Conventional methods to prescribe exercise intensity are ineffective for exhaustive interval training

Purpose To compare methods of relative intensity prescription for their ability to normalise performance (i.e., time to exhaustion), physiological, and perceptual responses to high-intensity interval training (HIIT) between individuals. Methods Sixteen male and two female cyclists (age: 38 ± 11 years, height: 177 ± 7 cm, body mass: 71.6 ± 7.9 kg, maximal oxygen uptake ( V̇ O2max): 54.3 ± 8.9 ml·kg−1 min −1 ) initially undertook an incremental test to exhaustion, a 3 min all-out test, and a 20 min time-trial to determine prescription benchmarks. Then, four HIIT sessions (4 min on, 2 min off) were each performed to exhaustion at: the work rate associated with the gas exchange threshold ( Ẇ GET ) plus 70% of the difference between Ẇ GET and the work rate associated with V̇ O2max ; 85% of the maximal work rate of the incremental test (85%Ẇ max ); 120% of the mean work rate of the 20 min time-trial (120%TT); and the work rate predicted to expend, in 4 min, 80% of the work capacity above critical power. Acute HIIT responses were modelled with participant as a random effect to provide estimates of inter-individual variability. Results For all dependent variables, the magnitude of inter-individual variability was high, and confidence intervals over-lapped substantially, indicating that the relative intensity normalisation methods were similarly poor. Inter-individual coefficients of variation for time to exhaustion varied from 44.2% (85%Ẇ max ) to 59.1% (120%TT), making it difficult to predict acute HIIT responses for an individual. Conclusion The present study suggests that the methods of intensity prescription investigated do not normalise acute responses to HIIT between individuals

Laboratory predictors of uphill cycling performance in trained cyclists

This study aimed to assess the relationship between an uphill time-trial (TT) performance and both aerobic and anaerobic parameters obtained from laboratory tests. Fifteen cyclists performed a Wingate anaerobic test, a graded exercise test (GXT) and a field-based 20-min TT with 2.7% mean gradient. After a 5-week non-supervised training period, 10 of them performed a second TT for analysis of pacing reproducibility. Stepwise multiple regressions demonstrated that 91% of TT mean power output variation (W kg-1) could be explained by peak oxygen uptake (ml kg-1.min-1) and the respiratory compensation point (W kg-1), with standardised beta coefficients of 0.64 and 0.39, respectively. The agreement between mean power output and power at respiratory compensation point showed a bias ± random error of 16.2 ± 51.8 W or 5.7 ± 19.7%. One-way repeated-measures analysis of variance revealed a significant effect of the time interval (123.1 ± 8.7; 97.8 ± 1.2 and 94.0 ± 7.2% of mean power output, for epochs 0-2, 2-18 and 18-20 min, respectively; P < 0.001), characterising a positive pacing profile. This study indicates that an uphill, 20-min TT-type performance is correlated to aerobic physiological GXT variables and that cyclists adopt reproducible pacing strategies when they are tested 5 weeks apart (coefficients of variation of 6.3; 1 and 4%, for 0-2, 2-18 and 18-20 min, respectively)

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Time to retire the raw analysis of individual responses

This letter critiques the data analysis of a study investigating peak oxygen uptake responses to cycling and running sprint interval training (Digby et al. 2023 J Strength Cond Res, 37(4), e313-e316). While the study effectively demonstrates the specificity principle in the context of sprint interval training, concerns arise regarding the methodology used to categorise participants as responders or non-responders. The letter highlights the disregard for the recommendations of a number of academics advocating for specific experimental designs and statistical analyses to examine inter-individual variability. Furthermore, the reliability of within-individual adaptive responses to training and the potential impact of measurement errors and biological fluctuations are considered. It is suggested that the (non-)responder categorisation adds nothing to the main findings of the study and should be avoided. The importance of using appropriate experimental designs and statistical analyses when investigating inter-individual variability is emphasised. An open-source beta-version simulator is introduced as an educational resource to demonstrate the limitations inherent in the responder counting approach

Variáveis laboratoriais, desempenho e pacing no ciclismo contra-relógio de 20 minutos realizado em subida

For a wider applicability of the 20-min time trial (TT) testing protocol in field, it is necessary to understand (1) how performance in an uphill course relates with typical laboratory measures and (2) the pacing profile adopted. Separated by at least 48 hours, 15 moderately trained cyclists, including 1 female (30.8±4.8 years; 176.5±8.0 cm; 78.9±14.5 kg; 56.1±7.7 ml.kg-1.min-1; mean ± standard deviation), initially performed a Wingate anaerobic test, a graded exercise test to exhaustion and a 20-min field time trial in a 2.7% gradient uphill course. After 5 weeks of nonsupervised training, 10 from 15 volunteers performed a second TT for comparison of the pacing adopted. Stepwise multiple linear regressions demonstrated that 91% of TT mean power output variation (W.kg-1) can be explained by peak oxygen consumption (ml.kg-1.min-1) and respiratory compensation point (W.kg-1), with standardized beta coefficients of 0.64 and 0.39 respectively. Performing TT on ascents premises a 94.6% mean power output adjustment in order to improve the agreement with respiratory compensation point power output, which Bland-Altman plot showed a bias ± random error of 0.4±49.7 W or -0.1±19.7 %. Repeated measures two-way ANOVA (TT X time) revealed a main effect of the time intervals (p < 0.001) on the power output of each portion (122.2±10.0; 97.8±1.2 e 95.1±7.1% for the portions 0-2, 2-18 e 18-20 min, respectively) characterizing a positive pacing profile, either in the first and in the second test (p = 0.116). Together, this information indicates that the 20-min TT testing protocol performed on ascent is apparently robust for performance monitoring of different competitive level cyclists. However, more specific new studies are important to confirm performance reproducibility and to verify the influence of power output instant feedback.Para maior empregabilidade do protocolo de teste contra-relógio (CR) de 20 min em campo, é necessária a compreensão (1) de como o desempenho em percurso de subida se relaciona com as medidas laboratoriais típicas e (2) do perfil de pacing adotado. Separados por pelo menos 48 horas, 15 ciclistas moderadamente treinados, incluindo 1 do sexo feminino (30,8±4,8 anos; 176,5±8,0 cm; 78,9±14,5 kg; 56,1±7,7 ml.kg-1.min-1; média ± desvio padrão), realizaram inicialmente um teste anaeróbio Wingate, um teste de esforço incremental até a exaustão e um contrarelógio de campo por 20 min em percurso de subida com 2,7% de inclinação média. Após 5 semanas de treinamento não supervisionado, 10 dos 15 voluntários realizaram um segundo CR para comparação do pacing adotado. As regressões lineares múltiplas stepwise demonstraram que 91% da variação na potência média produzida no CR (W.kg-1) pode ser explicada pelo pico do consumo de oxigênio (ml.kg-1.min-1) e pelo ponto de compensação respiratória (W.kg-1), com coeficientes beta padronizados de 0,64 e 0,39 respectivamente. A realização do CR em aclive pressupõe um ajuste de 94,6% da potência média, de modo a aperfeiçoar a concordância com a potência referente ao ponto de compensação respiratória, em que o diagrama de Bland-Altman demonstrou um viés ± erro aleatório de 0,4±49,7 W ou -0,1±19,7 %. A ANOVA two-way (CR X tempo) para medidas repetidas revelou efeito principal dos intervalos de tempo (p < 0,001) na potência média produzida em cada trecho (122,2±10,0; 97,8±1,2 e 95,1±7,1% para os trechos 0-2, 2-18 e 18-20 min, respectivamente) caracterizando perfil de pacing positivo, tanto no primeiro, quanto no segundo teste (p = 0,116). Em conjunto, estas informações indicam que o protocolo de teste CR de 20 min realizado em subida, aparentemente, seja robusto para monitorar o desempenho de ciclistas de diferentes níveis competitivos. Entretanto, novos estudos mais específicos são importantes para confirmar a reprodutibilidade do desempenho e para verificar a influência do feedback instantâneo da potência produzida

Optimising Exercise Intensity Prescription to Reduce Adaptive Variability Following High-Intensity Interval Training

The aim of this thesis was to optimise intensity prescription for high-intensity interval training (HIIT), ultimately enhancing the magnitude of the training stimulus, and reducing inter-individual variability in adaptive responses. In Chapter 4, it was demonstrated that %Δ, a method wherein maximal and submaximal performance determinants are considered to prescribe exercise intensity, elicits large inter- and intra-individual variability in performance, physiological, and perceptual responses to HIIT. In Chapter 5, the large interindividual variability observed in Chapter 4 was reproduced when %Δ and other methods of intensity prescription were tested, including percentage of maximal oxygen uptake, percentage of maximal work rate in an incremental test (%Ẇmax), percentage of average work rate sustained in a 20-min time-trial, and percentage expenditure of work capacity above critical power. In Chapter 6, it was demonstrated that prescribing HIIT with work intervals of variable power output may maximise the cardiorespiratory stress of training without incurring additional effort (quantified by ratings of perceived exertion) or metabolic stress (quantified by blood lactate concentration). In Chapter 7, it was demonstrated that most training sessions are completed by participants training at their maximal sustainable work rate, whereas sessions performed at 80%Ẇmax are often interrupted prematurely due to exhaustion, despite a similar training intensity on average. It was also demonstrated that the magnitude of inter-individual variability in adaptive responses, although only detected for maximal oxygen uptake and self-paced HIIT performance, was not influenced by how training intensity was prescribed. There were no prescription method effects on mean adaptive responses. Overall, this thesis questions some intensity prescription methods used for HIIT, provides evidence that varying power output during work intervals may maximise training stimulus, demonstrates that a maximal self-paced performance may be used as an intensity prescription benchmark, and challenges the belief that how training intensity is prescribed/normalised affects adaptive response variability

Adding intermittent vibration to varied-intensity work intervals: no extra benefit

Varied-intensity work intervals have been shown to induce higher fractions of maximal oxygen uptake during high-intensity interval training compared with constant-intensity work intervals. We assessed whether varied-intensity work intervals combined with intermittent vibration could further increase cyclists’ fraction of maximal oxygen uptake to potentially optimise adaptive stimulus. Thirteen cyclists (V̇O2max: 69.7±7.1 ml·kg-1·min-1) underwent a performance assessment and two high-intensity interval training sessions. Both comprised six 5-minute varied-intensity work intervals within which work rate was alternated between 100% (3x30-second blocks, with or without vibration) and 77% of maximal aerobic power (always without vibration). Adding vibration to varied-intensity work intervals did not elicit longer time above ninety percent of maximal oxygen uptake (415±221 versus 399±209 seconds, P=0.69). Heart rate- and perceptual-based training-load metrics were also not affected (all P≥0.59). When considering individual work intervals, no between-condition differences were found (fraction of maximal oxygen uptake, P=0.34; total oxygen uptake, P=0.053; mean minute ventilation, P=0.079; mean heart rate, P=0.88; blood lactate concentration, P=0.53; ratings of perceived exertion, P=0.29). Adding intermittent vibration to varied-intensity work intervals does not increase the fraction of maximal oxygen uptake elicited. Whether intermittent exposure to vibration can enhance cyclists’ adaptive stimulus triggered by high-intensity interval training remains to be determined