Effect of Heat Stress on Measures of Running Performance and Heart Rate Responses During a Competitive Season in Male Soccer Players

Measures of running performance and heart rate (HR) responses to match play during 3 different heat stress (HS) conditions were assessed in 7 National Collegiate Athletic Association (NCAA) Division I male soccer players. Total distance and distance covered within distinct velocity zones (walking [WALK], jogging [JOG], low-speed running, high-speed running, sprinting [SPRINT], low-intensity running [LIR], and high-intensity running [HIR]) were assessed using global positioning system units for more than 12 matches. Heat stress was monitored during each match, and matches were defined as low (HSlow, n = 4), moderate (HSmod, n = 4), or high (HShigh, n = 4) HS. Minutes played were significantly different across HS conditions (p = 0.03). Therefore, distance covered within each movement velocity was assessed relative to minutes played and as a percentage of total playing time. WALKrel was significantly greater during HShigh compared with HSlow (p = 0.035). LIRrel was significantly greater during HSmod (p = 0.015) compared with HSlow. A trend was observed for %WALK being higher during HShigh compared with HSlow (p = 0.066). %LIR was significantly greater during HShigh compared with HSlow (p = 0.048). High-intensity running was not significantly different across HS conditions. Percent of time spent >85% HRmax was significantly greater during HShigh (p = 0.002) and HSmod (p < 0.001) compared to HSlow. Percent of time spent between 65-84% HRmax was significantly greater during HSlow compared to HShigh (p < 0.001). Results indicate that HS resulted in increased LIR and %HR≥85, while HIR was maintained. High-intensity running performance may be conserved through decreased playing time or the adoption of pacing strategies. This may assist coaches in altering player management strategies to optimize team performance.