Regular Cold-Water Immersion Following HIIT Does Not Affect Intramuscular Adaptation Markers, Inflammatory Profile or Endurance Performance.

HIIT training over 5 weeks significantly increased V̇O2max regardless of cold-water immersion condition.

• A main effect of time was observed for V̇O2max (p ≤ 0.031)
• No main effect of condition (p ≥ 0.098) or interaction (p ≥ 0.088) was found
• Sixteen healthy males were divided into a training-only control group (n = 7) and a CWI group (n = 9)
• HIIT program consisted of three weekly sessions of 5–8 × 2-min bouts at 95% V̇O2max over 5 weeks

HIIT training significantly improved time to task failure (TTF) on a constant work-rate running test regardless of CWI.

• A main effect of time was observed for TTF (p ≤ 0.031)
• No main effect of condition (p ≥ 0.098) or interaction (p ≥ 0.088) was detected
• TTF was assessed using a constant work-rate running test to task failure
• Assessments were repeated at the end of weeks four and five

The satellite cell pool increased with HIIT training but was not affected by cold-water immersion.

• A main effect of time was observed for satellite cell pool (p ≤ 0.031)
• No main effect of condition (p ≥ 0.098) or interaction (p ≥ 0.088) was found
• Satellite cell pool was assessed via muscle biopsies taken at baseline and after weeks four and five

Muscle PGC-1α content increased with HIIT training and was not influenced by post-exercise cold-water immersion.

• A main effect of time was observed for PGC-1α content (p ≤ 0.031)
• No main effect of condition (p ≥ 0.098) or interaction (p ≥ 0.088) was found
• PGC-1α (peroxisome proliferator-activated receptor-γ coactivator 1-α) was measured from muscle biopsy samples

Muscle morphology, specifically connective tissue, changed with HIIT training but was not differentially affected by CWI.

• A main effect of time was observed for connective tissue morphology (p ≤ 0.031)
• No main effect of condition (p ≥ 0.098) or interaction (p ≥ 0.088) was found
• Muscle morphological changes were assessed via muscle biopsies

Muscle inflammatory markers did not change significantly over time or between conditions.

• No significant alterations were observed in inflammatory markers over time (p ≥ 0.395)
• No significant effect of condition on inflammatory markers (p ≥ 0.115)
• Inflammatory markers were assessed from muscle biopsy samples at baseline and post-training timepoints

Cold-water immersion was applied at 11.2°C for 15 minutes following each HIIT session over 5 weeks.

• Water temperature was 11.2°C ± 0.2°C
• Immersion duration was 15 minutes per session
• CWI was performed after each of the three weekly HIIT sessions
• The control group completed training only with no CWI