PMID 27378942

Research
All papers

Nitrate Intake Promotes Shift in Muscle Fiber Type Composition during Sprint Interval Training in Hypoxia

De Smet S, Van Thienen R, Deldicque L, James R, Sale C, Bishop DJ, Hespel P

Question

Does sprint interval training in hypoxia, alone or with nitrate supplementation, produce greater muscle and performance adaptations than normoxic sprint interval training?

Summary

Recreationally active men completed five weeks of cycling sprint interval training in normoxia or hypoxia, with or without nitrate supplementation. Fitness improved similarly across groups, while nitrate plus hypoxic SIT uniquely increased the proportion of type IIa muscle fibers; one eligible participant stopped because of SIT intolerance.

Methodology

  • Healthy recreationally active men recruited from KU Leuven.
  • 27 participants.
  • Cycle ergometer.
  • Work intervals: 30-s maximal sprint.
  • Recovery: 4.5-min active recovery at 50 W.
  • Intensity: Maximal sprinting in FiO2 15.0%; nitrate 6.45 mmol 3 h before sessions.
  • 30-40 min including warm-up and cool-down.
  • 3 sessions/week.
  • 5 weeks.
  • Matched-group training experiment
  • VO2max, Time trial, Fiber type, and Safety/tolerability were tracked.

Outcomes

VO2max

VO2max improved similarly in all three SIT groups.

Training effect p<0.05; no clear between-group advantage.

Improved

Type IIa fibers

Type IIa fiber proportion increased only with hypoxic SIT plus nitrate.

HN 45% to 56%, p<0.05; higher than H post-training.

Improved

Buffering capacity

Muscle buffering capacity did not significantly change.

No clear change

Tolerability

Most completed training, but one eligible participant stopped due to SIT intolerance.

27/30 eligible participants completed.

Mixed

Insights

  • Thirty-second all-out sprints require long recovery and may not be tolerated by everyone.
  • Hypoxia did not add clear endurance benefits compared with normoxic SIT.

Limitations

  • Small male-only sample.
  • No nitrate-only normoxic group.
  • Specialized hypoxia and supplement conditions.
  • Short intervention.

Safety

  • One eligible participant did not complete the study because of SIT intolerance.
  • Hypoxic sessions produced low oxygen saturation during SIT, with reported group averages around 85-87% in the final week.