How hard it isEmerging evidence
In a randomised crossover study of 14 active adults, the circuit averaged 141 heartbeats a minute and 1.44 litres of oxygen a minute, against 159 beats and 1.83 litres for a bike interval session of the same length. Bursts approached 90% of maximum heart rate and lactate rose, so it counts as vigorous exercise, but the authors placed it at the low end of interval training.
In 45 adults doing a 15-minute bodyweight circuit, heart rate averaged 89% of maximum but oxygen use only 59% of VO2 max (the most oxygen your body can use, a measure of aerobic fitness). In circuits, heart rate overstates the aerobic work.
Sources 2, 3
The one randomised trial of the circuitEmerging evidence
In the trial, 96 recreationally active students did the circuit 3 times a week for 8 weeks: one group did one round throughout, and another did two rounds in the second 4 weeks. Push-ups improved in both groups and men gained some strength, but aerobic capacity improved only in the women doing two rounds. It was one small trial.
Source 4
Daily micro-sessionsEmerging evidence
In 24 untrained young adults, a 6-minute circuit once or twice a day for 4 weeks, at about 71 to 74% of maximum heart rate, improved push-ups, burpees, single-leg squats and how healthy people felt, but not peak oxygen uptake, body fat or muscle.
Source 5
More time does moreEmerging evidence
Across 19 randomised trials of whole-body bodyweight interval training (657 people), training improved aerobic fitness, muscular fitness and body composition against no exercise. It improved aerobic fitness a little less than running or cycling training, and muscular fitness more, and the gains grew with total training time. The trials were small and rarely checked how hard people worked.
In 19 inactive young adults, an 11-minute routine of five 60-second bodyweight moves, 3 times a week for 6 weeks, raised peak oxygen uptake compared with no training.
Sources 6, 8
Weight and body fatMixed evidence
In 29 young adults doing the 7-minute workout every day for 6 weeks, BMI (body mass index) fell slightly, from 24.4 to 24.0, and waists by about 4 cm, compared with 29 who didn't. But the study didn't report randomisation, and it estimated body fat with bioimpedance scales.
In 24 sedentary women with obesity, a 12-station circuit 3 times a week for 8 weeks, starting with one round and adding a round every 2 weeks, cut body fat mass by about 3%, more than in a control group. Their VO2 max rose by about a third, but it was estimated from a submaximal test, not measured, and the abstract doesn't say the groups were randomised. In 33 inactive women, 5 weeks of bodyweight circuits improved insulin sensitivity, but clearly only in the middle-aged and those with insulin resistance. All small studies.
Sources 9, 10, 11
Older adultsEmerging evidence
In 54 women aged about 68 (41 finished), high-intensity interval circuits for an hour twice a week for 18 weeks raised estimated VO2 max as much as moderate continuous training, with no adverse events during sessions. One trial; use the easier versions and hold a wall for balance.
Source 12
The app in daily lifeMixed evidence
In a randomised crossover trial of 66 inactive UK adults, posted as a preprint and not yet peer reviewed, 2 weeks with a 7-minute workout app or a Couch to 5K app didn't change activity measured by a movement sensor on average, though people reported doing more. The two apps did about the same.
Source 13
High blood pressure and the holdsEmerging evidence
The circuit's authors advised people with high blood pressure or heart disease not to do the wall sit, plank and side plank, and to swap them for moving exercises. Since then, a review of 270 trials found that isometric training programmes (regular sessions of static holds, for 2 weeks or more) lowered resting blood pressure more than any other type of exercise, by about 8/4 mmHg, with the wall squat ranked best for the top number. But those were programmes of holds on their own: nobody has studied 30-second holds inside a fast circuit.
So follow the article's advice: swap the holds for moving exercises, or ask your doctor first. If you do them, keep breathing throughout, never hold your breath, and stop if you feel dizzy (our suggestion). Our wall sit workout for blood pressure follows the routine from the blood pressure trials.
Sources 1, 14