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.

Maytenus ilicifolia Extract Increases Oxygen Uptake without Changes in Neuromuscular Fatigue Development during a High-Intensity Interval Exercise.

OBJECTIVE: We investigated the effects of acute ingestion of Maytenus ilicifolia extract on metabolic and cardiopulmonary responses during a high-intensity interval exercise (HIIE), and its consequence on neuromuscular fatigue. METHODS: Ten healthy men underwent a HIIE (4 x 4 min, 3 min recovery) one hour after ingesting 400 mg of Maytenus ilicifolia extract (MIE) or placebo. Oxygen uptake (V̇O2), dioxide carbon production (V̇CO2), ventilation (V̇E) and heart rate (HR) were measured throughout the HIIE. Maximal voluntary contraction (MVC), voluntary activation (VA), and evoked 1, 10 and 100 Hz force twitch were measured before supplementation (baseline), and before (pre-HIIE) and after the HIIE (post-HIIE). RESULTS: The V̇O2, V̇E, V̇E/V̇O2 ratio and HR increased progressively throughout the HIIE under both conditions (p < 0.05). MIE increased HR, however, at bouts 1 and 2 and mean V̇O2 during HIIE. The mean respiratory exchange ratio during recovery was also reduced with MIE (p < 0.05). MVC and evoked force at 1, 10 and 100 Hz declined similarly after HIIE, regardless of the condition (MIE: -18 ± 17%, -50 ± 15%, -61 ± 13% and -34 ± 10% vs. placebo: -19 ± 15%, -48 ± 16%, -58 ± 12 and -29 ± 11%, respectively, p < 0.05). There was no effect of exercise or MIE on VA (p > 0.05). CONCLUSION: MIE increases heart rate in the first bouts and mean oxygen uptake during HIIE without changes in neuromuscular fatigue development.

Arterialized and venous blood lactate concentration difference during different exercise intensities.

OBJECTIVE: The purpose of this study was to investigate the difference between arterialized and venous blood lactate concentrations [La] during constant-load exercises at different intensities. METHODS: Fifteen physically active men cycled for 30 minutes (or until exhaustion) at the first lactate threshold (LT1), at 50% of the difference between the first and second lactate threshold (TT50%), at the second lactate threshold (LT2), and at 25% of the difference between LT2 and maximal aerobic power output (TW25%). Samples of both arterialized and venous blood were collected simultaneously at rest and every 5 minutes during the exercise. RESULTS: The arterialized blood [La] was higher at minute 5 than venous blood [La] for all exercise intensities (p < 0.05). After this period, the arterialized and venous [La] samples became similar until the end of the exercise (p > 0.05). The arterialized-venous difference during the first 10 minutes was greater for the two highest exercise intensities (LT2 and TW25%) compared with the two lowest (LT1 and TT50%, p < 0.05). Thereafter, arterialized-venous difference decreased progressively, reaching values close to zero for all exercise intensities (p > 0.05). CONCLUSION: These results suggest a delayed lactate appearance in the venous blood, which is accentuated at higher exercise intensities. The lactate measured in arterialized and venous blood is interchangeable only when blood samples are collected at least 10 minutes after the exercise starts.

Correction: Effect of caffeine on neuromuscular function following eccentric-based exercise.

[This corrects the article DOI: 10.1371/journal.pone.0224794.].

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.

Effect of caffeine on neuromuscular function following eccentric-based exercise.

This study investigated the effect of caffeine on neuromuscular function, power and sprint performance during the days following an eccentric-based exercise. Using a randomly counterbalanced, crossover and double-blinded design, eleven male jumpers and sprinters (age: 18.7 ± 2.7 years) performed a half-squat exercise (4 x 12 repetitions at 70% of 1 RM), with eccentric action emphasized by using a flexible strip attached to their knees (Tirante Musculador®). They ingested either a capsule of placebo or caffeine (5 mg.kg-1 body mass) 24, 48 and 72 h after. Neuromuscular function and muscle power (vertical countermovement-jump test) were assessed before and after the half-squat exercise and 50 min after the placebo or caffeine ingestion at each time-point post-exercise. Sprint performance was measured at pre-test and 75 min after the placebo or caffeine ingestion at each time-point post-exercise. Maximal voluntary contraction (overall fatigue) and twitch torque (peripheral fatigue) reduced after the half-squat exercise (-11 and -28%, respectively, P < 0.05) but returned to baseline 24 h post-exercise (P > 0.05) and were not affected by caffeine ingestion (P > 0.05). The voluntary activation (central fatigue) and sprint performance were not altered throughout the experiment and were not different between caffeine and placebo. However, caffeine increased height and power during the vertical countermovement-jump test at 48 and 72 h post half-squat exercise, when compared to the placebo (P < 0.05). In conclusion, caffeine improves muscle power 48 and 72 h after an eccentric-based exercise, but it has no effect on neuromuscular function and sprint performance.

The Effects of Acute and Chronic Sprint-Interval Training on Cytokine Responses Are Independent of Prior Caffeine Intake.

We examined the effect of acute and chronic sprint interval training (SIT), with or without prior caffeine intake, on levels of exercise-induced inflammatory plasma cytokines [interleukin (IL)-6, IL-10, tumor necrosis factor (TNF)-α]. Twenty physically-active men ingested either a placebo (n = 10) or caffeine (n = 10) 1 h before each SIT session(13-s × 30-s sprint/15 s of rest) during six training sessions (2 weeks). The early (before, immediately after, and 45 min after the exercise) and late (24 and 48 h after the exercise) cytokine and creatine kinase (CK) responses were analyzed for the first and last training sessions. Plasma IL-6 and IL-10 peaked 45 min after the exercise, and then returned to basal values within 24 h (p < 0.05) in both groups on both occasions (p > 0.05). On both occasions, and for both groups, plasma TNF-α increased from rest to immediately after the exercise and then decreased at 45 min before reaching values at or below basal levels 48 h after the exercise (p < 0.05). Serum CK increased from rest to 24 and 48 h post-exercise in the first training session (p < 0.05), but did not alter in the last training session for the PLA group (p > 0.05). Serum CK was unchanged in both the first and last training sessions for the CAF group (p > 0.05). Two weeks of SIT induced a late decrease in the IL-6/IL-10 ratio (p < 0.05) regardless of caffeine intake, suggesting an improved overall inflammatory status after training. In conclusion, a single session of SIT induces muscle damage that seems to be mitigated by caffeine intake. Two weeks of SIT improves the late SIT-induced muscle damage and inflammatory status, which seems to be independent of caffeine intake.

Separate and Combined Effects of Caffeine and Sodium-Bicarbonate Intake on Judo Performance.

UNLABELLED: The combined supplementation of caffeine (CAF) and sodium bicarbonate (NaHCO3) may have a potential ergogenic effect during intermittent-exercise tasks such as judo; however, its effect in this sport has not been tested. PURPOSE: To investigate the isolated and combined effects of CAF and NaHCO3 on judo performance. METHODS: Ten judokas performed 4 supplementation protocols-NaHCO3, CAF, NaHCO3 + CAF, and placebo (PLA) (cellulose)-followed by 3 Special Judo Fitness Tests (SJFTs) interspaced with 5 min rest. RESULTS: In the first SJFT, the combined supplement (NaHCO3 + CAF) resulted in a higher number of throws than with PLA (24.4 ± 0.9 and 23.2 ± 1.5 throws, respectively, P = .02). There was no significant difference between conditions for the 2nd SJFT (P = .11). In the 3rd SJFT, NaHCO3 and NaHCO3 + CAF resulted in more throws than with PLA (23.7 ± 1.6, 24.4 ± 1.0, and 22.0 ± 1.6 throws, P = .001 and P = .03, respectively). When the total throws performed in the 3 SJFTs were summed, they were higher than PLA only for NaHCO3 + CAF (68.8 ± 4.4 and 72.7 ± 3.1 throws, respectively, P = .003). Postexercise plasma lactate after each SJFT was higher in all experimental conditions than with PLA (P = .001). There was no significant difference in rating of perceived exertion across the conditions (P = .18). CONCLUSION: The results of the current study show that the combined supplementation of NaHCO3 + CAF increases judo performance compared with PLA.