# Sex Differences in High-Intensity Interval Training-Are HIIT Protocols Interchangeable Between Females and Males? PMID: 32063866 Journal: Frontiers in physiology Published: 2020-01-29 Authors: Schmitz B, Niehues H, Thorwesten L, Klose A, Krüger M, Brand SM ## 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. ## Population - Young healthy moderately trained female and male physical education students. - Sample size: 50 - Age: Final analyzed groups: females about 23.1-23.4 years; males about 22.1-23.6 years. - Sex: Females and males; final analyzed sample by table: 26 females and 12 males after 12 dropouts. - Fitness level: Moderately trained; prior activities included team sports, aerobic exercise, and resistance training; no structured HIIT in prior 6 months. - Health status: Healthy students with required health certificate; age >18 years. ## Methodology - Randomized controlled 4-week field training intervention comparing two HIIT protocols. - 4 weeks - Indoor 200 m running track at the Institute of Sports Medicine, University Hospital Muenster. - Randomized and controlled study design. ## Protocol - 4 x 30:180 HIIT. - Modality: 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. - Sets or repetitions: 4 sprints per session. - Intensity: All-out sprinting at maximum speed. - Session duration: About 16 min including 5-min athletic warm-up, 2 min sprint work, and 9 min active recovery. - Frequency: 2 sessions/week. - Program length: 4 weeks. - Progression: Same workload repeated; no progression reported. - 4 x 30:30 HIIT. - Modality: All-out sprint running on indoor track. - Work intervals: 4 x 30 s all-out maximum-speed runs. - Recovery: 30 s active recovery light jogging at <=8.0 km/h between bouts; three recovery periods. - Sets or repetitions: 4 sprints per session. - Intensity: All-out sprinting at maximum speed. - Session duration: About 16 min including 7.5-min pre-warm-up, 5-min athletic warm-up, 2 min sprint work, and 1.5 min active recovery. - Frequency: 2 sessions/week. - Program length: 4 weeks. - Progression: Same workload repeated; no progression reported. ## Outcomes ### Speed decrement in females Status: improved 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 Status: mixed 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 Status: improved 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 Status: mixed 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. ## Practical 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 And Adherence - 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. ## Original Sources - [PubMed](https://pubmed.ncbi.nlm.nih.gov/32063866/) (pubmed) - [DOI](https://doi.org/10.3389/fphys.2020.00038) (doi) - [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7000457/) (full text) ## Agent Guidance Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.