Shorter intervals at peak SV vs.V̇O2max may yield high SV with less physiological stress

Carbohydrate ingestion does not suppress increases in fatty acid-binding protein 4 concentrations post-acute aerobic exercise in healthy men: a randomized crossover study

BACKGROUND

Fatty acid-binding protein 4 (FABP4) has been associated with cardiovascular disease and diabetes. Acute aerobic exercise increases circulating FABP4 concentrations, but the underlying mechanisms remain unclear. The purpose of this study was to investigate the effects of inhibition of lipolysis by carbohydrate ingestion on circulating FABP4 concentrations during and after acute aerobic exercise in healthy men.

METHODS

Men aged between 20 and 40, with no exercise habits and no metabolic diseases, were recruited. In a randomized crossover design, the participants underwent a carbohydrate-ingestion exercise (CE) and a fasted exercise (FE) trial. The CE trial consisted of 40-min acute aerobic exercise with ingestion of carbohydrates and 60-min bed rest. The FE trial followed the same protocol as the CE trial but without carbohydrate ingestion. Venous blood samples were collected to measure hormones (adrenaline, noradrenaline, and insulin) metabolites (glycerol, free fatty acids, and glucose), and FABP4 concentrations. Ventilation and gas exchange were also collected to measure substrate oxidation.

RESULTS

Thirteen healthy men participated in and completed both the CE and FE trials. The insulin concentration was more than 4 times higher in the CE trial than in the FE trial (p < 0.004, effect size [ES] > 2.00). Free fatty acid concentrations were more than 4 times lower in the CE trial than in the FE trial (p < 0.02, ES > 2.04). However, there was no significant difference in the changes in circulating FABP4 concentrations between the CE and FE trials (p = 0.108), which did not change during aerobic exercise and significantly increased post-aerobic exercise in both trials (p < 0.002, ES > 1.212). Changes in FABP4 concentrations following aerobic exercise were not significantly correlated with changes in glycerol or free fatty acid concentrations during aerobic exercise.

CONCLUSIONS

The results suggest that suppression of lipolysis and elevation of insulin are not strongly involved in increases in FABP4 secretion following acute aerobic exercise.

Cardiovascular responses of exercises performed within the extreme exercise domain

Stroke volume (SV), heart rate (HR) and arterio-venous O2 difference (a-vO2diff) responses to heavy and severe-intensity exercise have been well documented; however, there is a lack of information on the SV, HR and a v-O2diff responses of work rates within extreme exercise domain. The aim of this study was, therefore, to focus on central and peripheral components of VO2 responses to exercises performed within the heavy, severe and extreme exercise domain. Eight well-trained male cyclists participated in this study. Maximal O2 consumption (VO2max) and corresponding work rate (P@VO2max) were determined by multisession constant work rate exercises. Cardiovascular responses to exercises were evaluated by nitrous-oxide rebreathing method with work rates from 40 % to 160 % of P@VO2max, VO2max corresponded to 324+/-39.4 W; however, maximal SV responses occurred at 205+/-54.3 W (p<0.01). Maximal cardiac output (Q), HR, and a vO2diff responses were revealed by the P@VO2max. VO2 response to exercise significantly decreased from severe-intense exercises to the first work rate of extreme exercise domain due to significant decreases in Q, SV, and HR responses (p<0.05), except a v-O2diff (p>0.05). Moreover, non-significant decreases in Q, SV, and a v-O2diff were evaluated as response to increase in work rate belonging to extreme work rates (p>0.05), except the HR (p<0.05). Work rates within the lower district of the extreme exercise domain have an important potential to improve peripheral component of VO2, while the P@VO2max seems the most appropriate intensity for aerobic endurance development as it maximizes the central component of VO2max.

Development potentials of commonly used high-intensity training strategies on central and peripheral components of maximal oxygen consumption

The aim of this study was to reveal the development potentials of five high-intensity training models on central and peripheral components of maximal oxygen consumption (VO_2max). Following VO_2max determination, maximal cardiac output (Q_max), maximal stroke volume (SV_max), and maximal arteriovenous O₂ difference (a-vO_{2diff_max}) were analysed. Short-interval- (short-HIIT), long-interval (long-HIIT), alternating work-rate continuous (alter-HIT), constant work-rate continuous (const-HIT), and sprint interval (SIT) sessions were performed on separate days with iso-effort and iso-time methods. Time spent (t_spent) at > 95% of VO_2max was the highest in long-HIIT (p < 0.05). The t_spent at > 90% of Q_max was higher in alter-HIT than long-HIIT and SIT (p < 0.05), while there was no significant difference for t_spent at > 90% of SV_max amongst high-intensity trainings. The t_spent at > 90% of a-vO_2diff__max was higher in short-HIIT and long-HIIT than other modalities (p < 0.05). It can be said that continuous modalities seem to have a higher potential to improve central part of VO_2max, while interval modalities may be better to develop peripheral component.

Is a verification phase useful for confirming maximal oxygen uptake in apparently healthy adults? A systematic review and meta-analysis

BACKGROUND

The 'verification phase' has emerged as a supplementary procedure to traditional maximal oxygen uptake (VO2max) criteria to confirm that the highest possible VO2 has been attained during a cardiopulmonary exercise test (CPET).

OBJECTIVE

To compare the highest VO2 responses observed in different verification phase procedures with their preceding CPET for confirmation that VO2max was likely attained.

METHODS

MEDLINE (accessed through PubMed), Web of Science, SPORTDiscus, and Cochrane (accessed through Wiley) were searched for relevant studies that involved apparently healthy adults, VO2max determination by indirect calorimetry, and a CPET on a cycle ergometer or treadmill that incorporated an appended verification phase. RevMan 5.3 software was used to analyze the pooled effect of the CPET and verification phase on the highest mean VO2. Meta-analysis effect size calculations incorporated random-effects assumptions due to the diversity of experimental protocols employed. I2 was calculated to determine the heterogeneity of VO2 responses, and a funnel plot was used to check the risk of bias, within the mean VO2 responses from the primary studies. Subgroup analyses were used to test the moderator effects of sex, cardiorespiratory fitness, exercise modality, CPET protocol, and verification phase protocol.

RESULTS

Eighty studies were included in the systematic review (total sample of 1,680 participants; 473 women; age 19-68 yr.; VO2max 3.3 ± 1.4 L/min or 46.9 ± 12.1 mL·kg-1·min-1). The highest mean VO2 values attained in the CPET and verification phase were similar in the 54 studies that were meta-analyzed (mean difference = 0.03 [95% CI = -0.01 to 0.06] L/min, P = 0.15). Furthermore, the difference between the CPET and verification phase was not affected by any of the potential moderators such as verification phase intensity (P = 0.11), type of recovery utilized (P = 0.36), VO2max verification criterion adoption (P = 0.29), same or alternate day verification procedure (P = 0.21), verification-phase duration (P = 0.35), or even according to sex, cardiorespiratory fitness level, exercise modality, and CPET protocol (P = 0.18 to P = 0.71). The funnel plot indicated that there was no significant publication bias.

CONCLUSIONS

The verification phase seems a robust procedure to confirm that the highest possible VO2 has been attained during a ramp or continuous step-incremented CPET. However, given the high concordance between the highest mean VO2 achieved in the CPET and verification phase, findings from the current study would question its necessity in all testing circumstances.

PROSPERO REGISTRATION ID

CRD42019123540.

Moderate Intensity Intermittent Exercise Modality May Prevent Cardiovascular Drift

Cardiovascular drift (CV-Drift) may occur after the ~10th min of submaximal continuous exercising. The purpose of this study was to examine whether CV-Drift is prevented by an intermittent exercise modality, instead of a continuous exercise. Seven well-trained male cyclists volunteered to take part in the study (V˙O_2max: 61.7 ± 6.13 mL·min⁻¹·kg⁻¹). Following familiarization sessions, athletes’ individual maximal O₂ consumption (V˙O_2max), maximum stroke volume responses (SV_max), and cardiac outputs (Qc) were evaluated by a nitrous-oxide re-breathing system and its gas analyzer. Then, continuous exercises were performed 30 min at cyclists’ 60% V˙O_2max, while intermittent exercises consisted of three 10 min with 1:0.5 workout/recovery ratios at the same intensity. Qc measurements were taken at the 5th, 9th, 12nd, 15th, 20th, 25th, and 30th min of continuous exercises versus 5th and 10th min of workout phases of intermittent exercise modality. Greater than a 5% SV decrement, with accompanying HR, increase, while Qc remained stable and was accepted as CV-Drift criterion. It was demonstrated that there were greater SV responses throughout intermittent exercises when compared to continuous exercises (138.9 ± 17.9 vs. 144.5 ± 14.6 mL, respectively; p ≤ 0.05) and less HR responses (140.1 ± 14.8 vs. 135.2 ± 11.6 bpm, respectively; p ≤ 0.05), while mean Qc responses were similar (19.4 ± 2.1 vs. 19.4 ± 1.5 L, respectively; p > 0.05). Moreover, the mean times spent at peak SV scores of exercise sessions were greater during intermittent exercise (1.5 vs. 10 min) (p < 0.001). In conclusion, intermittent exercises reduce CV-Drift risk and increases cardiac adaptation potentials of exercises with less physiological stress.

Re-Evaluation of Old Findings on Stroke Volume Responses to Exercise and Recovery by Nitrous-Oxide Rebreathin

It is important to verify the old findings of Cumming (1972) and Goldberg and Shephard (1980) who showed that stroke volume (SV) may be higher during recovery rather than during exercise, in order to organize the number of intervals throughout training sessions. The purpose of this study was to re-evaluate individual SV responses to various upright cycling exercises using the nitrous-oxide rebreathing method. Nine moderate to well-trained male athletes volunteered to take part in the study (maximal O₂ uptake (VO_2max): 60.2 ± 7 mL⋅min^-1⋅kg^-1). Workloads ranging from 40-100% of VO_2max were applied to determine individual peak SV (SV_peak) response. Results showed that SV responses were higher during exercise compared to recovery in all exercise loads from 40-100% of VO_2max. Mean SV responses to individual SVpeak loads were also higher during exercise compared to recovery (122.9 ± 2.5 versus 105.3 ± 5.93 mL). The highest SV responses to 10 min exercises of 40-70% of VO_2max were obtained in the 5^th or 7.5^th min of each stage (p≤0.05). Meanwhile, during 5 min exercises between 80-100% of VO_2max, peak SV responses were observed in the 3^rd min of loading (p≤0.05). In conclusion, individual SVpeak levels encountered over wide exercise intensity ranges showed that SVpeak development may also be correlated to exercise intensity corresponding to individual SV_peak loads.