Rest interval duration does not influence adaptations in acid/base transport proteins following 10 wk of sprint-interval training in active women

Exercise influence on monocarboxylate transporter 1 (MCT1) and 4 (MCT4) in the skeletal muscle: A systematic review

This review aims to systematically analyze the effect of exercise on muscle MCT protein levels and mRNA expression of their respective genes, considering exercise intensity, and duration (single-exercise session and training program) in humans and rodents, to observe whether both models offer aligned results. The review also aims to report methodological aspects that need to be improved in future studies. A systematic search was conducted in the PubMed and Web of Science databases, and the Preferred Reporting Items for Systematic review and Meta-Analyses (PRISMA) checklist was followed. After applying inclusion and exclusion criteria, 41 studies were included and evaluated using the Cochrane collaboration tool for risk of bias assessment. The main findings indicate that exercise is a powerful stimulus to increase MCT1 protein content in human muscle. MCT4 protein level increases can also be observed after a training program, although its responsiveness is lower compared to MCT1. Both transporters seem to change independently of exercise intensity, but the responses that occur with each intensity and each duration need to be better defined. The effect of exercise on muscle mRNA results is less defined, and more research is needed especially in humans. Moreover, results in rodents only agree with human results on the effect of a training program on MCT1 protein levels, indicating increases in both. Finally, we addressed important and feasible methodological aspects to improve the design of future studies.

Metabolomic responses to high-intensity interval exercise in equine skeletal muscle: effects of rest interval duration

High-intensity interval training has attracted considerable attention as a time-efficient strategy for inducing physiological adaptations, but the underlying mechanisms have yet to be elucidated. By using metabolomics techniques, we investigated changes in the metabolic network responses in Thoroughbred horses to high-intensity interval exercise performed with two distinct (15 min or 2 min) rest intervals. The peak plasma lactate level was higher during high-intensity exercise with a 2 min rest duration than that with a 15 min rest duration (24.5±6.8 versus 13.3±2.7 mmol l-1). The arterial oxygen saturation was lower at the end of all exercise sessions with a 2 min rest duration than that with a 15 min rest duration. Metabolomic analysis of skeletal muscle revealed marked changes in metabolite concentrations in the first and third bouts of the 15 min rest interval conditions. In contrast, there were no metabolite concentrations or pathways that significantly changed during the third bout of exercise performed with a 2 min rest interval. Our findings suggest that the activity of each energy production system is not necessarily reflected by apparent changes in metabolite concentrations, potentially due in part to a better match between metabolite flux into and out of the pathway and cycle, as well as between metabolite production and disposal. This study provides evidence that changes in metabolite concentrations vary greatly depending on the number of repetitions and the length of rest periods between exercises, even if the exercises themselves are identical.

Body composition, cardiorespiratory fitness, and neuromuscular adaptations induced by a home-based whole-body high intensity interval training

Background/objective

Bodyweight exercises performed at home could be a complementary approach to improve health-related fitness in people having little spare time and during stay-at-home periods. This study then investigated body composition, cardiorespiratory fitness, and neuromuscular adaptations to a home-based, video-directed, whole-body high-intensity interval training (WB-HIIT).

Methods

Fourteen subjects participated to an 8-week WB-HIIT (6 females, 23 ± 1 years) and fourteen were included in a non-exercise control group (CTL; 6 females, 24 ± 4 years). All took part to pre- and post-intervention assessments of body composition, peak oxygen uptake (VO₂peak) and first ventilatory threshold (VT1; index of aerobic capacity), dynamic (leg press 3-repetition maximum) and isometric strength (knee extensors maximal isometric contractions with assessment of voluntary activation), and muscle endurance during an isometric submaximal contraction maintained till exhaustion. WB-HIIT consisted in 30-s all-out whole-body exercises interspaced with 30 s of active recovery. Training sessions were performed at home by means of videos with demonstration of exercises. Heart rate was monitored during sessions.

Results

WB-HIIT increased VO₂peak (5%), VT1 (20%), leg lean mass (3%), dynamic (13%) and isometric strength (6%), and muscle endurance (28%; p < 0.05), while they did not improve in CTL. VO₂peak increase was correlated (r = 0.56; p < 0.05) with the time spent above 80% of maximal heart rate during training sessions. Isometric strength increase was correlated with change in voluntary activation (r = 0.74; p < 0.01).

Conclusion

The home-based WB-HIIT induced concomitant cardiorespiratory fitness and neuromuscular improvements. The predominant effect was observed for aerobic capacity and muscle endurance which could improve exercise tolerance and reduce fatigability.

High Intensity Interval Training: A Potential Method for Treating Sarcopenia

Sarcopenia, an age-related disease characterized by loss of muscle strength and muscle mass, has attracted the attention of medical experts due to its severe morbidity, low living quality, high expenditure of health care, and mortality. Traditionally, persistent aerobic exercise (PAE) is considered as a valid way to attenuate muscular atrophy. However, nowadays, high intensity interval training (HIIT) has emerged as a more effective and time-efficient method to replace traditional exercise modes. HIIT displays comprehensive effects on exercise capacity and skeletal muscle metabolism, and it provides a time-out for the recovery of cardiopulmonary and muscular functions without causing severe adverse effects. Studies demonstrated that compared with PAE, HIIT showed similar or even higher effects in improving muscle strength, enhancing physical performances and increasing muscle mass of elder people. Therefore, HIIT might become a promising way to cope with the age-related loss of muscle mass and muscle function. However, it is worth mentioning that no study of HIIT was conducted directly on sarcopenia patients, which is attributed to the suspicious of safety and validity. In this review, we will assess the effects of different training parameters on muscle and sarcopenia, summarize previous papers which compared the effects of HIIT and PAE in improving muscle quality and function, and evaluate the potential of HIIT to replace the status of PAE in treating old people with muscle atrophy and low modality; and point out drawbacks of temporary experiments. Our aim is to discuss the feasibility of HIIT to treat sarcopenia and provide a reference for clinical scientists who want to utilize HIIT as a new way to cope with sarcopenia.

Muscle Ionic Shifts During Exercise: Implications for Fatigue and Exercise Performance

Exercise causes major shifts in multiple ions (e.g., K⁺ , Na⁺ , H⁺ , lactate^- , Ca²⁺ , and Cl^- ) during muscle activity that contributes to development of muscle fatigue. Sarcolemmal processes can be impaired by the trans-sarcolemmal rundown of ion gradients for K⁺ , Na⁺ , and Ca²⁺ during fatiguing exercise, while changes in gradients for Cl^- and Cl^- conductance may exert either protective or detrimental effects on fatigue. Myocellular H⁺ accumulation may also contribute to fatigue development by lowering glycolytic rate and has been shown to act synergistically with inorganic phosphate (Pi) to compromise cross-bridge function. In addition, sarcoplasmic reticulum Ca²⁺ release function is severely affected by fatiguing exercise. Skeletal muscle has a multitude of ion transport systems that counter exercise-related ionic shifts of which the Na⁺ /K⁺ -ATPase is of major importance. Metabolic perturbations occurring during exercise can exacerbate trans-sarcolemmal ionic shifts, in particular for K⁺ and Cl^- , respectively via metabolic regulation of the ATP-sensitive K⁺ channel (K_ATP ) and the chloride channel isoform 1 (ClC-1). Ion transport systems are highly adaptable to exercise training resulting in an enhanced ability to counter ionic disturbances to delay fatigue and improve exercise performance. In this article, we discuss (i) the ionic shifts occurring during exercise, (ii) the role of ion transport systems in skeletal muscle for ionic regulation, (iii) how ionic disturbances affect sarcolemmal processes and muscle fatigue, (iv) how metabolic perturbations exacerbate ionic shifts during exercise, and (v) how pharmacological manipulation and exercise training regulate ion transport systems to influence exercise performance in humans. © 2021 American Physiological Society. Compr Physiol 11:1895-1959, 2021.

The effect of blood-flow-restricted interval training on lactate and H+ dynamics during dynamic exercise in man

AIM

To assess how blood-flow-restricted (BFR) interval-training affects the capacity of the leg muscles for pH regulation during dynamic exercise in physically trained men.

METHODS

Ten men (age: 25 ± 4y; V ˙ O 2 max : 50 ± 5 mL∙kg^-1 ∙min^-1 ) completed a 6-wk interval-cycling intervention (INT) with one leg under BFR (BFR-leg; ~180 mmHg) and the other without BFR (CON-leg). Before and after INT, thigh net H⁺ -release (lactate-dependent, lactate-independent and sum) and blood acid/base variables were measured during knee-extensor exercise at 25% (Ex25) and 90% (Ex90) of incremental peak power output. A muscle biopsy was collected before and after Ex90 to determine pH, lactate and density of H⁺ -transport/buffering systems.

RESULTS

After INT, net H⁺ release (BFR-leg: 15 ± 2; CON-leg: 13 ± 3; mmol·min^-1 ; Mean ± 95% CI), net lactate-independent H⁺ release (BFR-leg: 8 ± 1; CON-leg: 4 ± 1; mmol·min^-1 ) and net lactate-dependent H⁺ release (BFR-leg: 9 ± 3; CON-leg: 10 ± 3; mmol·min^-1 ) were similar between legs during Ex90 (P > .05), despite a ~142% lower muscle intracellular-to-interstitial lactate gradient in BFR-leg (-3 ± 4 vs 6 ± 6 mmol·L^-1 ; P < .05). In recovery from Ex90, net lactate-dependent H⁺ efflux decreased in BFR-leg with INT (P < .05 vs CON-leg) owing to lowered muscle lactate production (~58% vs CON-leg, P < .05). Net H⁺ gradient was not different between legs (~19%, P > .05; BFR-leg: 48 ± 30; CON-leg: 44 ± 23; mmol·L^-1 ). In BFR-leg, NHE1 density was higher than in CON-leg (~45%; P < .05) and correlated with total-net H⁺ -release (r = 0.71; P = .031) and lactate-independent H⁺ release (r = 0.74; P = .023) after INT, where arterial [ HCO 3 - ] and standard base excess in Ex25 were higher in BFR-leg than CON-leg.

CONCLUSION

Compared to a training control, BFR-interval training increases the capacity for pH regulation during dynamic exercise mainly via enhancement of muscle lactate-dependent H⁺ -transport function and blood H⁺ -buffering capacity.

Sex Differences in High-Intensity Interval Training-Are HIIT Protocols Interchangeable Between Females and Males?

Background: High-intensity interval training (HIIT) is a well-established training modality to improve aerobic and anaerobic capacity. However, sex-specific aspects of different HIIT protocols are incompletely understood. This study aimed to compare two HIIT protocols with different recovery periods in moderately trained females and males and to investigate whether sex affects high-intensity running speed and speed decrement.

Methods: Fifty moderately trained participants (30 females and 20 males) performed an exercise field test and were randomized by lactate threshold (LT) to one of two time- and workload-matched training groups. Participants performed a 4-week HIIT intervention with two exercise sessions/week: Group 1 (4 × 30,180 HIIT), 30-s all-out runs, 180-s active recovery and Group 2 (4 × 30,30 HIIT), 30-s all-out runs, 30-s active recovery. High-intensity runs were recorded, and speed per running bout, average speed per session, and speed decrement were determined. Blood lactate measurements were performed at baseline and follow-up at rest and immediately post-exercise.

Results: Females and males differed in running speed at LT and maximal running speed determined during exercise field test (speed at LT, females: 10.65 ± 0.84 km h⁻¹, males: 12.41 ± 0.98 km h⁻¹, p < 0.0001; maximal speed, females: 14.55 ± 1.05 km h⁻¹, males: 17.41 ± 0.68 km h⁻¹, p < 0.0001). Estimated maximal oxygen uptake was ~52.5 ml kg⁻¹ min⁻¹ for females and 62.6 ml kg⁻¹ min⁻¹ for males (p < 0.0001). Analysis of HIIT protocols revealed an effect of sex on change in speed decrement (baseline vs. follow-up) in that females showed significant improvements only in the 4 × 30:30 HIIT group (p = 0.0038). Moreover, females performing the 4 × 30:30 protocol presented increased speed per bout and average speed per session at follow-up (all p ≤ 0.0204), while no effect was detected for females performing the 4 × 30:180 protocol. Peak blood lactate levels increased in all HIIT groups (all p < 0.05, baseline vs. follow-up), but males performing the 4 × 30:180 protocol showed no difference in lactate levels.

Conclusions: If not matched for physical performance, females, but not males, performing a 4 × 30 HIIT protocol with shorter recovery periods (30 s) present increased average high-intensity running speed and reduced speed decrement compared to longer recovery periods (180 s). We conclude that female- and male-specific HIIT protocols should be established since anthropometric and physiological differences across sexes may affect training performance in real-world settings.

High-intensity interval training with long duration intervals is more effective than short duration intervals for improving glycolytic capacity in the rats' gastrocnemius muscle

Background There is little data regarding the ability of high-intensity interval training (HIIT) to increase of glycolytic capacity and intramuscular metabolic adaptations. The goal of this study was to evaluate the effects of HIIT (8 weeks, 5 times/week) with short (HIIT1 min: 16 × 1 min work and active recovery at 80-95% and 50-60% VO2max, respectively) and long (HIIT4 min: 4 × 4 min work and active recovery at 80-95% and 50-60% VO2max, respectively) duration intervals and 4 weeks detraining on the levels of phosphofructokinase (PFK), glycogen synthase 1 (GYS1), monocarboxylate transporter 4 (MCT4) and lactate dehydrogenase (LDH) activity in the rats' gastrocnemius muscle. Materials and methods Fifty-four male Wistar rats were assigned into three groups, including HIIT1 min, HIIT4 min and control (Ctrl). After 48 h of the last training session and after 4 weeks of detraining, the rats were sacrificed, and the gastrocnemius muscles were isolated. Results The PFK levels in the HIIT4 min group was significantly higher than in the HIIT1 min and Ctrl groups, and after the detraining period in the HIIT4 minDT group significantly decreased compared to the HIIT4 min group. The LDH activity in the HIIT4 min and HIIT1 min groups were significantly higher than the Ctrl group and the increasing trend in the HIIT4 min group was more than the HIIT1 min group. There was no significant change in LDH activity after detraining compared to training. No significant changes were observed in the level of GYS1 and MCT4 after HIIT. Conclusions Eight weeks of HIIT with long duration intervals induced more improvements in intramuscular glycolytic capacity than a short duration. After short-term detraining, some of these adaptations have remained.

High-Intensity Interval Training Augments Muscle Carnosine in the Absence of Dietary Beta-alanine Intake

PURPOSE

Cross-sectional studies suggest that training can increase muscle carnosine (MCarn), although longitudinal studies have failed to confirm this. A lack of control for dietary β-alanine intake or muscle fiber type shifting may have hampered their conclusions. The purpose of the present study was to investigate the effects of high-intensity interval training (HIIT) on MCarn.

METHODS

Twenty vegetarian men were randomly assigned to a control (CON) (n = 10) or HIIT (n = 10) group. High-intensity interval training was performed on a cycle ergometer for 12 wk, with progressive volume (6-12 series) and intensity (140%-170% lactate threshold [LT]). Muscle carnosine was quantified in whole-muscle and individual fibers; expression of selected genes (CARNS, CNDP2, ABAT, TauT, and PAT1) and muscle buffering capacity in vitro (βmin vitro) were also determined. Exercise tests were performed to evaluate total work done, V˙O2max, ventilatory thresholds (VT) and LT.

RESULTS

Total work done, VT, LT, V˙O2max, and βmin vitro were improved in the HIIT group (all P < 0.05), but not in CON (P > 0.05). MCarn (in mmol·kg dry muscle) increased in the HIIT (15.8 ± 5.7 to 20.6 ± 5.3; P = 0.012) but not the CON group (14.3 ± 5.3 to 15.0 ± 4.9; P = 0.99). In type I fibers, MCarn increased in the HIIT (from 14.4 ± 5.9 to 16.8 ± 7.6; P = 0.047) but not the CON group (from 14.0 ± 5.5 to 14.9 ± 5.4; P = 0.99). In type IIa fibers, MCarn increased in the HIIT group (from 18.8 ± 6.1 to 20.5 ± 6.4; P = 0.067) but not the CON group (from 19.7 ± 4.5 to 18.8 ± 4.4; P = 0.37). No changes in gene expression were shown.

CONCLUSIONS

In the absence of any dietary intake of β-alanine, HIIT increased MCarn content. The contribution of increased MCarn to the total increase in βmin vitro appears to be small.

Monitoring Exercise-Induced Muscle Fatigue and Adaptations: Making Sense of Popular or Emerging Indices and Biomarkers

Regular exercise with the appropriate intensity and duration may improve an athlete’s physical capacities by targeting different performance determinants across the endurance–strength spectrum aiming to delay fatigue. The mechanisms of muscle fatigue depend on exercise intensity and duration and may range from substrate depletion to acidosis and product inhibition of adenosinetriphosphatase (ATPase) and glycolysis. Fatigue mechanisms have been studied in isolated muscles; single muscle fibers (intact or skinned) or at the level of filamentous or isolated motor proteins; with each approach contributing to our understanding of the fatigue phenomenon. In vivo methods for monitoring fatigue include the assessment of various functional indices supported by the use of biochemical markers including blood lactate levels and more recently redox markers. Blood lactate measurements; as an accompaniment of functional assessment; are extensively used for estimating the contribution of the anaerobic metabolism to energy expenditure and to help interpret an athlete’s resistance to fatigue during high intensity exercise. Monitoring of redox indices is gaining popularity in the applied sports performance setting; as oxidative stress is not only a fatigue agent which may play a role in the pathophysiology of overtraining syndrome; but also constitutes an important signaling pathway for training adaptations; thus reflecting training status. Careful planning of sampling and interpretation of blood biomarkers should be applied; especially given that their levels can fluctuate according to an athlete’s lifestyle and training histories.

Time to Optimize Supplementation: Modifying Factors Influencing the Individual Responses to Extracellular Buffering Agents

Blood alkalosis, as indicated by an increased blood bicarbonate concentration and pH, has been shown to be beneficial for exercise performance. Sodium bicarbonate, sodium citrate, and sodium or calcium lactate, can all result in increased circulating bicarbonate and have all independently been shown to improve exercise capacity and performance under various circumstances. Although there is considerable evidence demonstrating the efficacy of these supplements in several sports-specific situations, it is commonly acknowledged that their efficacy is equivocal, due to contrasting evidence. Herein, we discuss the physiological and environmental factors that may modify the effectiveness of these supplements including, (i) absolute changes in circulating bicarbonate; (ii) supplement timing, (iii) the exercise task performed, (iv) monocarboxylate transporter (MCT) activity; (v) training status, and (vi) associated side-effects. The aim of this narrative review is to highlight the factors which may modify the response to these supplements, so that individuals can use this information to attempt to optimize supplementation and allow the greatest possibility of an ergogenic effect.