Brooke M. Shafer

Independent and combined effects of carbohydrate and caffeine ingestion on aerobic cycling performance in the fed state.

The purpose of this study was to examine the independent and combined effects of carbohydrate and caffeine ingestion on performance and various physiological parameters during aerobic cycling (∼1 h). Ten male cyclists (28 ± 9 years, 73 ± 6 kg, 66 ± 9 mL·kg(-1)·min(-1) maximal oxygen consumption) performed 20 min of steady-state (SS) cycling (60% peak power (W(max))) followed by a simulated 20-km time trial (TT) under placebo (PLA), carbohydrate (CHO), caffeine (CAF), and combined CAF-CHO conditions, all of which were performed in the fed state. CAF-CHO improved TT performance by 3.4% ± 2% (84 ± 57 s) compared with PLA (p < 0.05), whereas no differences were detected among CHO, CAF, and PLA. The SS respiratory exchange ratio was elevated in CHO (0.92 ± 0.03), CAF (0.96 ± 0.07), and CAF-CHO (0.95 ± 0.02) compared with PLA (0.89 ± 0.03) (p < 0.05). Post-SS and post-TT blood glucose levels were also elevated in CAF-CHO (88.3 ± 16.7 mg·dL(-1) and 111.2 ± 33.5 mg·dL(-1), respectively) compared with PLA (74.5 ± 9.8 mg·dL(-1) and 85.4 ± 17.6 mg·dL(-1), respectively) (p < 0.05). Treatment conditions did not differentially impact SS pulmonary ventilation, oxygen consumption, heart rate, peak quadriceps muscle strength, rating of perceived exertion, or blood lactate. CAF and CHO improved TT performance when taken together but not independently. Although the present work did not yield any definitive physiological mechanisms for the performance findings, these data suggest that cyclists in the fed state should ingest carbohydrate and caffeine together to improve time trial performance.

Effects of obstructive sleep apnea on hemodynamic parameters in patients entering cardiac rehabilitation.

PURPOSE: Obstructive sleep apnea (OSA) is a prevalent form of sleep-disordered breathing. Evidence suggests that OSA may lead to cardiac remodeling, although the literature is equivocal. Previous literature suggests a high percentage of individuals entering a cardiac rehabilitation (CR) program also have OSA. The objective of this study was to determine whether resting hemodynamic variables were altered in OSA subjects entering CR compared with those without OSA, as determined by impedance cardiography. METHODS: Subjects entering an early outpatient CR program were screened for OSA using an at-home screening device and verified by a sleep physician. Subjects were divided into an OSA group (n = 48) or a control group (n = 25) on the basis of the screening results. Hemodynamic variables were measured during supine rest using impedance cardiography. A 6-minute walk test was performed to assess functional capacity. RESULTS: The proportion of cardiac diagnoses was similar between groups. Overall, 66% of the subjects were positive for OSA. Subject groups did not differ by age, body mass index, heart rate, diastolic blood pressure, or functional capacity. Cardiac output, cardiac index, stroke volume, contractility index, and left cardiac work index were all significantly decreased in the OSA group compared with the control group (P < .05). CONCLUSIONS: Findings suggest that OSA results in decreased cardiac function in patients entering CR, likely because of pressure and volume changes associated with apneic events. This may place those individuals at a disadvantage in recovering from their cardiac event, and place them at increased risk for secondary complications.