PMID 35992158

Research
All papers

Reduced-exertion high-intensity interval training improves the fitness-fatness index in physically inactive adults

Leahy DJ, Dalleck LC, Ramos JS

Question

Does 8 weeks of reduced-exertion HIIT improve the fitness-fatness index more than moderate-intensity continuous training in physically inactive adults?

Summary

In inactive low-to-moderate-risk adults, 8 weeks of very short REHIT cycling improved the fitness-fatness index more than a longer moderate-intensity program. REHIT required only two 20-second sprints in a 10-minute session but used a specialized cycle ergometer and had more dropouts than the MICT group.

Methodology

  • Physically inactive university and hospital staff at low-to-moderate ACSM risk.
  • 32 participants.
  • Specialized CAR.O.L cycle ergometer.
  • Work intervals: 20 seconds.
  • Recovery: 3 minutes between sprints.
  • Intensity: All-out sprint efforts with machine-adjusted resistance.
  • 10 minutes.
  • 2 days/week weeks 1-2, 3 days/week weeks 3-4, 4 days/week weeks 5-8.
  • 8 weeks.
  • Randomized two-arm supervised exercise intervention
  • Fitness-fatness index, VO2max, Waist measures, and Adherence and safety were tracked.

Outcomes

FFI

Both groups improved FFI, with a larger improvement after REHIT.

REHIT 14.65 to 16.60; MICT 14.84 to 15.82; both p<0.001; change REHIT 1.95 +/- 0.63 vs MICT 0.99 +/- 0.47, p<0.001.

Improved

FFI responders

All REHIT completers were FFI responders compared with about half of MICT completers.

REHIT 12/12 vs MICT 8/15 improved FFI by at least 1 point, p=0.01.

Improved

VO2max

VO2max increased in both groups.

REHIT 25.3 to 28.4 mL/kg/min; MICT 26.2 to 28.0 mL/kg/min.

Improved

Adherence

Session adherence was high among completers, but REHIT had more withdrawals.

Adherence REHIT 89.2% and MICT 87.8%; dropouts REHIT 4/16 and MICT 1/16.

Mixed

Insights

  • Two 20-second all-out cycling sprints in a 10-minute session can improve a combined fitness-fatness metric in inactive adults.
  • The protocol is time-efficient but depends on a specialized bike that automatically adjusts resistance.
  • Dropout/tolerability should be monitored because more participants withdrew from REHIT than MICT.

Limitations

  • Small completed sample.
  • No no-exercise control group.
  • Diet and outside physical activity/sedentary behavior were not tightly controlled.
  • REHIT had more dropouts.
  • Commercial specialized bike limits direct replication.

Safety

  • No adverse events were reported.
  • Five randomized participants dropped out: REHIT illness n=3 and personal n=1; MICT illness n=1.
  • Participants were screened as low-to-moderate risk and without metabolic, cardiovascular, or pulmonary disease.