PMID 24244266

Research
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Application of the Speed-Duration Relationship to Normalize the Intensity of High-Intensity Interval Training

Ferguson C, Wilson J, Birch KM, Kemi OJ

Question

Can the speed-duration relationship identify treadmill speeds that normalize intensity for 4 x 4 min HIIT and maximize high-intensity work during repeated 4-minute bouts?

Summary

This laboratory treadmill study tested how to individualize 4-minute running intervals using each person's speed-duration relationship. In recreationally active young men, the speed predicted to cause exhaustion in 6 minutes was closest to allowing about four 4-minute high-intensity bouts with 4-minute recoveries.

Methodology

  • Healthy recreationally active young men accustomed to high-intensity exercise.
  • 11 participants.
  • Treadmill running.
  • Work intervals: 4 min at WR6, the speed predicted to induce intolerance in 6 min.
  • Recovery: 4 min brisk walking at 5.5 km/h.
  • Intensity: WR6 averaged 16.6 +/- 1.7 km/h and 88 +/- 3% of speed at VO2max.
  • Variable to intolerance; target work duration 960 s.
  • Acute testing only.
  • Within-subject laboratory exercise-tolerance study
  • Tolerable duration, Supra-critical-speed work, VO2peak and heart rate, and Blood lactate were tracked.

Outcomes

Tolerable duration

WR4 undershot, WR6 approximated, and WR8 exceeded the 960 s target work duration.

WR4 399 +/- 81 s, WR6 892 +/- 181 s, WR8 1517 +/- 346 s; all significantly different, p<0.050.

Mixed

WR6 intensity

WR6 was identified as the best speed for normalizing 4 x 4 min HIIT to the very-heavy domain.

Equivalent to 88 +/- 3% of speed at VO2max, range 83-93%.

Improved

Maximal HIIT

Four maximal bouts had similar tolerable durations, but later bouts completed less supra-critical-speed work than bout 1.

Bout durations did not differ; supra-CS work in bouts 2-4 was significantly lower than bout 1.

Mixed

Insights

  • For 4-minute running intervals, a pace that would cause exhaustion in exactly 4 minutes may be too hard to repeat for 4 bouts.
  • Work/rest structure and intensity normalization matter when comparing HIIT protocols.
  • This paper is best used for protocol design concepts, not user-facing health outcome claims.

Limitations

  • Small sample and smaller subgroups
  • Only young healthy active men
  • Acute laboratory study with no chronic outcomes
  • Requires multiple tests to determine individualized speeds
  • No adverse-event reporting

Safety

  • The article did not report adverse events or injuries.
  • Participants were screened as healthy, recreationally active men free from medical conditions and accustomed to high-intensity exercise.
  • All exercise was supervised in a laboratory, with procedures for stopping at intolerance and immediate cooldown.