Applied exercise sciences……
“….most High-intensity interval training studies are conducted in laboratory settings and evidence regarding the efficacy of time-efficient “low-volume” High-intensity interval training is based mainly on demanding “all-out” protocols.”
“Thus, the aim of this pilot study was to assess the feasibility and efficacy of two low-volume (≤ 30min time-effort/week), non-all-out High-intensity interval training protocols, performed 2 × per week over 8 weeks in a community-based fitness centre.”

34 sedentary men and women were randomised to either 2 × 4-minutes High-intensity interval training (2 × 4-HIIT) or 5 × 1-minute High-intensity interval training (5 × 1-HIIT) at 85–95% maximal heart rate, or an active control group performing moderate-intensity continuous training (76 minutes per week) at 65–75% HRmax.”

“2 × 4 minutes High-intensity interval training and 5 × 1 minute High-intensity interval training exhibited lower dropout rates than moderate-intensity continuous training.”

“…..the High-intensity interval training protocols required 60% less time commitment.”

“Only 5 × 1 minute High-intensity interval training significantly improved waist circumference and subjective work ability.”

“The present study indicates that low-volume High-intensity interval training can be feasibly implemented in a community-based setting. Moreover, our data suggest that practical (non-all-out) High-intensity interval training that requires as little as 30 minutes per week……may induce significant improvements in VO2max and cardiometabolic risk markers.”
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D.Reljic, et al
Effects of low-volume high-intensity interval training in a community setting: a pilot study
European Journal of Applied Physiology — Volume 118 #6 — June 2018 — page 1153