Browsing by Author "Jonvik, K.L."

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The impact of beetroot juice supplementation on muscular endurance, maximal strength and countermovement jump performance.
Jonvik, K.L. ; Hoogervorst, D. ; Peelen, H.B. ; Niet, M. de ; Verdijk, L.B. ; Loon, L.J.C. van ; Dijk, J.W. van
2021, Article / Letter to editor (European Journal of Sport Science, vol. 21, iss. 6, (2021), pp. 871-878)Purpose: Dietary nitrate has been shown to enhance muscle contractile function and has, therefore, been linked to increased muscle power and sprint exercise performance. However, the impact of dietary nitrate supplementation on maximal strength, performance and muscular endurance remains to be established. Methods: Fifteen recreationally active males (25 ±4 y, BMI 24 ±3 kg/m(2)) participated in a randomized double-blinded cross-over study comprising two 6-d supplementation periods; 140 mL/d nitrate-rich (BR; 985 mg/d) and nitrate-depleted (PLA; 0.37 mg/d) beetroot juice. Three hours following the last supplement, we assessed countermovement jump (CMJ) performance, maximal strength and power of the upper leg by voluntary isometric (30° and 60° angle) and isokinetic contractions (60, 120, 180 and 300°•s(-1)), and muscular endurance (total workload) by 30 reciprocal isokinetic voluntary contractions at 180°•s(-1). Results: Despite differences in plasma nitrate (BR: 879 ±239 vs. PLA: 33 ±13 μmol/L, Pn<n0.001) and nitrite (BR: 463 ±217 vs. PLA: 176 ±50 nmol/L, Pn<n0.001) concentrations prior to exercise testing, CMJ height (BR: 39.3 ±6.3 vs. PLA: 39.6 ±6.3 cm; Pn=n0.39) and muscular endurance (BR: 3.93 ±0.69 vs. PLA: 3.90 ±0.66 kJ; Pn=n0.74) were not different between treatments. In line, isometric strength (Pn>n0.50 for both angles) and isokinetic knee extension power (Pn>n0.33 for all velocities) did not differ between treatments. Isokinetic knee flexion power was significantly higher following BR compared with PLA ingestion at 60°•s(-1) (Pn=n0.001), but not at 120°•s(-1) (Pn=n0.24), 180°•s(-1) (Pn=n0.066), and 300°•s(-1) (Pn=n0.36). Conclusion: Nitrate supplementation does not improve maximal strength, countermovement jump performance and muscular endurance in healthy, active males.
A Nitrate-Rich Vegetable Intervention Elevates Plasma Nitrate and Nitrite Concentrations and Reduces Blood Pressure in Healthy Young Adults
Avoort, C.M.T. van der ; Jonvik, K.L. ; Nyakayiru, J. ; Loon, L.J.C. van ; Hopman, M. ; Verdijk, L.B.
2020, Article / Letter to editor (Journal of the Academy of Nutrition and Dietetics, (2020))
Sucrose but Not Nitrate Ingestion Reduces Strenuous Cycling-induced Intestinal Injury.
Jonvik, K.L. ; Lenaerts, K. ; Smeets, J.S.J. ; Kolkman, J.J. ; Loon, L.J.C. van ; Verdijk, L.B.
2019, Article / Letter to editor (Medicine and Science in Sports and Exercise, vol. 51, iss. 3, (2019), pp. 436-444)
Protein Supplementation Does Not Augment Adaptations to Endurance Exercise Training
Jonvik, K.L. ; Paulussen, K.J.M. ; Danen, S.L. ; Ceelen, I.J.M. ; Horstman, A.M. ; Wardenaar, F.C. ; Loon, L.J.C. van ; Dijk, J.W. van
2019, Article / Letter to editor (Medicine and Science in Sports and Exercise, vol. 51, iss. 10, (2019), pp. 2041-2049)
Protein Supplementation Does Not Further Augment Physiological Adaptations to Prolonged Endurance Exercise Training
Jonvik, K.L. ; Paulussen, K.J.M. ; Danen, S.L. ; Horstman, A.M. ; Wardenaar, F.C. ; Loon, L.J.C. van ; Dijk, J.W. van
2019, Article / Letter to editor (Medicine and Science in Sports and Exercise, vol. 51, iss. 6, (2019), pp. 791)
Repeated-sprint performance and plasma responses following beetroot juice supplementation do not differ between recreational, competitive and elite sprint athletes
Jonvik, K.L. ; Nyakayiru, J. ; Dijk, J.W. van ; Maase, K. ; Ballak, S.B. ; Senden, J.M.G. ; Loon, L.J.C. van ; Verdijk, L.B.
2018, Article / Letter to editor (European Journal of Sport Science, vol. 18, iss. 4, (2018), pp. 524-533)
The Effect of Beetroot Juice Supplementation on Dynamic Apnea and Intermittent Sprint Performance in Elite Female Water Polo Players
Jonvik, K.L. ; Dijk, J.W. van ; Senden, J.M.G. ; Loon, L.J.C. van ; Verdijk, L.B.
2018, Article / Letter to editor (International Journal of Sport Nutrition and Exercise Metabolism, vol. 28, iss. 5, (2018), pp. 468-473)
Habitual Dietary Nitrate Intake in Highly Trained Athletes.
Jonvik, K.L. ; Nyakayiru, J. ; Dijk, J.W. van ; Wardenaar, F.C. ; Loon, L.J.C. van ; Verdijk, L.B.
2017, Article / Letter to editor (International Journal of Sport Nutrition and Exercise Metabolism, vol. 27, iss. 2, (2017), pp. 148-157)Although beetroot juice, as a nitrate carrier, is a popular ergogenic supplement among athletes, nitrate is consumed through the regular diet as well. We aimed to assess the habitual dietary nitrate intake and identify the main contributing food sources in a large group of highly trained athletes. Dutch highly trained athletes (226 women and 327 men) completed 2-4 web-based 24-hr dietary recalls and questionnaires within a 2- to 4-week period. The nitrate content of food products and food groups was determined systematically based on values found in regulatory reports and scientific literature. These were then used to calculate each athlete's dietary nitrate intake from the web-based recalls. The median[IQR] habitual nitrate intake was 106[75-170] mg/d (range 19-525 mg/d). Nitrate intake correlated with energy intake (ρ = 0.28, p < .001), and strongly correlated with vegetable intake (ρ = 0.78, p < .001). In accordance, most of the dietary nitrate was consumed through vegetables, potatoes and fruit, accounting for 74% of total nitrate intake, with lettuce and spinach contributing most. When corrected for energy intake, nitrate intake was substantially higher in female vs male athletes (12.8[9.2-20.0] vs 9.4[6.2-13.8] mg/MJ; p < .001). This difference was attributed to the higher vegetable intake in female vs male athletes (150[88-236] vs 114[61-183] g/d; p < .001). In conclusion, median daily intake of dietary nitrate in highly trained athletes was 106 mg, with large interindividual variation. Dietary nitrate intake was strongly associated with the intake of vegetables. Increasing the intake of nitrate-rich vegetables in the diet might serve as an alternative strategy for nitrate supplementation.
Effects Of Acute Versus 6-day Sodium Nitrate Supplementation On Time-trial Performance In Trained Cyclists
Jonvik, K.L. ; Nyakayiru, J. ; Pinckaers, PJM ; Dijk, J.W. van ; Senden, J.M.G. ; Loon, L.J.C. van ; Verdijk, L.B.
2015, Article / Letter to editor (Medicine and Science in Sports and Exercise, vol. 47, iss. 5, (2015), pp. CP540-CP541)

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