High-Intensity Interval Training Decreases Resting Urinary Hypoxanthine Concentration in Young Active Men-A Metabolomic Approach
Question
Does a 10-day high-intensity interval training block alter the resting urinary metabolome of young active men?
Summary
In active young men, 10 consecutive days of exhausting individualized cycling HIIT caused large training stress but did not broadly change the resting urinary metabolome. The clearest training signal was lower urinary hypoxanthine after HIIT, which the authors interpreted as a possible purine-metabolism adaptation rather than a direct performance or health outcome.
Methodology
- Healthy, regularly active, competition-experienced men.
- 18 participants.
- Cycle ergometer.
- Work intervals: Mean 97 ± 14 seconds, equal to 60% of individual Tmax.
- Recovery: Recovery until heart rate decreased to 65% of HRmax.
- Intensity: Pmax from incremental VO2max testing; average 348 ± 31 W in the experimental group.
- 5-minute warm-up plus individualized interval set and HR-based recoveries.
- Daily.
- 10 consecutive days.
- Randomized controlled intervention with targeted metabolomic analysis.
- Urinary metabolome, and Training stress were tracked.
Outcomes
Hypoxanthine
Urinary hypoxanthine decreased after HIIT and differed from control, suggesting possible purine nucleotide adaptation.
Within EG V1 to V2 p = 0.0270; between EG and CG at V2 p = 0.0210 and at V3 p = 0.0006.
Overall metabolome
No broad resting urinary metabolome shift was observed after the 10-day HIIT block.
Authors reported no overall change except selected metabolites; no multivariate correction was performed.
Taurine and ADMA
Taurine and ADMA decreased by day +4 in the HIIT group, but the authors cautioned about biological relevance.
Taurine V1 to V3 p = 0.0031; ADMA V1 to V3 p = 0.0380.
Training stress
The HIIT block produced high physiological and psychological stress while participants increased training impulse over time.
Lactate increase 14.2 ± 2.7 mmol/L on day 1 and 16.3 ± 2.7 mmol/L on day 10; TRIMP 56.2 ± 13.4 to 96.6 ± 30.0; RPE 9.6 ± 0.5.
Insights
- Daily near-maximal cycling HIIT for 10 consecutive days is a heavy training block and not a general fitness template.
- Metabolomics findings are mechanistic context, not direct evidence of practical workout benefits.
- RPE and well-being monitoring are important when using dense high-intensity blocks.
Limitations
- Small male-only sample.
- Active/trained participants only.
- Control physical activity behavior was not recorded.
- Daily diet was not fully controlled.
- Targeted metabolomics covered only selected known compounds.
- No blood metabolomics or muscle mechanism measures.
- No false-discovery correction across metabolites.
Safety
- Two control participants dropped out due to illness or technical measurement errors in blood counts.
- Experimental participants showed reduced subjective well-being during the intervention.
- No exercise injuries or serious adverse events were reported.
- Participants were screened for medication use, chronic disease, and recent musculoskeletal injury.