Physiological mechanisms associated with the use of a passive heat intervention: positive implications for soccer substitutes

Purpose: Soccer substitutes are exposed to periods of limited activity before entering match-play, likely negating benefits of active warm-ups. This study aimed to determine the effects of using a passive heat intervention following a pre-match, and half-time warm-up, on muscle and core temperature in soccer players during ambient (18 °C) and cold (2 °C) conditions. Methods: On four occasions, 8 male players, completed a pre-match warm-up, followed by 45 min of rest. Following this, participants completed a half-time re-warm-up followed by an additional 45 min of rest, simulating a full match for an unplaying substitute. During periods of rest, participants wore either standardised tracksuit bottoms (CON), or heated trousers (HEAT), over typical soccer attire. Results: Vastus lateralis temperature declined less in HEAT compared to CON following the 1st half in 2 °C (Δ − 4.39 ± 0.81 vs. − 6.21 ± 1.32 °C, P = 0.002) and 18 °C (Δ − 2.48 ± 0.71 vs. − 3.54 ± 0.88 °C, P = 0.003). These findings were also observed in the 2nd half for the 2 °C (Δ − 4.36 ± 1.03 vs. − 6.26 ± 1.04 °C, P = 0.002) and 18 °C (Δ − 2.85 ± 0.57 vs. − 4.06 ± 1 °C, P = 0.018) conditions. In addition, core temperature declined less in HEAT compared to CON following the 1st (Δ − 0.41 ± 0.25 vs. − 0.84 ± 0.41 °C, P = 0.037) and 2nd (Δ − 0.25 ± 0.33 vs. − 0.64 ± 0.34 °C, P = 0.028) halves of passive rest in 2 °C, with no differences in the 18 °C condition. Perceptual data confirmed that participants were more comfortable in HEAT vs. CON in 2 °C (P < 0.01). Conclusions: Following active warm-ups, heated trousers attenuate the decline in muscle temperature in ambient and cold environments.