Recent research has suggested that dietary nitrate (NO₃⁻) supplementation might alter the physiological responses to exercise via specific effects on type II muscle. Severe-intensity exercise initiated from an elevated metabolic rate would be expected to enhance the proportional activation of higher-order (type II) muscle fibers. The purpose of this study was, therefore, to test the hypothesis that, compared with placebo (PL), NO₃⁻-rich beetroot juice (BR) supplementation would speed the phase II V̇o₂kinetics (τ_p) and enhance exercise tolerance during severe-intensity exercise initiated from a baseline of moderate-intensity exercise. Nine healthy, physically active subjects were assigned in a randomized, double-blind, crossover design to receive BR (140 ml/day, containing ∼8 mmol of NO₃⁻) and PL (140 ml/day, containing ∼0.003 mmol of NO₃⁻) for 6 days. On days 4, 5, and 6 of the supplementation periods, subjects completed a double-step exercise protocol that included transitions from unloaded to moderate-intensity exercise (U→M) followed immediately by moderate to severe-intensity exercise (M→S). Compared with PL, BR elevated resting plasma nitrite concentration (PL: 65 ± 32 vs. BR: 348 ± 170 nM, P < 0.01) and reduced the V̇o₂τ_pin M→S (PL: 46 ± 13 vs. BR: 36 ± 10 s, P < 0.05) but not U→M (PL: 25 ± 4 vs. BR: 27 ± 6 s, P > 0.05). During M→S exercise, the faster V̇o₂kinetics coincided with faster near-infrared spectroscopy-derived muscle [deoxyhemoglobin] kinetics (τ; PL: 20 ± 9 vs. BR: 10 ± 3 s, P < 0.05) and a 22% greater time-to-task failure (PL: 521 ± 158 vs. BR: 635 ± 258 s, P < 0.05). Dietary supplementation with NO₃⁻-rich BR juice speeds V̇o₂kinetics and enhances exercise tolerance during severe-intensity exercise when initiated from an elevated metabolic rate.

S lateralis (VL) muscles, and VL muscle oxygenation status (near-infrared spectroscopy) were recorded during metronome-guided knee extension exercise. Nine healthy adults completed four trials exercising at contraction intensities of 35% (L) or 70% (H) of one-repetition maximum (1RM) in control (no vibration, Vb−) or vibrated condition (superimposed 10-Hz vibration-like stimulus, Vb+). Maximum voluntary contraction and 1RM were tested pre- and postexercise. Results: During 1RM tests, muscle dynamic strength (P = 0.02) and power (P = 0.05) were significantly higher during vibrated rather than nonvibrated trials, and strength was significantly higher post- than preexercise (P = 0.002), except during LVb− trial. Median spectral frequency of VL and RF EMG activity was significantly higher during postexercise than preexercise 1RM test in the vibration trials but unchanged in the control trials (P < 0.02). The rate of muscle deoxygenation was 58% faster during H than L exercise (P = 0.001), and vibration superimposition tended to speed muscle deoxygenation rate (P = 0.065, 36% effect size) particularly during L trials. Conclusion: Vibration superimposition during knee extension exercise at low contraction intensity enhanced muscle performance. This effect appears to result from adaptation of neural factors such as motor unit excitability (recruitment and firing frequency, conduction velocity of excitation) in response to sensory receptor stimulation. Muscle vibration may increase the training effects derived from light-to-moderate exercise....

Ic and relaxation properties by Doppler ultrasound techniques. Methods: Resting cardiac dimensions were measured by M-mode echocardiography. Stroke volume was estimated by the Doppler technique, and systolic function by peak aortic flow velocity and ejection flow rate. Diastolic transmitral pressure gradient was assessed by pulse wave peak E-wave velocity, ventricular relaxation properties by tissue Doppler imaging (E′ velocity, adjusted for ventricular size), and ventricular filling pressure by E/E′ ratio. Results: Size-adjusted cardiac dimensions were significantly greater in the athletes. Peak V˙O2 values for the athletes and nonathletes were 57.4 ± 4.8 and 44.4 ± 6.6 mL·kg−1·min−1, respectively. Maximal cardiac index and stroke index were greater in the athletes (11.10± 1.52 vs 9.02 ± 2.05 L·min−1·m−2; 59 ± 8 vs 46 ± 10 mL·m−2). Athletes and nonathletes demonstrated similar maximal peak aortic velocity (231 ± 20 and 208 ± 45 cm·s−1, respectively) and ejection rate (13.3 ± 1.0 and 12.5 ± 2.8 mL·s−1·cm−2 × 10−2, respectively). No significant group differences were observed in Emax (155 ± 17 and 149 ± 23 cm·s−1 for athletes and nonathletes, respectively), adjusted E′max (5.9 ± 1.2 and 5.8 ± 1.2 cm·s−1·mm−1 for athletes and nonathletes, respectively), and E/E′max (265 ± 40 and 262 ± 56 for athletes and nonathletes, respectively). Conclusions: This study revealed no differences between young trained athletes and nonathletes in myocardial functional responses to progressive exercise, implying that greater aerobic fitness in these athletes reflected volume expansion of the cardiovascular system without contribution of enhanced systolic or diastolic ventricular function. Such findings should be considered limited to the context of young athletes with limited duration of athletic training....