Sex Differences in High-Intensity Interval Training-Are HIIT Protocols Interchangeable Between Females and Males?
Question
Whether two workload- and time-matched 4 x 30-second all-out running HIIT protocols with different recovery periods are interchangeable between moderately trained females and males, and whether sex affects high-intensity running speed and speed decrement.
Summary
This 4-week randomized running HIIT study compared two matched 4 x 30-second all-out sprint protocols that differed mainly in active recovery duration: 30 seconds versus 180 seconds. In moderately trained university students, females improved speed decrement and repeated-sprint performance only with the shorter 30-second recovery protocol, while males did not show the same pattern, suggesting that recovery duration and baseline performance differences can change HIIT responses by sex in real-world settings.
Methodology
- Young healthy moderately trained female and male physical education students.
- 50 participants.
- All-out sprint running on indoor track.
- Work intervals: 4 x 30 s all-out maximum-speed runs.
- Recovery: 180 s active recovery light jogging at <=8.0 km/h between bouts; three recovery periods.
- Intensity: All-out sprinting at maximum speed.
- About 16 min including 5-min athletic warm-up, 2 min sprint work, and 9 min active recovery.
- 2 sessions/week.
- 4 weeks.
- Randomized controlled 4-week field training intervention comparing two HIIT protocols.
- Speed decrement, Running speed per bout and average speed per session, Blood lactate, and Fitness test markers were tracked.
Outcomes
Speed decrement in females
Females improved speed decrement only in the 4 x 30:30 protocol, not the 4 x 30:180 protocol.
4 x 30:30 females: 15.0 +/- 3.6% to 11.6 +/- 3.7%, P = 0.004; 4 x 30:180 females: 3.7 +/- 2.5% to 4.3 +/- 1.4%, P = 0.41.
Sex x group interaction for speed decrement
After adjusting for baseline speed decrement, sex and HIIT protocol interacted significantly for follow-up speed decrement.
Sex x group interaction P < 0.001.
Responder rate in females
Females in the 4 x 30:30 group had a high response rate for improved speed decrement.
Responder analysis greater than 2 x typical error: 79% response rate.
Blood lactate
Peak lactate increased in females in both protocols and in males only in the 4 x 30:30 protocol; the 4 x 30:180 protocol showed a sex x time interaction.
4 x 30:180 sex x time interaction P = 0.0439; females P = 0.0030; 4 x 30:30 females P = 0.0002; 4 x 30:30 males P = 0.0478.
Insights
- A 4 x 30-second all-out sprint format supplies only 2 minutes of high-intensity work but can produce measurable repeated-sprint performance changes over 4 weeks in moderately trained users.
- Rest duration is not interchangeable: 30-second and 180-second recoveries can produce different adaptation patterns despite matched total session duration and workload.
- For performance-oriented programming, speed decrement across intervals can be a useful personalization signal.
- All-out sprint running protocols should be limited to fit users or adapted with safer modalities/progressions for general consumers.
Limitations
- Participants were not matched by physical fitness between sexes; effects may reflect baseline performance differences rather than sex biology alone.
- Menstrual cycle, oral contraceptive phase, and estrogen levels were not controlled.
- Final analyzed male sample was smaller than female sample, reducing power.
- No independent post-intervention test outside training-session data was used to confirm general improvement in intermittent exercise capacity.
- Young moderately trained physical education students limit generalization to sedentary or clinical users.
Safety
- No intervention-associated adverse events were reported.
- Twelve participants dropped out; six were due to injury/illness not associated with the intervention and six due to missing adherence.
- Participants were supervised and advised to avoid exercise and alcohol for at least 24 h before testing or training.