Purpose: To compare the dose–response relationship between traditional arbitrary speed thresholds versus an individualized approach, with changes in aerobic fitness in professional youth soccer players. Methods: A total of 14 youth soccer players completed a 1500-m time trial to estimate maximal aerobic speed (MAS, km·h−1) at the start and at the end of a 6-week period. Training load was monitored on a daily basis during this study. External load measures were total distance covered and total acceleration and deceleration distance >2 m·s−2. Arbitrary high-speed running measures were meters covered and time spent at >17 km·h−1 (m > high-speed distance, t > high-speed distance) and 21 km·h−1 (m > very-high-speed distance, t > very-high-speed distance). Individualized high-speed running measures were meters covered and time spent at >MAS km·h−1 (m > MAS, t > MAS) and 30% anaerobic speed reserve (m > 30ASR, t > 30ASR). In addition, internal load measures were also collected: heart rate exertion and rating of perceived exertion. Linear regression analysis was used to establish the dose–response relationship between mean weekly training load and changes in aerobic fitness. Results: Very large associations were found between t > MAS and changes in aerobic fitness (R 2 = .59). Large associations were found for t > 30ASR (R 2 = .38) and m > MAS (R 2 = .25). Unclear associations were found for all other variables. Conclusion: An individualized approach to monitoring training load, in particular t > MAS, may be a more appropriate method than using traditional arbitrary speed thresholds when monitoring the dose–response relationship between training load and changes in aerobic fitness.
John F. Fitzpatrick, Kirsty M. Hicks, and Philip R. Hayes
Susan Y. Kwiecien, Malachy P. McHugh, Stuart Goodall, Kirsty M. Hicks, Angus M. Hunter, and Glyn Howatson
Purpose: To evaluate the effectiveness between cold-water immersion (CWI) and phase-change-material (PCM) cooling on intramuscular, core, and skin-temperature and cardiovascular responses. Methods: In a randomized, crossover design, 11 men completed 15 min of 15°C CWI to the umbilicus and 2-h recovery or 3 h of 15°C PCM covering the quadriceps and 1 h of recovery, separated by 24 h. Vastus lateralis intramuscular temperature at 1 and 3 cm, core and skin temperature, heart-rate variability, and thermal comfort were recorded at baseline and 15-min intervals throughout treatment and recovery. Results: Intramuscular temperature decreased (P < .001) during and after both treatments. A faster initial effect was observed from 15 min of CWI (Δ: 4.3°C [1.7°C] 1 cm; 5.5°C [2.1°C] 3 cm; P = .01). However, over time (2 h 15 min), greater effects were observed from prolonged PCM treatment (Δ: 4.2°C [1.9°C] 1 cm; 2.2°C [2.2°C] 3 cm; treatment × time, P = .0001). During the first hour of recovery from both treatments, intramuscular temperature was higher from CWI at 1 cm (P = .013) but not 3 cm. Core temperature deceased 0.25° (0.32°) from CWI (P = .001) and 0.28°C (0.27°C) from PCM (P = .0001), whereas heart-rate variability increased during both treatments (P = .001), with no differences between treatments. Conclusions: The magnitude of temperature reduction from CWI was comparable with PCM, but intramuscular temperature was decreased for longer during PCM. PCM cooling packs offer an alternative for delivering prolonged cooling whenever application of CWI is impractical while also exerting a central effect on core temperature and heart rate.