Perceived exertion and performance modulation: effects of caffeine ingestion and subject expectation.

BACKGROUND: It is well established that caffeine has ergogenic effects on endurance performance. This evidence often comes from studies in which subjects receive either caffeine or placebo in double-blind, randomized and counterbalanced order. Here, we propose a new methodology which aims to estimate the effects of participant expectancy of ergogenic or anti-ergogenic effects on performance. METHODS: Sixteen physically active participants (non-athletes engaged in systematic physical training >3 months, at least three times a week) performed three 30-minute running tests after being told they would be provided with either a harmful treatment (lactic acid), a beneficial treatment (caffeine) or a placebo. In each blinded case, subjects were given caffeine. The velocity and Rating of Perceived Exertion (RPE) during the time trial were examined in light of the participant's expectancy before and after the endurance event using Bayesian multilevel models. RESULTS: For pre-exercise expectancy, there is a 92% probability that caffeine expectation decreases RPE (posterior median±SD -0.65±0.36) and a 79% probability that lactic acid expectation increases RPE (posterior median±SD 0.58±0.47) with expectations for placebo and 'not sure' falling in between (posterior median±SD: -0.37±0.32 and -0.22±0.37, respectively). In general, our interventions suggest an 81% probability that caffeine lowers RPE. However, there was no effect of caffeine supplementation on running velocity (median±SD 0.04±0.08 km.h-1). CONCLUSIONS: When a participant believed they are under a potentially positive treatment, their RPE decreased but if they believed themselves to be under a harmful treatment, their RPE increased, regardless of the actual positive intervention; neither caffeine nor the expectancy of a particular intervention improved actual performance as measured by running velocity in a 30-minute period.

Comparison betweent the effects of swimming and treadmill-based aerobic training protocols in diabetic rats / Comparação entre os efeitos de natação e protocolos de treinamento aeróbio em esteira em ratos diabéticos

Background: Type 1 diabetes mellitus (DM1) can cause damage to several physiological systems.Objectives: To compare and characterize the effects of aerobic exercise training (ET) performed by swimming with those of ET performed on a treadmill on the skeletal muscle and heart of rats with DM1. Methods: 41 male Wistar rats were randomized into four groups: nondiabetic control (CTR), diabetic control (DMC), diabetic trained on the treadmill (DMT), and diabetic trained by swimming (DMS). The trained groups performed aerobic exercise training for 8 weeks, 5 times a week, 60 min per day. Exercise tolerance, blood glucose, body weight, wet weight of the skeletal muscles and left ventricle (LV), muscle glycogen, cross-sectional area of skeletal muscles, and cross-sectional diameter and collagen volume fraction of the LV were evaluated.Results: The results were expressed as mean ± standard deviation of the mean and submitted to two-way ANOVA with post-hoc Bonferroni test. Aerobic ET protocols applied to animals with DM1, regardless of the ergometer, showed satisfactory results (p < 0.05) when compared to the control groups: improved exercise tolerance, increased glycogen content of the soleus and extensor digitorum longus (EDL) muscles and increased cross-sectional diameter of the left ventricular cardiomyocytes. In some variables, such as exercise tolerance and cross-sectional area of the soleus and EDL muscles, DMT showed better results than DMS (p < 0.05). On the other hand, DMS showed increased cross-sectional diameter of cardiomyocytes when compared with the DMT group. Conclusion: Both aerobic ET protocols offered benefits to animals with diabetes; however, due to the specific characteristics of each modality, different physiological adaptations were observed between the trained groups