Sustained high levels of physical activity lead to improved performance among "Race Across the USA" athletes.

OBJECTIVE: To investigate physiological and performance adaptations associated with extremely high daily sustained physical activity levels, we followed six runners participating in the 2015 Race Across the USA. Participants completed over 42.2 km a day for 140 days, covering nearly 5,000 km. This analysis examines the improvement in running speed and potential adaptation in mean submaximal heart rate (SHR) throughout the race. METHODS: Data were collected during three 1-week long periods corresponding to the race beginning, middle, and end and included heart rates (HRs), body mass, running distances and speeds. HR data were collected using ActiTrainer HR monitors. Running speeds and distances were also recorded throughout the entire race. RESULTS: Athletes ran significantly faster as the race progressed (p < .001), reducing their mean marathon time by over 63 min. Observed mean SHR during the middle of the race was significantly lower than at the beginning (p = .003); however, there was no significant difference between mean SHR at the middle and end of the race (p = .998). CONCLUSION: These results indicate an early training effect in SHR during the first half of the race, which suggests that other physiological and biomechanical mechanisms were responsible for the continued improvement in running speed and adaptation to the high levels of sustained physical activity.

Effect of strenuous exercise on urine concentrations of homovanillic acid, cortisol, and vanillylmandelic acid in sled dogs.

OBJECTIVE: To determine whether prolonged exercise by conditioned sled dogs affects urine concentrations of homovanillic acid (a metabolite of dopamine), vanillylmandelic acid (a metabolite of norepinephrine and epinephrine), and cortisol. ANIMALS: 24 conditioned Alaskan sled dogs (2 to 8.5 years old) that were in training for a multiday endurance race. PROCEDURES: Voided urine samples were collected from 4 groups of dogs (randomly selected from 54 dogs) after no exercise (control group; n = 6 dogs), completion of a 160km run (group A; 3), completion of a 420-km run (group B; 7), and completion of a 560-km run (group C; 6). Urine cortisol concentrations were determined by use of an immunoassay technique; urine vanillylmandelic acid and homovanillic acid concentrations were measured via high-performance liquid chromatography. RESULTS: Compared with the control group, urine cortisol concentration in groups A, B, and C was significantly different (5.33 x 10(4) +/- 2.62 x 10(4) microg/dL vs 1.04 x 10(4) +/- 2.31 x 10(5) microg/dL, 8.88 x 10(4) +/- 5.49 x 10(4) microg/dL, and 6.31 x 10(4) +/- 5.09 x 10(4) microg/dL, respectively). Urine homovanillic acid concentration did not differ among the 4 groups. Vanillylmandelic acid was not detected in any urine samples. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that prolonged exercise by sled dogs did not affect urine homovanillic acid concentration but did increase urinary cortisol secretion, which is indicative of adrenocortical stimulation. The apparent lack of vanillylmandelic acid in voided urine samples requires further investigation.

Temporal relationship between gastrointestinal protein loss, gastric ulceration or erosion, and strenuous exercise in racing Alaskan sled dogs.

BACKGROUND: Alterations in the appearance and function of gastrointestinal mucosa are common after strenuous exercise. However, the duration of exercise required to alter the gastrointestinal mucosa has not been reported. HYPOTHESIS: We used 42 sled dogs to test the hypothesis that the magnitude of exercise-induced gastrointestinal mucosal dysfunction is related to exercise duration. ANIMALS: Six dogs served as conditioned controls, and the remaining dogs were randomly chosen for examination after 1-5 consecutive days of running at 100 miles/d. METHODS: Gastroduodenoscopy and measurement of gastric permeability were performed 24 hours after cessation of exercise. Intestinal protein loss (represented by fecal alpha-1 protease inhibitor concentration) was measured within 6 hours of cessation of exercise. Twelve of the 42 dogs were examined again after 5 months of detraining to determine the effect of training on gastrointestinal mucosal function. RESULTS: Exercise increased gastric permeability (P = .04) and endoscopic severity of gastric lesions (P < .0001), but neither variable was significantly affected by distance traveled. Acute exercise had no effect on intestinal protein loss. Untrained dogs had significantly lower fecal alpha-1 protease inhibitor concentrations compared with trained, unexercised dogs. Training had no effect on gastric permeability to sucrose or the endoscopic appearance of the stomach. CONCLUSIONS AND CLINICAL IMPORTANCE: These data suggest that relatively modest exercise is required to increase intestinal protein loss, but more substantial exercise is required to cause alterations in the proximal gastrointestinal tract. However, none of these alterations appear to progress with increasing exercise duration.

Modeling the acute- and late-phase responses to peripheral airway cooling and desiccation.

Acute bronchoconstriction after isocapnic hyperpnea can be produced in most asthmatic individuals. However, the existence of a late-phase response is less certain. We used a canine model of isocapnic hyperpnea to test the hypothesis that this discrepancy is due to differences in the challenge threshold for the responses. Acute-phase and late-phase bronchoconstriction was measured in nine dogs after peripheral airway exposure to unconditioned air. Additionally, bronchoalveolar lavage fluid (BALF) was obtained during the late-phase response. The acute-phase response was a polynomial function with a decreasing slope at higher challenges, whereas the late-phase response suggested that a minimum threshold of challenge severity was needed to produce late-phase bronchoconstriction. BALF leukocyte and eicosanoid concentrations had linear relationships with challenge severity. Our data support the hypothesis that acute- and late-phase posthyperpnea responses have different dose-response relationships, a fact that may explain the frequent lack of a late-phase response. However, our data suggest that mild inflammation can be induced with relatively lower challenge severity.