Cold-Water Immersion Impairs Power Earlier than Strength Through Time-Dependent Reductions in Intramuscular Temperature in Human Dorsiflexor Muscles.

Peak power decreased significantly after only 10 minutes of cold-water immersion across all three experimental conditions.

• Peak power decreased by 50.3 ± 16.0% in the CWI-only condition after 10 min (P < 0.05)
• Peak power decreased by 55.0 ± 18.3% in the Ex + CWI condition after 10 min (P < 0.05)
• Peak power decreased by 62.0 ± 16.8% in the Heat + CWI condition after 10 min (P < 0.05)
• This early impairment in power occurred before substantial reductions in intramuscular temperature were expected

Maximal isometric torque (strength) did not decrease until at least 30 minutes of cold-water immersion, occurring later than the power impairment.

• Maximal isometric torque decreased to 81.1 ± 9.1% in the CWI-only condition after ≥30 min (P < 0.05)
• Maximal isometric torque decreased to 86.6 ± 14.3% in the Ex + CWI condition after ≥30 min (P < 0.05)
• Maximal isometric torque decreased to 88.7 ± 10.0% in the Heat + CWI condition after ≥30 min (P < 0.05)
• The later onset of strength impairment compared to power impairment indicates differential sensitivity to intramuscular temperature reductions

Decreases in M-wave peak-to-peak amplitude, 50-Hz torque, and postactivation potentiation were only evident following prolonged cold-water immersion.

• These neuromuscular measures were impaired only after prolonged CWI (P < 0.05)
• The delayed impairment of these measures suggests that peripheral muscle contractility changes require sustained intramuscular cooling
• M-wave changes indicate alterations in muscle membrane excitability only after extended cooling
• Postactivation potentiation reductions after prolonged CWI suggest impaired calcium handling at lower intramuscular temperatures

The study used a randomized crossover design with three experimental conditions to examine the effect of initial muscle temperature on CWI-induced neuromuscular impairment.

• Twelve healthy participants (nine males and three females) completed all three visits
• Conditions were: 1) 1-h CWI at 10°C only (CWI-only), 2) nonfatiguing exercise followed by 1-h CWI at 10°C (Ex + CWI), and 3) passive muscle preheating followed by 1-h CWI at 10°C (Heat + CWI)
• CWI involved immersion of the lower leg at 10°C for 60 minutes
• Skin temperature, intramuscular temperature, and neuromuscular function were periodically assessed in the dorsiflexors throughout the 1 hour of CWI

The study hypothesized that acute CWI (<30 min) would not affect neuromuscular function due to limited intramuscular temperature reductions, while prolonged CWI (>30 min) would impair muscle contractility.

• The hypothesis regarding strength was partially supported, as maximal isometric torque only decreased after ≥30 min
• The hypothesis regarding acute CWI not affecting neuromuscular function was not fully supported, as peak power was impaired as early as 10 min
• Results indicated that power is more sensitive to temperature changes than strength, which was not part of the original hypothesis
• The differential time course of impairment highlights that power and strength respond differently to progressive intramuscular cooling

Peak power was identified as more sensitive to reductions in intramuscular temperature than maximal isometric strength in dorsiflexor muscles.

• Power impairment was detected 20 minutes earlier than strength impairment (10 min vs. ≥30 min of CWI)
• This differential sensitivity was consistent across all three experimental conditions regardless of initial muscle temperature state
• The findings suggest that the velocity-dependent component of power production is more vulnerable to early temperature-induced changes than force production capacity
• These results reflect a time- and temperature-dependent effect on skeletal muscle function