Critical Power: An Important Fatigue Threshold in Exercise Physiology

Mechanistic influence of the torque cadence relationship on power output during exhaustive all-out field tests in professional cyclists

Understanding the torque-cadence-power relationship can be important in assessing a cyclist's performance potential. This study explored these relationships in elite male cyclists (N = 17; age: 24.1 ± 3.8 years; body mass: 66.0 ± 4.8 kg, critical power (CP): 5.5 ± 0.3 W.kg-1) through sprint, torque, and CP tests conducted in fresh and after accumulated work. Testing protocols, performed during a pre-season training camp, included maximal efforts across varied gear ratios and durations (15 s, 3 min, and 12 min), under stable environmental conditions (15-20°C). Results revealed reduced power output, torque, and cadence after accumulated work compared to fresh conditions (p ≤ .001). Sprint-derived maximum torque (Tmax) was strongly correlated with torque intercepts for CP fresh (r = .558, p = .020) and after accumulated work (r = .556, p = .020). The cadence relationships demonstrated a large negative correlation between maximum cadence (Cmax) and optimum cadence (Copt) from the sprint test and the 15 s, 3 min and 12 min cadence recorded during CP after accumulated work (r = -0.541 to -0.634, p = 0.006 to 0.025). These findings highlight that accumulated work-induced reductions in work capacity (W') and CP values were accompanied by lower cadences across all effort durations.

Utility of the Respiratory Compensation Point for Estimating Critical Power: Insights From Normoxia and Hypoxia

We examined the validity of the respiratory compensation point (RCP) in estimating critical power (CP) by determining the relative agreement between them following an acute intervention, hypoxia, which reduces RCP and CP. RCP and CP were determined in normoxia (N: FiO2 = 0.21) and hypoxia (H: FiO2 = 0.13) with RCP converted to a power output (W) via linear regression of the V̇O2-time relationship with correction for the mean response time. RCP and CP were lower in hypoxia compared to normoxia (p < 0.001), but there was no difference between CP and RCP in N or H (N: 174 ± 26 (CP) vs. 178 ± 30 (RCP) W; H: 133 ± 19 (CP) vs. 139 ± 22 (RCP) W, p = 0.53). In both N (r = 0.32, p = 0.31) and H (r = 0.00, p = 0.99), RCP was not correlated with CP. Moreover, the 95% limits of agreement (LOA) were unacceptably wide (N: 3 ± 64 W; H: 7 ± 57 W). There was no correlation between the change in RCP and the change in CP caused by hypoxia (W: r = 0.32), with similarly poor 95% LOA (W: -3 ± 62 W). The weak correlations and wide LOA within and between conditions suggest little practical values in using RCP to estimate CP.

Changes in torque complexity with fatigue are related to motor unit behaviour

Physiological complexity is believed to reflect a system's adaptability to environmental challenges having been proposed as an indirect indicator of the functional capacity of the neuromuscular system. This study aimed to investigate the association between torque complexity's changes with neuromuscular fatigue and motor unit parameters. Twenty-one healthy and young adults visited the laboratory on one occasion. Knee extension maximum voluntary isometric contractions and isometric contractions at 30% of maximum were collected at baseline and immediately after a fatiguing knee extension protocol, which consisted of a series of concentric and eccentric knee extensions at 90°/s until exhaustion. Torque signals were sampled continuously, and torque complexity was assessed through an entropy measure. Motor unit-related parameters were extracted from the submaximal trials and further analysed. Our findings demonstrate that torque complexity's alteration pre-to-post neuromuscular fatigue is highly correlated with vastus lateralis and medialis average firing rate (r = - 0.618 and r = - 0.659, respectively) and peak motor unit action potential amplitude (rs = - 0.801 and rs = - 0.703, respectively) pre-fatigue. Moreover, alterations in torque complexity were observed, indicating a loss of adaptability within the neuromuscular system with neuromuscular fatigue. Overall, our findings supported our hypothesis by demonstrating alterations in torque complexity with neuromuscular fatigue, rendering the system less adaptable. Moreover, our results added to the current knowledge by highlighting the association between torque complexity's changes with neuromuscular fatigue and motor unit parameters.

Guidelines for animal models of endurance and resistance exercise

BACKGROUND

This mini-review details the guideline for implementing the most common exercise patterns in small laboratory rodents (mice/rats) and the advantages and disadvantages of each, in ways that are comparable to humans. Also, criteria for targeted selection and control of workload and intensity of activity are proposed in different exercise programs.

NEW METHOD

As an available and low-cost intervention in physiological, biochemical and cellular-molecular assessments, different exercise programs can be effective in the prevention/treatment of many skeletal-structural, behavioral and neurodegenerative disorders. Exercise tolerance/intolerance is an indicator of the complex function of the physiological, metabolic, neuromuscular, cardiovascular and respiratory systems, and in this sense, animal models of exercise are of interest to researchers by creating a controllable and precise environment.

RESULTS

Considering the different species of laboratory animals and various exercise paradigms, selecting the type, intensity and duration of the program in an optimal manner is a difficult task, especially in conditions such as old age or illness, and if necessary, existing research tools and protocols should be reviewed. In fact, one of the most attractive applications of exercise models is the discovery of preventive/therapeutic strategies for many disorders, which necessitates more knowledge about exercise protocols.

CONCLUSIONS

Animal models of endurance/resistance exercise on land/water make it possible to evaluate physiological/pathological conditions. However, to obtain optimal and reproducible results in human samples, the effectiveness of anesthetic drugs, surgical procedures, and the stress caused by exercise tools and equipment must be carefully controlled.

Vigorous intensity heart rate-clamp exercise does not elicit recommended oxygen consumption rates

PURPOSE

This study examined the power output adjustments and subsequent shifts in metabolic (V̇O2) demands as well as minute ventilation (V ˙ E ), respiratory rate (RR), and rating of perceived exertion (RPE) responses during vigorous intensity (77-95% HRpeak) heart rate (HR)-clamp cycle ergometry.

METHODS

Fifteen males (mean ± SD age = 25.9 ± 4.4 years) performed a graded exercise test to exhaustion to determine peak parameters and three, randomly ordered, HR-clamp trials to exhaustion, up to 60 min, at the lower (HRL = 77% HRpeak), middle (HRM = 86% HRpeak), and higher (HRH = 95% HRpeak) end of the vigorous intensity range. Time course of changes were examined.

RESULTS

The times to exhaustion (Tlim) for the HRL, HRM, and HRH trials were 56.05 ± 10.09, 44.22 ± 19.00, and 9.74 ± 7.54 min, respectively. There were significant decreases in power output,V ˙ O 2 , andV ˙ E across time for each trial, but no changes in RR, and increases in RPE (p < 0.05). Responses were intensity specific for all variables such that mean values were lower for HRL than HRM, and HRL and HRM were lower than HRH. The meanV ˙ O 2 (HRL = 56.7 ± 3.8, HRM = 68.1 ± 4.3, and HRH = 90.5 ± 3.3%V ˙ O 2max ) responses fell below the recommendedV ˙ O 2 range for vigorous exercise at 10%Tlim for HRL, and at 90%Tlim for HRM, but remained above the recommended V̇O2 range for vigorous exercise until 70% of Tlim for HRH.

CONCLUSIONS

Only the HRM trial met the current guidelines of a vigorous intensityV ˙ O 2 sustained for at least 20 min. This study indicated that HR-clamp exercise cannot be consistently used to prescribe a desired metabolic stimulus for exercise performed in a single session.

Is there a critical rate of torque development?

The objective of this study was to test the hypothesis that neuromuscular fatigue influences the rate of torque development (RTD) in a similar manner to isometric torque. Nine men participated in this study and performed 5-min all-out isometric tests for knee extensors (KE) and plantar flexors (PF) muscles, to determine the end-test torque (ET) and the critical rate of torque development (critical RTD). Additionally, participants performed submaximal constant-torque tests to task failure for KE and PF muscles. Both maximal voluntary contraction and RTD exhibited hyperbolic behavior and reached an asymptote at the end of the 5-min all out isometric test with similar relative values (KE 29.5 ± 5.6% MVC and PF 50.9 ± 2.9% MVC and KE 25.1 ± 3.6 to 28.5 ± 4.4% RTD and PF 48.4 ± 6.5 to 52.4 ± 5.8% RTD). However, both % MVC and % RTD were statistically different between muscle groups (P < 0.05), even when normalized by muscle volume (P < 0.05). Torque and RTD after the constant-torque test were similar to the values of ET and critical RTD (P > 0.05), respectively. In this study, it was observed that neuromuscular fatigue affects RTD and torque similarly, with the magnitude of this effect varying according to the muscle size.

The Dynamics of Locomotor Neuromuscular Fatigue during Ramp-Incremental Cycling to Intolerance

INTRODUCTION

Traditional neuromuscular fatigue assessments are not task-specific and are unable to characterize neuromuscular performance decline during dynamic whole-body exercise. This study used interleaved maximal isokinetic cycling efforts to characterize the dynamics of the decline in neuromuscular performance during ramp-incremental (RI) cycle ergometry exercise to intolerance.

METHODS

Eleven young healthy participants (10 male/1 female) performed two RI cycle ergometry exercise tests to intolerance: 1) RI exercise with peak isokinetic power (Piso) at 80 rpm measured at baseline and immediately at intolerance from a maximal ~6 s effort, and 2) RI exercise where additional Piso measurements were interleaved every 90 s to characterize the decline in neuromuscular performance during the RI test. Muscle excitation was measured using EMG during all Piso assessments, and pulmonary gas exchange was measured throughout.

RESULTS

Baseline Piso was 832 ± 140 W and RI exercise reduced Piso to 349 ± 96 W at intolerance ( P = 0.001), which was not different from flywheel power at intolerance (303 ± 96 W; P = 0.292). There was no reduction in Piso between baseline cycling and gas exchange threshold (GET; baseline Piso vs mean Piso below GET: 828 ± 146 vs 815 ± 149 W; P = 1.00). Piso fell progressively above GET until intolerance (Piso every 90 s above GET: 759 ± 139, 684 ± 141, 535 ± 144, 374 ± 117 W; each P < 0.05 vs baseline and mean Piso below GET). Peak muscle excitation (EMG) was also reduced only above GET (73% ± 14% of baseline, at intolerance; P < 0.05). However, the reduction in peak Piso preceded the reduction in peak muscle excitation.

CONCLUSIONS

The dynamics of the decline in neuromuscular performance (reduction in Piso and EMG) during RI exercise are consistent with known intensity-dependent metabolic and traditional pre-post neuromuscular fatigue responses to discrete bouts of constant-power exercise.

Analysis of the factors influencing the proximity and agreement between critical power and maximal lactate steady state: a systematic review and meta-analyses

Identifying the boundary between heavy and severe exercise domains is crucial since it demarcates the transition from sustainable to unsustainable exercise. This systematic review aimed to determine differences and agreement between two indices used to determine this boundary, namely critical power (CP) and maximal lactate steady state (MLSS), and how moderators may affect these differences. Ten out of 782 studies found were included in the meta analyses. Random effect meta-analyses were performed to evaluate the mean differences (MD) between CP and MLSS, and moderators' effect on MD was assessed using meta-regression. CP and MLSS agreement was tested using Bland-Altman meta-analyses on the limits of agreements (LoA) of the MD. Power output (PO) at CP was higher (MD (95% LoA) = 12.42 [-19.23; 44.08] W, p = 0.005) than PO at MLSS, with no differences between CP and MLSS in terms of oxygen uptake (MD (95% LoA) = 0.09 [-0.34; 0.52] L⋅min-1, p = 0.097), heart rate (MD (95% LoA) = 0.61 [-15.84; 17.05] bpm, p = 0.784), and blood lactate concentration (MD (95% LoA) = 1.63 [-2.85; 6.11] mM, p = 0.240). Intensities at CP (p = 0.002) and MLSS (p = 0.010) influenced the MD expressed in W. In conclusion, solely when expressed in PO, CP was higher than MLSS, with larger differences in fitter and younger individuals, emphasizing the possible effect of the indicators used for assessing exercise intensity. Finally, the high interindividual variability observed in the differences between CP and MLSS could compromise their interchangeability in predicting the heavy to severe boundary regardless of the parameter used to assess exercise intensity.

Evaluating the impact of coenzyme Q10 and high-intensity interval training on lactate threshold and Plasma blood gases in rats: a randomized controlled trial

PURPOSE

Coenzyme Q10 (Q10) is a mitochondrial coenzyme that facilitates ATP production via oxidative phosphorylation. This study hypothesized that Q10 enhances mitochondrial efficiency and lactate threshold, while high-intensity interval training (HIIT) promotes metabolic adaptations, improving glucose utilization and buffering capacity for faster recovery after high-intensity exercise.

METHODS

A randomized controlled trial was conducted using 24 male Sprague-Dawley rats (250.4 ± 6.1 g, 8 weeks old). The rats were allocated into four groups: control (C), coenzyme Q10 (CoQ10), HIIT, and HIIT + Q10. The Q10 administration involved a dosage of 10 mg/kg/day, given 30 min prior to the HIIT protocol. Lactate threshold, blood gas parameters, oximetry values, metabolite levels, and electrolyte status were analyzed utilizing the Radiometer 900 device. The blood samples were collected at the fifth and tenth minutes following the HIIT training trials.

RESULTS

The HIIT + Q10 group exhibited a significant reduction in lactate threshold (p < 0.01), maintaining values below average. Significant improvements in blood gas parameters, including pH, pO2, and pCO2, were observed in this group. Enhanced oxygen transport capacity was indicated by improved oximetry parameters (Hb, HCT, sO2) and reduced COHb levels. Additionally, positive changes in HCO3- and base values indicated reduced metabolic stress. Q10 supplementation also stabilized electrolytes, particularly K+ and Na+.

CONCLUSION

The Q10 supplementation supported metabolic balance, improved oxygen transport, and stabilized acid-base levels during HIIT. It reduced lactate accumulation, enhanced glucose availability, and alleviated metabolic stress, thereby improving recovery efficiency and physiological adaptation.

Field-based tests for determining critical speed among runners and its practical application: a systematic review

Introduction

This review focuses exclusively on field-based critical speed (CS) tests for runners, aiming to evaluate key testing conditions to optimize field-based assessments and their practical applications.

Methods

A systematic search was conducted in PubMed, Scopus, SPORTDiscus, and Web of Science databases in July 2024 using terms like "critical power," "critical speed," "testing," and "field condition" along with related keywords. Following PRISMA 2020 guidelines, studies were systematically identified, screened, assessed for eligibility, and evaluated for the validity, reliability, and applicability of field-based methods for determining CS in runners.

Results

From an initial pool of 450 studies, 19 met the inclusion criteria. The time trial (TT) test and the 3-minute all-out test (3MT) emerged as the most frequently used field-based methods, demonstrating high reliability when conducted under specific conditions.

Conclusion

This review demonstrates that while field-based CS testing is a practical alternative to lab-based assessments, obtaining reliable results relies on following recommended testing settings, particularly for TT tests. By outlining the practical applications and conditions necessary for accurate CS assessment, this review supports athletes and coaches in applying CS testing effectively to enhance training strategies and performance.

Targeting lung heme iron by aerosol hemopexin adminstration in sickle cell disease pulmonary hypertension

Lung tissue from human patients and murine models of sickle cell disease pulmonary hypertension (SCD-PH) show perivascular regions with excessive iron accumulation. The iron accumulation arises from chronic hemolysis and extravasation of hemoglobin (Hb) into the lung adventitial spaces, where it is linked to nitric oxide depletion, oxidative stress, inflammation, and tissue hypoxia, which collectively drive SCD-PH. Here, we tested the hypothesis that intrapulmonary delivery of hemopexin (Hpx) to the deep lung is effective at scavenging heme-iron and attenuating the progression of SCD-PH. Herein, we evaluated in a murine model of hemolysis driven SCD-PH, if intrapulmonary Hpx administration bi-weekly for 10 weeks improves lung iron deposition, exercise tolerance, cardiovascular function, and multi-omic indices associated with SCD-PH. Data shows Hpx delivered with a micro-sprayer deposits Hpx in the alveolar regions. Hpx extravasates into the perivascular compartments but does not diffuse into the circulation. Histological examination shows Hpx therapy decreased lung iron deposition, 4-HNE, and HO-1 expression. This was associated with improved exercise tolerance, cardiopulmonary function, and multi-omic profile of whole lung and RV tissue. Our data provides proof of concept that treating lung heme-iron by direct administration of Hpx to the lung attenuates the progression of PH associated with SCD.

Blue plaque review series: A.V. Hill, athletic records and the birth of exercise physiology

One hundred years ago, A.V. Hill authored three manuscripts analysing athletic world records from a physiological perspective. That analysis, grounded in Hill's understanding of contemporary muscle bioenergetics, provides a fascinating sketch of the thoughts and speculations of one of the fathers of exercise physiology. In this review, we reflect on Hill's prose with the benefit of 100 years of hindsight, and illustrate how Hill was able to draw startlingly accurate conclusions from what limited data were available on the physiology of intense exercise. Hill discusses the energetics of running, swimming, rowing and cycling in both males and females, as well as addressing exercise performance in horses and the mechanics of jumping. He also considers sports nutrition, pacing strategy and ultra-endurance exercise. Perhaps most impactfully, he establishes that the speed-duration relationship has characteristics that reflect the underlying physiological basis of exercise performance. That physiology, in turn, differs depending on the duration of the event itself, providing one of the first descriptions of the task-dependent nature of mechanisms limiting exercise tolerance. A remarkable feature of Hill's papers is that they were written just a few years before a major revolution in muscle biochemistry, and yet Hill was still able to develop conceptually sound ideas about human performance. His hypotheses require only minor revision to bring them into line with current understanding. In reaching their centenary, therefore, the surprising feature of these papers is not how well they have aged, but how relevant they remain.

Physiological Resilience: What Is It and How Might It Be Trained?

Physiological resilience has recently been recognized as an additional factor that influences endurance exercise performance. It has thus been incorporated into a modified, contemporary version of "the Joyner model" which acknowledges that start-line values of V̇O2max, efficiency or economy, and metabolic thresholds are prone to deterioration, often with appreciable interindividual variability, during prolonged endurance exercise. The physiological underpinnings of resilience are elusive and sports physiologists are presently concerned with developing practical testing protocols which reflect an athlete's resilience characteristics. It is also important to consider why some athletes are more resilient than others and whether resilience can be enhanced-and, if so, which training programs or specific training sessions might stimulate its development. While data are scant, the available evidence suggests that training consistency and the accumulation of relatively large volumes of training over the longer-term (i.e., several years) might promote resilience. The inclusion of regular prolonged exercise sessions within a training program, especially when these include bouts of high-intensity exercise at race pace or above or a progressive increase in intensity in the face of developing fatigue, might also represent an effective means of enhancing resilience. Finally, resistance training, especially heavy strength and plyometric training, appears to have positive effects on resilience. Considerations of training for resilience, alongside other more established physiological determinants of performance, will likely be important in the long-term development of successful endurance athletes.

Vitamin D and its relationship to performance and health during a competitive period in elite women's basketball and volleyball players

Vitamin D [25(OH)D] is a key nutrient, although its level is often low in the general population. To investigate the relationship between vitamin D levels and muscle performance, and to analyze how vitamin D changes during a 16-week competitive season and its relationship to the performance tests performed. Participant characteristics: age 25.1 ± 4.7 years; height 1.8 ± 0.1 m, and body mass 73.9 ± 15.4 kg. Vitamin D levels (ng/mL) were at T1 (September): 33.7 ± 14.7 (n = 23), and at T2 (January): 26.1 ± 7.3 (n = 23). Over 16 weeks of competition, participants' blood was analyzed to determine their vitamin D levels. Their athletic abilities were evaluated through various tests: vertical jumps (standing jump and countermovement jump); 20-m sprint without direction changes; and intermittent endurance test; the vitamin D level decreased from T1 to T2 by -22. 40% [p < 0.05] but performance improved in all tests performed (SJ: 4.57%; CMJ: 6.94%; VO2max: 4.99% [p < 0.05]; 20 m: -1.83%). There is a relationship between vitamin D levels and physical performance in female indoor athletes. The results suggest that increased training load may also negatively affect vitamin D levels in elite female indoor athletes.

Biochemical origin of (near-) linear curvature constant (W')- V ˙ O 2 slow component ( Δ V ˙ O 2 sc ) and critical power (CP)- V ˙ O 2 transition time (t0.63) relationship in skeletal muscle

PURPOSE

The biochemical background of the (near-)linear direct relationship between the curvature constant (W') of the power-duration curve and the magnitude ( Δ V ˙ O 2sc ) of the slow component of theV ˙ O 2 on-kinetics (V ˙ O 2sc ) as well as reverse relationship between critical power (CP) and the characteristic transition time (t0.63, analogous to τp) of the primary phase II of theV ˙ O 2 on-kinetics encountered in experimental studies is studied.

METHODS

A computer model of the bioenergetic system in skeletal muscle, involving the each-step-activation mechanism of work transitions and Pi double-threshold mechanism of muscle fatigue, is used.

RESULTS

The activity (rate constant) (kadd) of the additional ATP usage, underlying the slow component, determines to a large extent the (near-)linear direct W'- Δ V ˙ O 2sc relationship, as an increase in kadd increases markedly both W' and Δ V ˙ O 2sc . t0.63 is a derivative of the changes in metabolite (M = PCr or Cr or Pi) concentrations between rest and the steady-state of the phase II M on-kinetics after the onset of exercise. The oxidative phosphorylation (OXPHOS) activity (kOX) mostly determines the (near)-linear inverse CP-t0.63 relationship, as an increase in kOX markedly decreases ΔM and t0.63, and elevates CP.

CONCLUSIONS

TheV ˙ O 2 on-kinetics (e.g.,V ˙ O 2sc or t0.63) cannot cause anything in the system, as it is an emergent property of the system functioning on the biochemical level. Physiological variables: muscleV ˙ O 2sc and W' as well as t0.63 and CP, and relationships between them, are determined by biochemical parameters, mainly kadd and kOX, respectively.

Physiological and perceptual response to critical power anchored HIIT: a sex comparison study

PURPOSE

The aim of this study was to test the hypothesis that using threshold-based high intensity interval training (HIITTHR) prescribed at an intensity above critical power (CP) in males and females matched for maximal oxygen uptake ( V ˙ O2max) (mL/kg lean mass/min) will yield no sex differences in time to fatigue.

METHODS

Thirteen males (mean ± SD: 22.0 ± 2.48 years, 181 ± 8.36 cm, 78.8 ± 11.4 kg) and eleven females (mean ± SD: 22.4 ± 2.69 years, 170 ± 5.73 cm, 65.2 ± 7.66 kg) initially undertook an incremental test to exhaustion to determine V ˙ O2max, and a CP test. Then, one HIIT session (4 min on, 2 min off) was performed to exhaustion at the work rate associated with 105%CP. Acute physiological and cardiovascular responses were recorded.

RESULTS

No sex differences were recorded in time to fatigue [Female vs. Male (min): 36.0 ± 18.5 vs. 39.3 ± 16.3], heart rate, rate of perceived exertion, or %oxygenated [haem]. Females displayed lower %deoxygenated [haem] at the end of interval 1, 2, 3, and 4 [Female vs. Male (%): 89.4 ± 21.2 vs. 110 ± 27.3, 92.0 ± 21.5 vs. 115 ± 27.6, 87.1 ± 23.7 vs. 112 ± 22.8, 88.9 ± 26.3 vs. 113 ± 23.5]. Large interindividual variability in performance, and physiological and perceptual response were present despite the use of threshold-based prescription.

CONCLUSION

The present study suggests that threshold-based prescription may help standardize the mean response exercise across sexes but does not eliminate physiological or perceptual variability. Furthermore, the lack of sex differences in TTF was accompanied by greater %deoxy[haem] in males, indicating tissue oxygenation is an unlikely determinant of HIIT performance. This study has been retrospectively registered at Trial Registration https://doi.org/10.17605/OSF.IO/KZVGC January 17th, 2023, following data collection but prior to data analyses.

Muscle endurance, neuromuscular fatigability, and cognitive control during prolonged dual-task in people with chronic obstructive pulmonary disease: a case-control study

PURPOSE

Recent studies suggest that, compared to healthy individuals, people with chronic obstructive pulmonary disease (pwCOPD) present a reduced capacity to perform cognitive-motor dual-task (CMDT). However, these studies were focused on short-duration CMDT offering limited insight to prolonged CMDT inducing fatigue, which can be encountered in daily life. The present study aimed to explore the effect of adding a cognitive task during repeated muscle contractions on muscle endurance, neuromuscular fatigability, and cognitive control in pwCOPD compared to healthy participants.

METHODS

Thirteen pwCOPD and thirteen age- and sex-matched healthy participants performed submaximal isometric contractions of the knee extensors until exhaustion in two experimental sessions: (1) without cognitive task and (2) with a concurrent working memory task (i.e., 1-back task). Neuromuscular fatigability (as well as central and peripheral components measured by peripheral magnetic stimulation), cognitive performance, and perceived muscle fatigue were assessed throughout the fatiguing tasks.

RESULTS

Independently to the experimental condition, pwCOPD exhibited lower muscle endurance compared to healthy participants (p = 0.039), mainly explained by earlier peripheral fatigue and faster attainment of higher perceived muscle fatigue (p < 0.05). However, neither effect of cognitive task (p = 0.223) nor interaction effect (group × condition; p = 0.136) was revealed for muscle endurance. Interestingly, cognitive control was significantly reduced only in pwCOPD at the end of CMDT (p < 0.015), suggesting greater difficulty for patients with dual tasking under fatigue.

CONCLUSION

These findings provide novel insights into how and why fatigue develops in COPD in dual-task context, offering a rationale for including such tasks in rehabilitation programs.

Increased exercise tolerance in humanized G6PD-deficient mice

ABSTRACT

Glucose-6-phosphate dehydrogenase (G6PD) deficiency affects 500 million people globally, affecting red blood cell (RBC) antioxidant pathways and increasing susceptibility to hemolysis under oxidative stress. Despite the systemic generation of reactive oxygen species during exercise, the effects of exercise on individuals with G6PD deficiency remain poorly understood This study used humanized mouse models expressing the G6PD Mediterranean variant (S188F, with 10% enzymatic activity) to investigate exercise performance and molecular outcomes. Surprisingly, despite decreased enzyme activity, G6PD-deficient mice have faster critical speed than mice expressing human canonical G6PD. After exercise, deficient mice did not exhibit differences in RBC morphology or hemolysis, but had improved cardiac function, including cardiac output, stroke volume, sarcomere length, and mitochondrial content. Proteomics analyses of cardiac and skeletal muscles (gastrocnemius, soleus) from G6PD-deficient compared with sufficient mice revealed improvements in mitochondrial function and increased protein turnover via ubiquitination, especially for mitochondrial and structural myofibrillar proteins. Mass spectrometry-based metabolomics revealed alterations in energy metabolism and fatty acid oxidation. These findings challenge the traditional assumptions regarding hemolytic risk during exercise in G6PD deficiency, suggesting a potential metabolic advantage in exercise performance for individuals carrying noncanonical G6PD variants.

The Impact of Critical Speed and Lean Body Mass on Load Carriage Performance for Army Reserve Officers' Training Corps Cadets

INTRODUCTION

Load carriage is an inherent part of tactical operations. Critical speed (CS) has been associated with technical and combat-specific performance measures (e.g., loaded running). The 3-min all-out exercise test provides estimates of CS and the maximal capacity to displace the body (D') at speeds above CS. The current study investigated the contributions of CS, D', lean body mass (LBM), thigh lean mass (TLM), and lower body isokinetic strength and endurance parameters related to load carriage time trials (LCTTs).

METHODS

Twenty-two Reserve Officers' Training Corps cadets (6 = females, age = 20.82 ± 1.59 years) underwent various assessments that included a running 3-minute all-out test to determine CS and D', isokinetic knee extension (KE) muscle strength and endurance, body composition assessed by dual-energy X-ray absorption, and two 21-kg LCTTs of 400 and 3,200 m, respectively. Pearson's product-moment correlations investigated relationships between selected predictor variables. Stepwise multiple linear regression analyses were used to determine the relationship between variables that predicted LCTT performance.

RESULTS

Significant correlations were as follows: LBM and CS (r = 0.651, P < .001), KE endurance work and CS (r = 0.645, P < .001), TLM and CS (r = 0.593, P < .05), and KE peak torque and CS (r = 0.529, P < .05). The stepwise regression analyses indicated that CS and LBM contributed significantly to predicting 3,200-m LCTT (F [2,19] = 81.85, R2 = 0.90, P < .001) with standardized β coefficients (-0.723 and -0.301, respectively). Thigh lean mass contributed significantly to predicting the 400-m LCTT (F [1,20] = 46.586, R2 = 0.70, P < .001) with a standardized β coefficient (-0.836).

CONCLUSION

The results of this study highlight that CS and LBM were the best predictors of the 3,200-m LCTT, and TLM was the best predictor of the 400-m LCTT. The findings of this study support that CS and LBM, including TLM, are important in predicting load carriage task completion in the time trial tasks.

Resolving Differences between MLSS and CP by Considering Rates of Change of Blood Lactate during Endurance Exercise

PURPOSE

This study aimed to develop a new method that more closely represents the heavy to severe exercise domain boundary by evaluating the rates of blood lactate accumulation during the constant power output exercise bouts that are used in the assessment of the maximal lactate steady state (MLSS).

METHODS

Eight well-trained male cyclists completed five exercise tests of up to 30 min for the determination of the traditional MLSS (MLSS TRAD ) and a further four maximal tests for the determination of critical power (CP). The rates of change of blood [lactate] between 10 min and the end of exercise in the MLSS tests were plotted against the corresponding power outputs, and a two-segment linear regression model was used to identify individualized break points in lactate accumulation versus power output (modified MLSS [MLSS MOD ]).

RESULTS

MLSS MOD was significantly higher than MLSS TRAD (297 ± 41 vs 278 ± 41 W, P < 0.001) but was not significantly different from CP (297 ± 41 W, P > 0.05); MLSS MOD and CP were closely aligned ( r = 0.97, bias = -0.52 W, SEE = 10 W, limits of agreement = -20 to 19 W). The rates of change of both blood [lactate] and V̇O 2 were significantly greater, and exercise intolerance occurred before 30 min, at a power output slightly above MLSS MOD .

CONCLUSIONS

A novel method for evaluating blood lactate kinetics during MLSS TRAD protocol produces MLSS MOD that is not different from CP and better represents the heavy to severe exercise domain boundary.

Fatigue assessment in distance runners: A scoping review of inertial sensor-based biomechanical outcomes and their relation to fatigue markers and assessment conditions

BACKGROUND

Fatigue manifests as a decline in performance during high-intensity and prolonged exercise. With technological advancements and the increasing adoption of inertial measurement units (IMUs) in sports biomechanics, there is an opportunity to enhance our understanding of running-related fatigue beyond controlled laboratory environments.

RESEARCH QUESTION

How have IMUs have been used to assess running biomechanics under fatiguing conditions?

METHODS

Following the PRISMA-ScR guidelines, our literature search covered six databases without date restrictions until September 2024. The Population, Concept, and Context criteria were used: Population (distance runners ranging from novice to competitive), Concept (fatigue induced by running a distance over 400 m), Context (assessment of fatigue using accelerometer, gyroscope, and/or magnetometer wearable devices). Biomechanical outcomes were extracted and synthesised, and interpreted in the context of three main study characteristics (cohort ability, testing environment, and the inclusion of physiological outcomes) to explore their potential role in influencing outcomes.

RESULTS

A total of 88 articles were included in the review. There was a high prevalence of treadmill-based studies (n=46, 52%), utilising only 1-2 sensors (n=69, 78%), and cohorts ranged in experience, from sedentary to elite-level runners, and were largely comprised of males (69% of all participants). The majority of biomechanical outcomes assessed showed varying responses to fatigue across studies, likely attributable to individual variability, exercise intensity, and differences in fatigue protocol settings and prescriptions. Spatiotemporal outcomes such as stride time and frequency (n=37, 42 %) and impact accelerations (n=55, 62%) were more widely assessed, with a fatigue response that appeared population and environment specific.

SIGNIFICANCE

There was notable heterogeneity in the IMU-based biomechanical outcomes and methods evaluated in this review. The review findings emphasise the need for standardisation of IMU-based outcomes and fatigue protocols to promote interpretable metrics and facilitate inter-study comparisons.

Fractional utilization of the 10-minute treadmill test velocity in running performance

This study aimed to evaluate the applicability of the 10-minute submaximal treadmill test (T10 test), a self-paced test, in determining critical speed (CS) and predicting running performance. Specifically, we sought to identify the percentage of T10 velocity (vT10) that runners performed in official distance races, and to compare physiological and performance indicators between sexes. 60 recreational runners (n=34 males and n=26 females) underwent a maximum incremental test, the novel T10 test, and ran 1200-m and 2400-m on the track. Runners self-reported their best performance times. Generalized Linear Model was used to compare running performances between sexes. For both males and females, the %vT10 in 5 km, 10 km, and half-marathon races occurred at 107.5% and 106.5%, 99.9% and 100.8%, and 92.6% and 97.1%, respectively. There was no interaction effect (p=0.520) and no main effect of sex (p=0.443). There was a main effect of distance (p<0.001), indicating that %vT10 in the 5km race differed from that found in the 10 km race (p=0.012), as well as in the half-marathon (p<0.001). Our findings suggest that %vT10 values can be used to determine pace in recreational endurance runners for race distances regardless of sex.

A comparison of critical power and the respiratory compensation point at slower and faster pedaling cadences

We investigated whether pedal cadence (60 vs. 100 rpm) affects oxygen uptake (V̇O2) and power output (PO) at two indexes of the heavy-to-severe-intensity domain boundary (i.e., critical power (CP) and respiratory compensation point (RCP)) and their correspondence. Fourteen adults (7 females, 23 ± 2 years) cycled at 60 and 100 rpm during: (i) a "step-ramp-step" protocol to identify V̇O2 and PO at RCP; (ii) 4-5 exhaustive constant-PO bouts for CP identification; and (iii) a constant-power bout at CP to identify V̇O2 at CP. Separate two-way repeated measures Analysis of variance assessed whether V̇O2 and PO were affected by index (CP vs. RCP) and cadence (60 vs. 100 rpm). The V̇O2 was not affected by index (mean difference (MD) = 73 ± 197 mL·min-1; p = 0.136) but there was an index × cadence interaction (p = 0.014), such that V̇O2 was higher at 100 versus 60 rpm for CP (MD = 142 ± 169 mL·min-1; p = 0.008), but not RCP (p = 0526). The PO was affected by cadence (MD = 13 ± 9 W; p < 0.001) and index (MD = 8 ± 11 W; p = 0.016), with no cadence × index interaction (p = 0.168). The systematic bias in PO confirms cadence-specificity of CP and RCP. The relationship between these indexes and their change in unison in PO suggests a mechanistic link between these two heavy-to-severe domain boundary candidates.

High-dose short-term creatine supplementation without beneficial effects in professional cyclists: a randomized controlled trial

BACKGROUND

Growing evidence supports the ergogenic effects of creatine supplementation on muscle power/strength, but its effects on endurance performance remain unclear. We assessed the effects of high-dose short-term creatine supplementation in professional cyclists during a training camp.

METHODS

The study followed a double-blind, randomized parallel design. Twenty-three professional U23 cyclists (19 ± 1 years, maximum oxygen uptake: 73.0 ± 4.6 mL/kg/min) participated in a 6-day training camp. Participants were randomized to consume daily either a recovery drink (containing carbohydrates and protein) with a 20-g creatine supplement (creatine group, n = 11) or just the recovery drink (placebo group, n = 12). Training loads and dietary intake were monitored, and indicators of fatigue/recovery (Hooper index, countermovement jump height), body composition, and performance (10-second sprint, 3-, 6-, and 12-minute time trials, respectively, as well as critical power and W') were assessed as study outcomes.

RESULTS

The training camp resulted in a significant (p < 0.001) increase of training loads (+50% for total training time and + 61% for training stress score, compared with the preceding month) that in turn induced an increase in fatigue indicators (significant time effect [p < 0.001] for delayed-onset muscle soreness, fatigue, and total Hooper index) and a decrease in performance (significant time effect [p = 0.020] for critical power, which decreased by -3.8%). However, no significant group-by-time interaction effect was found for any of the study outcomes (all p > 0.05).

CONCLUSIONS

High-dose short-term creatine supplementation seems to exert no consistent beneficial effects on recovery, body composition or performance indicators during a strenuous training period in professional cyclists.

The Respiratory Compensation Point: Mechanisms and Relation to the Maximal Metabolic Steady State

At a point during the latter third of an incremental exercise protocol, ventilation begins to exceed the rate of clearance of carbon dioxide (CO2) at the lungs ( V ˙ CO2). The onset of this hyperventilation, which is confirmed by a fall from a period of stability in end-tidal and arterial CO2 tensions (PCO2), is referred to as the respiratory compensation point (RCP). The mechanisms that contribute to the RCP remain debated as does its surrogacy for the maximal metabolic steady state of constant-power exercise (i.e., the highest work rate associated with maintenance of physiological steady state). The objective of this current opinion is to summarize the original research contributions that support and refute the hypotheses that: (i) the RCP represents a rapid, peripheral chemoreceptor-mediated reflex response engaged when the metabolic rate at which the buffering systems can no longer constrain the rise in hydrogen ions ([H+]) associated with rising lactate concentration and metabolic CO2 production is surpassed; and (ii) the metabolic rate at which this occurs is equivalent to the maximal metabolic steady state of constant power exercise. In doing so, we will shed light on potential mechanisms contributing to the RCP, attempt to reconcile disparate findings, make a case for its adoption for exercise intensity stratification and propose strategies for the use of RCP in aerobic exercise prescription.

The highest work rate associated with a predominantly aerobic contribution coincides with the highest work rate at which VO2max can be attained

PURPOSE

To estimate the highest power output at which predominant energy contribution is derived from the aerobic system (aerobic limit power: ALP) and to compare ALP with the upper boundary of the severe intensity exercise domain.

METHODS

Fifteen male individuals participated in this study. The upper boundary was estimated using i) linear relationship between time to achieve V ˙ O2max and time to task failure (PUPPERBOUND), ii) hyperbolic relationships between time to achieve V ˙ O2max vs. power output, and time to task failure vs. power output (PUPPERBOUND´), and iii) precalculated V ˙ O2max demand (IHIGH). ALP was estimated by aerobic, lactic, and phospholytic energy contributions using V ˙ O2 response, blood [lactate] response, and fast component of recovery V ˙ O2 kinetics, respectively.

RESULTS

ALP was determined as the highest power output providing predominant aerobic contribution; however, anaerobic pathways became the predominant energy source when ALP was exceeded by 5% (ALP + 5%) (from 46 to 52%; p = 0.003; ES:0.69). The V ˙ O2 during exercise at ALP was not statistically different from V ˙ O2max (p > 0.05), but V ˙ O2max could not be attained at ALP + 5% (p < 0.01; ES:0.63). ALP was similar to PUPPERBOUND and PUPPERBOUND´ (383 vs. 379 and 384 W; p > 0.05). There was a close agreement between ALP and PUPPERBOUND (r: 0.99; Bias: - 3 W; SEE: 6 W; TE: 8 W; LoA: - 17 to 10 W) and PUPPERBOUND´ (r: 0.98; Bias: 1 W; SEE: 8 W; TE: 8 W; LoA: - 15 to 17 W). ALP, PUPPERBOUND, and PUPPERBOUND´ were greater than IHIGH (339 ± 53 W; p < 0.001).

CONCLUSION

ALP may provide a new perspective to intensity domain framework.

Testing the predictive capacity of a muscle fatigue model on electrically stimulated adductor pollicis

PURPOSE

Based on the critical power (Pc or critical force; Fc) concept, a recent mathematical model formalised the proportional link between the decrease in maximal capacities during fatiguing exercises and the amount of impulse accumulated above Fc. This study aimed to provide experimental support to this mathematical model of muscle fatigability in the severe domain through testing (i) the model identifiability using non-exhausting tests and (ii) the model ability to predict time to exhaustion (tlim) and maximal force (Fmax) decrease.

METHODS

The model was tested on eight participants using electrically stimulated adductor pollicis muscle force. The Fmax was recorded every 15 s for all tests, including five constant tests to estimate the initial maximal force (Fi), Fc, and a time constant (τ). The model's parameters were used to compare the predicted and observed tlim values of the incremental ramp test and Fmax(t) of the sine test.

RESULTS

The results showed that the model accurately estimated Fi, Fc, and τ (CI95% = 2.7%Fi and 9.1 s for Fc and τ, respectively; median adjusted r2 = 0.96) and predicted tlim and Fmax with low systematic and random errors (11 ± 20% and - 1.8 ± 7.7%Fi, respectively).

CONCLUSION

This study revealed the potential applications of a novel mathematical formalisation that encompasses previous research on the critical power concept. The results indicated that the model's parameters can be determined from non-exhaustive tests, as long as maximal capacities are regularly assessed. With these parameters, the evolution of maximal capacities (i.e. fatigability) at any point during a known exercise and the time to exhaustion can be accurately predicted.

Sex differences in elite track and field performances and inferences about steroid doping

Females likely experience larger performance benefits from androgenic-anabolic steroids than males. We set out to determine if there were temporal differences in select athletics (track and field) records between females and males. Exploratory aims included: (1) evaluating the improvements in female and male world records over time, and (2) investigating the influence of doping programs on male and female world records before and after 1990, when sports governing bodies began to implement random out-of-competition and systematic in-competition drug testing. We collected the top 500 performances of all time for both sexes from an online database (worldathletics.org) in four running events (100, 200, 400 and 800 m) and two throwing events (discus throw and shot-put). Data were stratified into quintiles based on world record ranking (1st to 100th, 101st to 200th, etc.). The temporal distribution of the top 100 female performers was significantly earlier than the top 100 male performers (year: 2000 ± 1 vs. 2005 ± 1, respectively; P < 0.0001). Within the event, the top performances occurred significantly earlier for females in the 800 m (year: 1995 ± 15 vs. 2003 ± 12; P = 0.0007) and shot-put (year: 1992 ± 14 vs. 2003 ± 17; P = 0.0004). Among females, world records rapidly improved through the 1980s, but following 1990, the world records ceased to improve. Geographically, there was a greater representation of countries with state-sponsored doping programs, specifically among female performances. We postulate these sex differences in the temporal distribution of top performances are likely associated with enhanced effectiveness of exogenous androgens (steroid doping) among female athletes with lower endogenous androgen hormones compared to males.

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.

Effect of Vocal Function Exercises on the Voice Handicap Index, Vocal Fatigue Index, and Number of Vocal Fatigue Symptoms in Bank Workers: Single-Blinded Randomized Controlled Trial

Vocal fatigue (VF) is a significant portion of occupational voice disorders. Researchers have proposed numerous therapeutic approaches to alleviate VF. However, the efficacy of vocal function exercises (VFEs) as a safe, effective, and simple method is unclear. The current study aims to investigate the effect of VFEs on occupational-related VF in Iranian bank workers. A single-blinded randomized controlled trial with four-level blocking After screening 444 workers, 43 persons with vocal fatigue (VF) were allocated between intervention and control groups. The gender of participants was considered a confounding parameter. Intervention group participants (IGP) (20 males and two females) practiced vocal function exercises (VFEs) (online training) for two weeks, while control group participants (CGP) (20 males and a female) continued their routine lifestyle. The Number of Vocal Fatigue Symptoms (NoVFS), Maximum Phonation Time (MPT), Voice Handicap Index (VHI), and Vocal Fatigue Index (VFI) at pre-intervention and post-intervention levels were gathered and compared. According to the intergroup, pre-/post-intervention differences, and intragroup analysis, the IGP experienced a significant reduction in the NoVFS (P = 0.006, P = 0.009), the mean score VHI (P:0.006, P: 0.001, P: 0.001), the total mean score of VFI (P < 0.001, P < 0.001, P < 0.001), and the first (P = 0.005, P = 0.002, P < 0.001) and second (P = 0.006, P < 0.001) factors' mean score of VFI. Additionally, there was an improvement in the MPT (P < 0.001, P < 0.001, P < 0.001) and the third factor (P = 0.01, P = 0.004, P = 0.021) mean score of VFI. Vocal function exercises can alleviate symptoms, voice handicaps, tiredness, avoidance, and physical discomfort of vocal fatigue in bank workers. Additionally, it can improve glottal (pulmonary) sufficiency and rest recovery of vocal fatigue in this group of workers.

Understanding exercise (in)tolerance in sickle cell disease: impacts of hemolysis and exercise training on skeletal muscle oxygen delivery

Sickle cell disease (SCD) is characterized by central (cardiac) and peripheral vascular dysfunctions, significantly diminishing exercise capacity and quality of life. Although central cardiopulmonary abnormalities in SCD are known to reduce exercise capacity and quality of life; the impact of hemolysis and subsequent cell-free hemoglobin (Hb)-mediated peripheral vascular abnormalities on those outcomes are not fully understood. Despite the recognized benefits of exercise training for cardiovascular health and clinical management in chronic diseases like heart failure, there remains substantial debate on the advisability of regular physical activity for patients with SCD. This is primarily due to concerns that prolonged and/or high-intensity exercise might trigger metabolic shifts leading to vaso-occlusive crises. As a result, exercise recommendations for patients with SCD are often vague or nonexistent, reflecting a gap in knowledge about the mechanisms of exercise intolerance and the impact of exercise training on SCD-related health issues. This mini-review sheds light on recent developments in understanding how SCD affects exercise tolerance, with a special focus on the roles of hemolysis and the release of cell-free hemoglobin in altering cardiovascular and skeletal muscle function. Also highlighted here is the emerging research on the therapeutic effects and safety of exercise training in patients with SCD. In addition, the review identifies future research opportunities to fill existing gaps in our understanding of exercise (in)tolerance in SCD.

Intensity Matters: Effect of Different Work-Matched Efforts on Subsequent Performance in Cyclists

PURPOSE

To assess the effect of 2 work-matched efforts of different intensities on subsequent performance in well-trained cyclists.

METHODS

The present study followed a randomized controlled crossover design. Twelve competitive junior cyclists volunteered to participate (age, 17 [1] y; maximum oxygen uptake, 71.0 [4.7] mL·kg-1·min-1). The power-duration relationship was assessed through 2-minute, 5-minute, and 12-minute field tests under fresh conditions (control). On subsequent days and following a randomized order, participants repeated the aforementioned tests after 2 training sessions matched for mechanical work (∼15 kJ/kg) of different intensities (ie, a moderate-intensity continuous-training [60%-70% of critical power; CP] session or a session including high-intensity intervals [3-min repetition bouts at 110%-120% of the CP interspersed by 3-min rest periods]).

RESULTS

A significantly lower power output was found in the 2-minute test after the high-intensity training session compared not only with the control condition (-8%, P < .001) but also with the moderate-intensity continuous-training session (-7%, P = .003), with no significant differences between the latter conditions. No significant differences between conditions were found for the remaining tests. As a consequence, the high-intensity training session resulted in significantly lower W' values compared to both the control condition (-27%, P = .001) and the moderate-intensity continuous-training session (-26%, P = .012), with no differences between the 2 latter conditions and with no differences for CP.

CONCLUSION

A session including high-intensity intermittent efforts induces a greater fatigue, particularly in short-duration efforts and W', than a work-matched continuous-training session of moderate intensity.

Comparison of Physiological Responses between a W´BAL-INT Training Model and a Critical Power Test

This study aimed to compare acute physiological responses during the W prime (W´) balance training model (W´BAL-INT) with performance in the critical power test (CPTest). Additionally, the study sought to determine the extent of neuromuscular and metabolic fatigue associated with severe and extreme intensity domains. Fourteen road master cyclists (13 male, 1 female) completed graded incremental exercise tests to determine their maximum oxygen uptake and 12-, 7- and 3-min maximal efforts to assess CP and W´ (CPTest). Additionally, they participated in a reconstitutive intermittent training session following the W´BAL-INT model. Physiological responses including oxygen uptake (V˙O2), the heart rate (HR), blood lactate (BLa̅) concentration, and perceptual responses (RPE), were measured and compared to CPTest performance data. The W´BAL-INT induced steady-state physiological responses in V˙O2mean (F = 0.76, p = 0.655) and absolute HR, relative HR and HRCP (F = 0.70, p = 0.704; F = 1.11, p = 0.359; F = 1.70, p = 0.095, respectively) comparable to CPTest. During the 3-min work intervals in the training session, V˙O2 was stable and similar to V˙O2peak (54.2 ± 6.7 to 59.3 ± 4.9 ml·kg-1·min-1) in the CPTest. Furthermore, 4-min rest intervals facilitated recovery up to moderate fatigue levels (80-100% of W´ balance). HR responses were sensitive to interval intensity and accumulated time. Meanwhile, BLa̅ responses and the RPE increased fatigue development during W´BAL-INT. The W´BAL-INT training model generates consistent physiological responses in mean oxygen kinetics, the percentage of CP and the HR, similar to those observed during the CPTest. However, different physiological responses were observed in peak oxygen kinetics and W´ energy balance.

Critical Power and Maximal Lactate Steady State in Cycling: "Watts" the Difference?

From a physiological perspective, the delineation between steady-state and non-steady-state exercise, also referred to as the maximal metabolic steady state, holds paramount importance for evaluating athletic performance and designing and monitoring training programs. The critical power and the maximal lactate steady state are two widely used indices to estimate this threshold, yet previous studies consistently reported significant discrepancies between their associated power outputs. These findings have fueled the debate regarding the interchangeability of critical power and the maximal lactate steady state in practice. This paper reviews the methodological intricacies intrinsic to the determination of these thresholds, and elucidates how inappropriate determination methods and methodological inconsistencies between studies have contributed to the documented differences in the literature. Through a critical examination of relevant literature and by integration of our laboratory data, we demonstrate that differences between critical power and the maximal lactate steady state may be reconciled to only a few Watts when applying appropriate and strict determination criteria, so that both indices may be used to estimate the maximal metabolic steady-state threshold in practice. To this end, we have defined a set of good practice guidelines to assist scientists and coaches in obtaining the most valid critical power and maximal lactate steady state estimates.

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.

Characterizing the Exponential Profile of W' Recovery Following Partial Depletion

PURPOSE

The aim of this study was to characterize W' recovery kinetics in response to a partial W' depletion. We hypothesized that W' recovery following a partial depletion would be better described by a biexponential than by a monoexponential model.

METHODS

Nine healthy men performed a ramp incremental exercise test, three to five constant load trials to determine critical power and W', and 10 experimental trials to quantify W' depletion. Each experimental trial consisted of two constant load work bouts (WB1 and WB2) interspersed by a recovery interval. WB1 was designed to evoke a 25% or 75% W' depletion (DEP 25% and DEP 75% ). Subsequently, participants recovered for 30, 60, 120, 300, or 600 s and then performed WB2 to exhaustion to calculate the observed W' recovery (W' OBS ). W' OBS data were fitted using monoexponential and biexponential models, both with a variable and with a fixed model amplitude. Root mean square error and Akaike information criterion (AIC c ) were calculated to evaluate the models' goodness-of-fit.

RESULTS

The biexponential model fits were associated with overall lower root mean square error values (0.4% to 5.0%) when compared with the monoexponential models (2.9% to 8.0%). However, ΔAIC c resulted in negative values (-15.5 and -23.3) for the model fits where the amplitude was kept free, thereby favoring the use of a monoexponential model for both depletion conditions. For the model fits where the amplitude was fixed at 100%, ΔAIC c was negative for DEP 25% (-15.0) but positive for DEP 75% (11.2). W' OBS values were strongly correlated between both depletion conditions ( r = 0.92) and positively associated with V̇O 2peak , critical power, and gas exchange threshold ( r = 0.67 to 0.77).

CONCLUSIONS

The present study results did not provide evidence in favor of a biexponential modeling technique to characterize W' recovery following a partial depletion. Moreover, we demonstrated that fixed time constants were insufficient to model W' recovery across different depletion levels, and that W' recovery was positively associated with aerobic fitness. These findings underline the importance of employing variable and individualized time constants in future predictive W' models.

The Relationship Between the Moderate-Heavy Boundary and Critical Speed in Running

PURPOSE

Training characteristics such as duration, frequency, and intensity can be manipulated to optimize endurance performance, with an enduring interest in the role of training-intensity distribution to enhance training adaptations. Training intensity is typically separated into 3 zones, which align with the moderate-, heavy-, and severe-intensity domains. While estimates of the heavy- and severe-intensity boundary, that is, the critical speed (CS), can be derived from habitual training, determining the moderate-heavy boundary or first threshold (T1) requires testing, which can be costly and time-consuming. Therefore, the aim of this review was to examine the percentage at which T1 occurs relative to CS.

RESULTS

A systematic literature search yielded 26 studies with 527 participants, grouped by mean CS into low (11.5 km·h-1; 95% CI, 11.2-11.8), medium (13.4 km·h-1; 95% CI, 11.2-11.8), and high (16.0 km·h-1; 95% CI, 15.7-16.3) groups. Across all studies, T1 occurred at 82.3% of CS (95% CI, 81.1-83.6). In the medium- and high-CS groups, T1 occurred at a higher fraction of CS (83.2% CS, 95% CI, 81.3-85.1, and 84.2% CS, 95% CI, 82.3-86.1, respectively) relative to the low-CS group (80.6% CS, 95% CI, 78.0-83.2).

CONCLUSIONS

The study highlights some uncertainty in the fraction of T1 relative to CS, influenced by inconsistent approaches in determining both boundaries. However, our findings serve as a foundation for remote analysis and prescription of exercise intensity, although testing is recommended for more precise applications.

Sex differences in human performance

Sex as a biological variable is an underappreciated aspect of biomedical research, with its importance emerging in more recent years. This review assesses the current understanding of sex differences in human physical performance. Males outperform females in many physical capacities because they are faster, stronger and more powerful, particularly after male puberty. This review highlights key sex differences in physiological and anatomical systems (generally conferred via sex steroids and puberty) that contribute to these sex differences in human physical performance. Specifically, we address the effects of the primary sex steroids that affect human physical development, discuss insight gained from an observational study of 'real-world data' and elite athletes, and highlight the key physiological mechanisms that contribute to sex differences in several aspects of physical performance. Physiological mechanisms discussed include those for the varying magnitude of the sex differences in performance involving: (1) absolute muscular strength and power; (2) fatigability of limb muscles as a measure of relative performance; and (3) maximal aerobic power and endurance. The profound sex-based differences in human performance involving strength, power, speed and endurance, and that are largely attributable to the direct and indirect effects of sex-steroid hormones, sex chromosomes and epigenetics, provide a scientific rationale and framework for policy decisions on sex-based categories in sports during puberty and adulthood. Finally, we highlight the sex bias and problem in human performance research of insufficient studies and information on females across many areas of biology and physiology, creating knowledge gaps and opportunities for high-impact studies.

Measuring critical force in sport climbers: a validation study of the 4 min all-out test on finger flexors

PURPOSE

The critical force (CF) concept, differentiating steady and non-steady state conditions, extends the critical power paradigm for sport climbing. This study aimed to validate CF for finger flexors derived from the 4 min all-out test as a boundary for the highest sustainable work intensity in sport climbers.

METHODS

Twelve participants underwent multiple laboratory visits. Initially, they performed the 4 min intermittent contraction all-out test for CF determination. Subsequent verification visits involved finger-flexor contractions at various intensities, including CF, CF -2 kg, CF -4 kg, and CF -6 kg, lasting for 720 s or until failure, while monitoring muscle-oxygen dynamics of forearm muscles.

RESULTS

CF, determined from the mean force of last three contractions, was measured at 20.1 ± 5.7 kg, while the end-force at 16.8 ± 5.2 kg. In the verification trials, the mean time to failure at CF was 440 ± 140 s, with only one participant completing the 720 s task. When the load was continuously lowered (-2 kg, -4 kg, and -6 kg), a greater number of participants (38%, 69%, and 92%, respectively) successfully completed the 720 s task. Changes of muscle-oxygen dynamics showed a high variability and could not clearly distinguish between exhaustive and non-exhaustive trials.

CONCLUSIONS

CF, based on the mean force of the last three contractions, failed to reliably predict the highest sustainable work rate. In contrast, determining CF as the end-force of the last three contractions exhibited a stronger link to sustainable work. Caution is advised in interpreting forearm muscle-oxygen dynamics, lacking sensitivity for nuanced metabolic responses during climbing-related tasks.

Heat stress and the velocity-duration relationship in amateur runners

Tolerance to high-intensity constant power exercise can be characterized by the hyperbolic power-duration (or velocity-duration) relationship. The hyperbola is defined by the asymptote (critical power or velocity) and the curvature constant (W' or D'). The effects of thermoregulatory stress on middle-distance running performance are equivocal-possibly due to the complexities of the hyperbolic velocity-duration relationship for these relatively short duration events. We aimed to measure the effects of heat stress on the velocity-duration relationship in amateur runners. Fifteen participants (23 ± 6 years) completed a series of constant-velocity running bouts to intolerance in three heat indices (MILD: 20°C, VERY HOT: 38°C, EXTREME: 55°C). Critical velocity (CV) in MILD (3.52 ± 0.86 m/s) was higher than VERY HOT (3.39 ± 0.82 m/s) and EXTREME (3.29 ± 1.05 m/s; F[2.28] = 3.80, p < 0.035) with no effect of thermal stress on D' (F[2.28] = 2.48, p = 0.11). In amateur competitive/recreational runners, heat stress of ≥38°C heat index negatively affected CV. Thus, even during relatively short events, such as middle-distance running where fluid loss is not a primary concern, heat stress may negatively impact performance.

An empirical model for world record running speeds with distance, age, and sex: anaerobic and aerobic contributions to performance

The objective of this study is to derive mathematical equations that closely describe published data on world record running speed as a function of distance, age, and sex. Running speed declines with increasing distance and age. Over long distances, where aerobic metabolism is dominant, speed declines in proportion to the logarithm of distance. Over short distances, anaerobic metabolism contributes significantly to performance, and speed is increased relative to the trend of the long-distance data. Equations are derived that explicitly represent these effects. The decline in speed with age is represented by an age-dependent multiplicative factor, which exhibits increasing sensitivity to age as age increases. Using these equations, data are analyzed separately for males and females, and close fits to published data are demonstrated, particularly for younger age groups. These equations provide insight into the contributions of aerobic and anaerobic components of metabolism to athletic performance and a framework for comparisons of performance across wide ranges of distance and age.NEW & NOTEWORTHY World record speeds at different distances for men and women in different age categories are used to develop a model to predict running performance as a function of race distance, age, and sex. This empirical model quantifies the decline in running speed with distance and age in a way that provides insight into the aerobic and anaerobic contributions to running speed and may help with developing training strategies for different age groups at various distances.

Power output at the moderate-to-heavy intensity transition decreases in a non-linear fashion during prolonged exercise

PURPOSE

The aims of this study were to: (i) describe the time course of the decrease in power output at the moderate-to-heavy intensity transition during prolonged exercise; (ii) investigate the association between durability of the moderate-to-heavy intensity transition and exercise capacity; and (iii) explore physiological correlates of durability of the moderate-to-heavy intensity transition.

METHODS

Twelve trained cyclists (age: 40 ± 8 y, V ˙ O2peak: 52.3 ± 5.2 mL·min-1·kg-1) performed an exhaustive cycling protocol involving alternating incremental exercise tests to determine power output at the moderate-to-heavy intensity transition via the first ventilatory threshold (VT1), and 30-min bouts at 90% of the power output at the previously estimated VT1 in the rested state. The individual time course of VT1 was modelled using linear and second-order polynomial functions, and time to a 5% decrease in VT1 (Δ5%VT1) was estimated using the best-fitting model.

RESULTS

Power output at VT1 decreased according to a second-order polynomial function in 11 of 12 participants. Time-to-task failure (234 ± 66 min) was correlated with Δ5%VT1 (139 ± 78 min, rs = 0.676, p = 0.016), and these were strongly correlated with absolute and relative rates of fat oxidation at specific exercise intensities measured during the incremental test performed in the rested state.

CONCLUSIONS

These data: (i) identify a non-linear time course of decreases in the moderate-to-heavy intensity transition during prolonged exercise; (ii) support the importance of durability of the moderate-to-heavy intensity transition in prolonged exercise capacity; and (iii) suggest durability of the moderate-to-heavy intensity transition is related to fat oxidation rates.

Effects of Back Pressure on the Feasibility and Tolerability of Laryngeal Diadochokinetic Exercise: A Pilot Study

BACKGROUND

The term vocal demand response refers to how speakers meet vocal demands. Vocal loading tasks with predetermined demand parameters (duration, pitch, loudness, etc) have been used in research to study the vocal demand response; these have historically consisted of loud sustained vowel and loud speech tasks. Tasks founded on laryngeal diadochokinesis (LDDK) may be viable alternatives, especially if demand parameters such as exercise-rest ratio and fluid back pressure are concurrently modulated.

OBJECTIVES

To explore the effects of four fluid back pressure conditions (0, 5, 10, and 15 cm H2O) on several measures of subjective participant experience, feasibility, and tolerability during intervallic laryngeal diadochokinetic exercise.

METHODS

Participants (n = 12) completed 15-minute trials of LDDK in 30-second rest and exercise intervals against four counterbalanced back pressure conditions: 0, 5, 10, and 15 cm H2O. The effects of back pressure on (1) ratings of perceived vocal exertion, (2) prevalence of adverse effects such as shortness of breath or lightheadedness, (3) subjective difficulty of sustaining LDDK, (4) number of exercise intervals completed, (5) rankings of participant-preferred back pressure levels, and (6) expert ratings of auditory-perceptual diadochokinetic strength were assessed descriptively.

RESULTS

Perceived vocal exertion, lightheadedness, and subjective laryngeal diadochokinetic difficulty increased as back pressure increased. Number of intervals completed, auditory-perceptual diadochokinetic strength, and participant rankings of back pressure conditions, by contrast, decreased as back pressure increased. 0 and 5 cm H2O were the most preferred back pressure conditions overall.

DISCUSSION

Fluid back pressure was feasible and broadly tolerated during 15-minute trials of vocal exercise. However, the transition from 5 → 10 cm H2O appeared to represent an inflection point in our results: a minority of participants did not tolerate exercise at 10 cm H2O, becoming a majority at 15 cm H2O. We conclude that fluid back pressure should be restricted to values between 0 and 10 cm H2O during LDDK.

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.

Muscle Strength Preservation During Repeated Sets of Fatiguing Resistance Exercise: A Secondary Analysis

ABSTRACT

Nuzzo, JL. Muscle strength preservation during repeated sets of fatiguing resistance exercise: A secondary analysis. J Strength Cond Res 38(6): 1149-1156, 2024-During sustained or repeated maximal voluntary efforts, muscle fatigue (acute strength loss) is not linear. After a large initial decrease, muscle strength plateaus at approximately 40% of baseline. This plateau, which likely reflects muscle strength preservation, has been observed in sustained maximal isometric and repeated maximal isokinetic contractions. Whether this pattern of fatigue occurs with traditional resistance exercise repetitions with free weights and weight stack machines has not been overviewed. Here, the aim was to determine whether the number of repetitions completed across 4 or more consecutive repetitions-to-failure tests exhibits the same nonlinear pattern of muscle fatigue. A secondary analysis was applied to data extracted as part of a recent meta-analysis on repetitions-to-failure tests. Studies were eligible if they reported mean number of repetitions completed in 4-6 consecutive repetitions-to-failure tests at a given relative load. Twenty-nine studies were included. Overall, the results show that the number of repetitions completed in consecutive repetitions-to-failure tests at a given load generally decreases curvilinearly. The numbers of repetitions completed in sets 2, 3, 4, 5, and 6 were equal to approximately 70, 55, 50, 45, and 45% of the number of repetitions completed in set 1, respectively. Longer interset rest intervals typically attenuated repetition loss, but the curvilinear pattern remained. From the results, a chart was created to predict the number of repetitions across 6 sets of resistance exercise taken to failure based on the number of repetitions completed in set 1. The chart is a general guide and educational tool. It should be used cautiously. More data from a variety of exercises, relative loads, and interset rest intervals are needed for more precise estimates of number of repetitions completed during repeated sets of fatiguing resistance exercise.

Differential effects of exercise intensity and tolerable duration on exercise-induced diaphragm and expiratory muscle fatigue

We investigated the effect of exercise intensity and tolerable duration on the development of exercise-induced diaphragm and expiratory muscle fatigue. Ten healthy adults (25 ± 5 yr; 2 females) cycled to intolerance on three separate occasions: 1) 5% below critical power ( 0.05). In conclusion, the magnitude of exercise-induced diaphragm fatigue was greater after longer-duration severe exercise than after shorter-duration severe and heavy exercise. By contrast, the magnitude of exercise-induced expiratory muscle fatigue was unaffected by exercise intensity and tolerable duration.NEW & NOTEWORTHY Exercise-induced respiratory muscle fatigue contributes to limiting exercise tolerance. Accordingly, better understanding the exercise conditions under which respiratory muscle fatigue occurs is warranted. Although heavy-intensity as well as short- and long-duration severe-intensity exercise performed to intolerance elicit diaphragm and expiratory muscle fatigue, we find, for the first time, that the relationship between exercise intensity, exercise duration, and the magnitude of exercise-induced fatigue is different for the diaphragm compared with the expiratory muscles.

Is all work the same? Performance after accumulated work of differing intensities in male professional cyclists

OBJECTIVES

Although the ability to attenuate power output (PO) declines after accumulated work (i.e., 'durability') is increasingly recognized as a major determinant of cycling performance, the potential role of the intensity of the previous work is unclear. We assessed the effect of work-matched levels of accumulated work at different intensities on performance in male professional cyclists.

DESIGN

Observational field-based study.

METHODS

PO data was registered in 17 cyclists during a competition season, and the critical power (CP) was repeatedly determined every 4 weeks from training sessions and competitions. Participants' maximum mean power (MMP) for different durations (5 s, 5 min, 10 min, and 20 min) and the CP were determined under 'fresh' conditions (0 kJ·kg-1) and after varying levels of accumulated work (2.5, 5.0 and 7.5 kJ·kg-1) at intensities below and above the CP.

RESULTS

A significant decline was found for all MMP values following all levels of accumulated work above the CP (-4.0 %, -1.7 %, -1.8 %, and -3.2 % for 30s, 5 min, 10 min and 20 min-MMP, respectively; all p < 0.001), versus no change after any level of accumulated work below the CP (all p > 0.05). Similar results were observed for the CP, which decreased after all levels of accumulated work above (-2.2 %, -6.1 %, and -16.2 %, after 2.5, 5.0 and 7.5 kJ·kg-1, p < 0.001) but not below this indicator (p > 0.05).

CONCLUSIONS

In male professional cyclists, accumulated work above the CP impairs performance compared with work-matched, albeit less intense efforts. This raises concerns on the use of mechanical work per se as a single fatigue/stress indicator in these athletes.

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.

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.