The sense of effort and other specific sensations such as temperature, pain and other muscular sensations present two separate neurological mechanisms. While the former is centrally generated, the latter is based on afferent sensory feedback. An interaction of these sensations is likely the ultimate regulator of exercise performance. However, further investigation is required to fully understand these phenomena.

The mechanisms underpinning fatigue and exhaustion, and the specific sources of exercise-endurance intensity regulation and (in)tolerance have been investigated for over a century. Although several scientific theories are currently available, over the past five years a new framework called Psychobiological model has been proposed. This model gives greater attention to perceptual and motivational factors than its antecedents, and their respective influence on the conscious process of decision-making and behavioral regulation. In this review we present experimental evidences and summarize the key points of the Psychobiological model to explain intensity regulation and (in)tolerance in endurance exercise. Still, we discuss how the Psychobiological model explains training-induced adaptations related to improvements in performance, experimental manipulations, its predictions, and propose future directions for this investigative area. The Psychobiological model may give a new perspective to the results already published in the literature, helping scientists to better guide their research problems, as well as to analyze and interpret new findings more accurately.

PurposeTo investigate the effects of caffeine on performance, neuromuscular fatigue and perception of effort during high-intensity cycling exercise in moderate hypoxia.MethodsSeven adult male participants firstly underwent an incremental exercise test on a cycle ergometer in conditions of acute normobaric hypoxia (fraction inspired oxygen = 0.15) to establish peak power output (PPO). In the following two visits, they performed a time to exhaustion test (78 ± 3% PPO) in the same hypoxic conditions after caffeine ingestion (4 mg kg−1) and one after placebo ingestion in a double-blind, randomized, counterbalanced cross-over design.ResultsCaffeine significantly improved time to exhaustion by 12%. A significant decrease in subjective fatigue was found after caffeine consumption. Perception of effort and surface electromyographic signal amplitude of the vastus lateralis were lower and heart rate was higher in the caffeine condition when compared to placebo. However, caffeine did not reduce the peripheral and central fatigue induced by high-intensity cycling exercise in moderate hypoxia.ConclusionThe caffeine-induced improvement in time to exhaustion during high-intensity cycling exercise in moderate hypoxia seems to be mediated by a reduction in perception of effort, which occurs despite no reduction in neuromuscular fatigue.

BackgroundSeveral studies have demonstrated a positive association between physical activity (PA) and health-related quality of life (HRQL). However, studies have suggested that this association depends both on the PA intensity and the domain of HRQL evaluated. This study aimed to explore the association between physical, mental and overall HRQL with recommended levels of PA. PA levels were divided into moderate and vigorous intensity leisure-time PA and total leisure-time PA.MethodsThe study included 1001 adults, 582 women (46 ± 17 years) and 419 men (43 ± 16 years), residents in Rio Claro-SP, Brazil. All participants completed the SF-36 questionnaire to assess HRQL and the long version of the International Physical Activity Questionnaire (IPAQ) to assess level and intensities of leisure-time PA. Total leisure-time PA at moderate intensity was classified as: less than 9 min/week, 10-149 min/week, 150-299 min/week and 300 min/week or more. Total leisure-time PA at vigorous intensity was classified as: less than 9 min/week, 10 to 74.9 min/week, 75-149 min/week and 150 min/week or more. Multiple linear regression was performed in STATA version 12.0.ResultsAmong women, moderate intensity and total leisure-time PA were associated with physical health. Among men, moderate and vigorous intensity and total leisure-time PA were associated with physical health and overall HRQL. Furthermore, moderate intensity and total leisure-time PA were associated with mental health in men. However, vigorous intensity PA was not associated with mental health for this group.ConclusionThe different domains of HRQL were associated with different levels and intensities of PA in leisure-time according to gender of adults. These findings indicate the complexity and importance of evaluating the HRQL stratified by gender and consider the different levels and intensities of PA.

The aims of this study were to verify the relationship between rating of perceived exertion (RPE) and electromyography (EMG) increases during exhaustive constant-load cycling bouts and, to compare and to correlate the power outputs corresponding to perceived exertion threshold (PET) and neuromuscular fatigue threshold (NFT). 11 men completed 3-4 different exhaustive constant-load cycling bouts on a cycle ergometer, being RPE and EMG measured throughout the bouts. The linear regression of the RPEslope and EMGslope against the power output identified the PET and NFT intensity, respectively. There was a significant relationship between RPEslope and EMGslope (R(2)=0.69; P<0.01). However, the linearity of RPEslope (R(2)=0.93±0.07) was significantly higher (P<0.001) than EMGslope (R(2)=0.63±0.25). In addition, the RPEslope and EMGslope were related to time to exhaustion (r=-0.59 and r=-0.60; P<0.001). There was no significant difference (P=0.42) between PET (201.5±27.9W) and NFT (210.3±22.6W) and they were significantly correlated (r=0.78; P=0.005). Therefore, the RPE and EMG increases during exhaustive constant-load cycling bouts are related and, PET and NFT intensities are similar and closely associated.