Acute metformin administration increases mean power and the early Power phase during a Wingate test in healthy male subjects.

The present study tested the hypothesis that acute metformin would increase peak power measured during a Wingate test. Fourteen men (24 ± 6 years; 75.8 ± 10.2 kg; 177 ± 7 cm) participated in four test sessions, conducted in a crossover, counterbalanced, double-blind model. The first and second sessions consisted of anthropometric measurements and one Wingate test per day to assess test-retest reliability. In the last two sessions, the Wingate tests were performed on metformin (500 mg capsule, 1 hour before) or placebo (cellulose capsule, 1 hour before) condition. No differences were found between the placebo and metformin for peak power (1056.8 ± 215.8 W vs. 1095.2 ± 199.3 W, respectively; p = 0.24). Mean power (630.9 ± 87.8 W vs. 613.1 ± 94.8 W, respectively; p=0.01) and total work (18928 ± 2633 kJ vs. 18393 ± 2845 kJ, respectively; p = 0.01) in the metformin condition were higher than the placebo. The power were greater in metformin when compared to the placebo in moments 3 (p = 0.01), 4 (p = 0.01), 5 (p = 0.04), 6 (p = 0.04), 7 (p = 0.02), 8 (p = 0.03) and 9 (p = 0.01) seconds. There were no differences between conditions for the peak lactate (p = 0.08) and the rating of perceived exertion (p = 0.84). Acute metformin administration increased the early power phase and the mean power of a Wingate test.

Airflow restriction mask induces greater central fatigue after a non-exhaustive high-intensity interval exercise.

The airflow restriction mask (ARM) is a practical and inexpensive device for respiratory muscle training. Wearing an ARM has recently been combined with high-intensity interval exercise (HIIE), but its effect on neuromuscular fatigue is unknown. The present study investigated the effects of ARM wearing on neuromuscular fatigue after an HIIE session. Fourteen healthy men performed two HIIE sessions (4 × 4 min at 90% HRmax , 3 min recovery at 70% HRmax ) with or without an ARM. Neuromuscular fatigue was quantified via pre- to post-HIIE changes in maximal voluntary contraction (MVC), voluntary activation (VA, central fatigue), and potentialized evoked twitch force at 100, 10, and 1 Hz (peripheral fatigue). Blood pH and lactate were measured before and after the HIIE session, while HR, SpO2 , dyspnea, physical sensation of effort (P-RPE), and Task Effort and Awareness (TEA) were recorded every bout. The exercise-induced decrease in MVC was higher (p < 0.05) in the ARM (-28 ± 12%) than in the Control condition (-20 ± 11%). The VA decreased (p < 0.05) in the ARM (-11 ± 11%) but not in the control condition (-4 ± 5%, p > 0.05). Pre- to post-HIIE declines in evoked twitch at 100, 10, and 1 Hz were similar (p > 0.05) between ARM and control conditions (ARM: -18 ± 10, -43 ± 11 and -38 ± 12%; Control: -18 ± 14, -43 ± 12 and -37 ± 17%). When compared with the control, the HIIE bout wearing ARM was marked by higher heart rate, plasma lactate concentration, dyspnea, P-RPE and TEA, as well as lower SpO2 and blood pH. In conclusion, ARM increases perceptual and physiological stress during a HIIE, which may lead to a greater post-exercise central fatigue.

Caffeine intake improves muscular endurance and induces depletion of anaerobic work capacity in the bench press

Abstract Aim: To investigate the effects of caffeine (CAF) ingestion on anaerobic work capacity (AWC) and muscular endurance in the bench press exercise at predictive intensities equivalent to 20, 25, and 30% of 1RM. Methods: Thirteen males (age: 23 ± 3 years; body mass 83.5 ± 4.9 kg; height 172.8 ± 5.0 cm and 1RM 82 ± 24 kg) had their 1RM test evaluated in the bench press exercise and the time until failure was performed at intensities equivalent to 20%, 25%, and 30% of 1RM to CAF (350mg) or placebo (PLA, cellulose). AWC was measured from the linear equation: "Force = Critical Force + (AWC x 1/timeout)". Results: CAF enhanced the time until failure at 20% of 1RM (PLA = 202.6 ± 29.1s; CAF = 243.2 ± 20.6s), but there was no ergogenic effect at 25% (PLA = 188.8 ± 23.5 s; CAF = 195.6 ± 27.1 s), and 30% (PLA = 147.4 ± 15.8 s; CAF = 145.4 ± 14.8 s). AWC in CAF was lower than PLA (PLA = 6378.0 ± 1214.9 J; CAF = 3246.4 ± 1389.7 J; p = 0.03; Effect size = 0.88). Critical Force (N) was not different between treatments PLA 29.97 ± 11.54% of 1RM and CAF 3.74 ± 3.69% of 1 RM (p=0.47; Effect size= 0.28). Conclusion: Acute CAF intake (350mg) reduces the AWC and increases the time until failure at 20% of 1 RM, but not Critical Force and muscular endurance at 25% and 30% of 1 RM in the bench press.

Caffeine increases peripheral fatigue in low- but not in high-performing cyclists.

The influence of cyclists' performance levels on caffeine-induced increases in neuromuscular fatigue after a 4-km cycling time trial (TT) was investigated. Nineteen cyclists performed a 4-km cycling TT 1 h after ingesting caffeine (5 mg·kg-1) or placebo (cellulose). Changes from baseline to after exercise in voluntary activation (VA) and potentiated 1 Hz force twitch (Qtw,pot) were used as markers of central and peripheral fatigue, respectively. Participants were classified as "high performing" (HP, n = 8) or "low performing" (LP, n = 8) in accordance with their performance in a placebo trial. Compared with placebo, caffeine increased the power, anaerobic mechanical power, and anaerobic work, reducing the time to complete the trial in both groups (p < 0.05). There was a group versus supplement and a group versus supplement versus trial interaction for Qtw,pot, in which the postexercise reduction was greater after caffeine compared with placebo in the LP group (Qtw,pot = -34% ± 17% vs. -21% ± 11%, p = 0.02) but not in the HP group (Qtw,pot = -22% ± 8% vs. -23% ± 10%, p = 0.64). There was no effect of caffeine on VA, but there was a group versus trial interaction with lower postexercise values in the LP group than in the HP group (p = 0.03). Caffeine-induced improvement in 4-km cycling TT performance seems to come at the expense of greater locomotor muscle fatigue in LP but not in HP cyclists. Novelty Caffeine improves exercise performance at the expense of a greater end-exercise peripheral fatigue in low-performing athletes. Caffeine-induced improvement in exercise performance does not affect end-exercise peripheral fatigue in high-performing athletes. High-performing athletes seem to have augmented tolerance to central fatigue during a high-intensity time trial.

Chronic metformin intake improves anaerobic but not aerobic capacity in healthy rats.

The effect of chronic metformin intake on aerobic and anaerobic capacity was examined in healthy rats. Twenty rats completed 10 days of metformin (MET) ingestion (250 mg). After this period, the animals performed four high-intensity bouts until exhaustion at 9%, 11%, 13%, and 15% of body mass (BM) in swimming, separated by 24 h, with prior metformin (250 mg) or placebo (PL). The critical load (CL) and anaerobic work capacity (AWC - W') were calculated and considered aerobic and anaerobic capacity, respectively. There was no difference in CL between the MET and PL groups (p > 0.05). The AWC - W' was higher in the MET group than in the PL group (p = 0.004). Time until exhaustion (seconds) at all bouts were higher (p < 0.004) in the MET group (9% of BM = 434.5 ± 267.3, 11% of BM = 269.6 ± 214.2, 13% of BM = 174.0 ± 40.9, 15% of BM = 146.6 ± 15.9) compared to the PL group (9% of BM = 96.4 ± 22.3, 11% of BM = 65.5 ± 13.4, 13% of BM = 51.1 ± 5.5, 15% of BM = 40.8 ± 7.5). Glucose concentration was higher at 90 and 120 min than at 0 and 30 min for the MET group (intragroup) during the oral glucose test tolerance; there was no difference between the MET and PL groups for area under curve. MET ingestion enhances AWC - W' and times to exhaustion but not aerobic capacity.

Twice-a-day training improves mitochondrial efficiency, but not mitochondrial biogenesis, compared with once-daily training.

Exercise training performed with lowered muscle glycogen stores can amplify adaptations related to oxidative metabolism, but it is not known if this is affected by the "train-low" strategy used (i.e., once-daily versus twice-a-day training). Fifteen healthy men performed 3 wk of an endurance exercise (100-min) followed by a high-intensity interval exercise 2 (twice-a-day group, n = 8) or 14 h (once-daily group, n = 7) later; therefore, the second training session always started with low muscle glycogen in both groups. Mitochondrial efficiency (state 4 respiration) was improved only for the twice-a-day group (group × training interaction, P < 0.05). However, muscle citrate synthase activity, mitochondria, and lipid area in intermyofibrillar and subsarcolemmal regions, and PGC1α, PPARα, and electron transport chain relative protein abundance were not altered with training in either group (P > 0.05). Markers of aerobic fitness (e.g., peak oxygen uptake) were increased, and plasma lactate, O2 cost, and rating of perceived exertion during a 100-min exercise task were reduced in both groups, although the reduction in rating of perceived exertion was larger in the twice-a-day group (group × time × training interaction, P < 0.05). These findings suggest similar training adaptations with both training low approaches; however, improvements in mitochondrial efficiency and perceived effort seem to be more pronounced with twice-a-day training.NEW & NOTEWORTHY We assessed, for the first time, the differences between two "train-low" strategies (once-daily and twice-a-day) in terms of training-induced molecular, functional, and morphological adaptations. We found that both strategies had similar molecular and morphological adaptations; however, only the twice-a-day strategy increased mitochondrial efficiency and had a superior reduction in the rating of perceived exertion during a constant-load exercise compared with once-daily training. Our findings provide novel insights into skeletal muscle adaptations using the "train-low" strategy.

Cycling time trial performance is improved by carbohydrate ingestion during exercise regardless of a fed or fasted state.

PURPOSE: We tested the hypothesis that carbohydrate ingestion during exercise improves time trial (TT) performance and that this carbohydrate-induced improvement is greater when carbohydrates are ingested during exercise in a fasted rather than a fed state. METHODS: Nine males performed 105 minutes of constant-load exercise (50% of the difference between the first and second lactate thresholds), followed by a 10-km cycling TT. Exercise started at 9 am, 3 hours after either breakfast (FED, 824 kcal, 67% carbohydrate) or a 15-hour overnight fast (FAST). Before exercise, after every 15 minutes of exercise and at 5 km of the TT, participants ingested 2 mL kg-1 body mass of a non-caloric sweetened solution containing either carbohydrate (8% of maltodextrin, CHO) or placebo (0% carbohydrate, PLA). RESULTS: Irrespective of the fasting state, when carbohydrate was ingested during exercise, the rating of perceived exertion (RPE) was lower throughout the constant-load exercise, while the plasma glucose concentration and carbohydrate oxidation were higher during the last stages of the constant-load exercise (P < 0.05). Consequently, TT performance was faster when carbohydrate was ingested during exercise (18.5 ± 0.3 and 18.7 ± 0.4 minutes for the FEDCHO and FASTCHO conditions, respectively) than when the placebo was ingested during exercise (20.2 ± 0.8 and 21.7 ± 1.4 minutes for the FEDPLA and FASTPLA conditions, respectively), regardless of fasting. CONCLUSION: These findings indicate that even when breakfast is provided before exercise, carbohydrate ingestion during exercise is still beneficial for exercise performance. However, ingesting carbohydrate during exercise can overcome a lack of breakfast.

Ingestion of a drink containing carbohydrate increases the number of bench press repetitions / A ingestão de uma bebida com carboidrato aumenta o número de repetições no exercício supino reto

ABSTRACT Objective The aim of this study was to analyze the effects of carbohydrate ingestion prior to exercise on the number of bench press repetitions. Methods Eight male physically active (21.3±2.7 years, 176±5cm, 73.12±6.12kg), with a minimum experience of at least one year exercising regularly, visited the laboratory at three moments. During the first visit, candidates went through their anthropometric evaluation and the application of their maximum number of bench press repetitions. The experimental tests were performed during their second and third visits in a crossover and blind study. The participants performed the maximum number of repetitions with an intensity of 70% of their maximum repetition strength. One hour before the experimental trials, participants randomly ingested a solution containing either carbohydrate or a placebo. Results The ingestion of carbohydrate increases muscle resistance in relation to placebo (p=0.014; effect size=0.71). This is evidenced by the increase in the number of repetitions (12.9±2.4 and 11.3±1.9, respectively). The individual's perception of effort is higher in the carbohydrate group than in the placebo group after exhaustion (4±0.93 and 3.1±0.64, respectively, p=0.006, effect size=0.89). Conclusion It is concluded that a previous intake of carbohydrate is useful in improving performance in resistance exercises, providing an increase in the individual's perception of effort.

RESUMO Objetivo O presente estudo teve como objetivo verificar os efeitos da ingestão prévia de carboidrato no número de repetições durante o exercício supino reto em indivíduos praticantes de musculação. Métodos Oito participantes fisicamente ativos do sexo masculino (21,3±2,7 anos, 176±5cm, 73,12±6,12kg) com experiência mínima de um ano em treinamento de força visitaram o laboratório em três momentos. Durante a primeira visita foi realizada uma avaliação antropométrica e aplicação do teste de uma repetição máxima no exercício supino reto. Os testes experimentais foram realizados nas visitas dois e três em um modelo cross over e cego onde os participantes executaram o número máximo de repetições com uma intensidade de 70% de uma repetição máxima. Uma hora antes dos testes experimentais, de forma randômica, os participantes ingeriram uma solução contendo carboidrato ou placebo. Resultados A ingestão de carboidrato foi capaz de aumentar a resistência muscular em relação ao placebo (p=0.014; effect size=0.71), fato evidenciado pelo aumento no número de repetições (12,9±2,4 e 11,3±1,9, respectivamente). A percepção subjetiva de esforço foi maior no grupo carboidrato em relação ao grupo placebo após a exaustão (4±0,93 e 3,1±0,64, respectivamente p=0.006, effect size=0.89). Conclusão Concluímos que a ingestão prévia de carboidrato é útil em melhorar o desempenho em exercícios de resistência com aumento associado da percepção subjetiva de esforço.

Caffeine increases both total work performed above critical power and peripheral fatigue during a 4-km cycling time trial.

The link between total work performed above critical power (CP) and peripheral muscle fatigue during self-paced exercise is unknown. We investigated the influence of caffeine on the total work done above CP during a 4-km cycling time trial (TT) and the subsequent consequence on the development of central and peripheral fatigue. Nine cyclists performed three constant-load exercise trials to determine CP and two 4-km TTs ~75 min after oral caffeine (5 mg/kg) or cellulose (placebo) ingestion. Neuromuscular functions were assessed before and 50 min after supplementation and 1 min after TT. Oral supplementation alone had no effect on neuromuscular function ( P > 0.05). Compared with placebo, caffeine increased mean power output (~4%, P = 0.01) and muscle recruitment (as inferred by EMG, ~17%, P = 0.01) and reduced the time to complete the TT (~2%, P = 0.01). Work performed above CP during the caffeine trial (16.7 ± 2.1 kJ) was significantly higher than during the placebo (14.7 ± 2.1 kJ, P = 0.01). End-exercise decline in quadriceps twitch force (pre- to postexercise decrease in twitch force at 1 and 10 Hz) was more pronounced after caffeine compared with placebo (121 ± 13 and 137 ± 14 N vs. 146 ± 13 and 156 ± 11 N; P < 0.05). There was no effect of caffeine on central fatigue. In conclusion, caffeine increases muscle recruitment, which enables greater work performed above CP and higher end-exercise peripheral locomotor muscle fatigue. NEW & NOTEWORTHY The link between total work done above critical power and peripheral fatigue during a self-paced, high-intensity exercise is unclear. This study revealed that caffeine ingestion increases muscle recruitment, which enables greater work done above critical power and a greater degree of end-exercise decline in quadriceps twitch force during a 4-km cycling time trial. These findings suggest that caffeine increases performance at the expense of greater locomotor muscle fatigue.

Carbohydrate mouth rinse reduces rating of perceived exertion but does not affect performance and energy systems contribution during a high-intensity exercise

Aim: The study aimed to verify the effect of carbohydrate (CHO) mouth rinse on time to exhaustion, energy systems contribution and rating of perceived exertion (RPE) during a high-intensity exercise. Methods Fourteen men performed an incremental exercise test to determine their maximal oxygen uptake and peak power output (PPO) and two time-to-exhaustion tests at 110% of PPO. Participants rinsed their mouth with 25ml of 6.4% of CHO or placebo (PLA) solution immediately before the time-to-exhaustion test, using a crossover design. The contribution of the energy systems was calculated using the free software GEDAE-LaB®. Results: Time to exhaustion was similar between the conditions (CHO:174.3±42.8s; PLA:166.7±26.3s; p=0.33). In addition, there was no difference between the CHO and PLA condition for aerobic (CHO:135.1±41.2kJ and PLA:129.8±35.3kJ, p=0.34), anaerobic lactic (CHO:57.6±17.1kJ and PLA:53.4±15.1kJ, p=0.10), and anaerobic alactic (CHO:10.4±8.4kJ and PLA:13.2±9.2kJ, p=0.37) contribution. Consequently, total energy expenditure was similar between conditions (CHO:203.2±46.4kJ and PLA:196.5±45.2kJ, p=0.15). However, CHO mouth rinse reduced the RPE at the moment of exhaustion (CHO:18.2±1.0units and PLA:19.1±1.1units; p=0.02). Conclusion: CHO mouth rinse neither increased time to exhaustion nor altered energy systems contribution during a high-intensity exercise, but reduced the perceived effort at the exhaustion.(AU)

Effects of carbohydrate intake on time to exhaustion and anaerobic contribution during supramaximal exercise / Efeito da ingestão de carboidrato sobre o tempo de exaustão e contribuição anaeróbia durante exercício supramáximo

ABSTRACT Objective: This study evaluated the effect of carbohydrate intake on time to exhaustion and anaerobic contribution during supramaximal exercise on a cycle ergometer. Methods: The sample comprised ten participants with a mean age of 23.9±2.5 years, mean body mass of 75.1±12.3 kg, mean height of 170.0±1.0 cm, and mean body fat of 11.3±5.2%. The participants underwent an incremental test to determine maximal oxygen uptake and maximum power output, and two supramaximal tests with a constant load of 110% of the maximum power output to exhaustion. Thirty minutes before the supramaximal tests the participants consumed carbohydrates (2 g.kg-1) or placebo. Results: The times to exhaustion of carbohydrate and placebo did not differ (carbohydrate: 170.7±44.6s; placebo: 156.1±26.7s, p=0.17; effect size=0.39). Similarly, the anaerobic contributions of the two treatments did not differ (carbohydrate: 3.0±0.9 L; placebo: 2.7±1.1 L, p=0.23; effect size=0.29). Conclusion: Carbohydrate intake was not capable of increasing time to exhaustion and anaerobic contribution in physically active men cycling at 110% of maximum power output.

RESUMO Objetivo: Este estudo foi conduzido com o intuito de verificar o efeito da ingestão de carboidrato sobre o tempo de exaustão e a contribuição anaeróbia durante o exercício supramáximo em uma bicicleta ergométrica. Métodos: Dez participantes fizeram parte da amostra (idade: 23,9±2,5 anos; massa corporal: 75,1±12,3 kg; estatura: 170,0±1,0 cm; gordura corporal: 11,3±5,2%). Todos realizaram um teste incremental para determinar o consumo máximo de oxigênio e a potência máxima e dois testes supramáximos com carga constante de 110% da potência máxima até a exaustão. Os participantes ingeriram carboidrato (2 g.kg-1) ou placebo 30 minutos antes dos testes supramáximos. Resultados: Não houve diferença significativa no tempo de exaustão entre carboidrato e placebo (carboidrato: 170,7±44,6s; placebo: 156,1±26,7s, p=0,17; effect size=0,39). De forma similar, não houve diferença significativa na contribuição anaeróbia entre as condições (carboidrato: 3,0±0,9 L; placebo: 2,7±1,1 L, p=0,23; effect size=0,29). Conclusão: A ingestão de carboidrato não foi capaz de aumentar o tempo até a exaustão e a contribuição anaeróbia em exercícios à 110% da potência máxima em homens fisicamente ativos.