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Lawrence E. Armstrong, Elaine C. Lee, Douglas J. Casa, Evan C. Johnson, Matthew S. Ganio, Brendon P. McDermott, Jakob L. Vingren, Hyun M. Oh and Keith H. Williamson

Introduction:

Exertional hyponatremia (EH) during prolonged exercise involves all avenues of fluid-electrolyte gain and loss. Although previous research implicates retention of excess fluid, EH may involve either loss, gain, or no change of body mass. Thus, the etiology, predisposing factors, and recommendations for prevention are vague—except for advice to avoid excessive drinking.

Purpose:

This retrospective field study presents case reports of two unacquainted recreational cyclists (LC, 31y and AM, 39 years) who began exercise with normal serum electrolytes but finished a summer 164-km ride (ambient, 34±5°C) with a serum [Na+] of 130 mmol/L.

Methods:

To clarify the etiology of EH, their pre- and post-exercise measurements were compared to a control group (CON) of 31 normonatremic cyclists (mean ± SD; 37±6 years; 141±3 mmol Na+/L).

Results:

Anthropomorphic characteristics, exercise time, and post-exercise ratings of thermal sensation, perceived exertion and muscle cramp were similar for LC, AM and CON. These two hyponatremic cyclists consumed a large and similar volume of fluid (191 and 189 ml/kg), experienced an 11 mmol/L decrease of serum [Na+], reported low thirst sensations; however, LC gained 3.1 kg (+4.3% of body mass) during 8.9 hr of exercise and AM maintained body mass (+0.1kg, +0.1%, 10.6h). In the entire cohort (n = 33), post-event serum [Na+] was strongly correlated with total fluid intake (R2 = 0.45, p < .0001), and correlated moderately with dietary sodium intake (R2=0.28, p = .004) and body mass change (R2 = 0.22, p = .02). Linear regression analyses predicted the threshold of EH onset (<135 mmol Na+/L) as 168 ml fluid/kg.

Conclusions:

The wide range of serum [Na+] changes (+6 to -11 mmol/L) led us to recommend an individualized rehydration plan to athletes because the interactions of factors were complex and idiosyncratic.

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Marcia A. Chan, Alexander J. Koch, Stephen H. Benedict and Jeffrey A. Potteiger

The effect of carbohydrate supplementation (CHO) on interleukin 2 (IL-2) and interleukin 5 (IL-5) secretion following acute resistance exercise was examined in 9 resistance-trained males. Subjects completed a randomized, double-blind protocol with exercise separated by 14 days. The exercise consisted of a high intensity, short rest interval squat workout. Subjects consumed 1.0 g · kg body mass-1 CHO or an equal volume of placebo (PLC) 10 min prior to and 10 min following exercise. Blood was collected at rest (REST), immediately post exercise (POST), and at 1.5 h of recovery (1.5 h POST). Isolated peripheral blood mononuclear cells were stimulated with PHA and assayed for IL-2 and IL-5 secretion. IL-2 secretion was significantly decreased at POST for both the PLC and CHO groups. However, the degree of decrease was less in the CHO group (16%) than in the PLC group (48%), and this difference was statistically significant. These responses were transient, and the values returned to normal by 1.5 h POST. A mild and transient but significant decrease in IL-5 secretion by the PLC group was observed at POST (26%) compared to REST. No significant decrease was observed in IL-5 secretion for CHO from REST to POST (12%). These data support a possible effect of carbohydrate supplementation on IL-2 and IL-5 secretion following high-intensity resistance exercise.

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Andrea D. Marjerrison, Jonah D. Lee and Anthony D. Mahon

This study examined the effect of pre exercise carbohydrate (CHO) feeding on performance on a Wingate anaerobic test (WAnT) in 11 boys (10.2 ± 1.3 y old). Four WAnTs with 2 min recovery were performed 30 min after consuming a CHO (1 g CHO/kg) or placebo drink. Peak power (PP) and mean power (MP) were similar between trials. PP ranged from 241.1 ± 82.2 to 223.1 ± 57.9 W with carbohydrate and from 238.2 ± 76.1 to 223.4 ± 52.3 W with placebo. MP ranged from 176.3 ± 58.4 to 151.1 ± 37.5 W with carbohydrate versus 178.0 ± 45.8 to 159.1 ± 32.7 W with placebo. Pre exercise glucose was significantly higher in CHO versus placebo (7.0 ± 1.0 vs. 5.5 ± 0.5 mmol/L), but post exercise values were not different. Blood lactate was similar between trials but increased over time. This study found that the ingestion of a CHO solution before exercise did not influence power output during repeated performances of the WAnT.

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Elaine M. Murtagh, Colin Boreham, Alan Nevill, Gareth Davison, Tom Trinick, Ellie Duly, Mawloud El-Agnaf and Marie H. Murphy

Background:

Markers of inflammation are emerging as novel indices of cardiovascular risk. These markers have been shown to alter acutely after intense exercise; however, the effects of more moderate intensity exercise in healthy individuals is not known. Walking forms a cornerstone of physical activity promotion, so the inflammatory response to this exercise merits investigation. This study evaluated the effects of a 45-min walk on C-reactive protein (CRP) and interleukin 6 (IL-6), in sedentary, overweight men.

Methods:

Fifteen men (49.7 ± 5.9 y) walked for 45 min at 60 to 70% of predicted maximum heart rate. Fasted blood samples were taken prior to and immediately 1 hr and 24 h post-walk.

Results:

IL-6 decreased from 1 h post-walk to 24 h post-walk (P < 0.01). No significant changes were observed in CRP.

Conclusions:

These findings suggest that 45 min walking at 60 to 70% HRmax-p causes a decrease in IL-6 24 h post-exercise, but does not evoke a significant response in CRP levels.

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Dru A. Henson, David C. Nieman, E. Edward Pistilli, Brian Schilling, AnnaRita Colacino, Allan C. Utter, Omar R. Fagoaga, Debra M. Vinci and Sandra L. Nehlsen-Cannarella

The influence of 6% carbohydrate ingestion and age on PHA-induced lymphocyte proliferation and in vitro cytokine production was studied in 48 runners following a competitive marathon. Runners were randomly assigned to carbohydrate (C; n = 23) and placebo (P; n = 25) groups, with blood samples taken before, immediately after, and 1.5 hr post-race. C versus P ingestion resulted in higher plasma glucose, lower plasma corlisol, reduced neutrophilia, and mono-cytosis during recovery, but had no effect on the post-exercise reduction in T-lymphocytes or NK cells, or on race times. No group differences were observed for PHA-induced lymphocyte proliferation or cytokine production. However, for all subjects combined, lymphocyte proliferation and IFN-γ secretion decreased significantly below pre-race values by 1.5 hr of recovery, and these were negatively correlated with plasma cortisol. Young (<50 years; n = 36) and old (≥50 years; n = 12) runners exhibited parallel post-race declines in lymphocyte proliferation and IFN-γ secretion, with the older group exhibiting a 33–59% lower proliferation at each time point. In conclusion, PHA-induced lymphocyte proliferation and cytokine production decreased significantly following a marathon, and this decrease was strongly linked to cortisol and only partially linked to T-cell changes. This decrease occurred in both younger and older runners and was not influenced by carbohydrate.

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Allan H. Goldfarb, Richard J. Bloomer and Michael J. McKenzie

To examine the effects of an antioxidant treatment on blood lactate, protein carbonyls (PC), and glutathione status, 42 male rats were assigned to either a control treatment (water, C) or one of two Microhydrin® treatments (added to water, MH I or MH II). Rats from each treatment were assigned to either exercise (60 min of running) or rest. A treatment-by-time interaction was noted for blood lactate, with elevations only in the C and MH I treatments post-exercise (~ 2.54 and 2.5 mM, respectively). Both treatment and time main effects were noted for PC. Exercise resulted in an increase in PC for both Microhydrin treatments with significantly greater PC compared to C. Total blood glutathione was unaffected by treatment or exercise. Exercise increased the ratio of oxidized to total glutathione and the MH II treatment resulted in a greater ratio compared to the other treatments. In conclusion, MH II results in lower blood lactate, while resulting in an increase in the concentration of oxidized protein and glutathione, suggesting heightened oxidative stress.

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Nicola C. Sutton, David J. Childs, Oded Bar-Or and Neil Armstrong

The purpose of this study was to develop a nonmotorized treadmill sprint test (ExNMT) to assess children’s short-term power output, to establish the test’s repeatability, and to compare the results to corresponding Wingate anaerobic test (WAnT) measurements. Nineteen children (aged 10.9±0.3 years) completed 2 ExNMTs and 2 WAnTs. Statistical analysis revealed coefficients of repeatability for the ExNMT that compared very favorably with the WAnT for both peak power (26.6 vs. 44.5 W) and mean power (15.3 vs. 42.1 W). The validity of the ExNMT as a test of anaerobic performance is reflected by significant correlations (p ≤.05) with the WAnT (peak power, r = 0.82; mean power, r = 0.88) and reinforced by the relatively high post-exercise blood lactate concentrations (7.1 ± 1.3 vs. 5.6 ± 1.5 mmol · L−1 for the ExNMT and WAnT, respectively). This study has developed a promising laboratory running test with which to examine young people’s short-term power output.

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Stephen Hill, Wesley Box and Robert A. DiSilvestro

Lipid peroxides can be both a product and an initiator of oxidant stress. Conceivably, exercise can either increase concentrations of lipid peroxides (by causing oxidant stress), or decrease them (by accelerating peroxide breakdown). The net effect could depend on exercise intensity and nutritional intake of antioxidants. The present study examined the response of serum lipid peroxides to the combination of moderate intensity, weight resistance exercise plus intake of soy protein, a source of antioxidant phytochemicals. Recreationally trained, young adult men (N = 18) consumed soy protein or antioxidant-poor whey protein for 4 weeks (40 g protein/d) before a session of moderate intensity, weight resistance exercise. In the soy group, exercise decreased values for serum lipid peroxides at 5 min, 3 h, and 24 h post-exercise. The whey group showed the depression only at 24 h. In both the soy and whey groups, a small rise was seen for interleukin-8, which is consistent with the idea that the exercise session induced a moderate muscle stress. In summary, a moderate intensity, weight resistance exercise session, despite inducing mild inflammation, depressed plasma serum peroxide values, especially when combined with 4 weeks of soy consumption.

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Maple Liu, Linda J. Gillis, Nicholas R. Persadie, Stephanie A. Atkinson, Stuart M. Phillips and Brian W. Timmons

There is some evidence that a combination of factors can reduce inflammation and associated metabolic risk factors. We studied the early cardiometabolic and inflammatory adaptations to a short-term exercise intervention with and without milk in obese adolescents. Fifty-four adolescents were randomized to consume milk post exercise (MILK) or a carbohydrate beverage (CONT) during one-week of daily exercise. Insulin levels were not different between the groups post training. Glucose was reduced over time in both groups (-9 ± 13 mg/dl MILK and -6 ± 14 mg/dl CONT, p < .05) but not different between groups. There was a greater decrease in mean arterial pressure (MAP) in the MILK group (-3 ± 6 mmHg MILK vs. 2 ± 7 mmHg CONT, p < .04). Milk provided postexercise did not affect C-reactive protein (CRP), tumor necrosis factor-α (TNF-α) or interleukin-6 (IL-6). The exercise intervention led to an increase in TNF-α in both groups (0.27 ± 0.7 pg/ml MILK and 0.48 ± 0.6 pg/ml CONT, p < .001). The early adaptations to a short-term exercise intervention in obese adolescents include a reduction in MAP and an increase in some inflammatory markers.

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Mindy Millard-Stafford, Gordon L. Warren, Leah Moore Thomas, J. Andrew Doyle, Teresa Snow and Kristen Hitchcock

Post-exercise nutrition is critical to facilitate recovery from training. To determine if added protein (P) or increased carbohydrate (CHO) differentially improves recovery, eight runners ingested: 6% CHO (CHO6), 8% CHO + 2% protein (CHOP), and isocaloric 10% CHO (CHO10) following a 21-km run plus treadmill run to fatigue (RTF) at 90% VO2max. RTF was repeated after 2 h recovery. After 24 h, a 5 km time trial was performed. Insulin and blood glucose were higher (P < 0.05) following CHO10 compared to CHO-P and CHO6, but did not affect improvement from the first to second RTF (29.6% ± 6, 40.5% ± 8.8, 40.5% ± 14.5) or 5 km time (1100 ± 36.3, 1110 ± 37.3, 1118 ± 36.5 s). CK was not different, but perceived soreness with CHO-P (2.1 ± 0.5) was lower than CHO10 (5.2 ± 0.7). Additional calories from CHO or P above that provided in sports drinks does not improve subsequent performance after recovery; but less soreness suggests benefits with CHO-P.