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Purpose: To describe the metabolic demands of rugby league match play for positional groups and compare match distances obtained from high-speed-running classifications with those derived from high metabolic power. Methods: Global positioning system (GPS) data were collected from 25 players from a team competing in the National Rugby League competition over 39 matches. Players were classified into positional groups (adjustables, outside backs, hit-up forwards, and wide-running forwards). The GPS devices provided instantaneous raw velocity data at 5 Hz, which were exported to a customized spreadsheet. The spreadsheet provided calculations for speed-based distances (eg, total distance; high-speed running, >14.4 km/h; and very-high-speed running, >18.1 km/h) and metabolic-power variables (eg, energy expenditure; average metabolic power; and high-power distance, >20 W/kg). Results: The data show that speed-based distances and metabolic power varied between positional groups, although this was largely related to differences in time spent on field. The distance covered at high running speed was lower than that obtained from high-power thresholds for all positional groups; however, the difference between the 2 methods was greatest for hit-up forwards and adjustables. Conclusions: Positional differences existed for all metabolic parameters, although these are at least partially related to time spent on the field. Higher-speed running may underestimate the demands of match play when compared with high-power distance—although the degree of difference between the measures varied by position. The analysis of metabolic power may complement traditional speed-based classifications and improve our understanding of the demands of rugby league match play. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of the study was to investigate the effects of mental fatigue on intermittent running performance. Methods: Ten male intermittent team sports players performed two identical self-paced, intermittent running protocols. The two trials were separated by 7 d and preceded, in a randomized-counterbalanced order, by 90 min of either emotionally neutral documentaries (control) or the AX-continuous performance test (AX-CPT; mental fatigue). Subjective ratings of fatigue and vigor were measured before and after these treatments, and motivation was recorded before the intermittent running protocol. Velocity, heart rate, oxygen consumption, blood glucose and lactate concentrations, and ratings of perceived exertion (RPE) were measured throughout the 45-min intermittent running protocol. Session RPE was recorded 30 min after the intermittent running protocol. Results: Subjective ratings of fatigue were higher after the AX-CPT (P = 0.005). This mental fatigue significantly reduced velocity at low intensities (1.28 ± 0.18 m⋅s-1 vs 1.31 ± 0.17 m⋅s-1; P = 0.037), whereas high-intensity running and peak velocities were not significantly affected. Running velocity at all intensities significantly declined over time in both conditions (P < 0.001). Oxygen consumption was significantly lower in the mental fatigue condition (P = 0.007). Other physiological variables, vigor and motivation, were not significantly affected. Ratings of perceived exertion during the intermittent running protocol were not significantly different between conditions despite lower overall velocity in the mental fatigue condition. Session RPE was significantly higher in the mental fatigue condition (P = 0.013). Conclusion: Mental fatigue impairs intermittent running performance. This negative effect of mental fatigue seems to be mediated by higher perception of effort. [ABSTRACT FROM AUTHOR]

Objectives: This study compared the acute inflammatory and glucose responses following aerobic exercise in sedentary Indigenous Australian and Caucasian men, matched for fitness and body composition., Methods: Sedentary Indigenous (n = 10) and Caucasian (n = 9) Australian men who were free from chronic disease volunteered to participate. Following baseline testing, participants completed a 40 min cycling bout at ∼80% maximal heart rate. Fasting venous blood was collected pre, 0, 30, 60, and 240 min post-exercise for analysis of glucose, insulin, cortisol, tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, IL-1 receptor agonist (ra), and C-reactive protein (CRP)., Results: Resting TNF-α and glucose concentrations were significantly higher in the Indigenous group (P < 0.05). IL-6 and IL-1ra were elevated for longer in Caucasian (P < 0.05), compared with the Indigenous group (P > 0.05). The post-exercise (0 min) increase in cortisol and glucose for the Caucasians was higher (P < 0.05) than the attenuated responses within the Indigenous group (P > 0.05)., Conclusions: Despite being matched for fitness and body composition the Indigenous men had elevated resting TNF-α and glucose compared with the Caucasian men, which may have contributed to the suppressed post-exercise anti-inflammatory response of the Indigenous men; however, glucose normalized between groups post-exercise. As such, it is recommended for acute moderate-intensity exercise to be completed daily for long-term improvements in glucose regulation, irrespective of ancestry. Of note, results suggest it to be even more pertinent for exercise to be encouraged for Indigenous Australian men due to their elevated resting glucose levels at a younger age, when compared to the respective Caucasian group., (Copyright © 2013 Wiley Periodicals, Inc.)