration for the assessment of MLSS and at least 4 runs performed to the limit of tolerance for assessment of CS. The running speeds at CS and MLSS were significantly different (16.4 ± 1.3 vs. 15.2 ± 0.9 km/h, respectively; P < 0.001). Blood lactate concentration was higher and increased with time at a speed 0.5 km/h higher than MLSS compared to MLSS (P < 0.01); however, pulmonary \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{2}$$\end{document}V˙O2 did not change significantly between 10 and 30 min at either MLSS or MLSS + 0.5 km/h. In contrast, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{2}$$\end{document}V˙O2 increased significantly over time and reached \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{2\,\,\max }$$\end{document}V˙O2max at end-exercise at a speed ~ 0.4 km/h above CS (P < 0.05) but remained stable at a speed ~ 0.5 km/h below CS. The stability of \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{2}$$\end{document}V˙O2 at a speed exceeding MLSS suggests that MLSS underestimates the maximal metabolic steady state. These results indicate that CS more closely represents the maximal metabolic steady state when the latter is appropriately defined according to the ability to stabilise pulmonary \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\dot{V}{\text{O}}_{2}$$\end{document}V˙O2.

W' reconstitution rate at different intensities above critical torque: the role of muscle size and maximal strength

NEW FINDINGS

What is the central question of this study? Do muscle size, maximal force and exercise intensity influence the recovery time constant for the finite impulse above critical torque (τ_IET' )? What is the main finding and its importance? Muscle size and maximal strength have different influences on the parameters of the hyperbolic torque-time to task failure relationship. Greater muscle size and maximal strength, as well as exercise at an intensity of 60% MVC, prolong τ_IET' during intermittent isometric exercise.

ABSTRACT

Muscle perfusion and O₂ delivery limitations through muscle force generation appear to play a major role in defining the hyperbolic torque-time to task failure (T_lim ) relationship. Therefore, we aimed to determine the influence of muscle size and maximal strength on the recovery time constant for the finite impulse above critical torque (τ_IET' ). Ten men participated in the study and performed intermittent isometric tests until task-failure (T_lim ) for the knee-extensors (KE) (35% and 60% maximal voluntary contraction (MVC)) and plantar flexors (PF) (60% MVC). The τ_IET' was determined for each of these T_lim tests using the IET'_BAL model. The IET' (9738 ± 3080 vs. 2959 ± 1289 N m s) and end-test torque (ET)(84.5 ± 7.1 vs. 74.3 ± 12.7 N m) were significantly lower for PF compared to KE (P < 0.05). Exercise tolerance (T_lim ) was significantly longer for PF (239 ± 81 s) than KE (150 ± 55 s) at 60% MVC, and significantly longer for KE at 35% MVC (641 ± 158 s) than 60% MVC. The τ_IET' was significantly faster at 35% MVC (641 ± 177 s) than 60% MVC (1840 ± 354 s) for KE, both of which were significantly slower than PF at 60% MVC (317 ± 102 s). This study showed that τ_IET' during intermittent isometric exercise is slower with greater muscle size and maximal strength.

Critical speed estimated by statistically appropriate fitting procedures

PURPOSE

Intensity domains are recommended when prescribing exercise. The distinction between heavy and severe domains is made by the critical speed (CS), therefore requiring a mathematically accurate estimation of CS. The different model variants (distance versus time, running speed versus time, time versus running speed, and distance versus running speed) are mathematically equivalent. Nevertheless, error minimization along the correct axis is important to estimate CS and the distance that can be run above CS (d'). We hypothesized that comparing statistically appropriate fitting procedures, which minimize the error along the axis corresponding to the properly identified dependent variable, should provide similar estimations of CS and d' but that different estimations should be obtained when comparing statistically appropriate and inappropriate fitting procedure.

METHODS

Sixteen male runners performed a maximal incremental aerobic test and four exhaustive runs at 90, 100, 110, and 120% of their peak speed on a treadmill. Several fitting procedures (a combination of a two-parameter model variant and regression analysis: weighted least square) were used to estimate CS and d'.

RESULTS

Systematic biases (P < 0.001) were observed between each pair of fitting procedures for CS and d', even when comparing two statistically appropriate fitting procedures, though negligible, thus corroborating the hypothesis.

CONCLUSION

The differences suggest that a statistically appropriate fitting procedure should be chosen beforehand by the researcher. This is also important for coaches that need to prescribe training sessions to their athletes based on exercise intensity, and their choice should be maintained over the running seasons.

Influence of muscular contraction on vascular conductance during exercise above versus below critical power

We tested the hypothesis that limb vascular conductance (LVC) would increase during the immediate recovery phase of dynamic exercise above, but not below, critical power (CP) indicating a threshold for muscular contraction-induced impedance of limb blood flow (LBF). CP (115 ± 26 W) was determined in 7 men and 7 women who subsequently performed ∼5 min of near-supine cycling exercise both below and above CP. LVC demonstrated a greater increase during immediate recovery and remained significantly higher following exercise above, compared to below, CP (all p < 0.001). Power output was associated with the immediate increases in LVC following exercise above, but not below, CP (p < 0.001; r = 0.85). Additionally, variance in percent LBF impedance was significantly lower above (CV: 10.7 %), compared to below (CV: 53.2 %), CP (p < 0.01). CP appears to represent a threshold above which the characteristics of LBF impedance by muscular contraction become intensity-dependent. These data suggest a critical level of LBF impedance relative to contraction intensity exists and, once attained, may promote the progressive metabolic and neuromuscular responses known to occur above CP.

Relationship Between Critical Power and Different Lactate Threshold Markers in Recreational Cyclists

Purpose: To analyze the relationship between critical power (CP) and different lactate threshold (LT2) markers in cyclists.

Methods: Seventeen male recreational cyclists [33 ± 5 years, peak power output (PO) = 4.5 ± 0.7 W/kg] were included in the study. The PO associated with four different fixed (onset of blood lactate accumulation) and individualized (Dmax_exp, Dmax_pol, and LT_Δ1) LT2 markers was determined during a maximal incremental cycling test, and CP was calculated from three trials of 1-, 5-, and 20-min duration. The relationship and agreement between each LT2 marker and CP were then analyzed.

Results: Strong correlations (r = 0.81–0.98 for all markers) and trivial-to-small non-significant differences (Hedges’ g = 0.01–0.17, bias = 1–9 W, and p > 0.05) were found between all LT2 markers and CP with the exception of Dmax_exp, which showed the strongest correlation but was slightly higher than the CP (Hedges’ g = 0.43, bias = 20 W, and p < 0.001). Wide limits of agreement (LoA) were, however, found for all LT2 markers compared with CP (from ±22 W for Dmax_exp to ±52 W for Dmax_pol), and unclear to most likely practically meaningful differences (PO differences between markers >1%, albeit <5%) were found between markers attending to magnitude-based inferences.

Conclusion: LT2 markers show a strong association and overall trivial-to-small differences with CP. Nevertheless, given the wide LoA and the likelihood of potentially meaningful differences between these endurance-related markers, caution should be employed when using them interchangeably.

The balance of muscle oxygen supply and demand reveals critical metabolic rate and predicts time to exhaustion

We tested the hypothesis that during whole body exercise, the balance between muscle O₂ supply and metabolic demand may elucidate intensity domains, reveal a critical metabolic rate, and predict time to exhaustion. Seventeen active, healthy volunteers (12 males, 5 females; 32 ± 2 yr) participated in two distinct protocols. Study 1 (n = 7) consisted of constant work rate cycling in the moderate, heavy, and severe exercise intensity domains with concurrent measures of pulmonary V̇o₂ and local %SmO₂ [via near-infrared spectroscopy (NIRS)] on quadriceps and forearm sites. Average %SmO₂ at both sites displayed a domain-dependent response (P < 0.05). A negative %SmO₂ slope was evident during severe-domain exercise but was positive during exercise below critical power (CP) at both muscle sites. In study 2 (n = 10), quadriceps and forearm site %SmO₂ was measured during three continuous running trials to exhaustion and three intermittent intensity (ratio = 60 s severe: 30 s lower intensity) trials to exhaustion. Intensity-dependent negative %SmO₂ slopes were observed for all trials (P < 0.05) and predicted zero slope at critical velocity. %SmO₂ accurately predicted depletion and repletion of %D' balance on a second-by-second basis (R² = 0.99, P < 0.05; both sites). Time to exhaustion predictions during continuous and intermittent exercise were either not different or better with %SmO₂ [standard error of the estimate (SEE) < 20.52 s for quad, <44.03 s for forearm] versus running velocity (SEE < 65.76 s). Muscle O₂ balance provides a dynamic physiological delineation between sustainable and unsustainable exercise (consistent with a "critical metabolic rate") and predicts real-time depletion and repletion of finite work capacity and time to exhaustion.NEW & NOTEWORTHY Dynamic muscle O₂ saturation discriminates boundaries between exercise intensity domains, exposes a critical metabolic rate as the highest rate of steady state O₂ supply and demand, describes time series depletion and repletion for work above critical power, and predicts time to exhaustion during severe domain whole body exercise. These results highlight the matching of O₂ supply and demand as a primary determinant for sustainable exercise intensities from those that are unsustainable and lead to exhaustion.

Effect of Mathematical Modeling and Fitting Procedures on the Assessment of Critical Speed and Its Relationship With Aerobic Fitness Parameters

An accurate estimation of critical speed (CS) is important to accurately define the boundary between heavy and severe intensity domains when prescribing exercise. Hence, our aim was to compare CS estimates obtained by statistically appropriate fitting procedures, i.e., regression analyses that correctly consider the dependent variables of the underlying models. A second aim was to determine the correlations between estimated CS and aerobic fitness parameters, i.e., ventilatory threshold, respiratory compensation point, and maximal rate of oxygen uptake. Sixteen male runners performed a maximal incremental aerobic test and four exhaustive runs at 90, 100, 110, and 120% of the peak speed of the incremental test on a treadmill. Then, two mathematically equivalent formulations (time as function of running speed and distance as function of running speed) of three different mathematical models (two-parameter, three-parameter, and three-parameter exponential) were employed to estimate CS, the distance that can be run above CS (d'), and if applicable, the maximal instantaneous running speed (s max ). A significant effect of the mathematical model was observed when estimating CS, d', and s max (P < 0.001), but there was no effect of the fitting procedure (P > 0.77). The three-parameter model had the best fit quality (smallest Akaike information criterion) of the CS estimates but the highest 90% confidence intervals and combined standard error of estimates (%SEE). The 90% CI and %SEE were similar when comparing the two fitting procedures for a given model. High and very high correlations were obtained between CS and aerobic fitness parameters for the three different models (r ≥ 0.77) as well as reasonably small SEE (SEE ≤ 6.8%). However, our results showed no further support for selecting the best mathematical model to estimate critical speed. Nonetheless, we suggest coaches choosing a mathematical model beforehand to define intensity domains and maintaining it over the running seasons.

A comparative analysis of critical power models in elite road cyclists

The aims of this study were to compare four different critical power model's ability to ascertain critical power and W' in elite road cyclists, while making comparison to power output at respiratory compensation point, work rate (J·sec-1) at Wmax, and the work done above critical power during the Wmax test in relation to the W'. Ten male, elite endurance cyclists (V̇O2max ​= ​71.9 ​± ​5.9 ​ml ​kg-1·min-1) all familiar with critical power testing, participated in 3 testing sessions comprising 1. 15-s isokinetic (130 ​rpm) sprint, 1-min time trial, a ramp test to exhaustion, 2-3. a 4-min and/or 10-min self-paced maximal time trial separated by at least 24-h but limited to a 3-week period. The main findings show that all critical power models provided different W' (F(1.061,8.486) ​= ​39.07, p ​= ​0.0002) and critical powers (F(1.022,8.179) ​= ​32.31, p ​= ​0.0004), while there was no difference between each model's critical power and power output at respiratory compensation point (F(1.155, 9.243) ​= ​2.72, p ​= ​0.131). Differences between models or comparisons with respiratory compensation point were deemed not clinically useful in the provision of training prescription or performance monitoring if the aim is to equal work rate at compensation point. There was also no post-hoc difference between work completed at Wmax (kJ) (p ​= ​0.890) and W' using the nonlinear-3 model. Further research is required to investigate the physiological markers of intensity associated with respiratory compensation point and critical power work rate and the bioenergetic contribution to W'.

Effects of Vertical Lifting Distance on Upper-Body Muscle Fatigue

Manual material handling (MMH) is commonly demanded in the manufacturing industry. Occupational muscle fatigue of the arm, shoulder, and back, which arise from MMH tasks, can cause work absences and low efficiency. The available literature presents the lack of the fatigue comparison between targeted muscles, on the same part or on different parts. The main aim of the present study was to evaluate and compare the fatigue of upper-body muscles during repetitive bending tasks, an experiment involving 12 male subjects has been conducted to simulate material handling during furniture board drilling. The vertical lifting distance was chosen to be the single independent variable, and the three levels were 0, 250, and 500 mm. Surface electromyography (sEMG) was used to measure the muscle fatigue of the biceps brachii, upper trapezius, and multifidus, while the sEMG parameters, including the normalized electromyographic amplitude (Normalized EA) and mean power frequency (MPF), of the target muscles were analyzed. The experimental results reveal that during the manual handling tasks, the biceps brachii was the most relaxed muscle, contributing the least muscle tension, while the multifidus was the most easily fatigued muscle. Furthermore, the EMG MPF fatigue threshold (MPFFT) of multifidus muscle tension was tested to estimate its maximum workload in the long-term muscle contraction. In conclusion, bending angle should be maintained to a small range or bending should even be avoided during material-handling tasks.

The Relationship Between Neuromuscular Function and the W' in Elite Cyclists

PURPOSE

To assess the association between the W' and measures of neuromuscular function relating to the capacity of skeletal muscle to produce force in a group of elite cyclists.

METHODS

Twenty-two athletes specializing in a range of disciplines and competing internationally volunteered to participate. Athletes completed assessments of maximum voluntary torque (MVT), voluntary activation, and isometric maximum voluntary contraction to measure rate of torque development (RTD). This was followed by assessment of peak power output (PPO) and 3-, 5-, and 12-minute time trials to determine critical power. Pearson correlation was used to examine associations with critical power and W'. Goodness of fit was calculated, and significant relationships were included in a linear stepwise regression model.

RESULTS

Significant positive relationships were evident between W' and MVT (r = .82), PPO (r = .70), and RTD at 200 milliseconds (r = .59) but not with RTD at 50 milliseconds and voluntary activation. Correlations were also observed between critical power and RTD at 200 milliseconds and MVT (r = .54 and r = .51, respectively) but not with PPO, voluntary activation, or RTD at 50 milliseconds. The regression analysis found that 87% of the variability in W' (F1,18 = 68.75; P < .001) was explained by 2 variables: MVT (81%) and PPO (6%).

CONCLUSIONS

It is likely that muscle size and strength, as opposed to neural factors, contribute meaningfully to W'. These data can be used to establish training methods to enhance W' to improve cycling performance in well-trained athletes.

Using Field Based Data to Model Sprint Track Cycling Performance

Cycling performance models are used to study rider and sport characteristics to better understand performance determinants and optimise competition outcomes. Performance requirements cover the demands of competition a cyclist may encounter, whilst rider attributes are physical, technical and psychological characteristics contributing to performance. Several current models of endurance-cycling enhance understanding of performance in road cycling and track endurance, relying on a supply and demand perspective. However, they have yet to be developed for sprint-cycling, with current athlete preparation, instead relying on measures of peak-power, speed and strength to assess performance and guide training. Peak-power models do not adequately explain the demands of actual competition in events over 15-60 s, let alone, in World-Championship sprint cycling events comprising several rounds to medal finals. Whilst there are no descriptive studies of track-sprint cycling events, we present data from physiological interventions using track cycling and repeated sprint exercise research in multiple sports, to elucidate the demands of performance requiring several maximal sprints over a competition. This review will show physiological and power meter data, illustrating the role of all energy pathways in sprint performance. This understanding highlights the need to focus on the capacity required for a given race and over an event, and therefore the recovery needed for each subsequent race, within and between races, and how optimal pacing can be used to enhance performance. We propose a shift in sprint-cyclist preparation away from training just for peak power, to a more comprehensive model of the actual event demands.