Change in Exercise Performance and Markers of Acute Kidney Injury Following Heat Acclimation with Permissive Dehydration.

Implementing permissive dehydration (DEH) during short-term heat acclimation (HA) may accelerate adaptations to the heat. However, HA with DEH may augment risk for acute kidney injury (AKI). This study investigated the effect of HA with permissive DEH on time-trial performance and markers of AKI. Fourteen moderately trained men (age and VO2max = 25 ± 0.5 yr and 51.6 ± 1.8 mL.kg-1.min-1) were randomly assigned to DEH or euhydration (EUH). Time-trial performance and VO2max were assessed in a temperate environment before and after 7 d of HA. Heat acclimation consisted of 90 min of cycling in an environmental chamber (40 °C, 35% RH). Neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) were assessed pre- and post-exercise on day 1 and day 7 of HA. Following HA, VO2max did not change in either group (p = 0.099); however, time-trial performance significantly improved (3%, p < 0.01) with no difference between groups (p = 0.485). Compared to pre-exercise, NGAL was not significantly different following day 1 and 7 of HA (p = 0.113) with no difference between groups (p = 0.667). There was a significant increase in KIM-1 following day 1 and 7 of HA (p = 0.002) with no difference between groups (p = 0.307). Heat acclimation paired with permissive DEH does not amplify improvements in VO2max or time-trial performance in a temperate environment versus EUH and does not increase markers of AKI.

The effects of a novel bicarbonate loading protocol on serum bicarbonate concentration: a randomized controlled trial.

BACKGROUND: Previous studies have shown that sodium bicarbonate ingestion may enhance intense exercise performance, but may also cause severe gastrointestinal distress. The purpose of this study was to determine whether a modified sodium bicarbonate (SB) ingestion protocol would elevate serum bicarbonate concentration more than previous methods without causing gastrointestinal distress. METHODS: In randomized order, seven (5 men, 2 women) elite middle-distance runners ingested either placebo, Modified SB (600 mg·kg- 1 over 19.5 h), or Acute SB (300 mg·kg- 1) in opaque gelatin capsules. Baseline and post-ingestion blood samples were analyzed for bicarbonate, pH, sodium, hematocrit, and lactate. Repeated measures ANOVA (2 time points × 3 conditions) were analyzed to determine differences in serum bicarbonate, lactate, sodium, blood pH, and hematocrit. Gastrointestinal distress was assessed via self-report on a Likert scale of 1-10. Simple (condition) and repeated (time) within-participant contrasts were used to determine the location of any statistically significant main and interaction effects (p ≤ 0.05). RESULTS: Both Modified SB (7.6 mmol·L- 1, p < 0.01) and Acute SB (5.8 mmol·L- 1, p < 0.01) increased serum bicarbonate concentration compared to the placebo (p ≤ 0.05). Post-ingestion serum bicarbonate concentration was significantly higher for the Modified SB (34.7 ± 2.2 mmol·L- 1, 28.0% increase) trials than the Acute SB (33.5 ± 2.0 mmol·L- 1, 20.9% increase) trials (p = 0.05). There was no reported severe GI distress in the Modified SB trials, but two cases in the Acute SB trials. CONCLUSIONS: Modified SB elevated serum bicarbonate concentration more than Acute SB, without any severe gastrointestinal side effects. Consequently, it is recommended that future experimentation involving SB by researchers and athletes use the novel ingestion protocol described in this study due to its potential for improved effectiveness and reduced gastrointestinal impact. TRIAL REGISTRATION: ClinicalTrials.gov , NCT03813329 . Registered 23 January 2019 - Retrospectively registered.

Acute effects of unilateral static stretching on handgrip strength of the stretched and non-stretched limb.

PURPOSE: To determine the effects of an acute bout of unilateral static stretching on handgrip strength of both the stretched and non-stretched limb. It was reasoned that if the non-stretched limb experienced a decrease in force output, further evidence for a neural mechanism to explain a post-stretch force reduction would be obtained as no mechanical adaptation would have occurred. METHODS: Thirty participants performed maximum voluntary unilateral handgrip contractions of both limbs before and after stretching the finger flexors of the strength-dominant side only. Each trial was assessed for peak force, muscle activity (iEMG), and rate of force generation. RESULTS: Following the stretching bout, peak force and iEMG decreased by 4.4% (p = 0.001) and 6.4% (p = 0.000) respectively in the stretched limb only. However, rate of force generation was significantly impaired in both the stretched (- 17.3%; p = 0.000) and non-stretched limbs (- 10.8%; p = 0.003) 1 min post-stretch, and remained similarly depressed for both limbs 15 min later. CONCLUSION: Acute stretching negatively impacts rate of force generation more than peak force. Moreover, a reduced rate of force generation from the non-stretched limb indicates the presence of a cross-over inhibitory effect through the nervous system, which provides additional evidence for a neural mechanism.

Effects of aerobic exercise on lipid-effector molecules of the innate immune response.

INTRODUCTION: Consistent, moderate-to-vigorous-intensity exercise has been associated with a lower risk of upper respiratory tract infection (URI). However, the molecular basis for this apparent protection has not yet been fully resolved. Host-derived lipids such as cholesteryl esters (CE) have emerged as important effector molecules of innate defense against infections. Here, we compared antimicrobial CE in nasal fluid before and after moderate-to-vigorous exercise between active and inactive subjects. METHODS: Nasal fluid was collected from 14 healthy, recreationally active subjects (32 ± 11 yr, 7 men and 7 women) and 14 healthy, inactive subjects (25 ± 3 yr, 7 men and 7 women) before and after treadmill exercise at 70% heart rate reserve. Nasal fluid was analyzed for lysozyme, cholesteryl linoleate (CL), cholesteryl arachidonate (CA), and albumin (Alb) concentrations. RESULTS: Baseline concentrations (mean ± SEM, inactive vs active) of lysozyme (117.7 ± 31.1 vs 122.9 ± 15.5 µg·mL), CL + CA (15.3 ± 1.8 vs 26.2 ± 10.05 µg·mL), and Alb (156.6 ± 54.5 vs 126.9 ± 32.8 µg·mL) were similar to previously reported levels and did not differ significantly between study groups. However, postexercise, CL + CA concentration was significantly lower in inactive compared with active subjects (7.8 ± 1.5 vs 20.1 ± 4.8 µg·mL, P = 0.036) dropping below the antimicrobial effective range. Once adjusted to Alb concentrations, the changes were no longer significant, suggesting that plasma transudation accounted for the increased CA + CL concentration postexercise in the active group relative to the inactive group. CONCLUSIONS: Moderate-to-vigorous aerobic exercise acutely decreases the antimicrobial CE response in inactive subjects but does not modify baseline levels of CE between active and inactive subjects. This suggests that compared with active individuals, inactive individuals may be at greater risk for upper respiratory tract infection immediately postexercise.

Relevance of hand dominance to the bilateral deficit phenomenon.

During maximal voluntary contractions, the sum of forces exerted by homonymous muscles when activated unilaterally (UL) is, typically, larger than the sum of forces when activated bilaterally (BL). This phenomenon is known as the bilateral deficit (BLD). Our purpose was to determine if the dominant limb would be inhibited to a greater degree in the BL condition, thereby reducing any disparity in force output between the limbs. Maximum voluntary handgrip strength was measured in 40 left-handed and 40 right-handed individuals under both BL and UL conditions. The right-handers displayed 10.4 % greater right hand strength in both conditions; the left-handers exhibited 5.5 % greater left hand strength in the UL and 4.3 % in the BL condition. A BLD (-1.30 %) was present in the left-handed group only but a reduction in the force disparity between the hands was not evident. It was observed, however, that seven individuals from each group exhibited greater UL force with their non-dominant hand. Accordingly, we re-analyzed the data after rearranging the groups based on unilateral hand grip strength dominance. A significant reduction in force disparity between the hands occurred for the left-handed group only, the result of a significant inhibition of the stronger left hand. A trend towards a similar reduction occurred for the right-handers because of a significant force reduction of the stronger right hand. Consequently, it appears that for maximum handgrip contractions, the BLD may be related to preferential inhibition of the stronger hand, especially for individuals who are left-hand-strength-dominant in terms of unilateral force output.