This study investigated the effect of the environment, jersey color and ground conditions on injury rates in junior rugby-league players in a tropical environment. Injury, environment and ground condition data were collected during each game, over one season (n = 12 rounds). The study investigated three teams (n = 64): one under-16 team in striped jerseys and two under-14 teams in black and orange jerseys. The injury rates for the under-16 team (83.3/1000 hrs) were higher than for the under-14 teams in black (69.9/1000 hrs) and orange (59.9/1000 hrs) jerseys. In the under-16 team, a negative correlation (r = -0.66, p < 0.05) was found between players’ injuries and heat index, while in the under-14 team in black jerseys, a positive correlation was observed (r = 0.90, p < 0.01), although in the under-14 team in orange, no significant correlation was found (r = 0.140, p > 0.05). In the under-14 team in black, a significant correlation (r = 0.80, p < 0.01) between players’ injuries and the temperature was observed. However, no correlations were found with any other variables per group (p > 0.05) and injury rates were not different between the teams (p > 0.05). While ground conditions had no effect on injury rates, it appears that the heat acted as a protection against injury for teams with striped and orange jerseys. However, black jerseys may put players at an increased risk of injury during hot and humid day games.
This study aimed to compare selected hormonal responses to a single session of high intensity interval training performed with an increased fraction of inspired oxygen (hyperoxia) and under normoxic conditions. Twelve recreationally trained men (age 24 ± 3 years) performed two sessions of high intensity interval training on a cycle ergometer, in randomized order with hyperoxia (4 L·min-1 with a flowrate of 94% O2) and normoxia. Each session consisted of 5 intervals of 3 minutes at 85% of the maximal power output, interspersed by 2 min at 40% of the maximal power output. Serum cortisol, prolactin and vascular endothelial growth factor (VEGF) were assessed both before and immediately after each high intensity interval training session. Statistically significant differences in cortisol were found between hyperoxic and normoxic conditions (p = 0.011), with a significant increase in hyperoxia (61.4 ± 73.2%, p = 0.013, ES = -1.03), but not in normoxia (-1.3 ± 33.5%, p > 0.05, ES = 0.1). Prolactin increased similarly in both hyperoxia (118.1 ± 145.1%, p = 0.019, ES = -0.99) and normoxia (62.14 ± 75.43%, p = 0.005, ES = -0.5). VEGF was not statistically altered in either of the conditions. Our findings indicate that a single session of high intensity interval training in low-dose hyperoxia significantly increased cortisol concentrations in recreationally trained individuals compared to normoxia, while the difference was smaller in prolactin and diminished in VEGF concentrations.