Browsing by Author "Loon, L.J.C. van"

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Fragile bones of elite cyclists: to treat or not to treat?
Hilkens, L.P.M. ; Knuiman, P. ; Heijboer, M. ; Kempers, R. ; Jeukendrup, A.E. ; Loon, L.J.C. van ; Dijk, J.W. van
2021, Article / Letter to editor (Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology, (2021))
Last Word on Viewpoint: Fragile bones of elite cyclists: to treat or not to treat?
Hilkens, L.P.M. ; Knuiman, P. ; Heijboer, M. ; Kempers, R. ; Jeukendrup, A.E. ; Loon, L.J.C. van ; Dijk, J.W. van
2021, Article / Letter to editor (Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology, vol. 131, iss. 1, (2021), pp. 34-35)
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.
Whey protein supplementation does not accelerate recovery from a single bout of eccentric exercise.
Hilkens, L.P.M. ; Bock, J. De ; Kretzers, J. ; Kardinaal, A.F.M. ; Floris-Vollenbroek, E.G. ; Scholtens, P.A.M.J. ; Horstman, A.M. ; Loon, L.J.C. van ; Dijk, J.W. van
2021, Article / Letter to editor (Journal of Sports Sciences, vol. 39, iss. 3, (2021), pp. 322-331)The current double blind, randomized, placebo-controlled trial with two parallel groups aimed to assess the impact of whey protein supplementation on recovery of muscle function and muscle soreness following eccentric exercise. During a 9-day period, forty recreationally active males received twice daily supplementation with either whey protein (PRO; 60 g/day) or an iso-energetic amount of carbohydrate (CON). Muscle function and soreness were assessed before, and 0, 3, 24, 48, and 72 h after performing 100 drop jumps. Recovery of isometric maximal voluntary contraction (MVC) did not significantly differ between groups (timextreatment, P = 0.56). In contrast, the recovery of isokinetic MVC at 90°·s(-1) was faster in CON as opposed to PRO (timextreatment interaction, P = 0.044). Recovery of isokinetic MVC at 180°·s(-1) was also faster in CON as opposed to PRO (timextreatment interaction, P = 0.011). Recovery of countermovement jump performance did not differ between groups (timextreatment interaction, P = 0.52). Muscle soreness, CK and CRP showed a transient increase over time (P < 0.001), with no differences between groups. In conclusion, whey protein supplementation does not accelerate recovery of muscle function or attenuate muscle soreness and inflammation during 3 days of recovery from a single bout of eccentric exercise.
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))
Energy expenditure and dietary intake in professional football players in the Dutch Premier League: Implications for nutritional counselling
Brinkmans, N. ; Iedema, N. ; Plasqui, G. ; Wouters, L. ; Saris, W.H.M. ; Loon, L.J.C. van ; Dijk, J.W. van
2019, Article / Letter to editor (Journal of Sports Sciences, vol. 37, iss. 24, (2019), pp. 2759-2767)
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)
The Muscle Protein Synthetic Response to Whey Protein Ingestion Is Greater in Middle-Aged Women Compared With Men
Horstman, A.M. ; Kouw, I.W.K. ; Dijk, J.W. van ; Hamer, H.M. ; Groen, B.B.L. ; Kranenburg, J. van ; Gorissen, S.H.M. ; Loon, L.J.C. van
2019, Article / Letter to editor (Journal of Clinical Endocrinology and Metabolism, vol. 104, iss. 4, (2019), pp. 994-1004)
Basal and Postprandial Myofibrillar Protein Synthesis Rates Do Not Differ between Lean and Obese Middle-Aged Men
Kouw, I.W.K. ; Dijk, J.W. van ; Horstman, A.M. ; Kramer, I.F. ; Goessens, J.P.B. ; Dielen, F.M.H van ; Verdijk, L.B. ; Loon, L.J.C. van
2019, Article / Letter to editor (Journal of Nutrition, vol. 149, iss. 9, (2019), pp. 1533-1542)
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)
Increasing vegetable intake to obtain the health promoting and ergogenic effects of dietary nitrate
Avoort, C.M.T. van der ; Loon, L.J.C. van ; Hopman, M. ; Verdijk, L.B.
2018, Article / Letter to editor (European Journal of Clinical Nutrition, vol. 72, iss. 11, (2018), pp. 1485-1489)
Adipose tissue lipolytic inhibition enhances the glucoregulatory properties of exercise in type 2 diabetes patients
Hansen, D. ; Verboven, K. ; Dijk, J.W. van ; Zorenc, A. ; Minten, L. ; Smeets, K. ; Verdijk, L.B. ; Loon, L.J.C. van
2018, Article / Letter to editor (European Journal of Sport Science, vol. 18, iss. 9, (2018), pp. 1245-1254)
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)
COMMENTARY ON VIEWPOINT: A TIME FOR EXERCISE: THE EXERCISE WINDOW
Dijk, J.W. van ; Loon, L.J.C. van
2017, Article / Letter to editor (Journal of Applied Physiology, vol. 122, iss. 1, (2017), pp. 212-213)
Commentaries on Viewpoint: A time for exercise: the exercise window.
Boulé, N.G. ; Terada, T. ; Francois, M.E. ; Hawley, J.A. ; Cotter, J.D. ; Kruse, N.T. ; McDonald, M.W. ; Olver, T.D. ; Paoli, A. ; Sacchetti, M. ; Luigi, L. Di ; Dijk, J.W. van ; Loon, L.J.C. van ; Yardley, J. ; DiPietro, L. ; Gribok, A. ; Rumpler, W. et al. sine al.
2017, Article / Letter to editor (Journal of Applied Physiology: Respiratory, Environmental and Exercise Physiology, vol. 122, iss. 1, (2017), pp. 210-213)
Endurance-type exercise combined with acipimox administration provides superior benefits for glycemic control compared with endurance-type exercise alone in male patients with type 2 diabetes
Hansen, D. ; Verboven, K. ; Dijk, J.W. van ; Minten, L. ; Smeets, K. ; Loon, L.J.C. van
2017, Article / Letter to editor (Acta Cardiologica, vol. 72, iss. 1, (2017), pp. 119)
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.
Short-term muscle disuse lowers myofibrillar protein synthesis rates and induces anabolic resistance to protein ingestion.
Wall, B.T. ; Dirks, M.L. ; Snijders, T. ; Dijk, J.W. van ; Fritsch, M. ; Verdijk, L.B. ; Loon, L.J.C. van
2016, Article / Letter to editor (American Journal of Physiology : Endocrinology and Metabolism, vol. 310, iss. 2, (2016), pp. E137-47)Disuse leads to rapid loss of skeletal muscle mass and function. It has been hypothesized that short successive periods of muscle disuse throughout the lifespan play an important role in the development of sarcopenia. The physiological mechanisms underlying short-term muscle disuse atrophy remain to be elucidated. We assessed the impact of 5 days of muscle disuse on postabsorptive and postprandial myofibrillar protein synthesis rates in humans. Twelve healthy young (22 ± 1 yr) men underwent a 5-day period of one-legged knee immobilization (full leg cast). Quadriceps cross-sectional area (CSA) of both legs was assessed before and after immobilization. Continuous infusions of l-[ring-(2)H5]phenylalanine and l-[1-(13)C]leucine were combined with the ingestion of a 25-g bolus of intrinsically l-[1-(13)C]phenylalanine- and l-[1-(13)C]leucine-labeled dietary protein to assess myofibrillar muscle protein fractional synthetic rates in the immobilized and nonimmobilized control leg. Immobilization led to a 3.9 ± 0.6% decrease in quadriceps muscle CSA of the immobilized leg. Based on the l-[ring-(2)H5]phenylalanine tracer, immobilization reduced postabsorptive myofibrillar protein synthesis rates by 41 ± 13% (0.015 ± 0.002 vs. 0.032 ± 0.005%/h, P < 0.01) and postprandial myofibrillar protein synthesis rates by 53 ± 4% (0.020 ± 0.002 vs. 0.044 ± 0.003%/h, P < 0.01). Comparable results were found using the l-[1-(13)C]leucine tracer. Following protein ingestion, myofibrillar protein bound l-[1-(13)C]phenylalanine enrichments were 53 ± 18% lower in the immobilized compared with the control leg (0.007 ± 0.002 and 0.015 ± 0.002 mole% excess, respectively, P < 0.05). We conclude that 5 days of muscle disuse substantially lowers postabsorptive myofibrillar protein synthesis rates and induces anabolic resistance to protein ingestion.
Glycemic control during consecutive days with prolonged walking exercise in individuals with type 1 diabetes mellitus.
Dijk, J.W. van ; Eijsvogels, T.M.H. ; Nyakayiru, J. ; Schreuder, T.H. ; Hopman, M.T.E. ; Thijssen, D.H. ; Loon, L.J.C. van
2016, Article / Letter to editor (Diabetes Research and Clinical Practice, vol. 117, (2016), pp. 74-81)AIMS: Despite its general benefits for health, exercise complicates the maintenance of stable blood glucose concentrations in individuals with type 1 diabetes. The aim of the current study was to examine changes in food intake, insulin administration, and 24-h glycemic control in response to consecutive days with prolonged walking exercise (~8h daily) in individuals with type 1 diabetes. METHODS: Ten individuals with type 1 diabetes participating in the worlds' largest walking event were recruited for this observational study. Simultaneous measurements of 24-h glycemic control (continuous glucose monitoring), insulin administration and food intake were performed during a non-walking day (control) and during three subsequent days with prolonged walking exercise (daily distance 40 or 50km). RESULTS: Despite an increase in daily energy (31±18%; p<0.01) and carbohydrate (82±71g; p<0.01) intake during walking days, subjects lowered their insulin administration by 26±16% relative to the control day (p<0.01). Average 24-h blood glucose concentrations, the prevalence of hyperglycemia (blood glucose >10 mmol/L) and hypoglycemia (blood glucose <3.9mmol/L) did not differ between the control day and walking days (p>0.05 for all variables). The prolonged walking exercise was associated with a modest increase in glycemic variability compared with the control day (p<0.05). CONCLUSION: Prolonged walking exercise allows for profound reductions in daily insulin administration in persons with type 1 diabetes, despite large increments in energy and carbohydrate intake. When taking such adjustments into account, prolonged moderate-intensity exercise does not necessarily impair 24-h glycemic control.
A single dose of sodium nitrate does not improve oral glucose tolerance in patients with type 2 diabetes mellitus.
Cermak, N.M. ; Hansen, D. ; Kouw, I.W.K. ; Dijk, J.W. van ; Blackwell, J.R. ; Jones, A.M. ; Gibala, M.J. ; Loon, L.J.C. van
2015, Article / Letter to editor (Nutrition Research, vol. 35, iss. 8, (2015), pp. 674-680)Dietary nitrate (NO3(-)) supplementation has been proposed as an emerging treatment strategy for type 2 diabetes. We hypothesized that ingestion of a single bolus of dietary NO3(-) ingestion improves oral glucose tolerance in patients with type 2 diabetes. Seventeen men with type 2 diabetes (glycated hemoglobin, 7.3% ± 0.2%) participated in a randomized crossover experiment. The subjects ingested a glucose beverage 2.5 hours after consumption of either sodium NO3(-) (0.15 mmol NaNO3(-) • kg(-1)) or a placebo solution. Venous blood samples were collected before ingestion of the glucose beverage and every 30 minutes thereafter during a 2-hour period to assess postprandial plasma glucose and insulin concentrations. The results show that plasma NO3(-) and nitrite levels were increased after NaNO3(-) as opposed to placebo ingestion (treatment-effect, P = .001). Despite the elevated plasma NO3(-) and nitrite levels, ingestion of NaNO3(-) did not attenuate the postprandial rise in plasma glucose and insulin concentrations (time × treatment interaction, P = .41 for glucose, P = .93 for insulin). Despite the lack of effect on oral glucose tolerance, basal plasma glucose concentrations measured 2.5 hours after NaNO3(-) ingestion were lower when compared with the placebo treatment (7.5 ± 0.4 vs 8.3 ± 0.4 mmol/L, respectively; P = .04). We conclude that ingestion of a single dose of dietary NO3(-) does not improve subsequent oral glucose tolerance in patients with type 2 diabetes.
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)
Exercise strategies to optimize glycemic control in type 2 diabetes: a continuing glucose monitoring perspective.
Dijk, J.W. van ; Loon, L.J.C. van
2015, Article / Letter to editor (Diabetes Spectr, vol. 28, iss. 1, (2015), pp. 24-31)IN BRIEF The introduction of continuous glucose monitoring (CGM) several years ago enabled researchers to investigate the impact of exercise strategies on 24-hour glycemic control. Such unique information on the glucoregulatory properties of exercise will ultimately lead to more effective exercise programs to prevent and treat type 2 diabetes. This article reviews the role of exercise and physical activity in the treatment of type 2 diabetes, complemented by recent data obtained by CGM.
Circulating cardiac troponin T exhibits a diurnal rhythm.
Klinkenberg, L.J. ; Dijk, J.W. van ; Tan, F.E. ; Loon, L.J.C. van ; Dieijen-Visser, M.P. van ; Meex, S.J.
2014, Article / Letter to editor (Journal of the American College of Cardiology, vol. 63, iss. 17, (2014), pp. 1788-1795)OBJECTIVES: The goal of this study was to test the unverified assumption that chronically elevated cardiac troponin T (cTnT) levels fluctuate randomly around a homeostatic set point. BACKGROUND: The introduction of high-sensitivity cardiac troponin (cTn) assays has improved sensitivity for acute myocardial infarction (AMI). However, many patients with a single positive cTn test result do not have AMI. Therefore, the diagnosis of AMI relies strongly on serial testing and interpretation of cTn kinetics. Essential in this regard is a profound understanding of the biological variation of cTn. METHODS: Two studies were conducted to assess biological cTnT variation and to investigate the presence of a diurnal rhythm of cTnT. Study 1 comprised 23 male subjects with type 2 diabetes, with no acute cardiovascular disease. Serial venous blood samples were drawn over an 11-h period (8:30 am to 7:30 pm). In study 2, the presence of a diurnal cTnT rhythm was investigated by hourly sampling of 7 subjects from study 1 over 25 h. RESULTS: In study 1, we observed a gradual decrease in cTnT concentrations during the day (24 ± 2%). This decrease was present in all participants and was most prominent in subjects with the highest baseline cTnT values (Pearson's R 0.93). Diurnal variation of cTnT, as assessed in study 2, was characterized by peak concentrations during morning hours (8:30 am, 17.1 ± 2.9 ng/l), gradually decreasing values during daytime (8:30 pm, 11.9 ± 1.6 ng/l), and rising concentrations during nighttime (8:30 am the next day, 16.9 ± 2.8 ng/l). CONCLUSIONS: A diurnal cTnT rhythm substantiates the recommendation that all dynamic changes in cTnT should be interpreted in relation to the clinical presentation. Epidemiological studies and risk-stratification protocols with the use of cTnT may benefit from standardized sampling times. (Exercise and Glycemic Control in Type 2 Diabetes; NCT00945165).

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