We compared the effect of programmed (PFI) and thirst-driven (TDFI) fluid intake on prolonged cycling performance and exercise associated muscle cramps (EAMC). Eight male endurance athletes (26 ± 6 years) completed two trials consisting of 5 h of cycling at 61% $\dot{\mathrm{V}}{\mathrm{O}}_{2\mathrm{peak}}$ followed by a 20 km time-trial (TT) in a randomized crossover sequence at 30 °C, 35% relative humidity. EAMC was assessed after the TT with maximal voluntary isometric contractions of the shortened right plantar flexors. Water intake was either programmed to limit body mass loss to 1% (PFI) or consumed based on perceived thirst (TDFI). Body mass loss reached 1.5 ± 1.0% for PFI and 2.5 ± 0.9% for TDFI (p = 0.10). Power output during the 20 km TT was higher (p < 0.05) for PFI (278 ± 41 W) than TDFI (263 ± 39 W), but the total performance time, including the breaks to urinate, was similar (p = 0.48) between conditions. The prevalence of EAMC of the plantar flexors was similar between the drinking conditions. Cyclists competing in the heat for over 5 h may benefit from PFI aiming to limit body mass loss to <2% when a high intensity effort is required in the later phase of the race and when time lost for urination is not a consideration.

This study aimed to determine if the change in heart rate variability from pre- to post-firefighting is modulated by different work cycles. Thirteen male firefighters underwent two firefighting simulations that comprised two identical 25-minute work bouts intercalated by a passive recovery period of either 20 minutes (T20) or 5 minutes (T5). The square root of the mean squared differences of successive R-R intervals (RMSSD) and aural temperature were measured at rest before (PRE) and after (POST) firefighting simulations. The decrease in RMSSD was different between firefighting simulations (T20: -10 ± 21.2 ms, T5: -19.9 ± 20.9 ms, interaction, P = 0.02). Post-firefighting aural temperature was greater (P = 0.05) in T5 (37.18 ± 0.53°C) than in T20 (36.88 ± 0.49°C). In conclusion, a shorter recovery period of 5 minutes between firefighting work bouts decreases post-firefighting heart rate variability possibly attributed to a lower parasympathetic reactivation and a higher absolute value of body temperature.

Article: Fitness components associated with performance of a law enforcement physical employment standard in police cadets - The Journal of Sports Medicine and Physical Fitness 2021 Mar 15 - Minerva Medica - Journals

BACKGROUND: Although the 20-meter shuttle run test (20MSR) is frequently used by police organisations for recruitment purposes, to our knowledge no study has yet assessed the accuracy of this test to estimate maximal oxygen consumption (VO2max) in police recruits. OBJECTIVE: The primary objective of this study was to assess the validity of the 20MSR as a predictor of VO2max in police cadets. METHODS: 49 police cadets completed both an indirect calorimetry VO2max assessment and a 20MSR. Based on their results, estimated VO2max was calculated using an established equation. Furthermore, two models estimating the VO2max was also developed using the final stage completed and sex as independent variables in the first model (model A) as well as the final half-stage completed and sex in the second model (model B). RESULTS: A strong and significant bivariate correlation was found between measured VO2max and the final stage completed at the 20MSR (r = 0.874, p < 0.001). Nevertheless, limits of agreement analysis showed relatively large agreement errors between measured VO2max and estimated VO2max based on the established equation (0.46±6.29 ml·min–1·kg–1), model A (0.00±5.58 ml min–1 kg–1), and model B (0.00±5.48 ml min–1·kg–1). CONCLUSIONS: Although the 20MSR can be a useful tool to estimate cardiorespiratory fitness for research and conditioning purposes, the large agreement errors found in this study suggest that results at the 20MSR should be interpreted with caution when making “pass or fail” decisions.